一、背景

• 背景：記錄下iOS P2P通信的實(shí)現(xiàn)的流程废膘，以及實(shí)現(xiàn)過程中遇到的問題旬薯，方便后續(xù)bug調(diào)試，為代碼整潔規(guī)范化提供設(shè)計(jì)思路
• 目標(biāo)群體：iOS及客戶端開發(fā)人員
• 技術(shù)應(yīng)用場景：iPhone敛劝、iPad端音視頻會(huì)議通話
• 整體思路：1余爆、使用WebSocket連接信令服務(wù)器，執(zhí)行登錄操作（userId登錄夸盟，沒有則用游客身份登錄）蛾方，2、WebRTC實(shí)現(xiàn)P2P連接
  • 先入會(huì)者：1上陕、監(jiān)聽新人加入-->2桩砰、創(chuàng)建與新人的PeerConnection連接對(duì)象，發(fā)送_start信令-->3释簿、收到_startResp后創(chuàng)建offer亚隅，設(shè)置setLocalDescription為offer，發(fā)送_offer信令-->4庶溶、收到_answer信令煮纵，setRemoteDescription為answer-->5、互相發(fā)送可用的ice_candidate偏螺，WebRTC會(huì)篩選出最合適的ICE通道連接-->6行疏、雙方建立P2P連接，開始通信砖茸；
  • 后入會(huì)者：1隘擎、查詢會(huì)議成員列表，創(chuàng)建與會(huì)中所有人的PeerConnection對(duì)象-->2凉夯、收到_start信令后回復(fù)_startResp-->3货葬、收到_offer信令，setRemoteDescription為offer-->4劲够、創(chuàng)建answer震桶，setLocalDescription為answer，發(fā)送_answer給對(duì)方-->后續(xù)步驟同先入會(huì)者步驟5征绎、6

流程圖：

暫時(shí)無法在文檔外展示此內(nèi)容

二蹲姐、操作步驟

2.1 開發(fā)前的準(zhǔn)備工作

準(zhǔn)備工作一

• Xcode安裝好動(dòng)態(tài)庫管理器cocoaPods磨取，引入WebRTC、WebSocket兩個(gè)庫柴墩，代碼如下

pod 'GoogleWebRTC'

pod 'SocketRocket'

準(zhǔn)備工作二

創(chuàng)建EMServerBaseManager信令基類忙厌，實(shí)現(xiàn)EMServerManagerProtocol，公共的連接江咳、斷開的連接逢净、發(fā)送數(shù)據(jù)等方法聲明放此協(xié)議中，方便擴(kuò)展新的信令協(xié)議（WebSocket歼指、MQTT等爹土，目前服務(wù)端用的是WebSocket協(xié)議）；

2.2 進(jìn)入開發(fā)階段

1踩身、連接信令服務(wù)器

建立webSocket長連接胀茵，連接失敗就執(zhí)行重連操作，重連時(shí)間間隔以2的指數(shù)倍增長挟阻，網(wǎng)絡(luò)斷開的情況下就開啟一個(gè)定時(shí)器去檢查網(wǎng)絡(luò)情況琼娘，有網(wǎng)絡(luò)了就更新重連時(shí)間，馬上進(jìn)行重連赁濒；

- (void)connectServer {
  if (self.connectState == EMSocketConnectStateConnected || self.connectState == EMSocketConnectStateConnecting) return;
  self.isActivelyClose = NO; 
  [self webSocketClose]; 
  NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:EMSocketBaseUrl]];
  self.webSocket = [[SRWebSocket alloc] initWithURLRequest:request];
  self.webSocket.delegate = self;
  [self.webSocket open]; 
  self.connectState = EMSocketConnectStateConnecting;
}

//連接成功回調(diào)
- (void)webSocketDidOpen:(SRWebSocket *)webSocket { 
  self.reConnectTime = 0; // 重連間隔時(shí)長
  [self sendDataToServer:@{EMSocketMsg:EMSocketMsg_login}]; // 登錄
  [self initHeartBeat]; //開啟心跳
  self.connectState = EMSocketConnectStateConnected; 
} 

//連接失敗回調(diào)
- (void)webSocket:(SRWebSocket *)webSocket didFailWithError:(NSError *)error {
  self.connectState = EMSocketConnectStateDisConnected;
  //用戶主動(dòng)斷開連接轨奄，就不去進(jìn)行重連
  if(self.isActivelyClose) {
    return;
  }

  [self destoryHeartBeat]; //斷開連接時(shí)銷毀心跳

  /// 剛斷開連接，網(wǎng)絡(luò)狀態(tài)可能還沒有改變拒炎，導(dǎo)致網(wǎng)絡(luò)檢測定時(shí)器沒有打開
  __weak typeof(self) wSelf = self;
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    if(AFNetworkReachabilityManager.sharedManager.networkReachabilityStatus == AFNetworkReachabilityStatusNotReachable && !wSelf.netWorkTestingTimer) {
      [wSelf noNetWorkStartTestingTimer];//開啟網(wǎng)絡(luò)檢測定時(shí)器
    }
  });
  //判斷網(wǎng)絡(luò)環(huán)境
  if (![self checkNetWork]) //沒有網(wǎng)絡(luò)
  {
    [self noNetWorkStartTestingTimer];//開啟網(wǎng)絡(luò)檢測定時(shí)器
  }
  else //有網(wǎng)絡(luò)
  {
    [self reConnectServer];//連接失敗就重連
  }
}

//連接關(guān)閉,注意連接關(guān)閉不是連接斷開挪拟，關(guān)閉是 [socket close] 客戶端主動(dòng)關(guān)閉，斷開可能是斷網(wǎng)了击你，被動(dòng)斷開的玉组。
- (void)webSocket:(SRWebSocket *)webSocket didCloseWithCode:(NSInteger)code reason:(NSString *)reason wasClean:(BOOL)wasClean {
  // 在這里判斷 webSocket 的狀態(tài) 是否為 open
  self.connectState = EMSocketConnectStateDisConnected;
  if(self.webSocket.readyState == SR_OPEN || self.isActivelyClose) {
    return;
  }

  DLog(@"被關(guān)閉連接，code:%ld,reason:%@,wasClean:%d",code,reason,wasClean);

  [self destoryHeartBeat]; //斷開連接時(shí)銷毀心跳

  //判斷網(wǎng)絡(luò)環(huán)境
  if (![self checkNetWork]) //沒有網(wǎng)絡(luò)
  {
    [self noNetWorkStartTestingTimer];//開啟網(wǎng)絡(luò)檢測
  }
  else //有網(wǎng)絡(luò)
  {
    [self reConnectServer];//連接失敗就重連
  }
}

2丁侄、WebRtc P2P連接過程

1惯雳、創(chuàng)建peerConnectionFactory對(duì)象，設(shè)置默認(rèn)的視頻編解碼工廠類鸿摇，此處可以自定義視頻編解碼類石景；

- (RTCPeerConnectionFactory *)peerConnectionFactory {
  if (!_peerConnectionFactory) {
    [RTCPeerConnectionFactory initialize];
    RTCDefaultVideoDecoderFactory *decoderFactory = [[RTCDefaultVideoDecoderFactory alloc] init];
    RTCDefaultVideoEncoderFactory *encoderFactory = [[RTCDefaultVideoEncoderFactory alloc] init];
    NSArray *codecs = [encoderFactory supportedCodecs];
    [encoderFactory setPreferredCodec:codecs[2]];
    _peerConnectionFactory = [[RTCPeerConnectionFactory alloc] initWithEncoderFactory:encoderFactory decoderFactory:decoderFactory];
  }
  return _peerConnectionFactory;
}

2、創(chuàng)建新的PeerConnection對(duì)象拙吉，需要設(shè)置配置RTCConfiguration潮孽、約束RTCMediaConstraints；

// 創(chuàng)建新的PeerConnection
- (RTCPeerConnection *)createPeerConnection:(NSString *)connectionId {
  RTCPeerConnection *peerConnection = [self.peerConnectionFactory peerConnectionWithConfiguration:self.rtcConfig constraints:[self defaultPeerConnContraints] delegate:self];
  //把本地流加到連接中去
  [peerConnection addStream:self.localStream];
  return peerConnection;
}

- (RTCConfiguration *)rtcConfig {
  if (!_rtcConfig) {
    NSArray *ICEServers = [NSArray arrayWithObject:[self defaultSTUNServer]];
    RTCConfiguration *configuration = [[RTCConfiguration alloc] init];
    [configuration setIceServers:ICEServers];
    configuration.iceConnectionReceivingTimeout = 90000;// 90s超時(shí)
    _rtcConfig = configuration;
  }
  return _rtcConfig;
}

// 此處填寫透傳服務(wù)器的地址筷黔，username往史，password等
- (RTCIceServer *)defaultSTUNServer {
  RTCIceServer *defaultServer = [[RTCIceServer alloc] initWithURLStrings:@[@""] username:@"" credential:@""];
  return defaultServer;
}

- (RTCMediaConstraints *)defaultPeerConnContraints {
  // 配置信息的基礎(chǔ)單元，以鍵值對(duì)的方式
   NSMutableDictionary *mandatory = @{kRTCMediaConstraintsOfferToReceiveAudio:kRTCMediaConstraintsValueTrue}.mutableCopy;
   [mandatory setValue:kRTCMediaConstraintsValueTrue forKey:kRTCMediaConstraintsOfferToReceiveVideo];
  RTCMediaConstraints *media = [[RTCMediaConstraints alloc] initWithMandatoryConstraints:mandatory optionalConstraints:nil];
  return media;
}

3佛舱、創(chuàng)建本地媒體流信息椎例，添加本地音視頻軌道到媒體流中挨决，其中初始化數(shù)據(jù)源中，adaptOutputFormatToWidth可以指定視頻的寬高比订歪，幀率等等脖祈，當(dāng)前先用默認(rèn)的；

// 創(chuàng)建本地音視頻軌道
- (RTCMediaStream *)localStream {
  if (!_localStream) { 
    // 初始化媒體流陌粹，kEM_STREAM和kEM_AUDIO_0撒犀、kEM_VIDEO_0為專業(yè)標(biāo)識(shí)符。
    _localStream = [self.peerConnectionFactory mediaStreamWithStreamId:kEM_STREAM];
    // 添加音頻軌道
    self.localAudioTrack = [self.peerConnectionFactory audioTrackWithTrackId:kEM_AUDIO_0];
    [_localStream addAudioTrack:self.localAudioTrack];
    // 添加視頻軌道
    [_localStream addVideoTrack:self.localVideoTrack];
  }
  return _localStream;
}

- (RTCVideoTrack *)localVideoTrack {
  if (!_localVideoTrack) {
    // 獲取攝像頭
    AVCaptureDevice * device = [self defaultDevice]; 
    //獲取數(shù)據(jù)源
    RTCVideoSource *_source = [self.peerConnectionFactory videoSource];
//    [_source adaptOutputFormatToWidth:720 height:1280 fps:20];
    //拿到capture對(duì)象
    RTCCameraVideoCapturer *capture = [[RTCCameraVideoCapturer alloc] initWithDelegate:_source];
    AVCaptureDeviceFormat *format = [[RTCCameraVideoCapturer supportedFormatsForDevice:device] lastObject];
//    CGFloat fps = [[format videoSupportedFrameRateRanges] firstObject].maxFrameRate;
    if (self.cameraState == EMMediaDeviceStatePlay) {
      [capture startCaptureWithDevice:device format:format fps:20 completionHandler:^(NSError * error) {
      }];
    } 
    self.capture = capture; 
    _localVideoTrack = [self.peerConnectionFactory videoTrackWithSource:_source trackId:kEM_VIDEO_0];
  }
  return _localVideoTrack;
}

4掏秩、先入會(huì)者發(fā)送_start、創(chuàng)建offer荆姆，設(shè)置本地描述蒙幻，成功就發(fā)送_offer信令給對(duì)方，等待對(duì)方發(fā)送的answer存到本地遠(yuǎn)程描述胆筒；setStartState為保存start狀態(tài)邮破，方便后續(xù)斷線重連階段判斷是有誰發(fā)起start

/// 請求開始進(jìn)行 P2P 傳輸準(zhǔn)備
- (void)sendStartMsgToMemberId:(NSString *)memberId {
  NSDictionary *data = @{EMSocketMsg:EMSocketMsg_start,
              EMSocketToId: memberId};
  [self sendDataToServer:data completionHandler:nil]; 
  [self setStartState:false isSender:true fromId:memberId];
}

- (void)getSocketMsg:(NSNotification *)x {
  NSDictionary *dict = x.userInfo;
  NSString *msg = dict[EMSocketMsg];
  // 收到start回復(fù)
  if ([msg isEqualToString:EMSocketMsg_start_resp]) {
    NSString *fromId = dict[EMSocketFromId];
    [self setStartState:true isSender:true fromId:fromId];
    RTCPeerConnection *peerConnection = [wSelf.connectionDic objectForKey:fromId];
    /// 發(fā)送offer
    [wSelf createOffer:peerConnection];
  }
}

/**
 * 創(chuàng)建offer
 */
- (void)createOffer:(RTCPeerConnection *)peerConnection{
  __weak typeof(self) wSelf = self;
  [peerConnection offerForConstraints:[self defaultPeerConnContraints] completionHandler:^(RTCSessionDescription *_Nullable sdp, NSError *_Nullable error) {
    if(error){
      DLog(@"Failed to create offer SDP, err=%@", error);
    } else {
      RTCSessionDescription *newSdp = [wSelf getNewSdpWithType:(RTCSdpTypeOffer) sdp:sdp];
      [wSelf setLocalOffer:peerConnection withSdp:newSdp];
    }
  }];
}

- (void)setLocalOffer:(RTCPeerConnection *)pc withSdp:(RTCSessionDescription *)sdp {
  __weak RTCPeerConnection *weakPeerConnection = pc;
  __weak typeof(self) wSelf = self;
  [pc setLocalDescription:sdp completionHandler:^(NSError *_Nullable error) {
    if (!error) {
      DLog(@"Successed to set local offer sdp!");
      [wSelf sendOffer:weakPeerConnection withSdp:sdp];
    }else {
      DLog(@"Failed to set local offer sdp, err=%@", error);
    }
  }];
}

- (void)sendOffer:(RTCPeerConnection *)pc withSdp:(RTCSessionDescription *)sdp {
  NSString *currentId = [self getKeyFromConnectionDic:pc];
  NSDictionary *dict = [[NSDictionary alloc] initWithObjects:@[@"offer", sdp.sdp] forKeys: @[@"type", @"sdp"]];
  NSDictionary *data = @{EMSocketMsg:EMSocketMsg_offer,
             @"data":@{@"sdp":dict},
              EMSocketToId:currentId};
  [self sendDataToServer:data completionHandler:nil];
}

#pragma mark --收到 answer
- (void)answerWith:(NSDictionary *)dic{
  NSDictionary *dataDic = dic[@"data"]; 
  NSDictionary *sdp = dataDic[@"sdp"];
  NSString *sdpStr = sdp[@"sdp"];

  NSString *fromId = dic[EMSocketFromId];
  RTCPeerConnection *peerConnection = [self.connectionDic objectForKey:fromId];
  RTCSessionDescription *remoteSdp = [[RTCSessionDescription alloc] initWithType:RTCSdpTypeAnswer sdp:sdpStr]; 
  [peerConnection setRemoteDescription:remoteSdp completionHandler:^(NSError * _Nullable error) {
    if (error){
      DLog(@"Failed to setRemoteDescription, err=%@", error);
    }
  }];
}

5、后入會(huì)者查詢?nèi)簝?nèi)成員列表仆救，建立與他們的peerConnection抒和，等待_start信令，發(fā)送_start_resp響應(yīng)彤蔽，等待_offer信令到來摧莽，把offer設(shè)置到遠(yuǎn)程描述，創(chuàng)建answer設(shè)置到本地顿痪，發(fā)送給對(duì)方镊辕；

#pragma mark --收到 offer
- (void)offerWith:(NSDictionary *)dic {
  NSDictionary *dataDic = dic[@"data"];
  NSString *fromId = dic[EMSocketFromId];
  //拿到SDP
  NSDictionary *sdp = dataDic[@"sdp"];
  NSString *sdpStr = sdp[@"sdp"];
  //根據(jù)類型和SDP 生成SDP描述對(duì)象
  RTCSessionDescription *remoteSdp = [[RTCSessionDescription alloc] initWithType:RTCSdpTypeOffer sdp:sdpStr];
  //拿到當(dāng)前對(duì)應(yīng)的點(diǎn)對(duì)點(diǎn)連接
  RTCPeerConnection *peerConnection = [self.connectionDic objectForKey:fromId];
  // 需要判斷當(dāng)前peerConnection是否有answer或者offer，有就重置
  if (peerConnection.remoteDescription || peerConnection.localDescription) {
    // 創(chuàng)建一個(gè)新的連接
    peerConnection = [self createPeerConnection:fromId];
    //并且設(shè)置到Dic中去
    [self.connectionDic setObject:peerConnection forKey:fromId];
  }
  //設(shè)置給這個(gè)點(diǎn)對(duì)點(diǎn)連接
  __weak RTCPeerConnection *weakPeerConnection = peerConnection;
  __weak typeof(self) wSelf = self;
  [peerConnection setRemoteDescription:remoteSdp completionHandler:^(NSError * _Nullable error) {
    if (!error) {
      //創(chuàng)建一個(gè)answer,會(huì)把自己的SDP信息返回出去
      [weakPeerConnection answerForConstraints:[wSelf defaultPeerConnContraints] completionHandler:^(RTCSessionDescription * _Nullable sdp, NSError * _Nullable error) {
        if (!error) {
          RTCSessionDescription *newSdp = sdp;// [wSelf getNewSdpWithType:(RTCSdpTypeAnswer) sdp:sdp];
          [weakPeerConnection setLocalDescription:newSdp completionHandler:^(NSError * _Nullable error) {
            NSDictionary *dic = @{EMSocketMsg: EMSocketMsg_answer,
                       @"data": @{
                         @"sdp": @{@"sdp":newSdp.sdp,@"type":@"answer",}
                       },
                       EMSocketToId:fromId};
            [wSelf sendDataToServer:dic completionHandler:nil];
          }];
        } else {
          DLog(@"Failed to create answer an sdp, err=%@", error);
        }
      }];
    } else {
      DLog(@"Failed to setRemoteDescription, err=%@", error);
    }
  }];
}

6蚁袭、雙方互相設(shè)置好offer征懈、answer，建立P2P連接揩悄，WebRtc會(huì)把收集到的可用的candidate回調(diào)給本地卖哎，本地在通過信令服務(wù)器發(fā)送給對(duì)方就可以，對(duì)方收到遠(yuǎn)端的ice_candidate删性，給本地peerConnection addIceCandidate就可以了亏娜，IceCandidate可能會(huì)轉(zhuǎn)發(fā)多次，WebRtc會(huì)找到最合適的通道建立連接镇匀；

// 收到遠(yuǎn)端的ice_candidate
- (void)_ice_candidateWith:(NSDictionary *)dic {
  NSDictionary *dataDic = dic[@"data"];
  NSDictionary *candidateDic =dataDic[@"candidate"];
  NSString *sdpMid = candidateDic[@"sdpMid"];

  int sdpMLineIndex = [candidateDic[@"sdpMLineIndex"] intValue];
  NSString *sdp = candidateDic[@"candidate"];
  //生成遠(yuǎn)端網(wǎng)絡(luò)地址對(duì)象
  RTCIceCandidate *candidate = [[RTCIceCandidate alloc] initWithSdp:sdp sdpMLineIndex:sdpMLineIndex sdpMid:sdpMid];
  //添加到點(diǎn)對(duì)點(diǎn)連接中
  NSString *fromId = dic[EMSocketFromId];
  RTCPeerConnection *peerConnection = [_connectionDic objectForKey:fromId];
  [peerConnection addIceCandidate:candidate];
}

#pragma mark - RTCPeerConnectionDelegate
// 該方法用于收集可用的candidate
- (void)peerConnection:(RTCPeerConnection *)peerConnection didGenerateIceCandidate:(RTCIceCandidate *)candidate {
  NSString *userId = [self getKeyFromConnectionDic:peerConnection];
  NSDictionary *dic = @{
             EMSocketMsg: EMSocketMsg_ice_candidate,
             @"data":@{
                 @"candidate":@{
                     @"sdpMid":candidate.sdpMid ,
                     @"sdpMLineIndex":[NSNumber numberWithInteger:candidate.sdpMLineIndex],
                     @"candidate": candidate.sdp
                     }
                 } ,
             EMSocketToId:userId
             };
  [self sendDataToServer:dic completionHandler:nil];
}

7照藻、將對(duì)方視頻渲染到本地

/* *Called when media is received on a new stream from remote peer. */
- (void)peerConnection:(RTCPeerConnection *)peerConnection didAddStream:(RTCMediaStream *)stream {
  LOG_ME 
  dispatch_async(dispatch_get_main_queue(), ^{ 
    if (stream.videoTracks.count) {
      NSString *userId = [self getKeyFromConnectionDic:peerConnection];
//      RTCVideoTrack *remoteVideoTrack = stream.videoTracks[0]; 
      // 遠(yuǎn)端視頻軌道一定要保存在本地，否則會(huì)渲染不出來
      if ([self->_delegate respondsToSelector:@selector(webRtcManager:addRemoteStream:userId:)]) {
        [self->_delegate webRtcManager:self addRemoteStream:stream userId:userId];
      }
    }
  });
}

2.3 注意事項(xiàng)

1汗侵、iOS視頻編碼格式

iOS并不支持VP8的視頻編碼格式幸缕，但是WebRtc生成的offer群发、answer描述又都是把VP8放前，默認(rèn)是VP8編碼格式发乔，所以此處要對(duì)WebRTC生成的描述進(jìn)行處理熟妓，交互VP8跟H264編碼的順序（iOS對(duì)H264的支持度很高），然后再生成新的描述對(duì)象栏尚，存到本地起愈；

RTCSessionDescription *newSdp = [self getNewSdpWithType:(RTCSdpTypeOffer) sdp:sdp];
[elf setLocalOffer:peerConnection withSdp:newSdp];

2.4 參考資料

iOS WebSocket長鏈接

iOS WebRTC的使用

iOS webRTC SDP介紹及設(shè)置