Add -tcp flag to disable UDP and force audio through TCP tunnel

Adds Config.DisableUDP field. When set:
- DialWithDialer skips startUDP() entirely (no UDP socket, no UDP reader)
- WriteAudio skips WriteAudioUDP and goes straight to TCP-tunneled audio

Useful for debugging crypto/transport issues — rules out UDP-specific
problems like NAT, firewall, or OCB2 counter mismatches.

gumble/gumble/client.go

@@ -142,10 +142,14 @@ func DialWithDialer(dialer *net.Dialer, config *Config, tlsConfig *tls.Config) (
 
 	// Start UDP transport immediately so it's ready when CryptSetup
 	// arrives during the sync handshake.
-	if err := client.startUDP(); err != nil {
-		log.Warn("UDP setup failed, audio will use TCP tunnel: %v", err)
-	} else if client.udpConn != nil {
-		log.Info("UDP socket opened to %s, waiting for CryptSetup", client.udpConn.RemoteAddr())
+	if !client.Config.DisableUDP {
+		if err := client.startUDP(); err != nil {
+			log.Warn("UDP setup failed, audio will use TCP tunnel: %v", err)
+		} else if client.udpConn != nil {
+			log.Info("UDP socket opened to %s, waiting for CryptSetup", client.udpConn.RemoteAddr())
+		}
+	} else {
+		log.Info("UDP disabled by config, audio will use TCP tunnel")
 	}
 
 	go client.pingRoutine()
@@ -330,17 +334,21 @@ func (c *Client) EnableStereoEncoder() {
 var udpFallbackLogged bool
 
 func (c *Client) WriteAudio(format, target byte, sequence int64, final bool, data []byte, X, Y, Z *float32) error {
-	// Try UDP first
-	if sent, err := c.WriteAudioUDP(format, target, sequence, final, data, X, Y, Z); sent {
-		if err != nil {
-			log.Error("UDP send error: %v", err)
+	// Try UDP first (unless disabled)
+	if !c.Config.DisableUDP {
+		if sent, err := c.WriteAudioUDP(format, target, sequence, final, data, X, Y, Z); sent {
+			if err != nil {
+				log.Error("UDP send error: %v", err)
+			}
+			return err
 		}
-		return err
 	}
 	// Fall back to TCP tunnel — log once per process
 	if !udpFallbackLogged {
 		udpFallbackLogged = true
-		if c.udpConn == nil {
+		if c.Config.DisableUDP {
+			log.Info("UDP disabled, audio using TCP tunnel")
+		} else if c.udpConn == nil {
 			log.Info("no UDP socket, audio using TCP tunnel")
 		} else if !c.cryptOut.initialized {
 			log.Info("waiting for CryptSetup, audio using TCP tunnel")

gumble/gumble/config.go

@@ -25,6 +25,9 @@ type Config struct {
 	// AudioDataBytes is the number of bytes that an audio frame can use.
 	AudioDataBytes int
 
+	// DisableUDP forces all audio to use the TCP tunnel instead of UDP.
+	DisableUDP bool
+
 	// The event listeners used when client events are triggered.
 	Listeners      Listeners
 	AudioListeners AudioListeners