server: support reading back channels (#597) (#777)

examples/proxy-backchannel/client.go

@@ -0,0 +1,112 @@
+package main
+
+import (
+	"log"
+	"time"
+
+	"github.com/bluenviron/gortsplib/v4"
+	"github.com/bluenviron/gortsplib/v4/pkg/base"
+	"github.com/bluenviron/gortsplib/v4/pkg/description"
+	"github.com/bluenviron/gortsplib/v4/pkg/format"
+	"github.com/pion/rtp"
+)
+
+const (
+	existingStream = "rtsp://127.0.0.1:8554/mystream"
+	reconnectPause = 2 * time.Second
+)
+
+func findG711BackChannel(desc *description.Session) (*description.Media, *format.G711) {
+	for _, media := range desc.Medias {
+		if media.IsBackChannel {
+			for _, forma := range media.Formats {
+				if g711, ok := forma.(*format.G711); ok {
+					return media, g711
+				}
+			}
+		}
+	}
+	return nil, nil
+}
+
+type client struct {
+	server *server
+}
+
+func (c *client) initialize() {
+	// start a separated routine
+	go c.run()
+}
+
+func (c *client) run() {
+	for {
+		err := c.read()
+		log.Printf("ERR: %s\n", err)
+
+		time.Sleep(reconnectPause)
+	}
+}
+
+func (c *client) read() error {
+	rc := gortsplib.Client{
+		RequestBackChannels: true,
+	}
+
+	// parse URL
+	u, err := base.ParseURL(existingStream)
+	if err != nil {
+		return err
+	}
+
+	// connect to the server
+	err = rc.Start(u.Scheme, u.Host)
+	if err != nil {
+		return err
+	}
+	defer rc.Close()
+
+	// find available medias
+	desc, _, err := rc.Describe(u)
+	if err != nil {
+		return err
+	}
+
+	// find the back channel
+	backChannelMedia, _ := findG711BackChannel(desc)
+	if backChannelMedia == nil {
+		panic("back channel not found")
+	}
+
+	writeToClient := func(pkt *rtp.Packet) {
+		rc.WritePacketRTP(backChannelMedia, pkt)
+	}
+
+	// setup all medias
+	err = rc.SetupAll(desc.BaseURL, desc.Medias)
+	if err != nil {
+		return err
+	}
+
+	// notify the server that we are ready
+	stream := c.server.setStreamReady(desc, writeToClient)
+	defer c.server.setStreamUnready()
+
+	log.Printf("stream is ready and can be read from the server at rtsp://localhost:8554/stream\n")
+
+	// called when a RTP packet arrives
+	rc.OnPacketRTPAny(func(medi *description.Media, forma format.Format, pkt *rtp.Packet) {
+		log.Printf("received RTP packet from the client, routing to readers")
+
+		// route incoming packets to the server stream
+		stream.WritePacketRTP(medi, pkt)
+	})
+
+	// start playing
+	_, err = rc.Play(nil)
+	if err != nil {
+		return err
+	}
+
+	// wait until a fatal error
+	return rc.Wait()
+}