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/provider/privateinternetaccess/connection.go

@@ -1,16 +1,16 @@
 package privateinternetaccess
 
 import (
-	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/constants"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-func (p *PIA) GetConnection(selection configuration.ServerSelection) (
+func (p *PIA) GetConnection(selection settings.ServerSelection) (
 	connection models.Connection, err error) {
 	protocol := constants.UDP
-	if selection.OpenVPN.TCP {
+	if *selection.OpenVPN.TCP {
 		protocol = constants.TCP
 	}
 

internal/provider/privateinternetaccess/filter.go

@@ -1,12 +1,12 @@
 package privateinternetaccess
 
 import (
-	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
-func (p *PIA) filterServers(selection configuration.ServerSelection) (
+func (p *PIA) filterServers(selection settings.ServerSelection) (
 	servers []models.PIAServer, err error) {
 	for _, server := range p.servers {
 		switch {

internal/provider/privateinternetaccess/openvpnconf.go

@@ -3,16 +3,16 @@ package privateinternetaccess
 import (
 	"strconv"
 
-	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/constants"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 )
 
 func (p *PIA) BuildConf(connection models.Connection,
-	settings configuration.OpenVPN) (lines []string, err error) {
+	settings settings.OpenVPN) (lines []string, err error) {
 	var defaultCipher, defaultAuth, X509CRL, certificate string
-	switch settings.EncPreset {
+	switch *settings.PIAEncPreset {
 	case constants.PIAEncryptionPresetNormal:
 		defaultCipher = constants.AES128cbc
 		defaultAuth = constants.SHA1
@@ -34,8 +34,9 @@ func (p *PIA) BuildConf(connection models.Connection,
 		settings.Ciphers = []string{defaultCipher}
 	}
 
-	if settings.Auth == "" {
-		settings.Auth = defaultAuth
+	auth := *settings.Auth
+	if auth == "" {
+		auth = defaultAuth
 	}
 
 	lines = []string{
@@ -43,12 +44,13 @@ func (p *PIA) BuildConf(connection models.Connection,
 		"nobind",
 		"tls-exit",
 		"dev " + settings.Interface,
-		"verb " + strconv.Itoa(settings.Verbosity),
+		"verb " + strconv.Itoa(*settings.Verbosity),
 
 		// PIA specific
 		"remote-cert-tls server",
 		"reneg-sec 0",
 		"auth-user-pass " + constants.OpenVPNAuthConf,
+		"auth " + auth,
 
 		// Added constant values
 		"auth-nocache",
@@ -66,25 +68,21 @@ func (p *PIA) BuildConf(connection models.Connection,
 		lines = append(lines, utils.CipherLines(settings.Ciphers, settings.Version)...)
 	}
 
-	if settings.Auth != "" {
-		lines = append(lines, "auth "+settings.Auth)
-	}
-
 	if connection.Protocol == constants.UDP {
 		lines = append(lines, "explicit-exit-notify")
 	}
 
-	if !settings.Root {
+	if !*settings.Root {
 		lines = append(lines, "user "+settings.ProcUser)
 		lines = append(lines, "persist-tun")
 		lines = append(lines, "persist-key")
 	}
 
-	if settings.MSSFix > 0 {
-		lines = append(lines, "mssfix "+strconv.Itoa(int(settings.MSSFix)))
+	if *settings.MSSFix > 0 {
+		lines = append(lines, "mssfix "+strconv.Itoa(int(*settings.MSSFix)))
 	}
 
-	if !settings.IPv6 {
+	if !*settings.IPv6 {
 		lines = append(lines, `pull-filter ignore "route-ipv6"`)
 		lines = append(lines, `pull-filter ignore "ifconfig-ipv6"`)
 	}

internal/provider/privateinternetaccess/port.go

@@ -4,21 +4,23 @@ import (
 	"errors"
 	"fmt"
 
-	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/configuration/settings"
 	"github.com/qdm12/gluetun/internal/constants"
 )
 
-func getPort(openvpnSelection configuration.OpenVPNSelection) (
+func getPort(openvpnSelection settings.OpenVPNSelection) (
 	port uint16, err error) {
-	if openvpnSelection.CustomPort == 0 {
-		return getDefaultPort(openvpnSelection.TCP, openvpnSelection.EncPreset), nil
+	customPort := *openvpnSelection.CustomPort
+	tcp := *openvpnSelection.TCP
+	if customPort == 0 {
+		return getDefaultPort(tcp, *openvpnSelection.PIAEncPreset), nil
 	}
 
-	if err := checkPort(openvpnSelection.CustomPort, openvpnSelection.TCP); err != nil {
+	if err := checkPort(customPort, tcp); err != nil {
 		return 0, err
 	}
 
-	return openvpnSelection.CustomPort, nil
+	return customPort, nil
 }
 
 func getDefaultPort(tcp bool, encryptionPreset string) (port uint16) {