Merge branch 'master' into pmtu

- Migrate `DOT` to `DNS_SERVER`
- Migrate `DOT_PROVIDERS` to `DNS_UPSTREAM_RESOLVERS`
- Migrate `DOT_PRIVATE_ADDRESS` to `DNS_PRIVATE_ADDRESSES`
- Migrate `DOT_CACHING` to `DNS_CACHING`
- Migrate `DOT_IPV6` to `DNS_UPSTREAM_IPV6`

.devcontainer/Dockerfile

@@ -1,2 +1,2 @@
-FROM qmcgaw/godevcontainer:v0.20-alpine
+FROM ghcr.io/qdm12/godevcontainer:v0.21-alpine
 RUN apk add wireguard-tools htop openssl

.devcontainer/README.md

@@ -19,16 +19,16 @@ It works on Linux, Windows (WSL2) and OSX.
     mkdir -p ~/.ssh
     ```
 
-1. **For Docker on OSX**: ensure the project directory and your home directory `~` are accessible by Docker.
+1. **For OSX hosts**: ensure the project directory and your home directory `~` are accessible by Docker.
 1. Open the command palette in Visual Studio Code (CTRL+SHIFT+P).
-1. Select `Dev Containers: Open Folder in Container...` and choose the project directory.
+1. Select `Dev-Containers: Open Folder in Container...` and choose the project directory.
 
 ## Customization
 
 For any customization to take effect, you should "rebuild and reopen":
 
 1. Open the command palette in Visual Studio Code (CTRL+SHIFT+P)
-2. Select `Dev Containers: Rebuild Container`
+2. Select `Dev-Containers: Rebuild Container`
 
 Changes you can make are notably:
 

.devcontainer/devcontainer.json

@@ -82,6 +82,9 @@
                 "gopls": {
                     "usePlaceholders": false,
                     "staticcheck": true,
+                    "ui.diagnostic.analyses": {
+                        "ST1000": false
+                    },
                     "formatting.gofumpt": true,
                 },
                 "go.lintTool": "golangci-lint",

.github/ISSUE_TEMPLATE/provider.md

@@ -6,12 +6,35 @@ labels: ":bulb: New provider"
 
 ---
 
-One of the following is required:
+Important notes:
 
-- Publicly accessible URL to a zip file containing the Openvpn configuration files
+- There is no need to support both OpenVPN and Wireguard for a provider, but it's better to support both if possible
-- Publicly accessible URL to a structured (JSON etc.) list of servers **and attach** an example Openvpn configuration file for both TCP and UDP
+- We do **not** implement authentication to access servers information behind a login. This is way too time consuming unfortunately
+- If it's not possible to support a provider natively, you can still use the [the custom provider](https://github.com/qdm12/gluetun-wiki/blob/main/setup/providers/custom.md)
+
+## For Wireguard
+
+Wireguard can be natively supported ONLY if:
+
+- the `PrivateKey` field value is the same across all servers for one user account
+- the `Address` field value is:
+  - can be found in a structured (JSON etc.) list of servers publicly available; OR
+  - the same across all servers for one user account
+- the `PublicKey` field value is:
+  - can be found in a structured (JSON etc.) list of servers publicly available; OR
+  - the same across all servers for one user account
+- the `Endpoint` field value:
+  - can be found in a structured (JSON etc.) list of servers publicly available
+  - can be determined using a pattern, for example using country codes in hostnames
+
+If any of these conditions are not met, Wireguard cannot be natively supported or there is no advantage compared to using a custom Wireguard configuration file.
+
+If **all** of these conditions are met, please provide an answer for each of them.
+
+## For OpenVPN
+
+OpenVPN can be natively supported ONLY if one of the following can be provided, by preference in this order:
+
+- Publicly accessible URL to a structured (JSON etc.) list of servers **and attach** an example Openvpn configuration file for both TCP and UDP; OR
+- Publicly accessible URL to a zip file containing the Openvpn configuration files; OR
 - Publicly accessible URL to the list of servers **and attach** an example Openvpn configuration file for both TCP and UDP
-
-If the list of servers requires to login **or** is hidden behind an interactive configurator,
-you can only use a custom Openvpn configuration file.
-[The Wiki's OpenVPN configuration file page](https://github.com/qdm12/gluetun-wiki/blob/main/setup/openvpn-configuration-file.md) describes how to do so.

.github/pull_request_template.md

@@ -0,0 +1,12 @@
+# Description
+
+<!-- Please describe the reason for the changes being proposed. -->
+
+# Issue
+
+<!-- Please link to the issue(s) this change relates to. -->
+
+# Assertions
+
+* [ ] I am aware that we do not accept manual changes to the servers.json file <!-- If this is your goal, please consult https://github.com/qdm12/gluetun-wiki/blob/main/setup/servers.md#update-using-the-command-line -->
+* [ ] I am aware that any changes to settings should be reflected in the [wiki](https://github.com/qdm12/gluetun-wiki/)

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
     env:
       DOCKER_BUILDKIT: "1"
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - uses: reviewdog/action-misspell@v1
         with:
@@ -59,13 +59,40 @@ jobs:
       - name: Run tests in test container
         run: |
           touch coverage.txt
-          docker run --rm \
+          docker run --rm --device /dev/net/tun \
           -v "$(pwd)/coverage.txt:/tmp/gobuild/coverage.txt" \
           test-container
 
       - name: Build final image
         run: docker build -t final-image .
 
+  verify-private:
+    if: |
+      github.repository == 'qdm12/gluetun' &&
+      (
+        github.event_name == 'push' ||
+        github.event_name == 'release' ||
+        (github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository && github.actor != 'dependabot[bot]')
+      )
+    needs: [verify]
+    runs-on: ubuntu-latest
+    environment: secrets
+    steps:
+      - uses: actions/checkout@v5
+
+      - run: docker build -t qmcgaw/gluetun .
+
+      - name: Setup Go for CI utility
+        uses: actions/setup-go@v6
+        with:
+          go-version-file: ci/go.mod
+
+      - name: Build utility
+        run: go build -C ./ci -o runner ./cmd/main.go
+
+      - name: Run Gluetun container with Mullvad configuration
+        run: echo -e "${{ secrets.MULLVAD_WIREGUARD_PRIVATE_KEY }}\n${{ secrets.MULLVAD_WIREGUARD_ADDRESS }}" | ./ci/runner mullvad
+
   codeql:
     runs-on: ubuntu-latest
     permissions:
@@ -73,15 +100,15 @@ jobs:
       contents: read
       security-events: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
-          go-version: "^1.23"
+          go-version-file: go.mod
-      - uses: github/codeql-action/init@v3
+      - uses: github/codeql-action/init@v4
         with:
           languages: go
-      - uses: github/codeql-action/autobuild@v3
+      - uses: github/codeql-action/autobuild@v4
-      - uses: github/codeql-action/analyze@v3
+      - uses: github/codeql-action/analyze@v4
 
   publish:
     if: |
@@ -98,7 +125,7 @@ jobs:
       packages: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       # extract metadata (tags, labels) for Docker
       # https://github.com/docker/metadata-action

.github/workflows/closed-issue.yml

@@ -9,7 +9,7 @@ jobs:
       issues: write
     runs-on: ubuntu-latest
     steps:
-      - uses: peter-evans/create-or-update-comment@v4
+      - uses: peter-evans/create-or-update-comment@v5
         with:
           token: ${{ github.token }}
           issue-number: ${{ github.event.issue.number }}

.github/workflows/configs/mlc-config.json

@@ -8,6 +8,7 @@
   "retryOn429": false,
   "fallbackRetryDelay": "30s",
   "aliveStatusCodes": [
-    200
+    200,
+    429
   ]
 }

.github/workflows/labels.yml

@@ -11,7 +11,7 @@ jobs:
       issues: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: crazy-max/ghaction-github-labeler@v5
         with:
           yaml-file: .github/labels.yml

.github/workflows/markdown.yml

@@ -18,12 +18,12 @@ jobs:
       actions: read
       contents: read
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
-      - uses: DavidAnson/markdownlint-cli2-action@v16
+      - uses: DavidAnson/markdownlint-cli2-action@v20
         with:
           globs: "**.md"
-          config: .markdownlint.json
+          config: .markdownlint-cli2.jsonc
 
       - uses: reviewdog/action-misspell@v1
         with:

.github/workflows/opened-issue.yml

@@ -9,7 +9,7 @@ jobs:
       issues: write
     runs-on: ubuntu-latest
     steps:
-      - uses: peter-evans/create-or-update-comment@v4
+      - uses: peter-evans/create-or-update-comment@v5
         with:
           token: ${{ github.token }}
           issue-number: ${{ github.event.issue.number }}

.golangci.yml

@@ -1,27 +1,70 @@
-linters-settings:
+version: "2"
-  misspell:
-    locale: US
 
-issues:
+formatters:
-  exclude-rules:
+  enable:
-    - path: _test\.go
+    - gci
-      linters:
+    - gofumpt
-        - dupl
+    - goimports
-        - err113
+  exclusions:
-        - containedctx
+    generated: lax
-        - maintidx
+    paths:
-    - path: "internal\\/server\\/.+\\.go"
+      - third_party$
-      linters:
+      - builtin$
-        - dupl
+      - examples$
-    - text: "returns interface \\(github\\.com\\/vishvananda\\/netlink\\.Link\\)"
-      linters:
-        - ireturn
-    - path: "internal\\/openvpn\\/pkcs8\\/descbc\\.go"
-      text: "newCipherDESCBCBlock returns interface \\(github\\.com\\/youmark\\/pkcs8\\.Cipher\\)"
-      linters:
-        - ireturn
 
 linters:
+  settings:
+    misspell:
+      locale: US
+    goconst:
+      ignore-string-values:
+        # commonly used settings strings
+        - "^disabled$"
+        # Firewall and routing strings
+        - "^(ACCEPT|DROP)$"
+        - "^--delete$"
+        - "^all$"
+        - "^(tcp|udp)$"
+        # Server route strings
+        - "^/status$"
+
+  exclusions:
+    generated: lax
+    presets:
+      - comments
+      - common-false-positives
+      - legacy
+      - std-error-handling
+    rules:
+      - linters:
+          - containedctx
+          - dupl
+          - err113
+          - maintidx
+        path: _test\.go
+      - linters:
+          - dupl
+        path: internal\/server\/.+\.go
+      - linters:
+          - ireturn
+        text: returns interface \(github\.com\/vishvananda\/netlink\.Link\)
+      - linters:
+          - ireturn
+        path: internal\/openvpn\/pkcs8\/descbc\.go
+        text: newCipherDESCBCBlock returns interface \(github\.com\/youmark\/pkcs8\.Cipher\)
+      - linters:
+          - revive
+        path: internal\/provider\/(common|utils)\/.+\.go
+        text: "var-naming: avoid (bad|meaningless) package names"
+      - linters:
+          - err113
+          - mnd
+        path: ci\/.+\.go
+
+    paths:
+      - third_party$
+      - builtin$
+      - examples$
   enable:
     # - cyclop
     # - errorlint
@@ -42,7 +85,6 @@ linters:
     - exhaustive
     - fatcontext
     - forcetypeassert
-    - gci
     - gocheckcompilerdirectives
     - gochecknoglobals
     - gochecknoinits
@@ -51,9 +93,7 @@ linters:
     - gocritic
     - gocyclo
     - godot
-    - gofumpt
     - goheader
-    - goimports
     - gomoddirectives
     - goprintffuncname
     - gosec
@@ -86,7 +126,6 @@ linters:
     - rowserrcheck
     - sqlclosecheck
     - tagalign
-    - tenv
     - thelper
     - tparallel
     - unconvert

.markdownlint-cli2.jsonc

@@ -0,0 +1,9 @@
+{
+  "config": {
+    "default": true,
+    "MD013": false,
+  },
+  "ignores": [
+    ".github/pull_request_template.md"
+  ]
+}

.markdownlint.json

@@ -1,3 +0,0 @@
-{
-  "MD013": false
-}

.vscode/launch.json

@@ -1,35 +0,0 @@
-{
-    "version": "0.2.0",
-    "configurations": [
-        {
-            "name": "Update a VPN provider servers data",
-            "type": "go",
-            "request": "launch",
-            "cwd": "${workspaceFolder}",
-            "program": "cmd/gluetun/main.go",
-            "args": [
-                "update",
-                "${input:updateMode}",
-                "-providers",
-                "${input:provider}"
-            ],
-        }
-    ],
-    "inputs": [
-        {
-            "id": "provider",
-            "type": "promptString",
-            "description": "Please enter a provider (or comma separated list of providers)",
-        },
-        {
-            "id": "updateMode",
-            "type": "pickString",
-            "description": "Update mode to use",
-            "options": [
-                "-maintainer",
-                "-enduser"
-            ],
-            "default": "-maintainer"
-        },
-    ]
-}

.vscode/tasks.json

@@ -0,0 +1,51 @@
+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "Update a VPN provider servers data",
+            "type": "shell",
+            "command": "go",
+            "args": [
+                "run",
+                "./cmd/gluetun/main.go",
+                "update",
+                "${input:updateMode}",
+                "-providers",
+                "${input:provider}"
+            ],
+        },
+        {
+            "label": "Add a Gluetun Github Git remote",
+            "type": "shell",
+            "command": "git",
+            "args": [
+                "remote",
+                "add",
+                "${input:githubRemoteUsername}",
+                "git@github.com:${input:githubRemoteUsername}/gluetun.git"
+            ],
+        }
+    ],
+    "inputs": [
+        {
+            "id": "provider",
+            "type": "promptString",
+            "description": "Please enter a provider (or comma separated list of providers)",
+        },
+        {
+            "id": "updateMode",
+            "type": "pickString",
+            "description": "Update mode to use",
+            "options": [
+                "-maintainer",
+                "-enduser"
+            ],
+            "default": "-maintainer"
+        },
+        {
+            "id": "githubRemoteUsername",
+            "type": "promptString",
+            "description": "Please enter a Github username",
+        },
+    ]
+}

Dockerfile

@@ -1,14 +1,14 @@
-ARG ALPINE_VERSION=3.20
+ARG ALPINE_VERSION=3.22
-ARG GO_ALPINE_VERSION=3.20
+ARG GO_ALPINE_VERSION=3.22
-ARG GO_VERSION=1.23
+ARG GO_VERSION=1.25
-ARG XCPUTRANSLATE_VERSION=v0.6.0
+ARG XCPUTRANSLATE_VERSION=v0.9.0
-ARG GOLANGCI_LINT_VERSION=v1.61.0
+ARG GOLANGCI_LINT_VERSION=v2.4.0
 ARG MOCKGEN_VERSION=v1.6.0
 ARG BUILDPLATFORM=linux/amd64
 
-FROM --platform=${BUILDPLATFORM} qmcgaw/xcputranslate:${XCPUTRANSLATE_VERSION} AS xcputranslate
+FROM --platform=${BUILDPLATFORM} ghcr.io/qdm12/xcputranslate:${XCPUTRANSLATE_VERSION} AS xcputranslate
-FROM --platform=${BUILDPLATFORM} qmcgaw/binpot:golangci-lint-${GOLANGCI_LINT_VERSION} AS golangci-lint
+FROM --platform=${BUILDPLATFORM} ghcr.io/qdm12/binpot:golangci-lint-${GOLANGCI_LINT_VERSION} AS golangci-lint
-FROM --platform=${BUILDPLATFORM} qmcgaw/binpot:mockgen-${MOCKGEN_VERSION} AS mockgen
+FROM --platform=${BUILDPLATFORM} ghcr.io/qdm12/binpot:mockgen-${MOCKGEN_VERSION} AS mockgen
 
 FROM --platform=${BUILDPLATFORM} golang:${GO_VERSION}-alpine${GO_ALPINE_VERSION} AS base
 COPY --from=xcputranslate /xcputranslate /usr/local/bin/xcputranslate
@@ -32,7 +32,7 @@ ENTRYPOINT go test -race -coverpkg=./... -coverprofile=coverage.txt -covermode=a
 
 FROM --platform=${BUILDPLATFORM} base AS lint
 COPY .golangci.yml ./
-RUN golangci-lint run --timeout=10m
+RUN golangci-lint run
 
 FROM --platform=${BUILDPLATFORM} base AS mocks
 RUN git init && \
@@ -85,7 +85,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     OPENVPN_PASSWORD= \
     OPENVPN_USER_SECRETFILE=/run/secrets/openvpn_user \
     OPENVPN_PASSWORD_SECRETFILE=/run/secrets/openvpn_password \
-    OPENVPN_VERSION=2.4 \
+    OPENVPN_VERSION=2.6 \
     OPENVPN_VERBOSITY=1 \
     OPENVPN_FLAGS= \
     OPENVPN_CIPHERS= \
@@ -125,6 +125,8 @@ ENV VPN_SERVICE_PROVIDER=pia \
     VPN_PORT_FORWARDING_STATUS_FILE="/tmp/gluetun/forwarded_port" \
     VPN_PORT_FORWARDING_USERNAME= \
     VPN_PORT_FORWARDING_PASSWORD= \
+    VPN_PORT_FORWARDING_UP_COMMAND= \
+    VPN_PORT_FORWARDING_DOWN_COMMAND= \
     # # Cyberghost only:
     OPENVPN_CERT= \
     OPENVPN_KEY= \
@@ -162,19 +164,20 @@ ENV VPN_SERVICE_PROVIDER=pia \
     # Health
     HEALTH_SERVER_ADDRESS=127.0.0.1:9999 \
     HEALTH_TARGET_ADDRESS=cloudflare.com:443 \
-    HEALTH_SUCCESS_WAIT_DURATION=5s \
+    HEALTH_ICMP_TARGET_IP=1.1.1.1 \
-    HEALTH_VPN_DURATION_INITIAL=6s \
+    HEALTH_RESTART_VPN=on \
-    HEALTH_VPN_DURATION_ADDITION=5s \
+    # DNS
-    # DNS over TLS
+    DNS_SERVER=on \
-    DOT=on \
+    DNS_UPSTREAM_RESOLVER_TYPE=DoT \
-    DOT_PROVIDERS=cloudflare \
+    DNS_UPSTREAM_RESOLVERS=cloudflare \
-    DOT_PRIVATE_ADDRESS=127.0.0.1/8,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16,169.254.0.0/16,::1/128,fc00::/7,fe80::/10,::ffff:7f00:1/104,::ffff:a00:0/104,::ffff:a9fe:0/112,::ffff:ac10:0/108,::ffff:c0a8:0/112 \
+    DNS_BLOCK_IPS= \
-    DOT_CACHING=on \
+    DNS_BLOCK_IP_PREFIXES=127.0.0.1/8,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16,169.254.0.0/16,::1/128,fc00::/7,fe80::/10,::ffff:7f00:1/104,::ffff:a00:0/104,::ffff:a9fe:0/112,::ffff:ac10:0/108,::ffff:c0a8:0/112 \
-    DOT_IPV6=off \
+    DNS_CACHING=on \
+    DNS_UPSTREAM_IPV6=off \
     BLOCK_MALICIOUS=on \
     BLOCK_SURVEILLANCE=off \
     BLOCK_ADS=off \
-    UNBLOCK= \
+    DNS_UNBLOCK_HOSTNAMES= \
     DNS_UPDATE_PERIOD=24h \
     DNS_ADDRESS=127.0.0.1 \
     DNS_KEEP_NAMESERVER=off \
@@ -224,9 +227,6 @@ EXPOSE 8000/tcp 8888/tcp 8388/tcp 8388/udp
 HEALTHCHECK --interval=5s --timeout=5s --start-period=10s --retries=3 CMD /gluetun-entrypoint healthcheck
 ARG TARGETPLATFORM
 RUN apk add --no-cache --update -l wget && \
-    apk add --no-cache --update -X "https://dl-cdn.alpinelinux.org/alpine/v3.12/main" openvpn\~2.4 && \
-    apk add --no-cache --update -X "https://dl-cdn.alpinelinux.org/alpine/v3.16/main" openssl\~1.1 && \
-    mv /usr/sbin/openvpn /usr/sbin/openvpn2.4 && \
     apk add --no-cache --update -X "https://dl-cdn.alpinelinux.org/alpine/v3.17/main" openvpn\~2.5 && \
     mv /usr/sbin/openvpn /usr/sbin/openvpn2.5 && \
     apk del openvpn && \

README.md

@@ -1,6 +1,6 @@
 # Gluetun VPN client
 
-Lightweight swiss-knife-like VPN client to multiple VPN service providers
+Lightweight swiss-army-knife-like VPN client to multiple VPN service providers
 
 ![Title image](https://raw.githubusercontent.com/qdm12/gluetun/master/title.svg)
 
@@ -26,7 +26,6 @@ Lightweight swiss-knife-like VPN client to multiple VPN service providers
 [![GitHub issues](https://img.shields.io/github/issues/qdm12/gluetun.svg)](https://github.com/qdm12/gluetun/issues)
 [![GitHub closed issues](https://img.shields.io/github/issues-closed/qdm12/gluetun.svg)](https://github.com/qdm12/gluetun/issues?q=is%3Aissue+is%3Aclosed)
 
-[![Lines of code](https://img.shields.io/tokei/lines/github/qdm12/gluetun)](https://github.com/qdm12/gluetun)
 ![Code size](https://img.shields.io/github/languages/code-size/qdm12/gluetun)
 ![GitHub repo size](https://img.shields.io/github/repo-size/qdm12/gluetun)
 ![Go version](https://img.shields.io/github/go-mod/go-version/qdm12/gluetun)
@@ -56,7 +55,7 @@ Lightweight swiss-knife-like VPN client to multiple VPN service providers
 
 ## Features
 
-- Based on Alpine 3.20 for a small Docker image of 35.6MB
+- Based on Alpine 3.22 for a small Docker image of 41.1MB
 - Supports: **AirVPN**, **Cyberghost**, **ExpressVPN**, **FastestVPN**, **Giganews**, **HideMyAss**, **IPVanish**, **IVPN**, **Mullvad**, **NordVPN**, **Perfect Privacy**, **Privado**, **Private Internet Access**, **PrivateVPN**, **ProtonVPN**, **PureVPN**,  **SlickVPN**, **Surfshark**, **TorGuard**, **VPNSecure.me**, **VPNUnlimited**, **Vyprvpn**, **WeVPN**, **Windscribe** servers
 - Supports OpenVPN for all providers listed
 - Supports Wireguard both kernelspace and userspace
@@ -88,7 +87,7 @@ Go to the [Wiki](https://github.com/qdm12/gluetun-wiki)!
 Here's a docker-compose.yml for the laziest:
 
 ```yml
-version: "3"
+---
 services:
   gluetun:
     image: qmcgaw/gluetun

ci/cmd/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/signal"
+
+	"github.com/qdm12/gluetun/ci/internal"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Println("Usage: " + os.Args[0] + " <command>")
+		os.Exit(1)
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
+
+	var err error
+	switch os.Args[1] {
+	case "mullvad":
+		err = internal.MullvadTest(ctx)
+	default:
+		err = fmt.Errorf("unknown command: %s", os.Args[1])
+	}
+	stop()
+	if err != nil {
+		fmt.Println("❌", err)
+		os.Exit(1)
+	}
+	fmt.Println("✅ Test completed successfully.")
+}

ci/go.mod

@@ -0,0 +1,36 @@
+module github.com/qdm12/gluetun/ci
+
+go 1.25.0
+
+require (
+	github.com/docker/docker v28.5.1+incompatible
+	github.com/opencontainers/image-spec v1.1.1
+)
+
+require (
+	github.com/Microsoft/go-winio v0.6.2 // indirect
+	github.com/containerd/errdefs v1.0.0 // indirect
+	github.com/containerd/errdefs/pkg v0.3.0 // indirect
+	github.com/containerd/log v0.1.0 // indirect
+	github.com/distribution/reference v0.6.0 // indirect
+	github.com/docker/go-connections v0.6.0 // indirect
+	github.com/docker/go-units v0.5.0 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-logr/logr v1.4.3 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/moby/docker-image-spec v1.3.1 // indirect
+	github.com/moby/sys/atomicwriter v0.1.0 // indirect
+	github.com/moby/term v0.5.2 // indirect
+	github.com/morikuni/aec v1.0.0 // indirect
+	github.com/opencontainers/go-digest v1.0.0 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0 // indirect
+	go.opentelemetry.io/otel v1.38.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.38.0 // indirect
+	go.opentelemetry.io/otel/metric v1.38.0 // indirect
+	go.opentelemetry.io/otel/trace v1.38.0 // indirect
+	golang.org/x/sys v0.35.0 // indirect
+	golang.org/x/time v0.14.0 // indirect
+	gotest.tools/v3 v3.5.2 // indirect
+)

ci/go.sum

@@ -0,0 +1,97 @@
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+github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c/go.mod h1:xomTg63KZ2rFqZQzSB4Vz2SUXa1BpHTVz9L5PTmPC4E=
+github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
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+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
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+gotest.tools/v3 v3.5.2/go.mod h1:LtdLGcnqToBH83WByAAi/wiwSFCArdFIUV/xxN4pcjA=

ci/internal/mullvad.go

@@ -0,0 +1,193 @@
+package internal
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/docker/docker/api/types/container"
+	"github.com/docker/docker/api/types/network"
+	"github.com/docker/docker/client"
+	v1 "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+func MullvadTest(ctx context.Context) error {
+	secrets, err := readSecrets(ctx)
+	if err != nil {
+		return fmt.Errorf("reading secrets: %w", err)
+	}
+
+	const timeout = 15 * time.Second
+	ctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+
+	client, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
+	if err != nil {
+		return fmt.Errorf("creating Docker client: %w", err)
+	}
+	defer client.Close()
+
+	config := &container.Config{
+		Image:       "qmcgaw/gluetun",
+		StopTimeout: ptrTo(3),
+		Env: []string{
+			"VPN_SERVICE_PROVIDER=mullvad",
+			"VPN_TYPE=wireguard",
+			"LOG_LEVEL=debug",
+			"SERVER_COUNTRIES=USA",
+			"WIREGUARD_PRIVATE_KEY=" + secrets.mullvadWireguardPrivateKey,
+			"WIREGUARD_ADDRESSES=" + secrets.mullvadWireguardAddress,
+		},
+	}
+	hostConfig := &container.HostConfig{
+		AutoRemove: true,
+		CapAdd:     []string{"NET_ADMIN", "NET_RAW"},
+	}
+	networkConfig := (*network.NetworkingConfig)(nil)
+	platform := (*v1.Platform)(nil)
+	const containerName = "" // auto-generated name
+
+	response, err := client.ContainerCreate(ctx, config, hostConfig, networkConfig, platform, containerName)
+	if err != nil {
+		return fmt.Errorf("creating container: %w", err)
+	}
+	for _, warning := range response.Warnings {
+		fmt.Println("Warning during container creation:", warning)
+	}
+	containerID := response.ID
+	defer stopContainer(client, containerID)
+
+	beforeStartTime := time.Now()
+
+	err = client.ContainerStart(ctx, containerID, container.StartOptions{})
+	if err != nil {
+		return fmt.Errorf("starting container: %w", err)
+	}
+
+	return waitForLogLine(ctx, client, containerID, beforeStartTime)
+}
+
+func ptrTo[T any](v T) *T { return &v }
+
+type secrets struct {
+	mullvadWireguardPrivateKey string
+	mullvadWireguardAddress    string
+}
+
+func readSecrets(ctx context.Context) (secrets, error) {
+	expectedSecrets := [...]string{
+		"Mullvad Wireguard private key",
+		"Mullvad Wireguard address",
+	}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	lines := make([]string, 0, len(expectedSecrets))
+
+	for i := range expectedSecrets {
+		fmt.Println("🤫 reading", expectedSecrets[i], "from Stdin...")
+		if !scanner.Scan() {
+			break
+		}
+		lines = append(lines, strings.TrimSpace(scanner.Text()))
+		if ctx.Err() != nil {
+			return secrets{}, ctx.Err()
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return secrets{}, fmt.Errorf("reading secrets from stdin: %w", err)
+	}
+
+	if len(lines) < len(expectedSecrets) {
+		return secrets{}, fmt.Errorf("expected %d secrets via Stdin, but only received %d",
+			len(expectedSecrets), len(lines))
+	}
+	for i, line := range lines {
+		if line == "" {
+			return secrets{}, fmt.Errorf("secret on line %d/%d was empty", i+1, len(lines))
+		}
+	}
+
+	return secrets{
+		mullvadWireguardPrivateKey: lines[0],
+		mullvadWireguardAddress:    lines[1],
+	}, nil
+}
+
+func stopContainer(client *client.Client, containerID string) {
+	const stopTimeout = 5 * time.Second // must be higher than 3s, see above [container.Config]'s StopTimeout field
+	stopCtx, stopCancel := context.WithTimeout(context.Background(), stopTimeout)
+	defer stopCancel()
+
+	err := client.ContainerStop(stopCtx, containerID, container.StopOptions{})
+	if err != nil {
+		fmt.Println("failed to stop container:", err)
+	}
+}
+
+var successRegexp = regexp.MustCompile(`^.+Public IP address is .+$`)
+
+func waitForLogLine(ctx context.Context, client *client.Client, containerID string,
+	beforeStartTime time.Time,
+) error {
+	logOptions := container.LogsOptions{
+		ShowStdout: true,
+		Follow:     true,
+		Since:      beforeStartTime.Format(time.RFC3339Nano),
+	}
+
+	reader, err := client.ContainerLogs(ctx, containerID, logOptions)
+	if err != nil {
+		return fmt.Errorf("error getting container logs: %w", err)
+	}
+	defer reader.Close()
+
+	var linesSeen []string
+	scanner := bufio.NewScanner(reader)
+	for ctx.Err() == nil {
+		if scanner.Scan() {
+			line := scanner.Text()
+			if len(line) > 8 { // remove Docker log prefix
+				line = line[8:]
+			}
+			linesSeen = append(linesSeen, line)
+			if successRegexp.MatchString(line) {
+				fmt.Println("✅ Success line logged")
+				return nil
+			}
+			continue
+		}
+		err := scanner.Err()
+		if err != nil && err != io.EOF {
+			logSeenLines(linesSeen)
+			return fmt.Errorf("reading log stream: %w", err)
+		}
+
+		// The scanner is either done or cannot read because of EOF
+		fmt.Println("The log scanner stopped")
+		logSeenLines(linesSeen)
+
+		// Check if the container is still running
+		inspect, err := client.ContainerInspect(ctx, containerID)
+		if err != nil {
+			return fmt.Errorf("inspecting container: %w", err)
+		}
+		if !inspect.State.Running {
+			return fmt.Errorf("container stopped unexpectedly while waiting for log line. Exit code: %d", inspect.State.ExitCode)
+		}
+	}
+
+	return ctx.Err()
+}
+
+func logSeenLines(lines []string) {
+	fmt.Println("Logs seen so far:")
+	for _, line := range lines {
+		fmt.Println("  " + line)
+	}
+}

cmd/gluetun/main.go

@@ -270,7 +270,6 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 
 	err = printVersions(ctx, logger, []printVersionElement{
 		{name: "Alpine", getVersion: alpineConf.Version},
-		{name: "OpenVPN 2.4", getVersion: ovpnConf.Version24},
 		{name: "OpenVPN 2.5", getVersion: ovpnConf.Version25},
 		{name: "OpenVPN 2.6", getVersion: ovpnConf.Version26},
 		{name: "IPtables", getVersion: firewallConf.Version},
@@ -381,7 +380,7 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 
 	portForwardLogger := logger.New(log.SetComponent("port forwarding"))
 	portForwardLooper := portforward.NewLoop(allSettings.VPN.Provider.PortForwarding,
-		routingConf, httpClient, firewallConf, portForwardLogger, puid, pgid)
+		routingConf, httpClient, firewallConf, portForwardLogger, cmder, puid, pgid)
 	portForwardRunError, err := portForwardLooper.Start(ctx)
 	if err != nil {
 		return fmt.Errorf("starting port forwarding loop: %w", err)
@@ -415,6 +414,13 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 		return fmt.Errorf("starting public ip loop: %w", err)
 	}
 
+	healthLogger := logger.New(log.SetComponent("healthcheck"))
+	healthcheckServer := healthcheck.NewServer(allSettings.Health, healthLogger)
+	healthServerHandler, healthServerCtx, healthServerDone := goshutdown.NewGoRoutineHandler(
+		"HTTP health server", goroutine.OptionTimeout(defaultShutdownTimeout))
+	go healthcheckServer.Run(healthServerCtx, healthServerDone)
+	healthChecker := healthcheck.NewChecker(healthLogger)
+
 	updaterLogger := logger.New(log.SetComponent("updater"))
 
 	unzipper := unzip.New(httpClient)
@@ -425,8 +431,8 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 
 	vpnLogger := logger.New(log.SetComponent("vpn"))
 	vpnLooper := vpn.NewLoop(allSettings.VPN, ipv6Supported, allSettings.Firewall.VPNInputPorts,
-		providers, storage, ovpnConf, netLinker, firewallConf, routingConf, portForwardLooper,
+		providers, storage, allSettings.Health, healthChecker, healthcheckServer, ovpnConf, netLinker, firewallConf,
-		cmder, publicIPLooper, dnsLooper, vpnLogger, httpClient,
+		routingConf, portForwardLooper, cmder, publicIPLooper, dnsLooper, vpnLogger, httpClient,
 		buildInfo, *allSettings.Version.Enabled)
 	vpnHandler, vpnCtx, vpnDone := goshutdown.NewGoRoutineHandler(
 		"vpn", goroutine.OptionTimeout(time.Second))
@@ -477,12 +483,6 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 	<-httpServerReady
 	controlGroupHandler.Add(httpServerHandler)
 
-	healthLogger := logger.New(log.SetComponent("healthcheck"))
-	healthcheckServer := healthcheck.NewServer(allSettings.Health, healthLogger, vpnLooper)
-	healthServerHandler, healthServerCtx, healthServerDone := goshutdown.NewGoRoutineHandler(
-		"HTTP health server", goroutine.OptionTimeout(defaultShutdownTimeout))
-	go healthcheckServer.Run(healthServerCtx, healthServerDone)
-
 	orderHandler := goshutdown.NewOrderHandler("gluetun",
 		order.OptionTimeout(totalShutdownTimeout),
 		order.OptionOnSuccess(defaultShutdownOnSuccess),
@@ -581,6 +581,7 @@ type Linker interface {
 	LinkDel(link netlink.Link) (err error)
 	LinkSetUp(link netlink.Link) (linkIndex int, err error)
 	LinkSetDown(link netlink.Link) (err error)
+	LinkSetMTU(link netlink.Link, mtu int) error
 }
 
 type clier interface {

go.mod

@@ -1,29 +1,29 @@
 module github.com/qdm12/gluetun
 
-go 1.23
+go 1.25.0
 
 require (
-	github.com/breml/rootcerts v0.2.18
+	github.com/breml/rootcerts v0.3.3
 	github.com/fatih/color v1.18.0
 	github.com/golang/mock v1.6.0
-	github.com/klauspost/compress v1.17.11
+	github.com/klauspost/compress v1.18.1
 	github.com/klauspost/pgzip v1.2.6
-	github.com/pelletier/go-toml/v2 v2.2.2
+	github.com/pelletier/go-toml/v2 v2.2.4
-	github.com/qdm12/dns/v2 v2.0.0-rc8
+	github.com/qdm12/dns/v2 v2.0.0-rc9
-	github.com/qdm12/gosettings v0.4.3
+	github.com/qdm12/gosettings v0.4.4
 	github.com/qdm12/goshutdown v0.3.0
 	github.com/qdm12/gosplash v0.2.0
 	github.com/qdm12/gotree v0.3.0
 	github.com/qdm12/log v0.1.0
 	github.com/qdm12/ss-server v0.6.0
-	github.com/stretchr/testify v1.9.0
+	github.com/stretchr/testify v1.11.1
-	github.com/ulikunitz/xz v0.5.11
+	github.com/ulikunitz/xz v0.5.15
-	github.com/vishvananda/netlink v1.2.1
+	github.com/vishvananda/netlink v1.3.1
 	github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a
 	golang.org/x/exp v0.0.0-20241009180824-f66d83c29e7c
-	golang.org/x/net v0.30.0
+	golang.org/x/net v0.46.0
-	golang.org/x/sys v0.26.0
+	golang.org/x/sys v0.37.0
-	golang.org/x/text v0.19.0
+	golang.org/x/text v0.30.0
 	golang.zx2c4.com/wireguard v0.0.0-20231211153847-12269c276173
 	golang.zx2c4.com/wireguard/wgctrl v0.0.0-20230429144221-925a1e7659e6
 	gopkg.in/ini.v1 v1.67.0
@@ -47,13 +47,13 @@ require (
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.60.1 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
-	github.com/qdm12/goservices v0.1.0 // indirect
+	github.com/qdm12/goservices v0.1.1-0.20251104135713-6bee97bd4978 // indirect
 	github.com/riobard/go-bloom v0.0.0-20200614022211-cdc8013cb5b3 // indirect
-	github.com/vishvananda/netns v0.0.4 // indirect
+	github.com/vishvananda/netns v0.0.5 // indirect
-	golang.org/x/crypto v0.28.0 // indirect
+	golang.org/x/crypto v0.43.0 // indirect
-	golang.org/x/mod v0.21.0 // indirect
+	golang.org/x/mod v0.28.0 // indirect
-	golang.org/x/sync v0.8.0 // indirect
+	golang.org/x/sync v0.17.0 // indirect
-	golang.org/x/tools v0.26.0 // indirect
+	golang.org/x/tools v0.37.0 // indirect
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 // indirect
 	google.golang.org/protobuf v1.35.1 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

go.sum

@@ -1,10 +1,9 @@
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
-github.com/breml/rootcerts v0.2.18 h1:KjZaNT7AX/akUjzpStuwTMQs42YHlPyc6NmdwShVba0=
+github.com/breml/rootcerts v0.3.3 h1://GnaRtQ/9BY2+GtMk2wtWxVdCRysiaPr5/xBwl7NKw=
-github.com/breml/rootcerts v0.2.18/go.mod h1:S/PKh+4d1HUn4HQovEB8hPJZO6pUZYrIhmXBhsegfXw=
+github.com/breml/rootcerts v0.3.3/go.mod h1:S/PKh+4d1HUn4HQovEB8hPJZO6pUZYrIhmXBhsegfXw=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
-github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fatih/color v1.18.0 h1:S8gINlzdQ840/4pfAwic/ZE0djQEH3wM94VfqLTZcOM=
@@ -17,8 +16,8 @@ github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/josharian/native v1.1.0 h1:uuaP0hAbW7Y4l0ZRQ6C9zfb7Mg1mbFKry/xzDAfmtLA=
 github.com/josharian/native v1.1.0/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
-github.com/klauspost/compress v1.17.11 h1:In6xLpyWOi1+C7tXUUWv2ot1QvBjxevKAaI6IXrJmUc=
+github.com/klauspost/compress v1.18.1 h1:bcSGx7UbpBqMChDtsF28Lw6v/G94LPrrbMbdC3JH2co=
-github.com/klauspost/compress v1.17.11/go.mod h1:pMDklpSncoRMuLFrf1W9Ss9KT+0rH90U12bZKk7uwG0=
+github.com/klauspost/compress v1.18.1/go.mod h1:ZQFFVG+MdnR0P+l6wpXgIL4NTtwiKIdBnrBd8Nrxr+0=
 github.com/klauspost/pgzip v1.2.6 h1:8RXeL5crjEUFnR2/Sn6GJNWtSQ3Dk8pq4CL3jvdDyjU=
 github.com/klauspost/pgzip v1.2.6/go.mod h1:Ch1tH69qFZu15pkjo5kYi6mth2Zzwzt50oCQKQE9RUs=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
@@ -42,8 +41,8 @@ github.com/mikioh/ipaddr v0.0.0-20190404000644-d465c8ab6721 h1:RlZweED6sbSArvlE9
 github.com/mikioh/ipaddr v0.0.0-20190404000644-d465c8ab6721/go.mod h1:Ickgr2WtCLZ2MDGd4Gr0geeCH5HybhRJbonOgQpvSxc=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
-github.com/pelletier/go-toml/v2 v2.2.2 h1:aYUidT7k73Pcl9nb2gScu7NSrKCSHIDE89b3+6Wq+LM=
+github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
-github.com/pelletier/go-toml/v2 v2.2.2/go.mod h1:1t835xjRzz80PqgE6HHgN2JOsmgYu/h4qDAS4n929Rs=
+github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v1.20.5 h1:cxppBPuYhUnsO6yo/aoRol4L7q7UFfdm+bR9r+8l63Y=
@@ -54,12 +53,12 @@ github.com/prometheus/common v0.60.1 h1:FUas6GcOw66yB/73KC+BOZoFJmbo/1pojoILArPA
 github.com/prometheus/common v0.60.1/go.mod h1:h0LYf1R1deLSKtD4Vdg8gy4RuOvENW2J/h19V5NADQw=
 github.com/prometheus/procfs v0.15.1 h1:YagwOFzUgYfKKHX6Dr+sHT7km/hxC76UB0learggepc=
 github.com/prometheus/procfs v0.15.1/go.mod h1:fB45yRUv8NstnjriLhBQLuOUt+WW4BsoGhij/e3PBqk=
-github.com/qdm12/dns/v2 v2.0.0-rc8 h1:kbgKPkbT+79nScfuZ0ZcVhksTGo8IUqQ8TTQGnQlZ18=
+github.com/qdm12/dns/v2 v2.0.0-rc9 h1:qDzRkHr6993jknNB/ZOCnZOyIG6bsZcl2MIfdeUd0kI=
-github.com/qdm12/dns/v2 v2.0.0-rc8/go.mod h1:VaF02KWEL7xNV4oKfG4N9nEv/kR6bqyIcBReCV5NJhw=
+github.com/qdm12/dns/v2 v2.0.0-rc9/go.mod h1:98foWgXJZ+g8gJIuO+fdO+oWpFei5WShMFTeN4Im2lE=
-github.com/qdm12/goservices v0.1.0 h1:9sODefm/yuIGS7ynCkEnNlMTAYn9GzPhtcK4F69JWvc=
+github.com/qdm12/goservices v0.1.1-0.20251104135713-6bee97bd4978 h1:TRGpCU1l0lNwtogEUSs5U+RFceYxkAJUmrGabno7J5c=
-github.com/qdm12/goservices v0.1.0/go.mod h1:/JOFsAnHFiSjyoXxa5FlfX903h20K5u/3rLzCjYVMck=
+github.com/qdm12/goservices v0.1.1-0.20251104135713-6bee97bd4978/go.mod h1:D1Po4CRQLYjccnAR2JsVlN1sBMgQrcNLONbvyuzcdTg=
-github.com/qdm12/gosettings v0.4.3 h1:oGAjiKVtml9oHVlPQo6H3yk6TmtWpVYicNeGFcM7AP8=
+github.com/qdm12/gosettings v0.4.4 h1:SM6tOZDf6k8qbjWU8KWyBF4mWIixfsKCfh9DGRLHlj4=
-github.com/qdm12/gosettings v0.4.3/go.mod h1:CPrt2YC4UsURTrslmhxocVhMCW03lIrqdH2hzIf5prg=
+github.com/qdm12/gosettings v0.4.4/go.mod h1:CPrt2YC4UsURTrslmhxocVhMCW03lIrqdH2hzIf5prg=
 github.com/qdm12/goshutdown v0.3.0 h1:pqBpJkdwlZlfTEx4QHtS8u8CXx6pG0fVo6S1N0MpSEM=
 github.com/qdm12/goshutdown v0.3.0/go.mod h1:EqZ46No00kCTZ5qzdd3qIzY6ayhMt24QI8Mh8LVQYmM=
 github.com/qdm12/gosplash v0.2.0 h1:DOxCEizbW6ZG+FgpH2oK1atT6bM8MHL9GZ2ywSS4zZY=
@@ -74,43 +73,36 @@ github.com/riobard/go-bloom v0.0.0-20200614022211-cdc8013cb5b3 h1:f/FNXud6gA3MNr
 github.com/riobard/go-bloom v0.0.0-20200614022211-cdc8013cb5b3/go.mod h1:HgjTstvQsPGkxUsCd2KWxErBblirPizecHcpD3ffK+s=
 github.com/rogpeppe/go-internal v1.13.1 h1:KvO1DLK/DRN07sQ1LQKScxyZJuNnedQ5/wKSR38lUII=
 github.com/rogpeppe/go-internal v1.13.1/go.mod h1:uMEvuHeurkdAXX61udpOXGD/AzZDWNMNyH2VO9fmH0o=
-github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
-github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
-github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/ulikunitz/xz v0.5.15 h1:9DNdB5s+SgV3bQ2ApL10xRc35ck0DuIX/isZvIk+ubY=
-github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
+github.com/ulikunitz/xz v0.5.15/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
-github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/vishvananda/netlink v1.3.1 h1:3AEMt62VKqz90r0tmNhog0r/PpWKmrEShJU0wJW6bV0=
-github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/vishvananda/netlink v1.3.1/go.mod h1:ARtKouGSTGchR8aMwmkzC0qiNPrrWO5JS/XMVl45+b4=
-github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+github.com/vishvananda/netns v0.0.5 h1:DfiHV+j8bA32MFM7bfEunvT8IAqQ/NzSJHtcmW5zdEY=
-github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/vishvananda/netns v0.0.5/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
-github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
-github.com/ulikunitz/xz v0.5.11 h1:kpFauv27b6ynzBNT/Xy+1k+fK4WswhN/6PN5WhFAGw8=
-github.com/ulikunitz/xz v0.5.11/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
-github.com/vishvananda/netlink v1.2.1 h1:pfLv/qlJUwOTPvtWREA7c3PI4u81YkqZw1DYhI2HmLA=
-github.com/vishvananda/netlink v1.2.1/go.mod h1:i6NetklAujEcC6fK0JPjT8qSwWyO0HLn4UKG+hGqeJs=
-github.com/vishvananda/netns v0.0.4 h1:Oeaw1EM2JMxD51g9uhtC0D7erkIjgmj8+JZc26m1YX8=
-github.com/vishvananda/netns v0.0.4/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
 github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a h1:fZHgsYlfvtyqToslyjUt3VOPF4J7aK/3MPcK7xp3PDk=
 github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a/go.mod h1:ul22v+Nro/R083muKhosV54bj5niojjWZvU8xrevuH4=
 github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200302210943-78000ba7a073/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.28.0 h1:GBDwsMXVQi34v5CCYUm2jkJvu4cbtru2U4TN2PSyQnw=
+golang.org/x/crypto v0.43.0 h1:dduJYIi3A3KOfdGOHX8AVZ/jGiyPa3IbBozJ5kNuE04=
-golang.org/x/crypto v0.28.0/go.mod h1:rmgy+3RHxRZMyY0jjAJShp2zgEdOqj2AO7U0pYmeQ7U=
+golang.org/x/crypto v0.43.0/go.mod h1:BFbav4mRNlXJL4wNeejLpWxB7wMbc79PdRGhWKncxR0=
 golang.org/x/exp v0.0.0-20241009180824-f66d83c29e7c h1:7dEasQXItcW1xKJ2+gg5VOiBnqWrJc+rq0DPKyvvdbY=
 golang.org/x/exp v0.0.0-20241009180824-f66d83c29e7c/go.mod h1:NQtJDoLvd6faHhE7m4T/1IY708gDefGGjR/iUW8yQQ8=
 golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.21.0 h1:vvrHzRwRfVKSiLrG+d4FMl/Qi4ukBCE6kZlTUkDYRT0=
+golang.org/x/mod v0.28.0 h1:gQBtGhjxykdjY9YhZpSlZIsbnaE2+PgjfLWUQTnoZ1U=
-golang.org/x/mod v0.21.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
+golang.org/x/mod v0.28.0/go.mod h1:yfB/L0NOf/kmEbXjzCPOx1iK1fRutOydrCMsqRhEBxI=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96bSt6lcn1PtDYWL6XObtHCRCNQM=
-golang.org/x/net v0.30.0 h1:AcW1SDZMkb8IpzCdQUaIq2sP4sZ4zw+55h6ynffypl4=
+golang.org/x/net v0.46.0 h1:giFlY12I07fugqwPuWJi68oOnpfqFnJIJzaIIm2JVV4=
-golang.org/x/net v0.30.0/go.mod h1:2wGyMJ5iFasEhkwi13ChkO/t1ECNC4X4eBKkVFyYFlU=
+golang.org/x/net v0.46.0/go.mod h1:Q9BGdFy1y4nkUwiLvT5qtyhAnEHgnQ/zd8PfU6nc210=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.8.0 h1:3NFvSEYkUoMifnESzZl15y791HH1qU2xm6eCJU5ZPXQ=
+golang.org/x/sync v0.17.0 h1:l60nONMj9l5drqw6jlhIELNv9I0A4OFgRsG9k2oT9Ug=
-golang.org/x/sync v0.8.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.17.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -120,20 +112,20 @@ golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.26.0 h1:KHjCJyddX0LoSTb3J+vWpupP9p0oznkqVk/IfjymZbo=
+golang.org/x/sys v0.37.0 h1:fdNQudmxPjkdUTPnLn5mdQv7Zwvbvpaxqs831goi9kQ=
-golang.org/x/sys v0.26.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.37.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.19.0 h1:kTxAhCbGbxhK0IwgSKiMO5awPoDQ0RpfiVYBfK860YM=
+golang.org/x/text v0.30.0 h1:yznKA/E9zq54KzlzBEAWn1NXSQ8DIp/NYMy88xJjl4k=
-golang.org/x/text v0.19.0/go.mod h1:BuEKDfySbSR4drPmRPG/7iBdf8hvFMuRexcpahXilzY=
+golang.org/x/text v0.30.0/go.mod h1:yDdHFIX9t+tORqspjENWgzaCVXgk0yYnYuSZ8UzzBVM=
 golang.org/x/time v0.0.0-20220210224613-90d013bbcef8 h1:vVKdlvoWBphwdxWKrFZEuM0kGgGLxUOYcY4U/2Vjg44=
 golang.org/x/time v0.0.0-20220210224613-90d013bbcef8/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
-golang.org/x/tools v0.26.0 h1:v/60pFQmzmT9ExmjDv2gGIfi3OqfKoEP6I5+umXlbnQ=
+golang.org/x/tools v0.37.0 h1:DVSRzp7FwePZW356yEAChSdNcQo6Nsp+fex1SUW09lE=
-golang.org/x/tools v0.26.0/go.mod h1:TPVVj70c7JJ3WCazhD8OdXcZg/og+b9+tH/KxylGwH0=
+golang.org/x/tools v0.37.0/go.mod h1:MBN5QPQtLMHVdvsbtarmTNukZDdgwdwlO5qGacAzF0w=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
@@ -150,7 +142,6 @@ gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntN
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/ini.v1 v1.67.0 h1:Dgnx+6+nfE+IfzjUEISNeydPJh9AXNNsWbGP9KzCsOA=
 gopkg.in/ini.v1 v1.67.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gvisor.dev/gvisor v0.0.0-20230927004350-cbd86285d259 h1:TbRPT0HtzFP3Cno1zZo7yPzEEnfu8EjLfl6IU9VfqkQ=

internal/cli/openvpnconfig.go

@@ -56,6 +56,7 @@ func (c *CLI) OpenvpnConfig(logger OpenvpnConfigLogger, reader *reader.Reader,
 	if err != nil {
 		return err
 	}
+	allSettings.SetDefaults()
 
 	ipv6Supported, err := ipv6Checker.IsIPv6Supported()
 	if err != nil {

internal/command/split.go

@@ -0,0 +1,150 @@
+package command
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+	"unicode/utf8"
+)
+
+var (
+	ErrCommandEmpty            = errors.New("command is empty")
+	ErrSingleQuoteUnterminated = errors.New("unterminated single-quoted string")
+	ErrDoubleQuoteUnterminated = errors.New("unterminated double-quoted string")
+	ErrEscapeUnterminated      = errors.New("unterminated backslash-escape")
+)
+
+// Split splits a command string into a slice of arguments.
+// This is especially important for commands such as:
+// /bin/sh -c "echo hello"
+// which should be split into: ["/bin/sh", "-c", "echo hello"]
+// It supports backslash-escapes, single-quotes and double-quotes.
+// It does not support:
+// - the $" quoting style.
+// - expansion (brace, shell or pathname).
+func Split(command string) (words []string, err error) {
+	if command == "" {
+		return nil, fmt.Errorf("%w", ErrCommandEmpty)
+	}
+
+	const bufferSize = 1024
+	buffer := bytes.NewBuffer(make([]byte, bufferSize))
+
+	startIndex := 0
+
+	for startIndex < len(command) {
+		// skip any split characters at the start
+		character, runeSize := utf8.DecodeRuneInString(command[startIndex:])
+		switch {
+		case strings.ContainsRune(" \n\t", character):
+			startIndex += runeSize
+		case character == '\\':
+			// Look ahead to eventually skip an escaped newline
+			if command[startIndex+runeSize:] == "" {
+				return nil, fmt.Errorf("%w: %q", ErrEscapeUnterminated, command)
+			}
+			character, runeSize := utf8.DecodeRuneInString(command[startIndex+runeSize:])
+			if character == '\n' {
+				startIndex += runeSize + runeSize // backslash and newline
+			}
+		default:
+			var word string
+			buffer.Reset()
+			word, startIndex, err = splitWord(command, startIndex, buffer)
+			if err != nil {
+				return nil, fmt.Errorf("splitting word in %q: %w", command, err)
+			}
+			words = append(words, word)
+		}
+	}
+	return words, nil
+}
+
+// WARNING: buffer must be cleared before calling this function.
+func splitWord(input string, startIndex int, buffer *bytes.Buffer) (
+	word string, newStartIndex int, err error,
+) {
+	cursor := startIndex
+	for cursor < len(input) {
+		character, runeLength := utf8.DecodeRuneInString(input[cursor:])
+		cursor += runeLength
+		if character == '"' ||
+			character == '\'' ||
+			character == '\\' ||
+			character == ' ' ||
+			character == '\n' ||
+			character == '\t' {
+			buffer.WriteString(input[startIndex : cursor-runeLength])
+		}
+
+		switch {
+		case strings.ContainsRune(" \n\t", character): // spacing character
+			return buffer.String(), cursor, nil
+		case character == '"':
+			return handleDoubleQuoted(input, cursor, buffer)
+		case character == '\'':
+			return handleSingleQuoted(input, cursor, buffer)
+		case character == '\\':
+			return handleEscaped(input, cursor, buffer)
+		}
+	}
+
+	buffer.WriteString(input[startIndex:])
+	return buffer.String(), len(input), nil
+}
+
+func handleDoubleQuoted(input string, startIndex int, buffer *bytes.Buffer) (
+	word string, newStartIndex int, err error,
+) {
+	cursor := startIndex
+	for cursor < len(input) {
+		nextCharacter, nextRuneLength := utf8.DecodeRuneInString(input[cursor:])
+		cursor += nextRuneLength
+		switch nextCharacter {
+		case '"': // end of the double quoted string
+			buffer.WriteString(input[startIndex : cursor-nextRuneLength])
+			return splitWord(input, cursor, buffer)
+		case '\\': // escaped character
+			escapedCharacter, escapedRuneLength := utf8.DecodeRuneInString(input[cursor:])
+			cursor += escapedRuneLength
+			if !strings.ContainsRune("$`\"\n\\", escapedCharacter) {
+				break
+			}
+			buffer.WriteString(input[startIndex : cursor-nextRuneLength-escapedRuneLength])
+			if escapedCharacter != '\n' {
+				// skip backslash entirely for the newline character
+				buffer.WriteRune(escapedCharacter)
+			}
+			startIndex = cursor
+		}
+	}
+	return "", 0, fmt.Errorf("%w", ErrDoubleQuoteUnterminated)
+}
+
+func handleSingleQuoted(input string, startIndex int, buffer *bytes.Buffer) (
+	word string, newStartIndex int, err error,
+) {
+	closingQuoteIndex := strings.IndexRune(input[startIndex:], '\'')
+	if closingQuoteIndex == -1 {
+		return "", 0, fmt.Errorf("%w", ErrSingleQuoteUnterminated)
+	}
+	buffer.WriteString(input[startIndex : startIndex+closingQuoteIndex])
+	const singleQuoteRuneLength = 1
+	startIndex += closingQuoteIndex + singleQuoteRuneLength
+	return splitWord(input, startIndex, buffer)
+}
+
+func handleEscaped(input string, startIndex int, buffer *bytes.Buffer) (
+	word string, newStartIndex int, err error,
+) {
+	if input[startIndex:] == "" {
+		return "", 0, fmt.Errorf("%w", ErrEscapeUnterminated)
+	}
+	character, runeLength := utf8.DecodeRuneInString(input[startIndex:])
+	if character != '\n' { // backslash-escaped newline is ignored
+		buffer.WriteString(input[startIndex : startIndex+runeLength])
+	}
+	startIndex += runeLength
+	return splitWord(input, startIndex, buffer)
+}

internal/command/split_test.go

@@ -0,0 +1,110 @@
+package command
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Split(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		command    string
+		words      []string
+		errWrapped error
+		errMessage string
+	}{
+		"empty": {
+			command:    "",
+			errWrapped: ErrCommandEmpty,
+			errMessage: "command is empty",
+		},
+		"concrete_sh_command": {
+			command: `/bin/sh -c "echo 123"`,
+			words:   []string{"/bin/sh", "-c", "echo 123"},
+		},
+		"single_word": {
+			command: "word1",
+			words:   []string{"word1"},
+		},
+		"two_words_single_space": {
+			command: "word1 word2",
+			words:   []string{"word1", "word2"},
+		},
+		"two_words_multiple_space": {
+			command: "word1    word2",
+			words:   []string{"word1", "word2"},
+		},
+		"two_words_no_expansion": {
+			command: "word1*    word2?",
+			words:   []string{"word1*", "word2?"},
+		},
+		"escaped_single quote": {
+			command: "ain\\'t good",
+			words:   []string{"ain't", "good"},
+		},
+		"escaped_single_quote_all_single_quoted": {
+			command: "'ain'\\''t good'",
+			words:   []string{"ain't good"},
+		},
+		"empty_single_quoted": {
+			command: "word1 ''  word2",
+			words:   []string{"word1", "", "word2"},
+		},
+		"escaped_newline": {
+			command: "word1\\\nword2",
+			words:   []string{"word1word2"},
+		},
+		"quoted_newline": {
+			command: "text \"with\na\" quoted newline",
+			words:   []string{"text", "with\na", "quoted", "newline"},
+		},
+		"quoted_escaped_newline": {
+			command: "\"word1\\d\\\\\\\" word2\\\nword3 word4\"",
+			words:   []string{"word1\\d\\\" word2word3 word4"},
+		},
+		"escaped_separated_newline": {
+			command: "word1 \\\n word2",
+			words:   []string{"word1", "word2"},
+		},
+		"double_quotes_no_spacing": {
+			command: "word1\"word2\"word3",
+			words:   []string{"word1word2word3"},
+		},
+		"unterminated_single_quote": {
+			command:    "'abc'\\''def",
+			errWrapped: ErrSingleQuoteUnterminated,
+			errMessage: `splitting word in "'abc'\\''def": unterminated single-quoted string`,
+		},
+		"unterminated_double_quote": {
+			command:    "\"abc'def",
+			errWrapped: ErrDoubleQuoteUnterminated,
+			errMessage: `splitting word in "\"abc'def": unterminated double-quoted string`,
+		},
+		"unterminated_escape": {
+			command:    "abc\\",
+			errWrapped: ErrEscapeUnterminated,
+			errMessage: `splitting word in "abc\\": unterminated backslash-escape`,
+		},
+		"unterminated_escape_only": {
+			command:    "   \\",
+			errWrapped: ErrEscapeUnterminated,
+			errMessage: `unterminated backslash-escape: "   \\"`,
+		},
+	}
+
+	for name, testCase := range testCases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			words, err := Split(testCase.command)
+
+			assert.Equal(t, testCase.words, words)
+			assert.ErrorIs(t, err, testCase.errWrapped)
+			if testCase.errWrapped != nil {
+				assert.EqualError(t, err, testCase.errMessage)
+			}
+		})
+	}
+}

internal/configuration/settings/deprecated.go

@@ -9,9 +9,11 @@ import (
 
 func readObsolete(r *reader.Reader) (warnings []string) {
 	keyToMessage := map[string]string{
-		"DOT_VERBOSITY":           "DOT_VERBOSITY is obsolete, use LOG_LEVEL instead.",
+		"DOT_VERBOSITY":                "DOT_VERBOSITY is obsolete, use LOG_LEVEL instead.",
-		"DOT_VERBOSITY_DETAILS":   "DOT_VERBOSITY_DETAILS is obsolete because it was specific to Unbound.",
+		"DOT_VERBOSITY_DETAILS":        "DOT_VERBOSITY_DETAILS is obsolete because it was specific to Unbound.",
-		"DOT_VALIDATION_LOGLEVEL": "DOT_VALIDATION_LOGLEVEL is obsolete because DNSSEC validation is not implemented.",
+		"DOT_VALIDATION_LOGLEVEL":      "DOT_VALIDATION_LOGLEVEL is obsolete because DNSSEC validation is not implemented.",
+		"HEALTH_VPN_DURATION_INITIAL":  "HEALTH_VPN_DURATION_INITIAL is obsolete",
+		"HEALTH_VPN_DURATION_ADDITION": "HEALTH_VPN_DURATION_ADDITION is obsolete",
 	}
 	sortedKeys := maps.Keys(keyToMessage)
 	slices.Sort(sortedKeys)

internal/configuration/settings/dns.go

@@ -1,9 +1,13 @@
 package settings
 
 import (
+	"errors"
 	"fmt"
 	"net/netip"
+	"time"
 
+	"github.com/qdm12/dns/v2/pkg/provider"
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
 	"github.com/qdm12/gosettings"
 	"github.com/qdm12/gosettings/reader"
 	"github.com/qdm12/gotree"
@@ -11,10 +15,31 @@ import (
 
 // DNS contains settings to configure DNS.
 type DNS struct {
+	// ServerEnabled is true if the server should be running
+	// and used. It defaults to true, and cannot be nil
+	// in the internal state.
+	ServerEnabled *bool
+	// UpstreamType can be dot or plain, and defaults to dot.
+	UpstreamType string `json:"upstream_type"`
+	// UpdatePeriod is the period to update DNS block lists.
+	// It can be set to 0 to disable the update.
+	// It defaults to 24h and cannot be nil in
+	// the internal state.
+	UpdatePeriod *time.Duration
+	// Providers is a list of DNS providers
+	Providers []string `json:"providers"`
+	// Caching is true if the server should cache
+	// DNS responses.
+	Caching *bool `json:"caching"`
+	// IPv6 is true if the server should connect over IPv6.
+	IPv6 *bool `json:"ipv6"`
+	// Blacklist contains settings to configure the filter
+	// block lists.
+	Blacklist DNSBlacklist
 	// ServerAddress is the DNS server to use inside
 	// the Go program and for the system.
 	// It defaults to '127.0.0.1' to be used with the
-	// DoT server. It cannot be the zero value in the internal
+	// local server. It cannot be the zero value in the internal
 	// state.
 	ServerAddress netip.Addr
 	// KeepNameserver is true if the existing DNS server
@@ -23,20 +48,40 @@ type DNS struct {
 	// outside the VPN tunnel since it would go through
 	// the local DNS server of your Docker/Kubernetes
 	// configuration, which is likely not going through the tunnel.
-	// This will also disable the DNS over TLS server and the
+	// This will also disable the DNS forwarder server and the
 	// `ServerAddress` field will be ignored.
 	// It defaults to false and cannot be nil in the
 	// internal state.
 	KeepNameserver *bool
-	// DOT contains settings to configure the DoT
-	// server.
-	DoT DoT
 }
 
+var (
+	ErrDNSUpstreamTypeNotValid = errors.New("DNS upstream type is not valid")
+	ErrDNSUpdatePeriodTooShort = errors.New("update period is too short")
+)
+
 func (d DNS) validate() (err error) {
-	err = d.DoT.validate()
+	if !helpers.IsOneOf(d.UpstreamType, "dot", "doh", "plain") {
+		return fmt.Errorf("%w: %s", ErrDNSUpstreamTypeNotValid, d.UpstreamType)
+	}
+
+	const minUpdatePeriod = 30 * time.Second
+	if *d.UpdatePeriod != 0 && *d.UpdatePeriod < minUpdatePeriod {
+		return fmt.Errorf("%w: %s must be bigger than %s",
+			ErrDNSUpdatePeriodTooShort, *d.UpdatePeriod, minUpdatePeriod)
+	}
+
+	providers := provider.NewProviders()
+	for _, providerName := range d.Providers {
+		_, err := providers.Get(providerName)
+		if err != nil {
+			return err
+		}
+	}
+
+	err = d.Blacklist.validate()
 	if err != nil {
-		return fmt.Errorf("validating DoT settings: %w", err)
+		return err
 	}
 
 	return nil
@@ -44,9 +89,15 @@ func (d DNS) validate() (err error) {
 
 func (d *DNS) Copy() (copied DNS) {
 	return DNS{
+		ServerEnabled:  gosettings.CopyPointer(d.ServerEnabled),
+		UpstreamType:   d.UpstreamType,
+		UpdatePeriod:   gosettings.CopyPointer(d.UpdatePeriod),
+		Providers:      gosettings.CopySlice(d.Providers),
+		Caching:        gosettings.CopyPointer(d.Caching),
+		IPv6:           gosettings.CopyPointer(d.IPv6),
+		Blacklist:      d.Blacklist.copy(),
 		ServerAddress:  d.ServerAddress,
 		KeepNameserver: gosettings.CopyPointer(d.KeepNameserver),
-		DoT:            d.DoT.copy(),
 	}
 }
 
@@ -54,16 +105,48 @@ func (d *DNS) Copy() (copied DNS) {
 // settings object with any field set in the other
 // settings.
 func (d *DNS) overrideWith(other DNS) {
+	d.ServerEnabled = gosettings.OverrideWithPointer(d.ServerEnabled, other.ServerEnabled)
+	d.UpstreamType = gosettings.OverrideWithComparable(d.UpstreamType, other.UpstreamType)
+	d.UpdatePeriod = gosettings.OverrideWithPointer(d.UpdatePeriod, other.UpdatePeriod)
+	d.Providers = gosettings.OverrideWithSlice(d.Providers, other.Providers)
+	d.Caching = gosettings.OverrideWithPointer(d.Caching, other.Caching)
+	d.IPv6 = gosettings.OverrideWithPointer(d.IPv6, other.IPv6)
+	d.Blacklist.overrideWith(other.Blacklist)
 	d.ServerAddress = gosettings.OverrideWithValidator(d.ServerAddress, other.ServerAddress)
 	d.KeepNameserver = gosettings.OverrideWithPointer(d.KeepNameserver, other.KeepNameserver)
-	d.DoT.overrideWith(other.DoT)
 }
 
 func (d *DNS) setDefaults() {
-	localhost := netip.AddrFrom4([4]byte{127, 0, 0, 1})
+	d.ServerEnabled = gosettings.DefaultPointer(d.ServerEnabled, true)
-	d.ServerAddress = gosettings.DefaultValidator(d.ServerAddress, localhost)
+	d.UpstreamType = gosettings.DefaultComparable(d.UpstreamType, "dot")
+	const defaultUpdatePeriod = 24 * time.Hour
+	d.UpdatePeriod = gosettings.DefaultPointer(d.UpdatePeriod, defaultUpdatePeriod)
+	d.Providers = gosettings.DefaultSlice(d.Providers, []string{
+		provider.Cloudflare().Name,
+	})
+	d.Caching = gosettings.DefaultPointer(d.Caching, true)
+	d.IPv6 = gosettings.DefaultPointer(d.IPv6, false)
+	d.Blacklist.setDefaults()
+	d.ServerAddress = gosettings.DefaultValidator(d.ServerAddress,
+		netip.AddrFrom4([4]byte{127, 0, 0, 1}))
 	d.KeepNameserver = gosettings.DefaultPointer(d.KeepNameserver, false)
-	d.DoT.setDefaults()
+}
+
+func (d DNS) GetFirstPlaintextIPv4() (ipv4 netip.Addr) {
+	localhost := netip.AddrFrom4([4]byte{127, 0, 0, 1})
+	if d.ServerAddress.Compare(localhost) != 0 && d.ServerAddress.Is4() {
+		return d.ServerAddress
+	}
+
+	providers := provider.NewProviders()
+	provider, err := providers.Get(d.Providers[0])
+	if err != nil {
+		// Settings should be validated before calling this function,
+		// so an error happening here is a programming error.
+		panic(err)
+	}
+
+	return provider.Plain.IPv4[0].Addr()
 }
 
 func (d DNS) String() string {
@@ -77,11 +160,63 @@ func (d DNS) toLinesNode() (node *gotree.Node) {
 		return node
 	}
 	node.Appendf("DNS server address to use: %s", d.ServerAddress)
-	node.AppendNode(d.DoT.toLinesNode())
+
+	node.Appendf("DNS forwarder server enabled: %s", gosettings.BoolToYesNo(d.ServerEnabled))
+	if !*d.ServerEnabled {
+		return node
+	}
+
+	node.Appendf("Upstream resolver type: %s", d.UpstreamType)
+
+	upstreamResolvers := node.Append("Upstream resolvers:")
+	for _, provider := range d.Providers {
+		upstreamResolvers.Append(provider)
+	}
+
+	node.Appendf("Caching: %s", gosettings.BoolToYesNo(d.Caching))
+	node.Appendf("IPv6: %s", gosettings.BoolToYesNo(d.IPv6))
+
+	update := "disabled"
+	if *d.UpdatePeriod > 0 {
+		update = "every " + d.UpdatePeriod.String()
+	}
+	node.Appendf("Update period: %s", update)
+
+	node.AppendNode(d.Blacklist.toLinesNode())
+
 	return node
 }
 
 func (d *DNS) read(r *reader.Reader) (err error) {
+	d.ServerEnabled, err = r.BoolPtr("DNS_SERVER", reader.RetroKeys("DOT"))
+	if err != nil {
+		return err
+	}
+
+	d.UpstreamType = r.String("DNS_UPSTREAM_RESOLVER_TYPE")
+
+	d.UpdatePeriod, err = r.DurationPtr("DNS_UPDATE_PERIOD")
+	if err != nil {
+		return err
+	}
+
+	d.Providers = r.CSV("DNS_UPSTREAM_RESOLVERS", reader.RetroKeys("DOT_PROVIDERS"))
+
+	d.Caching, err = r.BoolPtr("DNS_CACHING", reader.RetroKeys("DOT_CACHING"))
+	if err != nil {
+		return err
+	}
+
+	d.IPv6, err = r.BoolPtr("DNS_UPSTREAM_IPV6", reader.RetroKeys("DOT_IPV6"))
+	if err != nil {
+		return err
+	}
+
+	err = d.Blacklist.read(r)
+	if err != nil {
+		return err
+	}
+
 	d.ServerAddress, err = r.NetipAddr("DNS_ADDRESS", reader.RetroKeys("DNS_PLAINTEXT_ADDRESS"))
 	if err != nil {
 		return err
@@ -92,10 +227,5 @@ func (d *DNS) read(r *reader.Reader) (err error) {
 		return err
 	}
 
-	err = d.DoT.read(r)
-	if err != nil {
-		return fmt.Errorf("DNS over TLS settings: %w", err)
-	}
-
 	return nil
 }

internal/configuration/settings/dnsblacklist.go

@@ -149,23 +149,45 @@ func (b *DNSBlacklist) read(r *reader.Reader) (err error) {
 		return err
 	}
 
-	b.AddBlockedIPs, b.AddBlockedIPPrefixes,
+	b.AddBlockedIPs, b.AddBlockedIPPrefixes, err = readDNSBlockedIPs(r)
-		err = readDoTPrivateAddresses(r) // TODO v4 split in 2
 	if err != nil {
 		return err
 	}
 
-	b.AllowedHosts = r.CSV("UNBLOCK") // TODO v4 change name
+	b.AllowedHosts = r.CSV("DNS_UNBLOCK_HOSTNAMES", reader.RetroKeys("UNBLOCK"))
 
 	return nil
 }
 
-var ErrPrivateAddressNotValid = errors.New("private address is not a valid IP or CIDR range")
+func readDNSBlockedIPs(r *reader.Reader) (ips []netip.Addr,
-
-func readDoTPrivateAddresses(reader *reader.Reader) (ips []netip.Addr,
 	ipPrefixes []netip.Prefix, err error,
 ) {
-	privateAddresses := reader.CSV("DOT_PRIVATE_ADDRESS")
+	ips, err = r.CSVNetipAddresses("DNS_BLOCK_IPS")
+	if err != nil {
+		return nil, nil, err
+	}
+	ipPrefixes, err = r.CSVNetipPrefixes("DNS_BLOCK_IP_PREFIXES")
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// TODO v4 remove this block below
+	privateIPs, privateIPPrefixes, err := readDNSPrivateAddresses(r)
+	if err != nil {
+		return nil, nil, err
+	}
+	ips = append(ips, privateIPs...)
+	ipPrefixes = append(ipPrefixes, privateIPPrefixes...)
+
+	return ips, ipPrefixes, nil
+}
+
+var ErrPrivateAddressNotValid = errors.New("private address is not a valid IP or CIDR range")
+
+func readDNSPrivateAddresses(r *reader.Reader) (ips []netip.Addr,
+	ipPrefixes []netip.Prefix, err error,
+) {
+	privateAddresses := r.CSV("DOT_PRIVATE_ADDRESS", reader.IsRetro("DNS_BLOCK_IP_PREFIXES"))
 	if len(privateAddresses) == 0 {
 		return nil, nil, nil
 	}

internal/configuration/settings/dot.go

@@ -1,170 +0,0 @@
-package settings
-
-import (
-	"errors"
-	"fmt"
-	"net/netip"
-	"time"
-
-	"github.com/qdm12/dns/v2/pkg/provider"
-	"github.com/qdm12/gosettings"
-	"github.com/qdm12/gosettings/reader"
-	"github.com/qdm12/gotree"
-)
-
-// DoT contains settings to configure the DoT server.
-type DoT struct {
-	// Enabled is true if the DoT server should be running
-	// and used. It defaults to true, and cannot be nil
-	// in the internal state.
-	Enabled *bool
-	// UpdatePeriod is the period to update DNS block lists.
-	// It can be set to 0 to disable the update.
-	// It defaults to 24h and cannot be nil in
-	// the internal state.
-	UpdatePeriod *time.Duration
-	// Providers is a list of DNS over TLS providers
-	Providers []string `json:"providers"`
-	// Caching is true if the DoT server should cache
-	// DNS responses.
-	Caching *bool `json:"caching"`
-	// IPv6 is true if the DoT server should connect over IPv6.
-	IPv6 *bool `json:"ipv6"`
-	// Blacklist contains settings to configure the filter
-	// block lists.
-	Blacklist DNSBlacklist
-}
-
-var ErrDoTUpdatePeriodTooShort = errors.New("update period is too short")
-
-func (d DoT) validate() (err error) {
-	const minUpdatePeriod = 30 * time.Second
-	if *d.UpdatePeriod != 0 && *d.UpdatePeriod < minUpdatePeriod {
-		return fmt.Errorf("%w: %s must be bigger than %s",
-			ErrDoTUpdatePeriodTooShort, *d.UpdatePeriod, minUpdatePeriod)
-	}
-
-	providers := provider.NewProviders()
-	for _, providerName := range d.Providers {
-		_, err := providers.Get(providerName)
-		if err != nil {
-			return err
-		}
-	}
-
-	err = d.Blacklist.validate()
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func (d *DoT) copy() (copied DoT) {
-	return DoT{
-		Enabled:      gosettings.CopyPointer(d.Enabled),
-		UpdatePeriod: gosettings.CopyPointer(d.UpdatePeriod),
-		Providers:    gosettings.CopySlice(d.Providers),
-		Caching:      gosettings.CopyPointer(d.Caching),
-		IPv6:         gosettings.CopyPointer(d.IPv6),
-		Blacklist:    d.Blacklist.copy(),
-	}
-}
-
-// overrideWith overrides fields of the receiver
-// settings object with any field set in the other
-// settings.
-func (d *DoT) overrideWith(other DoT) {
-	d.Enabled = gosettings.OverrideWithPointer(d.Enabled, other.Enabled)
-	d.UpdatePeriod = gosettings.OverrideWithPointer(d.UpdatePeriod, other.UpdatePeriod)
-	d.Providers = gosettings.OverrideWithSlice(d.Providers, other.Providers)
-	d.Caching = gosettings.OverrideWithPointer(d.Caching, other.Caching)
-	d.IPv6 = gosettings.OverrideWithPointer(d.IPv6, other.IPv6)
-	d.Blacklist.overrideWith(other.Blacklist)
-}
-
-func (d *DoT) setDefaults() {
-	d.Enabled = gosettings.DefaultPointer(d.Enabled, true)
-	const defaultUpdatePeriod = 24 * time.Hour
-	d.UpdatePeriod = gosettings.DefaultPointer(d.UpdatePeriod, defaultUpdatePeriod)
-	d.Providers = gosettings.DefaultSlice(d.Providers, []string{
-		provider.Cloudflare().Name,
-	})
-	d.Caching = gosettings.DefaultPointer(d.Caching, true)
-	d.IPv6 = gosettings.DefaultPointer(d.IPv6, false)
-	d.Blacklist.setDefaults()
-}
-
-func (d DoT) GetFirstPlaintextIPv4() (ipv4 netip.Addr) {
-	providers := provider.NewProviders()
-	provider, err := providers.Get(d.Providers[0])
-	if err != nil {
-		// Settings should be validated before calling this function,
-		// so an error happening here is a programming error.
-		panic(err)
-	}
-
-	return provider.DoT.IPv4[0].Addr()
-}
-
-func (d DoT) String() string {
-	return d.toLinesNode().String()
-}
-
-func (d DoT) toLinesNode() (node *gotree.Node) {
-	node = gotree.New("DNS over TLS settings:")
-
-	node.Appendf("Enabled: %s", gosettings.BoolToYesNo(d.Enabled))
-	if !*d.Enabled {
-		return node
-	}
-
-	update := "disabled" //nolint:goconst
-	if *d.UpdatePeriod > 0 {
-		update = "every " + d.UpdatePeriod.String()
-	}
-	node.Appendf("Update period: %s", update)
-
-	upstreamResolvers := node.Append("Upstream resolvers:")
-	for _, provider := range d.Providers {
-		upstreamResolvers.Append(provider)
-	}
-
-	node.Appendf("Caching: %s", gosettings.BoolToYesNo(d.Caching))
-	node.Appendf("IPv6: %s", gosettings.BoolToYesNo(d.IPv6))
-
-	node.AppendNode(d.Blacklist.toLinesNode())
-
-	return node
-}
-
-func (d *DoT) read(reader *reader.Reader) (err error) {
-	d.Enabled, err = reader.BoolPtr("DOT")
-	if err != nil {
-		return err
-	}
-
-	d.UpdatePeriod, err = reader.DurationPtr("DNS_UPDATE_PERIOD")
-	if err != nil {
-		return err
-	}
-
-	d.Providers = reader.CSV("DOT_PROVIDERS")
-
-	d.Caching, err = reader.BoolPtr("DOT_CACHING")
-	if err != nil {
-		return err
-	}
-
-	d.IPv6, err = reader.BoolPtr("DOT_IPV6")
-	if err != nil {
-		return err
-	}
-
-	err = d.Blacklist.read(reader)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}

internal/configuration/settings/health.go

@@ -2,6 +2,7 @@ package settings
 
 import (
 	"fmt"
+	"net/netip"
 	"os"
 	"time"
 
@@ -24,16 +25,16 @@ type Health struct {
 	// HTTP server. It defaults to 500 milliseconds.
 	ReadTimeout time.Duration
 	// TargetAddress is the address (host or host:port)
-	// to TCP dial to periodically for the health check.
+	// to TCP TLS dial to periodically for the health check.
 	// It cannot be the empty string in the internal state.
 	TargetAddress string
-	// SuccessWait is the duration to wait to re-run the
+	// ICMPTargetIP is the IP address to use for ICMP echo requests
-	// healthcheck after a successful healthcheck.
+	// in the health checker. It can be set to an unspecified address (0.0.0.0)
-	// It defaults to 5 seconds and cannot be zero in
+	// such that the VPN server IP is used, which is also the default behavior.
-	// the internal state.
+	ICMPTargetIP netip.Addr
-	SuccessWait time.Duration
+	// RestartVPN indicates whether to restart the VPN connection
-	// VPN has health settings specific to the VPN loop.
+	// when the healthcheck fails.
-	VPN HealthyWait
+	RestartVPN *bool
 }
 
 func (h Health) Validate() (err error) {
@@ -42,11 +43,6 @@ func (h Health) Validate() (err error) {
 		return fmt.Errorf("server listening address is not valid: %w", err)
 	}
 
-	err = h.VPN.validate()
-	if err != nil {
-		return fmt.Errorf("health VPN settings: %w", err)
-	}
-
 	return nil
 }
 
@@ -56,8 +52,8 @@ func (h *Health) copy() (copied Health) {
 		ReadHeaderTimeout: h.ReadHeaderTimeout,
 		ReadTimeout:       h.ReadTimeout,
 		TargetAddress:     h.TargetAddress,
-		SuccessWait:       h.SuccessWait,
+		ICMPTargetIP:      h.ICMPTargetIP,
-		VPN:               h.VPN.copy(),
+		RestartVPN:        gosettings.CopyPointer(h.RestartVPN),
 	}
 }
 
@@ -69,8 +65,8 @@ func (h *Health) OverrideWith(other Health) {
 	h.ReadHeaderTimeout = gosettings.OverrideWithComparable(h.ReadHeaderTimeout, other.ReadHeaderTimeout)
 	h.ReadTimeout = gosettings.OverrideWithComparable(h.ReadTimeout, other.ReadTimeout)
 	h.TargetAddress = gosettings.OverrideWithComparable(h.TargetAddress, other.TargetAddress)
-	h.SuccessWait = gosettings.OverrideWithComparable(h.SuccessWait, other.SuccessWait)
+	h.ICMPTargetIP = gosettings.OverrideWithComparable(h.ICMPTargetIP, other.ICMPTargetIP)
-	h.VPN.overrideWith(other.VPN)
+	h.RestartVPN = gosettings.OverrideWithPointer(h.RestartVPN, other.RestartVPN)
 }
 
 func (h *Health) SetDefaults() {
@@ -80,9 +76,8 @@ func (h *Health) SetDefaults() {
 	const defaultReadTimeout = 500 * time.Millisecond
 	h.ReadTimeout = gosettings.DefaultComparable(h.ReadTimeout, defaultReadTimeout)
 	h.TargetAddress = gosettings.DefaultComparable(h.TargetAddress, "cloudflare.com:443")
-	const defaultSuccessWait = 5 * time.Second
+	h.ICMPTargetIP = gosettings.DefaultComparable(h.ICMPTargetIP, netip.IPv4Unspecified()) // use the VPN server IP
-	h.SuccessWait = gosettings.DefaultComparable(h.SuccessWait, defaultSuccessWait)
+	h.RestartVPN = gosettings.DefaultPointer(h.RestartVPN, true)
-	h.VPN.setDefaults()
 }
 
 func (h Health) String() string {
@@ -93,10 +88,12 @@ func (h Health) toLinesNode() (node *gotree.Node) {
 	node = gotree.New("Health settings:")
 	node.Appendf("Server listening address: %s", h.ServerAddress)
 	node.Appendf("Target address: %s", h.TargetAddress)
-	node.Appendf("Duration to wait after success: %s", h.SuccessWait)
+	icmpTarget := "VPN server IP"
-	node.Appendf("Read header timeout: %s", h.ReadHeaderTimeout)
+	if !h.ICMPTargetIP.IsUnspecified() {
-	node.Appendf("Read timeout: %s", h.ReadTimeout)
+		icmpTarget = h.ICMPTargetIP.String()
-	node.AppendNode(h.VPN.toLinesNode("VPN"))
+	}
+	node.Appendf("ICMP target IP: %s", icmpTarget)
+	node.Appendf("Restart VPN on healthcheck failure: %s", gosettings.BoolToYesNo(h.RestartVPN))
 	return node
 }
 
@@ -104,16 +101,13 @@ func (h *Health) Read(r *reader.Reader) (err error) {
 	h.ServerAddress = r.String("HEALTH_SERVER_ADDRESS")
 	h.TargetAddress = r.String("HEALTH_TARGET_ADDRESS",
 		reader.RetroKeys("HEALTH_ADDRESS_TO_PING"))
-
+	h.ICMPTargetIP, err = r.NetipAddr("HEALTH_ICMP_TARGET_IP")
-	h.SuccessWait, err = r.Duration("HEALTH_SUCCESS_WAIT_DURATION")
 	if err != nil {
 		return err
 	}
-
+	h.RestartVPN, err = r.BoolPtr("HEALTH_RESTART_VPN")
-	err = h.VPN.read(r)
 	if err != nil {
-		return fmt.Errorf("VPN health settings: %w", err)
+		return err
 	}
-
 	return nil
 }

internal/configuration/settings/healthywait.go

@@ -1,76 +0,0 @@
-package settings
-
-import (
-	"time"
-
-	"github.com/qdm12/gosettings"
-	"github.com/qdm12/gosettings/reader"
-	"github.com/qdm12/gotree"
-)
-
-type HealthyWait struct {
-	// Initial is the initial duration to wait for the program
-	// to be healthy before taking action.
-	// It cannot be nil in the internal state.
-	Initial *time.Duration
-	// Addition is the duration to add to the Initial duration
-	// after Initial has expired to wait longer for the program
-	// to be healthy.
-	// It cannot be nil in the internal state.
-	Addition *time.Duration
-}
-
-func (h HealthyWait) validate() (err error) {
-	return nil
-}
-
-func (h *HealthyWait) copy() (copied HealthyWait) {
-	return HealthyWait{
-		Initial:  gosettings.CopyPointer(h.Initial),
-		Addition: gosettings.CopyPointer(h.Addition),
-	}
-}
-
-// overrideWith overrides fields of the receiver
-// settings object with any field set in the other
-// settings.
-func (h *HealthyWait) overrideWith(other HealthyWait) {
-	h.Initial = gosettings.OverrideWithPointer(h.Initial, other.Initial)
-	h.Addition = gosettings.OverrideWithPointer(h.Addition, other.Addition)
-}
-
-func (h *HealthyWait) setDefaults() {
-	const initialDurationDefault = 6 * time.Second
-	const additionDurationDefault = 5 * time.Second
-	h.Initial = gosettings.DefaultPointer(h.Initial, initialDurationDefault)
-	h.Addition = gosettings.DefaultPointer(h.Addition, additionDurationDefault)
-}
-
-func (h HealthyWait) String() string {
-	return h.toLinesNode("Health").String()
-}
-
-func (h HealthyWait) toLinesNode(kind string) (node *gotree.Node) {
-	node = gotree.New(kind + " wait durations:")
-	node.Appendf("Initial duration: %s", *h.Initial)
-	node.Appendf("Additional duration: %s", *h.Addition)
-	return node
-}
-
-func (h *HealthyWait) read(r *reader.Reader) (err error) {
-	h.Initial, err = r.DurationPtr(
-		"HEALTH_VPN_DURATION_INITIAL",
-		reader.RetroKeys("HEALTH_OPENVPN_DURATION_INITIAL"))
-	if err != nil {
-		return err
-	}
-
-	h.Addition, err = r.DurationPtr(
-		"HEALTH_VPN_DURATION_ADDITION",
-		reader.RetroKeys("HEALTH_OPENVPN_DURATION_ADDITION"))
-	if err != nil {
-		return err
-	}
-
-	return nil
-}

internal/configuration/settings/openvpn.go

@@ -19,7 +19,7 @@ import (
 // OpenVPN contains settings to configure the OpenVPN client.
 type OpenVPN struct {
 	// Version is the OpenVPN version to run.
-	// It can only be "2.4".
+	// It can only be "2.5" or "2.6".
 	Version string `json:"version"`
 	// User is the OpenVPN authentication username.
 	// It cannot be nil in the internal state if OpenVPN is used.
@@ -90,7 +90,7 @@ var ivpnAccountID = regexp.MustCompile(`^(i|ivpn)\-[a-zA-Z0-9]{4}\-[a-zA-Z0-9]{4
 
 func (o OpenVPN) validate(vpnProvider string) (err error) {
 	// Validate version
-	validVersions := []string{openvpn.Openvpn24}
+	validVersions := []string{openvpn.Openvpn25, openvpn.Openvpn26}
 	if err = validate.IsOneOf(o.Version, validVersions...); err != nil {
 		return fmt.Errorf("%w: %w", ErrOpenVPNVersionIsNotValid, err)
 	}
@@ -289,7 +289,7 @@ func (o *OpenVPN) overrideWith(other OpenVPN) {
 }
 
 func (o *OpenVPN) setDefaults(vpnProvider string) {
-	o.Version = gosettings.DefaultComparable(o.Version, openvpn.Openvpn24)
+	o.Version = gosettings.DefaultComparable(o.Version, openvpn.Openvpn26)
 	o.User = gosettings.DefaultPointer(o.User, "")
 	if vpnProvider == providers.Mullvad {
 		o.Password = gosettings.DefaultPointer(o.Password, "m")

internal/configuration/settings/portforward.go

@@ -29,6 +29,14 @@ type PortForwarding struct {
 	// to write to a file. It cannot be nil for the
 	// internal state
 	Filepath *string `json:"status_file_path"`
+	// UpCommand is the command to use when the port forwarding is up.
+	// It can be the empty string to indicate not to run a command.
+	// It cannot be nil in the internal state.
+	UpCommand *string `json:"up_command"`
+	// DownCommand is the command to use after the port forwarding goes down.
+	// It can be the empty string to indicate to NOT run a command.
+	// It cannot be nil in the internal state.
+	DownCommand *string `json:"down_command"`
 	// ListeningPort is the port traffic would be redirected to from the
 	// forwarded port. The redirection is disabled if it is set to 0, which
 	// is its default as well.
@@ -84,6 +92,8 @@ func (p *PortForwarding) Copy() (copied PortForwarding) {
 		Enabled:       gosettings.CopyPointer(p.Enabled),
 		Provider:      gosettings.CopyPointer(p.Provider),
 		Filepath:      gosettings.CopyPointer(p.Filepath),
+		UpCommand:     gosettings.CopyPointer(p.UpCommand),
+		DownCommand:   gosettings.CopyPointer(p.DownCommand),
 		ListeningPort: gosettings.CopyPointer(p.ListeningPort),
 		Username:      p.Username,
 		Password:      p.Password,
@@ -94,6 +104,8 @@ func (p *PortForwarding) OverrideWith(other PortForwarding) {
 	p.Enabled = gosettings.OverrideWithPointer(p.Enabled, other.Enabled)
 	p.Provider = gosettings.OverrideWithPointer(p.Provider, other.Provider)
 	p.Filepath = gosettings.OverrideWithPointer(p.Filepath, other.Filepath)
+	p.UpCommand = gosettings.OverrideWithPointer(p.UpCommand, other.UpCommand)
+	p.DownCommand = gosettings.OverrideWithPointer(p.DownCommand, other.DownCommand)
 	p.ListeningPort = gosettings.OverrideWithPointer(p.ListeningPort, other.ListeningPort)
 	p.Username = gosettings.OverrideWithComparable(p.Username, other.Username)
 	p.Password = gosettings.OverrideWithComparable(p.Password, other.Password)
@@ -103,6 +115,8 @@ func (p *PortForwarding) setDefaults() {
 	p.Enabled = gosettings.DefaultPointer(p.Enabled, false)
 	p.Provider = gosettings.DefaultPointer(p.Provider, "")
 	p.Filepath = gosettings.DefaultPointer(p.Filepath, "/tmp/gluetun/forwarded_port")
+	p.UpCommand = gosettings.DefaultPointer(p.UpCommand, "")
+	p.DownCommand = gosettings.DefaultPointer(p.DownCommand, "")
 	p.ListeningPort = gosettings.DefaultPointer(p.ListeningPort, 0)
 }
 
@@ -135,6 +149,13 @@ func (p PortForwarding) toLinesNode() (node *gotree.Node) {
 	}
 	node.Appendf("Forwarded port file path: %s", filepath)
 
+	if *p.UpCommand != "" {
+		node.Appendf("Forwarded port up command: %s", *p.UpCommand)
+	}
+	if *p.DownCommand != "" {
+		node.Appendf("Forwarded port down command: %s", *p.DownCommand)
+	}
+
 	if p.Username != "" {
 		credentialsNode := node.Appendf("Credentials:")
 		credentialsNode.Appendf("Username: %s", p.Username)
@@ -163,6 +184,12 @@ func (p *PortForwarding) read(r *reader.Reader) (err error) {
 			"PRIVATE_INTERNET_ACCESS_VPN_PORT_FORWARDING_STATUS_FILE",
 		))
 
+	p.UpCommand = r.Get("VPN_PORT_FORWARDING_UP_COMMAND",
+		reader.ForceLowercase(false))
+
+	p.DownCommand = r.Get("VPN_PORT_FORWARDING_DOWN_COMMAND",
+		reader.ForceLowercase(false))
+
 	p.ListeningPort, err = r.Uint16Ptr("VPN_PORT_FORWARDING_LISTENING_PORT")
 	if err != nil {
 		return err

internal/configuration/settings/serverselection.go

@@ -17,7 +17,7 @@ import (
 	"github.com/qdm12/gotree"
 )
 
-type ServerSelection struct { //nolint:maligned
+type ServerSelection struct {
 	// VPN is the VPN type which can be 'openvpn'
 	// or 'wireguard'. It cannot be the empty string
 	// in the internal state.
@@ -354,11 +354,8 @@ func (ss *ServerSelection) setDefaults(vpnProvider string, portForwardingEnabled
 	ss.SecureCoreOnly = gosettings.DefaultPointer(ss.SecureCoreOnly, false)
 	ss.TorOnly = gosettings.DefaultPointer(ss.TorOnly, false)
 	ss.MultiHopOnly = gosettings.DefaultPointer(ss.MultiHopOnly, false)
-	defaultPortForwardOnly := false
+	defaultPortForwardOnly := portForwardingEnabled &&
-	if portForwardingEnabled && helpers.IsOneOf(vpnProvider,
+		helpers.IsOneOf(vpnProvider, providers.PrivateInternetAccess, providers.Protonvpn)
-		providers.PrivateInternetAccess, providers.Protonvpn) {
-		defaultPortForwardOnly = true
-	}
 	ss.PortForwardOnly = gosettings.DefaultPointer(ss.PortForwardOnly, defaultPortForwardOnly)
 	ss.OpenVPN.setDefaults(vpnProvider)
 	ss.Wireguard.setDefaults()

internal/configuration/settings/settings.go

@@ -4,7 +4,9 @@ import (
 	"fmt"
 	"net/netip"
 
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
 	"github.com/qdm12/gluetun/internal/constants/providers"
+	"github.com/qdm12/gluetun/internal/constants/vpn"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/pprof"
 	"github.com/qdm12/gosettings/reader"
@@ -160,13 +162,25 @@ func (s Settings) Warnings() (warnings []string) {
 			" so this will likely not work anymore. See https://github.com/qdm12/gluetun/issues/1498.")
 	}
 
+	if helpers.IsOneOf(s.VPN.Provider.Name, providers.SlickVPN) &&
+		s.VPN.Type == vpn.OpenVPN {
+		warnings = append(warnings, "OpenVPN 2.5 and 2.6 use OpenSSL 3 "+
+			"which prohibits the usage of weak security in today's standards. "+
+			s.VPN.Provider.Name+" uses weak security which is out "+
+			"of Gluetun's control so the only workaround is to allow such weaknesses "+
+			`using the OpenVPN option tls-cipher "DEFAULT:@SECLEVEL=0". `+
+			"You might want to reach to your provider so they upgrade their certificates. "+
+			"Once this is done, you will have to let the Gluetun maintainers know "+
+			"by creating an issue, attaching the new certificate and we will update Gluetun.")
+	}
+
 	// TODO remove in v4
 	if s.DNS.ServerAddress.Unmap().Compare(netip.AddrFrom4([4]byte{127, 0, 0, 1})) != 0 {
 		warnings = append(warnings, "DNS address is set to "+s.DNS.ServerAddress.String()+
-			" so the DNS over TLS (DoT) server will not be used."+
+			" so the local forwarding DNS server will not be used."+
-			" The default value changed to 127.0.0.1 so it uses the internal DoT serves."+
+			" The default value changed to 127.0.0.1 so it uses the internal DNS server."+
-			" If the DoT server fails to start, the IPv4 address of the first plaintext DNS server"+
+			" If this server fails to start, the IPv4 address of the first plaintext DNS server"+
-			" corresponding to the first DoT provider chosen is used.")
+			" corresponding to the first DNS provider chosen is used.")
 	}
 
 	return warnings

internal/configuration/settings/settings_test.go

@@ -30,7 +30,7 @@ func Test_Settings_String(t *testing.T) {
 |   |           ├── Protocol: UDP
 |   |           └── Private Internet Access encryption preset: strong
 |   └── OpenVPN settings:
-|       ├── OpenVPN version: 2.4
+|       ├── OpenVPN version: 2.6
 |       ├── User: [not set]
 |       ├── Password: [not set]
 |       ├── Private Internet Access encryption preset: strong
@@ -40,17 +40,17 @@ func Test_Settings_String(t *testing.T) {
 ├── DNS settings:
 |   ├── Keep existing nameserver(s): no
 |   ├── DNS server address to use: 127.0.0.1
-|   └── DNS over TLS settings:
+|   ├── DNS forwarder server enabled: yes
-|       ├── Enabled: yes
+|   ├── Upstream resolver type: dot
-|       ├── Update period: every 24h0m0s
+|   ├── Upstream resolvers:
-|       ├── Upstream resolvers:
+|   |   └── Cloudflare
-|       |   └── Cloudflare
+|   ├── Caching: yes
-|       ├── Caching: yes
+|   ├── IPv6: no
-|       ├── IPv6: no
+|   ├── Update period: every 24h0m0s
-|       └── DNS filtering settings:
+|   └── DNS filtering settings:
-|           ├── Block malicious: yes
+|       ├── Block malicious: yes
-|           ├── Block ads: no
+|       ├── Block ads: no
-|           └── Block surveillance: yes
+|       └── Block surveillance: yes
 ├── Firewall settings:
 |   └── Enabled: yes
 ├── Log settings:
@@ -58,12 +58,8 @@ func Test_Settings_String(t *testing.T) {
 ├── Health settings:
 |   ├── Server listening address: 127.0.0.1:9999
 |   ├── Target address: cloudflare.com:443
-|   ├── Duration to wait after success: 5s
+|   ├── ICMP target IP: VPN server IP
-|   ├── Read header timeout: 100ms
+|   └── Restart VPN on healthcheck failure: yes
-|   ├── Read timeout: 500ms
-|   └── VPN wait durations:
-|       ├── Initial duration: 6s
-|       └── Additional duration: 5s
 ├── Shadowsocks server settings:
 |   └── Enabled: no
 ├── HTTP proxy settings:

internal/configuration/settings/shadowsocks.go

@@ -15,7 +15,7 @@ type Shadowsocks struct {
 	// It defaults to false, and cannot be nil in the internal state.
 	Enabled *bool
 	// Settings are settings for the TCP+UDP server.
-	tcpudp.Settings
+	Settings tcpudp.Settings
 }
 
 func (s Shadowsocks) validate() (err error) {

internal/configuration/settings/wireguard.go

@@ -45,6 +45,7 @@ type Wireguard struct {
 	// It has been lowered to 1320 following quite a bit of
 	// investigation in the issue:
 	// https://github.com/qdm12/gluetun/issues/2533.
+	// Note this should now be replaced with the PMTUD feature.
 	MTU uint16 `json:"mtu"`
 	// Implementation is the Wireguard implementation to use.
 	// It can be "auto", "userspace" or "kernelspace".

internal/constants/openvpn/versions.go

@@ -1,5 +1,6 @@
 package openvpn
 
 const (
-	Openvpn24 = "2.4"
+	Openvpn25 = "2.5"
+	Openvpn26 = "2.6"
 )

internal/dns/plaintext.go

@@ -10,15 +10,7 @@ import (
 func (l *Loop) useUnencryptedDNS(fallback bool) {
 	settings := l.GetSettings()
 
-	// Try with user provided plaintext ip address
+	targetIP := settings.GetFirstPlaintextIPv4()
-	// if it's not 127.0.0.1 (default for DoT), otherwise
-	// use the first DoT provider ipv4 address found.
-	var targetIP netip.Addr
-	if settings.ServerAddress.Compare(netip.AddrFrom4([4]byte{127, 0, 0, 1})) != 0 {
-		targetIP = settings.ServerAddress
-	} else {
-		targetIP = settings.DoT.GetFirstPlaintextIPv4()
-	}
 
 	if fallback {
 		l.logger.Info("falling back on plaintext DNS at address " + targetIP.String())
@@ -27,14 +19,15 @@ func (l *Loop) useUnencryptedDNS(fallback bool) {
 	}
 
 	const dialTimeout = 3 * time.Second
+	const defaultDNSPort = 53
 	settingsInternalDNS := nameserver.SettingsInternalDNS{
-		IP:      targetIP,
+		AddrPort: netip.AddrPortFrom(targetIP, defaultDNSPort),
-		Timeout: dialTimeout,
+		Timeout:  dialTimeout,
 	}
 	nameserver.UseDNSInternally(settingsInternalDNS)
 
 	settingsSystemWide := nameserver.SettingsSystemDNS{
-		IP:         targetIP,
+		IPs:        []netip.Addr{targetIP},
 		ResolvPath: l.resolvConf,
 	}
 	err := nameserver.UseDNSSystemWide(settingsSystemWide)

internal/dns/run.go

@@ -26,12 +26,12 @@ func (l *Loop) Run(ctx context.Context, done chan<- struct{}) {
 	}
 
 	for ctx.Err() == nil {
-		// Upper scope variables for the DNS over TLS server only
+		// Upper scope variables for the DNS forwarder server only
 		// Their values are to be used if DOT=off
 		var runError <-chan error
 
 		settings := l.GetSettings()
-		for !*settings.KeepNameserver && *settings.DoT.Enabled {
+		for !*settings.KeepNameserver && *settings.ServerEnabled {
 			var err error
 			runError, err = l.setupServer(ctx)
 			if err == nil {
@@ -56,7 +56,7 @@ func (l *Loop) Run(ctx context.Context, done chan<- struct{}) {
 		}
 
 		settings = l.GetSettings()
-		if !*settings.KeepNameserver && !*settings.DoT.Enabled {
+		if !*settings.KeepNameserver && !*settings.ServerEnabled {
 			const fallback = false
 			l.useUnencryptedDNS(fallback)
 		}
@@ -101,6 +101,6 @@ func (l *Loop) runWait(ctx context.Context, runError <-chan error) (exitLoop boo
 func (l *Loop) stopServer() {
 	stopErr := l.server.Stop()
 	if stopErr != nil {
-		l.logger.Error("stopping DoT server: " + stopErr.Error())
+		l.logger.Error("stopping server: " + stopErr.Error())
 	}
 }

internal/dns/settings.go

@@ -4,11 +4,13 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/qdm12/dns/v2/pkg/doh"
 	"github.com/qdm12/dns/v2/pkg/dot"
 	cachemiddleware "github.com/qdm12/dns/v2/pkg/middlewares/cache"
 	"github.com/qdm12/dns/v2/pkg/middlewares/cache/lru"
 	filtermiddleware "github.com/qdm12/dns/v2/pkg/middlewares/filter"
 	"github.com/qdm12/dns/v2/pkg/middlewares/filter/mapfilter"
+	"github.com/qdm12/dns/v2/pkg/plain"
 	"github.com/qdm12/dns/v2/pkg/provider"
 	"github.com/qdm12/dns/v2/pkg/server"
 	"github.com/qdm12/gluetun/internal/configuration/settings"
@@ -22,33 +24,62 @@ func (l *Loop) SetSettings(ctx context.Context, settings settings.DNS) (
 	return l.state.SetSettings(ctx, settings)
 }
 
-func buildDoTSettings(settings settings.DNS,
+func buildServerSettings(settings settings.DNS,
 	filter *mapfilter.Filter, logger Logger) (
 	serverSettings server.Settings, err error,
 ) {
 	serverSettings.Logger = logger
 
-	var dotSettings dot.Settings
 	providersData := provider.NewProviders()
-	dotSettings.UpstreamResolvers = make([]provider.Provider, len(settings.DoT.Providers))
+	upstreamResolvers := make([]provider.Provider, len(settings.Providers))
-	for i := range settings.DoT.Providers {
+	for i := range settings.Providers {
 		var err error
-		dotSettings.UpstreamResolvers[i], err = providersData.Get(settings.DoT.Providers[i])
+		upstreamResolvers[i], err = providersData.Get(settings.Providers[i])
 		if err != nil {
 			panic(err) // this should already had been checked
 		}
 	}
-	dotSettings.IPVersion = "ipv4"
+
-	if *settings.DoT.IPv6 {
+	ipVersion := "ipv4"
-		dotSettings.IPVersion = "ipv6"
+	if *settings.IPv6 {
+		ipVersion = "ipv6"
 	}
 
-	serverSettings.Dialer, err = dot.New(dotSettings)
+	var dialer server.Dialer
-	if err != nil {
+	switch settings.UpstreamType {
-		return server.Settings{}, fmt.Errorf("creating DNS over TLS dialer: %w", err)
+	case "dot":
+		dialerSettings := dot.Settings{
+			UpstreamResolvers: upstreamResolvers,
+			IPVersion:         ipVersion,
+		}
+		dialer, err = dot.New(dialerSettings)
+		if err != nil {
+			return server.Settings{}, fmt.Errorf("creating DNS over TLS dialer: %w", err)
+		}
+	case "doh":
+		dialerSettings := doh.Settings{
+			UpstreamResolvers: upstreamResolvers,
+			IPVersion:         ipVersion,
+		}
+		dialer, err = doh.New(dialerSettings)
+		if err != nil {
+			return server.Settings{}, fmt.Errorf("creating DNS over HTTPS dialer: %w", err)
+		}
+	case "plain":
+		dialerSettings := plain.Settings{
+			UpstreamResolvers: upstreamResolvers,
+			IPVersion:         ipVersion,
+		}
+		dialer, err = plain.New(dialerSettings)
+		if err != nil {
+			return server.Settings{}, fmt.Errorf("creating plain DNS dialer: %w", err)
+		}
+	default:
+		panic("unknown upstream type: " + settings.UpstreamType)
 	}
+	serverSettings.Dialer = dialer
 
-	if *settings.DoT.Caching {
+	if *settings.Caching {
 		lruCache, err := lru.New(lru.Settings{})
 		if err != nil {
 			return server.Settings{}, fmt.Errorf("creating LRU cache: %w", err)

internal/dns/setup.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/netip"
 
 	"github.com/qdm12/dns/v2/pkg/check"
 	"github.com/qdm12/dns/v2/pkg/nameserver"
@@ -20,14 +21,14 @@ func (l *Loop) setupServer(ctx context.Context) (runError <-chan error, err erro
 
 	settings := l.GetSettings()
 
-	dotSettings, err := buildDoTSettings(settings, l.filter, l.logger)
+	serverSettings, err := buildServerSettings(settings, l.filter, l.logger)
 	if err != nil {
-		return nil, fmt.Errorf("building DoT settings: %w", err)
+		return nil, fmt.Errorf("building server settings: %w", err)
 	}
 
-	server, err := server.New(dotSettings)
+	server, err := server.New(serverSettings)
 	if err != nil {
-		return nil, fmt.Errorf("creating DoT server: %w", err)
+		return nil, fmt.Errorf("creating server: %w", err)
 	}
 
 	runError, err = server.Start(ctx)
@@ -37,11 +38,12 @@ func (l *Loop) setupServer(ctx context.Context) (runError <-chan error, err erro
 	l.server = server
 
 	// use internal DNS server
+	const defaultDNSPort = 53
 	nameserver.UseDNSInternally(nameserver.SettingsInternalDNS{
-		IP: settings.ServerAddress,
+		AddrPort: netip.AddrPortFrom(settings.ServerAddress, defaultDNSPort),
 	})
 	err = nameserver.UseDNSSystemWide(nameserver.SettingsSystemDNS{
-		IP:         settings.ServerAddress,
+		IPs:        []netip.Addr{settings.ServerAddress},
 		ResolvPath: l.resolvConf,
 	})
 	if err != nil {

internal/dns/state/settings.go

@@ -27,7 +27,7 @@ func (s *State) SetSettings(ctx context.Context, settings settings.DNS) (
 
 	// Check for only update period change
 	tempSettings := s.settings.Copy()
-	*tempSettings.DoT.UpdatePeriod = *settings.DoT.UpdatePeriod
+	*tempSettings.UpdatePeriod = *settings.UpdatePeriod
 	onlyUpdatePeriodChanged := reflect.DeepEqual(tempSettings, settings)
 
 	s.settings = settings
@@ -40,7 +40,7 @@ func (s *State) SetSettings(ctx context.Context, settings settings.DNS) (
 
 	// Restart
 	_, _ = s.statusApplier.ApplyStatus(ctx, constants.Stopped)
-	if *settings.DoT.Enabled {
+	if *settings.ServerEnabled {
 		outcome, _ = s.statusApplier.ApplyStatus(ctx, constants.Running)
 	}
 	return outcome

internal/dns/ticker.go

@@ -14,7 +14,7 @@ func (l *Loop) RunRestartTicker(ctx context.Context, done chan<- struct{}) {
 	timer.Stop()
 	timerIsStopped := true
 	settings := l.GetSettings()
-	if period := *settings.DoT.UpdatePeriod; period > 0 {
+	if period := *settings.UpdatePeriod; period > 0 {
 		timer.Reset(period)
 		timerIsStopped = false
 	}
@@ -43,14 +43,14 @@ func (l *Loop) RunRestartTicker(ctx context.Context, done chan<- struct{}) {
 			_, _ = l.statusManager.ApplyStatus(ctx, constants.Running)
 
 			settings := l.GetSettings()
-			timer.Reset(*settings.DoT.UpdatePeriod)
+			timer.Reset(*settings.UpdatePeriod)
 		case <-l.updateTicker:
 			if !timer.Stop() {
 				<-timer.C
 			}
 			timerIsStopped = true
 			settings := l.GetSettings()
-			newUpdatePeriod := *settings.DoT.UpdatePeriod
+			newUpdatePeriod := *settings.UpdatePeriod
 			if newUpdatePeriod == 0 {
 				continue
 			}

internal/dns/update.go

@@ -12,7 +12,7 @@ func (l *Loop) updateFiles(ctx context.Context) (err error) {
 	settings := l.GetSettings()
 
 	l.logger.Info("downloading hostnames and IP block lists")
-	blacklistSettings := settings.DoT.Blacklist.ToBlockBuilderSettings(l.client)
+	blacklistSettings := settings.Blacklist.ToBlockBuilderSettings(l.client)
 
 	blockBuilder, err := blockbuilder.New(blacklistSettings)
 	if err != nil {

internal/firewall/delete.go

@@ -16,7 +16,7 @@ func isDeleteMatchInstruction(instruction string) bool {
 	fields := strings.Fields(instruction)
 	for i, field := range fields {
 		switch {
-		case field != "-D" && field != "--delete": //nolint:goconst
+		case field != "-D" && field != "--delete":
 			continue
 		case i == len(fields)-1: // malformed: missing chain name
 			return false

internal/firewall/firewall.go

@@ -9,7 +9,7 @@ import (
 	"github.com/qdm12/gluetun/internal/routing"
 )
 
-type Config struct { //nolint:maligned
+type Config struct {
 	runner         CmdRunner
 	logger         Logger
 	iptablesMutex  sync.Mutex

internal/firewall/ip6tables.go

@@ -58,7 +58,7 @@ var ErrPolicyNotValid = errors.New("policy is not valid")
 
 func (c *Config) setIPv6AllPolicies(ctx context.Context, policy string) error {
 	switch policy {
-	case "ACCEPT", "DROP": //nolint:goconst
+	case "ACCEPT", "DROP":
 	default:
 		return fmt.Errorf("%w: %s", ErrPolicyNotValid, policy)
 	}

internal/firewall/iptables.go

@@ -149,7 +149,7 @@ func (c *Config) acceptOutputTrafficToVPN(ctx context.Context,
 ) error {
 	protocol := connection.Protocol
 	if protocol == "tcp-client" {
-		protocol = "tcp" //nolint:goconst
+		protocol = "tcp"
 	}
 	instruction := fmt.Sprintf("%s OUTPUT -d %s -o %s -p %s -m %s --dport %d -j ACCEPT",
 		appendOrDelete(remove), connection.IP, defaultInterface, protocol,

internal/firewall/list.go

@@ -22,7 +22,7 @@ type chainRule struct {
 	packets         uint64
 	bytes           uint64
 	target          string       // "ACCEPT", "DROP", "REJECT" or "REDIRECT"
-	protocol        string       // "tcp", "udp" or "" for all protocols.
+	protocol        string       // "icmp", "tcp", "udp" or "" for all protocols.
 	inputInterface  string       // input interface, for example "tun0" or "*""
 	outputInterface string       // output interface, for example "eth0" or "*""
 	source          netip.Prefix // source IP CIDR, for example 0.0.0.0/0. Must be valid.
@@ -323,10 +323,12 @@ var ErrProtocolUnknown = errors.New("unknown protocol")
 
 func parseProtocol(s string) (protocol string, err error) {
 	switch s {
-	case "0":
+	case "0", "all":
-	case "6":
+	case "1", "icmp":
+		protocol = "icmp"
+	case "6", "tcp":
 		protocol = "tcp"
-	case "17":
+	case "17", "udp":
 		protocol = "udp"
 	default:
 		return "", fmt.Errorf("%w: %s", ErrProtocolUnknown, s)

internal/firewall/list_test.go

@@ -56,7 +56,9 @@ num pkts bytes target     prot opt in     out     source               destinati
 num pkts bytes target     prot opt in     out     source               destination
 1   0     0 ACCEPT     17   --  tun0   *       0.0.0.0/0            0.0.0.0/0            udp dpt:55405
 2   0     0 ACCEPT     6    --  tun0   *       0.0.0.0/0            0.0.0.0/0            tcp dpt:55405
-3   0     0 DROP       0    --  tun0   *       1.2.3.4              0.0.0.0/0
+3   0     0 ACCEPT     1    --  tun0   *       0.0.0.0/0            0.0.0.0/0
+4   0     0 DROP       0    --  tun0   *       1.2.3.4              0.0.0.0/0
+5   0     0 ACCEPT     all  --  tun0   *       1.2.3.4              0.0.0.0/0
 `,
 			table: chain{
 				name:    "INPUT",
@@ -92,6 +94,17 @@ num pkts bytes target     prot opt in     out     source               destinati
 						lineNumber:      3,
 						packets:         0,
 						bytes:           0,
+						target:          "ACCEPT",
+						protocol:        "icmp",
+						inputInterface:  "tun0",
+						outputInterface: "*",
+						source:          netip.MustParsePrefix("0.0.0.0/0"),
+						destination:     netip.MustParsePrefix("0.0.0.0/0"),
+					},
+					{
+						lineNumber:      4,
+						packets:         0,
+						bytes:           0,
 						target:          "DROP",
 						protocol:        "",
 						inputInterface:  "tun0",
@@ -99,6 +112,17 @@ num pkts bytes target     prot opt in     out     source               destinati
 						source:          netip.MustParsePrefix("1.2.3.4/32"),
 						destination:     netip.MustParsePrefix("0.0.0.0/0"),
 					},
+					{
+						lineNumber:      5,
+						packets:         0,
+						bytes:           0,
+						target:          "ACCEPT",
+						protocol:        "",
+						inputInterface:  "tun0",
+						outputInterface: "*",
+						source:          netip.MustParsePrefix("1.2.3.4/32"),
+						destination:     netip.MustParsePrefix("0.0.0.0/0"),
+					},
 				},
 			},
 		},

internal/firewall/support.go

@@ -92,7 +92,7 @@ func testIptablesPath(ctx context.Context, path string,
 	// Set policy as the existing policy so no mutation is done.
 	// This is an extra check for some buggy kernels where setting the policy
 	// does not work.
-	cmd = exec.CommandContext(ctx, path, "-L", "INPUT")
+	cmd = exec.CommandContext(ctx, path, "-nL", "INPUT")
 	output, err = runner.Run(cmd)
 	if err != nil {
 		unsupportedMessage = fmt.Sprintf("%s (%s)", output, err)

internal/firewall/support_test.go

@@ -24,7 +24,7 @@ func newDeleteTestRuleMatcher(path string) *cmdMatcher {
 
 func newListInputRulesMatcher(path string) *cmdMatcher {
 	return newCmdMatcher(path,
-		"^-L$", "^INPUT$")
+		"^-nL$", "^INPUT$")
 }
 
 func newSetPolicyMatcher(path, inputPolicy string) *cmdMatcher { //nolint:unparam

internal/healthcheck/checker.go

@@ -0,0 +1,250 @@
+package healthcheck
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/healthcheck/dns"
+	"github.com/qdm12/gluetun/internal/healthcheck/icmp"
+)
+
+type Checker struct {
+	tlsDialAddr string
+	dialer      *net.Dialer
+	echoer      *icmp.Echoer
+	dnsClient   *dns.Client
+	logger      Logger
+	icmpTarget  netip.Addr
+	configMutex sync.Mutex
+
+	icmpNotPermitted bool
+	smallCheckName   string
+
+	// Internal periodic service signals
+	stop context.CancelFunc
+	done <-chan struct{}
+}
+
+func NewChecker(logger Logger) *Checker {
+	return &Checker{
+		dialer: &net.Dialer{
+			Resolver: &net.Resolver{
+				PreferGo: true,
+			},
+		},
+		echoer:    icmp.NewEchoer(logger),
+		dnsClient: dns.New(),
+		logger:    logger,
+	}
+}
+
+// SetConfig sets the TCP+TLS dial address and the ICMP echo IP address
+// to target by the [Checker].
+// This function MUST be called before calling [Checker.Start].
+func (c *Checker) SetConfig(tlsDialAddr string, icmpTarget netip.Addr) {
+	c.configMutex.Lock()
+	defer c.configMutex.Unlock()
+	c.tlsDialAddr = tlsDialAddr
+	c.icmpTarget = icmpTarget
+}
+
+// Start starts the checker by first running a blocking 2s-timed TCP+TLS check,
+// and, on success, starts the periodic checks in a separate goroutine:
+// - a "small" ICMP echo check every 15 seconds
+// - a "full" TCP+TLS check every 5 minutes
+// It returns a channel `runError` that receives an error (nil or not) when a periodic check is performed.
+// It returns an error if the initial TCP+TLS check fails.
+// The Checker has to be ultimately stopped by calling [Checker.Stop].
+func (c *Checker) Start(ctx context.Context) (runError <-chan error, err error) {
+	if c.tlsDialAddr == "" || c.icmpTarget.IsUnspecified() {
+		panic("call Checker.SetConfig with non empty values before Checker.Start")
+	}
+
+	// connection isn't under load yet when the checker starts, so a short
+	// 6 seconds timeout suffices and provides quick enough feedback that
+	// the new connection is not working.
+	const timeout = 6 * time.Second
+	tcpTLSCheckCtx, tcpTLSCheckCancel := context.WithTimeout(ctx, timeout)
+	err = tcpTLSCheck(tcpTLSCheckCtx, c.dialer, c.tlsDialAddr)
+	tcpTLSCheckCancel()
+	if err != nil {
+		return nil, fmt.Errorf("startup check: %w", err)
+	}
+
+	ready := make(chan struct{})
+	ctx, cancel := context.WithCancel(context.Background())
+	c.stop = cancel
+	done := make(chan struct{})
+	c.done = done
+	c.smallCheckName = "ICMP echo"
+	const smallCheckPeriod = time.Minute
+	smallCheckTimer := time.NewTimer(smallCheckPeriod)
+	const fullCheckPeriod = 5 * time.Minute
+	fullCheckTimer := time.NewTimer(fullCheckPeriod)
+	runErrorCh := make(chan error)
+	runError = runErrorCh
+	go func() {
+		defer close(done)
+		close(ready)
+		for {
+			select {
+			case <-ctx.Done():
+				fullCheckTimer.Stop()
+				smallCheckTimer.Stop()
+				return
+			case <-smallCheckTimer.C:
+				err := c.smallPeriodicCheck(ctx)
+				if err != nil {
+					err = fmt.Errorf("small periodic check: %w", err)
+				}
+				runErrorCh <- err
+				smallCheckTimer.Reset(smallCheckPeriod)
+			case <-fullCheckTimer.C:
+				err := c.fullPeriodicCheck(ctx)
+				if err != nil {
+					err = fmt.Errorf("full periodic check: %w", err)
+				}
+				runErrorCh <- err
+				fullCheckTimer.Reset(fullCheckPeriod)
+			}
+		}
+	}()
+	<-ready
+	return runError, nil
+}
+
+func (c *Checker) Stop() error {
+	c.stop()
+	<-c.done
+	c.icmpTarget = netip.Addr{}
+	return nil
+}
+
+func (c *Checker) smallPeriodicCheck(ctx context.Context) error {
+	c.configMutex.Lock()
+	ip := c.icmpTarget
+	c.configMutex.Unlock()
+	const maxTries = 3
+	const timeout = 10 * time.Second
+	const extraTryTime = 10 * time.Second // 10s added for each subsequent retry
+	check := func(ctx context.Context) error {
+		if c.icmpNotPermitted {
+			return c.dnsClient.Check(ctx)
+		}
+		err := c.echoer.Echo(ctx, ip)
+		if errors.Is(err, icmp.ErrNotPermitted) {
+			c.icmpNotPermitted = true
+			c.smallCheckName = "plain DNS over UDP"
+			c.logger.Infof("%s; permanently falling back to %s checks.", c.smallCheckName, err)
+			return c.dnsClient.Check(ctx)
+		}
+		return err
+	}
+	return withRetries(ctx, maxTries, timeout, extraTryTime, c.logger, c.smallCheckName, check)
+}
+
+func (c *Checker) fullPeriodicCheck(ctx context.Context) error {
+	const maxTries = 2
+	// 20s timeout in case the connection is under stress
+	// See https://github.com/qdm12/gluetun/issues/2270
+	const timeout = 20 * time.Second
+	const extraTryTime = 10 * time.Second // 10s added for each subsequent retry
+	check := func(ctx context.Context) error {
+		return tcpTLSCheck(ctx, c.dialer, c.tlsDialAddr)
+	}
+	return withRetries(ctx, maxTries, timeout, extraTryTime, c.logger, "TCP+TLS dial", check)
+}
+
+func tcpTLSCheck(ctx context.Context, dialer *net.Dialer, targetAddress string) error {
+	// TODO use mullvad API if current provider is Mullvad
+
+	address, err := makeAddressToDial(targetAddress)
+	if err != nil {
+		return err
+	}
+
+	const dialNetwork = "tcp4"
+	connection, err := dialer.DialContext(ctx, dialNetwork, address)
+	if err != nil {
+		return fmt.Errorf("dialing: %w", err)
+	}
+
+	if strings.HasSuffix(address, ":443") {
+		host, _, err := net.SplitHostPort(address)
+		if err != nil {
+			return fmt.Errorf("splitting host and port: %w", err)
+		}
+		tlsConfig := &tls.Config{
+			MinVersion: tls.VersionTLS12,
+			ServerName: host,
+		}
+		tlsConnection := tls.Client(connection, tlsConfig)
+		err = tlsConnection.HandshakeContext(ctx)
+		if err != nil {
+			return fmt.Errorf("running TLS handshake: %w", err)
+		}
+	}
+
+	err = connection.Close()
+	if err != nil {
+		return fmt.Errorf("closing connection: %w", err)
+	}
+
+	return nil
+}
+
+func makeAddressToDial(address string) (addressToDial string, err error) {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		addrErr := new(net.AddrError)
+		ok := errors.As(err, &addrErr)
+		if !ok || addrErr.Err != "missing port in address" {
+			return "", fmt.Errorf("splitting host and port from address: %w", err)
+		}
+		host = address
+		const defaultPort = "443"
+		port = defaultPort
+	}
+	address = net.JoinHostPort(host, port)
+	return address, nil
+}
+
+var ErrAllCheckTriesFailed = errors.New("all check tries failed")
+
+func withRetries(ctx context.Context, maxTries uint, tryTimeout, extraTryTime time.Duration,
+	logger Logger, checkName string, check func(ctx context.Context) error,
+) error {
+	try := uint(0)
+	var errs []error
+	for {
+		timeout := tryTimeout + time.Duration(try)*extraTryTime //nolint:gosec
+		checkCtx, cancel := context.WithTimeout(ctx, timeout)
+		err := check(checkCtx)
+		cancel()
+		switch {
+		case err == nil:
+			return nil
+		case ctx.Err() != nil:
+			return fmt.Errorf("%s: %w", checkName, ctx.Err())
+		}
+		logger.Debugf("%s attempt %d/%d failed: %s", checkName, try+1, maxTries, err)
+		errs = append(errs, err)
+		try++
+		if try < maxTries {
+			continue
+		}
+		errStrings := make([]string, len(errs))
+		for i, err := range errs {
+			errStrings[i] = fmt.Sprintf("attempt %d: %s", i+1, err.Error())
+		}
+		return fmt.Errorf("%w: after %d %s attempts (%s)",
+			ErrAllCheckTriesFailed, maxTries, checkName, strings.Join(errStrings, "; "))
+	}
+}

internal/healthcheck/checker_test.go

@@ -7,12 +7,11 @@ import (
 	"testing"
 	"time"
 
-	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
-func Test_Server_healthCheck(t *testing.T) {
+func Test_Checker_fullcheck(t *testing.T) {
 	t.Parallel()
 
 	t.Run("canceled real dialer", func(t *testing.T) {
@@ -21,26 +20,28 @@ func Test_Server_healthCheck(t *testing.T) {
 		dialer := &net.Dialer{}
 		const address = "cloudflare.com:443"
 
-		server := &Server{
+		checker := &Checker{
-			dialer: dialer,
+			dialer:      dialer,
-			config: settings.Health{
+			tlsDialAddr: address,
-				TargetAddress: address,
-			},
 		}
 
 		canceledCtx, cancel := context.WithCancel(context.Background())
 		cancel()
 
-		err := server.healthCheck(canceledCtx)
+		err := checker.fullPeriodicCheck(canceledCtx)
 
 		require.Error(t, err)
-		assert.Contains(t, err.Error(), "operation was canceled")
+		assert.EqualError(t, err, "TCP+TLS dial: context canceled")
 	})
 
 	t.Run("dial localhost:0", func(t *testing.T) {
 		t.Parallel()
 
-		listener, err := net.Listen("tcp4", "localhost:0")
+		const timeout = 100 * time.Millisecond
+		ctx, cancel := context.WithTimeout(context.Background(), timeout)
+		defer cancel()
+		listenConfig := &net.ListenConfig{}
+		listener, err := listenConfig.Listen(ctx, "tcp4", "localhost:0")
 		require.NoError(t, err)
 		t.Cleanup(func() {
 			err = listener.Close()
@@ -50,18 +51,12 @@ func Test_Server_healthCheck(t *testing.T) {
 		listeningAddress := listener.Addr()
 
 		dialer := &net.Dialer{}
-		server := &Server{
+		checker := &Checker{
-			dialer: dialer,
+			dialer:      dialer,
-			config: settings.Health{
+			tlsDialAddr: listeningAddress.String(),
-				TargetAddress: listeningAddress.String(),
-			},
 		}
 
-		const timeout = 100 * time.Millisecond
+		err = checker.fullPeriodicCheck(ctx)
-		ctx, cancel := context.WithTimeout(context.Background(), timeout)
-		defer cancel()
-
-		err = server.healthCheck(ctx)
 
 		assert.NoError(t, err)
 	})

internal/healthcheck/dns/dns.go

@@ -0,0 +1,66 @@
+package dns
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+
+	"github.com/qdm12/dns/v2/pkg/provider"
+)
+
+// Client is a simple plaintext UDP DNS client, to be used for healthchecks.
+// Note the client connects to a DNS server only over UDP on port 53,
+// because we don't want to use DoT or DoH and impact the TCP connections
+// when running a healthcheck.
+type Client struct {
+	serverAddrs []netip.AddrPort
+	dnsIPIndex  int
+}
+
+func New() *Client {
+	return &Client{
+		serverAddrs: concatAddrPorts([][]netip.AddrPort{
+			provider.Cloudflare().Plain.IPv4,
+			provider.Google().Plain.IPv4,
+			provider.Quad9().Plain.IPv4,
+			provider.OpenDNS().Plain.IPv4,
+			provider.LibreDNS().Plain.IPv4,
+			provider.Quadrant().Plain.IPv4,
+			provider.CiraProtected().Plain.IPv4,
+		}),
+	}
+}
+
+func concatAddrPorts(addrs [][]netip.AddrPort) []netip.AddrPort {
+	var result []netip.AddrPort
+	for _, addrList := range addrs {
+		result = append(result, addrList...)
+	}
+	return result
+}
+
+var ErrLookupNoIPs = errors.New("no IPs found from DNS lookup")
+
+func (c *Client) Check(ctx context.Context) error {
+	dnsAddr := c.serverAddrs[c.dnsIPIndex].Addr()
+	resolver := &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, _, _ string) (net.Conn, error) {
+			dialer := net.Dialer{}
+			return dialer.DialContext(ctx, "udp", dnsAddr.String())
+		},
+	}
+	ips, err := resolver.LookupIP(ctx, "ip", "github.com")
+	switch {
+	case err != nil:
+		c.dnsIPIndex = (c.dnsIPIndex + 1) % len(c.serverAddrs)
+		return err
+	case len(ips) == 0:
+		c.dnsIPIndex = (c.dnsIPIndex + 1) % len(c.serverAddrs)
+		return fmt.Errorf("%w", ErrLookupNoIPs)
+	default:
+		return nil
+	}
+}

internal/healthcheck/handler.go

@@ -9,13 +9,15 @@ import (
 type handler struct {
 	healthErr   error
 	healthErrMu sync.RWMutex
+	logger      Logger
 }
 
 var errHealthcheckNotRunYet = errors.New("healthcheck did not run yet")
 
-func newHandler() *handler {
+func newHandler(logger Logger) *handler {
 	return &handler{
 		healthErr: errHealthcheckNotRunYet,
+		logger:    logger,
 	}
 }
 

internal/healthcheck/health.go

@@ -1,122 +0,0 @@
-package healthcheck
-
-import (
-	"context"
-	"crypto/tls"
-	"errors"
-	"fmt"
-	"net"
-	"strings"
-	"time"
-)
-
-func (s *Server) runHealthcheckLoop(ctx context.Context, done chan<- struct{}) {
-	defer close(done)
-
-	timeoutIndex := 0
-	healthcheckTimeouts := []time.Duration{
-		2 * time.Second,
-		4 * time.Second,
-		6 * time.Second,
-		8 * time.Second,
-		// This can be useful when the connection is under stress
-		// See https://github.com/qdm12/gluetun/issues/2270
-		10 * time.Second,
-	}
-	s.vpn.healthyTimer = time.NewTimer(s.vpn.healthyWait)
-
-	for {
-		previousErr := s.handler.getErr()
-
-		timeout := healthcheckTimeouts[timeoutIndex]
-		healthcheckCtx, healthcheckCancel := context.WithTimeout(
-			ctx, timeout)
-		err := s.healthCheck(healthcheckCtx)
-		healthcheckCancel()
-
-		s.handler.setErr(err)
-
-		switch {
-		case previousErr != nil && err == nil: // First success
-			s.logger.Info("healthy!")
-			timeoutIndex = 0
-			s.vpn.healthyTimer.Stop()
-			s.vpn.healthyWait = *s.config.VPN.Initial
-		case previousErr == nil && err != nil: // First failure
-			s.logger.Debug("unhealthy: " + err.Error())
-			s.vpn.healthyTimer.Stop()
-			s.vpn.healthyTimer = time.NewTimer(s.vpn.healthyWait)
-		case previousErr != nil && err != nil: // Nth failure
-			if timeoutIndex < len(healthcheckTimeouts)-1 {
-				timeoutIndex++
-			}
-			select {
-			case <-s.vpn.healthyTimer.C:
-				timeoutIndex = 0 // retry next with the smallest timeout
-				s.onUnhealthyVPN(ctx, err.Error())
-			default:
-			}
-		case previousErr == nil && err == nil: // Nth success
-			timer := time.NewTimer(s.config.SuccessWait)
-			select {
-			case <-ctx.Done():
-				return
-			case <-timer.C:
-			}
-		}
-	}
-}
-
-func (s *Server) healthCheck(ctx context.Context) (err error) {
-	// TODO use mullvad API if current provider is Mullvad
-
-	address, err := makeAddressToDial(s.config.TargetAddress)
-	if err != nil {
-		return err
-	}
-
-	const dialNetwork = "tcp4"
-	connection, err := s.dialer.DialContext(ctx, dialNetwork, address)
-	if err != nil {
-		return fmt.Errorf("dialing: %w", err)
-	}
-
-	if strings.HasSuffix(address, ":443") {
-		host, _, err := net.SplitHostPort(address)
-		if err != nil {
-			return fmt.Errorf("splitting host and port: %w", err)
-		}
-		tlsConfig := &tls.Config{
-			MinVersion: tls.VersionTLS12,
-			ServerName: host,
-		}
-		tlsConnection := tls.Client(connection, tlsConfig)
-		err = tlsConnection.HandshakeContext(ctx)
-		if err != nil {
-			return fmt.Errorf("running TLS handshake: %w", err)
-		}
-	}
-
-	err = connection.Close()
-	if err != nil {
-		return fmt.Errorf("closing connection: %w", err)
-	}
-
-	return nil
-}
-
-func makeAddressToDial(address string) (addressToDial string, err error) {
-	host, port, err := net.SplitHostPort(address)
-	if err != nil {
-		addrErr := new(net.AddrError)
-		ok := errors.As(err, &addrErr)
-		if !ok || addrErr.Err != "missing port in address" {
-			return "", fmt.Errorf("splitting host and port from address: %w", err)
-		}
-		host = address
-		const defaultPort = "443"
-		port = defaultPort
-	}
-	address = net.JoinHostPort(host, port)
-	return address, nil
-}

internal/healthcheck/icmp/apple_ipv4.go

@@ -0,0 +1,49 @@
+package icmp
+
+import (
+	"net"
+	"time"
+
+	"golang.org/x/net/ipv4"
+)
+
+var _ net.PacketConn = &ipv4Wrapper{}
+
+// ipv4Wrapper is a wrapper around ipv4.PacketConn to implement
+// the net.PacketConn interface. It's only used for Darwin or iOS.
+type ipv4Wrapper struct {
+	ipv4Conn *ipv4.PacketConn
+}
+
+func ipv4ToNetPacketConn(ipv4 *ipv4.PacketConn) *ipv4Wrapper {
+	return &ipv4Wrapper{ipv4Conn: ipv4}
+}
+
+func (i *ipv4Wrapper) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
+	n, _, addr, err = i.ipv4Conn.ReadFrom(p)
+	return n, addr, err
+}
+
+func (i *ipv4Wrapper) WriteTo(p []byte, addr net.Addr) (n int, err error) {
+	return i.ipv4Conn.WriteTo(p, nil, addr)
+}
+
+func (i *ipv4Wrapper) Close() error {
+	return i.ipv4Conn.Close()
+}
+
+func (i *ipv4Wrapper) LocalAddr() net.Addr {
+	return i.ipv4Conn.LocalAddr()
+}
+
+func (i *ipv4Wrapper) SetDeadline(t time.Time) error {
+	return i.ipv4Conn.SetDeadline(t)
+}
+
+func (i *ipv4Wrapper) SetReadDeadline(t time.Time) error {
+	return i.ipv4Conn.SetReadDeadline(t)
+}
+
+func (i *ipv4Wrapper) SetWriteDeadline(t time.Time) error {
+	return i.ipv4Conn.SetWriteDeadline(t)
+}

internal/healthcheck/icmp/echo.go

@@ -0,0 +1,193 @@
+package icmp
+
+import (
+	"bytes"
+	"context"
+	cryptorand "crypto/rand"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"math/rand/v2"
+	"net"
+	"net/netip"
+	"strings"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+var (
+	ErrICMPBodyUnsupported  = errors.New("ICMP body type is not supported")
+	ErrICMPEchoDataMismatch = errors.New("ICMP data mismatch")
+)
+
+type Echoer struct {
+	buffer       []byte
+	randomSource io.Reader
+	logger       Logger
+}
+
+func NewEchoer(logger Logger) *Echoer {
+	const maxICMPEchoSize = 1500
+	buffer := make([]byte, maxICMPEchoSize)
+	var seed [32]byte
+	_, _ = cryptorand.Read(seed[:])
+	randomSource := rand.NewChaCha8(seed)
+	return &Echoer{
+		buffer:       buffer,
+		randomSource: randomSource,
+		logger:       logger,
+	}
+}
+
+var (
+	ErrTimedOut     = errors.New("timed out waiting for ICMP echo reply")
+	ErrNotPermitted = errors.New("not permitted")
+)
+
+func (i *Echoer) Echo(ctx context.Context, ip netip.Addr) (err error) {
+	var ipVersion string
+	var conn net.PacketConn
+	if ip.Is4() {
+		ipVersion = "v4"
+		conn, err = listenICMPv4(ctx)
+	} else {
+		ipVersion = "v6"
+		conn, err = listenICMPv6(ctx)
+	}
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrNotPermitted)
+		}
+		return fmt.Errorf("listening for ICMP packets: %w", err)
+	}
+
+	go func() {
+		<-ctx.Done()
+		conn.Close()
+	}()
+
+	const echoDataSize = 32
+	id, message := buildMessageToSend(ipVersion, echoDataSize, i.randomSource)
+
+	encodedMessage, err := message.Marshal(nil)
+	if err != nil {
+		return fmt.Errorf("encoding ICMP message: %w", err)
+	}
+
+	_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice()})
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "sendto: operation not permitted") {
+			err = fmt.Errorf("%w", ErrNotPermitted)
+		}
+		return fmt.Errorf("writing ICMP message: %w", err)
+	}
+
+	receivedData, err := receiveEchoReply(conn, id, i.buffer, ipVersion, i.logger)
+	if err != nil {
+		if errors.Is(err, net.ErrClosed) && ctx.Err() != nil {
+			return fmt.Errorf("%w", ErrTimedOut)
+		}
+		return fmt.Errorf("receiving ICMP echo reply: %w", err)
+	}
+
+	sentData := message.Body.(*icmp.Echo).Data //nolint:forcetypeassert
+	if !bytes.Equal(receivedData, sentData) {
+		return fmt.Errorf("%w: sent %x and received %x", ErrICMPEchoDataMismatch, sentData, receivedData)
+	}
+
+	return nil
+}
+
+func buildMessageToSend(ipVersion string, size uint, randomSource io.Reader) (id int, message *icmp.Message) {
+	const uint16Bytes = 2
+	idBytes := make([]byte, uint16Bytes)
+	_, _ = randomSource.Read(idBytes)
+	id = int(binary.BigEndian.Uint16(idBytes))
+
+	var icmpType icmp.Type
+	switch ipVersion {
+	case "v4":
+		icmpType = ipv4.ICMPTypeEcho
+	case "v6":
+		icmpType = ipv6.ICMPTypeEchoRequest
+	default:
+		panic(fmt.Sprintf("IP version %q not supported", ipVersion))
+	}
+	messageBodyData := make([]byte, size)
+	_, _ = randomSource.Read(messageBodyData)
+
+	// See https://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml#icmp-parameters-types
+	message = &icmp.Message{
+		Type:     icmpType, // echo request
+		Code:     0,        // no code
+		Checksum: 0,        // calculated at encoding (ipv4) or sending (ipv6)
+		Body: &icmp.Echo{
+			ID:   id,
+			Seq:  0, // only one packet
+			Data: messageBodyData,
+		},
+	}
+	return id, message
+}
+
+func receiveEchoReply(conn net.PacketConn, id int, buffer []byte, ipVersion string, logger Logger,
+) (data []byte, err error) {
+	var icmpProtocol int
+	const (
+		icmpv4Protocol = 1
+		icmpv6Protocol = 58
+	)
+	switch ipVersion {
+	case "v4":
+		icmpProtocol = icmpv4Protocol
+	case "v6":
+		icmpProtocol = icmpv6Protocol
+	default:
+		panic(fmt.Sprintf("unknown IP version: %s", ipVersion))
+	}
+
+	for {
+		// Note we need to read the whole packet in one call to ReadFrom, so the buffer
+		// must be large enough to read the entire reply packet. See:
+		// https://groups.google.com/g/golang-nuts/c/5dy2Q4nPs08/m/KmuSQAGEtG4J
+		bytesRead, returnAddr, err := conn.ReadFrom(buffer)
+		if err != nil {
+			return nil, fmt.Errorf("reading from ICMP connection: %w", err)
+		}
+		packetBytes := buffer[:bytesRead]
+
+		// Parse the ICMP message
+		message, err := icmp.ParseMessage(icmpProtocol, packetBytes)
+		if err != nil {
+			return nil, fmt.Errorf("parsing message: %w", err)
+		}
+
+		switch body := message.Body.(type) {
+		case *icmp.Echo:
+			if id != body.ID {
+				logger.Warnf("ignoring ICMP echo reply mismatching expected id %d "+
+					"(id: %d, type: %d, code: %d, length: %d, return address %s)",
+					id, body.ID, message.Type, message.Code, len(packetBytes), returnAddr)
+				continue // not the ID we are looking for
+			}
+			return body.Data, nil
+		case *icmp.DstUnreach:
+			logger.Debugf("ignoring ICMP destination unreachable message (type: 3, code: %d, return address %s, expected-id %d)",
+				message.Code, returnAddr, id)
+			// See https://github.com/qdm12/gluetun/pull/2923#issuecomment-3377532249
+			// on why we ignore this message. If it is actually unreachable, the timeout on waiting for
+			// the echo reply will do instead of returning an error error.
+			continue
+		case *icmp.TimeExceeded:
+			logger.Debugf("ignoring ICMP time exceeded message (type: 11, code: %d, return address %s, expected-id %d)",
+				message.Code, returnAddr, id)
+			continue
+		default:
+			return nil, fmt.Errorf("%w: %T (type %d, code %d, return address %s, expected-id %d)",
+				ErrICMPBodyUnsupported, body, message.Type, message.Code, returnAddr, id)
+		}
+	}
+}

internal/healthcheck/icmp/interfaces.go

@@ -0,0 +1,6 @@
+package icmp
+
+type Logger interface {
+	Debugf(format string, args ...any)
+	Warnf(format string, args ...any)
+}

internal/healthcheck/icmp/listen.go

@@ -0,0 +1,35 @@
+package icmp
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"runtime"
+
+	"golang.org/x/net/ipv4"
+)
+
+func listenICMPv4(ctx context.Context) (conn net.PacketConn, err error) {
+	var listenConfig net.ListenConfig
+	const listenAddress = ""
+	packetConn, err := listenConfig.ListenPacket(ctx, "ip4:icmp", listenAddress)
+	if err != nil {
+		return nil, fmt.Errorf("listening for ICMP packets: %w", err)
+	}
+
+	if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
+		packetConn = ipv4ToNetPacketConn(ipv4.NewPacketConn(packetConn))
+	}
+
+	return packetConn, nil
+}
+
+func listenICMPv6(ctx context.Context) (conn net.PacketConn, err error) {
+	var listenConfig net.ListenConfig
+	const listenAddress = ""
+	packetConn, err := listenConfig.ListenPacket(ctx, "ip6:ipv6-icmp", listenAddress)
+	if err != nil {
+		return nil, fmt.Errorf("listening for ICMPv6 packets: %w", err)
+	}
+	return packetConn, nil
+}

internal/healthcheck/interfaces.go

@@ -0,0 +1,9 @@
+package healthcheck
+
+type Logger interface {
+	Debugf(format string, args ...any)
+	Info(s string)
+	Infof(format string, args ...any)
+	Warnf(format string, args ...any)
+	Error(s string)
+}

internal/healthcheck/logger.go

@@ -1,7 +0,0 @@
-package healthcheck
-
-type Logger interface {
-	Debug(s string)
-	Info(s string)
-	Error(s string)
-}

internal/healthcheck/openvpn.go

@@ -1,25 +0,0 @@
-package healthcheck
-
-import (
-	"context"
-	"time"
-
-	"github.com/qdm12/gluetun/internal/constants"
-)
-
-type vpnHealth struct {
-	loop         StatusApplier
-	healthyWait  time.Duration
-	healthyTimer *time.Timer
-}
-
-func (s *Server) onUnhealthyVPN(ctx context.Context, lastErrMessage string) {
-	s.logger.Info("program has been unhealthy for " +
-		s.vpn.healthyWait.String() + ": restarting VPN (healthcheck error: " + lastErrMessage + ")")
-	s.logger.Info("👉 See https://github.com/qdm12/gluetun-wiki/blob/main/faq/healthcheck.md")
-	s.logger.Info("DO NOT OPEN AN ISSUE UNLESS YOU READ AND TRIED EACH POSSIBLE SOLUTION")
-	_, _ = s.vpn.loop.ApplyStatus(ctx, constants.Stopped)
-	_, _ = s.vpn.loop.ApplyStatus(ctx, constants.Running)
-	s.vpn.healthyWait += *s.config.VPN.Addition
-	s.vpn.healthyTimer = time.NewTimer(s.vpn.healthyWait)
-}

internal/healthcheck/run.go

@@ -10,9 +10,6 @@ import (
 func (s *Server) Run(ctx context.Context, done chan<- struct{}) {
 	defer close(done)
 
-	loopDone := make(chan struct{})
-	go s.runHealthcheckLoop(ctx, loopDone)
-
 	server := http.Server{
 		Addr:              s.config.ServerAddress,
 		Handler:           s.handler,
@@ -37,6 +34,5 @@ func (s *Server) Run(ctx context.Context, done chan<- struct{}) {
 		s.logger.Error(err.Error())
 	}
 
-	<-loopDone
 	<-serverDone
 }

internal/healthcheck/server.go

@@ -2,7 +2,6 @@ package healthcheck
 
 import (
 	"context"
-	"net"
 
 	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/models"
@@ -11,30 +10,21 @@ import (
 type Server struct {
 	logger  Logger
 	handler *handler
-	dialer  *net.Dialer
 	config  settings.Health
-	vpn     vpnHealth
 }
 
-func NewServer(config settings.Health,
+func NewServer(config settings.Health, logger Logger) *Server {
-	logger Logger, vpnLoop StatusApplier,
-) *Server {
 	return &Server{
 		logger:  logger,
-		handler: newHandler(),
+		handler: newHandler(logger),
-		dialer: &net.Dialer{
+		config:  config,
-			Resolver: &net.Resolver{
-				PreferGo: true,
-			},
-		},
-		config: config,
-		vpn: vpnHealth{
-			loop:        vpnLoop,
-			healthyWait: *config.VPN.Initial,
-		},
 	}
 }
 
+func (s *Server) SetError(err error) {
+	s.handler.setErr(err)
+}
+
 type StatusApplier interface {
 	ApplyStatus(ctx context.Context, status models.LoopStatus) (
 		outcome string, err error)

internal/httpserver/run.go

@@ -20,8 +20,10 @@ func (s *Server) Run(ctx context.Context, ready chan<- struct{}, done chan<- str
 
 	crashed := make(chan struct{})
 	shutdownDone := make(chan struct{})
+	listenCtx, listenCancel := context.WithCancel(ctx)
 	go func() {
 		defer close(shutdownDone)
+		defer listenCancel()
 		select {
 		case <-ctx.Done():
 		case <-crashed:
@@ -37,7 +39,8 @@ func (s *Server) Run(ctx context.Context, ready chan<- struct{}, done chan<- str
 		}
 	}()
 
-	listener, err := net.Listen("tcp", s.address)
+	listenConfig := &net.ListenConfig{}
+	listener, err := listenConfig.Listen(listenCtx, "tcp", s.address)
 	if err != nil {
 		close(s.addressSet)
 		close(crashed) // stop shutdown goroutine

internal/mod/load.go

@@ -76,9 +76,9 @@ func initModule(path string) (err error) {
 		const flags = 0
 		err = unix.FinitModule(int(file.Fd()), moduleParams, flags)
 		switch {
-		case err == nil, err == unix.EEXIST: //nolint:goerr113
+		case err == nil, err == unix.EEXIST: //nolint:err113
 			return nil
-		case err != unix.ENOSYS: //nolint:goerr113
+		case err != unix.ENOSYS: //nolint:err113
 			if strings.HasSuffix(err.Error(), "operation not permitted") {
 				err = fmt.Errorf("%w; did you set the SYS_MODULE capability to your container?", err)
 			}

internal/natpmp/externaladdress_test.go

@@ -2,6 +2,7 @@ package natpmp
 
 import (
 	"context"
+	"net"
 	"net/netip"
 	"testing"
 	"time"
@@ -23,14 +24,15 @@ func Test_Client_ExternalAddress(t *testing.T) {
 		durationSinceStartOfEpoch time.Duration
 		externalIPv4Address       netip.Addr
 		err                       error
-		errMessage                string
+		errMessageRegex           string
 	}{
 		"failure": {
 			ctx:                 canceledCtx,
 			gateway:             netip.AddrFrom4([4]byte{127, 0, 0, 1}),
 			initialConnDuration: initialConnectionDuration,
-			err:                 context.Canceled,
+			err:                 net.ErrClosed,
-			errMessage:          "executing remote procedure call: reading from udp connection: context canceled",
+			errMessageRegex: "executing remote procedure call: setting connection deadline: " +
+				"set udp 127.0.0.1:[1-9][0-9]{1,4}: use of closed network connection",
 		},
 		"success": {
 			ctx:                 context.Background(),
@@ -60,7 +62,7 @@ func Test_Client_ExternalAddress(t *testing.T) {
 			durationSinceStartOfEpoch, externalIPv4Address, err := client.ExternalAddress(testCase.ctx, testCase.gateway)
 			assert.ErrorIs(t, err, testCase.err)
 			if testCase.err != nil {
-				assert.EqualError(t, err, testCase.errMessage)
+				assert.Regexp(t, testCase.errMessageRegex, err.Error())
 			}
 			assert.Equal(t, testCase.durationSinceStartOfEpoch, durationSinceStartOfEpoch)
 			assert.Equal(t, testCase.externalIPv4Address, externalIPv4Address)

internal/natpmp/rpc.go

@@ -45,8 +45,10 @@ func (c *Client) rpc(ctx context.Context, gateway netip.Addr,
 		cancel()
 		<-endGoroutineDone
 	}()
+	ctxListeningReady := make(chan struct{})
 	go func() {
 		defer close(endGoroutineDone)
+		close(ctxListeningReady)
 		// Context is canceled either by the parent context or
 		// when this function returns.
 		<-ctx.Done()
@@ -60,6 +62,7 @@ func (c *Client) rpc(ctx context.Context, gateway netip.Addr,
 		}
 		err = fmt.Errorf("%w; closing connection: %w", err, closeErr)
 	}()
+	<-ctxListeningReady // really to make unit testing reliable
 
 	const maxResponseSize = 16
 	response = make([]byte, maxResponseSize)

internal/netlink/family.go

@@ -13,7 +13,7 @@ const (
 func FamilyToString(family int) string {
 	switch family {
 	case FamilyAll:
-		return "all" //nolint:goconst
+		return "all"
 	case FamilyV4:
 		return "v4"
 	case FamilyV6:

internal/netlink/link.go

@@ -62,6 +62,10 @@ func (n *NetLink) LinkSetDown(link Link) (err error) {
 	return netlink.LinkSetDown(linkToNetlinkLink(&link))
 }
 
+func (n *NetLink) LinkSetMTU(link Link, mtu int) error {
+	return netlink.LinkSetMTU(linkToNetlinkLink(&link), mtu)
+}
+
 type netlinkLinkImpl struct {
 	attrs    *netlink.LinkAttrs
 	linkType string

internal/openvpn/start.go

@@ -13,7 +13,8 @@ import (
 var ErrVersionUnknown = errors.New("OpenVPN version is unknown")
 
 const (
-	binOpenvpn24 = "openvpn2.4"
+	binOpenvpn25 = "openvpn2.5"
+	binOpenvpn26 = "openvpn2.6"
 )
 
 func start(ctx context.Context, starter CmdStarter, version string, flags []string) (
@@ -21,8 +22,10 @@ func start(ctx context.Context, starter CmdStarter, version string, flags []stri
 ) {
 	var bin string
 	switch version {
-	case openvpn.Openvpn24:
+	case openvpn.Openvpn25:
-		bin = binOpenvpn24
+		bin = binOpenvpn25
+	case openvpn.Openvpn26:
+		bin = binOpenvpn26
 	default:
 		return nil, nil, nil, fmt.Errorf("%w: %s", ErrVersionUnknown, version)
 	}

internal/openvpn/version.go

@@ -8,8 +8,12 @@ import (
 	"strings"
 )
 
-func (c *Configurator) Version24(ctx context.Context) (version string, err error) {
+func (c *Configurator) Version25(ctx context.Context) (version string, err error) {
-	return c.version(ctx, binOpenvpn24)
+	return c.version(ctx, binOpenvpn25)
+}
+
+func (c *Configurator) Version26(ctx context.Context) (version string, err error) {
+	return c.version(ctx, binOpenvpn26)
 }
 
 var ErrVersionTooShort = errors.New("version output is too short")

internal/pmtud/apple_ipv4.go

@@ -0,0 +1,49 @@
+package pmtud
+
+import (
+	"net"
+	"time"
+
+	"golang.org/x/net/ipv4"
+)
+
+var _ net.PacketConn = &ipv4Wrapper{}
+
+// ipv4Wrapper is a wrapper around ipv4.PacketConn to implement
+// the net.PacketConn interface. It's only used for Darwin or iOS.
+type ipv4Wrapper struct {
+	ipv4Conn *ipv4.PacketConn
+}
+
+func ipv4ToNetPacketConn(ipv4 *ipv4.PacketConn) *ipv4Wrapper {
+	return &ipv4Wrapper{ipv4Conn: ipv4}
+}
+
+func (i *ipv4Wrapper) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
+	n, _, addr, err = i.ipv4Conn.ReadFrom(p)
+	return n, addr, err
+}
+
+func (i *ipv4Wrapper) WriteTo(p []byte, addr net.Addr) (n int, err error) {
+	return i.ipv4Conn.WriteTo(p, nil, addr)
+}
+
+func (i *ipv4Wrapper) Close() error {
+	return i.ipv4Conn.Close()
+}
+
+func (i *ipv4Wrapper) LocalAddr() net.Addr {
+	return i.ipv4Conn.LocalAddr()
+}
+
+func (i *ipv4Wrapper) SetDeadline(t time.Time) error {
+	return i.ipv4Conn.SetDeadline(t)
+}
+
+func (i *ipv4Wrapper) SetReadDeadline(t time.Time) error {
+	return i.ipv4Conn.SetReadDeadline(t)
+}
+
+func (i *ipv4Wrapper) SetWriteDeadline(t time.Time) error {
+	return i.ipv4Conn.SetWriteDeadline(t)
+}

internal/pmtud/check.go

@@ -0,0 +1,83 @@
+package pmtud
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+
+	"golang.org/x/net/icmp"
+)
+
+var (
+	ErrICMPNextHopMTUTooLow  = errors.New("ICMP Next Hop MTU is too low")
+	ErrICMPNextHopMTUTooHigh = errors.New("ICMP Next Hop MTU is too high")
+)
+
+func checkMTU(mtu, minMTU, physicalLinkMTU int) (err error) {
+	switch {
+	case mtu < minMTU:
+		return fmt.Errorf("%w: %d", ErrICMPNextHopMTUTooLow, mtu)
+	case mtu > physicalLinkMTU:
+		return fmt.Errorf("%w: %d is larger than physical link MTU %d",
+			ErrICMPNextHopMTUTooHigh, mtu, physicalLinkMTU)
+	default:
+		return nil
+	}
+}
+
+func checkInvokingReplyIDMatch(icmpProtocol int, received []byte,
+	outboundMessage *icmp.Message,
+) (match bool, err error) {
+	inboundMessage, err := icmp.ParseMessage(icmpProtocol, received)
+	if err != nil {
+		return false, fmt.Errorf("parsing invoking packet: %w", err)
+	}
+	inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
+	if !ok {
+		return false, fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, inboundMessage.Body)
+	}
+	outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
+	return inboundBody.ID == outboundBody.ID, nil
+}
+
+var ErrICMPIDMismatch = errors.New("ICMP id mismatch")
+
+func checkEchoReply(icmpProtocol int, received []byte,
+	outboundMessage *icmp.Message, truncatedBody bool,
+) (err error) {
+	inboundMessage, err := icmp.ParseMessage(icmpProtocol, received)
+	if err != nil {
+		return fmt.Errorf("parsing invoking packet: %w", err)
+	}
+	inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
+	if !ok {
+		return fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, inboundMessage.Body)
+	}
+	outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
+	if inboundBody.ID != outboundBody.ID {
+		return fmt.Errorf("%w: sent id %d and received id %d",
+			ErrICMPIDMismatch, outboundBody.ID, inboundBody.ID)
+	}
+	err = checkEchoBodies(outboundBody.Data, inboundBody.Data, truncatedBody)
+	if err != nil {
+		return fmt.Errorf("checking sent and received bodies: %w", err)
+	}
+	return nil
+}
+
+var ErrICMPEchoDataMismatch = errors.New("ICMP data mismatch")
+
+func checkEchoBodies(sent, received []byte, receivedTruncated bool) (err error) {
+	if len(received) > len(sent) {
+		return fmt.Errorf("%w: sent %d bytes and received %d bytes",
+			ErrICMPEchoDataMismatch, len(sent), len(received))
+	}
+	if receivedTruncated {
+		sent = sent[:len(received)]
+	}
+	if !bytes.Equal(received, sent) {
+		return fmt.Errorf("%w: sent %x and received %x",
+			ErrICMPEchoDataMismatch, sent, received)
+	}
+	return nil
+}

internal/pmtud/df.go

@@ -0,0 +1,10 @@
+//go:build !linux && !windows
+
+package pmtud
+
+// setDontFragment for platforms other than Linux and Windows
+// is not implemented, so we just return assuming the don't
+// fragment flag is set on IP packets.
+func setDontFragment(fd uintptr) (err error) {
+	return nil
+}

internal/pmtud/df_linux.go

@@ -0,0 +1,12 @@
+//go:build linux
+
+package pmtud
+
+import (
+	"syscall"
+)
+
+func setDontFragment(fd uintptr) (err error) {
+	return syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP,
+		syscall.IP_MTU_DISCOVER, syscall.IP_PMTUDISC_PROBE)
+}

internal/pmtud/df_windows.go

@@ -0,0 +1,13 @@
+//go:build windows
+
+package pmtud
+
+import (
+	"syscall"
+)
+
+func setDontFragment(fd uintptr) (err error) {
+	// https://docs.microsoft.com/en-us/troubleshoot/windows/win32/header-library-requirement-socket-ipproto-ip
+	// #define IP_DONTFRAGMENT        14     /* don't fragment IP datagrams */
+	return syscall.SetsockoptInt(syscall.Handle(fd), syscall.IPPROTO_IP, 14, 1)
+}

internal/pmtud/errors.go

@@ -0,0 +1,29 @@
+package pmtud
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+	"time"
+)
+
+var (
+	ErrICMPNotPermitted                            = errors.New("ICMP not permitted")
+	ErrICMPDestinationUnreachable                  = errors.New("ICMP destination unreachable")
+	ErrICMPCommunicationAdministrativelyProhibited = errors.New("communication administratively prohibited")
+	ErrICMPBodyUnsupported                         = errors.New("ICMP body type is not supported")
+)
+
+func wrapConnErr(err error, timedCtx context.Context, pingTimeout time.Duration) error { //nolint:revive
+	switch {
+	case strings.HasSuffix(err.Error(), "sendto: operation not permitted"):
+		err = fmt.Errorf("%w", ErrICMPNotPermitted)
+	case errors.Is(timedCtx.Err(), context.DeadlineExceeded):
+		err = fmt.Errorf("%w (timed out after %s)", net.ErrClosed, pingTimeout)
+	case timedCtx.Err() != nil:
+		err = timedCtx.Err()
+	}
+	return err
+}

internal/pmtud/interfaces.go

@@ -0,0 +1,7 @@
+package pmtud
+
+type Logger interface {
+	Debug(msg string)
+	Debugf(msg string, args ...any)
+	Warnf(msg string, args ...any)
+}

internal/pmtud/ipv4.go

@@ -0,0 +1,159 @@
+package pmtud
+
+import (
+	"context"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"net/netip"
+	"runtime"
+	"strings"
+	"syscall"
+	"time"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+)
+
+const (
+	// see https://en.wikipedia.org/wiki/Maximum_transmission_unit#MTUs_for_common_media
+	minIPv4MTU     = 68
+	icmpv4Protocol = 1
+)
+
+func listenICMPv4(ctx context.Context) (conn net.PacketConn, err error) {
+	var listenConfig net.ListenConfig
+	listenConfig.Control = func(_, _ string, rawConn syscall.RawConn) error {
+		var setDFErr error
+		err := rawConn.Control(func(fd uintptr) {
+			setDFErr = setDontFragment(fd) // runs when calling ListenPacket
+		})
+		if err == nil {
+			err = setDFErr
+		}
+		return err
+	}
+
+	const listenAddress = ""
+	packetConn, err := listenConfig.ListenPacket(ctx, "ip4:icmp", listenAddress)
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
+		return nil, err
+	}
+
+	if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
+		packetConn = ipv4ToNetPacketConn(ipv4.NewPacketConn(packetConn))
+	}
+
+	return packetConn, nil
+}
+
+func findIPv4NextHopMTU(ctx context.Context, ip netip.Addr,
+	physicalLinkMTU int, pingTimeout time.Duration, logger Logger,
+) (mtu int, err error) {
+	if ip.Is6() {
+		panic("IP address is not v4")
+	}
+	conn, err := listenICMPv4(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("listening for ICMP packets: %w", err)
+	}
+	ctx, cancel := context.WithTimeout(ctx, pingTimeout)
+	defer cancel()
+	go func() {
+		<-ctx.Done()
+		conn.Close()
+	}()
+
+	// First try to send a packet which is too big to get the maximum MTU
+	// directly.
+	outboundID, outboundMessage := buildMessageToSend("v4", physicalLinkMTU)
+	encodedMessage, err := outboundMessage.Marshal(nil)
+	if err != nil {
+		return 0, fmt.Errorf("encoding ICMP message: %w", err)
+	}
+
+	_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice()})
+	if err != nil {
+		err = wrapConnErr(err, ctx, pingTimeout)
+		return 0, fmt.Errorf("writing ICMP message: %w", err)
+	}
+
+	buffer := make([]byte, physicalLinkMTU)
+
+	for { // for loop in case we read an echo reply for another ICMP request
+		// Note we need to read the whole packet in one call to ReadFrom, so the buffer
+		// must be large enough to read the entire reply packet. See:
+		// https://groups.google.com/g/golang-nuts/c/5dy2Q4nPs08/m/KmuSQAGEtG4J
+		bytesRead, _, err := conn.ReadFrom(buffer)
+		if err != nil {
+			err = wrapConnErr(err, ctx, pingTimeout)
+			return 0, fmt.Errorf("reading from ICMP connection: %w", err)
+		}
+		packetBytes := buffer[:bytesRead]
+		// Side note: echo reply should be at most the number of bytes
+		// sent, and can be lower, more precisely 576-ipHeader bytes,
+		// in case the next hop we are reaching replies with a destination
+		// unreachable and wants to ensure the response makes it way back
+		// by keeping a low packet size, see:
+		// https://datatracker.ietf.org/doc/html/rfc1122#page-59
+
+		inboundMessage, err := icmp.ParseMessage(icmpv4Protocol, packetBytes)
+		if err != nil {
+			return 0, fmt.Errorf("parsing message: %w", err)
+		}
+
+		switch typedBody := inboundMessage.Body.(type) {
+		case *icmp.DstUnreach:
+			const fragmentationRequiredAndDFFlagSetCode = 4
+			const communicationAdministrativelyProhibitedCode = 13
+			switch inboundMessage.Code {
+			case fragmentationRequiredAndDFFlagSetCode:
+			case communicationAdministrativelyProhibitedCode:
+				return 0, fmt.Errorf("%w: %w (code %d)",
+					ErrICMPDestinationUnreachable,
+					ErrICMPCommunicationAdministrativelyProhibited,
+					inboundMessage.Code)
+			default:
+				return 0, fmt.Errorf("%w: code %d",
+					ErrICMPDestinationUnreachable, inboundMessage.Code)
+			}
+
+			// See https://datatracker.ietf.org/doc/html/rfc1191#section-4
+			// Note: the go library does not handle this NextHopMTU section.
+			nextHopMTU := packetBytes[6:8]
+			mtu = int(binary.BigEndian.Uint16(nextHopMTU))
+			err = checkMTU(mtu, minIPv4MTU, physicalLinkMTU)
+			if err != nil {
+				return 0, fmt.Errorf("checking next-hop-mtu found: %w", err)
+			}
+
+			// The code below is really for sanity checks
+			packetBytes = packetBytes[8:]
+			header, err := ipv4.ParseHeader(packetBytes)
+			if err != nil {
+				return 0, fmt.Errorf("parsing IPv4 header: %w", err)
+			}
+			packetBytes = packetBytes[header.Len:] // truncated original datagram
+
+			const truncated = true
+			err = checkEchoReply(icmpv4Protocol, packetBytes, outboundMessage, truncated)
+			if err != nil {
+				return 0, fmt.Errorf("checking echo reply: %w", err)
+			}
+			return mtu, nil
+		case *icmp.Echo:
+			inboundID := uint16(typedBody.ID) //nolint:gosec
+			if inboundID == outboundID {
+				return physicalLinkMTU, nil
+			}
+			logger.Debugf("discarding received ICMP echo reply with id %d mismatching sent id %d",
+				inboundID, outboundID)
+			continue
+		default:
+			return 0, fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, typedBody)
+		}
+	}
+}

internal/pmtud/ipv6.go

@@ -0,0 +1,122 @@
+package pmtud
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"strings"
+	"time"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv6"
+)
+
+const (
+	minIPv6MTU     = 1280
+	icmpv6Protocol = 58
+)
+
+func listenICMPv6(ctx context.Context) (conn net.PacketConn, err error) {
+	var listenConfig net.ListenConfig
+	const listenAddress = ""
+	packetConn, err := listenConfig.ListenPacket(ctx, "ip6:ipv6-icmp", listenAddress)
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
+		return nil, err
+	}
+	return packetConn, nil
+}
+
+func getIPv6PacketTooBig(ctx context.Context, ip netip.Addr,
+	physicalLinkMTU int, pingTimeout time.Duration, logger Logger,
+) (mtu int, err error) {
+	if ip.Is4() {
+		panic("IP address is not v6")
+	}
+	conn, err := listenICMPv6(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("listening for ICMP packets: %w", err)
+	}
+	ctx, cancel := context.WithTimeout(ctx, pingTimeout)
+	defer cancel()
+	go func() {
+		<-ctx.Done()
+		conn.Close()
+	}()
+
+	// First try to send a packet which is too big to get the maximum MTU
+	// directly.
+	outboundID, outboundMessage := buildMessageToSend("v6", physicalLinkMTU)
+	encodedMessage, err := outboundMessage.Marshal(nil)
+	if err != nil {
+		return 0, fmt.Errorf("encoding ICMP message: %w", err)
+	}
+
+	_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice(), Zone: ip.Zone()})
+	if err != nil {
+		err = wrapConnErr(err, ctx, pingTimeout)
+		return 0, fmt.Errorf("writing ICMP message: %w", err)
+	}
+
+	buffer := make([]byte, physicalLinkMTU)
+
+	for { // for loop if we encounter another ICMP packet with an unknown id.
+		// Note we need to read the whole packet in one call to ReadFrom, so the buffer
+		// must be large enough to read the entire reply packet. See:
+		// https://groups.google.com/g/golang-nuts/c/5dy2Q4nPs08/m/KmuSQAGEtG4J
+		bytesRead, _, err := conn.ReadFrom(buffer)
+		if err != nil {
+			err = wrapConnErr(err, ctx, pingTimeout)
+			return 0, fmt.Errorf("reading from ICMP connection: %w", err)
+		}
+		packetBytes := buffer[:bytesRead]
+
+		packetBytes = packetBytes[ipv6.HeaderLen:]
+
+		inboundMessage, err := icmp.ParseMessage(icmpv6Protocol, packetBytes)
+		if err != nil {
+			return 0, fmt.Errorf("parsing message: %w", err)
+		}
+
+		switch typedBody := inboundMessage.Body.(type) {
+		case *icmp.PacketTooBig:
+			// https://datatracker.ietf.org/doc/html/rfc1885#section-3.2
+			mtu = typedBody.MTU
+			err = checkMTU(mtu, minIPv6MTU, physicalLinkMTU)
+			if err != nil {
+				return 0, fmt.Errorf("checking MTU: %w", err)
+			}
+
+			// Sanity checks
+			const truncatedBody = true
+			err = checkEchoReply(icmpv6Protocol, typedBody.Data, outboundMessage, truncatedBody)
+			if err != nil {
+				return 0, fmt.Errorf("checking invoking message: %w", err)
+			}
+			return typedBody.MTU, nil
+		case *icmp.DstUnreach:
+			// https://datatracker.ietf.org/doc/html/rfc1885#section-3.1
+			idMatch, err := checkInvokingReplyIDMatch(icmpv6Protocol, packetBytes, outboundMessage)
+			if err != nil {
+				return 0, fmt.Errorf("checking invoking message id: %w", err)
+			} else if idMatch {
+				return 0, fmt.Errorf("%w", ErrICMPDestinationUnreachable)
+			}
+			logger.Debug("discarding received ICMP destination unreachable reply with an unknown id")
+			continue
+		case *icmp.Echo:
+			inboundID := uint16(typedBody.ID) //nolint:gosec
+			if inboundID == outboundID {
+				return physicalLinkMTU, nil
+			}
+			logger.Debugf("discarding received ICMP echo reply with id %d mismatching sent id %d",
+				inboundID, outboundID)
+			continue
+		default:
+			return 0, fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, typedBody)
+		}
+	}
+}

internal/pmtud/message.go

@@ -0,0 +1,58 @@
+package pmtud
+
+import (
+	cryptorand "crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"math/rand/v2"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+func buildMessageToSend(ipVersion string, mtu int) (id uint16, message *icmp.Message) {
+	var seed [32]byte
+	_, _ = cryptorand.Read(seed[:])
+	randomSource := rand.NewChaCha8(seed)
+
+	const uint16Bytes = 2
+	idBytes := make([]byte, uint16Bytes)
+	_, _ = randomSource.Read(idBytes)
+	id = binary.BigEndian.Uint16(idBytes)
+
+	var ipHeaderLength int
+	var icmpType icmp.Type
+	switch ipVersion {
+	case "v4":
+		ipHeaderLength = ipv4.HeaderLen
+		icmpType = ipv4.ICMPTypeEcho
+	case "v6":
+		ipHeaderLength = ipv6.HeaderLen
+		icmpType = ipv6.ICMPTypeEchoRequest
+	default:
+		panic(fmt.Sprintf("IP version %q not supported", ipVersion))
+	}
+	const pingHeaderLength = 0 +
+		1 + // type
+		1 + // code
+		2 + // checksum
+		2 + // identifier
+		2 // sequence number
+	pingBodyDataSize := mtu - ipHeaderLength - pingHeaderLength
+	messageBodyData := make([]byte, pingBodyDataSize)
+	_, _ = randomSource.Read(messageBodyData)
+
+	// See https://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml#icmp-parameters-types
+	message = &icmp.Message{
+		Type:     icmpType, // echo request
+		Code:     0,        // no code
+		Checksum: 0,        // calculated at encoding (ipv4) or sending (ipv6)
+		Body: &icmp.Echo{
+			ID:   int(id),
+			Seq:  0, // only one packet
+			Data: messageBodyData,
+		},
+	}
+	return id, message
+}

internal/pmtud/nooplogger.go

@@ -0,0 +1,7 @@
+package pmtud
+
+type noopLogger struct{}
+
+func (noopLogger) Debug(_ string)            {}
+func (noopLogger) Debugf(_ string, _ ...any) {}
+func (noopLogger) Warnf(_ string, _ ...any)  {}

internal/pmtud/pmtud.go

@@ -0,0 +1,271 @@
+package pmtud
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"math"
+	"net"
+	"net/netip"
+	"strings"
+	"time"
+
+	"golang.org/x/net/icmp"
+)
+
+var ErrMTUNotFound = errors.New("path MTU discovery failed to find MTU")
+
+// PathMTUDiscover discovers the maximum MTU for the path to the given ip address.
+// If the physicalLinkMTU is zero, it defaults to 1500 which is the ethernet standard MTU.
+// If the pingTimeout is zero, it defaults to 1 second.
+// If the logger is nil, a no-op logger is used.
+// It returns [ErrMTUNotFound] if the MTU could not be determined.
+func PathMTUDiscover(ctx context.Context, ip netip.Addr,
+	physicalLinkMTU int, pingTimeout time.Duration, logger Logger) (
+	mtu int, err error,
+) {
+	if physicalLinkMTU == 0 {
+		const ethernetStandardMTU = 1500
+		physicalLinkMTU = ethernetStandardMTU
+	}
+	if pingTimeout == 0 {
+		pingTimeout = time.Second
+	}
+	if logger == nil {
+		logger = &noopLogger{}
+	}
+
+	if ip.Is4() {
+		logger.Debug("finding IPv4 next hop MTU")
+		mtu, err = findIPv4NextHopMTU(ctx, ip, physicalLinkMTU, pingTimeout, logger)
+		switch {
+		case err == nil:
+			return mtu, nil
+		case errors.Is(err, net.ErrClosed) || errors.Is(err, ErrICMPCommunicationAdministrativelyProhibited): // blackhole
+		default:
+			return 0, fmt.Errorf("finding IPv4 next hop MTU: %w", err)
+		}
+	} else {
+		logger.Debug("requesting IPv6 ICMP packet-too-big reply")
+		mtu, err = getIPv6PacketTooBig(ctx, ip, physicalLinkMTU, pingTimeout, logger)
+		switch {
+		case err == nil:
+			return mtu, nil
+		case errors.Is(err, net.ErrClosed): // blackhole
+		default:
+			return 0, fmt.Errorf("getting IPv6 packet-too-big message: %w", err)
+		}
+	}
+
+	// Fall back method: send echo requests with different packet
+	// sizes and check which ones succeed to find the maximum MTU.
+	logger.Debug("falling back to sending different sized echo packets")
+	minMTU := minIPv4MTU
+	if ip.Is6() {
+		minMTU = minIPv6MTU
+	}
+	return pmtudMultiSizes(ctx, ip, minMTU, physicalLinkMTU, pingTimeout, logger)
+}
+
+type pmtudTestUnit struct {
+	mtu       int
+	echoID    uint16
+	sentBytes int
+	ok        bool
+}
+
+func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
+	minMTU, maxPossibleMTU int, pingTimeout time.Duration,
+	logger Logger,
+) (maxMTU int, err error) {
+	var ipVersion string
+	var conn net.PacketConn
+	if ip.Is4() {
+		ipVersion = "v4"
+		conn, err = listenICMPv4(ctx)
+	} else {
+		ipVersion = "v6"
+		conn, err = listenICMPv6(ctx)
+	}
+	if err != nil {
+		if strings.HasSuffix(err.Error(), "socket: operation not permitted") {
+			err = fmt.Errorf("%w: you can try adding NET_RAW capability to resolve this", ErrICMPNotPermitted)
+		}
+		return 0, fmt.Errorf("listening for ICMP packets: %w", err)
+	}
+
+	mtusToTest := makeMTUsToTest(minMTU, maxPossibleMTU)
+	if len(mtusToTest) == 1 { // only minMTU because minMTU == maxPossibleMTU
+		return minMTU, nil
+	}
+	logger.Debugf("testing the following MTUs: %v", mtusToTest)
+
+	tests := make([]pmtudTestUnit, len(mtusToTest))
+	for i := range mtusToTest {
+		tests[i] = pmtudTestUnit{mtu: mtusToTest[i]}
+	}
+
+	timedCtx, cancel := context.WithTimeout(ctx, pingTimeout)
+	defer cancel()
+	go func() {
+		<-timedCtx.Done()
+		conn.Close()
+	}()
+
+	for i := range tests {
+		id, message := buildMessageToSend(ipVersion, tests[i].mtu)
+		tests[i].echoID = id
+
+		encodedMessage, err := message.Marshal(nil)
+		if err != nil {
+			return 0, fmt.Errorf("encoding ICMP message: %w", err)
+		}
+		tests[i].sentBytes = len(encodedMessage)
+
+		_, err = conn.WriteTo(encodedMessage, &net.IPAddr{IP: ip.AsSlice()})
+		if err != nil {
+			if strings.HasSuffix(err.Error(), "sendto: operation not permitted") {
+				err = fmt.Errorf("%w", ErrICMPNotPermitted)
+			}
+			return 0, fmt.Errorf("writing ICMP message: %w", err)
+		}
+	}
+
+	err = collectReplies(conn, ipVersion, tests, logger)
+	switch {
+	case err == nil: // max possible MTU is working
+		return tests[len(tests)-1].mtu, nil
+	case err != nil && errors.Is(err, net.ErrClosed):
+		// we have timeouts (IPv4 testing or IPv6 PMTUD blackholes)
+		// so find the highest MTU which worked.
+		// Note we start from index len(tests) - 2 since the max MTU
+		// cannot be working if we had a timeout.
+		for i := len(tests) - 2; i >= 0; i-- { //nolint:mnd
+			if tests[i].ok {
+				return pmtudMultiSizes(ctx, ip, tests[i].mtu, tests[i+1].mtu-1,
+					pingTimeout, logger)
+			}
+		}
+
+		// All MTUs failed.
+		return 0, fmt.Errorf("%w: ICMP might be blocked", ErrMTUNotFound)
+	case err != nil:
+		return 0, fmt.Errorf("collecting ICMP echo replies: %w", err)
+	default:
+		panic("unreachable")
+	}
+}
+
+// Create the MTU slice of length 11 such that:
+// - the first element is the minMTU
+// - the last element is the maxMTU
+// - elements in-between are separated as close to each other
+// The number 11 is chosen to find the final MTU in 3 searches,
+// with a total search space of 1728 MTUs which is enough;
+// to find it in 2 searches requires 37 parallel queries which
+// could be blocked by firewalls.
+func makeMTUsToTest(minMTU, maxMTU int) (mtus []int) {
+	const mtusLength = 11 // find the final MTU in 3 searches
+	diff := maxMTU - minMTU
+	switch {
+	case minMTU > maxMTU:
+		panic("minMTU > maxMTU")
+	case diff <= mtusLength:
+		mtus = make([]int, 0, diff)
+		for mtu := minMTU; mtu <= maxMTU; mtu++ {
+			mtus = append(mtus, mtu)
+		}
+	default:
+		step := float64(diff) / float64(mtusLength-1)
+		mtus = make([]int, 0, mtusLength)
+		for mtu := float64(minMTU); len(mtus) < mtusLength-1; mtu += step {
+			mtus = append(mtus, int(math.Round(mtu)))
+		}
+		mtus = append(mtus, maxMTU) // last element is the maxMTU
+	}
+
+	return mtus
+}
+
+func collectReplies(conn net.PacketConn, ipVersion string,
+	tests []pmtudTestUnit, logger Logger,
+) (err error) {
+	echoIDToTestIndex := make(map[uint16]int, len(tests))
+	for i, test := range tests {
+		echoIDToTestIndex[test.echoID] = i
+	}
+
+	// The theoretical limit is 4GiB for IPv6 MTU path discovery jumbograms, but that would
+	// create huge buffers which we don't really want to support anyway.
+	// The standard frame maximum MTU is 1500 bytes, and there are Jumbo frames with
+	// a conventional maximum of 9000 bytes. However, some manufacturers support up
+	// 9216-20 = 9196 bytes for the maximum MTU. We thus use buffers of size 9196 to
+	// match eventual Jumbo frames. More information at:
+	// https://en.wikipedia.org/wiki/Maximum_transmission_unit#MTUs_for_common_media
+	const maxPossibleMTU = 9196
+	buffer := make([]byte, maxPossibleMTU)
+
+	idsFound := 0
+	for idsFound < len(tests) {
+		// Note we need to read the whole packet in one call to ReadFrom, so the buffer
+		// must be large enough to read the entire reply packet. See:
+		// https://groups.google.com/g/golang-nuts/c/5dy2Q4nPs08/m/KmuSQAGEtG4J
+		bytesRead, _, err := conn.ReadFrom(buffer)
+		if err != nil {
+			return fmt.Errorf("reading from ICMP connection: %w", err)
+		}
+		packetBytes := buffer[:bytesRead]
+
+		ipPacketLength := len(packetBytes)
+
+		var icmpProtocol int
+		switch ipVersion {
+		case "v4":
+			icmpProtocol = icmpv4Protocol
+		case "v6":
+			icmpProtocol = icmpv6Protocol
+		default:
+			panic(fmt.Sprintf("unknown IP version: %s", ipVersion))
+		}
+
+		// Parse the ICMP message
+		// Note: this parsing works for a truncated 556 bytes ICMP reply packet.
+		message, err := icmp.ParseMessage(icmpProtocol, packetBytes)
+		if err != nil {
+			return fmt.Errorf("parsing message: %w", err)
+		}
+
+		echoBody, ok := message.Body.(*icmp.Echo)
+		if !ok {
+			return fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, message.Body)
+		}
+
+		id := uint16(echoBody.ID) //nolint:gosec
+		testIndex, testing := echoIDToTestIndex[id]
+		if !testing { // not an id we expected so ignore it
+			logger.Warnf("ignoring ICMP reply with unexpected ID %d (type: %d, code: %d, length: %d)",
+				echoBody.ID, message.Type, message.Code, ipPacketLength)
+			continue
+		}
+		idsFound++
+		sentBytes := tests[testIndex].sentBytes
+
+		// echo reply should be at most the number of bytes sent,
+		// and can be lower, more precisely 556 bytes, in case
+		// the host we are reaching wants to stay out of trouble
+		// and ensure its echo reply goes through without
+		// fragmentation, see the following page:
+		// https://datatracker.ietf.org/doc/html/rfc1122#page-59
+		const conservativeReplyLength = 556
+		truncated := ipPacketLength < sentBytes &&
+			ipPacketLength == conservativeReplyLength
+		// Check the packet size is the same if the reply is not truncated
+		if !truncated && sentBytes != ipPacketLength {
+			return fmt.Errorf("%w: sent %dB and received %dB",
+				ErrICMPEchoDataMismatch, sentBytes, ipPacketLength)
+		}
+		// Truncated reply or matching reply size
+		tests[testIndex].ok = true
+	}
+	return nil
+}

internal/pmtud/pmtud_integration_test.go

@@ -0,0 +1,22 @@
+//go:build integration
+
+package pmtud
+
+import (
+	"context"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_PathMTUDiscover(t *testing.T) {
+	t.Parallel()
+	const physicalLinkMTU = 1500
+	const timeout = time.Second
+	mtu, err := PathMTUDiscover(context.Background(), netip.MustParseAddr("1.1.1.1"),
+		physicalLinkMTU, timeout, nil)
+	require.NoError(t, err)
+	t.Log("MTU found:", mtu)
+}

internal/pmtud/pmtud_test.go

@@ -0,0 +1,55 @@
+package pmtud
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_makeMTUsToTest(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		minMTU int
+		maxMTU int
+		mtus   []int
+	}{
+		"0_0": {
+			mtus: []int{0},
+		},
+		"0_1": {
+			maxMTU: 1,
+			mtus:   []int{0, 1},
+		},
+		"0_8": {
+			maxMTU: 8,
+			mtus:   []int{0, 1, 2, 3, 4, 5, 6, 7, 8},
+		},
+		"0_12": {
+			maxMTU: 12,
+			mtus:   []int{0, 1, 2, 4, 5, 6, 7, 8, 10, 11, 12},
+		},
+		"0_80": {
+			maxMTU: 80,
+			mtus:   []int{0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 80},
+		},
+		"0_100": {
+			maxMTU: 100,
+			mtus:   []int{0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100},
+		},
+		"1280_1500": {
+			minMTU: 1280,
+			maxMTU: 1500,
+			mtus:   []int{1280, 1302, 1324, 1346, 1368, 1390, 1412, 1434, 1456, 1478, 1500},
+		},
+	}
+
+	for name, testCase := range testCases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			mtus := makeMTUsToTest(testCase.minMTU, testCase.maxMTU)
+			assert.Equal(t, testCase.mtus, mtus)
+		})
+	}
+}

internal/portforward/interfaces.go

@@ -3,6 +3,7 @@ package portforward
 import (
 	"context"
 	"net/netip"
+	"os/exec"
 )
 
 type Service interface {
@@ -29,3 +30,8 @@ type Logger interface {
 	Warn(s string)
 	Error(s string)
 }
+
+type Cmder interface {
+	Start(cmd *exec.Cmd) (stdoutLines, stderrLines <-chan string,
+		waitError <-chan error, startErr error)
+}

internal/portforward/loop.go

@@ -20,6 +20,7 @@ type Loop struct {
 	client      *http.Client
 	portAllower PortAllower
 	logger      Logger
+	cmder       Cmder
 	// Fixed parameters
 	uid, gid int
 	// Internal channels and locks
@@ -34,7 +35,7 @@ type Loop struct {
 
 func NewLoop(settings settings.PortForwarding, routing Routing,
 	client *http.Client, portAllower PortAllower,
-	logger Logger, uid, gid int,
+	logger Logger, cmder Cmder, uid, gid int,
 ) *Loop {
 	return &Loop{
 		settings: Settings{
@@ -42,6 +43,8 @@ func NewLoop(settings settings.PortForwarding, routing Routing,
 			Service: service.Settings{
 				Enabled:       settings.Enabled,
 				Filepath:      *settings.Filepath,
+				UpCommand:     *settings.UpCommand,
+				DownCommand:   *settings.DownCommand,
 				ListeningPort: *settings.ListeningPort,
 			},
 		},
@@ -49,6 +52,7 @@ func NewLoop(settings settings.PortForwarding, routing Routing,
 		client:      client,
 		portAllower: portAllower,
 		logger:      logger,
+		cmder:       cmder,
 		uid:         uid,
 		gid:         gid,
 	}
@@ -115,7 +119,7 @@ func (l *Loop) run(runCtx context.Context, runDone chan<- struct{},
 		*serviceSettings.Enabled = *serviceSettings.Enabled && *l.settings.VPNIsUp
 
 		l.service = service.New(serviceSettings, l.routing, l.client,
-			l.portAllower, l.logger, l.uid, l.gid)
+			l.portAllower, l.logger, l.cmder, l.uid, l.gid)
 
 		var err error
 		serviceRunError, err = l.service.Start(runCtx)

internal/portforward/service/command.go

@@ -0,0 +1,59 @@
+package service
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/qdm12/gluetun/internal/command"
+)
+
+func runCommand(ctx context.Context, cmder Cmder, logger Logger,
+	commandTemplate string, ports []uint16,
+) (err error) {
+	portStrings := make([]string, len(ports))
+	for i, port := range ports {
+		portStrings[i] = fmt.Sprint(int(port))
+	}
+	portsString := strings.Join(portStrings, ",")
+	commandString := strings.ReplaceAll(commandTemplate, "{{PORTS}}", portsString)
+	args, err := command.Split(commandString)
+	if err != nil {
+		return fmt.Errorf("parsing command: %w", err)
+	}
+
+	cmd := exec.CommandContext(ctx, args[0], args[1:]...) // #nosec G204
+	stdout, stderr, waitError, err := cmder.Start(cmd)
+	if err != nil {
+		return err
+	}
+
+	streamCtx, streamCancel := context.WithCancel(context.Background())
+	streamDone := make(chan struct{})
+	go streamLines(streamCtx, streamDone, logger, stdout, stderr)
+
+	err = <-waitError
+	streamCancel()
+	<-streamDone
+	return err
+}
+
+func streamLines(ctx context.Context, done chan<- struct{},
+	logger Logger, stdout, stderr <-chan string,
+) {
+	defer close(done)
+
+	var line string
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case line = <-stdout:
+			logger.Info(line)
+		case line = <-stderr:
+			logger.Error(line)
+		}
+	}
+}

internal/portforward/service/command_test.go

@@ -0,0 +1,28 @@
+//go:build linux
+
+package service
+
+import (
+	"context"
+	"testing"
+
+	gomock "github.com/golang/mock/gomock"
+	"github.com/qdm12/gluetun/internal/command"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_Service_runCommand(t *testing.T) {
+	t.Parallel()
+	ctrl := gomock.NewController(t)
+
+	ctx := context.Background()
+	cmder := command.New()
+	const commandTemplate = `/bin/sh -c "echo {{PORTS}}"`
+	ports := []uint16{1234, 5678}
+	logger := NewMockLogger(ctrl)
+	logger.EXPECT().Info("1234,5678")
+
+	err := runCommand(ctx, cmder, logger, commandTemplate, ports)
+
+	require.NoError(t, err)
+}

internal/portforward/service/interfaces.go

@@ -3,6 +3,7 @@ package service
 import (
 	"context"
 	"net/netip"
+	"os/exec"
 
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
@@ -32,3 +33,8 @@ type PortForwarder interface {
 		ports []uint16, err error)
 	KeepPortForward(ctx context.Context, objects utils.PortForwardObjects) (err error)
 }
+
+type Cmder interface {
+	Start(cmd *exec.Cmd) (stdoutLines, stderrLines <-chan string,
+		waitError <-chan error, startErr error)
+}

internal/portforward/service/mocks_generate_test.go

@@ -0,0 +1,3 @@
+package service
+
+//go:generate mockgen -destination=mocks_test.go -package=$GOPACKAGE . Logger

internal/portforward/service/mocks_test.go

@@ -0,0 +1,82 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/qdm12/gluetun/internal/portforward/service (interfaces: Logger)
+
+// Package service is a generated GoMock package.
+package service
+
+import (
+	reflect "reflect"
+
+	gomock "github.com/golang/mock/gomock"
+)
+
+// MockLogger is a mock of Logger interface.
+type MockLogger struct {
+	ctrl     *gomock.Controller
+	recorder *MockLoggerMockRecorder
+}
+
+// MockLoggerMockRecorder is the mock recorder for MockLogger.
+type MockLoggerMockRecorder struct {
+	mock *MockLogger
+}
+
+// NewMockLogger creates a new mock instance.
+func NewMockLogger(ctrl *gomock.Controller) *MockLogger {
+	mock := &MockLogger{ctrl: ctrl}
+	mock.recorder = &MockLoggerMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockLogger) EXPECT() *MockLoggerMockRecorder {
+	return m.recorder
+}
+
+// Debug mocks base method.
+func (m *MockLogger) Debug(arg0 string) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "Debug", arg0)
+}
+
+// Debug indicates an expected call of Debug.
+func (mr *MockLoggerMockRecorder) Debug(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Debug", reflect.TypeOf((*MockLogger)(nil).Debug), arg0)
+}
+
+// Error mocks base method.
+func (m *MockLogger) Error(arg0 string) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "Error", arg0)
+}
+
+// Error indicates an expected call of Error.
+func (mr *MockLoggerMockRecorder) Error(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Error", reflect.TypeOf((*MockLogger)(nil).Error), arg0)
+}
+
+// Info mocks base method.
+func (m *MockLogger) Info(arg0 string) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "Info", arg0)
+}
+
+// Info indicates an expected call of Info.
+func (mr *MockLoggerMockRecorder) Info(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Info", reflect.TypeOf((*MockLogger)(nil).Info), arg0)
+}
+
+// Warn mocks base method.
+func (m *MockLogger) Warn(arg0 string) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "Warn", arg0)
+}
+
+// Warn indicates an expected call of Warn.
+func (mr *MockLoggerMockRecorder) Warn(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Warn", reflect.TypeOf((*MockLogger)(nil).Warn), arg0)
+}