本节主要是说webrtc收到turn服务器发过来的AllocateResponse后的做法过程。

接收处理AllocateResponse调用栈

最后是OnAllocateSuccess之后生成turn类型的candidate。

AllocationSequence::OnReadpacket

判断是否是某个replay服务器发过来的消息。如果不是，则判断是否是其他webrtc发过来的，会判断udpport是否创建成功。。

void AllocationSequence::OnReadPacket(rtc::AsyncPacketSocket* socket,
                                      const char* data,
                                      size_t size,
                                      const rtc::SocketAddress& remote_addr,
                                      const int64_t& packet_time_us) {
  RTC_DCHECK(socket == udp_socket_.get());
  bool turn_port_found = false;
  // Try to find the TurnPort that matches the remote address. Note that the
  // message could be a STUN binding response if the TURN server is also used as
  // a STUN server. We don't want to parse every message here to check if it is
  // a STUN binding response, so we pass the message to TurnPort regardless of
  // the message type. The TurnPort will just ignore the message since it will
  // not find any request by transaction ID.
  for (auto* port : relay_ports_) {
    if (port->CanHandleIncomingPacketsFrom(remote_addr)) {
      if (port->HandleIncomingPacket(socket, data, size, remote_addr,
                                     packet_time_us)) {
        return;
      }
      turn_port_found = true;
    }
  }
  if (udp_port_) {
    const ServerAddresses& stun_servers = udp_port_->server_addresses();
    // Pass the packet to the UdpPort if there is no matching TurnPort, or if
    // the TURN server is also a STUN server.
    if (!turn_port_found ||
        stun_servers.find(remote_addr) != stun_servers.end()) {
      RTC_DCHECK(udp_port_->SharedSocket());
      udp_port_->HandleIncomingPacket(socket, data, size, remote_addr,
                                      packet_time_us);
    }
  }
}

TurnPort::HandleIncomingPacket

StunRequestManager::CheckResponse(const char data, size_t size)
-》
StunRequestManager::CheckResponse(StunMessage msg)
—》
TurnAllocateRequest::OnResponse

TurnAllocateRequest::OnResponse

1、从映射中获取本机外网的映射地址
2、获取relay服务器的地址
3、生成candidate

void TurnAllocateRequest::OnResponse(StunMessage* response) {
  RTC_LOG(LS_INFO) << port_->ToString()
                   << ": TURN allocate requested successfully, id="
                   << rtc::hex_encode(id())
                   << ", code=0"  // Makes logging easier to parse.
                      ", rtt="
                   << Elapsed();
  // Check mandatory attributes as indicated in RFC5766, Section 6.3.
  const StunAddressAttribute* mapped_attr =
      response->GetAddress(STUN_ATTR_XOR_MAPPED_ADDRESS);
  if (!mapped_attr) {
    RTC_LOG(LS_WARNING) << port_->ToString()
                        << ": Missing STUN_ATTR_XOR_MAPPED_ADDRESS "
                           "attribute in allocate success response";
    return;
  }
  // Using XOR-Mapped-Address for stun.
  port_->OnStunAddress(mapped_attr->GetAddress());
  const StunAddressAttribute* relayed_attr =
      response->GetAddress(STUN_ATTR_XOR_RELAYED_ADDRESS);
  if (!relayed_attr) {
    RTC_LOG(LS_WARNING) << port_->ToString()
                        << ": Missing STUN_ATTR_XOR_RELAYED_ADDRESS "
                           "attribute in allocate success response";
    return;
  }
  const StunUInt32Attribute* lifetime_attr =
      response->GetUInt32(STUN_ATTR_TURN_LIFETIME);
  if (!lifetime_attr) {
    RTC_LOG(LS_WARNING) << port_->ToString()
                        << ": Missing STUN_ATTR_TURN_LIFETIME attribute in "
                           "allocate success response";
    return;
  }
  // Notify the port the allocate succeeded, and schedule a refresh request.
  port_->OnAllocateSuccess(relayed_attr->GetAddress(),
                           mapped_attr->GetAddress());
  port_->ScheduleRefresh(lifetime_attr->value());
}

TurnPort::OnAllocateSuccess

void TurnPort::OnAllocateSuccess(const rtc::SocketAddress& address,
                                 const rtc::SocketAddress& stun_address) {
  state_ = STATE_READY;
  rtc::SocketAddress related_address = stun_address;
  // For relayed candidate, Base is the candidate itself.
  AddAddress(address,          // Candidate address.
             address,          // Base address.
             related_address,  // Related address.
             UDP_PROTOCOL_NAME,
             ProtoToString(server_address_.proto),  // The first hop protocol.
             "",  // TCP canddiate type, empty for turn candidates.
             RELAY_PORT_TYPE, GetRelayPreference(server_address_.proto),
             server_priority_, ReconstructedServerUrl(false /* use_hostname */),
             true);
}