chore(settings): refactor settings processing (#756)

- Better settings tree structure logged using `qdm12/gotree`
- Read settings from environment variables, then files, then secret files
- Settings methods to default them, merge them and override them
- `DNS_PLAINTEXT_ADDRESS` default changed to `127.0.0.1` to use DoT. Warning added if set to something else.
- `HTTPPROXY_LISTENING_ADDRESS` instead of `HTTPPROXY_PORT` (with retro-compatibility)

internal/configuration/settings/dot.go

@@ -0,0 +1,113 @@
+package settings
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
+	"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 and cryptographic files for DNSSEC validation.
+	// 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
+	// Unbound contains settings to configure Unbound.
+	Unbound Unbound
+	// 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 < minUpdatePeriod {
+		return fmt.Errorf("%w: %s must be bigger than %s",
+			ErrDoTUpdatePeriodTooShort, *d.UpdatePeriod, minUpdatePeriod)
+	}
+
+	err = d.Unbound.validate()
+	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:      helpers.CopyBoolPtr(d.Enabled),
+		UpdatePeriod: helpers.CopyDurationPtr(d.UpdatePeriod),
+		Unbound:      d.Unbound.copy(),
+		Blacklist:    d.Blacklist.copy(),
+	}
+}
+
+// mergeWith merges the other settings into any
+// unset field of the receiver settings object.
+func (d *DoT) mergeWith(other DoT) {
+	d.Enabled = helpers.MergeWithBool(d.Enabled, other.Enabled)
+	d.UpdatePeriod = helpers.MergeWithDuration(d.UpdatePeriod, other.UpdatePeriod)
+	d.Unbound.mergeWith(other.Unbound)
+	d.Blacklist.mergeWith(other.Blacklist)
+}
+
+// overrideWith overrides fields of the receiver
+// settings object with any field set in the other
+// settings.
+func (d *DoT) overrideWith(other DoT) {
+	d.Enabled = helpers.OverrideWithBool(d.Enabled, other.Enabled)
+	d.UpdatePeriod = helpers.OverrideWithDuration(d.UpdatePeriod, other.UpdatePeriod)
+	d.Unbound.overrideWith(other.Unbound)
+	d.Blacklist.overrideWith(other.Blacklist)
+}
+
+func (d *DoT) setDefaults() {
+	d.Enabled = helpers.DefaultBool(d.Enabled, true)
+	const defaultUpdatePeriod = 24 * time.Hour
+	d.UpdatePeriod = helpers.DefaultDuration(d.UpdatePeriod, defaultUpdatePeriod)
+	d.Unbound.setDefaults()
+	d.Blacklist.setDefaults()
+}
+
+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", helpers.BoolPtrToYesNo(d.Enabled))
+	if !*d.Enabled {
+		return node
+	}
+
+	update := "disabled"
+	if *d.UpdatePeriod > 0 {
+		update = "every " + d.UpdatePeriod.String()
+	}
+	node.Appendf("Update period: %s", update)
+
+	node.AppendNode(d.Unbound.toLinesNode())
+	node.AppendNode(d.Blacklist.toLinesNode())
+
+	return node
+}