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。