c++ - 用于端口转发的 libssh2 示例代码

Question

我正在寻找如何使用 libssh2 设置 ssh 端口转发的示例。我查看了 API，但在端口转发领域的文档方式非常少。

例如，当使用 PuTTY 的 plink 时，有要监听的远程端口，还有应该将流量发送到的本地端口。开发人员有责任设置它吗？有人可以举例说明如何做到这一点吗？

此外，将远程端口连接到本地端口的示例也很有用。我是否使用 libssh2_channel_direct_tcpip_ex()？

如果需要的话，我愿意悬赏来获得一些这样的工作示例。

Answer 1

使 libssh2 端口转发工作的关键是发现它基本上只是为您提供进入该端口的数据。您必须实际将数据发送到您打开的本地端口:

(注意，这段代码还不完整，没有错误检查，线程产生也不正确，但它给出了如何完成这个的大纲。)

void reverse_port_forward(CMainDlg* dlg, addrinfo * hubaddr, std::string username, std::string password, int port)
{
  int iretval;
  unsigned long mode = 1;
  int last_socket_err = 0;
  int other_port = 0;
  fd_set read_set, write_set;

  SOCKET sshsock = socket(AF_INET, SOCK_STREAM, 0);
  iretval = connect(sshsock, hubaddr->ai_addr, hubaddr->ai_addrlen);
  if (iretval != 0)
    ::PostQuitMessage(0);

  LIBSSH2_SESSION * session = NULL;
  session = libssh2_session_init();

  iretval = libssh2_session_startup(session, sshsock);
  if (iretval)
    ::PostQuitMessage(0);

  iretval = libssh2_userauth_password(session, username.c_str(), password.c_str());

  dlg->m_track_status(dlg, 1, 0, "Authorized");

  LIBSSH2_LISTENER* listener = NULL;
  listener = libssh2_channel_forward_listen_ex(session, "127.0.0.1", port, &other_port, 1);
  if (!listener)
    ::PostQuitMessage(0);

  LIBSSH2_CHANNEL* channel = NULL;

  ioctlsocket(sshsock, FIONBIO, &mode);
  libssh2_session_set_blocking(session, 0); // non-blocking
  int err = LIBSSH2_ERROR_EAGAIN;
  while (err == LIBSSH2_ERROR_EAGAIN)
  {
    channel = libssh2_channel_forward_accept(listener);
    if (channel) break;
    err = libssh2_session_last_errno(session);
    boost::this_thread::yield();
  }

  if (channel)
  {
    char buf[MAX_BUF_LEN];
    char* chunk;
    long bytes_read = 0;
    long bytes_written = 0;
    int total_set = 0;
    timeval wait;
    wait.tv_sec = 0;
    wait.tv_usec = 2000;

    sockaddr_in localhost;
    localhost.sin_family = AF_INET;
    localhost.sin_addr.s_addr = inet_addr("127.0.0.1");
    localhost.sin_port = htons(5900);
    SOCKET local_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    ioctlsocket(local_sock, FIONBIO, &mode);
    iretval = connect(local_sock, (sockaddr*) &localhost, sizeof(localhost) );
    if (iretval == SOCKET_ERROR)
      iretval = WSAGetLastError();

    while (1)
    {
      bytes_read = libssh2_channel_read(channel, buf, MAX_BUF_LEN);
      if (bytes_read >= 0){
        FD_ZERO(&read_set);
        FD_ZERO(&write_set);
        FD_SET(local_sock, &write_set);

        // wait until the socket can be written to
        while (select(0, &read_set, &write_set, NULL, &wait) < 1)
          boost::this_thread::yield();

        if (FD_ISSET(local_sock, &write_set))
        {
          FD_CLR(local_sock, &write_set);
          chunk = buf;

          // everything may not get written in this call because we're non blocking.  So
          // keep writing more data until we've emptied the buffer pointer.
          while ((bytes_written = send(local_sock, chunk, bytes_read, 0)) < bytes_read)
          {
            // if it couldn't write anything because the buffer is full, bytes_written
            // will be negative which won't help our pointer math much
            if (bytes_written > 0)
            {
              chunk = buf + bytes_written;
              bytes_read -= bytes_written;
              if (bytes_read == 0)
                break;
            }
            FD_ZERO(&read_set);
            FD_ZERO(&write_set);
            FD_SET(local_sock, &write_set);

            // wait until the socket can be written to
            while (select(0, &read_set, &write_set, NULL, &wait) < 1)
              boost::this_thread::yield();
          }

        }
      }

      FD_ZERO(&read_set);
      FD_ZERO(&write_set);
      FD_SET(local_sock, &read_set);
      select(0, &read_set, &write_set, NULL, &wait);
      if (FD_ISSET(local_sock, &read_set))
      {
        FD_CLR(local_sock, &read_set);
        bytes_read = recv(local_sock, buf, MAX_BUF_LEN, 0);
        if (bytes_read >= 0)
        {
          while ((bytes_written = libssh2_channel_write_ex(channel, 0, buf, bytes_read)) == LIBSSH2_ERROR_EAGAIN)
            boost::this_thread::yield();
        }
      }
      boost::this_thread::yield();
    } // while
  } // if channel
}

附言要完成这项工作，需要 libssh2 的最新 SVN 版本。先前版本中存在错误，导致端口转发无法使用。