CODEWITHSUNDEEP
csftplibssh
phoebus
phoebus

Reputation: 1329

C - libssh and sftp - client/server - creating sftp session hangs

I implemented a client/server communication over SSH with libssh. I also want to implement file upload from client to the server now and have been following the doc for it.

However, it hangs on the call sftp = sftp_new(session);. Do I have to explicitly open another ssh_channel for it on the server side as well? I only added the sftp code on the client so far.

Upvotes: 1

Views: 1832

Answers (1)

phoebus
phoebus

Reputation: 1329

For all who are struggling as well, I finally found the solution.

I found on the thread of this question that libssh/sftp.h does have separate functions for the server at the very end. To enable them, you have to use #define WITH_SERVER.

Despite the comment on the doc that you don't have to handle channels yourself, you do have to open a new channel on the server side for the SFTP communication. Implementing this worked for me:

while ((msg = ssh_message_get(session)))
{

    if (ssh_message_type(msg) == SSH_REQUEST_CHANNEL_OPEN && ssh_message_subtype(msg) == SSH_CHANNEL_SESSION)
    {
        printf("[+] Got channel open request, opening new channel for sftp\n");
        sftpChannel = ssh_message_channel_request_open_reply_accept(msg);
        ssh_message_free(msg);
    }

    if (ssh_message_type(msg) == SSH_REQUEST_CHANNEL && ssh_message_subtype(msg) == SSH_CHANNEL_REQUEST_SUBSYSTEM)
    {
        if (!strcmp(ssh_message_channel_request_subsystem(msg), "sftp"))
        {
            ssh_message_channel_request_reply_success(msg);
            ssh_message_free(msg);

            // setup SFTP session
            sftp_session sftp = sftp_server_new(session, sftpChannel);
            if (sftp == NULL)
            {
                fprintf(stderr, "Error allocating SFTP session: %s\n", ssh_get_error(session));
            }                           
            int rc = sftp_server_init(sftp);
            if (rc != SSH_OK)
            {
               fprintf(stderr, "Error initializing SFTP session: %i.\n", sftp_get_error(sftp));
               sftp_free(sftp);
            }

            // handle communication...
         }
    }
}

Upvotes: 2

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