githubmirror/nmap

libssh2/src/channel.c
3 075 строк104 KB
dmiller
Update libssh2 to 1.11.1
14 апр 2025, 20:20
14 апр 2025, 20:202bc341d
/* Copyright (C) Sara Golemon <sarag@libssh2.org>
 * Copyright (C) Mikhail Gusarov <dottedmag@dottedmag.net>
 * Copyright (C) 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.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "libssh2_priv.h"

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_INTTYPES_H
#include <inttypes.h>
#endif

#include <assert.h>

#include "channel.h"
#include "transport.h"
#include "packet.h"
#include "session.h"

/*
 *  _libssh2_channel_nextid
 *
 * Determine the next channel ID we can use at our end
 */
uint32_t
_libssh2_channel_nextid(LIBSSH2_SESSION * session)
{
    uint32_t id = session->next_channel;
    LIBSSH2_CHANNEL *channel;

    channel = _libssh2_list_first(&session->channels);

    while(channel) {
        if(channel->local.id > id) {
            id = channel->local.id;
        }
        channel = _libssh2_list_next(&channel->node);
    }

    /* This is a shortcut to avoid waiting for close packets on channels we've
     * forgotten about, This *could* be a problem if we request and close 4
     * billion or so channels in too rapid succession for the remote end to
     * respond, but the worst case scenario is that some data meant for
     * another channel Gets picked up by the new one.... Pretty unlikely all
     * told...
     */
    session->next_channel = id + 1;
    _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                   "Allocated new channel ID#%u", id));
    return id;
}

/*
 * _libssh2_channel_locate
 *
 * Locate a channel pointer by number
 */
LIBSSH2_CHANNEL *
_libssh2_channel_locate(LIBSSH2_SESSION *session, uint32_t channel_id)
{
    LIBSSH2_CHANNEL *channel;
    LIBSSH2_LISTENER *l;

    for(channel = _libssh2_list_first(&session->channels);
        channel;
        channel = _libssh2_list_next(&channel->node)) {
        if(channel->local.id == channel_id)
            return channel;
    }

    /* We didn't find the channel in the session, let's then check its
       listeners since each listener may have its own set of pending channels
    */
    for(l = _libssh2_list_first(&session->listeners); l;
        l = _libssh2_list_next(&l->node)) {
        for(channel = _libssh2_list_first(&l->queue);
            channel;
            channel = _libssh2_list_next(&channel->node)) {
            if(channel->local.id == channel_id)
                return channel;
        }
    }

    return NULL;
}

/*
 * _libssh2_channel_open
 *
 * Establish a generic session channel
 */
LIBSSH2_CHANNEL *
_libssh2_channel_open(LIBSSH2_SESSION * session, const char *channel_type,
                      uint32_t channel_type_len,
                      uint32_t window_size,
                      uint32_t packet_size,
                      const unsigned char *message,
                      size_t message_len)
{
    static const unsigned char reply_codes[3] = {
        SSH_MSG_CHANNEL_OPEN_CONFIRMATION,
        SSH_MSG_CHANNEL_OPEN_FAILURE,
        0
    };
    unsigned char *s;
    int rc;

    if(session->open_state == libssh2_NB_state_idle) {
        session->open_channel = NULL;
        session->open_packet = NULL;
        session->open_data = NULL;
        /* 17 = packet_type(1) + channel_type_len(4) + sender_channel(4) +
         * window_size(4) + packet_size(4) */
        session->open_packet_len = channel_type_len + 17;
        session->open_local_channel = _libssh2_channel_nextid(session);

        /* Zero the whole thing out */
        memset(&session->open_packet_requirev_state, 0,
               sizeof(session->open_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Opening Channel - win %d pack %d", window_size,
                       packet_size));
        session->open_channel =
            LIBSSH2_CALLOC(session, sizeof(LIBSSH2_CHANNEL));
        if(!session->open_channel) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate space for channel data");
            return NULL;
        }
        session->open_channel->channel_type_len = channel_type_len;
        session->open_channel->channel_type =
            LIBSSH2_ALLOC(session, channel_type_len);
        if(!session->open_channel->channel_type) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Failed allocating memory for channel type name");
            LIBSSH2_FREE(session, session->open_channel);
            session->open_channel = NULL;
            return NULL;
        }
        memcpy(session->open_channel->channel_type, channel_type,
               channel_type_len);

        /* REMEMBER: local as in locally sourced */
        session->open_channel->local.id = session->open_local_channel;
        session->open_channel->remote.window_size = window_size;
        session->open_channel->remote.window_size_initial = window_size;
        session->open_channel->remote.packet_size = packet_size;
        session->open_channel->session = session;

        _libssh2_list_add(&session->channels,
                          &session->open_channel->node);

        s = session->open_packet =
            LIBSSH2_ALLOC(session, session->open_packet_len);
        if(!session->open_packet) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate temporary space for packet");
            goto channel_error;
        }
        *(s++) = SSH_MSG_CHANNEL_OPEN;
        _libssh2_store_str(&s, channel_type, channel_type_len);
        _libssh2_store_u32(&s, session->open_local_channel);
        _libssh2_store_u32(&s, window_size);
        _libssh2_store_u32(&s, packet_size);

        /* Do not copy the message */

        session->open_state = libssh2_NB_state_created;
    }

    if(session->open_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session,
                                     session->open_packet,
                                     session->open_packet_len,
                                     message, message_len);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending channel-open request");
            return NULL;
        }
        else if(rc) {
            _libssh2_error(session, rc,
                           "Unable to send channel-open request");
            goto channel_error;
        }

        session->open_state = libssh2_NB_state_sent;
    }

    if(session->open_state == libssh2_NB_state_sent) {
        rc = _libssh2_packet_requirev(session, reply_codes,
                                      &session->open_data,
                                      &session->open_data_len, 1,
                                      session->open_packet + 5 +
                                      channel_type_len, 4,
                                      &session->open_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN, "Would block");
            return NULL;
        }
        else if(rc) {
            _libssh2_error(session, rc, "Unexpected error");
            goto channel_error;
        }

        if(session->open_data_len < 1) {
            _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                           "Unexpected packet size");
            goto channel_error;
        }

        if(session->open_data[0] == SSH_MSG_CHANNEL_OPEN_CONFIRMATION) {

            if(session->open_data_len < 17) {
                _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                               "Unexpected packet size");
                goto channel_error;
            }

            session->open_channel->remote.id =
                _libssh2_ntohu32(session->open_data + 5);
            session->open_channel->local.window_size =
                _libssh2_ntohu32(session->open_data + 9);
            session->open_channel->local.window_size_initial =
                _libssh2_ntohu32(session->open_data + 9);
            session->open_channel->local.packet_size =
                _libssh2_ntohu32(session->open_data + 13);
            _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                           "Connection Established - ID: %u/%u win: %u/%u"
                           " pack: %u/%u",
                           session->open_channel->local.id,
                           session->open_channel->remote.id,
                           session->open_channel->local.window_size,
                           session->open_channel->remote.window_size,
                           session->open_channel->local.packet_size,
                           session->open_channel->remote.packet_size));
            LIBSSH2_FREE(session, session->open_packet);
            session->open_packet = NULL;
            LIBSSH2_FREE(session, session->open_data);
            session->open_data = NULL;

            session->open_state = libssh2_NB_state_idle;
            return session->open_channel;
        }

        if(session->open_data[0] == SSH_MSG_CHANNEL_OPEN_FAILURE) {
            unsigned int reason_code =
                _libssh2_ntohu32(session->open_data + 5);
            switch(reason_code) {
            case SSH_OPEN_ADMINISTRATIVELY_PROHIBITED:
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Channel open failure "
                               "(administratively prohibited)");
                break;
            case SSH_OPEN_CONNECT_FAILED:
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Channel open failure (connect failed)");
                break;
            case SSH_OPEN_UNKNOWN_CHANNELTYPE:
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Channel open failure (unknown channel type)");
                break;
            case SSH_OPEN_RESOURCE_SHORTAGE:
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Channel open failure (resource shortage)");
                break;
            default:
                _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_FAILURE,
                               "Channel open failure");
            }
        }
    }

channel_error:

    if(session->open_data) {
        LIBSSH2_FREE(session, session->open_data);
        session->open_data = NULL;
    }
    if(session->open_packet) {
        LIBSSH2_FREE(session, session->open_packet);
        session->open_packet = NULL;
    }
    if(session->open_channel) {
        unsigned char channel_id[4];
        LIBSSH2_FREE(session, session->open_channel->channel_type);

        _libssh2_list_remove(&session->open_channel->node);

        /* Clear out packets meant for this channel */
        _libssh2_htonu32(channel_id, session->open_channel->local.id);
        while((_libssh2_packet_ask(session, SSH_MSG_CHANNEL_DATA,
                                   &session->open_data,
                                   &session->open_data_len, 1,
                                   channel_id, 4) >= 0)
              ||
              (_libssh2_packet_ask(session, SSH_MSG_CHANNEL_EXTENDED_DATA,
                                   &session->open_data,
                                   &session->open_data_len, 1,
                                   channel_id, 4) >= 0)) {
            LIBSSH2_FREE(session, session->open_data);
            session->open_data = NULL;
        }

        LIBSSH2_FREE(session, session->open_channel);
        session->open_channel = NULL;
    }

    session->open_state = libssh2_NB_state_idle;
    return NULL;
}

/*
 * libssh2_channel_open_ex
 *
 * Establish a generic session channel
 */
LIBSSH2_API LIBSSH2_CHANNEL *
libssh2_channel_open_ex(LIBSSH2_SESSION *session, const char *type,
                        unsigned int type_len,
                        unsigned int window_size, unsigned int packet_size,
                        const char *msg, unsigned int msg_len)
{
    LIBSSH2_CHANNEL *ptr;

    if(!session)
        return NULL;

    BLOCK_ADJUST_ERRNO(ptr, session,
                       _libssh2_channel_open(session, type, type_len,
                                             window_size, packet_size,
                                             (unsigned char *)msg,
                                             msg_len));
    return ptr;
}

/*
 * libssh2_channel_direct_tcpip_ex
 *
 * Tunnel TCP/IP connect through the SSH session to direct host/port
 */
static LIBSSH2_CHANNEL *
channel_direct_tcpip(LIBSSH2_SESSION * session, const char *host,
                     int port, const char *shost, int sport)
{
    LIBSSH2_CHANNEL *channel;
    unsigned char *s;

    if(session->direct_state == libssh2_NB_state_idle) {
        session->direct_host_len = strlen(host);
        session->direct_shost_len = strlen(shost);
        /* host_len(4) + port(4) + shost_len(4) + sport(4) */
        session->direct_message_len =
            session->direct_host_len + session->direct_shost_len + 16;

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Requesting direct-tcpip session from %s:%d to %s:%d",
                       shost, sport, host, port));

        s = session->direct_message =
            LIBSSH2_ALLOC(session, session->direct_message_len);
        if(!session->direct_message) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate memory for "
                           "direct-tcpip connection");
            return NULL;
        }
        _libssh2_store_str(&s, host, session->direct_host_len);
        _libssh2_store_u32(&s, port);
        _libssh2_store_str(&s, shost, session->direct_shost_len);
        _libssh2_store_u32(&s, sport);
    }

    channel =
        _libssh2_channel_open(session, "direct-tcpip",
                              sizeof("direct-tcpip") - 1,
                              LIBSSH2_CHANNEL_WINDOW_DEFAULT,
                              LIBSSH2_CHANNEL_PACKET_DEFAULT,
                              session->direct_message,
                              session->direct_message_len);

    if(!channel &&
        libssh2_session_last_errno(session) == LIBSSH2_ERROR_EAGAIN) {
        /* The error code is still set to LIBSSH2_ERROR_EAGAIN, set our state
           to created to avoid re-creating the package on next invoke */
        session->direct_state = libssh2_NB_state_created;
        return NULL;
    }
    /* by default we set (keep?) idle state... */
    session->direct_state = libssh2_NB_state_idle;

    LIBSSH2_FREE(session, session->direct_message);
    session->direct_message = NULL;

    return channel;
}

/*
 * libssh2_channel_direct_tcpip_ex
 *
 * Tunnel TCP/IP connect through the SSH session to direct host/port
 */
LIBSSH2_API LIBSSH2_CHANNEL *
libssh2_channel_direct_tcpip_ex(LIBSSH2_SESSION *session, const char *host,
                                int port, const char *shost, int sport)
{
    LIBSSH2_CHANNEL *ptr;

    if(!session)
        return NULL;

    BLOCK_ADJUST_ERRNO(ptr, session,
                       channel_direct_tcpip(session, host, port,
                                            shost, sport));
    return ptr;
}

/*
 * libssh2_channel_direct_streamlocal_ex
 *
 * Tunnel TCP/IP connect through the SSH session to direct UNIX socket
 */
static LIBSSH2_CHANNEL *
channel_direct_streamlocal(LIBSSH2_SESSION * session, const char *socket_path,
                           const char *shost, int sport)
{
    LIBSSH2_CHANNEL *channel;
    unsigned char *s;

    if(session->direct_state == libssh2_NB_state_idle) {
        session->direct_host_len = strlen(socket_path);
        session->direct_shost_len = strlen(shost);
        session->direct_message_len =
            session->direct_host_len + session->direct_shost_len + 12;

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Requesting direct-streamlocal session to %s",
                       socket_path));

        s = session->direct_message =
            LIBSSH2_ALLOC(session, session->direct_message_len);
        if(!session->direct_message) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                "Unable to allocate memory for direct-streamlocal connection");
            return NULL;
        }
        _libssh2_store_str(&s, socket_path, session->direct_host_len);
        _libssh2_store_str(&s, shost, session->direct_shost_len);
        _libssh2_store_u32(&s, sport);
    }

    channel =
        _libssh2_channel_open(session, "direct-streamlocal@openssh.com",
                              sizeof("direct-streamlocal@openssh.com") - 1,
                              LIBSSH2_CHANNEL_WINDOW_DEFAULT,
                              LIBSSH2_CHANNEL_PACKET_DEFAULT,
                              session->direct_message,
                              session->direct_message_len);

    if(!channel &&
        libssh2_session_last_errno(session) == LIBSSH2_ERROR_EAGAIN) {
        /* The error code is still set to LIBSSH2_ERROR_EAGAIN, set our state
           to created to avoid re-creating the package on next invoke */
        session->direct_state = libssh2_NB_state_created;
        return NULL;
    }
    /* by default we set (keep?) idle state... */
    session->direct_state = libssh2_NB_state_idle;

    LIBSSH2_FREE(session, session->direct_message);
    session->direct_message = NULL;

    return channel;
}

/*
 * libssh2_channel_direct_streamlocal_ex
 *
 * Tunnel TCP/IP connect through the SSH session to direct UNIX socket
 */
LIBSSH2_API LIBSSH2_CHANNEL *
libssh2_channel_direct_streamlocal_ex(LIBSSH2_SESSION * session,
                                      const char *socket_path,
                                      const char *shost, int sport)
{
    LIBSSH2_CHANNEL *ptr;

    if(!session)
        return NULL;

    BLOCK_ADJUST_ERRNO(ptr, session,
                       channel_direct_streamlocal(session,
                       socket_path, shost, sport));
    return ptr;
}

/*
 * channel_forward_listen
 *
 * Bind a port on the remote host and listen for connections
 */
static LIBSSH2_LISTENER *
channel_forward_listen(LIBSSH2_SESSION * session, const char *host,
                       int port, int *bound_port, int queue_maxsize)
{
    unsigned char *s;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_REQUEST_SUCCESS, SSH_MSG_REQUEST_FAILURE, 0 };
    int rc;

    if(!host)
        host = "0.0.0.0";

    if(session->fwdLstn_state == libssh2_NB_state_idle) {
        session->fwdLstn_host_len = (uint32_t)strlen(host);
        /* 14 = packet_type(1) + request_len(4) + want_replay(1) + host_len(4)
           + port(4) */
        session->fwdLstn_packet_len =
            session->fwdLstn_host_len +
            (uint32_t)(sizeof("tcpip-forward") - 1) + 14;

        /* Zero the whole thing out */
        memset(&session->fwdLstn_packet_requirev_state, 0,
               sizeof(session->fwdLstn_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Requesting tcpip-forward session for %s:%d", host,
                       port));

        s = session->fwdLstn_packet =
            LIBSSH2_ALLOC(session, session->fwdLstn_packet_len);
        if(!session->fwdLstn_packet) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate memory for setenv packet");
            return NULL;
        }

        *(s++) = SSH_MSG_GLOBAL_REQUEST;
        _libssh2_store_str(&s, "tcpip-forward", sizeof("tcpip-forward") - 1);
        *(s++) = 0x01;          /* want_reply */

        _libssh2_store_str(&s, host, session->fwdLstn_host_len);
        _libssh2_store_u32(&s, port);

        session->fwdLstn_state = libssh2_NB_state_created;
    }

    if(session->fwdLstn_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session,
                                     session->fwdLstn_packet,
                                     session->fwdLstn_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN,
                           "Would block sending global-request packet for "
                           "forward listen request");
            return NULL;
        }
        else if(rc) {
            _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                           "Unable to send global-request packet for forward "
                           "listen request");
            LIBSSH2_FREE(session, session->fwdLstn_packet);
            session->fwdLstn_packet = NULL;
            session->fwdLstn_state = libssh2_NB_state_idle;
            return NULL;
        }
        LIBSSH2_FREE(session, session->fwdLstn_packet);
        session->fwdLstn_packet = NULL;

        session->fwdLstn_state = libssh2_NB_state_sent;
    }

    if(session->fwdLstn_state == libssh2_NB_state_sent) {
        unsigned char *data;
        size_t data_len;
        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      0, NULL, 0,
                                      &session->fwdLstn_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, LIBSSH2_ERROR_EAGAIN, "Would block");
            return NULL;
        }
        else if(rc || (data_len < 1)) {
            _libssh2_error(session, LIBSSH2_ERROR_PROTO, "Unknown");
            session->fwdLstn_state = libssh2_NB_state_idle;
            return NULL;
        }

        if(data[0] == SSH_MSG_REQUEST_SUCCESS) {
            LIBSSH2_LISTENER *listener;

            listener = LIBSSH2_CALLOC(session, sizeof(LIBSSH2_LISTENER));
            if(!listener)
                _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                               "Unable to allocate memory for listener queue");
            else {
                listener->host =
                    LIBSSH2_ALLOC(session, session->fwdLstn_host_len + 1);
                if(!listener->host) {
                    _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                   "Unable to allocate memory "
                                   "for listener queue");
                    LIBSSH2_FREE(session, listener);
                    listener = NULL;
                }
                else {
                    listener->session = session;
                    memcpy(listener->host, host, session->fwdLstn_host_len);
                    listener->host[session->fwdLstn_host_len] = 0;
                    if(data_len >= 5 && !port) {
                        listener->port = _libssh2_ntohu32(data + 1);
                        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                                       "Dynamic tcpip-forward port "
                                       "allocated: %d",
                                       listener->port));
                    }
                    else
                        listener->port = port;

                    listener->queue_size = 0;
                    listener->queue_maxsize = queue_maxsize;

                    /* append this to the parent's list of listeners */
                    _libssh2_list_add(&session->listeners, &listener->node);

                    if(bound_port) {
                        *bound_port = listener->port;
                    }
                }
            }

            LIBSSH2_FREE(session, data);
            session->fwdLstn_state = libssh2_NB_state_idle;
            return listener;
        }
        else if(data[0] == SSH_MSG_REQUEST_FAILURE) {
            LIBSSH2_FREE(session, data);
            _libssh2_error(session, LIBSSH2_ERROR_REQUEST_DENIED,
                           "Unable to complete request for forward-listen");
            session->fwdLstn_state = libssh2_NB_state_idle;
            return NULL;
        }
    }

    session->fwdLstn_state = libssh2_NB_state_idle;

    return NULL;
}

/*
 * libssh2_channel_forward_listen_ex
 *
 * Bind a port on the remote host and listen for connections
 */
LIBSSH2_API LIBSSH2_LISTENER *
libssh2_channel_forward_listen_ex(LIBSSH2_SESSION *session, const char *host,
                                  int port, int *bound_port, int queue_maxsize)
{
    LIBSSH2_LISTENER *ptr;

    if(!session)
        return NULL;

    BLOCK_ADJUST_ERRNO(ptr, session,
                       channel_forward_listen(session, host, port, bound_port,
                                              queue_maxsize));
    return ptr;
}

/*
 * _libssh2_channel_forward_cancel
 *
 * Stop listening on a remote port and free the listener
 * Toss out any pending (un-accept()ed) connections
 *
 * Return 0 on success, LIBSSH2_ERROR_EAGAIN if would block, -1 on error
 */
int _libssh2_channel_forward_cancel(LIBSSH2_LISTENER *listener)
{
    LIBSSH2_SESSION *session = listener->session;
    LIBSSH2_CHANNEL *queued;
    unsigned char *packet, *s;
    size_t host_len = strlen(listener->host);
    /* 14 = packet_type(1) + request_len(4) + want_replay(1) + host_len(4) +
       port(4) */
    size_t packet_len =
        host_len + 14 + sizeof("cancel-tcpip-forward") - 1;
    int rc;
    int retcode = 0;

    if(listener->chanFwdCncl_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Cancelling tcpip-forward session for %s:%d",
                       listener->host, listener->port));

        s = packet = LIBSSH2_ALLOC(session, packet_len);
        if(!packet) {
            _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                           "Unable to allocate memory for setenv packet");
            return LIBSSH2_ERROR_ALLOC;
        }

        *(s++) = SSH_MSG_GLOBAL_REQUEST;
        _libssh2_store_str(&s, "cancel-tcpip-forward",
                           sizeof("cancel-tcpip-forward") - 1);
        *(s++) = 0x00;          /* want_reply */

        _libssh2_store_str(&s, listener->host, host_len);
        _libssh2_store_u32(&s, listener->port);

        listener->chanFwdCncl_state = libssh2_NB_state_created;
    }
    else {
        packet = listener->chanFwdCncl_data;
    }

    if(listener->chanFwdCncl_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, packet, packet_len, NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending forward request");
            listener->chanFwdCncl_data = packet;
            return rc;
        }
        else if(rc) {
            _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                           "Unable to send global-request packet for forward "
                           "listen request");
            /* set the state to something we don't check for, for the
               unfortunate situation where we get an EAGAIN further down
               when trying to bail out due to errors! */
            listener->chanFwdCncl_state = libssh2_NB_state_sent;
            retcode = LIBSSH2_ERROR_SOCKET_SEND;
        }
        LIBSSH2_FREE(session, packet);

        listener->chanFwdCncl_state = libssh2_NB_state_sent;
    }

    queued = _libssh2_list_first(&listener->queue);
    while(queued) {
        LIBSSH2_CHANNEL *next = _libssh2_list_next(&queued->node);

        rc = _libssh2_channel_free(queued);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        queued = next;
    }
    LIBSSH2_FREE(session, listener->host);

    /* remove this entry from the parent's list of listeners */
    _libssh2_list_remove(&listener->node);

    LIBSSH2_FREE(session, listener);

    return retcode;
}

/*
 * libssh2_channel_forward_cancel
 *
 * Stop listening on a remote port and free the listener
 * Toss out any pending (un-accept()ed) connections
 *
 * Return 0 on success, LIBSSH2_ERROR_EAGAIN if would block, -1 on error
 */
LIBSSH2_API int
libssh2_channel_forward_cancel(LIBSSH2_LISTENER *listener)
{
    int rc;

    if(!listener)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, listener->session,
                 _libssh2_channel_forward_cancel(listener));
    return rc;
}

/*
 * channel_forward_accept
 *
 * Accept a connection
 */
static LIBSSH2_CHANNEL *
channel_forward_accept(LIBSSH2_LISTENER *listener)
{
    int rc;

    do {
        rc = _libssh2_transport_read(listener->session);
    } while(rc > 0);

    if(_libssh2_list_first(&listener->queue)) {
        LIBSSH2_CHANNEL *channel = _libssh2_list_first(&listener->queue);

        /* detach channel from listener's queue */
        _libssh2_list_remove(&channel->node);

        listener->queue_size--;

        /* add channel to session's channel list */
        _libssh2_list_add(&channel->session->channels, &channel->node);

        return channel;
    }

    if(rc == LIBSSH2_ERROR_EAGAIN) {
        _libssh2_error(listener->session, LIBSSH2_ERROR_EAGAIN,
                       "Would block waiting for packet");
    }
    else
        _libssh2_error(listener->session, LIBSSH2_ERROR_CHANNEL_UNKNOWN,
                       "Channel not found");
    return NULL;
}

/*
 * libssh2_channel_forward_accept
 *
 * Accept a connection
 */
LIBSSH2_API LIBSSH2_CHANNEL *
libssh2_channel_forward_accept(LIBSSH2_LISTENER *listener)
{
    LIBSSH2_CHANNEL *ptr;

    if(!listener)
        return NULL;

    BLOCK_ADJUST_ERRNO(ptr, listener->session,
                       channel_forward_accept(listener));
    return ptr;

}

/*
 * channel_setenv
 *
 * Set an environment variable prior to requesting a shell/program/subsystem
 */
static int channel_setenv(LIBSSH2_CHANNEL *channel,
                          const char *varname, unsigned int varname_len,
                          const char *value, unsigned int value_len)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s, *data;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_CHANNEL_SUCCESS, SSH_MSG_CHANNEL_FAILURE, 0 };
    size_t data_len;
    int rc;

    if(channel->setenv_state == libssh2_NB_state_idle) {
        /* 21 = packet_type(1) + channel_id(4) + request_len(4) +
         * request(3)"env" + want_reply(1) + varname_len(4) + value_len(4) */
        channel->setenv_packet_len = varname_len + value_len + 21;

        /* Zero the whole thing out */
        memset(&channel->setenv_packet_requirev_state, 0,
               sizeof(channel->setenv_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Setting remote environment variable: %s=%s on "
                       "channel %u/%u",
                       varname, value, channel->local.id, channel->remote.id));

        s = channel->setenv_packet =
            LIBSSH2_ALLOC(session, channel->setenv_packet_len);
        if(!channel->setenv_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory "
                                  "for setenv packet");
        }

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, "env", sizeof("env") - 1);
        *(s++) = 0x01;
        _libssh2_store_str(&s, varname, varname_len);
        _libssh2_store_str(&s, value, value_len);

        channel->setenv_state = libssh2_NB_state_created;
    }

    if(channel->setenv_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session,
                                     channel->setenv_packet,
                                     channel->setenv_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending setenv request");
            return rc;
        }
        else if(rc) {
            LIBSSH2_FREE(session, channel->setenv_packet);
            channel->setenv_packet = NULL;
            channel->setenv_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                                  "Unable to send channel-request packet for "
                                  "setenv request");
        }
        LIBSSH2_FREE(session, channel->setenv_packet);
        channel->setenv_packet = NULL;

        _libssh2_htonu32(channel->setenv_local_channel, channel->local.id);

        channel->setenv_state = libssh2_NB_state_sent;
    }

    if(channel->setenv_state == libssh2_NB_state_sent) {
        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      1, channel->setenv_local_channel, 4,
                                      &channel->
                                      setenv_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        if(rc) {
            channel->setenv_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Failed getting response for "
                                  "channel-setenv");
        }
        else if(data_len < 1) {
            channel->setenv_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                                  "Unexpected packet size");
        }

        if(data[0] == SSH_MSG_CHANNEL_SUCCESS) {
            LIBSSH2_FREE(session, data);
            channel->setenv_state = libssh2_NB_state_idle;
            return 0;
        }

        LIBSSH2_FREE(session, data);
    }

    channel->setenv_state = libssh2_NB_state_idle;
    return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED,
                          "Unable to complete request for channel-setenv");
}

/*
 * libssh2_channel_setenv_ex
 *
 * Set an environment variable prior to requesting a shell/program/subsystem
 */
LIBSSH2_API int
libssh2_channel_setenv_ex(LIBSSH2_CHANNEL *channel,
                          const char *varname, unsigned int varname_len,
                          const char *value, unsigned int value_len)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 channel_setenv(channel, varname, varname_len,
                                value, value_len));
    return rc;
}

/*
 * channel_request_pty
 * Duh... Request a PTY
 */
static int channel_request_pty(LIBSSH2_CHANNEL *channel,
                               const char *term, unsigned int term_len,
                               const char *modes, unsigned int modes_len,
                               int width, int height,
                               int width_px, int height_px)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_CHANNEL_SUCCESS, SSH_MSG_CHANNEL_FAILURE, 0 };
    int rc;

    if(channel->reqPTY_state == libssh2_NB_state_idle) {
        /* 41 = packet_type(1) + channel(4) + pty_req_len(4) + "pty_req"(7) +
         * want_reply(1) + term_len(4) + width(4) + height(4) + width_px(4) +
         * height_px(4) + modes_len(4) */
        if(term_len + modes_len > 256) {
            return _libssh2_error(session, LIBSSH2_ERROR_INVAL,
                                  "term + mode lengths too large");
        }

        channel->reqPTY_packet_len = term_len + modes_len + 41;

        /* Zero the whole thing out */
        memset(&channel->reqPTY_packet_requirev_state, 0,
               sizeof(channel->reqPTY_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Allocating tty on channel %u/%u", channel->local.id,
                       channel->remote.id));

        s = channel->reqPTY_packet;

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, (char *)"pty-req", sizeof("pty-req") - 1);

        *(s++) = 0x01;

        _libssh2_store_str(&s, term, term_len);
        _libssh2_store_u32(&s, width);
        _libssh2_store_u32(&s, height);
        _libssh2_store_u32(&s, width_px);
        _libssh2_store_u32(&s, height_px);
        _libssh2_store_str(&s, modes, modes_len);

        channel->reqPTY_state = libssh2_NB_state_created;
    }

    if(channel->reqPTY_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, channel->reqPTY_packet,
                                     channel->reqPTY_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending pty request");
            return rc;
        }
        else if(rc) {
            channel->reqPTY_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Unable to send pty-request packet");
        }
        _libssh2_htonu32(channel->reqPTY_local_channel, channel->local.id);

        channel->reqPTY_state = libssh2_NB_state_sent;
    }

    if(channel->reqPTY_state == libssh2_NB_state_sent) {
        unsigned char *data;
        size_t data_len;
        unsigned char code;
        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      1, channel->reqPTY_local_channel, 4,
                                      &channel->reqPTY_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if(rc || data_len < 1) {
            channel->reqPTY_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                                  "Failed to require the PTY package");
        }

        code = data[0];

        LIBSSH2_FREE(session, data);
        channel->reqPTY_state = libssh2_NB_state_idle;

        if(code == SSH_MSG_CHANNEL_SUCCESS)
            return 0;
    }

    return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED,
                          "Unable to complete request for "
                          "channel request-pty");
}

/**
 * channel_request_auth_agent
 * The actual re-entrant method which requests an auth agent.
 * */
static int channel_request_auth_agent(LIBSSH2_CHANNEL *channel,
                                      const char *request_str,
                                      int request_str_len)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_CHANNEL_SUCCESS, SSH_MSG_CHANNEL_FAILURE, 0 };
    int rc;

    if(channel->req_auth_agent_state == libssh2_NB_state_idle) {
        /* Only valid options are "auth-agent-req" and
         * "auth-agent-req_at_openssh.com" so we make sure it is not
         * actually longer than the longest possible. */
        if(request_str_len > 26) {
            return _libssh2_error(session, LIBSSH2_ERROR_INVAL,
                                  "request_str length too large");
        }

        /*
         *  Length: 24 or 36 = packet_type(1) + channel(4) + req_len(4) +
         *    request_str (variable) + want_reply (1) */
        channel->req_auth_agent_packet_len = 10 + request_str_len;

        /* Zero out the requireev state to reset */
        memset(&channel->req_auth_agent_requirev_state, 0,
               sizeof(channel->req_auth_agent_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Requesting auth agent on channel %u/%u",
                       channel->local.id, channel->remote.id));

        /*
         *  byte      SSH_MSG_CHANNEL_REQUEST
         *  uint32    recipient channel
         *  string    "auth-agent-req"
         *  boolean   want reply
         * */
        s = channel->req_auth_agent_packet;
        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, (char *)request_str, request_str_len);
        *(s++) = 0x01;

        channel->req_auth_agent_state = libssh2_NB_state_created;
    }

    if(channel->req_auth_agent_state == libssh2_NB_state_created) {
        /* Send the packet, we can use sizeof() on the packet because it
         * is always completely filled; there are no variable length fields. */
        rc = _libssh2_transport_send(session, channel->req_auth_agent_packet,
                                     channel->req_auth_agent_packet_len,
                                     NULL, 0);

        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending auth-agent request");
            return rc;
        }
        else if(rc) {
            channel->req_auth_agent_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Unable to send auth-agent request");
        }
        _libssh2_htonu32(channel->req_auth_agent_local_channel,
                         channel->local.id);
        channel->req_auth_agent_state = libssh2_NB_state_sent;
    }

    if(channel->req_auth_agent_state == libssh2_NB_state_sent) {
        unsigned char *data;
        size_t data_len;
        unsigned char code;

        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      1, channel->req_auth_agent_local_channel,
                                      4,
                                      &channel->req_auth_agent_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if(rc) {
            channel->req_auth_agent_state = libssh2_NB_state_idle;
            return _libssh2_error(session, LIBSSH2_ERROR_PROTO,
                                  "Failed to request auth-agent");
        }

        code = data[0];

        LIBSSH2_FREE(session, data);
        channel->req_auth_agent_state = libssh2_NB_state_idle;

        if(code == SSH_MSG_CHANNEL_SUCCESS)
            return 0;
    }

    return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED,
                          "Unable to complete request for auth-agent");
}

/*
 * libssh2_channel_request_auth_agent
 *
 * Requests that agent forwarding be enabled for the session. The
 * request must be sent over a specific channel, which starts the agent
 * listener on the remote side. Once the channel is closed, the agent
 * listener continues to exist.
 */
LIBSSH2_API int
libssh2_channel_request_auth_agent(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    rc = LIBSSH2_ERROR_CHANNEL_UNKNOWN;

    /* The current RFC draft for agent forwarding says you're supposed to
     * send "auth-agent-req," but most SSH servers out there right now
     * actually expect "auth-agent-req@openssh.com", so we try that
     * first. */
    if(channel->req_auth_agent_try_state == libssh2_NB_state_idle) {
        BLOCK_ADJUST(rc, channel->session,
                     channel_request_auth_agent(channel,
                                                "auth-agent-req@openssh.com",
                                                26));

        /* If we failed (but not with EAGAIN), then we move onto
         * the next step to try another request type. */
        if(rc != LIBSSH2_ERROR_NONE &&
           rc != LIBSSH2_ERROR_EAGAIN)
            channel->req_auth_agent_try_state = libssh2_NB_state_sent;
    }

    if(channel->req_auth_agent_try_state == libssh2_NB_state_sent) {
        BLOCK_ADJUST(rc, channel->session,
                     channel_request_auth_agent(channel,
                                                "auth-agent-req", 14));

        /* If we failed without an EAGAIN, then move on with this
         * state machine. */
        if(rc != LIBSSH2_ERROR_NONE &&
           rc != LIBSSH2_ERROR_EAGAIN)
            channel->req_auth_agent_try_state = libssh2_NB_state_sent1;
    }

    /* If things are good, reset the try state. */
    if(rc == LIBSSH2_ERROR_NONE)
        channel->req_auth_agent_try_state = libssh2_NB_state_idle;

    return rc;
}

/*
 * libssh2_channel_request_pty_ex
 * Duh... Request a PTY
 */
LIBSSH2_API int
libssh2_channel_request_pty_ex(LIBSSH2_CHANNEL *channel, const char *term,
                               unsigned int term_len, const char *modes,
                               unsigned int modes_len, int width, int height,
                               int width_px, int height_px)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 channel_request_pty(channel, term, term_len, modes,
                                     modes_len, width, height,
                                     width_px, height_px));
    return rc;
}

static int
channel_request_pty_size(LIBSSH2_CHANNEL * channel, int width,
                         int height, int width_px, int height_px)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s;
    int rc;
    int retcode = LIBSSH2_ERROR_PROTO;

    if(channel->reqPTY_state == libssh2_NB_state_idle) {
        channel->reqPTY_packet_len = 39;

        /* Zero the whole thing out */
        memset(&channel->reqPTY_packet_requirev_state, 0,
               sizeof(channel->reqPTY_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "changing tty size on channel %u/%u",
                       channel->local.id,
                       channel->remote.id));

        s = channel->reqPTY_packet;

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, (char *)"window-change",
                           sizeof("window-change") - 1);
        *(s++) = 0x00; /* Don't reply */
        _libssh2_store_u32(&s, width);
        _libssh2_store_u32(&s, height);
        _libssh2_store_u32(&s, width_px);
        _libssh2_store_u32(&s, height_px);

        channel->reqPTY_state = libssh2_NB_state_created;
    }

    if(channel->reqPTY_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, channel->reqPTY_packet,
                                     channel->reqPTY_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending window-change request");
            return rc;
        }
        else if(rc) {
            channel->reqPTY_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Unable to send window-change packet");
        }
        _libssh2_htonu32(channel->reqPTY_local_channel, channel->local.id);
        retcode = LIBSSH2_ERROR_NONE;
    }

    channel->reqPTY_state = libssh2_NB_state_idle;
    return retcode;
}

LIBSSH2_API int
libssh2_channel_request_pty_size_ex(LIBSSH2_CHANNEL *channel, int width,
                                    int height, int width_px, int height_px)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 channel_request_pty_size(channel, width, height, width_px,
                                          height_px));
    return rc;
}

/* Keep this an even number */
#define LIBSSH2_X11_RANDOM_COOKIE_LEN       32

/*
 * channel_x11_req
 * Request X11 forwarding
 */
static int
channel_x11_req(LIBSSH2_CHANNEL *channel, int single_connection,
                const char *auth_proto, const char *auth_cookie,
                int screen_number)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_CHANNEL_SUCCESS, SSH_MSG_CHANNEL_FAILURE, 0 };
    size_t proto_len =
        auth_proto ? strlen(auth_proto) : (sizeof("MIT-MAGIC-COOKIE-1") - 1);
    size_t cookie_len =
        auth_cookie ? strlen(auth_cookie) : LIBSSH2_X11_RANDOM_COOKIE_LEN;
    int rc;

    if(channel->reqX11_state == libssh2_NB_state_idle) {
        /* 30 = packet_type(1) + channel(4) + x11_req_len(4) + "x11-req"(7) +
         * want_reply(1) + single_cnx(1) + proto_len(4) + cookie_len(4) +
         * screen_num(4) */
        channel->reqX11_packet_len = proto_len + cookie_len + 30;

        /* Zero the whole thing out */
        memset(&channel->reqX11_packet_requirev_state, 0,
               sizeof(channel->reqX11_packet_requirev_state));

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Requesting x11-req for channel %u/%u: single=%d "
                       "proto=%s cookie=%s screen=%d",
                       channel->local.id, channel->remote.id,
                       single_connection,
                       auth_proto ? auth_proto : "MIT-MAGIC-COOKIE-1",
                       auth_cookie ? auth_cookie : "<random>", screen_number));

        s = channel->reqX11_packet =
            LIBSSH2_ALLOC(session, channel->reqX11_packet_len);
        if(!channel->reqX11_packet) {
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for pty-request");
        }

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, "x11-req", sizeof("x11-req") - 1);

        *(s++) = 0x01;          /* want_reply */
        *(s++) = single_connection ? 0x01 : 0x00;

        _libssh2_store_str(&s, auth_proto ? auth_proto : "MIT-MAGIC-COOKIE-1",
                           proto_len);

        _libssh2_store_u32(&s, (uint32_t)cookie_len);
        if(auth_cookie) {
            memcpy(s, auth_cookie, cookie_len);
        }
        else {
            int i;
            /* note: the extra +1 below is necessary since the sprintf()
               loop will always write 3 bytes so the last one will write
               the trailing zero at the LIBSSH2_X11_RANDOM_COOKIE_LEN/2
               border */
            unsigned char buffer[(LIBSSH2_X11_RANDOM_COOKIE_LEN / 2) + 1];

            if(_libssh2_random(buffer, LIBSSH2_X11_RANDOM_COOKIE_LEN / 2)) {
                return _libssh2_error(session, LIBSSH2_ERROR_RANDGEN,
                                      "Unable to get random bytes "
                                      "for x11-req cookie");
            }
            for(i = 0; i < (LIBSSH2_X11_RANDOM_COOKIE_LEN / 2); i++) {
                snprintf((char *)&s[i*2], 3, "%02X", buffer[i]);
            }
        }
        s += cookie_len;

        _libssh2_store_u32(&s, screen_number);
        channel->reqX11_state = libssh2_NB_state_created;
    }

    if(channel->reqX11_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, channel->reqX11_packet,
                                     channel->reqX11_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending X11-req packet");
            return rc;
        }
        if(rc) {
            LIBSSH2_FREE(session, channel->reqX11_packet);
            channel->reqX11_packet = NULL;
            channel->reqX11_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Unable to send x11-req packet");
        }
        LIBSSH2_FREE(session, channel->reqX11_packet);
        channel->reqX11_packet = NULL;

        _libssh2_htonu32(channel->reqX11_local_channel, channel->local.id);

        channel->reqX11_state = libssh2_NB_state_sent;
    }

    if(channel->reqX11_state == libssh2_NB_state_sent) {
        size_t data_len;
        unsigned char *data;
        unsigned char code;

        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      1, channel->reqX11_local_channel, 4,
                                      &channel->reqX11_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if(rc || data_len < 1) {
            channel->reqX11_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "waiting for x11-req response packet");
        }

        code = data[0];
        LIBSSH2_FREE(session, data);
        channel->reqX11_state = libssh2_NB_state_idle;

        if(code == SSH_MSG_CHANNEL_SUCCESS)
            return 0;
    }

    return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED,
                          "Unable to complete request for channel x11-req");
}

/*
 * libssh2_channel_x11_req_ex
 * Request X11 forwarding
 */
LIBSSH2_API int
libssh2_channel_x11_req_ex(LIBSSH2_CHANNEL *channel, int single_connection,
                           const char *auth_proto, const char *auth_cookie,
                           int screen_number)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 channel_x11_req(channel, single_connection, auth_proto,
                                 auth_cookie, screen_number));
    return rc;
}


/*
 * _libssh2_channel_process_startup
 *
 * Primitive for libssh2_channel_(shell|exec|subsystem)
 */
int
_libssh2_channel_process_startup(LIBSSH2_CHANNEL *channel,
                                 const char *request, size_t request_len,
                                 const char *message, size_t message_len)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char *s;
    static const unsigned char reply_codes[3] =
        { SSH_MSG_CHANNEL_SUCCESS, SSH_MSG_CHANNEL_FAILURE, 0 };
    int rc;

    if(channel->process_state == libssh2_NB_state_end) {
        return _libssh2_error(session, LIBSSH2_ERROR_BAD_USE,
                              "Channel can not be reused");
    }

    if(channel->process_state == libssh2_NB_state_idle) {
        /* 10 = packet_type(1) + channel(4) + request_len(4) + want_reply(1) */
        channel->process_packet_len = request_len + 10;

        /* Zero the whole thing out */
        memset(&channel->process_packet_requirev_state, 0,
               sizeof(channel->process_packet_requirev_state));

        if(message)
            channel->process_packet_len += + 4;

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "starting request(%s) on channel %u/%u, message=%s",
                       request, channel->local.id, channel->remote.id,
                       message ? message : "<null>"));
        s = channel->process_packet =
            LIBSSH2_ALLOC(session, channel->process_packet_len);
        if(!channel->process_packet)
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory "
                                  "for channel-process request");

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, request, request_len);
        *(s++) = 0x01;

        if(message)
            _libssh2_store_u32(&s, (uint32_t)message_len);

        channel->process_state = libssh2_NB_state_created;
    }

    if(channel->process_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session,
                                     channel->process_packet,
                                     channel->process_packet_len,
                                     (unsigned char *)message, message_len);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending channel request");
            return rc;
        }
        else if(rc) {
            LIBSSH2_FREE(session, channel->process_packet);
            channel->process_packet = NULL;
            channel->process_state = libssh2_NB_state_end;
            return _libssh2_error(session, rc,
                                  "Unable to send channel request");
        }
        LIBSSH2_FREE(session, channel->process_packet);
        channel->process_packet = NULL;

        _libssh2_htonu32(channel->process_local_channel, channel->local.id);

        channel->process_state = libssh2_NB_state_sent;
    }

    if(channel->process_state == libssh2_NB_state_sent) {
        unsigned char *data;
        size_t data_len;
        unsigned char code;
        rc = _libssh2_packet_requirev(session, reply_codes, &data, &data_len,
                                      1, channel->process_local_channel, 4,
                                      &channel->process_packet_requirev_state);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if(rc || data_len < 1) {
            channel->process_state = libssh2_NB_state_end;
            return _libssh2_error(session, rc,
                                  "Failed waiting for channel success");
        }

        code = data[0];
        LIBSSH2_FREE(session, data);
        channel->process_state = libssh2_NB_state_end;

        if(code == SSH_MSG_CHANNEL_SUCCESS)
            return 0;
    }

    return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_REQUEST_DENIED,
                          "Unable to complete request for "
                          "channel-process-startup");
}

/*
 * libssh2_channel_process_startup
 *
 * Primitive for libssh2_channel_(shell|exec|subsystem)
 */
LIBSSH2_API int
libssh2_channel_process_startup(LIBSSH2_CHANNEL *channel,
                                const char *req, unsigned int req_len,
                                const char *msg, unsigned int msg_len)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_process_startup(channel, req, req_len,
                                                  msg, msg_len));
    return rc;
}


/*
 * libssh2_channel_set_blocking
 *
 * Set a channel's BEHAVIOR blocking on or off. The socket will remain non-
 * blocking.
 */
LIBSSH2_API void
libssh2_channel_set_blocking(LIBSSH2_CHANNEL * channel, int blocking)
{
    if(channel)
        (void)_libssh2_session_set_blocking(channel->session, blocking);
}

/*
 * _libssh2_channel_flush
 *
 * Flush data from one (or all) stream
 * Returns number of bytes flushed, or negative on failure
 */
int
_libssh2_channel_flush(LIBSSH2_CHANNEL *channel, int streamid)
{
    if(channel->flush_state == libssh2_NB_state_idle) {
        LIBSSH2_PACKET *packet =
            _libssh2_list_first(&channel->session->packets);
        channel->flush_refund_bytes = 0;
        channel->flush_flush_bytes = 0;

        while(packet) {
            unsigned char packet_type;
            LIBSSH2_PACKET *next = _libssh2_list_next(&packet->node);

            if(packet->data_len < 1) {
                packet = next;
                _libssh2_debug((channel->session, LIBSSH2_TRACE_ERROR,
                               "Unexpected packet length"));
                continue;
            }

            packet_type = packet->data[0];

            if(((packet_type == SSH_MSG_CHANNEL_DATA)
                || (packet_type == SSH_MSG_CHANNEL_EXTENDED_DATA))
               && ((packet->data_len >= 5)
                   && (_libssh2_ntohu32(packet->data + 1)
                       == channel->local.id))) {
                /* It's our channel at least */
                int packet_stream_id;

                if(packet_type == SSH_MSG_CHANNEL_DATA) {
                    packet_stream_id = 0;
                }
                else if(packet->data_len >= 9) {
                    packet_stream_id = _libssh2_ntohu32(packet->data + 5);
                }
                else {
                    channel->flush_state = libssh2_NB_state_idle;
                    return _libssh2_error(channel->session,
                                          LIBSSH2_ERROR_PROTO,
                                          "Unexpected packet length");
                }

                if((streamid == LIBSSH2_CHANNEL_FLUSH_ALL)
                    || ((packet_type == SSH_MSG_CHANNEL_EXTENDED_DATA)
                        && ((streamid == LIBSSH2_CHANNEL_FLUSH_EXTENDED_DATA)
                            || (streamid == packet_stream_id)))
                    || ((packet_type == SSH_MSG_CHANNEL_DATA)
                        && (streamid == 0))) {
                    size_t bytes_to_flush = packet->data_len -
                        packet->data_head;

                    _libssh2_debug((channel->session, LIBSSH2_TRACE_CONN,
                                   "Flushing %ld bytes of data from stream "
                                   "%d on channel %u/%u",
                                   (long)bytes_to_flush, packet_stream_id,
                                   channel->local.id, channel->remote.id));

                    /* It's one of the streams we wanted to flush */
                    channel->flush_refund_bytes += packet->data_len - 13;
                    channel->flush_flush_bytes += bytes_to_flush;

                    LIBSSH2_FREE(channel->session, packet->data);

                    /* remove this packet from the parent's list */
                    _libssh2_list_remove(&packet->node);
                    LIBSSH2_FREE(channel->session, packet);
                }
            }
            packet = next;
        }

        channel->flush_state = libssh2_NB_state_created;
    }

    channel->read_avail -= channel->flush_flush_bytes;
    channel->remote.window_size -= (uint32_t)channel->flush_flush_bytes;

    if(channel->flush_refund_bytes) {
        int rc =
            _libssh2_channel_receive_window_adjust(channel,
                                         (uint32_t)channel->flush_refund_bytes,
                                         1, NULL);
        if(rc == LIBSSH2_ERROR_EAGAIN)
            return rc;
    }

    channel->flush_state = libssh2_NB_state_idle;

    return (int)channel->flush_flush_bytes;
}

/*
 * libssh2_channel_flush_ex
 *
 * Flush data from one (or all) stream
 * Returns number of bytes flushed, or negative on failure
 */
LIBSSH2_API int
libssh2_channel_flush_ex(LIBSSH2_CHANNEL *channel, int stream)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_flush(channel, stream));
    return rc;
}

/*
 * libssh2_channel_get_exit_status
 *
 * Return the channel's program exit status. Note that the actual protocol
 * provides the full 32bit this function returns.  We cannot abuse it to
 * return error values in case of errors so we return a zero if channel is
 * NULL.
 */
LIBSSH2_API int
libssh2_channel_get_exit_status(LIBSSH2_CHANNEL *channel)
{
    if(!channel)
        return 0;

    return channel->exit_status;
}

/*
 * libssh2_channel_get_exit_signal
 *
 * Get exit signal (without leading "SIG"), error message, and language
 * tag into newly allocated buffers of indicated length.  Caller can
 * use NULL pointers to indicate that the value should not be set.  The
 * *_len variables are set if they are non-NULL even if the
 * corresponding string parameter is NULL.  Returns LIBSSH2_ERROR_NONE
 * on success, or an API error code.
 */
LIBSSH2_API int
libssh2_channel_get_exit_signal(LIBSSH2_CHANNEL *channel,
                                char **exitsignal,
                                size_t *exitsignal_len,
                                char **errmsg,
                                size_t *errmsg_len,
                                char **langtag,
                                size_t *langtag_len)
{
    size_t namelen = 0;

    if(channel) {
        LIBSSH2_SESSION *session = channel->session;

        if(channel->exit_signal) {
            namelen = strlen(channel->exit_signal);
            if(exitsignal) {
                *exitsignal = LIBSSH2_ALLOC(session, namelen + 1);
                if(!*exitsignal) {
                    return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for signal name");
                }
                memcpy(*exitsignal, channel->exit_signal, namelen);
                (*exitsignal)[namelen] = '\0';
            }
            if(exitsignal_len)
                *exitsignal_len = namelen;
        }
        else {
            if(exitsignal)
                *exitsignal = NULL;
            if(exitsignal_len)
                *exitsignal_len = 0;
        }

        /* TODO: set error message and language tag */

        if(errmsg)
            *errmsg = NULL;

        if(errmsg_len)
            *errmsg_len = 0;

        if(langtag)
            *langtag = NULL;

        if(langtag_len)
            *langtag_len = 0;
    }

    return LIBSSH2_ERROR_NONE;
}

/*
 * _libssh2_channel_receive_window_adjust
 *
 * Adjust the receive window for a channel by adjustment bytes. If the amount
 * to be adjusted is less than LIBSSH2_CHANNEL_MINADJUST and force is 0 the
 * adjustment amount will be queued for a later packet.
 *
 * Calls _libssh2_error() !
 */
int
_libssh2_channel_receive_window_adjust(LIBSSH2_CHANNEL * channel,
                                       uint32_t adjustment,
                                       unsigned char force,
                                       unsigned int *store)
{
    int rc;

    if(store)
        *store = channel->remote.window_size;

    if(channel->adjust_state == libssh2_NB_state_idle) {
        if(!force
            && (adjustment + channel->adjust_queue <
                LIBSSH2_CHANNEL_MINADJUST)) {
            _libssh2_debug((channel->session, LIBSSH2_TRACE_CONN,
                           "Queueing %u bytes for receive window adjustment "
                           "for channel %u/%u",
                           adjustment, channel->local.id, channel->remote.id));
            channel->adjust_queue += adjustment;
            return 0;
        }

        if(!adjustment && !channel->adjust_queue) {
            return 0;
        }

        adjustment += channel->adjust_queue;
        channel->adjust_queue = 0;

        /* Adjust the window based on the block we just freed */
        channel->adjust_adjust[0] = SSH_MSG_CHANNEL_WINDOW_ADJUST;
        _libssh2_htonu32(&channel->adjust_adjust[1], channel->remote.id);
        _libssh2_htonu32(&channel->adjust_adjust[5], adjustment);
        _libssh2_debug((channel->session, LIBSSH2_TRACE_CONN,
                       "Adjusting window %u bytes for data on "
                       "channel %u/%u",
                       adjustment, channel->local.id, channel->remote.id));

        channel->adjust_state = libssh2_NB_state_created;
    }

    rc = _libssh2_transport_send(channel->session, channel->adjust_adjust, 9,
                                 NULL, 0);
    if(rc == LIBSSH2_ERROR_EAGAIN) {
        _libssh2_error(channel->session, rc,
                       "Would block sending window adjust");
        return rc;
    }
    else if(rc) {
        channel->adjust_queue = adjustment;
        return _libssh2_error(channel->session, LIBSSH2_ERROR_SOCKET_SEND,
                              "Unable to send transfer-window adjustment "
                              "packet, deferring");
    }
    else {
        channel->remote.window_size += adjustment;
    }

    channel->adjust_state = libssh2_NB_state_idle;

    return 0;
}

#ifndef LIBSSH2_NO_DEPRECATED
/*
 * libssh2_channel_receive_window_adjust (DEPRECATED, DO NOT USE!)
 *
 * Adjust the receive window for a channel by adjustment bytes. If the amount
 * to be adjusted is less than LIBSSH2_CHANNEL_MINADJUST and force is 0 the
 * adjustment amount will be queued for a later packet.
 *
 * Returns the new size of the receive window (as understood by remote end).
 * Note that it might return EAGAIN too which is highly stupid.
 *
 */
LIBSSH2_API unsigned long
libssh2_channel_receive_window_adjust(LIBSSH2_CHANNEL *channel,
                                      unsigned long adj,
                                      unsigned char force)
{
    unsigned int window;
    int rc;

    if(!channel)
        return (unsigned long)LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_receive_window_adjust(channel,
                                                        (uint32_t)adj,
                                                        force, &window));

    /* stupid - but this is how it was made to work before and this is just
       kept for backwards compatibility */
    return rc ? (unsigned long)rc : window;
}
#endif

/*
 * libssh2_channel_receive_window_adjust2
 *
 * Adjust the receive window for a channel by adjustment bytes. If the amount
 * to be adjusted is less than LIBSSH2_CHANNEL_MINADJUST and force is 0 the
 * adjustment amount will be queued for a later packet.
 *
 * Stores the new size of the receive window in the data 'window' points to.
 *
 * Returns the "normal" error code: 0 for success, negative for failure.
 */
LIBSSH2_API int
libssh2_channel_receive_window_adjust2(LIBSSH2_CHANNEL *channel,
                                       unsigned long adj,
                                       unsigned char force,
                                       unsigned int *window)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_receive_window_adjust(channel,
                                                        (uint32_t)adj,
                                                        force, window));
    return rc;
}

int
_libssh2_channel_extended_data(LIBSSH2_CHANNEL *channel, int ignore_mode)
{
    if(channel->extData2_state == libssh2_NB_state_idle) {
        _libssh2_debug((channel->session, LIBSSH2_TRACE_CONN,
                       "Setting channel %u/%u handle_extended_data"
                       " mode to %d",
                       channel->local.id, channel->remote.id, ignore_mode));
        channel->remote.extended_data_ignore_mode = (char)ignore_mode;

        channel->extData2_state = libssh2_NB_state_created;
    }

    if(channel->extData2_state == libssh2_NB_state_idle) {
        if(ignore_mode == LIBSSH2_CHANNEL_EXTENDED_DATA_IGNORE) {
            int rc =
                _libssh2_channel_flush(channel,
                                       LIBSSH2_CHANNEL_FLUSH_EXTENDED_DATA);
            if(LIBSSH2_ERROR_EAGAIN == rc)
                return rc;
        }
    }

    channel->extData2_state = libssh2_NB_state_idle;
    return 0;
}

/*
 * libssh2_channel_handle_extended_data2
 *
 */
LIBSSH2_API int
libssh2_channel_handle_extended_data2(LIBSSH2_CHANNEL *channel,
                                      int mode)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, _libssh2_channel_extended_data(channel,
                                                                      mode));
    return rc;
}

#ifndef LIBSSH2_NO_DEPRECATED
/*
 * libssh2_channel_handle_extended_data (DEPRECATED, DO NOT USE!)
 *
 * How should extended data look to the calling app?  Keep it in separate
 * channels[_read() _read_stdder()]? (NORMAL) Merge the extended data to the
 * standard data? [everything via _read()]? (MERGE) Ignore it entirely [toss
 * out packets as they come in]? (IGNORE)
 */
LIBSSH2_API void
libssh2_channel_handle_extended_data(LIBSSH2_CHANNEL *channel,
                                     int ignore_mode)
{
    (void)libssh2_channel_handle_extended_data2(channel, ignore_mode);
}
#endif


/*
 * _libssh2_channel_read
 *
 * Read data from a channel
 *
 * It is important to not return 0 until the currently read channel is
 * complete. If we read stuff from the wire but it was no payload data to fill
 * in the buffer with, we MUST make sure to return LIBSSH2_ERROR_EAGAIN.
 *
 * The receive window must be maintained (enlarged) by the user of this
 * function.
 */
ssize_t _libssh2_channel_read(LIBSSH2_CHANNEL *channel, int stream_id,
                              char *buf, size_t buflen)
{
    LIBSSH2_SESSION *session = channel->session;
    int rc;
    size_t bytes_read = 0;
    size_t bytes_want;
    int unlink_packet;
    LIBSSH2_PACKET *read_packet;
    LIBSSH2_PACKET *read_next;

    _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                   "channel_read() wants %ld bytes from channel %u/%u "
                   "stream #%d",
                   (long)buflen, channel->local.id, channel->remote.id,
                   stream_id));

    /* expand the receiving window first if it has become too narrow */
    if((channel->read_state == libssh2_NB_state_jump1) ||
       (channel->remote.window_size <
        channel->remote.window_size_initial / 4 * 3 + buflen)) {

        uint32_t adjustment = (uint32_t)(channel->remote.window_size_initial +
            buflen - channel->remote.window_size);
        if(adjustment < LIBSSH2_CHANNEL_MINADJUST)
            adjustment = LIBSSH2_CHANNEL_MINADJUST;

        /* the actual window adjusting may not finish so we need to deal with
           this special state here */
        channel->read_state = libssh2_NB_state_jump1;
        rc = _libssh2_channel_receive_window_adjust(channel, adjustment,
                                                    0, NULL);
        if(rc)
            return rc;

        channel->read_state = libssh2_NB_state_idle;
    }

    /* Process all pending incoming packets. Tests prove that this way
       produces faster transfers. */
    do {
        rc = _libssh2_transport_read(session);
    } while(rc > 0);

    if((rc < 0) && (rc != LIBSSH2_ERROR_EAGAIN))
        return _libssh2_error(session, rc, "transport read");

    read_packet = _libssh2_list_first(&session->packets);
    while(read_packet && (bytes_read < buflen)) {
        /* previously this loop condition also checked for
           !channel->remote.close but we cannot let it do this:

           We may have a series of packets to read that are still pending even
           if a close has been received. Acknowledging the close too early
           makes us flush buffers prematurely and loose data.
        */

        LIBSSH2_PACKET *readpkt = read_packet;

        /* In case packet gets destroyed during this iteration */
        read_next = _libssh2_list_next(&readpkt->node);

        if(readpkt->data_len < 5) {
            read_packet = read_next;

            if(readpkt->data_len != 1 ||
                readpkt->data[0] != SSH_MSG_REQUEST_FAILURE) {
                _libssh2_debug((channel->session, LIBSSH2_TRACE_ERROR,
                               "Unexpected packet length"));
            }

            continue;
        }

        channel->read_local_id =
            _libssh2_ntohu32(readpkt->data + 1);

        /*
         * Either we asked for a specific extended data stream
         * (and data was available),
         * or the standard stream (and data was available),
         * or the standard stream with extended_data_merge
         * enabled and data was available
         */
        if((stream_id
             && (readpkt->data[0] == SSH_MSG_CHANNEL_EXTENDED_DATA)
             && (channel->local.id == channel->read_local_id)
             && (readpkt->data_len >= 9)
             && (stream_id == (int) _libssh2_ntohu32(readpkt->data + 5)))
            || (!stream_id && (readpkt->data[0] == SSH_MSG_CHANNEL_DATA)
                && (channel->local.id == channel->read_local_id))
            || (!stream_id
                && (readpkt->data[0] == SSH_MSG_CHANNEL_EXTENDED_DATA)
                && (channel->local.id == channel->read_local_id)
                && (channel->remote.extended_data_ignore_mode ==
                    LIBSSH2_CHANNEL_EXTENDED_DATA_MERGE))) {

            /* figure out much more data we want to read */
            bytes_want = buflen - bytes_read;
            unlink_packet = FALSE;

            if(bytes_want >= (readpkt->data_len - readpkt->data_head)) {
                /* we want more than this node keeps, so adjust the number and
                   delete this node after the copy */
                bytes_want = readpkt->data_len - readpkt->data_head;
                unlink_packet = TRUE;
            }

            _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                           "channel_read() got %ld of data from %u/%u/%d%s",
                           (long)bytes_want, channel->local.id,
                           channel->remote.id, stream_id,
                           unlink_packet ? " [ul]" : ""));

            /* copy data from this struct to the target buffer */
            memcpy(&buf[bytes_read],
                   &readpkt->data[readpkt->data_head], bytes_want);

            /* advance pointer and counter */
            readpkt->data_head += bytes_want;
            bytes_read += bytes_want;

            /* if drained, remove from list */
            if(unlink_packet) {
                /* detach readpkt from session->packets list */
                _libssh2_list_remove(&readpkt->node);

                LIBSSH2_FREE(session, readpkt->data);
                LIBSSH2_FREE(session, readpkt);
            }
        }

        /* check the next struct in the chain */
        read_packet = read_next;
    }

    if(!bytes_read) {
        /* If the channel is already at EOF or even closed, we need to signal
           that back. We may have gotten that info while draining the incoming
           transport layer until EAGAIN so we must not be fooled by that
           return code. */
        if(channel->remote.eof || channel->remote.close)
            return 0;
        else if(rc != LIBSSH2_ERROR_EAGAIN)
            return 0;

        /* if the transport layer said EAGAIN then we say so as well */
        return _libssh2_error(session, rc, "would block");
    }

    channel->read_avail -= bytes_read;
    channel->remote.window_size -= (uint32_t)bytes_read;

    return bytes_read;
}

/*
 * libssh2_channel_read_ex
 *
 * Read data from a channel (blocking or non-blocking depending on set state)
 *
 * When this is done non-blocking, it is important to not return 0 until the
 * currently read channel is complete. If we read stuff from the wire but it
 * was no payload data to fill in the buffer with, we MUST make sure to return
 * LIBSSH2_ERROR_EAGAIN.
 *
 * This function will first make sure there's a receive window enough to
 * receive a full buffer's wort of contents. An application may choose to
 * adjust the receive window more to increase transfer performance.
 */
LIBSSH2_API ssize_t
libssh2_channel_read_ex(LIBSSH2_CHANNEL *channel, int stream_id, char *buf,
                        size_t buflen)
{
    ssize_t rc;
    unsigned long recv_window;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    recv_window = libssh2_channel_window_read_ex(channel, NULL, NULL);

    if(buflen > recv_window) {
        BLOCK_ADJUST(rc, channel->session,
                     _libssh2_channel_receive_window_adjust(channel,
                                                   (uint32_t)buflen, 1, NULL));
    }

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_read(channel, stream_id, buf, buflen));
    return rc;
}

/*
 * _libssh2_channel_packet_data_len
 *
 * Return the size of the data block of the current packet, or 0 if there
 * isn't a packet.
 */
size_t
_libssh2_channel_packet_data_len(LIBSSH2_CHANNEL * channel, int stream_id)
{
    LIBSSH2_SESSION *session = channel->session;
    LIBSSH2_PACKET *read_packet;
    LIBSSH2_PACKET *next_packet;
    uint32_t read_local_id;

    read_packet = _libssh2_list_first(&session->packets);
    if(!read_packet)
        return 0;

    while(read_packet) {

        next_packet = _libssh2_list_next(&read_packet->node);

        if(read_packet->data_len < 5) {
            read_packet = next_packet;
            _libssh2_debug((channel->session, LIBSSH2_TRACE_ERROR,
                           "Unexpected packet length"));
            continue;
        }

        read_local_id = _libssh2_ntohu32(read_packet->data + 1);

        /*
         * Either we asked for a specific extended data stream
         * (and data was available),
         * or the standard stream (and data was available),
         * or the standard stream with extended_data_merge
         * enabled and data was available
         */
        if((stream_id
             && (read_packet->data[0] == SSH_MSG_CHANNEL_EXTENDED_DATA)
             && (channel->local.id == read_local_id)
             && (read_packet->data_len >= 9)
             && (stream_id == (int) _libssh2_ntohu32(read_packet->data + 5)))
            ||
            (!stream_id
             && (read_packet->data[0] == SSH_MSG_CHANNEL_DATA)
             && (channel->local.id == read_local_id))
            ||
            (!stream_id
             && (read_packet->data[0] == SSH_MSG_CHANNEL_EXTENDED_DATA)
             && (channel->local.id == read_local_id)
             && (channel->remote.extended_data_ignore_mode
                 == LIBSSH2_CHANNEL_EXTENDED_DATA_MERGE))) {
            return read_packet->data_len - read_packet->data_head;
        }

        read_packet = next_packet;
    }

    return 0;
}

/*
 * _libssh2_channel_write
 *
 * Send data to a channel. Note that if this returns EAGAIN, the caller must
 * call this function again with the SAME input arguments.
 *
 * Returns: number of bytes sent, or if it returns a negative number, that is
 * the error code!
 */
ssize_t
_libssh2_channel_write(LIBSSH2_CHANNEL *channel, int stream_id,
                       const unsigned char *buf, size_t buflen)
{
    int rc = 0;
    LIBSSH2_SESSION *session = channel->session;
    ssize_t wrote = 0; /* counter for this specific this call */

    /* In theory we could split larger buffers into several smaller packets
     * but it turns out to be really hard and nasty to do while still offering
     * the API/prototype.
     *
     * Instead we only deal with the first 32K in this call and for the parent
     * function to call it again with the remainder! 32K is a conservative
     * limit based on the text in RFC4253 section 6.1.
     */
    if(buflen > 32700)
        buflen = 32700;

    if(channel->write_state == libssh2_NB_state_idle) {
        unsigned char *s = channel->write_packet;

        _libssh2_debug((channel->session, LIBSSH2_TRACE_CONN,
                       "Writing %ld bytes on channel %u/%u, stream #%d",
                       (long)buflen, channel->local.id, channel->remote.id,
                       stream_id));

        if(channel->local.close)
            return _libssh2_error(channel->session,
                                  LIBSSH2_ERROR_CHANNEL_CLOSED,
                                  "We have already closed this channel");
        else if(channel->local.eof)
            return _libssh2_error(channel->session,
                                  LIBSSH2_ERROR_CHANNEL_EOF_SENT,
                                  "EOF has already been received, "
                                  "data might be ignored");

        /* drain the incoming flow first, mostly to make sure we get all
         * pending window adjust packets */
        do
            rc = _libssh2_transport_read(session);
        while(rc > 0);

        if((rc < 0) && (rc != LIBSSH2_ERROR_EAGAIN)) {
            return _libssh2_error(channel->session, rc,
                                  "Failure while draining incoming flow");
        }

        if(channel->local.window_size <= 0) {
            /* there's no room for data so we stop */

            /* Waiting on the socket to be writable would be wrong because we
             * would be back here immediately, but a readable socket might
             * herald an incoming window adjustment.
             */
            session->socket_block_directions = LIBSSH2_SESSION_BLOCK_INBOUND;

            return rc == LIBSSH2_ERROR_EAGAIN ? rc : 0;
        }

        channel->write_bufwrite = buflen;

        *(s++) = stream_id ? SSH_MSG_CHANNEL_EXTENDED_DATA :
            SSH_MSG_CHANNEL_DATA;
        _libssh2_store_u32(&s, channel->remote.id);
        if(stream_id)
            _libssh2_store_u32(&s, stream_id);

        /* Don't exceed the remote end's limits */
        /* REMEMBER local means local as the SOURCE of the data */
        if(channel->write_bufwrite > channel->local.window_size) {
            _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                           "Splitting write block due to %u byte "
                           "window_size on %u/%u/%d",
                           channel->local.window_size, channel->local.id,
                           channel->remote.id, stream_id));
            channel->write_bufwrite = channel->local.window_size;
        }
        if(channel->write_bufwrite > channel->local.packet_size) {
            _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                           "Splitting write block due to %u byte "
                           "packet_size on %u/%u/%d",
                           channel->local.packet_size, channel->local.id,
                           channel->remote.id, stream_id));
            channel->write_bufwrite = channel->local.packet_size;
        }
        /* store the size here only, the buffer is passed in as-is to
           _libssh2_transport_send() */
        _libssh2_store_u32(&s, (uint32_t)channel->write_bufwrite);
        channel->write_packet_len = s - channel->write_packet;

        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Sending %ld bytes on channel %u/%u, stream_id=%d",
                       (long)channel->write_bufwrite, channel->local.id,
                       channel->remote.id, stream_id));

        channel->write_state = libssh2_NB_state_created;
    }

    if(channel->write_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, channel->write_packet,
                                     channel->write_packet_len,
                                     buf, channel->write_bufwrite);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return _libssh2_error(session, rc,
                                  "Unable to send channel data");
        }
        else if(rc) {
            channel->write_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "Unable to send channel data");
        }
        /* Shrink local window size */
        channel->local.window_size -= (uint32_t)channel->write_bufwrite;

        wrote += channel->write_bufwrite;

        /* Since _libssh2_transport_write() succeeded, we must return
           now to allow the caller to provide the next chunk of data.

           We cannot move on to send the next piece of data that may
           already have been provided in this same function call, as we
           risk getting EAGAIN for that and we can't return information
           both about sent data as well as EAGAIN. So, by returning short
           now, the caller will call this function again with new data to
           send */

        channel->write_state = libssh2_NB_state_idle;

        return wrote;
    }

    return LIBSSH2_ERROR_INVAL; /* reaching this point is really bad */
}

/*
 * libssh2_channel_write_ex
 *
 * Send data to a channel
 */
LIBSSH2_API ssize_t
libssh2_channel_write_ex(LIBSSH2_CHANNEL *channel, int stream_id,
                         const char *buf, size_t buflen)
{
    ssize_t rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 _libssh2_channel_write(channel, stream_id,
                                        (unsigned char *)buf, buflen));
    return rc;
}

/*
 * channel_send_eof
 *
 * Send EOF on channel
 */
static int channel_send_eof(LIBSSH2_CHANNEL *channel)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char packet[5];    /* packet_type(1) + channelno(4) */
    int rc;

    _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                   "Sending EOF on channel %u/%u",
                   channel->local.id, channel->remote.id));
    packet[0] = SSH_MSG_CHANNEL_EOF;
    _libssh2_htonu32(packet + 1, channel->remote.id);
    rc = _libssh2_transport_send(session, packet, 5, NULL, 0);
    if(rc == LIBSSH2_ERROR_EAGAIN) {
        _libssh2_error(session, rc,
                       "Would block sending EOF");
        return rc;
    }
    else if(rc) {
        return _libssh2_error(session, LIBSSH2_ERROR_SOCKET_SEND,
                              "Unable to send EOF on channel");
    }
    channel->local.eof = 1;

    return 0;
}

/*
 * libssh2_channel_send_eof
 *
 * Send EOF on channel
 */
LIBSSH2_API int
libssh2_channel_send_eof(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, channel_send_eof(channel));
    return rc;
}

/*
 * libssh2_channel_eof
 *
 * Read channel's eof status
 */
LIBSSH2_API int
libssh2_channel_eof(LIBSSH2_CHANNEL * channel)
{
    LIBSSH2_SESSION *session;
    LIBSSH2_PACKET *packet;
    LIBSSH2_PACKET *next_packet;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    session = channel->session;
    packet = _libssh2_list_first(&session->packets);

    while(packet) {

        next_packet = _libssh2_list_next(&packet->node);

        if(packet->data_len < 1) {
            packet = next_packet;
            _libssh2_debug((channel->session, LIBSSH2_TRACE_ERROR,
                           "Unexpected packet length"));
            continue;
        }

        if(((packet->data[0] == SSH_MSG_CHANNEL_DATA)
            || (packet->data[0] == SSH_MSG_CHANNEL_EXTENDED_DATA))
            && ((packet->data_len >= 5)
            && (channel->local.id == _libssh2_ntohu32(packet->data + 1)))) {
            /* There's data waiting to be read yet, mask the EOF status */
            return 0;
        }
        packet = next_packet;
    }

    return channel->remote.eof;
}

/*
 * channel_wait_eof
 *
 * Awaiting channel EOF
 */
static int channel_wait_eof(LIBSSH2_CHANNEL *channel)
{
    LIBSSH2_SESSION *session = channel->session;
    int rc;

    if(channel->wait_eof_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Awaiting EOF for channel %u/%u", channel->local.id,
                       channel->remote.id));

        channel->wait_eof_state = libssh2_NB_state_created;
    }

    /*
     * While channel is not eof, read more packets from the network.
     * Either the EOF will be set or network timeout will occur.
     */
    do {
        if(channel->remote.eof) {
            break;
        }

        if((channel->remote.window_size == channel->read_avail) &&
            session->api_block_mode)
            return _libssh2_error(session, LIBSSH2_ERROR_CHANNEL_WINDOW_FULL,
                                  "Receiving channel window "
                                  "has been exhausted");

        rc = _libssh2_transport_read(session);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            return rc;
        }
        else if(rc < 0) {
            channel->wait_eof_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc,
                                  "_libssh2_transport_read() bailed out");
        }
    } while(1);

    channel->wait_eof_state = libssh2_NB_state_idle;

    return 0;
}

/*
 * libssh2_channel_wait_eof
 *
 * Awaiting channel EOF
 */
LIBSSH2_API int
libssh2_channel_wait_eof(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, channel_wait_eof(channel));
    return rc;
}

int _libssh2_channel_close(LIBSSH2_CHANNEL * channel)
{
    LIBSSH2_SESSION *session = channel->session;
    int rc = 0;

    if(channel->local.close) {
        /* Already closed, act like we sent another close,
         * even though we didn't... shhhhhh */
        channel->close_state = libssh2_NB_state_idle;
        return 0;
    }

    if(!channel->local.eof) {
        rc = channel_send_eof(channel);
        if(rc) {
            if(rc == LIBSSH2_ERROR_EAGAIN) {
                return rc;
            }
            _libssh2_error(session, rc,
                           "Unable to send EOF, but closing channel anyway");
        }
    }

    /* ignore if we have received a remote eof or not, as it is now too
       late for us to wait for it. Continue closing! */

    if(channel->close_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_CONN, "Closing channel %u/%u",
                       channel->local.id, channel->remote.id));

        channel->close_packet[0] = SSH_MSG_CHANNEL_CLOSE;
        _libssh2_htonu32(channel->close_packet + 1, channel->remote.id);

        channel->close_state = libssh2_NB_state_created;
    }

    if(channel->close_state == libssh2_NB_state_created) {
        rc = _libssh2_transport_send(session, channel->close_packet, 5,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc,
                           "Would block sending close-channel");
            return rc;

        }
        else if(rc) {
            _libssh2_error(session, rc,
                           "Unable to send close-channel request, "
                           "but closing anyway");
            /* skip waiting for the response and fall through to
               LIBSSH2_CHANNEL_CLOSE below */

        }
        else
            channel->close_state = libssh2_NB_state_sent;
    }

    if(channel->close_state == libssh2_NB_state_sent) {
        /* We must wait for the remote SSH_MSG_CHANNEL_CLOSE message */

        while(!channel->remote.close && !rc &&
               (session->socket_state != LIBSSH2_SOCKET_DISCONNECTED))
            rc = _libssh2_transport_read(session);
    }

    if(rc != LIBSSH2_ERROR_EAGAIN) {
        /* set the local close state first when we're perfectly confirmed to
           not do any more EAGAINs */
        channel->local.close = 1;

        /* We call the callback last in this function to make it keep the local
           data as long as EAGAIN is returned. */
        if(channel->close_cb) {
            LIBSSH2_CHANNEL_CLOSE(session, channel);
        }

        channel->close_state = libssh2_NB_state_idle;
    }

    /* return 0 or an error */
    return rc >= 0 ? 0 : rc;
}

/*
 * libssh2_channel_close
 *
 * Close a channel
 */
LIBSSH2_API int
libssh2_channel_close(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, _libssh2_channel_close(channel));
    return rc;
}

/*
 * channel_wait_closed
 *
 * Awaiting channel close after EOF
 */
static int channel_wait_closed(LIBSSH2_CHANNEL *channel)
{
    LIBSSH2_SESSION *session = channel->session;
    int rc;

    if(!channel->remote.eof) {
        return _libssh2_error(session, LIBSSH2_ERROR_INVAL,
                              "libssh2_channel_wait_closed() invoked when "
                              "channel is not in EOF state");
    }

    if(channel->wait_closed_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Awaiting close of channel %u/%u", channel->local.id,
                       channel->remote.id));

        channel->wait_closed_state = libssh2_NB_state_created;
    }

    /*
     * While channel is not closed, read more packets from the network.
     * Either the channel will be closed or network timeout will occur.
     */
    if(!channel->remote.close) {
        do {
            rc = _libssh2_transport_read(session);
            if(channel->remote.close)
                /* it is now closed, move on! */
                break;
        } while(rc > 0);
        if(rc < 0)
            return rc;
    }

    channel->wait_closed_state = libssh2_NB_state_idle;

    return 0;
}

/*
 * libssh2_channel_wait_closed
 *
 * Awaiting channel close after EOF
 */
LIBSSH2_API int
libssh2_channel_wait_closed(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, channel_wait_closed(channel));
    return rc;
}

/*
 * _libssh2_channel_free
 *
 * Make sure a channel is closed, then remove the channel from the session
 * and free its resource(s)
 *
 * Returns 0 on success, negative on failure
 */
int _libssh2_channel_free(LIBSSH2_CHANNEL *channel)
{
    LIBSSH2_SESSION *session = channel->session;
    unsigned char channel_id[4];
    unsigned char *data;
    size_t data_len;
    int rc;

    assert(session);

    if(channel->free_state == libssh2_NB_state_idle) {
        _libssh2_debug((session, LIBSSH2_TRACE_CONN,
                       "Freeing channel %u/%u resources", channel->local.id,
                       channel->remote.id));

        channel->free_state = libssh2_NB_state_created;
    }

    /* Allow channel freeing even when the socket has lost its connection */
    if(!channel->local.close
        && (session->socket_state == LIBSSH2_SOCKET_CONNECTED)) {
        rc = _libssh2_channel_close(channel);

        if(rc == LIBSSH2_ERROR_EAGAIN)
            return rc;

        /* ignore all other errors as they otherwise risk blocking the channel
           free from happening */
    }

    channel->free_state = libssh2_NB_state_idle;

    if(channel->exit_signal) {
        LIBSSH2_FREE(session, channel->exit_signal);
    }

    /*
     * channel->remote.close *might* not be set yet, Well...
     * We've sent the close packet, what more do you want?
     * Just let packet_add ignore it when it finally arrives
     */

    /* Clear out packets meant for this channel */
    _libssh2_htonu32(channel_id, channel->local.id);
    while((_libssh2_packet_ask(session, SSH_MSG_CHANNEL_DATA, &data,
                               &data_len, 1, channel_id, 4) >= 0)
          ||
          (_libssh2_packet_ask(session, SSH_MSG_CHANNEL_EXTENDED_DATA, &data,
                               &data_len, 1, channel_id, 4) >= 0)) {
        LIBSSH2_FREE(session, data);
    }

    /* free "channel_type" */
    if(channel->channel_type) {
        LIBSSH2_FREE(session, channel->channel_type);
    }

    /* Unlink from channel list */
    _libssh2_list_remove(&channel->node);

    /*
     * Make sure all memory used in the state variables are free
     */
    if(channel->setenv_packet) {
        LIBSSH2_FREE(session, channel->setenv_packet);
    }
    if(channel->reqX11_packet) {
        LIBSSH2_FREE(session, channel->reqX11_packet);
    }
    if(channel->process_packet) {
        LIBSSH2_FREE(session, channel->process_packet);
    }

    LIBSSH2_FREE(session, channel);

    return 0;
}

/*
 * libssh2_channel_free
 *
 * Make sure a channel is closed, then remove the channel from the session
 * and free its resource(s)
 *
 * Returns 0 on success, negative on failure
 */
LIBSSH2_API int
libssh2_channel_free(LIBSSH2_CHANNEL *channel)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session, _libssh2_channel_free(channel));
    return rc;
}
/*
 * libssh2_channel_window_read_ex
 *
 * Check the status of the read window. Returns the number of bytes which the
 * remote end may send without overflowing the window limit read_avail (if
 * passed) will be populated with the number of bytes actually available to be
 * read window_size_initial (if passed) will be populated with the
 * window_size_initial as defined by the channel_open request
 */
LIBSSH2_API unsigned long
libssh2_channel_window_read_ex(LIBSSH2_CHANNEL *channel,
        /* FIXME: -> size_t */ unsigned long *read_avail,
                               unsigned long *window_size_initial)
{
    if(!channel)
        return 0; /* no channel, no window! */

    if(window_size_initial) {
        *window_size_initial = channel->remote.window_size_initial;
    }

    if(read_avail) {
        size_t bytes_queued = 0;
        LIBSSH2_PACKET *next_packet;
        LIBSSH2_PACKET *packet =
            _libssh2_list_first(&channel->session->packets);

        while(packet) {
            unsigned char packet_type;
               next_packet = _libssh2_list_next(&packet->node);

            if(packet->data_len < 1) {
                packet = next_packet;
                _libssh2_debug((channel->session, LIBSSH2_TRACE_ERROR,
                               "Unexpected packet length"));
                continue;
            }

            packet_type = packet->data[0];

            if(((packet_type == SSH_MSG_CHANNEL_DATA)
                || (packet_type == SSH_MSG_CHANNEL_EXTENDED_DATA))
               && ((packet->data_len >= 5)
                   && (_libssh2_ntohu32(packet->data + 1) ==
                       channel->local.id))) {
                bytes_queued += packet->data_len - packet->data_head;
            }

            packet = next_packet;
        }

        *read_avail = (unsigned long)bytes_queued;
    }

    return channel->remote.window_size;
}

/*
 * libssh2_channel_window_write_ex
 *
 * Check the status of the write window Returns the number of bytes which may
 * be safely written on the channel without blocking window_size_initial (if
 * passed) will be populated with the size of the initial window as defined by
 * the channel_open request
 */
LIBSSH2_API unsigned long
libssh2_channel_window_write_ex(LIBSSH2_CHANNEL *channel,
                                unsigned long *window_size_initial)
{
    if(!channel)
        return 0; /* no channel, no window! */

    if(window_size_initial) {
        /* For locally initiated channels this is very often 0, so it's not
         * *that* useful as information goes */
        *window_size_initial = channel->local.window_size_initial;
    }

    return channel->local.window_size;
}

/* A signal can be delivered to the remote process/service using the
   following message.  Some systems may not implement signals, in which
   case they SHOULD ignore this message.

      byte      SSH_MSG_CHANNEL_REQUEST
      uint32    recipient channel
      string    "signal"
      boolean   FALSE
      string    signal name (without the "SIG" prefix)

   'signal name' values will be encoded as discussed in the passage
   describing SSH_MSG_CHANNEL_REQUEST messages using "exit-signal" in
   this section.
 */
static int channel_signal(LIBSSH2_CHANNEL *channel,
                          const char *signame,
                          size_t signame_len)
{
    LIBSSH2_SESSION *session = channel->session;
    int retcode = LIBSSH2_ERROR_PROTO;

    if(channel->sendsignal_state == libssh2_NB_state_idle) {
        unsigned char *s;

        /* 20 = packet_type(1) + channel(4) +
                signal_len + sizeof(signal) - 1 + want_reply(1) +
                signame_len_len(4) */
        channel->sendsignal_packet_len = 20 + signame_len;

        s = channel->sendsignal_packet =
            LIBSSH2_ALLOC(session, channel->sendsignal_packet_len);
        if(!channel->sendsignal_packet)
            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                  "Unable to allocate memory for "
                                  "signal request");

        *(s++) = SSH_MSG_CHANNEL_REQUEST;
        _libssh2_store_u32(&s, channel->remote.id);
        _libssh2_store_str(&s, "signal", sizeof("signal") - 1);
        *(s++) = 0x00;  /* Don't reply */
        _libssh2_store_str(&s, signame, signame_len);

        channel->sendsignal_state = libssh2_NB_state_created;
    }

    if(channel->sendsignal_state == libssh2_NB_state_created) {
        int rc;

        rc = _libssh2_transport_send(session, channel->sendsignal_packet,
                                     channel->sendsignal_packet_len,
                                     NULL, 0);
        if(rc == LIBSSH2_ERROR_EAGAIN) {
            _libssh2_error(session, rc, "Would block sending signal request");
            return rc;
        }
        else if(rc) {
            LIBSSH2_FREE(session, channel->sendsignal_packet);
            channel->sendsignal_state = libssh2_NB_state_idle;
            return _libssh2_error(session, rc, "Unable to send signal packet");
        }
        LIBSSH2_FREE(session, channel->sendsignal_packet);
        retcode = LIBSSH2_ERROR_NONE;
    }

    channel->sendsignal_state = libssh2_NB_state_idle;

    return retcode;
}

LIBSSH2_API int
libssh2_channel_signal_ex(LIBSSH2_CHANNEL *channel,
                          const char *signame,
                          size_t signame_len)
{
    int rc;

    if(!channel)
        return LIBSSH2_ERROR_BAD_USE;

    BLOCK_ADJUST(rc, channel->session,
                 channel_signal(channel, signame, signame_len));
    return rc;
}