main.go

// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

//go:build !js
// +build !js

// broadcast demonstrates how to broadcast a video to many peers, while only requiring the broadcaster to upload once.
package main

import (
	"encoding/base64"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"net/http"
	"strconv"

	"github.com/pion/interceptor"
	"github.com/pion/interceptor/pkg/intervalpli"
	"github.com/pion/webrtc/v4"
)

func main() { // nolint:gocognit
	port := flag.Int("port", 8080, "http server port")
	flag.Parse()

	sdpChan := httpSDPServer(*port)

	// Everything below is the Pion WebRTC API, thanks for using it ❤️.
	offer := webrtc.SessionDescription{}
	decode(<-sdpChan, &offer)
	fmt.Println("")

	peerConnectionConfig := webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	}

	m := &webrtc.MediaEngine{}
	if err := m.RegisterDefaultCodecs(); err != nil {
		panic(err)
	}

	// Create a InterceptorRegistry. This is the user configurable RTP/RTCP Pipeline.
	// This provides NACKs, RTCP Reports and other features. If you use `webrtc.NewPeerConnection`
	// this is enabled by default. If you are manually managing You MUST create a InterceptorRegistry
	// for each PeerConnection.
	i := &interceptor.Registry{}

	// Use the default set of Interceptors
	if err := webrtc.RegisterDefaultInterceptors(m, i); err != nil {
		panic(err)
	}

	// Register a intervalpli factory
	// This interceptor sends a PLI every 3 seconds. A PLI causes a video keyframe to be generated by the sender.
	// This makes our video seekable and more error resilent, but at a cost of lower picture quality and higher bitrates
	// A real world application should process incoming RTCP packets from viewers and forward them to senders
	intervalPliFactory, err := intervalpli.NewReceiverInterceptor()
	if err != nil {
		panic(err)
	}
	i.Add(intervalPliFactory)

	// Create a new RTCPeerConnection
	peerConnection, err := webrtc.NewAPI(webrtc.WithMediaEngine(m), webrtc.WithInterceptorRegistry(i)).NewPeerConnection(peerConnectionConfig)
	if err != nil {
		panic(err)
	}
	defer func() {
		if cErr := peerConnection.Close(); cErr != nil {
			fmt.Printf("cannot close peerConnection: %v\n", cErr)
		}
	}()

	// Allow us to receive 1 video track
	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeVideo); err != nil {
		panic(err)
	}

	localTrackChan := make(chan *webrtc.TrackLocalStaticRTP)
	// Set a handler for when a new remote track starts, this just distributes all our packets
	// to connected peers
	peerConnection.OnTrack(func(remoteTrack *webrtc.TrackRemote, receiver *webrtc.RTPReceiver) { //nolint: revive
		// Create a local track, all our SFU clients will be fed via this track
		localTrack, newTrackErr := webrtc.NewTrackLocalStaticRTP(remoteTrack.Codec().RTPCodecCapability, "video", "pion")
		if newTrackErr != nil {
			panic(newTrackErr)
		}
		localTrackChan <- localTrack

		rtpBuf := make([]byte, 1400)
		for {
			i, _, readErr := remoteTrack.Read(rtpBuf)
			if readErr != nil {
				panic(readErr)
			}

			// ErrClosedPipe means we don't have any subscribers, this is ok if no peers have connected yet
			if _, err = localTrack.Write(rtpBuf[:i]); err != nil && !errors.Is(err, io.ErrClosedPipe) {
				panic(err)
			}
		}
	})

	// Set the remote SessionDescription
	err = peerConnection.SetRemoteDescription(offer)
	if err != nil {
		panic(err)
	}

	// Create answer
	answer, err := peerConnection.CreateAnswer(nil)
	if err != nil {
		panic(err)
	}

	// Create channel that is blocked until ICE Gathering is complete
	gatherComplete := webrtc.GatheringCompletePromise(peerConnection)

	// Sets the LocalDescription, and starts our UDP listeners
	err = peerConnection.SetLocalDescription(answer)
	if err != nil {
		panic(err)
	}

	// Block until ICE Gathering is complete, disabling trickle ICE
	// we do this because we only can exchange one signaling message
	// in a production application you should exchange ICE Candidates via OnICECandidate
	<-gatherComplete

	// Get the LocalDescription and take it to base64 so we can paste in browser
	fmt.Println(encode(peerConnection.LocalDescription()))

	localTrack := <-localTrackChan
	for {
		fmt.Println("")
		fmt.Println("Curl an base64 SDP to start sendonly peer connection")

		recvOnlyOffer := webrtc.SessionDescription{}
		decode(<-sdpChan, &recvOnlyOffer)

		// Create a new PeerConnection
		peerConnection, err := webrtc.NewPeerConnection(peerConnectionConfig)
		if err != nil {
			panic(err)
		}

		rtpSender, err := peerConnection.AddTrack(localTrack)
		if err != nil {
			panic(err)
		}

		// Read incoming RTCP packets
		// Before these packets are returned they are processed by interceptors. For things
		// like NACK this needs to be called.
		go func() {
			rtcpBuf := make([]byte, 1500)
			for {
				if _, _, rtcpErr := rtpSender.Read(rtcpBuf); rtcpErr != nil {
					return
				}
			}
		}()

		// Set the remote SessionDescription
		err = peerConnection.SetRemoteDescription(recvOnlyOffer)
		if err != nil {
			panic(err)
		}

		// Create answer
		answer, err := peerConnection.CreateAnswer(nil)
		if err != nil {
			panic(err)
		}

		// Create channel that is blocked until ICE Gathering is complete
		gatherComplete = webrtc.GatheringCompletePromise(peerConnection)

		// Sets the LocalDescription, and starts our UDP listeners
		err = peerConnection.SetLocalDescription(answer)
		if err != nil {
			panic(err)
		}

		// Block until ICE Gathering is complete, disabling trickle ICE
		// we do this because we only can exchange one signaling message
		// in a production application you should exchange ICE Candidates via OnICECandidate
		<-gatherComplete

		// Get the LocalDescription and take it to base64 so we can paste in browser
		fmt.Println(encode(peerConnection.LocalDescription()))
	}
}

// JSON encode + base64 a SessionDescription
func encode(obj *webrtc.SessionDescription) string {
	b, err := json.Marshal(obj)
	if err != nil {
		panic(err)
	}

	return base64.StdEncoding.EncodeToString(b)
}

// Decode a base64 and unmarshal JSON into a SessionDescription
func decode(in string, obj *webrtc.SessionDescription) {
	b, err := base64.StdEncoding.DecodeString(in)
	if err != nil {
		panic(err)
	}

	if err = json.Unmarshal(b, obj); err != nil {
		panic(err)
	}
}

// httpSDPServer starts a HTTP Server that consumes SDPs
func httpSDPServer(port int) chan string {
	sdpChan := make(chan string)
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		body, _ := io.ReadAll(r.Body)
		fmt.Fprintf(w, "done") //nolint: errcheck
		sdpChan <- string(body)
	})

	go func() {
		// nolint: gosec
		panic(http.ListenAndServe(":"+strconv.Itoa(port), nil))
	}()

	return sdpChan
}