support rtsp udp transport

pkg/rtsp/ports.go

@@ -0,0 +1,75 @@
+package rtsp
+
+import (
+	"fmt"
+	"net"
+	"sync"
+)
+
+var mu sync.Mutex
+
+type UDPPortPair struct {
+	RTPListener  *net.UDPConn
+	RTCPListener *net.UDPConn
+	RTPPort      int
+	RTCPPort     int
+}
+
+func (p *UDPPortPair) Close() {
+	if p.RTPListener != nil {
+		_ = p.RTPListener.Close()
+	}
+	if p.RTCPListener != nil {
+		_ = p.RTCPListener.Close()
+	}
+}
+
+func GetUDPPorts(ip net.IP, maxAttempts int) (*UDPPortPair, error) {
+	mu.Lock()
+	defer mu.Unlock()
+
+	if ip == nil {
+		ip = net.IPv4(0, 0, 0, 0)
+	}
+
+	for i := 0; i < maxAttempts; i++ {
+		// Get a random even port from the OS
+		tempListener, err := net.ListenUDP("udp", &net.UDPAddr{IP: ip, Port: 0})
+		if err != nil {
+			continue
+		}
+
+		addr := tempListener.LocalAddr().(*net.UDPAddr)
+		basePort := addr.Port
+		tempListener.Close()
+
+		// 11. RTP over Network and Transport Protocols (https://www.ietf.org/rfc/rfc3550.txt)
+		// For UDP and similar protocols,
+		// RTP SHOULD use an even destination port number and the corresponding
+		// RTCP stream SHOULD use the next higher (odd) destination port number
+		if basePort%2 == 1 {
+			basePort--
+		}
+
+		// Try to bind both ports
+		rtpListener, err := net.ListenUDP("udp", &net.UDPAddr{IP: ip, Port: basePort})
+		if err != nil {
+			continue
+		}
+
+		rtcpListener, err := net.ListenUDP("udp", &net.UDPAddr{IP: ip, Port: basePort + 1})
+		if err != nil {
+			rtpListener.Close()
+			continue
+		}
+
+		return &UDPPortPair{
+			RTPListener:  rtpListener,
+			RTCPListener: rtcpListener,
+			RTPPort:      basePort,
+			RTCPPort:     basePort + 1,
+		}, nil
+	}
+
+	return nil, fmt.Errorf("failed to allocate consecutive UDP ports after %d attempts", maxAttempts)
+}