feat(healthcheck): combination of ICMP and TCP+TLS checks (#2923)

- New option: `HEALTH_ICMP_TARGET_IP` defaults to `0.0.0.0` meaning use the VPN server public IP address.
- Options removed: `HEALTH_VPN_INITIAL_DURATION` and `HEALTH_VPN_ADDITIONAL_DURATION` - times and retries are handpicked and hardcoded.
- Less aggressive checks and less false positive detection

internal/healthcheck/checker.go

@@ -0,0 +1,239 @@
+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
+
+	// 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 if one of the periodic checks fail.
+// It returns an error if the initial TCP+TLS check fails.
+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
+	const smallCheckPeriod = 15 * time.Second
+	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 {
+					runErrorCh <- fmt.Errorf("periodic small check: %w", err)
+					return
+				}
+				smallCheckTimer.Reset(smallCheckPeriod)
+			case <-fullCheckTimer.C:
+				err := c.fullPeriodicCheck(ctx)
+				if err != nil {
+					runErrorCh <- fmt.Errorf("periodic full check: %w", err)
+					return
+				}
+				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 = 3 * time.Second
+	const extraTryTime = time.Second // 1s 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.logger.Warnf("%s; permanently falling back to plaintext DNS checks.", err)
+			return c.dnsClient.Check(ctx)
+		}
+		return err
+	}
+	return withRetries(ctx, maxTries, timeout, extraTryTime, c.logger, "ICMP echo", check)
+}
+
+func (c *Checker) fullPeriodicCheck(ctx context.Context) error {
+	const maxTries = 2
+	// 10s timeout in case the connection is under stress
+	// See https://github.com/qdm12/gluetun/issues/2270
+	const timeout = 10 * time.Second
+	const extraTryTime = 3 * time.Second // 3s 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,
+	warner Logger, checkName string, check func(ctx context.Context) error,
+) error {
+	try := uint(0)
+	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 context error: %w", checkName, ctx.Err())
+		default:
+			warner.Warnf("%s attempt %d/%d failed: %v", checkName, try+1, maxTries, err)
+			try++
+			if try == maxTries {
+				return fmt.Errorf("%w: %s: after %d attempts", ErrAllCheckTriesFailed, checkName, maxTries)
+			}
+		}
+	}
+}

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) {
@@ -21,20 +20,18 @@ func Test_Server_healthCheck(t *testing.T) {
 		dialer := &net.Dialer{}
 		const address = "cloudflare.com:443"
 
-		server := &Server{
-			dialer: dialer,
-			config: settings.Health{
-				TargetAddress: address,
-			},
+		checker := &Checker{
+			dialer:      dialer,
+			tlsDialAddr: 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 error: context canceled")
 	})
 
 	t.Run("dial localhost:0", func(t *testing.T) {
@@ -54,14 +51,12 @@ func Test_Server_healthCheck(t *testing.T) {
 		listeningAddress := listener.Addr()
 
 		dialer := &net.Dialer{}
-		server := &Server{
-			dialer: dialer,
-			config: settings.Health{
-				TargetAddress: listeningAddress.String(),
-			},
+		checker := &Checker{
+			dialer:      dialer,
+			tlsDialAddr: listeningAddress.String(),
 		}
 
-		err = server.healthCheck(ctx)
+		err = checker.fullPeriodicCheck(ctx)
 
 		assert.NoError(t, err)
 	})

internal/healthcheck/dns/dns.go

@@ -0,0 +1,39 @@
+package dns
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+)
+
+// 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{}
+
+func New() *Client {
+	return &Client{}
+}
+
+var ErrLookupNoIPs = errors.New("no IPs found from DNS lookup")
+
+func (c *Client) Check(ctx context.Context) error {
+	resolver := &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, _, _ string) (net.Conn, error) {
+			dialer := net.Dialer{}
+			return dialer.DialContext(ctx, "udp", "1.1.1.1:53")
+		},
+	}
+	ips, err := resolver.LookupIP(ctx, "ip", "github.com")
+	switch {
+	case err != nil:
+		return err
+	case len(ips) == 0:
+		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 +1,190 @@
+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, _, 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)",
+					id, body.ID, message.Type, message.Code, len(packetBytes))
+				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, expected-id %d)", message.Code, 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, expected-id %d)", message.Code, id)
+			continue
+		default:
+			return nil, fmt.Errorf("%w: %T (type %d, code %d, expected-id %d)",
+				ErrICMPBodyUnsupported, body, message.Type, message.Code, 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

@@ -1,7 +1,8 @@
 package healthcheck
 
 type Logger interface {
-	Debug(s string)
+	Debugf(format string, args ...any)
 	Info(s string)
+	Warnf(format string, args ...any)
 	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 HAVE READ AND TRIED EVERY 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,
-	logger Logger, vpnLoop StatusApplier,
-) *Server {
+func NewServer(config settings.Health, logger Logger) *Server {
 	return &Server{
 		logger:  logger,
-		handler: newHandler(),
-		dialer: &net.Dialer{
-			Resolver: &net.Resolver{
-				PreferGo: true,
-			},
-		},
-		config: config,
-		vpn: vpnHealth{
-			loop:        vpnLoop,
-			healthyWait: *config.VPN.Initial,
-		},
+		handler: newHandler(logger),
+		config:  config,
 	}
 }
 
+func (s *Server) SetError(err error) {
+	s.handler.setErr(err)
+}
+
 type StatusApplier interface {
 	ApplyStatus(ctx context.Context, status models.LoopStatus) (
 		outcome string, err error)