automatically append listening port to endpoint address (#352)

frontend/src/lang/translations/de.json

@@ -354,7 +354,7 @@
         "endpoint": {
           "label": "Endpoint Address",
           "placeholder": "Endpoint Address",
-          "description": "The endpoint address that peers will connect to."
+          "description": "The endpoint address that peers will connect to. (e.g. wg.example.com or wg.example.com:51820)"
         },
         "networks": {
           "label": "IP Networks",

frontend/src/lang/translations/en.json

@@ -355,7 +355,7 @@
         "endpoint": {
           "label": "Endpoint Address",
           "placeholder": "Endpoint Address",
-          "description": "The endpoint address that peers will connect to."
+          "description": "The endpoint address that peers will connect to. (e.g. wg.example.com or wg.example.com:51820)"
         },
         "networks": {
           "label": "IP Networks",

internal/app/wireguard/wireguard_interfaces.go

@@ -456,6 +456,10 @@ func (m Manager) saveInterface(ctx context.Context, iface *domain.Interface) (
 	*domain.Interface,
 	error,
 ) {
+	if err := iface.Validate(); err != nil {
+		return nil, fmt.Errorf("interface validation failed: %w", err)
+	}
+
 	stateChanged := m.hasInterfaceStateChanged(ctx, iface)
 
 	if err := m.handleInterfacePreSaveHooks(stateChanged, iface); err != nil {

internal/domain/interface.go

@@ -3,6 +3,7 @@ package domain
 import (
 	"fmt"
 	"math"
+	"net"
 	"regexp"
 	"strconv"
 	"strings"
@@ -71,8 +72,24 @@ type Interface struct {
 	PeerDefPostDown string // default action that is executed after the device is down
 }
 
-func (i *Interface) IsValid() bool {
-	return true // TODO: implement check
+// Validate performs checks to ensure that the interface is valid.
+func (i *Interface) Validate() error {
+	// validate peer default endpoint, add port if needed
+	if i.PeerDefEndpoint != "" {
+		host, port, err := net.SplitHostPort(i.PeerDefEndpoint)
+		switch {
+		case err != nil && !strings.Contains(err.Error(), "missing port in address"):
+			return fmt.Errorf("invalid default endpoint: %w", err)
+		case err != nil && strings.Contains(err.Error(), "missing port in address"):
+			// In this case, the entire string is the host, and there's no port.
+			host = i.PeerDefEndpoint
+			port = strconv.Itoa(i.ListenPort)
+		}
+
+		i.PeerDefEndpoint = net.JoinHostPort(host, port)
+	}
+
+	return nil
 }
 
 func (i *Interface) IsDisabled() bool {