From 0484e478903cbeae8647a4347f9e0a51f83f01ed Mon Sep 17 00:00:00 2001
From: Pierre HUBERT <pierre.git@communiquons.org>
Date: Sat, 11 Apr 2020 12:14:55 +0200
Subject: [PATCH] Send signals to the client

---
 go.mod   |   1 +
 relay.go | 117 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ws.go    |  22 +++++++++++
 3 files changed, 140 insertions(+)

diff --git a/go.mod b/go.mod
index 89d4bcb..9a36f53 100644
--- a/go.mod
+++ b/go.mod
@@ -4,6 +4,7 @@ go 1.14
 
 require (
 	github.com/gorilla/websocket v0.0.0-20200319175051-b65e62901fc1
+	github.com/pion/rtcp v1.2.1
 	github.com/pion/webrtc/v2 v2.2.4
 	gopkg.in/yaml.v2 v2.2.8
 )
diff --git a/relay.go b/relay.go
index 6357421..c1623e0 100644
--- a/relay.go
+++ b/relay.go
@@ -6,9 +6,12 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
+	"io"
 	"log"
 	"time"
 
+	"github.com/pion/rtcp"
 	"github.com/pion/webrtc/v2"
 )
 
@@ -124,6 +127,8 @@ func processCloseRequests() {
 /// Start new call
 func newCall(mainOffer receivedSignal, ch chan receivedSignal) {
 
+	log.Printf("Starting new call: %s", mainOffer.callHash)
+
 	// Since we are answering use PayloadTypes declared by offerer
 	mediaEngine := webrtc.MediaEngine{}
 	err := mediaEngine.PopulateFromSDP(mainOffer.offer)
@@ -133,4 +138,116 @@ func newCall(mainOffer receivedSignal, ch chan receivedSignal) {
 		return
 	}
 
+	// Create the API object with the MediaEngine
+	api := webrtc.NewAPI(webrtc.WithMediaEngine(mediaEngine))
+
+	// Setup config
+	peerConnectionConfig := webrtc.Configuration{
+		ICEServers: callConf.iceServers,
+	}
+
+	// Create a new RTCPeerConnection
+	peerConnection, err := api.NewPeerConnection(peerConnectionConfig)
+	if err != nil {
+		log.Println("Error: could not create peer connection!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	// Allow us to receive 1 audio & 1 video track
+	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeVideo); err != nil {
+		log.Println("Error: could not prepare to receive video track!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeAudio); err != nil {
+		log.Println("Error: could not prepare to receive audio track!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	localTrackChan := make(chan *webrtc.Track)
+
+	// Set a handler for when a new remote track starts, this just distributes all our packets
+	// to connected peers
+	peerConnection.OnTrack(func(remoteTrack *webrtc.Track, receiver *webrtc.RTPReceiver) {
+
+		// Send a PLI on an interval so that the publisher is pushing a keyframe every rtcpPLIInterval
+		// This can be less wasteful by processing incoming RTCP events, then we would emit a NACK/PLI when a viewer requests it
+		go func() {
+			rtcpPLIInterval := time.Second * 3
+			ticker := time.NewTicker(rtcpPLIInterval)
+			for range ticker.C {
+				if rtcpSendErr := peerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: remoteTrack.SSRC()}}); rtcpSendErr != nil {
+					fmt.Println(rtcpSendErr)
+				}
+			}
+		}()
+
+		// Create a local track, all our SFU clients will be fed via this track
+		localTrack, newTrackErr := peerConnection.NewTrack(remoteTrack.PayloadType(), remoteTrack.SSRC(), remoteTrack.ID(), remoteTrack.Label())
+		if newTrackErr != nil {
+			log.Println("New track error!", err)
+			askForClose(mainOffer.callHash)
+			return
+		}
+
+		// Send the track to the main goroutine (in order to respond correctly to SDP requests & responses)
+		localTrackChan <- localTrack
+
+		rtpBuf := make([]byte, 1400)
+		for {
+			i, readErr := remoteTrack.Read(rtpBuf)
+			if readErr != nil {
+
+				// Could not read from remote track
+				log.Println("Read error!", err)
+				askForClose(mainOffer.callHash)
+				break
+
+			}
+
+			// 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 && err != io.ErrClosedPipe {
+				log.Println("Write error!", err)
+				askForClose(mainOffer.callHash)
+				break
+			}
+		}
+	})
+
+	// Set the remote SessionDescription
+	err = peerConnection.SetRemoteDescription(mainOffer.offer)
+	if err != nil {
+		log.Println("Set remote description error!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	// Create answer
+	answer, err := peerConnection.CreateAnswer(nil)
+	if err != nil {
+		log.Println("Create answer error!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	// Sets the LocalDescription, and starts our UDP listeners
+	err = peerConnection.SetLocalDescription(answer)
+	if err != nil {
+		log.Println("Set local description error!", err)
+		askForClose(mainOffer.callHash)
+		return
+	}
+
+	// Forward ice candidates
+	peerConnection.OnICECandidate(func(c *webrtc.ICECandidate) {
+		if c != nil {
+			sendSignal(mainOffer.callHash, mainOffer.peerID, c.ToJSON())
+		}
+	})
+
+	// Send anwser
+	sendSignal(mainOffer.callHash, mainOffer.peerID, answer)
 }
diff --git a/ws.go b/ws.go
index 8bfa278..2f1643b 100644
--- a/ws.go
+++ b/ws.go
@@ -21,6 +21,8 @@ type WsMessage struct {
 	Data     interface{}
 }
 
+var outMsgChan = make(chan interface{})
+
 // Open websocket connection
 func openWs(conf *Config) {
 
@@ -44,6 +46,13 @@ func openWs(conf *Config) {
 		c.Close()
 	}()
 
+	// Send outgoing messages
+	go func() {
+		for {
+			c.WriteJSON(<-outMsgChan)
+		}
+	}()
+
 	// Read remote messages
 	for {
 
@@ -81,3 +90,16 @@ func openWs(conf *Config) {
 	}
 
 }
+
+/// Send a signal to the API
+func sendSignal(callHash, peerID string, data interface{}) {
+
+	msg := WsMessage{
+		Title:    "signal",
+		PeerID:   peerID,
+		CallHash: callHash,
+		Data:     data,
+	}
+
+	outMsgChan <- msg
+}