不过该方式很少用，一般都是用udp的candidate或者turn的candidate。

调用栈

AllocationSequence::CreateTCPPorts

void AllocationSequence::CreateTCPPorts() {
  if (IsFlagSet(PORTALLOCATOR_DISABLE_TCP)) {
    RTC_LOG(LS_VERBOSE) << "AllocationSequence: TCP ports disabled, skipping.";
    return;
  }
  std::unique_ptr<Port> port = TCPPort::Create(
      session_->network_thread(), session_->socket_factory(), network_,
      session_->allocator()->min_port(), session_->allocator()->max_port(),
      session_->username(), session_->password(),
      session_->allocator()->allow_tcp_listen());
  if (port) {
    session_->AddAllocatedPort(port.release(), this, true);
    // Since TCPPort is not created using shared socket, |port| will not be
    // added to the dequeue.
  }
}

在TCPPort::Create中主要是调用了

TCPPort::TryCreateServerSocket

BasicPacketSocketFactory::CreateServerTcpSocket

AsyncPacketSocket* BasicPacketSocketFactory::CreateServerTcpSocket(
    const SocketAddress& local_address,
    uint16_t min_port,
    uint16_t max_port,
    int opts) {
  // Fail if TLS is required.
  if (opts & PacketSocketFactory::OPT_TLS) {
    RTC_LOG(LS_ERROR) << "TLS support currently is not available.";
    return NULL;
  }
  AsyncSocket* socket =
      socket_factory()->CreateAsyncSocket(local_address.family(), SOCK_STREAM);
  if (!socket) {
    return NULL;
  }
  if (BindSocket(socket, local_address, min_port, max_port) < 0) {
    RTC_LOG(LS_ERROR) << "TCP bind failed with error " << socket->GetError();
    delete socket;
    return NULL;
  }
  // Set TCP_NODELAY (via OPT_NODELAY) for improved performance; this causes
  // small media packets to be sent immediately rather than being buffered up,
  // reducing latency.
  if (socket->SetOption(Socket::OPT_NODELAY, 1) != 0) {
    RTC_LOG(LS_ERROR) << "Setting TCP_NODELAY option failed with error "
                      << socket->GetError();
  }
  // If using fake TLS, wrap the TCP socket in a pseudo-SSL socket.
  if (opts & PacketSocketFactory::OPT_TLS_FAKE) {
    RTC_DCHECK(!(opts & PacketSocketFactory::OPT_TLS));
    socket = new AsyncSSLSocket(socket);
  }
  if (opts & PacketSocketFactory::OPT_STUN)
    return new cricket::AsyncStunTCPSocket(socket, true);
  return new AsyncTCPSocket(socket, true);
}

可见里面还包括了tls的处理

AllocationSequence::CreateTCPPorts
-》
BasicPortAllocatorSession::AddAllocatedPort
-》

TCPPort::PrepareAddress