feat: introduce WithForceLocalReplySocket

sip/transport_layer.go

@@ -43,6 +43,10 @@ type TransportLayer struct {
 	// dnsPreferSRV does always SRV lookup first
 	dnsPreferSRV bool
 	dnsPreferIP  int // 0 - no preference , 1 -ip4, 2 - ip6
+
+	// forceLocalReplySocket forces using the connection that received the request
+	// for UDP responses, instead of trying to match by Via header
+	forceLocalReplySocket bool
 }
 
 type TransportLayerOption func(l *TransportLayer)
@@ -67,6 +71,12 @@ func WithTransportLayerDNSLookupSRV(preferSRV bool) TransportLayerOption {
 	}
 }
 
+func WithTransportLayerForceLocalReplySocket(force bool) TransportLayerOption {
+	return func(l *TransportLayer) {
+		l.forceLocalReplySocket = force
+	}
+}
+
 // TODO will be exposed
 // withTransportLayerDNSLookupIP allows to set which ip4 or ip6 to prefer on resolve
 // default is ip4
@@ -465,6 +475,8 @@ func (l *TransportLayer) serverRequestConnection(ctx context.Context, req *Reque
 	}
 
 	sourceAddr := req.MessageData.Source()
+
+	// For reliable transports, always use the connection that received the request
 	if IsReliable(network) && sourceAddr != "" {
 		// If the "sent-protocol" is a reliable transport protocol such as
 		//  TCP or SCTP, or TLS over those, the response MUST be sent using
@@ -477,6 +489,16 @@ func (l *TransportLayer) serverRequestConnection(ctx context.Context, req *Reque
 		}
 	}
 
+	// For unreliable transports (UDP), if forceLocalReplySocket is enabled,
+	// always try to use the connection that received the request first
+	// The connection pool stores connections by remote address (source address)
+	if !IsReliable(network) && l.forceLocalReplySocket && sourceAddr != "" {
+		conn := transport.GetConnection(sourceAddr)
+		if conn != nil {
+			return conn, nil
+		}
+	}
+
 	viaHop := req.Via()
 	if viaHop == nil {
 		return nil, fmt.Errorf("no Via Header present")
@@ -771,6 +793,12 @@ func (l *TransportLayer) allTransports() []transport {
 	return []transport{l.udp, l.tcp, l.tls, l.ws, l.wss}
 }
 
+// SetForceLocalReplySocket sets the forceLocalReplySocket flag on the transport layer.
+// This allows setting the flag after the transport layer is created.
+func (l *TransportLayer) SetForceLocalReplySocket(force bool) {
+	l.forceLocalReplySocket = force
+}
+
 func IsReliable(network string) bool {
 	switch network {
 	case "udp", "UDP":

ua.go

@@ -80,6 +80,18 @@ func WithUserAgentTransportLayerOptions(o ...sip.TransportLayerOption) UserAgent
 	}
 }
 
+// WithForceLocalReplySocket forces the transport layer to use the connection
+// that received the request for UDP responses, instead of trying to match by Via header.
+// This ensures responses are sent from the same socket that received the request.
+// This applies to both server and client transactions.
+func WithForceLocalReplySocket() UserAgentOption {
+	return func(ua *UserAgent) error {
+		// Add the transport layer option
+		ua.tpOptions = append(ua.tpOptions, sip.WithTransportLayerForceLocalReplySocket(true))
+		return nil
+	}
+}
+
 // NewUA creates User Agent
 // User Agent will create transport and transaction layer
 // Check options for customizing user agent