Howto implement SFTP with Qt/QNetworkAccessManager (C++)

Question

I\'m new to Qt and I would like to implement FTP and SFTP support for my software. As I googled I discovered that there doesn\'t exist a sftp library for Qt but it should be pos

Answer 1

I do this using libssh. Very straight forward. https://api.libssh.org/stable/libssh_tutor_sftp.html

Don't forget to add your sftp server into known hosts in your system.

ssh-keyscan -H mysftpserver.com >> ~/.ssh/known_hosts

Example code:

#include "sftpuploader.h"
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

int verify_knownhost(ssh_session session)
{
    int state, hlen;
    unsigned char *hash = NULL;
    char *hexa;
    char buf[10];

    state = ssh_is_server_known(session);

    hlen = ssh_get_pubkey_hash(session, &hash);
    if (hlen < 0)
        return -1;

    switch (state)
    {
    case SSH_SERVER_KNOWN_OK:
        break; /* ok */

    case SSH_SERVER_KNOWN_CHANGED:
        fprintf(stderr, "Host key for server changed: it is now:\n");
        ssh_print_hexa("Public key hash", hash, hlen);
        fprintf(stderr, "For security reasons, connection will be stopped\n");
        free(hash);
        return -1;

    case SSH_SERVER_FOUND_OTHER:
        fprintf(stderr, "The host key for this server was not found but an other"
                        "type of key exists.\n");
        fprintf(stderr, "An attacker might change the default server key to"
                        "confuse your client into thinking the key does not exist\n");
        free(hash);
        return -1;

    case SSH_SERVER_FILE_NOT_FOUND:
        fprintf(stderr, "Could not find known host file.\n");
        fprintf(stderr, "If you accept the host key here, the file will be"
                        "automatically created.\n");
        /* fallback to SSH_SERVER_NOT_KNOWN behavior */

    case SSH_SERVER_NOT_KNOWN:
        hexa = ssh_get_hexa(hash, hlen);
        fprintf(stderr,"The server is unknown. Do you trust the host key?\n");
        fprintf(stderr, "Public key hash: %s\n", hexa);
        free(hexa);
        if (fgets(buf, sizeof(buf), stdin) == NULL)
        {
            free(hash);
            return -1;
        }
        if (strncasecmp(buf, "yes", 3) != 0)
        {
            free(hash);
            return -1;
        }
        if (ssh_write_knownhost(session) < 0)
        {
            fprintf(stderr, "Error %s\n", strerror(errno));
            free(hash);
            return -1;
        }
        break;

    case SSH_SERVER_ERROR:
        fprintf(stderr, "Error %s", ssh_get_error(session));
        free(hash);
        return -1;
    }

    free(hash);
    return 0;
}

bool upload(const QString &localFile,
                          const QString &dest,
                          const QString &host,
                          const QString &username,
                          const QString &passwd)
{
    bool retVal = false;

    QFileInfo info(localFile);

    m_localFilename = info.canonicalFilePath();
    m_remoteFilename = dest + "/" + info.fileName();

    int verbosity = SSH_LOG_PROTOCOL;
    int port = 22;
    int rc;
    sftp_session sftp;
    sftp_file file;
    int access_type;
    int nwritten;
    QByteArray dataToWrite;
    ssh_session my_ssh_session;

    QFile myfile(m_localFilename);

    if(!myfile.exists())
    {
        qDebug() << "SFTPUploader: File doesn't exist " << m_localFilename;
        return retVal;
    }

    my_ssh_session = ssh_new();
    if(my_ssh_session == NULL)
    {
        return retVal;
    }

    ssh_options_set(my_ssh_session, SSH_OPTIONS_HOST, host.toUtf8());
    ssh_options_set(my_ssh_session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
    ssh_options_set(my_ssh_session, SSH_OPTIONS_PORT, &port);

    rc = ssh_connect(my_ssh_session);
    if (rc != SSH_OK)
    {
        qDebug() << "SFTPUploader: Error connecting to localhost: " << ssh_get_error(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }
    else
    {
        qDebug() << "SFTPUploader: SSH connected";
    }

    // Verify the server's identity
    // For the source code of verify_knowhost(), check previous example
    if (verify_knownhost(my_ssh_session) < 0)
    {
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        qDebug() << "SFTPUploader: verify_knownhost failed";
        return retVal;
    }

    rc = ssh_userauth_password(my_ssh_session, username.toUtf8(), passwd.toUtf8());
    if (rc != SSH_AUTH_SUCCESS)
    {
        qDebug() << "SFTPUploader: Error authenticating with password: " << ssh_get_error(my_ssh_session);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }
    else
    {
        qDebug() << "SFTPUploader: Authentication sucess";
    }

    sftp = sftp_new(my_ssh_session);
    if (sftp == NULL)
    {
        qDebug() << "SFTPUploader: Error allocating SFTP session:" << ssh_get_error(my_ssh_session);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }

    rc = sftp_init(sftp);
    if (rc != SSH_OK)
    {
        qDebug() << "SFTPUploader: Error initializing SFTP session:", sftp_get_error(sftp);
        sftp_free(sftp);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }

    access_type = O_WRONLY | O_CREAT | O_TRUNC;
    file = sftp_open(sftp, dest.toUtf8(), access_type, S_IRWXU);
    if (file == NULL)
    {
        qDebug() << "SFTPUploader: Can't open file for writing:", ssh_get_error(my_ssh_session);
        sftp_free(sftp);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }

    if(myfile.open(QFile::ReadOnly))
    {
        dataToWrite = myfile.readAll();
    }

    nwritten = sftp_write(file, dataToWrite, dataToWrite.size());
    if (nwritten != dataToWrite.size())
    {
        qDebug() << "SFTPUploader: Can't write data to file: ", ssh_get_error(my_ssh_session);
        sftp_close(file);
        sftp_free(sftp);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }

    rc = sftp_close(file);
    if (rc != SSH_OK)
    {
        qDebug() << "SFTPUploader: Can't close the written file:" << ssh_get_error(my_ssh_session);
        sftp_free(sftp);
        ssh_disconnect(my_ssh_session);
        ssh_free(my_ssh_session);
        return retVal;
    }
    else
    {
        qDebug() << "SFTPUploader: Success";
        retVal = true;
    }
    return retVal;
}