WebRTC的ICE之TURN协议的交互流程和中继转发Relay媒体数据的turnserver的测试

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前言

TURN协议：文档RFC5766

文档中TURN协议工作原理图

                                     Peer AServer-Reflexive    +---------+Transport Address   |         |192.0.2.150:32102   |         ||              /|         |TURN              |            / ^|  Peer A |Client's              Server            |           /  ||         |Host Transport        Transport         |         //   ||         |Address               Address           |       //     |+---------+10.1.1.2:49721       192.0.2.15:3478     |+-+  //     Peer A|               |               ||N| /       Host Transport|   +-+         |               ||A|/        Address|   | |         |               v|T|     192.168.100.2:49582|   | |         |               /+-++---------+|   | |         |+---------+   /              +---------+|         ||   |N|         ||         | //               |         || TURN    |v   | |         v| TURN    |/                 |         || Client  |----|A|----------| Server  |------------------|  Peer B ||         |    | |^         |         |^                ^|         ||         |    |T||         |         ||                ||         |+---------+    | ||         +---------+|                |+---------+| ||                    |                || ||                    |                |+-+|                    |                ||                    |                ||                    |                |Client's                   |            Peer BServer-Reflexive    Relayed             TransportTransport Address   Transport Address   Address192.0.2.1:7000      192.0.2.15:50000     192.0.2.210:49191

WebRTC中走中继Relay 调用流程图

一、TURN协议

TURN                                 TURN           Peer          Peerclient                               server          A             B|-- Allocate request --------------->|             |             ||                                    |             |             ||<--------------- Allocate failure --|             |             ||                 (401 Unauthorized) |             |             ||                                    |             |             ||-- Allocate request --------------->|             |             ||                                    |             |             ||<---------- Allocate success resp --|             |             ||            (192.0.2.15:50000)      |             |             |//                                   //            //            //|                                    |             |             ||-- Refresh request ---------------->|             |             ||                                    |             |             ||<----------- Refresh success resp --|             |             ||                                    |             |             |

TURN                                 TURN           Peer          Peerclient                               server          A             B|                                    |             |             ||-- CreatePermission req (Peer A) -->|             |             ||<-- CreatePermission success resp --|             |             ||                                    |             |             ||--- Send ind (Peer A)-------------->|             |             ||                                    |=== data ===>|             ||                                    |             |             ||                                    |<== data ====|             ||<-------------- Data ind (Peer A) --|             |             ||                                    |             |             ||                                    |             |             ||--- Send ind (Peer B)-------------->|             |             ||                                    | dropped     |             ||                                    |             |             ||                                    |<== data ==================||                            dropped |             |             ||                                    |             |             |
--------------------------------------------------------------------------------------

TURN                                 TURN           Peer          Peerclient                               server          A             B|                                    |             |             ||-- ChannelBind req ---------------->|             |             || (Peer A to 0x4001)                 |             |             ||                                    |             |             ||<---------- ChannelBind succ resp --|             |             ||                                    |             |             ||-- [0x4001] data ------------------>|             |             ||                                    |=== data ===>|             ||                                    |             |             ||                                    |<== data ====|             ||<------------------ [0x4001] data --|             |             ||                                    |             |             ||--- Send ind (Peer A)-------------->|             |             ||                                    |=== data ===>|             ||                                    |             |             ||                                    |<== data ====|             ||<------------------ [0x4001] data --|             |             ||                                    |             |             |Figure 4

1、连接Turn Server 流程

和国标gb28181的协议差不多 都是先发送一包AllocateRequest到服务返回一个错误码然后在发送一个AllocateRequest请求带上 用户名和密码 然后Trunserver返回映射turn上ip地址和port端口

① 抓包交换流程图

② TURN协议格式解析

协议基础与消息结构

TURN协议基于STUN协议扩展，采用STUN消息格式（头部+属性列表），同时新增了专用于中继功能的方法和属性‌

1. 消息头（Header）：

• Class‌：固定为0x00（请求）或0x10（指示消息）‌

• Method‌：定义操作类型（如Allocate、ChannelBind等）‌

• Length‌：消息总长度（不含头部）‌
  ‌

• Transaction ID‌：16字节唯一标识符，用于匹配请求与响应‌

‌2. 属性列表（Attribute）‌：

• 每个属性由Type（2字节）、Length（2字节）和Value（可变长）组成‌

• 例如：XOR-RELAYED-ADDRESS表示中继地址，CHANNEL-NUMBER标识信道号‌

关键方法类型

TURN协议新增以下STUN方法

• Allocate‌：客户端向服务器申请中继地址，响应中包含XOR-RELAYED-ADDRESS属性‌
• Refresh‌：延长中继地址的生命周期（通过LIFETIME属性设置超时时间）‌
• ChannelBind‌：绑定信道号（CHANNEL-NUMBER）与特定Peer地址，启用ChannelData传输‌
• Send/Data Indication‌：用于中继数据传输（Send为客户端→服务器，Data为服务器→客户端

核心属性类型

新增属性包括：

• XOR-RELAYED-ADDRESS‌：服务器分配的中继地址（IP+端口），用于标识客户端的中继端点‌
• XOR-MAPPRE-ADDRES: 本机映射外网地址（IP+port）
• CHANNEL-NUMBER‌：2字节信道号（范围0x4000-0x7FFF），用于ChannelData报文的高效传输‌
• LIFETIME‌：中继地址有效期（默认10分钟），客户端需定期刷新‌
• DONT-FRAGMENT‌：标志位，指示客户端支持IP分片重组‌

错误码与状态‌

TURN协议扩展了STUN错误码：

• 401（未认证）‌：请求未携带有效凭证，需重新发送认证信息‌78‌
• 437（Allocation Mismatch）‌：客户端尝试使用未分配的信道或地址‌
• 508（Insufficient Capacity）‌：服务器资源不足，无法分配中继地址‌

数据传输机制‌

1‌. Send/Data Indication‌：

• 使用STUN消息格式，Send携带应用数据发送至服务器，Data由服务器转发至Peer‌
• 头部包含XOR-PEER-ADDRESS属性，标识目标Peer地址‌67。
  ‌

2. ChannelData消息‌：

• 非STUN格式，头部仅4字节（信道号+数据长度），减少传输开销‌
• 需通过ChannelBind预先绑定信道号与Peer地址‌

③ 发送Allocate Request UDP 信息包信息

第一次返回 401 Unauthorized 信息 带有NONE（新生成的一次性随机数），REALM（标识服务器或服务的域）

再次发送 Allocate Request UDP 包 带上 协议、用户名和sha-1(user:realm:paasword)签名

TURN服务返回 本机映射外网地址和TURN服务分配中继地址、有效时间

④ 发送CreatePermission Request

返回数据

发送数据Send Indication

！【】

接收 Data Indiaction

⑤ Channel-Bind Request

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发送数据 ChannelData Message

2、 TURN测试Demo

TURN测试demo

二 、 iceCandidate收集的时机有两种

1、创建PeerConnection对象传入的参数ice_candidate_pool_size大于0会创建连接池的个数， 如果没有不会创建连接池ICE的速度就会有点慢

设置ice配置

bool Conductor::CreatePeerConnection(bool dtls) {RTC_DCHECK(peer_connection_factory_);RTC_DCHECK(!peer_connection_);RTC_LOG(LS_INFO) << __FUNCTION__;webrtc::PeerConnectionInterface::RTCConfiguration config;config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan; //这个 config.enable_dtls_srtp = dtls; //是否加密webrtc::PeerConnectionInterface::IceServer server;server.uri = GetPeerConnectionString();config.ice_candidate_pool_size = 0; // 大于0 就在sdp之前进行stun和turn连接创建， 反之啥事情都不做server.username = user_name_;server.password = pass_word_;std::vector<std::string> turnservers;turnservers.push_back(turn_url_);server.urls = turnservers;// 设置走 turn server 进行转发媒体数据 哈config.type = webrtc::PeerConnectionInterface::kRelay;config.servers.push_back(server);peer_connection_ = peer_connection_factory_->CreatePeerConnection(config, nullptr, nullptr, this);return peer_connection_ != nullptr;
}

在CreatePeerConnection方法中

1. 异步创建BasicPortAllocator对象中如果ice_candidate_pool_size大于在SetConfiguration方法中就会进行连接turn和stun服务
2. 创建负责ICE管理类JsepTransportController

bool PortAllocator::SetConfiguration(const ServerAddresses& stun_servers,const std::vector<RelayServerConfig>& turn_servers,int candidate_pool_size,bool prune_turn_ports,webrtc::TurnCustomizer* turn_customizer,const absl::optional<int>& stun_candidate_keepalive_interval) 
{CheckRunOnValidThreadIfInitialized();// A positive candidate pool size would lead to the creation of a pooled// allocator session and starting getting ports, which we should only do on// the network thread.RTC_DCHECK(candidate_pool_size == 0 || thread_checker_.IsCurrent());bool ice_servers_changed = (stun_servers != stun_servers_ || turn_servers != turn_servers_);stun_servers_ = stun_servers;turn_servers_ = turn_servers;prune_turn_ports_ = prune_turn_ports;if (candidate_pool_frozen_) {if (candidate_pool_size != candidate_pool_size_) {RTC_LOG(LS_ERROR) << "Trying to change candidate pool size after pool was frozen.";return false;}return true;}if (candidate_pool_size < 0) {RTC_LOG(LS_ERROR) << "Can't set negative pool size.";return false;}candidate_pool_size_ = candidate_pool_size;// If ICE servers changed, throw away any existing pooled sessions and create// new ones.///// 20250328 ice[stun、turn]信息改变 就清除当前端口连接池会话if (ice_servers_changed) {pooled_sessions_.clear();}turn_customizer_ = turn_customizer;// If |candidate_pool_size_| is less than the number of pooled sessions, get// rid of the extras.while (candidate_pool_size_ < static_cast<int>(pooled_sessions_.size())) {pooled_sessions_.back().reset(nullptr);pooled_sessions_.pop_back();}///// |stun_candidate_keepalive_interval_| will be used in STUN port allocation// in future sessions. We also update the ready ports in the pooled sessions.// Ports in sessions that are taken and owned by P2PTransportChannel will be// updated there via IceConfig.// ICE的心跳包  的stun_candidate_keepalive_interval_ = stun_candidate_keepalive_interval;for (const auto& session : pooled_sessions_) {session->SetStunKeepaliveIntervalForReadyPorts(stun_candidate_keepalive_interval_);}// If |candidate_pool_size_| is greater than the number of pooled sessions,// create new sessions.while (static_cast<int>(pooled_sessions_.size()) < candidate_pool_size_) {IceParameters iceCredentials = IceCredentialsIterator::CreateRandomIceCredentials();PortAllocatorSession* pooled_session = CreateSessionInternal("", 0, iceCredentials.ufrag, iceCredentials.pwd);pooled_session->set_pooled(true);//20250327  触发MSG_CONFIG_START信号   探测stun和turn 服务连通性 pooled_session->StartGettingPorts();pooled_sessions_.push_back(std::unique_ptr<PortAllocatorSession>(pooled_session));}return true;
}

2、 设置sdp时获取 iceCandidate

整体调用流程

调用流程图

bool TurnPort::HandleIncomingPacket(rtc::AsyncPacketSocket* socket,const char* data,size_t size,const rtc::SocketAddress& remote_addr,int64_t packet_time_us) {if (socket != socket_) {// The packet was received on a shared socket after we've allocated a new// socket for this TURN port.return false;}// This is to guard against a STUN response from previous server after// alternative server redirection. TODO(guoweis): add a unit test for this// race condition.if (remote_addr != server_address_.address) {RTC_LOG(LS_WARNING) << ToString()<< ": Discarding TURN message from unknown address: "<< remote_addr.ToString() << " server_address_: "<< server_address_.address.ToString();return false;}// The message must be at least the size of a channel header.if (size < TURN_CHANNEL_HEADER_SIZE) {RTC_LOG(LS_WARNING) << ToString()<< ": Received TURN message that was too short";return false;}if (state_ == STATE_DISCONNECTED) {RTC_LOG(LS_WARNING)<< ToString()<< ": Received TURN message while the TURN port is disconnected";return false;}// Check the message type, to see if is a Channel Data message.// The message will either be channel data, a TURN data indication, or// a response to a previous request.uint16_t msg_type = rtc::GetBE16(data);if (IsTurnChannelData(msg_type)) {HandleChannelData(msg_type, data, size, packet_time_us);return true;}if (msg_type == TURN_DATA_INDICATION) {HandleDataIndication(data, size, packet_time_us);return true;}if (SharedSocket() && (msg_type == STUN_BINDING_RESPONSE ||msg_type == STUN_BINDING_ERROR_RESPONSE)) {RTC_LOG(LS_VERBOSE)<< ToString()<< ": Ignoring STUN binding response message on shared socket.";return false;}// This must be a response for one of our requests.// Check success responses, but not errors, for MESSAGE-INTEGRITY.
#if TURN_LOGstd::cout << "[turn][hash()  = " << hash() << "]" << std::endl;RTC_LOG(LS_INFO) << "[turn][hash()  = " << hash() << "]";
#endif // #if TURN_LOGif (IsStunSuccessResponseType(msg_type) &&!StunMessage::ValidateMessageIntegrity(data, size, hash())) {RTC_LOG(LS_WARNING) << ToString()<< ": Received TURN message with invalid ""message integrity, msg_type: "<< msg_type;return true;}request_manager_.CheckResponse(data, size);return true;
}

总结

WebRTC源码分析地址：https://github.com/chensongpoixs/cwebrtc