hotfix(portforward): log both external and internal ports when they diverge

- useful for ProtonVPN only
- clarify things up for the user

internal/portforward/service/helpers.go

@@ -2,6 +2,10 @@ package service
 
 import (
 	"fmt"
+	"maps"
+	"slices"
+	"sort"
+	"strconv"
 	"strings"
 )
 
@@ -20,3 +24,28 @@ func portsToString(ports []uint16) (s string) {
 			" and " + portStrings[len(portStrings)-1]
 	}
 }
+
+func portPairsToString(internalToExternalPort map[uint16]uint16) (s string) {
+	switch len(internalToExternalPort) {
+	case 0:
+		return "no port forwarded"
+	case 1:
+		internal := slices.Collect(maps.Keys(internalToExternalPort))[0]
+		return "port forwarded is " + portPairToString(internal, internalToExternalPort[internal])
+	default:
+		portStrings := make([]string, 0, len(internalToExternalPort))
+		for internal, external := range internalToExternalPort {
+			portStrings = append(portStrings, portPairToString(internal, external))
+		}
+		sort.StringSlice(portStrings).Sort()
+		return "ports forwarded are " + strings.Join(portStrings[:len(portStrings)-1], ", ") +
+			" and " + portStrings[len(portStrings)-1]
+	}
+}
+
+func portPairToString(internal, external uint16) string {
+	if internal == external {
+		return strconv.FormatUint(uint64(external), 10)
+	}
+	return fmt.Sprintf("%d (internal port %d)", external, internal)
+}