libssh2的简单应用

首先，libssh2.lib的这个库一定要有（下载地址提供：http://download.csdn.net/detail/wyc6668205/5651661）

其次，介绍一下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。