libssh2的简单应用

libssh2的官网：www.libssh2.org；虽然这个网站里面内容是全英文的，我想所有的计算机从事者都能看懂这里面写的内容，这里面提供了很多例子，比如FTP的，shell命令的等等，我在这里介绍一下shell命令的发送和接收返回数据。

example里有个文件名叫exec.c 这个文件是实现shell命令的一个例子:

* Sample showing how to use libssh2 to execute a command remotely.  *  * The sample code has fixed values for host name, user name, password  * and command to run.  *  * Run it like this:  *  * $ ./ssh2_exec 127.0.0.1 user password "uptime"  *  */      #include "libssh2_config.h"  #include <libssh2.h>     #ifdef HAVE_WINSOCK2_H  #include <winsock2.h>  #endif  #ifdef HAVE_SYS_SOCKET_H  #include <sys/socket.h>  #endif  #ifdef HAVE_NETINET_IN_H  #include <netinet/in.h>  #endif  #ifdef HAVE_SYS_SELECT_H  #include <sys/select.h>  #endif  #ifdef HAVE_UNISTD_H  #include <unistd.h>  #endif  #ifdef HAVE_ARPA_INET_H  #include <arpa/inet.h>  #endif     #include <sys/time.h>  #include <sys/types.h>  #include <stdlib.h>  #include <fcntl.h>  #include <errno.h>  #include <stdio.h>  #include <ctype.h>     static int waitsocket(int socket_fd, LIBSSH2_SESSION *session)  {      struct timeval timeout;      int rc;      fd_set fd;      fd_set *writefd = NULL;      fd_set *readfd = NULL;      int dir;         timeout.tv_sec = 10;      timeout.tv_usec = 0;         FD_ZERO(&fd);         FD_SET(socket_fd, &fd);         /* now make sure we wait in the correct direction */       dir = libssh2_session_block_directions(session);           if(dir & LIBSSH2_SESSION_BLOCK_INBOUND)          readfd = &fd;         if(dir & LIBSSH2_SESSION_BLOCK_OUTBOUND)          writefd = &fd;         rc = select(socket_fd + 1, readfd, writefd, NULL, &timeout);         return rc;  }     int main(int argc, char *argv[])  {      const char *hostname = "127.0.0.1";      const char *commandline = "uptime";      const char *username    = "user";      const char *password    = "password";      unsigned long hostaddr;      int sock;      struct sockaddr_in sin;      const char *fingerprint;      LIBSSH2_SESSION *session;      LIBSSH2_CHANNEL *channel;      int rc;      int exitcode;      char *exitsignal=(char *)"none";      int bytecount = 0;      size_t len;      LIBSSH2_KNOWNHOSTS *nh;      int type;     #ifdef WIN32      WSADATA wsadata;      WSAStartup(MAKEWORD(2,0), &wsadata);  #endif      if (argc > 1)          /* must be ip address only */           hostname = argv[1];         if (argc > 2) {          username = argv[2];      }      if (argc > 3) {          password = argv[3];      }      if (argc > 4) {          commandline = argv[4];      }         rc = libssh2_init (0);        if (rc != 0) {          fprintf (stderr, "libssh2 initialization failed (%d)\n", rc);          return 1;      }         hostaddr = inet_addr(hostname);         /* Ultra basic "connect to port 22 on localhost"      * Your code is responsible for creating the socket establishing the      * connection      */       sock = socket(AF_INET, SOCK_STREAM, 0);         sin.sin_family = AF_INET;      sin.sin_port = htons(22);      sin.sin_addr.s_addr = hostaddr;      if (connect(sock, (struct sockaddr*)(&sin),                  sizeof(struct sockaddr_in)) != 0) {          fprintf(stderr, "failed to connect!\n");          return -1;      }         /* Create a session instance */       session = libssh2_session_init();        if (!session)          return -1;         /* tell libssh2 we want it all done non-blocking */       libssh2_session_set_blocking(session, 0);           /* ... start it up. This will trade welcome banners, exchange keys,      * and setup crypto, compression, and MAC layers      */       while ((rc = libssh2_session_handshake(session, sock)) ==               LIBSSH2_ERROR_EAGAIN);      if (rc) {          fprintf(stderr, "Failure establishing SSH session: %d\n", rc);          return -1;      }         nh = libssh2_knownhost_init(session);        if(!nh) {          /* eeek, do cleanup here */           return 2;      }         /* read all hosts from here */       libssh2_knownhost_readfile(nh, "known_hosts",                                   LIBSSH2_KNOWNHOST_FILE_OPENSSH);         /* store all known hosts to here */       libssh2_knownhost_writefile(nh, "dumpfile",                                    LIBSSH2_KNOWNHOST_FILE_OPENSSH);         fingerprint = libssh2_session_hostkey(session, &len, &type);        if(fingerprint) {          struct libssh2_knownhost *host;  #if LIBSSH2_VERSION_NUM >= 0x010206          /* introduced in 1.2.6 */           int check = libssh2_knownhost_checkp(nh, hostname, 22,                                                 fingerprint, len,                                               LIBSSH2_KNOWNHOST_TYPE_PLAIN|                                               LIBSSH2_KNOWNHOST_KEYENC_RAW,                                               &host);  #else          /* 1.2.5 or older */           int check = libssh2_knownhost_check(nh, hostname,                                                fingerprint, len,                                              LIBSSH2_KNOWNHOST_TYPE_PLAIN|                                              LIBSSH2_KNOWNHOST_KEYENC_RAW,                                              &host);  #endif          fprintf(stderr, "Host check: %d, key: %s\n", check,                  (check <= LIBSSH2_KNOWNHOST_CHECK_MISMATCH)?                  host->key:"<none>");             /*****          * At this point, we could verify that 'check' tells us the key is          * fine or bail out.          *****/       }      else {          /* eeek, do cleanup here */           return 3;      }      libssh2_knownhost_free(nh);           if ( strlen(password) != 0 ) {          /* We could authenticate via password */           while ((rc = libssh2_userauth_password(session, username, password)) ==                   LIBSSH2_ERROR_EAGAIN);          if (rc) {              fprintf(stderr, "Authentication by password failed.\n");              goto shutdown;          }      }      else {          /* Or by public key */           while ((rc = libssh2_userauth_publickey_fromfile(session, username,                                                             "/home/user/"                                                           ".ssh/id_rsa.pub",                                                           "/home/user/"                                                           ".ssh/id_rsa",                                                           password)) ==                 LIBSSH2_ERROR_EAGAIN);          if (rc) {              fprintf(stderr, "\tAuthentication by public key failed\n");              goto shutdown;          }      }     #if 0      libssh2_trace(session, ~0 );    #endif         /* Exec non-blocking on the remove host */       while( (channel = libssh2_channel_open_session(session)) == NULL &&               libssh2_session_last_error(session,NULL,NULL,0) ==               LIBSSH2_ERROR_EAGAIN )      {          waitsocket(sock, session);      }      if( channel == NULL )      {          fprintf(stderr,"Error\n");          exit( 1 );      }      while( (rc = libssh2_channel_exec(channel, commandline)) ==               LIBSSH2_ERROR_EAGAIN )      {          waitsocket(sock, session);      }      if( rc != 0 )      {          fprintf(stderr,"Error\n");          exit( 1 );      }      for( ;; )      {          /* loop until we block */           int rc;          do          {              char buffer[0x4000];              rc = libssh2_channel_read( channel, buffer, sizeof(buffer) );                if( rc > 0 )              {                  int i;                  bytecount += rc;                  fprintf(stderr, "We read:\n");                  for( i=0; i < rc; ++i )                      fputc( buffer[i], stderr);                  fprintf(stderr, "\n");              }              else {                  if( rc != LIBSSH2_ERROR_EAGAIN )                      /* no need to output this for the EAGAIN case */                       fprintf(stderr, "libssh2_channel_read returned %d\n", rc);              }          }          while( rc > 0 );             /* this is due to blocking that would occur otherwise so we loop on            this condition */           if( rc == LIBSSH2_ERROR_EAGAIN )          {              waitsocket(sock, session);          }          else              break;      }      exitcode = 127;      while( (rc = libssh2_channel_close(channel)) == LIBSSH2_ERROR_EAGAIN )            waitsocket(sock, session);         if( rc == 0 )      {          exitcode = libssh2_channel_get_exit_status( channel );            libssh2_channel_get_exit_signal(channel, &exitsignal,                                            NULL, NULL, NULL, NULL, NULL);      }         if (exitsignal)          fprintf(stderr, "\nGot signal: %s\n", exitsignal);      else          fprintf(stderr, "\nEXIT: %d bytecount: %d\n", exitcode, bytecount);         libssh2_channel_free(channel);        channel = NULL;     shutdown:         libssh2_session_disconnect(session,                                   "Normal Shutdown, Thank you for playing");      libssh2_session_free(session);       #ifdef WIN32      closesocket(sock);  #else      close(sock);  #endif      fprintf(stderr, "all done\n");         libssh2_exit();           return 0;  }

做windows连接linux服务器发送shell命令的主要方法有几个简单介绍下：

1.WSAStartup()，打开socket链接库

2.socket()，初始化一个socket套接字

3.connect()，连接到ssh服务器

4.libssh2_session_init()，初始化一个ssh连接

5.libssh2_session_handshake()，将socket和session握手通信

6.libssh2_userauth_password()，验证登陆

7.libssh2_channel_open_session()，打开通道

8.libssh2_channel_exec()，发送shell命令

9.libssh2_channel_read()，读取命令处理结果

这里的8.libssh2_channel_exec()，发送shell命令和心目中想象的不太一样，不能循环发送命令，发送第一次命令时，该命令执行，但是第二次再发送时会返回一个

名字叫LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED的ERROR，也就是说这个函数只能发送一次shell命令就不能再用了，太麻烦了。

在这里这种需求怎么解决：

当调用完libssh2_channel_exec()时，将通道释放掉libssh2_channel_close()，然后再重新打开libssh2_channel_open()，再使用这个libssh2_channel_exec()发送shell命令。

但是在这里可能会出现一个问题，在libssh2_channel_open()的时候并没有把通道打开，调用libssh2_session_last_error()发现这个错误代码是LIBSSH2_ERROR_EAGAIN，在官方网站的解释是这不是一个错误，是一个阻塞的过程，也就是现在这个链接已经阻塞了，需要等等再打开。这也就是最上面那个waitsocket()的作用了。