sftp.c

/* Copyright (c) 2004-2008, Sara Golemon <sarag@libssh2.org>
 * Copyright (c) 2007 Eli Fant <elifantu@mail.ru>
 * Copyright (c) 2009-2014 by Daniel Stenberg
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms,
 * with or without modification, are permitted provided
 * that the following conditions are met:
 *
 *   Redistributions of source code must retain the above
 *   copyright notice, this list of conditions and the
 *   following disclaimer.
 *
 *   Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 *   Neither the name of the copyright holder nor the names
 *   of any other contributors may be used to endorse or
 *   promote products derived from this software without
 *   specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 */

#include <assert.h>

#include "libssh2_priv.h"
#include "libssh2_sftp.h"
#include "channel.h"
#include "session.h"
#include "sftp.h"

/* Note: Version 6 was documented at the time of writing
 * However it was marked as "DO NOT IMPLEMENT" due to pending changes
 *
 * This release of libssh2 implements Version 5 with automatic downgrade
 * based on server's declaration
 */

/* SFTP packet types */
#define SSH_FXP_INIT                            1
#define SSH_FXP_VERSION                         2
#define SSH_FXP_OPEN                            3
#define SSH_FXP_CLOSE                           4
#define SSH_FXP_READ                            5
#define SSH_FXP_WRITE                           6
#define SSH_FXP_LSTAT                           7
#define SSH_FXP_FSTAT                           8
#define SSH_FXP_SETSTAT                         9
#define SSH_FXP_FSETSTAT                        10
#define SSH_FXP_OPENDIR                         11
#define SSH_FXP_READDIR                         12
#define SSH_FXP_REMOVE                          13
#define SSH_FXP_MKDIR                           14
#define SSH_FXP_RMDIR                           15
#define SSH_FXP_REALPATH                        16
#define SSH_FXP_STAT                            17
#define SSH_FXP_RENAME                          18
#define SSH_FXP_READLINK                        19
#define SSH_FXP_SYMLINK                         20
#define SSH_FXP_STATUS                          101
#define SSH_FXP_HANDLE                          102
#define SSH_FXP_DATA                            103
#define SSH_FXP_NAME                            104
#define SSH_FXP_ATTRS                           105
#define SSH_FXP_EXTENDED                        200
#define SSH_FXP_EXTENDED_REPLY                  201

/* S_IFREG */
#define LIBSSH2_SFTP_ATTR_PFILETYPE_FILE        0100000
/* S_IFDIR */
#define LIBSSH2_SFTP_ATTR_PFILETYPE_DIR         0040000

#define SSH_FXE_STATVFS_ST_RDONLY               0x00000001
#define SSH_FXE_STATVFS_ST_NOSUID               0x00000002

/* This is the maximum packet length to accept, as larger than this indicate
   some kind of server problem. */
#define LIBSSH2_SFTP_PACKET_MAXLEN  80000

static int sftp_packet_ask(LIBSSH2_SFTP *sftp, unsigned char packet_type,
                           uint32_t request_id, unsigned char **data,
                           size_t *data_len);
static void sftp_packet_flush(LIBSSH2_SFTP *sftp);

/* sftp_attrsize
 * Size that attr with this flagset will occupy when turned into a bin struct
 */
static int sftp_attrsize(unsigned long flags)
{
    return (4 +                                 /* flags(4) */
            ((flags & LIBSSH2_SFTP_ATTR_SIZE) ? 8 : 0) +
            ((flags & LIBSSH2_SFTP_ATTR_UIDGID) ? 8 : 0) +
            ((flags & LIBSSH2_SFTP_ATTR_PERMISSIONS) ? 4 : 0) +
            ((flags & LIBSSH2_SFTP_ATTR_ACMODTIME) ? 8 : 0));
    /* atime + mtime as u32 */
}

/* _libssh2_store_u64
 */
static void _libssh2_store_u64(unsigned char **ptr, libssh2_uint64_t value)
{
    uint32_t msl = (uint32_t)(value >> 32);
    unsigned char *buf = *ptr;

    buf[0] = (unsigned char)((msl >> 24) & 0xFF);
    buf[1] = (unsigned char)((msl >> 16) & 0xFF);
    buf[2] = (unsigned char)((msl >> 8)  & 0xFF);
    buf[3] = (unsigned char)( msl        & 0xFF);

    buf[4] = (unsigned char)((value >> 24) & 0xFF);
    buf[5] = (unsigned char)((value >> 16) & 0xFF);
    buf[6] = (unsigned char)((value >> 8)  & 0xFF);
    buf[7] = (unsigned char)( value        & 0xFF);

    *ptr += 8;
}

/*
 * Search list of zombied FXP_READ request IDs.
 *
 * Returns NULL if ID not in list.
 */
static struct sftp_zombie_requests *
find_zombie_request(LIBSSH2_SFTP *sftp, uint32_t request_id)
{
    struct sftp_zombie_requests *zombie =
        _libssh2_list_first(&sftp->zombie_requests);

    while(zombie) {
        if(zombie->request_id == request_id)
            break;
        else
            zombie = _libssh2_list_next(&zombie->node);
    }

    return zombie;
}

static void
remove_zombie_request(LIBSSH2_SFTP *sftp, uint32_t request_id)
{
    LIBSSH2_SESSION *session = sftp->channel->session;

    struct sftp_zombie_requests *zombie = find_zombie_request(sftp,
                                                              request_id);
    if(zombie) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Removing request ID %ld from the list of zombie requests",
                       request_id);

        _libssh2_list_remove(&zombie->node);
        LIBSSH2_FREE(session, zombie);
    }
}

static int
add_zombie_request(LIBSSH2_SFTP *sftp, uint32_t request_id)
{
    LIBSSH2_SESSION *session = sftp->channel->session;

    struct sftp_zombie_requests *zombie;

    _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                   "Marking request ID %ld as a zombie request", request_id);

    zombie = LIBSSH2_ALLOC(sftp->channel->session,
                           sizeof(struct sftp_zombie_requests));
    if (!zombie)
        return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                              "malloc fail for zombie request  ID");
    else {
        zombie->request_id = request_id;
        _libssh2_list_add(&sftp->zombie_requests, &zombie->node);
        return LIBSSH2_ERROR_NONE;
    }
}

/*
 * sftp_packet_add
 *
 * Add a packet to the SFTP packet brigade
 */
static int
sftp_packet_add(LIBSSH2_SFTP *sftp, unsigned char *data,
                size_t data_len)
{
    LIBSSH2_SESSION *session = sftp->channel->session;
    LIBSSH2_SFTP_PACKET *packet;
    uint32_t request_id;

    _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                   "Received packet type %d (len %d)",
                   (int) data[0], data_len);

    /*
     * Experience shows that if we mess up EAGAIN handling somewhere or
     * otherwise get out of sync with the channel, this is where we first get
     * a wrong byte and if so we need to bail out at once to aid tracking the
     * problem better.
     */

    switch(data[0]) {
    case SSH_FXP_INIT:
    case SSH_FXP_VERSION:
    case SSH_FXP_OPEN:
    case SSH_FXP_CLOSE:
    case SSH_FXP_READ:
    case SSH_FXP_WRITE:
    case SSH_FXP_LSTAT:
    case SSH_FXP_FSTAT:
    case SSH_FXP_SETSTAT:
    case SSH_FXP_FSETSTAT:
    case SSH_FXP_OPENDIR:
    case SSH_FXP_READDIR:
    case SSH_FXP_REMOVE:
    case SSH_FXP_MKDIR:
    case SSH_FXP_RMDIR:
    case SSH_FXP_REALPATH:
    case SSH_FXP_STAT:
    case SSH_FXP_RENAME:
    case SSH_FXP_READLINK:
    case SSH_FXP_SYMLINK:
    case SSH_FXP_STATUS:
    case SSH_FXP_HANDLE:
    case SSH_FXP_DATA:
    case SSH_FXP_NAME:
    case SSH_FXP_ATTRS:
    case SSH_FXP_EXTENDED:
    case SSH_FXP_EXTENDED_REPLY:
        break;
    default:
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "Out of sync with the world");
    }

    request_id = _libssh2_ntohu32(&data[1]);

    _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Received packet id %d",
                   request_id);

    /* Don't add the packet if it answers a request we've given up on. */
    if((data[0] == SSH_FXP_STATUS || data[0] == SSH_FXP_DATA)
       && find_zombie_request(sftp, request_id)) {

        /* If we get here, the file ended before the response arrived. We
           are no longer interested in the request so we discard it */

        LIBSSH2_FREE(session, data);

        remove_zombie_request(sftp, request_id);
        return LIBSSH2_ERROR_NONE;
    }

    packet = LIBSSH2_ALLOC(session, sizeof(LIBSSH2_SFTP_PACKET));
    if (!packet) {
        return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                              "Unable to allocate datablock for SFTP packet");
    }

    packet->data = data;
    packet->data_len = data_len;
    packet->request_id = request_id;

    _libssh2_list_add(&sftp->packets, &packet->node);

    return LIBSSH2_ERROR_NONE;
}

/*
 * sftp_packet_read
 *
 * Frame an SFTP packet off the channel
 */
static int
sftp_packet_read(LIBSSH2_SFTP *sftp)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *packet = NULL;
    ssize_t rc;
    unsigned long recv_window;
    int packet_type;

    _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "recv packet");

    switch(sftp->packet_state) {
    case libssh2_NB_state_sent: /* EAGAIN from window adjusting */
        sftp->packet_state = libssh2_NB_state_idle;

        packet = sftp->partial_packet;
        goto window_adjust;

    case libssh2_NB_state_sent1: /* EAGAIN from channel read */
        sftp->packet_state = libssh2_NB_state_idle;

        packet = sftp->partial_packet;

        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "partial read cont, len: %lu", sftp->partial_len);
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "partial read cont, already recvd: %lu",
                       sftp->partial_received);
        /* fall-through */
    default:
        if(!packet) {
            /* only do this if there's not already a packet buffer allocated
               to use */

            /* each packet starts with a 32 bit length field */
            rc = _libssh2_channel_read(channel, 0,
                                       (char *)&sftp->partial_size[
                                           sftp->partial_size_len],
                                       4 - sftp->partial_size_len);
            if (rc == LIBSSH2_ERROR_EAGAIN)
                return rc;
            else if (rc < 0)
                return _libssh2_error(session, rc, "channel read");

            sftp->partial_size_len += rc;

            if(4 != sftp->partial_size_len)
                /* we got a short read for the length part */
                return LIBSSH2_ERROR_EAGAIN;

            sftp->partial_len = _libssh2_ntohu32(sftp->partial_size);
            /* make sure we don't proceed if the packet size is unreasonably
               large */
            if (sftp->partial_len > LIBSSH2_SFTP_PACKET_MAXLEN)
                return _libssh2_error(session,
                                      LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED,
                                      "SFTP packet too large");

            _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                           "Data begin - Packet Length: %lu",
                           sftp->partial_len);
            packet = LIBSSH2_ALLOC(session, sftp->partial_len);
            if (!packet)
                return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                      "Unable to allocate SFTP packet");
            sftp->partial_size_len = 0;
            sftp->partial_received = 0; /* how much of the packet already
                                           received */
            sftp->partial_packet = packet;

          window_adjust:
            recv_window = libssh2_channel_window_read_ex(channel, NULL, NULL);

            if(sftp->partial_len > recv_window) {
                /* ask for twice the data amount we need at once */
                rc = _libssh2_channel_receive_window_adjust(channel,
                                                            sftp->partial_len*2,
                                                            1, NULL);
                /* store the state so that we continue with the correct
                   operation at next invoke */
                sftp->packet_state = (rc == LIBSSH2_ERROR_EAGAIN)?
                    libssh2_NB_state_sent:
                    libssh2_NB_state_idle;

                if(rc == LIBSSH2_ERROR_EAGAIN)
                    return rc;
            }
        }

        /* Read as much of the packet as we can */
        while (sftp->partial_len > sftp->partial_received) {
            rc = _libssh2_channel_read(channel, 0,
                                       (char *)&packet[sftp->partial_received],
                                       sftp->partial_len -
                                       sftp->partial_received);

            if (rc == LIBSSH2_ERROR_EAGAIN) {
                /*
                 * We received EAGAIN, save what we have and return EAGAIN to
                 * the caller. Set 'partial_packet' so that this function
                 * knows how to continue on the next invoke.
                 */
                sftp->packet_state = libssh2_NB_state_sent1;
                return rc;
            }
            else if (rc < 0) {
                LIBSSH2_FREE(session, packet);
                sftp->partial_packet = NULL;
                return _libssh2_error(session, rc,
                                      "Error waiting for SFTP packet");
            }
            sftp->partial_received += rc;
        }

        sftp->partial_packet = NULL;

        /* sftp_packet_add takes ownership of the packet and might free it
           so we take a copy of the packet type before we call it. */
        packet_type = packet[0];
        rc = sftp_packet_add(sftp, packet, sftp->partial_len);
        if (rc) {
            LIBSSH2_FREE(session, packet);
            return rc;
        }
        else {
            return packet_type;
        }
    }
    /* WON'T REACH */
}
/*
 * sftp_packetlist_flush
 *
 * Remove all pending packets in the packet_list and the corresponding one(s)
 * in the SFTP packet brigade.
 */
static void sftp_packetlist_flush(LIBSSH2_SFTP_HANDLE *handle)
{
    struct sftp_pipeline_chunk *chunk;
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_SESSION *session = sftp->channel->session;

    /* remove pending packets, if any */
    chunk = _libssh2_list_first(&handle->packet_list);
    while(chunk) {
        unsigned char *data;
        size_t data_len;
        int rc;
        struct sftp_pipeline_chunk *next = _libssh2_list_next(&chunk->node);

        rc = sftp_packet_ask(sftp, SSH_FXP_STATUS,
                             chunk->request_id, &data, &data_len);
        if(rc)
            rc = sftp_packet_ask(sftp, SSH_FXP_DATA,
                                 chunk->request_id, &data, &data_len);

        if(!rc)
            /* we found a packet, free it */
            LIBSSH2_FREE(session, data);
        else if(chunk->sent)
            /* there was no incoming packet for this request, mark this
               request as a zombie if it ever sent the request */
            add_zombie_request(sftp, chunk->request_id);

        _libssh2_list_remove(&chunk->node);
        LIBSSH2_FREE(session, chunk);
        chunk = next;
    }
}


/*
 * sftp_packet_ask()
 *
 * Checks if there's a matching SFTP packet available.
 */
static int
sftp_packet_ask(LIBSSH2_SFTP *sftp, unsigned char packet_type,
                uint32_t request_id, unsigned char **data,
                size_t *data_len)
{
    LIBSSH2_SESSION *session = sftp->channel->session;
    LIBSSH2_SFTP_PACKET *packet = _libssh2_list_first(&sftp->packets);

    if(!packet)
        return -1;

    /* Special consideration when getting VERSION packet */

    while (packet) {
        if((packet->data[0] == packet_type) &&
           ((packet_type == SSH_FXP_VERSION) ||
            (packet->request_id == request_id))) {

            /* Match! Fetch the data */
            *data = packet->data;
            *data_len = packet->data_len;

            /* unlink and free this struct */
            _libssh2_list_remove(&packet->node);
            LIBSSH2_FREE(session, packet);

            return 0;
        }
        /* check next struct in the list */
        packet = _libssh2_list_next(&packet->node);
    }
    return -1;
}

/* sftp_packet_require
 * A la libssh2_packet_require
 */
static int
sftp_packet_require(LIBSSH2_SFTP *sftp, unsigned char packet_type,
                    uint32_t request_id, unsigned char **data,
                    size_t *data_len)
{
    LIBSSH2_SESSION *session = sftp->channel->session;
    int rc;

    _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Requiring packet %d id %ld",
                   (int) packet_type, request_id);

    if (sftp_packet_ask(sftp, packet_type, request_id, data, data_len) == 0) {
        /* The right packet was available in the packet brigade */
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Got %d",
                       (int) packet_type);
        return LIBSSH2_ERROR_NONE;
    }

    while (session->socket_state == LIBSSH2_SOCKET_CONNECTED) {
        rc = sftp_packet_read(sftp);
        if (rc < 0)
            return rc;

        /* data was read, check the queue again */
        if (!sftp_packet_ask(sftp, packet_type, request_id, data, data_len)) {
            /* The right packet was available in the packet brigade */
            _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Got %d",
                           (int) packet_type);
            return LIBSSH2_ERROR_NONE;
        }
    }

    /* Only reached if the socket died */
    return LIBSSH2_ERROR_SOCKET_DISCONNECT;
}

/* sftp_packet_requirev
 * Require one of N possible responses
 */
static int
sftp_packet_requirev(LIBSSH2_SFTP *sftp, int num_valid_responses,
                     const unsigned char *valid_responses,
                     uint32_t request_id, unsigned char **data,
                     size_t *data_len)
{
    int i;
    int rc;

    /* If no timeout is active, start a new one */
    if (sftp->requirev_start == 0)
        sftp->requirev_start = time(NULL);

    while (sftp->channel->session->socket_state == LIBSSH2_SOCKET_CONNECTED) {
        for(i = 0; i < num_valid_responses; i++) {
            if (sftp_packet_ask(sftp, valid_responses[i], request_id,
                                data, data_len) == 0) {
                /*
                 * Set to zero before all returns to say
                 * the timeout is not active
                 */
                sftp->requirev_start = 0;
                return LIBSSH2_ERROR_NONE;
            }
        }

        rc = sftp_packet_read(sftp);
        if ((rc < 0) && (rc != LIBSSH2_ERROR_EAGAIN)) {
            sftp->requirev_start = 0;
            return rc;
        } else if (rc <= 0) {
            /* prevent busy-looping */
            long left =
                LIBSSH2_READ_TIMEOUT - (long)(time(NULL) - sftp->requirev_start);

            if (left <= 0) {
                sftp->requirev_start = 0;
                return LIBSSH2_ERROR_TIMEOUT;
            }
            else if (rc == LIBSSH2_ERROR_EAGAIN) {
                return rc;
            }
        }
    }

    sftp->requirev_start = 0;

    /* Only reached if the socket died */
    return LIBSSH2_ERROR_SOCKET_DISCONNECT;
}

/* sftp_attr2bin
 * Populate attributes into an SFTP block
 */
static ssize_t
sftp_attr2bin(unsigned char *p, const LIBSSH2_SFTP_ATTRIBUTES * attrs)
{
    unsigned char *s = p;
    uint32_t flag_mask =
        LIBSSH2_SFTP_ATTR_SIZE | LIBSSH2_SFTP_ATTR_UIDGID |
        LIBSSH2_SFTP_ATTR_PERMISSIONS | LIBSSH2_SFTP_ATTR_ACMODTIME;

    /* TODO: When we add SFTP4+ functionality flag_mask can get additional
       bits */

    if (!attrs) {
        _libssh2_htonu32(s, 0);
        return 4;
    }

    _libssh2_store_u32(&s, attrs->flags & flag_mask);

    if (attrs->flags & LIBSSH2_SFTP_ATTR_SIZE) {
        _libssh2_store_u64(&s, attrs->filesize);
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_UIDGID) {
        _libssh2_store_u32(&s, attrs->uid);
        _libssh2_store_u32(&s, attrs->gid);
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_PERMISSIONS) {
        _libssh2_store_u32(&s, attrs->permissions);
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_ACMODTIME) {
        _libssh2_store_u32(&s, attrs->atime);
        _libssh2_store_u32(&s, attrs->mtime);
    }

    return (s - p);
}

/* sftp_bin2attr
 */
static int
sftp_bin2attr(LIBSSH2_SFTP_ATTRIBUTES * attrs, const unsigned char *p)
{
    const unsigned char *s = p;

    memset(attrs, 0, sizeof(LIBSSH2_SFTP_ATTRIBUTES));
    attrs->flags = _libssh2_ntohu32(s);
    s += 4;

    if (attrs->flags & LIBSSH2_SFTP_ATTR_SIZE) {
        attrs->filesize = _libssh2_ntohu64(s);
        s += 8;
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_UIDGID) {
        attrs->uid = _libssh2_ntohu32(s);
        s += 4;
        attrs->gid = _libssh2_ntohu32(s);
        s += 4;
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_PERMISSIONS) {
        attrs->permissions = _libssh2_ntohu32(s);
        s += 4;
    }

    if (attrs->flags & LIBSSH2_SFTP_ATTR_ACMODTIME) {
        attrs->atime = _libssh2_ntohu32(s);
        s += 4;
        attrs->mtime = _libssh2_ntohu32(s);
        s += 4;
    }

    return (s - p);
}

/* ************
 * SFTP API *
 ************ */

LIBSSH2_CHANNEL_CLOSE_FUNC(libssh2_sftp_dtor);

/* libssh2_sftp_dtor
 * Shutdown an SFTP stream when the channel closes
 */
LIBSSH2_CHANNEL_CLOSE_FUNC(libssh2_sftp_dtor)
{
    LIBSSH2_SFTP *sftp = (LIBSSH2_SFTP *) (*channel_abstract);

    (void) session_abstract;
    (void) channel;

    /* Free the partial packet storage for sftp_packet_read */
    if (sftp->partial_packet) {
        LIBSSH2_FREE(session, sftp->partial_packet);
    }

    /* Free the packet storage for _libssh2_sftp_packet_readdir */
    if (sftp->readdir_packet) {
        LIBSSH2_FREE(session, sftp->readdir_packet);
    }

    LIBSSH2_FREE(session, sftp);
}

/*
 * sftp_init
 *
 * Startup an SFTP session
 */
static LIBSSH2_SFTP *sftp_init(LIBSSH2_SESSION *session)
{
    unsigned char *data, *s;
    size_t data_len;
    ssize_t rc;
    LIBSSH2_SFTP *sftp_handle;

    if (session->sftpInit_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Initializing SFTP subsystem");

        /*
         * The 'sftpInit_sftp' and 'sftpInit_channel' struct fields within the
         * session struct are only to be used during the setup phase. As soon
         * as the SFTP session is created they are cleared and can thus be
         * re-used again to allow any amount of SFTP handles per sessions.
         *
         * Note that you MUST NOT try to call libssh2_sftp_init() again to get
         * another handle until the previous call has finished and either
         * successfully made a handle or failed and returned error (not
         * including *EAGAIN).
         */

        assert(session->sftpInit_sftp == NULL);
        session->sftpInit_sftp = NULL;
        session->sftpInit_state = libssh2_NB_state_created;
    }

    sftp_handle = session->sftpInit_sftp;

    if (session->sftpInit_state == libssh2_NB_state_created) {
        session->sftpInit_channel =
            _libssh2_channel_open(session, "session", sizeof("session") - 1,
                                  LIBSSH2_CHANNEL_WINDOW_DEFAULT,
                                  LIBSSH2_CHANNEL_PACKET_DEFAULT, NULL, 0);
        if (!session->sftpInit_channel) {
            if (libssh2_session_last_errno(session) == LIBSSH2_ERROR_EAGAIN) {
                _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                               "Would block starting up channel");
            }
            else {
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Unable to startup channel");
                session->sftpInit_state = libssh2_NB_state_idle;
            }
            return NULL;
        }

        session->sftpInit_state = libssh2_NB_state_sent;
    }

    if (session->sftpInit_state == libssh2_NB_state_sent) {
        int ret = _libssh2_channel_process_startup(session->sftpInit_channel,
                                                   "subsystem",
                                                   sizeof("subsystem") - 1, "sftp",
                                                   strlen("sftp"));
        if (ret == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block to request SFTP subsystem");
            return NULL;
        } else if (ret) {
            _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                           "Unable to request SFTP subsystem");
            goto sftp_init_error;
        }

        session->sftpInit_state = libssh2_NB_state_sent1;
    }

    if (session->sftpInit_state == libssh2_NB_state_sent1) {
        rc = _libssh2_channel_extended_data(session->sftpInit_channel,
                                            LIBSSH2_CHANNEL_EXTENDED_DATA_IGNORE);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block requesting handle extended data");
            return NULL;
        }

        sftp_handle =
            session->sftpInit_sftp =
            LIBSSH2_CALLOC(session, sizeof(LIBSSH2_SFTP));
        if (!sftp_handle) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate a new SFTP structure");
            goto sftp_init_error;
        }
        sftp_handle->channel = session->sftpInit_channel;
        sftp_handle->request_id = 0;

        _libssh2_htonu32(session->sftpInit_buffer, 5);
        session->sftpInit_buffer[4] = SSH_FXP_INIT;
        _libssh2_htonu32(session->sftpInit_buffer + 5, LIBSSH2_SFTP_VERSION);
        session->sftpInit_sent = 0; /* nothing's sent yet */

        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Sending FXP_INIT packet advertising version %d support",
                       (int) LIBSSH2_SFTP_VERSION);

        session->sftpInit_state = libssh2_NB_state_sent2;
    }

    if (session->sftpInit_state == libssh2_NB_state_sent2) {
        /* sent off what's left of the init buffer to send */
        rc = _libssh2_channel_write(session->sftpInit_channel, 0,
                                    session->sftpInit_buffer +
                                    session->sftpInit_sent,
                                    9 - session->sftpInit_sent);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block sending SSH_FXP_INIT");
            return NULL;
        }
        else if(rc < 0) {
            _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                           "Unable to send SSH_FXP_INIT");
            goto sftp_init_error;
        }
        else {
            /* add up the number of bytes sent */
            session->sftpInit_sent += rc;

            if(session->sftpInit_sent == 9)
                /* move on */
                session->sftpInit_state = libssh2_NB_state_sent3;

            /* if less than 9, we remain in this state to send more later on */
        }
    }

    rc = sftp_packet_require(sftp_handle, SSH_FXP_VERSION,
                             0, &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
         _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                        "Would block receiving SSH_FXP_VERSION");
         return NULL;
    }
    else if (rc) {
        _libssh2_error(session, rc,
                       "Timeout waiting for response from SFTP subsystem");
        goto sftp_init_error;
    }
    if (data_len < 5) {
        _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                       "Invalid SSH_FXP_VERSION response");
        LIBSSH2_FREE(session, data);
        goto sftp_init_error;
    }

    s = data + 1;
    sftp_handle->version = _libssh2_ntohu32(s);
    s += 4;
    if (sftp_handle->version > LIBSSH2_SFTP_VERSION) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Truncating remote SFTP version from %lu",
                       sftp_handle->version);
        sftp_handle->version = LIBSSH2_SFTP_VERSION;
    }
    _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                   "Enabling SFTP version %lu compatibility",
                   sftp_handle->version);
    while (s < (data + data_len)) {
        size_t extname_len, extdata_len;

        extname_len = _libssh2_ntohu32(s);
        s += 4;
        /* the extension name starts here */
        s += extname_len;

        extdata_len = _libssh2_ntohu32(s);
        s += 4;

        /* TODO: Actually process extensions */
        s += extdata_len;

    }
    LIBSSH2_FREE(session, data);

    /* Make sure that when the channel gets closed, the SFTP service is shut
       down too */
    sftp_handle->channel->abstract = sftp_handle;
    sftp_handle->channel->close_cb = libssh2_sftp_dtor;

    session->sftpInit_state = libssh2_NB_state_idle;

    /* clear the sftp and channel pointers in this session struct now */
    session->sftpInit_sftp = NULL;
    session->sftpInit_channel = NULL;

    _libssh2_list_init(&sftp_handle->sftp_handles);

    return sftp_handle;

  sftp_init_error:
    while (_libssh2_channel_free(session->sftpInit_channel) ==
           LIBSSH2_ERROR_EAGAIN);
    session->sftpInit_channel = NULL;
    if (session->sftpInit_sftp) {
        LIBSSH2_FREE(session, session->sftpInit_sftp);
        session->sftpInit_sftp = NULL;
    }
    session->sftpInit_state = libssh2_NB_state_idle;
    return NULL;
}

/*
 * libssh2_sftp_init
 *
 * Startup an SFTP session
 */
LIBSSH2_API LIBSSH2_SFTP *libssh2_sftp_init(LIBSSH2_SESSION *session)
{
    LIBSSH2_SFTP *ptr;

    if(!session)
        return NULL;

    if(!(session->state & LIBSSH2_STATE_AUTHENTICATED)) {
        _libssh2_error(session, LIBSSH2_ERROR_INVAL,
                       "session not authenticated yet");
        return NULL;
    }

    BLOCK_ADJUST_ERRNO(ptr, session, sftp_init(session));
    return ptr;
}

/*
 * sftp_shutdown
 *
 * Shuts down the SFTP subsystem
 */
static int
sftp_shutdown(LIBSSH2_SFTP *sftp)
{
    int rc;
    LIBSSH2_SESSION *session = sftp->channel->session;
    /*
     * Make sure all memory used in the state variables are free
     */
    if (sftp->partial_packet) {
        LIBSSH2_FREE(session, sftp->partial_packet);
        sftp->partial_packet = NULL;
    }
    if (sftp->open_packet) {
        LIBSSH2_FREE(session, sftp->open_packet);
        sftp->open_packet = NULL;
    }
    if (sftp->readdir_packet) {
        LIBSSH2_FREE(session, sftp->readdir_packet);
        sftp->readdir_packet = NULL;
    }
    if (sftp->fstat_packet) {
        LIBSSH2_FREE(session, sftp->fstat_packet);
        sftp->fstat_packet = NULL;
    }
    if (sftp->unlink_packet) {
        LIBSSH2_FREE(session, sftp->unlink_packet);
        sftp->unlink_packet = NULL;
    }
    if (sftp->rename_packet) {
        LIBSSH2_FREE(session, sftp->rename_packet);
        sftp->rename_packet = NULL;
    }
    if (sftp->fstatvfs_packet) {
        LIBSSH2_FREE(session, sftp->fstatvfs_packet);
        sftp->fstatvfs_packet = NULL;
    }
    if (sftp->statvfs_packet) {
        LIBSSH2_FREE(session, sftp->statvfs_packet);
        sftp->statvfs_packet = NULL;
    }
    if (sftp->mkdir_packet) {
        LIBSSH2_FREE(session, sftp->mkdir_packet);
        sftp->mkdir_packet = NULL;
    }
    if (sftp->rmdir_packet) {
        LIBSSH2_FREE(session, sftp->rmdir_packet);
        sftp->rmdir_packet = NULL;
    }
    if (sftp->stat_packet) {
        LIBSSH2_FREE(session, sftp->stat_packet);
        sftp->stat_packet = NULL;
    }
    if (sftp->symlink_packet) {
        LIBSSH2_FREE(session, sftp->symlink_packet);
        sftp->symlink_packet = NULL;
    }
    if (sftp->fsync_packet) {
        LIBSSH2_FREE(session, sftp->fsync_packet);
        sftp->fsync_packet = NULL;
    }

    sftp_packet_flush(sftp);

    /* TODO: We should consider walking over the sftp_handles list and kill
     * any remaining sftp handles ... */

    rc = _libssh2_channel_free(sftp->channel);

    return rc;
}

/* libssh2_sftp_shutdown
 * Shutsdown the SFTP subsystem
 */
LIBSSH2_API int
libssh2_sftp_shutdown(LIBSSH2_SFTP *sftp)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session, sftp_shutdown(sftp));
    return rc;
}

/* *******************************
 * SFTP File and Directory Ops *
 ******************************* */

/* sftp_open
 */
static LIBSSH2_SFTP_HANDLE *
sftp_open(LIBSSH2_SFTP *sftp, const char *filename,
          size_t filename_len, uint32_t flags, long mode,
          int open_type)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    LIBSSH2_SFTP_HANDLE *fp;
    LIBSSH2_SFTP_ATTRIBUTES attrs = {
        LIBSSH2_SFTP_ATTR_PERMISSIONS, 0, 0, 0, 0, 0, 0
    };
    unsigned char *s;
    ssize_t rc;
    int open_file = (open_type == LIBSSH2_SFTP_OPENFILE)?1:0;

    if (sftp->open_state == libssh2_NB_state_idle) {
        /* packet_len(4) + packet_type(1) + request_id(4) + filename_len(4) +
           flags(4) */
        sftp->open_packet_len = filename_len + 13 +
            (open_file? (4 + sftp_attrsize(LIBSSH2_SFTP_ATTR_PERMISSIONS)) : 0);

        /* surprise! this starts out with nothing sent */
        sftp->open_packet_sent = 0;
        s = sftp->open_packet = LIBSSH2_ALLOC(session, sftp->open_packet_len);
        if (!sftp->open_packet) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate memory for FXP_OPEN or "
                           "FXP_OPENDIR packet");
            return NULL;
        }
        /* Filetype in SFTP 3 and earlier */
        attrs.permissions = mode |
            (open_file ? LIBSSH2_SFTP_ATTR_PFILETYPE_FILE :
             LIBSSH2_SFTP_ATTR_PFILETYPE_DIR);

        _libssh2_store_u32(&s, sftp->open_packet_len - 4);
        *(s++) = open_file? SSH_FXP_OPEN : SSH_FXP_OPENDIR;
        sftp->open_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->open_request_id);
        _libssh2_store_str(&s, filename, filename_len);

        if (open_file) {
            _libssh2_store_u32(&s, flags);
            s += sftp_attr2bin(s, &attrs);
        }

        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Sending %s open request",
                       open_file? "file" : "directory");

        sftp->open_state = libssh2_NB_state_created;
    }

    if (sftp->open_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->open_packet+
                                    sftp->open_packet_sent,
                                    sftp->open_packet_len -
                                    sftp->open_packet_sent);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block sending FXP_OPEN or FXP_OPENDIR command");
            return NULL;
        }
        else if(rc < 0) {
            _libssh2_error(session, rc, "Unable to send FXP_OPEN*");
            LIBSSH2_FREE(session, sftp->open_packet);
            sftp->open_packet = NULL;
            sftp->open_state = libssh2_NB_state_idle;
            return NULL;
        }

        /* bump the sent counter and remain in this state until the whole
           data is off */
        sftp->open_packet_sent += rc;

        if(sftp->open_packet_len == sftp->open_packet_sent) {
            LIBSSH2_FREE(session, sftp->open_packet);
            sftp->open_packet = NULL;

            sftp->open_state = libssh2_NB_state_sent;
        }
    }

    if (sftp->open_state == libssh2_NB_state_sent) {
        size_t data_len;
        unsigned char *data;
        static const unsigned char fopen_responses[2] =
            { SSH_FXP_HANDLE, SSH_FXP_STATUS };
        rc = sftp_packet_requirev(sftp, 2, fopen_responses,
                                  sftp->open_request_id, &data,
                                  &data_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block waiting for status message");
            return NULL;
        }
        sftp->open_state = libssh2_NB_state_idle;
        if (rc) {
            _libssh2_error(session, rc, "Timeout waiting for status message");
            return NULL;
        }

        /* OPEN can basically get STATUS or HANDLE back, where HANDLE implies
           a fine response while STATUS means error. It seems though that at
           times we get an SSH_FX_OK back in a STATUS, followed the "real"
           HANDLE so we need to properly deal with that. */
        if (data[0] == SSH_FXP_STATUS) {
            int badness = 1;

            if(data_len < 9) {
                _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                               "Too small FXP_STATUS");
                LIBSSH2_FREE(session, data);
                return NULL;
            }

            sftp->last_errno = _libssh2_ntohu32(data + 5);

            if(LIBSSH2_FX_OK == sftp->last_errno) {
                _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "got HANDLE FXOK!");

                LIBSSH2_FREE(session, data);

                /* silly situation, but check for a HANDLE */
                rc = sftp_packet_require(sftp, SSH_FXP_HANDLE,
                                         sftp->open_request_id, &data,
                                         &data_len);
                if(rc == LIBSSH2_ERROR_EAGAIN) {
                    /* go back to sent state and wait for something else */
                    sftp->open_state = libssh2_NB_state_sent;
                    return NULL;
                }
                else if(!rc)
                    /* we got the handle so this is not a bad situation */
                    badness = 0;
            }

            if(badness) {
                _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                               "Failed opening remote file");
                _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "got FXP_STATUS %d",
                               sftp->last_errno);
                LIBSSH2_FREE(session, data);
                return NULL;
            }
        }

        if(data_len < 10) {
            _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                           "Too small FXP_HANDLE");
            LIBSSH2_FREE(session, data);
            return NULL;
        }

        fp = LIBSSH2_CALLOC(session, sizeof(LIBSSH2_SFTP_HANDLE));
        if (!fp) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate new SFTP handle structure");
            LIBSSH2_FREE(session, data);
            return NULL;
        }
        fp->handle_type = open_file ? LIBSSH2_SFTP_HANDLE_FILE :
            LIBSSH2_SFTP_HANDLE_DIR;

        fp->handle_len = _libssh2_ntohu32(data + 5);
        if (fp->handle_len > SFTP_HANDLE_MAXLEN)
            /* SFTP doesn't allow handles longer than 256 characters */
            fp->handle_len = SFTP_HANDLE_MAXLEN;

        if(fp->handle_len > (data_len - 9))
            /* do not reach beyond the end of the data we got */
            fp->handle_len = data_len - 9;

        memcpy(fp->handle, data + 9, fp->handle_len);

        LIBSSH2_FREE(session, data);

        /* add this file handle to the list kept in the sftp session */
        _libssh2_list_add(&sftp->sftp_handles, &fp->node);

        fp->sftp = sftp; /* point to the parent struct */

        fp->u.file.offset = 0;
        fp->u.file.offset_sent = 0;

        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Open command successful");
        return fp;
    }
    return NULL;
}

/* libssh2_sftp_open_ex
 */
LIBSSH2_API LIBSSH2_SFTP_HANDLE *
libssh2_sftp_open_ex(LIBSSH2_SFTP *sftp, const char *filename,
                     unsigned int filename_len, unsigned long flags, long mode,
                     int open_type)
{
    LIBSSH2_SFTP_HANDLE *hnd;

    if(!sftp)
        return NULL;

    BLOCK_ADJUST_ERRNO(hnd, sftp->channel->session,
                       sftp_open(sftp, filename, filename_len, flags, mode,
                                 open_type));
    return hnd;
}

/*
 * sftp_read
 *
 * Read from an SFTP file handle
 *
 */
static ssize_t sftp_read(LIBSSH2_SFTP_HANDLE * handle, char *buffer,
                         size_t buffer_size)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t count = 0;
    struct sftp_pipeline_chunk *chunk;
    struct sftp_pipeline_chunk *next;
    ssize_t rc;
    struct _libssh2_sftp_handle_file_data *filep =
        &handle->u.file;
    size_t bytes_in_buffer = 0;
    char *sliding_bufferp = buffer;

    /* This function can be interrupted in three different places where it
       might need to wait for data from the network.  It returns EAGAIN to
       allow non-blocking clients to do other work but these client are
       expected to call this function again (possibly many times) to finish
       the operation.

       The tricky part is that if we previously aborted a sftp_read due to
       EAGAIN, we must continue at the same spot to continue the previously
       interrupted operation.  This is done using a state machine to record
       what phase of execution we were at.  The state is stored in
       sftp->read_state.

       libssh2_NB_state_idle: The first phase is where we prepare multiple
       FXP_READ packets to do optimistic read-ahead.  We send off as many as
       possible in the second phase without waiting for a response to each
       one; this is the key to fast reads. But we may have to adjust the
       channel window size to do this which may interrupt this function while
       waiting.  The state machine saves the phase as libssh2_NB_state_idle so
       it returns here on the next call.

       libssh2_NB_state_sent: The second phase is where we send the FXP_READ
       packets.  Writing them to the channel can be interrupted with EAGAIN
       but the state machine ensures we skip the first phase on the next call
       and resume sending.

       libssh2_NB_state_sent2: In the third phase (indicated by ) we read the
       data from the responses that have arrived so far.  Reading can be
       interrupted with EAGAIN but the state machine ensures we skip the first
       and second phases on the next call and resume sending.
    */

    switch (sftp->read_state) {
    case libssh2_NB_state_idle:

        /* Some data may already have been read from the server in the
           previous call but didn't fit in the buffer at the time.  If so, we
           return that now as we can't risk being interrupted later with data
           partially written to the buffer. */
        if(filep->data_left) {
            size_t copy = MIN(buffer_size, filep->data_left);

            memcpy(buffer, &filep->data[ filep->data_len - filep->data_left],
                   copy);

            filep->data_left -= copy;
            filep->offset += copy;

            if(!filep->data_left) {
                LIBSSH2_FREE(session, filep->data);
                filep->data = NULL;
            }

            return copy;
        }

        if (filep->eof) {
            return 0;
        } else {
            /* We allow a number of bytes being requested at any given time
               without having been acked - until we reach EOF. */

            /* Number of bytes asked for that haven't been acked yet */
            size_t already = (size_t)(filep->offset_sent - filep->offset);

            size_t max_read_ahead = buffer_size*4;
            unsigned long recv_window;

            if(max_read_ahead > LIBSSH2_CHANNEL_WINDOW_DEFAULT*4)
                max_read_ahead = LIBSSH2_CHANNEL_WINDOW_DEFAULT*4;

            /* if the buffer_size passed in now is smaller than what has
               already been sent, we risk getting count become a very large
               number */
            if(max_read_ahead > already)
                count = max_read_ahead - already;

            /* 'count' is how much more data to ask for, and 'already' is how
               much data that already has been asked for but not yet returned.
               Specificly, 'count' means how much data that have or will be
               asked for by the nodes that are already added to the linked
               list. Some of those read requests may not actually have been
               sent off successfully yet.

               If 'already' is very large it should be perfectly fine to have
               count set to 0 as then we don't have to ask for more data
               (right now).

               buffer_size*4 is just picked more or less out of the air. The
               idea is that when reading SFTP from a remote server, we send
               away multiple read requests guessing that the client will read
               more than only this 'buffer_size' amount of memory. So we ask
               for maximum buffer_size*4 amount of data so that we can return
               them very fast in subsequent calls.
            */

            recv_window = libssh2_channel_window_read_ex(sftp->channel,
                                                         NULL, NULL);
            if(max_read_ahead > recv_window) {
                /* more data will be asked for than what the window currently
                   allows, expand it! */

                rc = _libssh2_channel_receive_window_adjust(sftp->channel,
                                                            max_read_ahead*8,
                                                            1, NULL);
                /* if this returns EAGAIN, we will get back to this function
                   at next call */
                assert(rc != LIBSSH2_ERROR_EAGAIN || !filep->data_left);
                assert(rc != LIBSSH2_ERROR_EAGAIN || !filep->eof);
                if (rc)
                    return rc;
            }
        }

        while(count > 0) {
            unsigned char *s;

            /* 25 = packet_len(4) + packet_type(1) + request_id(4) +
               handle_len(4) + offset(8) + count(4) */
            uint32_t packet_len = (uint32_t)handle->handle_len + 25;
            uint32_t request_id;

            uint32_t size = count;
            if (size < buffer_size)
                size = buffer_size;
            if (size > MAX_SFTP_READ_SIZE)
                size = MAX_SFTP_READ_SIZE;

            chunk = LIBSSH2_ALLOC(session, packet_len +
                                  sizeof(struct sftp_pipeline_chunk));
            if (!chunk)
                return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                      "malloc fail for FXP_WRITE");

            chunk->offset = filep->offset_sent;
            chunk->len = size;
            chunk->lefttosend = packet_len;
            chunk->sent = 0;

            s = chunk->packet;

            _libssh2_store_u32(&s, packet_len - 4);
            *s++ = SSH_FXP_READ;
            request_id = sftp->request_id++;
            chunk->request_id = request_id;
            _libssh2_store_u32(&s, request_id);
            _libssh2_store_str(&s, handle->handle, handle->handle_len);
            _libssh2_store_u64(&s, filep->offset_sent);
            filep->offset_sent += size; /* advance offset at once */
            _libssh2_store_u32(&s, size);

            /* add this new entry LAST in the list */
            _libssh2_list_add(&handle->packet_list, &chunk->node);
            count -= MIN(size,count); /* deduct the size we used, as we might
                                       * have to create more packets */
            _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                           "read request id %d sent (offset: %d, size: %d)",
                           request_id, (int)chunk->offset, (int)chunk->len);
        }

    case libssh2_NB_state_sent:

        sftp->read_state = libssh2_NB_state_idle;

        /* move through the READ packets that haven't been sent and send as
           many as possible - remember that we don't block */
        chunk = _libssh2_list_first(&handle->packet_list);

        while(chunk) {
            if(chunk->lefttosend) {

                rc = _libssh2_channel_write(channel, 0,
                                            &chunk->packet[chunk->sent],
                                            chunk->lefttosend);
                if(rc < 0) {
                    sftp->read_state = libssh2_NB_state_sent;
                    return rc;
                }

                /* remember where to continue sending the next time */
                chunk->lefttosend -= rc;
                chunk->sent += rc;

                if(chunk->lefttosend) {
                    /* We still have data left to send for this chunk.
                     * If there is at least one completely sent chunk,
                     * we can get out of this loop and start reading.  */
                    if (chunk != _libssh2_list_first(&handle->packet_list)) {
                        break;
                    } else {
                        continue;
                    }
                }
            }

            /* move on to the next chunk with data to send */
            chunk = _libssh2_list_next(&chunk->node);
        }

    case libssh2_NB_state_sent2:

        sftp->read_state = libssh2_NB_state_idle;

        /*
         * Count all ACKed packets and act on the contents of them.
         */
        chunk = _libssh2_list_first(&handle->packet_list);

        while(chunk) {
            unsigned char *data;
            size_t data_len;
            uint32_t rc32;
            static const unsigned char read_responses[2] = {
                SSH_FXP_DATA, SSH_FXP_STATUS
            };

            if(chunk->lefttosend) {
                /* if the chunk still has data left to send, we shouldn't wait
                   for an ACK for it just yet */
                if (bytes_in_buffer > 0) {
                    return bytes_in_buffer;
                } else {
                    /* we should never reach this point */
                    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                          "sftp_read() internal error");
                }
            }

            rc = sftp_packet_requirev(sftp, 2, read_responses,
                                      chunk->request_id, &data, &data_len);

            if (rc==LIBSSH2_ERROR_EAGAIN && bytes_in_buffer != 0) {
                /* do not return EAGAIN if we have already
                 * written data into the buffer */
                return bytes_in_buffer;
            }

            if (rc < 0) {
                sftp->read_state = libssh2_NB_state_sent2;
                return rc;
            }

            /*
             * We get DATA or STATUS back. STATUS can be error, or it is
             * FX_EOF when we reach the end of the file.
             */

            switch (data[0]) {
            case SSH_FXP_STATUS:
                /* remove the chunk we just processed */

                _libssh2_list_remove(&chunk->node);
                LIBSSH2_FREE(session, chunk);

                /* we must remove all outstanding READ requests, as either we
                   got an error or we're at end of file */
                sftp_packetlist_flush(handle);

                rc32 = _libssh2_ntohu32(data + 5);
                LIBSSH2_FREE(session, data);

                if (rc32 == LIBSSH2_FX_EOF) {
                    filep->eof = TRUE;
                    return bytes_in_buffer;
                }
                else {
                    sftp->last_errno = rc32;
                    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                          "SFTP READ error");
                }
                break;

            case SSH_FXP_DATA:
                if (chunk->offset != filep->offset) {
                    /* This could happen if the server returns less bytes than
                       requested, which shouldn't happen for normal files. See:
                       https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
                       #section-6.4
                    */
                    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                          "Read Packet At Unexpected Offset");
                }

                rc32 = _libssh2_ntohu32(data + 5);
                if (rc32 > (data_len - 9))
                    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                          "SFTP Protocol badness");

                if(rc32 > chunk->len) {
                    /* A chunk larger than we requested was returned to us.
                       This is a protocol violation and we don't know how to
                       deal with it. Bail out! */
                    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                          "FXP_READ response too big");
                }

                if(rc32 != chunk->len) {
                    /* a short read does not imply end of file, but we must
                       adjust the offset_sent since it was advanced with a
                       full chunk->len before */
                    filep->offset_sent -= (chunk->len - rc32);
                }

                if((bytes_in_buffer + rc32) > buffer_size) {
                    /* figure out the overlap amount */
                    filep->data_left = (bytes_in_buffer + rc32) - buffer_size;

                    /* getting the full packet would overflow the buffer, so
                       only get the correct amount and keep the remainder */
                    rc32 = (uint32_t)buffer_size - bytes_in_buffer;

                    /* store data to keep for next call */
                    filep->data = data;
                    filep->data_len = data_len;
                }
                else
                    filep->data_len = 0;

                /* copy the received data from the received FXP_DATA packet to
                   the buffer at the correct index */
                memcpy(sliding_bufferp, data + 9, rc32);
                filep->offset += rc32;
                bytes_in_buffer += rc32;
                sliding_bufferp += rc32;

                if(filep->data_len == 0)
                    /* free the allocated data if not stored to keep */
                    LIBSSH2_FREE(session, data);

                /* remove the chunk we just processed keeping track of the
                 * next one in case we need it */
                next = _libssh2_list_next(&chunk->node);
                _libssh2_list_remove(&chunk->node);
                LIBSSH2_FREE(session, chunk);

                /* check if we have space left in the buffer
                 * and either continue to the next chunk or stop
                 */
                if (bytes_in_buffer < buffer_size) {
                    chunk = next;
                } else {
                    chunk = NULL;
                }

                break;
            default:
                return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                      "SFTP Protocol badness: unrecognised "
                                      "read request response");
            }
        }

        if (bytes_in_buffer > 0)
            return bytes_in_buffer;

        break;

    default:
        assert(!"State machine error; unrecognised read state");
    }

    /* we should never reach this point */
    return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                          "sftp_read() internal error");
}

/* libssh2_sftp_read
 * Read from an SFTP file handle
 */
LIBSSH2_API ssize_t
libssh2_sftp_read(LIBSSH2_SFTP_HANDLE *hnd, char *buffer,
                  size_t buffer_maxlen)
{
    ssize_t rc;
    if(!hnd)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session,
                 sftp_read(hnd, buffer, buffer_maxlen));
    return rc;
}

/* sftp_readdir
 * Read from an SFTP directory handle
 */
static ssize_t sftp_readdir(LIBSSH2_SFTP_HANDLE *handle, char *buffer,
                            size_t buffer_maxlen, char *longentry,
                            size_t longentry_maxlen,
                            LIBSSH2_SFTP_ATTRIBUTES *attrs)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    uint32_t num_names;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + handle_len(4) */
    uint32_t packet_len = handle->handle_len + 13;
    unsigned char *s, *data;
    static const unsigned char read_responses[2] = {
        SSH_FXP_NAME, SSH_FXP_STATUS };
    ssize_t retcode;

    if (sftp->readdir_state == libssh2_NB_state_idle) {
        if (handle->u.dir.names_left) {
            /*
             * A prior request returned more than one directory entry,
             * feed it back from the buffer
             */
            LIBSSH2_SFTP_ATTRIBUTES attrs_dummy;
            size_t real_longentry_len;
            size_t real_filename_len;
            size_t filename_len;
            size_t longentry_len;

            s = (unsigned char *) handle->u.dir.next_name;
            real_filename_len = _libssh2_ntohu32(s);

            s += 4;

            filename_len = real_filename_len;
            if (filename_len >= buffer_maxlen) {
                filename_len = (size_t)LIBSSH2_ERROR_BUFFER_TOO_SMALL;
                goto end;
            }

            memcpy(buffer, s, filename_len);
            buffer[filename_len] = '\0';           /* zero terminate */
            s += real_filename_len;

            real_longentry_len = _libssh2_ntohu32(s);
            s += 4;

            if (longentry && (longentry_maxlen>1)) {
                longentry_len = real_longentry_len;

                if (longentry_len >= longentry_maxlen) {
                    filename_len = (size_t)LIBSSH2_ERROR_BUFFER_TOO_SMALL;
                    goto end;
                }

                memcpy(longentry, s, longentry_len);
                longentry[longentry_len] = '\0'; /* zero terminate */
            }
            s += real_longentry_len;

            if (attrs)
                memset(attrs, 0, sizeof(LIBSSH2_SFTP_ATTRIBUTES));

            s += sftp_bin2attr(attrs ? attrs : &attrs_dummy, s);

            handle->u.dir.next_name = (char *) s;
          end:

            if ((--handle->u.dir.names_left) == 0)
                LIBSSH2_FREE(session, handle->u.dir.names_packet);

            _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                           "libssh2_sftp_readdir_ex() return %d",
                           filename_len);
            return (ssize_t)filename_len;
        }

        /* Request another entry(entries?) */

        s = sftp->readdir_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->readdir_packet)
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for "
                                  "FXP_READDIR packet");

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_READDIR;
        sftp->readdir_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->readdir_request_id);
        _libssh2_store_str(&s, handle->handle, handle->handle_len);

        sftp->readdir_state = libssh2_NB_state_created;
    }

    if (sftp->readdir_state == libssh2_NB_state_created) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Reading entries from directory handle");
        retcode = _libssh2_channel_write(channel, 0, sftp->readdir_packet,
                                         packet_len);
        if (retcode == LIBSSH2_ERROR_EAGAIN) {
            return retcode;
        }
        else if ((ssize_t)packet_len != retcode) {
            LIBSSH2_FREE(session, sftp->readdir_packet);
            sftp->readdir_packet = NULL;
            sftp->readdir_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "_libssh2_channel_write() failed");
        }

        LIBSSH2_FREE(session, sftp->readdir_packet);
        sftp->readdir_packet = NULL;

        sftp->readdir_state = libssh2_NB_state_sent;
    }

    retcode = sftp_packet_requirev(sftp, 2, read_responses,
                                   sftp->readdir_request_id, &data,
                                   &data_len);
    if (retcode == LIBSSH2_ERROR_EAGAIN)
        return retcode;
    else if (retcode) {
        sftp->readdir_state = libssh2_NB_state_idle;
        return _libssh2_error(session, retcode,
                              "Timeout waiting for status message");
    }

    if (data[0] == SSH_FXP_STATUS) {
        retcode = _libssh2_ntohu32(data + 5);
        LIBSSH2_FREE(session, data);
        if (retcode == LIBSSH2_FX_EOF) {
            sftp->readdir_state = libssh2_NB_state_idle;
            return 0;
        }
        else {
            sftp->last_errno = retcode;
            sftp->readdir_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                  "SFTP Protocol Error");
        }
    }

    sftp->readdir_state = libssh2_NB_state_idle;

    num_names = _libssh2_ntohu32(data + 5);
    _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "%lu entries returned",
                   num_names);
    if (!num_names) {
        LIBSSH2_FREE(session, data);
        return 0;
    }

    handle->u.dir.names_left = num_names;
    handle->u.dir.names_packet = data;
    handle->u.dir.next_name = (char *) data + 9;

    /* use the name popping mechanism from the start of the function */
    return sftp_readdir(handle, buffer, buffer_maxlen, longentry,
                        longentry_maxlen, attrs);
}

/* libssh2_sftp_readdir_ex
 * Read from an SFTP directory handle
 */
LIBSSH2_API int
libssh2_sftp_readdir_ex(LIBSSH2_SFTP_HANDLE *hnd, char *buffer,
                        size_t buffer_maxlen, char *longentry,
                        size_t longentry_maxlen,
                        LIBSSH2_SFTP_ATTRIBUTES *attrs)
{
    int rc;
    if(!hnd)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session,
                 sftp_readdir(hnd, buffer, buffer_maxlen, longentry,
                              longentry_maxlen, attrs));
    return rc;
}

/*
 * sftp_write
 *
 * Write data to an SFTP handle. Returns the number of bytes written, or
 * a negative error code.
 *
 * We recommend sending very large data buffers to this function!
 *
 * Concept:
 *
 * - Detect how much of the given buffer that was already sent in a previous
 *   call by inspecting the linked list of outgoing chunks. Make sure to skip
 *   passed the data that has already been taken care of.
 *
 * - Split all (new) outgoing data in chunks no larger than N.
 *
 * - Each N bytes chunk gets created as a separate SFTP packet.
 *
 * - Add all created outgoing packets to the linked list.
 *
 * - Walk through the list and send the chunks that haven't been sent,
 *   as many as possible until EAGAIN. Some of the chunks may have been put
 *   in the list in a previous invoke.
 *
 * - For all the chunks in the list that have been completely sent off, check
 *   for ACKs. If a chunk has been ACKed, it is removed from the linked
 *   list and the "acked" counter gets increased with that data amount.
 *
 * - Return TOTAL bytes acked so far.
 *
 * Caveats:
 * -  be careful: we must not return a higher number than what was given!
 *
 * TODO:
 *   Introduce an option that disables this sort of "speculative" ahead writing
 *   as there's a risk that it will do harm to some app.
 */

static ssize_t sftp_write(LIBSSH2_SFTP_HANDLE *handle, const char *buffer,
                          size_t count)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    uint32_t retcode;
    uint32_t packet_len;
    unsigned char *s, *data;
    ssize_t rc;
    struct sftp_pipeline_chunk *chunk;
    struct sftp_pipeline_chunk *next;
    size_t acked = 0;
    size_t org_count = count;
    size_t already;

    switch(sftp->write_state) {
    default:
    case libssh2_NB_state_idle:

        /* Number of bytes sent off that haven't been acked and therefor we
           will get passed in here again.

           Also, add up the number of bytes that actually already have been
           acked but we haven't been able to return as such yet, so we will
           get that data as well passed in here again.
        */
        already = (size_t) (handle->u.file.offset_sent - handle->u.file.offset)+
            handle->u.file.acked;

        if(count >= already) {
            /* skip the part already made into packets */
            buffer += already;
            count -= already;
        }
        else
            /* there is more data already fine than what we got in this call */
            count = 0;

        sftp->write_state = libssh2_NB_state_idle;
        while(count) {
            /* TODO: Possibly this should have some logic to prevent a very
               very small fraction to be left but lets ignore that for now */
            uint32_t size = MIN(MAX_SFTP_OUTGOING_SIZE, count);
            uint32_t request_id;

            /* 25 = packet_len(4) + packet_type(1) + request_id(4) +
               handle_len(4) + offset(8) + count(4) */
            packet_len = handle->handle_len + size + 25;

            chunk = LIBSSH2_ALLOC(session, packet_len +
                                  sizeof(struct sftp_pipeline_chunk));
            if (!chunk)
                return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                      "malloc fail for FXP_WRITE");

            chunk->len = size;
            chunk->sent = 0;
            chunk->lefttosend = packet_len;

            s = chunk->packet;
            _libssh2_store_u32(&s, packet_len - 4);

            *(s++) = SSH_FXP_WRITE;
            request_id = sftp->request_id++;
            chunk->request_id = request_id;
            _libssh2_store_u32(&s, request_id);
            _libssh2_store_str(&s, handle->handle, handle->handle_len);
            _libssh2_store_u64(&s, handle->u.file.offset_sent);
            handle->u.file.offset_sent += size; /* advance offset at once */
            _libssh2_store_str(&s, buffer, size);

            /* add this new entry LAST in the list */
            _libssh2_list_add(&handle->packet_list, &chunk->node);

            buffer += size;
            count -= size; /* deduct the size we used, as we might have
                              to create more packets */
        }

        /* move through the WRITE packets that haven't been sent and send as many
           as possible - remember that we don't block */
        chunk = _libssh2_list_first(&handle->packet_list);

        while(chunk) {
            if(chunk->lefttosend) {
                rc = _libssh2_channel_write(channel, 0,
                                            &chunk->packet[chunk->sent],
                                            chunk->lefttosend);
                if(rc < 0)
                    /* remain in idle state */
                    return rc;

                /* remember where to continue sending the next time */
                chunk->lefttosend -= rc;
                chunk->sent += rc;

                if(chunk->lefttosend)
                    /* data left to send, get out of loop */
                    break;
            }

            /* move on to the next chunk with data to send */
            chunk = _libssh2_list_next(&chunk->node);
        }

        /* fall-through */
    case libssh2_NB_state_sent:

        sftp->write_state = libssh2_NB_state_idle;
        /*
         * Count all ACKed packets
         */
        chunk = _libssh2_list_first(&handle->packet_list);

        while(chunk) {
            if(chunk->lefttosend)
                /* if the chunk still has data left to send, we shouldn't wait
                   for an ACK for it just yet */
                break;

            else if(acked)
                /* if we have sent data that is acked, we must return that
                   info before we call a function that might return EAGAIN */
                break;

            /* we check the packets in order */
            rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                                     chunk->request_id, &data, &data_len);
            if (rc < 0) {
                if (rc == LIBSSH2_ERROR_EAGAIN)
                    sftp->write_state = libssh2_NB_state_sent;
                return rc;
            }

            retcode = _libssh2_ntohu32(data + 5);
            LIBSSH2_FREE(session, data);

            sftp->last_errno = retcode;
            if (retcode == LIBSSH2_FX_OK) {
                acked += chunk->len; /* number of payload data that was acked
                                        here */

                /* we increase the offset value for all acks */
                handle->u.file.offset += chunk->len;

                next = _libssh2_list_next(&chunk->node);

                _libssh2_list_remove(&chunk->node); /* remove from list */
                LIBSSH2_FREE(session, chunk); /* free memory */

                chunk = next;
            }
            else {
                /* flush all pending packets from the outgoing list */
                sftp_packetlist_flush(handle);

                /* since we return error now, the application will not get any
                   outstanding data acked, so we need to rewind the offset to
                   where the application knows it has reached with acked data */
                handle->u.file.offset -= handle->u.file.acked;

                /* then reset the offset_sent to be the same as the offset */
                handle->u.file.offset_sent = handle->u.file.offset;

                /* clear the acked counter since we can have no pending data to
                   ack after an error */
                handle->u.file.acked = 0;

                /* the server returned an error for that written chunk, propagate
                   this back to our parent function */
                return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                      "FXP write failed");
            }
        }
        break;
    }

    /* if there were acked data in a previous call that wasn't returned then,
       add that up and try to return it all now. This can happen if the app
       first sends a huge buffer of data, and then in a second call it sends a
       smaller one. */
    acked += handle->u.file.acked;

    if(acked) {
        ssize_t ret = MIN(acked, org_count);
        /* we got data acked so return that amount, but no more than what
           was asked to get sent! */

        /* store the remainder. 'ret' is always equal to or less than 'acked'
           here */
        handle->u.file.acked = acked - ret;

        return ret;
    }

    else
        return 0; /* nothing was acked, and no EAGAIN was received! */
}

/* libssh2_sftp_write
 * Write data to a file handle
 */
LIBSSH2_API ssize_t
libssh2_sftp_write(LIBSSH2_SFTP_HANDLE *hnd, const char *buffer,
                   size_t count)
{
    ssize_t rc;
    if(!hnd)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session,
                 sftp_write(hnd, buffer, count));
    return rc;

}

static int sftp_fsync(LIBSSH2_SFTP_HANDLE *handle)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    /* 34 = packet_len(4) + packet_type(1) + request_id(4) +
       string_len(4) + strlen("fsync@openssh.com")(17) + handle_len(4) */
    uint32_t packet_len = handle->handle_len + 34;
    size_t data_len;
    unsigned char *packet, *s, *data;
    ssize_t rc;
    uint32_t retcode;

    if (sftp->fsync_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Issuing fsync command");
        s = packet = LIBSSH2_ALLOC(session, packet_len);
        if (!packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_EXTENDED "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_EXTENDED;
        sftp->fsync_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->fsync_request_id);
        _libssh2_store_str(&s, "fsync@openssh.com", 17);
        _libssh2_store_str(&s, handle->handle, handle->handle_len);

        sftp->fsync_state = libssh2_NB_state_created;
    } else {
        packet = sftp->fsync_packet;
    }

    if (sftp->fsync_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, packet, packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN ||
            (0 <= rc && rc < (ssize_t)packet_len)) {
            sftp->fsync_packet = packet;
            return LIBSSH2_ERROR_EAGAIN;
        }

        LIBSSH2_FREE(session, packet);
        sftp->fsync_packet = NULL;

        if (rc < 0) {
            sftp->fsync_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "_libssh2_channel_write() failed");
        }
        sftp->fsync_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                             sftp->fsync_request_id, &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->fsync_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP EXTENDED REPLY");
    }

    sftp->fsync_state = libssh2_NB_state_idle;

    retcode = _libssh2_ntohu32(data + 5);
    LIBSSH2_FREE(session, data);

    if (retcode != LIBSSH2_FX_OK) {
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "fsync failed");
    }

    return 0;
}

/* libssh2_sftp_fsync
 * Commit data on the handle to disk.
 */
LIBSSH2_API int
libssh2_sftp_fsync(LIBSSH2_SFTP_HANDLE *hnd)
{
    int rc;
    if(!hnd)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session,
                 sftp_fsync(hnd));
    return rc;
}


/*
 * sftp_fstat
 *
 * Get or Set stat on a file
 */
static int sftp_fstat(LIBSSH2_SFTP_HANDLE *handle,
                      LIBSSH2_SFTP_ATTRIBUTES *attrs, int setstat)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + handle_len(4) */
    uint32_t packet_len =
        handle->handle_len + 13 + (setstat ? sftp_attrsize(attrs->flags) : 0);
    unsigned char *s, *data;
    static const unsigned char fstat_responses[2] =
        { SSH_FXP_ATTRS, SSH_FXP_STATUS };
    ssize_t rc;

    if (sftp->fstat_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Issuing %s command",
                       setstat ? "set-stat" : "stat");
        s = sftp->fstat_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->fstat_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for "
                                  "FSTAT/FSETSTAT packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = setstat ? SSH_FXP_FSETSTAT : SSH_FXP_FSTAT;
        sftp->fstat_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->fstat_request_id);
        _libssh2_store_str(&s, handle->handle, handle->handle_len);

        if (setstat) {
            s += sftp_attr2bin(s, attrs);
        }

        sftp->fstat_state = libssh2_NB_state_created;
    }

    if (sftp->fstat_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->fstat_packet,
                                    packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if ((ssize_t)packet_len != rc) {
            LIBSSH2_FREE(session, sftp->fstat_packet);
            sftp->fstat_packet = NULL;
            sftp->fstat_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  (setstat ? "Unable to send FXP_FSETSTAT"
                                   : "Unable to send FXP_FSTAT command"));
        }
        LIBSSH2_FREE(session, sftp->fstat_packet);
        sftp->fstat_packet = NULL;

        sftp->fstat_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_requirev(sftp, 2, fstat_responses,
                              sftp->fstat_request_id, &data,
                              &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN)
        return rc;
    else if (rc) {
        sftp->fstat_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Timeout waiting for status message");
    }

    sftp->fstat_state = libssh2_NB_state_idle;

    if (data[0] == SSH_FXP_STATUS) {
        uint32_t retcode;

        retcode = _libssh2_ntohu32(data + 5);
        LIBSSH2_FREE(session, data);
        if (retcode == LIBSSH2_FX_OK) {
            return 0;
        } else {
            sftp->last_errno = retcode;
            return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                  "SFTP Protocol Error");
        }
    }

    sftp_bin2attr(attrs, data + 5);
    LIBSSH2_FREE(session, data);

    return 0;
}

/* libssh2_sftp_fstat_ex
 * Get or Set stat on a file
 */
LIBSSH2_API int
libssh2_sftp_fstat_ex(LIBSSH2_SFTP_HANDLE *hnd,
                      LIBSSH2_SFTP_ATTRIBUTES *attrs, int setstat)
{
    int rc;
    if(!hnd || !attrs)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session,
                 sftp_fstat(hnd, attrs, setstat));
    return rc;
}


/* libssh2_sftp_seek64
 * Set the read/write pointer to an arbitrary position within the file
 */
LIBSSH2_API void
libssh2_sftp_seek64(LIBSSH2_SFTP_HANDLE *handle, libssh2_uint64_t offset)
{
    if(!handle)
        return;
    if(handle->u.file.offset == offset && handle->u.file.offset_sent == offset)
        return;

    handle->u.file.offset = handle->u.file.offset_sent = offset;
    /* discard all pending requests and currently read data */
    sftp_packetlist_flush(handle);

    /* free the left received buffered data */
    if (handle->u.file.data_left) {
        LIBSSH2_FREE(handle->sftp->channel->session, handle->u.file.data);
        handle->u.file.data_left = handle->u.file.data_len = 0;
        handle->u.file.data = NULL;
    }

    /* reset EOF to False */
    handle->u.file.eof = FALSE;
}

/* libssh2_sftp_seek
 * Set the read/write pointer to an arbitrary position within the file
 */
LIBSSH2_API void
libssh2_sftp_seek(LIBSSH2_SFTP_HANDLE *handle, size_t offset)
{
    libssh2_sftp_seek64(handle, (libssh2_uint64_t)offset);
}

/* libssh2_sftp_tell
 * Return the current read/write pointer's offset
 */
LIBSSH2_API size_t
libssh2_sftp_tell(LIBSSH2_SFTP_HANDLE *handle)
{
    if(!handle)
        return 0; /* no handle, no size */

    /* NOTE: this may very well truncate the size if it is larger than what
       size_t can hold, so libssh2_sftp_tell64() is really the function you
       should use */
    return (size_t)(handle->u.file.offset);
}

/* libssh2_sftp_tell64
 * Return the current read/write pointer's offset
 */
LIBSSH2_API libssh2_uint64_t
libssh2_sftp_tell64(LIBSSH2_SFTP_HANDLE *handle)
{
    if(!handle)
        return 0; /* no handle, no size */

    return handle->u.file.offset;
}

/*
 * Flush all remaining incoming SFTP packets and zombies.
 */
static void sftp_packet_flush(LIBSSH2_SFTP *sftp)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    LIBSSH2_SFTP_PACKET *packet = _libssh2_list_first(&sftp->packets);
    struct sftp_zombie_requests *zombie =
        _libssh2_list_first(&sftp->zombie_requests);

    while(packet) {
        LIBSSH2_SFTP_PACKET *next;

        /* check next struct in the list */
        next =  _libssh2_list_next(&packet->node);
        _libssh2_list_remove(&packet->node);
        LIBSSH2_FREE(session, packet->data);
        LIBSSH2_FREE(session, packet);

        packet = next;
    }

    while(zombie) {
        /* figure out the next node */
        struct sftp_zombie_requests *next = _libssh2_list_next(&zombie->node);
        /* unlink the current one */
        _libssh2_list_remove(&zombie->node);
        /* free the memory */
        LIBSSH2_FREE(session, zombie);
        zombie = next;
    }

}

/* sftp_close_handle
 *
 * Close a file or directory handle.
 * Also frees handle resource and unlinks it from the SFTP structure.
 * The handle is no longer usable after return of this function, unless
 * the return value is LIBSSH2_ERROR_EAGAIN in which case this function
 * should be called again.
 */
static int
sftp_close_handle(LIBSSH2_SFTP_HANDLE *handle)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + handle_len(4) */
    uint32_t packet_len = handle->handle_len + 13;
    unsigned char *s, *data = NULL;
    int rc = 0;

    if (handle->close_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Closing handle");
        s = handle->close_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!handle->close_packet) {
            handle->close_state = libssh2_NB_state_idle;
            rc = _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                "Unable to allocate memory for FXP_CLOSE "
                                "packet");
        } else {

            _libssh2_store_u32(&s, packet_len - 4);
            *(s++) = SSH_FXP_CLOSE;
            handle->close_request_id = sftp->request_id++;
            _libssh2_store_u32(&s, handle->close_request_id);
            _libssh2_store_str(&s, handle->handle, handle->handle_len);
            handle->close_state = libssh2_NB_state_created;
        }
    }

    if (handle->close_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, handle->close_packet,
                                    packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        } else if ((ssize_t)packet_len != rc) {
            handle->close_state = libssh2_NB_state_idle;
            rc = _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                "Unable to send FXP_CLOSE command");
        } else
            handle->close_state = libssh2_NB_state_sent;

        LIBSSH2_FREE(session, handle->close_packet);
        handle->close_packet = NULL;
    }

    if (handle->close_state == libssh2_NB_state_sent) {
        rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                                 handle->close_request_id, &data,
                                 &data_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;

        } else if (rc) {
            _libssh2_error(session, rc,
                           "Error waiting for status message");
        }

        handle->close_state = libssh2_NB_state_sent1;
    }

    if(!data) {
        /* if it reaches this point with data unset, something unwanted
           happened for which we should have set an error code */
        assert(rc);

    } else {
        int retcode = _libssh2_ntohu32(data + 5);
        LIBSSH2_FREE(session, data);

        if (retcode != LIBSSH2_FX_OK) {
            sftp->last_errno = retcode;
            handle->close_state = libssh2_NB_state_idle;
            rc = _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                "SFTP Protocol Error");
        }
    }

    /* remove this handle from the parent's list */
    _libssh2_list_remove(&handle->node);

    if ((handle->handle_type == LIBSSH2_SFTP_HANDLE_DIR)
        && handle->u.dir.names_left) {
        LIBSSH2_FREE(session, handle->u.dir.names_packet);
    }
    else {
        if(handle->u.file.data)
            LIBSSH2_FREE(session, handle->u.file.data);
    }

    sftp_packetlist_flush(handle);
    sftp->read_state = libssh2_NB_state_idle;

    handle->close_state = libssh2_NB_state_idle;

    LIBSSH2_FREE(session, handle);

    return rc;
}

/* libssh2_sftp_close_handle
 *
 * Close a file or directory handle
 * Also frees handle resource and unlinks it from the SFTP structure
 */
LIBSSH2_API int
libssh2_sftp_close_handle(LIBSSH2_SFTP_HANDLE *hnd)
{
    int rc;
    if(!hnd)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, hnd->sftp->channel->session, sftp_close_handle(hnd));
    return rc;
}

/* sftp_unlink
 * Delete a file from the remote server
 */
static int sftp_unlink(LIBSSH2_SFTP *sftp, const char *filename,
                       size_t filename_len)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    int retcode;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + filename_len(4) */
    uint32_t packet_len = filename_len + 13;
    unsigned char *s, *data;
    int rc;

    if (sftp->unlink_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Unlinking %s", filename);
        s = sftp->unlink_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->unlink_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_REMOVE "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_REMOVE;
        sftp->unlink_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->unlink_request_id);
        _libssh2_store_str(&s, filename, filename_len);
        sftp->unlink_state = libssh2_NB_state_created;
    }

    if (sftp->unlink_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->unlink_packet,
                                    packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        } else if ((ssize_t)packet_len != rc) {
            LIBSSH2_FREE(session, sftp->unlink_packet);
            sftp->unlink_packet = NULL;
            sftp->unlink_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send FXP_REMOVE command");
        }
        LIBSSH2_FREE(session, sftp->unlink_packet);
        sftp->unlink_packet = NULL;

        sftp->unlink_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                             sftp->unlink_request_id, &data,
                             &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    }
    else if (rc) {
        sftp->unlink_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP STATUS");
    }

    sftp->unlink_state = libssh2_NB_state_idle;

    retcode = _libssh2_ntohu32(data + 5);
    LIBSSH2_FREE(session, data);

    if (retcode == LIBSSH2_FX_OK) {
        return 0;
    } else {
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error");
    }
}

/* libssh2_sftp_unlink_ex
 * Delete a file from the remote server
 */
LIBSSH2_API int
libssh2_sftp_unlink_ex(LIBSSH2_SFTP *sftp, const char *filename,
                       unsigned int filename_len)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_unlink(sftp, filename, filename_len));
    return rc;
}

/*
 * sftp_rename
 *
 * Rename a file on the remote server
 */
static int sftp_rename(LIBSSH2_SFTP *sftp, const char *source_filename,
                       unsigned int source_filename_len,
                       const char *dest_filename,
                       unsigned int dest_filename_len, long flags)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    int retcode;
    uint32_t packet_len =
        source_filename_len + dest_filename_len + 17 + (sftp->version >=
                                                        5 ? 4 : 0);
    /* packet_len(4) + packet_type(1) + request_id(4) +
       source_filename_len(4) + dest_filename_len(4) + flags(4){SFTP5+) */
    unsigned char *data;
    ssize_t rc;

    if (sftp->version < 2) {
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "Server does not support RENAME");
    }

    if (sftp->rename_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Renaming %s to %s",
                       source_filename, dest_filename);
        sftp->rename_s = sftp->rename_packet =
            LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->rename_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_RENAME "
                                  "packet");
        }

        _libssh2_store_u32(&sftp->rename_s, packet_len - 4);
        *(sftp->rename_s++) = SSH_FXP_RENAME;
        sftp->rename_request_id = sftp->request_id++;
        _libssh2_store_u32(&sftp->rename_s, sftp->rename_request_id);
        _libssh2_store_str(&sftp->rename_s, source_filename,
                           source_filename_len);
        _libssh2_store_str(&sftp->rename_s, dest_filename, dest_filename_len);

        if (sftp->version >= 5)
            _libssh2_store_u32(&sftp->rename_s, flags);

        sftp->rename_state = libssh2_NB_state_created;
    }

    if (sftp->rename_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->rename_packet,
                                    sftp->rename_s - sftp->rename_packet);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        } else if ((ssize_t)packet_len != rc) {
            LIBSSH2_FREE(session, sftp->rename_packet);
            sftp->rename_packet = NULL;
            sftp->rename_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send FXP_RENAME command");
        }
        LIBSSH2_FREE(session, sftp->rename_packet);
        sftp->rename_packet = NULL;

        sftp->rename_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                             sftp->rename_request_id, &data,
                             &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->rename_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP STATUS");
    }

    sftp->rename_state = libssh2_NB_state_idle;

    retcode = _libssh2_ntohu32(data + 5);
    LIBSSH2_FREE(session, data);

    sftp->last_errno = retcode;

    /* now convert the SFTP error code to libssh2 return code or error
       message */
    switch (retcode) {
    case LIBSSH2_FX_OK:
        retcode = LIBSSH2_ERROR_NONE;
        break;

    case LIBSSH2_FX_FILE_ALREADY_EXISTS:
        retcode = _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                 "File already exists and "
                                 "SSH_FXP_RENAME_OVERWRITE not specified");
        break;

    case LIBSSH2_FX_OP_UNSUPPORTED:
        retcode = _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                 "Operation Not Supported");
        break;

    default:
        retcode = _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                 "SFTP Protocol Error");
        break;
    }

    return retcode;
}

/* libssh2_sftp_rename_ex
 * Rename a file on the remote server
 */
LIBSSH2_API int
libssh2_sftp_rename_ex(LIBSSH2_SFTP *sftp, const char *source_filename,
                       unsigned int source_filename_len,
                       const char *dest_filename,
                       unsigned int dest_filename_len, long flags)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_rename(sftp, source_filename, source_filename_len,
                             dest_filename, dest_filename_len, flags));
    return rc;
}

/*
 * sftp_fstatvfs
 *
 * Get file system statistics
 */
static int sftp_fstatvfs(LIBSSH2_SFTP_HANDLE *handle, LIBSSH2_SFTP_STATVFS *st)
{
    LIBSSH2_SFTP *sftp = handle->sftp;
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    /* 17 = packet_len(4) + packet_type(1) + request_id(4) + ext_len(4)
       + handle_len (4) */
    /* 20 = strlen ("fstatvfs@openssh.com") */
    uint32_t packet_len = handle->handle_len + 20 + 17;
    unsigned char *packet, *s, *data;
    ssize_t rc;
    unsigned int flag;
    static const unsigned char responses[2] =
        { SSH_FXP_EXTENDED_REPLY, SSH_FXP_STATUS };

    if (sftp->fstatvfs_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Getting file system statistics");
        s = packet = LIBSSH2_ALLOC(session, packet_len);
        if (!packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_EXTENDED "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_EXTENDED;
        sftp->fstatvfs_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->fstatvfs_request_id);
        _libssh2_store_str(&s, "fstatvfs@openssh.com", 20);
        _libssh2_store_str(&s, handle->handle, handle->handle_len);

        sftp->fstatvfs_state = libssh2_NB_state_created;
    }
    else {
        packet = sftp->fstatvfs_packet;
    }

    if (sftp->fstatvfs_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, packet, packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN ||
            (0 <= rc && rc < (ssize_t)packet_len)) {
            sftp->fstatvfs_packet = packet;
            return LIBSSH2_ERROR_EAGAIN;
        }

        LIBSSH2_FREE(session, packet);
        sftp->fstatvfs_packet = NULL;

        if (rc < 0) {
            sftp->fstatvfs_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "_libssh2_channel_write() failed");
        }
        sftp->fstatvfs_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_requirev(sftp, 2, responses, sftp->fstatvfs_request_id,
                              &data, &data_len);

    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->fstatvfs_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP EXTENDED REPLY");
    }

    if (data[0] == SSH_FXP_STATUS) {
        int retcode = _libssh2_ntohu32(data + 5);
        sftp->fstatvfs_state = libssh2_NB_state_idle;
        LIBSSH2_FREE(session, data);
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error");
    }

    if (data_len < 93) {
        LIBSSH2_FREE(session, data);
        sftp->fstatvfs_state = libssh2_NB_state_idle;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error: short response");
    }

    sftp->fstatvfs_state = libssh2_NB_state_idle;

    st->f_bsize = _libssh2_ntohu64(data + 5);
    st->f_frsize = _libssh2_ntohu64(data + 13);
    st->f_blocks = _libssh2_ntohu64(data + 21);
    st->f_bfree = _libssh2_ntohu64(data + 29);
    st->f_bavail = _libssh2_ntohu64(data + 37);
    st->f_files = _libssh2_ntohu64(data + 45);
    st->f_ffree = _libssh2_ntohu64(data + 53);
    st->f_favail = _libssh2_ntohu64(data + 61);
    st->f_fsid = _libssh2_ntohu64(data + 69);
    flag = (unsigned int)_libssh2_ntohu64(data + 77);
    st->f_namemax = _libssh2_ntohu64(data + 85);

    st->f_flag = (flag & SSH_FXE_STATVFS_ST_RDONLY)
        ? LIBSSH2_SFTP_ST_RDONLY : 0;
    st->f_flag |= (flag & SSH_FXE_STATVFS_ST_NOSUID)
        ? LIBSSH2_SFTP_ST_NOSUID : 0;

    LIBSSH2_FREE(session, data);
    return 0;
}

/* libssh2_sftp_fstatvfs
 * Get filesystem space and inode utilization (requires fstatvfs@openssh.com
 * support on the server)
 */
LIBSSH2_API int
libssh2_sftp_fstatvfs(LIBSSH2_SFTP_HANDLE *handle, LIBSSH2_SFTP_STATVFS *st)
{
    int rc;
    if(!handle || !st)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, handle->sftp->channel->session, sftp_fstatvfs(handle, st));
    return rc;
}

/*
 * sftp_statvfs
 *
 * Get file system statistics
 */
static int sftp_statvfs(LIBSSH2_SFTP *sftp, const char *path,
                        unsigned int path_len, LIBSSH2_SFTP_STATVFS *st)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    /* 17 = packet_len(4) + packet_type(1) + request_id(4) + ext_len(4)
       + path_len (4) */
    /* 19 = strlen ("statvfs@openssh.com") */
    uint32_t packet_len = path_len + 19 + 17;
    unsigned char *packet, *s, *data;
    ssize_t rc;
    unsigned int flag;
    static const unsigned char responses[2] =
        { SSH_FXP_EXTENDED_REPLY, SSH_FXP_STATUS };

    if (sftp->statvfs_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Getting file system statistics of %s", path);
        s = packet = LIBSSH2_ALLOC(session, packet_len);
        if (!packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_EXTENDED "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_EXTENDED;
        sftp->statvfs_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->statvfs_request_id);
        _libssh2_store_str(&s, "statvfs@openssh.com", 19);
        _libssh2_store_str(&s, path, path_len);

        sftp->statvfs_state = libssh2_NB_state_created;
    }
    else {
        packet = sftp->statvfs_packet;
    }

    if (sftp->statvfs_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, packet, packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN ||
            (0 <= rc && rc < (ssize_t)packet_len)) {
            sftp->statvfs_packet = packet;
            return LIBSSH2_ERROR_EAGAIN;
        }

        LIBSSH2_FREE(session, packet);
        sftp->statvfs_packet = NULL;

        if (rc < 0) {
            sftp->statvfs_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "_libssh2_channel_write() failed");
        }
        sftp->statvfs_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_requirev(sftp, 2, responses, sftp->statvfs_request_id,
                              &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->statvfs_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP EXTENDED REPLY");
    }

    if (data[0] == SSH_FXP_STATUS) {
        int retcode = _libssh2_ntohu32(data + 5);
        sftp->statvfs_state = libssh2_NB_state_idle;
        LIBSSH2_FREE(session, data);
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error");
    }

    if (data_len < 93) {
        LIBSSH2_FREE(session, data);
        sftp->statvfs_state = libssh2_NB_state_idle;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error: short response");
    }

    sftp->statvfs_state = libssh2_NB_state_idle;

    st->f_bsize = _libssh2_ntohu64(data + 5);
    st->f_frsize = _libssh2_ntohu64(data + 13);
    st->f_blocks = _libssh2_ntohu64(data + 21);
    st->f_bfree = _libssh2_ntohu64(data + 29);
    st->f_bavail = _libssh2_ntohu64(data + 37);
    st->f_files = _libssh2_ntohu64(data + 45);
    st->f_ffree = _libssh2_ntohu64(data + 53);
    st->f_favail = _libssh2_ntohu64(data + 61);
    st->f_fsid = _libssh2_ntohu64(data + 69);
    flag = (unsigned int)_libssh2_ntohu64(data + 77);
    st->f_namemax = _libssh2_ntohu64(data + 85);

    st->f_flag = (flag & SSH_FXE_STATVFS_ST_RDONLY)
        ? LIBSSH2_SFTP_ST_RDONLY : 0;
    st->f_flag |= (flag & SSH_FXE_STATVFS_ST_NOSUID)
        ? LIBSSH2_SFTP_ST_NOSUID : 0;

    LIBSSH2_FREE(session, data);
    return 0;
}

/* libssh2_sftp_statvfs_ex
 * Get filesystem space and inode utilization (requires statvfs@openssh.com
 * support on the server)
 */
LIBSSH2_API int
libssh2_sftp_statvfs(LIBSSH2_SFTP *sftp, const char *path,
                     size_t path_len, LIBSSH2_SFTP_STATVFS *st)
{
    int rc;
    if(!sftp || !st)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session, sftp_statvfs(sftp, path, path_len,
                                                          st));
    return rc;
}


/*
 * sftp_mkdir
 *
 * Create an SFTP directory
 */
static int sftp_mkdir(LIBSSH2_SFTP *sftp, const char *path,
                      unsigned int path_len, long mode)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    LIBSSH2_SFTP_ATTRIBUTES attrs = {
        LIBSSH2_SFTP_ATTR_PERMISSIONS, 0, 0, 0, 0, 0, 0
    };
    size_t data_len;
    int retcode;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + path_len(4) */
    ssize_t packet_len = path_len + 13 +
        sftp_attrsize(LIBSSH2_SFTP_ATTR_PERMISSIONS);
    unsigned char *packet, *s, *data;
    int rc;

    if (sftp->mkdir_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP,
                       "Creating directory %s with mode 0%lo", path, mode);
        s = packet = LIBSSH2_ALLOC(session, packet_len);
        if (!packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_MKDIR "
                                  "packet");
        }
        /* Filetype in SFTP 3 and earlier */
        attrs.permissions = mode | LIBSSH2_SFTP_ATTR_PFILETYPE_DIR;

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_MKDIR;
        sftp->mkdir_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->mkdir_request_id);
        _libssh2_store_str(&s, path, path_len);

        s += sftp_attr2bin(s, &attrs);

        sftp->mkdir_state = libssh2_NB_state_created;
    }
    else {
        packet = sftp->mkdir_packet;
    }

    if (sftp->mkdir_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, packet, packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            sftp->mkdir_packet = packet;
            return rc;
        }
        if (packet_len != rc) {
            LIBSSH2_FREE(session, packet);
            sftp->mkdir_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "_libssh2_channel_write() failed");
        }
        LIBSSH2_FREE(session, packet);
        sftp->mkdir_state = libssh2_NB_state_sent;
        sftp->mkdir_packet = NULL;
    }

    rc = sftp_packet_require(sftp, SSH_FXP_STATUS, sftp->mkdir_request_id,
                             &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->mkdir_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP STATUS");
    }

    sftp->mkdir_state = libssh2_NB_state_idle;

    retcode = _libssh2_ntohu32(data + 5);
    LIBSSH2_FREE(session, data);

    if (retcode == LIBSSH2_FX_OK) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "OK!");
        return 0;
    } else {
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error");
    }
}

/*
 * libssh2_sftp_mkdir_ex
 *
 * Create an SFTP directory
 */
LIBSSH2_API int
libssh2_sftp_mkdir_ex(LIBSSH2_SFTP *sftp, const char *path,
                      unsigned int path_len, long mode)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_mkdir(sftp, path, path_len, mode));
    return rc;
}

/* sftp_rmdir
 * Remove a directory
 */
static int sftp_rmdir(LIBSSH2_SFTP *sftp, const char *path,
                      unsigned int path_len)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    int retcode;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + path_len(4) */
    ssize_t packet_len = path_len + 13;
    unsigned char *s, *data;
    int rc;

    if (sftp->rmdir_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "Removing directory: %s",
                       path);
        s = sftp->rmdir_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->rmdir_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_RMDIR "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);
        *(s++) = SSH_FXP_RMDIR;
        sftp->rmdir_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->rmdir_request_id);
        _libssh2_store_str(&s, path, path_len);

        sftp->rmdir_state = libssh2_NB_state_created;
    }

    if (sftp->rmdir_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->rmdir_packet,
                                    packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        } else if (packet_len != rc) {
            LIBSSH2_FREE(session, sftp->rmdir_packet);
            sftp->rmdir_packet = NULL;
            sftp->rmdir_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send FXP_RMDIR command");
        }
        LIBSSH2_FREE(session, sftp->rmdir_packet);
        sftp->rmdir_packet = NULL;

        sftp->rmdir_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_require(sftp, SSH_FXP_STATUS,
                             sftp->rmdir_request_id, &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN) {
        return rc;
    } else if (rc) {
        sftp->rmdir_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Error waiting for FXP STATUS");
    }

    sftp->rmdir_state = libssh2_NB_state_idle;

    retcode = _libssh2_ntohu32(data + 5);
    LIBSSH2_FREE(session, data);

    if (retcode == LIBSSH2_FX_OK) {
        return 0;
    } else {
        sftp->last_errno = retcode;
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "SFTP Protocol Error");
    }
}

/* libssh2_sftp_rmdir_ex
 * Remove a directory
 */
LIBSSH2_API int
libssh2_sftp_rmdir_ex(LIBSSH2_SFTP *sftp, const char *path,
                      unsigned int path_len)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_rmdir(sftp, path, path_len));
    return rc;
}

/* sftp_stat
 * Stat a file or symbolic link
 */
static int sftp_stat(LIBSSH2_SFTP *sftp, const char *path,
                     unsigned int path_len, int stat_type,
                     LIBSSH2_SFTP_ATTRIBUTES * attrs)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + path_len(4) */
    ssize_t packet_len =
        path_len + 13 +
        ((stat_type ==
          LIBSSH2_SFTP_SETSTAT) ? sftp_attrsize(attrs->flags) : 0);
    unsigned char *s, *data;
    static const unsigned char stat_responses[2] =
        { SSH_FXP_ATTRS, SSH_FXP_STATUS };
    int rc;

    if (sftp->stat_state == libssh2_NB_state_idle) {
        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "%s %s",
                       (stat_type == LIBSSH2_SFTP_SETSTAT) ? "Set-statting" :
                       (stat_type ==
                        LIBSSH2_SFTP_LSTAT ? "LStatting" : "Statting"), path);
        s = sftp->stat_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->stat_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for FXP_*STAT "
                                  "packet");
        }

        _libssh2_store_u32(&s, packet_len - 4);

        switch (stat_type) {
        case LIBSSH2_SFTP_SETSTAT:
            *(s++) = SSH_FXP_SETSTAT;
            break;

        case LIBSSH2_SFTP_LSTAT:
            *(s++) = SSH_FXP_LSTAT;
            break;

        case LIBSSH2_SFTP_STAT:
        default:
            *(s++) = SSH_FXP_STAT;
        }
        sftp->stat_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->stat_request_id);
        _libssh2_store_str(&s, path, path_len);

        if (stat_type == LIBSSH2_SFTP_SETSTAT)
            s += sftp_attr2bin(s, attrs);

        sftp->stat_state = libssh2_NB_state_created;
    }

    if (sftp->stat_state == libssh2_NB_state_created) {
        rc = _libssh2_channel_write(channel, 0, sftp->stat_packet, packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        } else if (packet_len != rc) {
            LIBSSH2_FREE(session, sftp->stat_packet);
            sftp->stat_packet = NULL;
            sftp->stat_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send STAT/LSTAT/SETSTAT command");
        }
        LIBSSH2_FREE(session, sftp->stat_packet);
        sftp->stat_packet = NULL;

        sftp->stat_state = libssh2_NB_state_sent;
    }

    rc = sftp_packet_requirev(sftp, 2, stat_responses,
                              sftp->stat_request_id, &data, &data_len);
    if (rc == LIBSSH2_ERROR_EAGAIN)
        return rc;
    else if (rc) {
        sftp->stat_state = libssh2_NB_state_idle;
        return _libssh2_error(session, rc,
                              "Timeout waiting for status message");
    }

    sftp->stat_state = libssh2_NB_state_idle;

    if (data[0] == SSH_FXP_STATUS) {
        int retcode;

        retcode = _libssh2_ntohu32(data + 5);
        LIBSSH2_FREE(session, data);
        if (retcode == LIBSSH2_FX_OK) {
            return 0;
        } else {
            sftp->last_errno = retcode;
            return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                  "SFTP Protocol Error");
        }
    }

    memset(attrs, 0, sizeof(LIBSSH2_SFTP_ATTRIBUTES));
    sftp_bin2attr(attrs, data + 5);
    LIBSSH2_FREE(session, data);

    return 0;
}

/* libssh2_sftp_stat_ex
 * Stat a file or symbolic link
 */
LIBSSH2_API int
libssh2_sftp_stat_ex(LIBSSH2_SFTP *sftp, const char *path,
                     unsigned int path_len, int stat_type,
                     LIBSSH2_SFTP_ATTRIBUTES *attrs)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_stat(sftp, path, path_len, stat_type, attrs));
    return rc;
}

/* sftp_symlink
 * Read or set a symlink
 */
static int sftp_symlink(LIBSSH2_SFTP *sftp, const char *path,
                        unsigned int path_len, char *target,
                        unsigned int target_len, int link_type)
{
    LIBSSH2_CHANNEL *channel = sftp->channel;
    LIBSSH2_SESSION *session = channel->session;
    size_t data_len, link_len;
    /* 13 = packet_len(4) + packet_type(1) + request_id(4) + path_len(4) */
    ssize_t packet_len =
        path_len + 13 +
        ((link_type == LIBSSH2_SFTP_SYMLINK) ? (4 + target_len) : 0);
    unsigned char *s, *data;
    static const unsigned char link_responses[2] =
        { SSH_FXP_NAME, SSH_FXP_STATUS };
    int retcode;

    if ((sftp->version < 3) && (link_type != LIBSSH2_SFTP_REALPATH)) {
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "Server does not support SYMLINK or READLINK");
    }

    if (sftp->symlink_state == libssh2_NB_state_idle) {
        s = sftp->symlink_packet = LIBSSH2_ALLOC(session, packet_len);
        if (!sftp->symlink_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for "
                                  "SYMLINK/READLINK/REALPATH packet");
        }

        _libssh2_debug(session, LIBSSH2_TRACE_SFTP, "%s %s on %s",
                       (link_type ==
                        LIBSSH2_SFTP_SYMLINK) ? "Creating" : "Reading",
                       (link_type ==
                        LIBSSH2_SFTP_REALPATH) ? "realpath" : "symlink", path);

        _libssh2_store_u32(&s, packet_len - 4);

        switch (link_type) {
        case LIBSSH2_SFTP_REALPATH:
            *(s++) = SSH_FXP_REALPATH;
            break;

        case LIBSSH2_SFTP_SYMLINK:
            *(s++) = SSH_FXP_SYMLINK;
            break;

        case LIBSSH2_SFTP_READLINK:
        default:
            *(s++) = SSH_FXP_READLINK;
        }
        sftp->symlink_request_id = sftp->request_id++;
        _libssh2_store_u32(&s, sftp->symlink_request_id);
        _libssh2_store_str(&s, path, path_len);

        if (link_type == LIBSSH2_SFTP_SYMLINK)
            _libssh2_store_str(&s, target, target_len);

        sftp->symlink_state = libssh2_NB_state_created;
    }

    if (sftp->symlink_state == libssh2_NB_state_created) {
        ssize_t rc = _libssh2_channel_write(channel, 0, sftp->symlink_packet,
                                            packet_len);
        if (rc == LIBSSH2_ERROR_EAGAIN)
            return rc;
        else if (packet_len != rc) {
            LIBSSH2_FREE(session, sftp->symlink_packet);
            sftp->symlink_packet = NULL;
            sftp->symlink_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send SYMLINK/READLINK command");
        }
        LIBSSH2_FREE(session, sftp->symlink_packet);
        sftp->symlink_packet = NULL;

        sftp->symlink_state = libssh2_NB_state_sent;
    }

    retcode = sftp_packet_requirev(sftp, 2, link_responses,
                                   sftp->symlink_request_id, &data,
                                   &data_len);
    if (retcode == LIBSSH2_ERROR_EAGAIN)
        return retcode;
    else if (retcode) {
        sftp->symlink_state = libssh2_NB_state_idle;
        return _libssh2_error(session, retcode,
                              "Error waiting for status message");
    }

    sftp->symlink_state = libssh2_NB_state_idle;

    if (data[0] == SSH_FXP_STATUS) {
        retcode = _libssh2_ntohu32(data + 5);
        LIBSSH2_FREE(session, data);
        if (retcode == LIBSSH2_FX_OK)
            return LIBSSH2_ERROR_NONE;
        else {
            sftp->last_errno = retcode;
            return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                                  "SFTP Protocol Error");
        }
    }

    if (_libssh2_ntohu32(data + 5) < 1) {
        LIBSSH2_FREE(session, data);
        return _libssh2_error(session, LIBSSH2_ERROR_SFTP_PROTOCOL,
                              "Invalid READLINK/REALPATH response, "
                              "no name entries");
    }

    /* this reads a u32 and stores it into a signed 32bit value */
    link_len = _libssh2_ntohu32(data + 9);
    if (link_len < target_len) {
        memcpy(target, data + 13, link_len);
        target[link_len] = 0;
        retcode = (int)link_len;
    }
    else
        retcode = LIBSSH2_ERROR_BUFFER_TOO_SMALL;
    LIBSSH2_FREE(session, data);

    return retcode;
}

/* libssh2_sftp_symlink_ex
 * Read or set a symlink
 */
LIBSSH2_API int
libssh2_sftp_symlink_ex(LIBSSH2_SFTP *sftp, const char *path,
                        unsigned int path_len, char *target,
                        unsigned int target_len, int link_type)
{
    int rc;
    if(!sftp)
        return LIBSSH2_ERROR_BAD_USE;
    BLOCK_ADJUST(rc, sftp->channel->session,
                 sftp_symlink(sftp, path, path_len, target, target_len,
                              link_type));
    return rc;
}

/* libssh2_sftp_last_error
 * Returns the last error code reported by SFTP
 */
LIBSSH2_API unsigned long
libssh2_sftp_last_error(LIBSSH2_SFTP *sftp)
{
    if(!sftp)
        return 0;

    return sftp->last_errno;
}

/* libssh2_sftp_get_channel
 * Return the channel of sftp, then caller can control the channel's behavior.
 */
LIBSSH2_API LIBSSH2_CHANNEL *
libssh2_sftp_get_channel(LIBSSH2_SFTP *sftp)
{
    if (!sftp)
        return NULL;

    return sftp->channel;
}