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/publicip.go

@@ -0,0 +1,89 @@
+package settings
+
+import (
+	"fmt"
+	"path/filepath"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings/helpers"
+	"github.com/qdm12/gotree"
+)
+
+// PublicIP contains settings for port forwarding.
+type PublicIP struct {
+	// Period is the period to get the public IP address.
+	// It can be set to 0 to disable periodic checking.
+	// It cannot be nil for the internal state.
+	// TODO change to value and add enabled field
+	Period *time.Duration
+	// IPFilepath is the public IP address status file path
+	// to use. It can be the empty string to indicate not
+	// to write to a file. It cannot be nil for the
+	// internal state
+	IPFilepath *string
+}
+
+func (p PublicIP) validate() (err error) {
+	const minPeriod = 5 * time.Second
+	if *p.Period < minPeriod {
+		return fmt.Errorf("%w: %s must be at least %s",
+			ErrPublicIPPeriodTooShort, p.Period, minPeriod)
+	}
+
+	if *p.IPFilepath != "" { // optional
+		_, err := filepath.Abs(*p.IPFilepath)
+		if err != nil {
+			return fmt.Errorf("%w: %s", ErrPublicIPFilepathNotValid, err)
+		}
+	}
+
+	return nil
+}
+
+func (p *PublicIP) copy() (copied PublicIP) {
+	return PublicIP{
+		Period:     helpers.CopyDurationPtr(p.Period),
+		IPFilepath: helpers.CopyStringPtr(p.IPFilepath),
+	}
+}
+
+func (p *PublicIP) mergeWith(other PublicIP) {
+	p.Period = helpers.MergeWithDuration(p.Period, other.Period)
+	p.IPFilepath = helpers.MergeWithStringPtr(p.IPFilepath, other.IPFilepath)
+}
+
+func (p *PublicIP) overrideWith(other PublicIP) {
+	p.Period = helpers.OverrideWithDuration(p.Period, other.Period)
+	p.IPFilepath = helpers.OverrideWithStringPtr(p.IPFilepath, other.IPFilepath)
+}
+
+func (p *PublicIP) setDefaults() {
+	const defaultPeriod = 12 * time.Hour
+	p.Period = helpers.DefaultDuration(p.Period, defaultPeriod)
+	p.IPFilepath = helpers.DefaultStringPtr(p.IPFilepath, "/tmp/gluetun/ip")
+}
+
+func (p PublicIP) String() string {
+	return p.toLinesNode().String()
+}
+
+func (p PublicIP) toLinesNode() (node *gotree.Node) {
+	node = gotree.New("Public IP settings:")
+
+	if *p.Period == 0 {
+		node.Appendf("Enabled: no")
+		return node
+	}
+
+	updatePeriod := "disabled"
+	if *p.Period > 0 {
+		updatePeriod = "every " + p.Period.String()
+	}
+	node.Appendf("Fetching: %s", updatePeriod)
+
+	if *p.IPFilepath != "" {
+		node.Appendf("IP file path: %s", *p.IPFilepath)
+	}
+
+	return node
+}