c ++ libssh-ssh_channel_read（）始终返回0，而ssh_channel_is_open（）返回false

Question

这是我第一次以编程方式实现ssh，并且对为什么我的代码无法正常工作感到困惑-更具体地说， ssh_channel_read（）始终返回读取的0个字节。 我不知道我在做什么错！ 我一直在逐步遵循API指示，但显然我会无意间忽略某些内容。

我正在尝试使用用户名+密码连接到我的Pi。 这是完整的代码，您可以复制粘贴并将其编译为：

g++ main.cpp -lssh -o myapp

在代码之后，您可以看到我得到的输出。 请别苛刻，就像我说的那样，这是我第一次使用SSH：

#include <iostream>
#include <string>
#include <libssh/libsshpp.hpp>

int main(int argc, const char **argv)
{
   int vbs                    = SSH_LOG_RARE;
   int timeout_ms             = 1000;
   ssh_session session        = ssh_new();

   ssh_channel channel;

   char        buffer[256];
   int         bytes_red;

   if (session == NULL)
   {
      std::cout << "Failed to create ssh session." << std::endl;
      exit(-1);
   }

   ssh_set_blocking(session, 1);

   std::cout << "Created SSH session..." << std::endl;

   ssh_options_set(session, SSH_OPTIONS_HOST, "192.168.1.5");
   ssh_options_set(session, SSH_OPTIONS_PORT_STR, "22");
   ssh_options_set(session, SSH_OPTIONS_USER, "pi@192.168.1.5");
   ssh_options_set(session,SSH_OPTIONS_LOG_VERBOSITY, &vbs);

   int con_result             = ssh_connect(session);
   int auth_result            = ssh_userauth_password(session, "pi", "1234");

   std::cout << "Connecton Result is: "   << con_result  << std::endl;
   std::cout << "Auth Result is: "        << auth_result << std::endl;

   ///////////////////////////////////////////
   // Did we create the session successfully?
   ///////////////////////////////////////////
   if (con_result != SSH_OK)
   {
      std::cout << "SSH connection failed. Error code is:  " << con_result << std::endl;
      ssh_free(session);
      return con_result;
   }

   ///////////////////////////////////////////
   // Did we authenticate?
   ///////////////////////////////////////////
   if (auth_result != SSH_AUTH_SUCCESS)
   {
      std::cout << "SSH authentication failed. Error code is:  " << auth_result << std::endl;
      ssh_free(session);
      return auth_result;
   }

   ///////////////////////////////////////////
   // Create a new ssh_channel
   ///////////////////////////////////////////
   channel = ssh_channel_new(session);

   if (channel == NULL)
   {
      std::cout << "Failed to create SSH channel." << std::endl;
      ssh_free(session);
      return SSH_ERROR;
   }

   if (ssh_channel_is_open(channel))
      std::cout << "Channel is open" << std::endl;
   else
      std::cout << "Channel is closed" << std::endl;

   while(!ssh_channel_is_eof(channel))
   {
      bytes_red = ssh_channel_read_timeout(channel, buffer, sizeof(buffer), 0, timeout_ms);

//    if (bytes_red)
         std::cout << "Bytes read: " << bytes_red << std::endl;
   }

   std::cout << "Exiting ..." << std::endl;

   ssh_channel_close(channel);
   ssh_channel_free(channel);
   ssh_free(session);

  return 0;
}

这是运行时得到的输出：

$./myapp
Created SSH session...
[2018/05/19 14:57:14.246759, 1] socket_callback_connected:  Socket connection callback: 1 (0)
[2018/05/19 14:57:14.301270, 1] ssh_client_connection_callback:  SSH server banner: SSH-2.0-OpenSSH_7.4p1 Raspbian-10+deb9u1
[2018/05/19 14:57:14.301321, 1] ssh_analyze_banner:  Analyzing banner: SSH-2.0-OpenSSH_7.4p1 Raspbian-10+deb9u1
[2018/05/19 14:57:14.301337, 1] ssh_analyze_banner:  We are talking to an OpenSSH client version: 7.4 (70400)
Connecton Result is: 0
Auth Result is: 0
Channel is closed
[2018/05/19 14:57:14.669298, 1] ssh_packet_process:  Couldn't do anything with packet type 80
Bytes read: 0
Bytes read: 0
Bytes read: 0
Bytes read: 0
Bytes read: 0
^C
$

我可以看到错误消息“通道已关闭”，但是为什么呢？ 我究竟做错了什么？

在此之后，我还想将数据发送到服务器，并明显获得反馈。 据我所读， ssh_channel_write（）是要使用的函数。

之前，我还没有通过编程方式处理过SSH，在撰写本文时，我正在学习这一内容。

非常感谢您的帮助。

更新资料

感谢贾拉，我已经解决了这个问题！ 这是有效的最终代码！

#include <iostream>
#include <string>
#include <libssh/libsshpp.hpp>

int main(int argc, const char **argv)
{
   int vbs                    = SSH_LOG_RARE;
   int timeout_ms             = 1000;
   ssh_session session = ssh_new();

   ssh_channel channel;

   char        buffer[256];
   int         bytes_red;

   if (session == NULL)
   {
      std::cout << "Failed to create ssh session." << std::endl;
      exit(-1);
   }

   ssh_set_blocking(session, 1);

   std::cout << "Created SSH session..." << std::endl;

   ssh_options_set(session, SSH_OPTIONS_HOST, "192.168.1.5");
   ssh_options_set(session, SSH_OPTIONS_PORT_STR, "22");
   ssh_options_set(session, SSH_OPTIONS_USER, "pi@192.168.1.5");
   ssh_options_set(session, SSH_OPTIONS_LOG_VERBOSITY, &vbs);

   int con_result             = ssh_connect(session);
   int auth_result            = ssh_userauth_password(session, "pi", "1234");

   std::cout << "Connecton Result is: "   << con_result  << std::endl;
   std::cout << "Auth Result is: "        << auth_result << std::endl;

   ///////////////////////////////////////////
   // Did we create the session successfully?
   ///////////////////////////////////////////
   if (con_result != SSH_OK)
   {
      std::cout << "SSH connection failed. Error code is:  " << con_result << std::endl;
      ssh_free(session);
      return con_result;
   }

   ///////////////////////////////////////////
   // Did we authenticate?
   ///////////////////////////////////////////
   if (auth_result != SSH_AUTH_SUCCESS)
   {
      std::cout << "SSH authentication failed. Error code is:  " << auth_result << std::endl;
      ssh_free(session);
      return auth_result;
   }

   ///////////////////////////////////////////
   // Create a new ssh_channel
   ///////////////////////////////////////////
   channel = ssh_channel_new(session);

   if (channel == NULL)
   {
      std::cout << "Failed to create SSH channel." << std::endl;
      ssh_free(session);
      return SSH_ERROR;
   }

   ssh_channel_open_session(channel);

   if (ssh_channel_is_open(channel))
      std::cout << "Channel is open" << std::endl;
   else
      std::cout << "Channel is closed" << std::endl;

   int rc = ssh_channel_request_exec(channel, "ls");


   while(!ssh_channel_is_eof(channel))
   {
      bytes_red = ssh_channel_read_timeout(channel, buffer, sizeof(buffer), 0, timeout_ms);

//    if (bytes_red)
//       std::cout << "Bytes read: " << bytes_red << std::endl;

      std::cout << buffer << std::endl;
   }

   std::cout << "Exiting ..." << std::endl;

   ssh_channel_close(channel);
   ssh_channel_free(channel);
   ssh_free(session);

  return 0;
}

编译： g++ main.cpp -lssh -o myapp ，这是我运行它时得到的：

./myapp
Created SSH session...
[2018/05/19 16:01:41.830861, 1] socket_callback_connected:  Socket connection callback: 1 (0)
[2018/05/19 16:01:41.884875, 1] ssh_client_connection_callback:  SSH server banner: SSH-2.0-OpenSSH_7.4p1 Raspbian-10+deb9u1
[2018/05/19 16:01:41.884929, 1] ssh_analyze_banner:  Analyzing banner: SSH-2.0-OpenSSH_7.4p1 Raspbian-10+deb9u1
[2018/05/19 16:01:41.884945, 1] ssh_analyze_banner:  We are talking to an OpenSSH client version: 7.4 (70400)
Connecton Result is: 0
Auth Result is: 0
[2018/05/19 16:01:42.258668, 1] ssh_packet_process:  Couldn't do anything with packet type 80
Channel is open
Desktop
Documents
Downloads
Music
Pictures
Public
python_games
Templates
Videos
����s
Exiting ...

我只需要处理有趣的字符就可以了。 当我刚开始使用它时，这直接来自我的源代码编辑器，因此代码并不完美。

Answer 1

ssh_channel_new为新频道分配了资源。 它不会打开它。

根据您要实现的目标，然后应在该通道上调用适当的ssh_channel_open_XXXX函数。

一个简单的例子可以在这里找到： https : //github.com/substack/libssh/blob/c073979235eb0d0587ac9cb3c192e91e32d34b06/examples/exec.c

首先ssh_channel_open_session以打开会话（外壳）通道，然后ssh_channel_request_exec以执行lsof命令。

写入通道的方式/时间取决于打开的通道类型。 在此处可以看到一个写入会话通道的示例（在主机上调用cat > /dev/null以将写入的数据通过管道传输到/ dev / null之后）： https : //github.com/substack/libssh/blob/c073979235eb0d0587ac9cb3c192e91e32d34b06 /examples/senddata.c