use the next available port for wireguard (#2024)

check if WgPort is available, if not find the next free port

client/internal/connect_test.go

@@ -0,0 +1,57 @@
+package internal
+
+import (
+	"net"
+	"testing"
+)
+
+func Test_freePort(t *testing.T) {
+	tests := []struct {
+		name    string
+		port    int
+		want    int
+		wantErr bool
+	}{
+		{
+			name:    "available",
+			port:    51820,
+			want:    51820,
+			wantErr: false,
+		},
+		{
+			name:    "notavailable",
+			port:    51830,
+			want:    51831,
+			wantErr: false,
+		},
+		{
+			name:    "noports",
+			port:    65535,
+			want:    0,
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+
+		c1, err := net.ListenUDP("udp", &net.UDPAddr{Port: 51830})
+		if err != nil {
+			t.Errorf("freePort error = %v", err)
+		}
+		c2, err := net.ListenUDP("udp", &net.UDPAddr{Port: 65535})
+		if err != nil {
+			t.Errorf("freePort error = %v", err)
+		}
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := freePort(tt.port)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("freePort() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("freePort() = %v, want %v", got, tt.want)
+			}
+		})
+		c1.Close()
+		c2.Close()
+	}
+}