对github上用C++实现webrtc的peerconnection的example的解析

在寻找WebRTC实现的过程中，找到了一个github上用C++的实现，感觉不错，特此记录学习。WebRTC的具体原理，参考以下链接，本文主要记录该例子在C++中如何实现。下图是该例子的大纲，分为client和server两个部分。

weixin_45591821

175人浏览 · 2023-10-11 17:49:15

weixin_45591821 · 2023-10-11 17:49:15 发布

前言

在寻找WebRTC实现的过程中，找到了一个github上用C++的实现，感觉不错，特此记录学习。
WebRTC的具体原理，参考以下链接，本文主要记录该例子在C++中如何实现。
https://antmedia.io/webrtc-signaling-servers-everything-you-need-to-know/
下图是该例子的大纲，分为client和server两个部分。
在这里插入图片描述

Server

除main以外的文件用途

Data_socket

用于创建数据包，提供发送和解析的功能

Peer_channel

用来判断peer_connection是否连接成功，提供一些对channel的操作，可以同时和多个client连接
需要peer_id来对client进行区分

###Util
提供了int转换到string和size_t转换到string的功能

server端main函数

void HandleBrowserRequest(DataSocket* ds, bool* quit) {
  assert(ds && ds->valid());
  assert(quit);

  const std::string& path = ds->request_path();

  *quit = (path.compare("/quit") == 0);

  if (*quit) {
    ds->Send("200 OK", true, "text/html", "",
             "<html><body>Quitting...</body></html>");
  } else if (ds->method() == DataSocket::OPTIONS) {
    // We'll get this when a browsers do cross-resource-sharing requests.
    // The headers to allow cross-origin script support will be set inside
    // Send.
    ds->Send("200 OK", true, "", "", "");
  } else {
    // Here we could write some useful output back to the browser depending on
    // the path.
    printf("Received an invalid request: %s\n", ds->request_path().c_str());
    ds->Send("500 Sorry", true, "text/html", "",
             "<html><body>Sorry, not yet implemented</body></html>");
  }
}

int main(int argc, char* argv[]) {
  absl::SetProgramUsageMessage(
      "Example usage: ./peerconnection_server --port=8888\n");
  absl::ParseCommandLine(argc, argv);

  // InitFieldTrialsFromString stores the char*, so the char array must outlive
  // the application.
  const std::string force_field_trials = absl::GetFlag(FLAGS_force_fieldtrials);
  webrtc::field_trial::InitFieldTrialsFromString(force_field_trials.c_str());

  int port = absl::GetFlag(FLAGS_port);

  // Abort if the user specifies a port that is outside the allowed
  // range [1, 65535].
  if ((port < 1) || (port > 65535)) {
    printf("Error: %i is not a valid port.\n", port);
    return -1;
  }

  ListeningSocket listener;
  if (!listener.Create()) {
    printf("Failed to create server socket\n");
    return -1;
  } else if (!listener.Listen(port)) {
    printf("Failed to listen on server socket\n");
    return -1;
  }

  printf("Server listening on port %i\n", port);

  PeerChannel clients;
  typedef std::vector<DataSocket*> SocketArray;
  SocketArray sockets;
  bool quit = false;
  while (!quit) {
    // fd_set有两个成员变量，fd_count数据类型是unsingled int，fd_array[64]是unsingled int64
    fd_set socket_set;
    // 将socket_set的fd_count清空
    FD_ZERO(&socket_set);

    if (listener.valid())
    // 在count<64的情况下，将新监听到的client的socket添加到fd_array中
      FD_SET(listener.socket(), &socket_set);

    for (SocketArray::iterator i = sockets.begin(); i != sockets.end(); ++i)
      FD_SET((*i)->socket(), &socket_set);

    struct timeval timeout = {10, 0};
    if (select(FD_SETSIZE, &socket_set, NULL, NULL, &timeout) == SOCKET_ERROR) {
      printf("select failed\n");
      break;
    }

    for (SocketArray::iterator i = sockets.begin(); i != sockets.end(); ++i) {
      DataSocket* s = *i;
      bool socket_done = true;
      // 检查当前的socket是否在socket_set里
      if (FD_ISSET(s->socket(), &socket_set)) {
        // 判断是否接收到header，从client处接收到信息
        if (s->OnDataAvailable(&socket_done) && s->request_received()) {
          ChannelMember* member = clients.Lookup(s);
          // 判断是否peer_connected
          if (member || PeerChannel::IsPeerConnection(s)) {
            if (!member) {
              if (s->PathEquals("/sign_in")) {
                clients.AddMember(s);
              } else {
                printf("No member found for: %s\n", s->request_path().c_str());
                s->Send("500 Error", true, "text/plain", "",
                        "Peer most likely gone.");
              }
            } else if (member->is_wait_request(s)) {
              // no need to do anything.
              socket_done = false;
            } else { // 如果socket尚未添加到set里
              ChannelMember* target = clients.IsTargetedRequest(s); // 根据peer_id来进行判断，如果存在，返回一个client
              if (target) {
                // 向client发送request，来创建peer_connection
                member->ForwardRequestToPeer(s, target);
              } else if (s->PathEquals("/sign_out")) {
                s->Send("200 OK", true, "text/plain", "", "");
              } else {
                printf("Couldn't find target for request: %s\n",
                       s->request_path().c_str());
                s->Send("500 Error", true, "text/plain", "",
                        "Peer most likely gone.");
              }
            }
          } else { // 既不在set里，也没有达成peer_connection
          // 根据DataSocket，发送相对应的内容
            HandleBrowserRequest(s, &quit);
            if (quit) { // 在HandleBrowserRequest中，会对quit做一些判断，如果为false，清除socket并关闭所有的listerner和clients
              printf("Quitting...\n");
              FD_CLR(listener.socket(), &socket_set);
              listener.Close();
              clients.CloseAll();
            }
          }
        }
      } else { 
        socket_done = false; 
      }

      if (socket_done) { // socket完成，接受完该socket后，将连接断掉
        printf("Disconnecting socket\n");
        clients.OnClosing(s);
        assert(s->valid());  // Close must not have been called yet.
        FD_CLR(s->socket(), &socket_set);
        delete (*i);
        i = sockets.erase(i);
        if (i == sockets.end())
          break;
      }
    }
    // check timeout
    clients.CheckForTimeout();
    // 服务器端socket处理
    if (FD_ISSET(listener.socket(), &socket_set)) {
      DataSocket* s = listener.Accept();
      if (sockets.size() >= kMaxConnections) {
        delete s;  // sorry, that's all we can take.
        printf("Connection limit reached\n");
      } else {
        sockets.push_back(s);
        printf("New connection...\n");
      }
    }
  }
  // 释放资源
  for (SocketArray::iterator i = sockets.begin(); i != sockets.end(); ++i)
    delete (*i);
  sockets.clear();

  return 0;
}

主要步骤

解析命令行
设置port
监听socket
通过PeerChannel来实现对client端的一对多的控制
SockerArray来实现对若干个（数量小于64）socket的相关操作
主要loop
6.1 通过遍历SocketArray来实现socket的解析
6.2 遍历完成后，将接收到的新的socket添加到socketArray中，以待loop中的下一次循环
释放资源

Client端

除main以外的文件用途

conductor

初始化peer_connection并执行相关操作，包括但不限于创建，删除，修改peer_connection,对track和channel的修改

default

提供相关的默认值

flag_defs

为client端的peer_connection提供测试信号

main_wnd

wnd由HWND声明，是windows_handle，窗口句柄，用以程序与用户的交互，并实现UI部分

peer_connection_client

与client相关的操作，也包括client的相关状态
一些根据状态改变进行的操作，如OnClose(),OnRead()

main

  // Main loop.
  MSG msg;
  BOOL gm;
  while ((gm = ::GetMessage(&msg, NULL, 0, 0)) != 0 && gm != -1) {
    if (!wnd.PreTranslateMessage(&msg)) {
      ::TranslateMessage(&msg);
      ::DispatchMessage(&msg);
    }
  }

  if (conductor->connection_active() || client.is_connected()) {
    while ((conductor->connection_active() || client.is_connected()) &&
           (gm = ::GetMessage(&msg, NULL, 0, 0)) != 0 && gm != -1) {
      if (!wnd.PreTranslateMessage(&msg)) {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
      }
    }
  }

  rtc::CleanupSSL();
  return 0;
}