libssh2的簡單應用

盛夏發表於2013-06-26

首先，libssh2.lib的這個庫一定要有（下載地址提供：http://download.csdn.net/detail/wyc6668205/5651661）

其次，介紹一下libssh2的官網：www.libssh2.org；雖然這個網站裡面內容是全英文的，我想所有的計算機從事者都能看懂這裡面寫的內容，這裡面提供了很多例子，比如FTP的，shell命令的等等，我在這裡介紹一下shell命令的傳送和接收返回資料。

example裡有個檔名叫exec.c 這個檔案是實現shell命令的一個例子

/*
 * 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連線linux伺服器傳送shell命令的主要方法有幾個簡單介紹下：

1.WSAStartup()，開啟socket連結庫

2.socket()，初始化一個socket套接字

3.connect()，連線到ssh伺服器

4.libssh2_session_init()，初始化一個ssh連線

5.libssh2_session_handshake()，將socket和session握手通訊

6.libssh2_userauth_password()，驗證登陸

7.libssh2_channel_open_session()，開啟通道

8.libssh2_channel_exec()，傳送shell命令

9.libssh2_channel_read()，讀取命令處理結果


這裡的8.libssh2_channel_exec()，傳送shell命令和心目中想象的不太一樣，不能迴圈傳送命令，傳送第一次命令時，該命令執行，但是第二次再傳送時會返回一個

名字叫LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED的ERROR，也就是說這個函式只能傳送一次shell命令就不能再用了，太麻煩了。


在這裡這種需求怎麼解決：

當呼叫完libssh2_channel_exec()時，將通道釋放掉libssh2_channel_close()，然後再重新開啟libssh2_channel_open()，再使用這個libssh2_channel_exec()傳送shell命令。

但是在這裡可能會出現一個問題，在libssh2_channel_open()的時候並沒有把通道開啟，呼叫libssh2_session_last_error()發現這個錯誤程式碼是LIBSSH2_ERROR_EAGAIN，在官方網站的解釋是這不是一個錯誤，是一個阻塞的過程，也就是現在這個連結已經阻塞了，需要等等再開啟。這也就是最上面那個waitsocket()的作用了。







相關文章