channel.c

/* channel.c
 *
 */

/* lsh, an implementation of the ssh protocol
 *
 * Copyright (C) 1998 Niels Mller
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#if HAVE_CONFIG_H
#include "config.h"
#endif

#include <assert.h>
#include <string.h>

#include "channel.h"

#include "format.h"
#include "io.h"
#include "lsh_string.h"
#include "read_data.h"
#include "ssh.h"
#include "werror.h"
#include "xalloc.h"

#define GABA_DEFINE
#include "channel.h.x"
#undef GABA_DEFINE

#include "channel.c.x"

struct exception *
make_channel_open_exception(uint32_t error_code, const char *msg)
{
  NEW(channel_open_exception, self);

#define MAX_ERROR 4
  static const char *msgs[MAX_ERROR + 1] = {
    "",
    "Administratively prohibited",
    "Connect failed",
    "Unknown channel type",
    "Resource shortage"
  };

  assert(error_code > 0);
  assert(error_code <= MAX_ERROR);
#undef MAX_ERROR
  
  self->super.type = EXC_CHANNEL_OPEN;
  self->super.msg = msg ? msg : msgs[error_code];
  self->error_code = error_code;

  return &self->super;
}


struct lsh_string *
format_global_failure(void)
{
  return ssh_format("%c", SSH_MSG_REQUEST_FAILURE);
}

struct lsh_string *
format_global_success(void)
{
  return ssh_format("%c", SSH_MSG_REQUEST_SUCCESS);
}

/* The advertised rec_max_size must be a little smaller than SSH_MAX_PACKET,
 * to make sure that our peer won't send us packets exceeding our limit for
 * the connection. */

/* NOTE: It would make some sense to use the connection's
 * rec_max_packet instead of the SSH_MAX_PACKET constant. */

#define SSH_MAX_DATA_SIZE (SSH_MAX_PACKET - SSH_CHANNEL_MAX_PACKET_FUZZ)

static void
check_rec_max_packet(struct ssh_channel *channel)
{
  /* Never advertise a larger rec_max_packet than we're willing to
   * handle. */

  if (channel->rec_max_packet > SSH_MAX_DATA_SIZE)
    {
      debug("check_rec_max_packet: Reduced rec_max_packet from %i to %i.\n",
	    channel->rec_max_packet, SSH_MAX_DATA_SIZE);
      channel->rec_max_packet = SSH_MAX_DATA_SIZE;
    }
}

struct lsh_string *
format_open_confirmation(struct ssh_channel *channel,
			 uint32_t channel_number,
			 const char *format, ...)
{
  va_list args;
  uint32_t l1, l2;
  struct lsh_string *packet;
  
#define CONFIRM_FORMAT "%c%i%i%i%i"
#define CONFIRM_ARGS \
  SSH_MSG_CHANNEL_OPEN_CONFIRMATION, channel->channel_number, \
  channel_number, channel->rec_window_size, channel->rec_max_packet
    
  check_rec_max_packet(channel);

  debug("format_open_confirmation: rec_window_size = %i,\n"
	"                          rec_max_packet = %i,\n",
       channel->rec_window_size,
       channel->rec_max_packet);
  l1 = ssh_format_length(CONFIRM_FORMAT, CONFIRM_ARGS);

  va_start(args, format);
  l2 = ssh_vformat_length(format, args);
  va_end(args);

  packet = lsh_string_alloc(l1 + l2);

  ssh_format_write(CONFIRM_FORMAT, packet, 0, CONFIRM_ARGS);

  va_start(args, format);
  ssh_vformat_write(format, packet, l1, args);
  va_end(args);

  return packet;
#undef CONFIRM_FORMAT
#undef CONFIRM_ARGS
}

struct lsh_string *
format_open_failure(uint32_t channel, uint32_t reason,
		    const char *msg, const char *language)
{
  return ssh_format("%c%i%i%z%z", SSH_MSG_CHANNEL_OPEN_FAILURE,
		    channel, reason, msg, language);
}

struct lsh_string *
format_channel_success(uint32_t channel)
{
  return ssh_format("%c%i", SSH_MSG_CHANNEL_SUCCESS, channel);
}

struct lsh_string *
format_channel_failure(uint32_t channel)
{
  return ssh_format("%c%i", SSH_MSG_CHANNEL_FAILURE, channel);
}

struct lsh_string *
prepare_window_adjust(struct ssh_channel *channel,
		      uint32_t add)
{
  channel->rec_window_size += add;
  
  return ssh_format("%c%i%i",
		    SSH_MSG_CHANNEL_WINDOW_ADJUST,
		    channel->channel_number, add);
}

/* GABA:
   (class
     (name exc_finish_channel_handler)
     (super exception_handler)
     (vars
       (table object channel_table)
       ; Non-zero if the channel has already been deallocated.
       (dead . int)
       ; Local channel number 
       (channel_number . uint32_t)))
*/

static void
do_exc_finish_channel_handler(struct exception_handler *s,
			      const struct exception *e)
{
  CAST(exc_finish_channel_handler, self, s);

  switch (e->type)
    {
    case EXC_FINISH_PENDING:
      if (self->dead)
	werror("channel.c: EXC_FINISH_PENDING on dead channel.\n");

      self->table->pending_close = 1;

      /* NOTE: We don't need to raise a EXC_FINISH_READ here. Only
       * code in a live channel is supposed to raise
       * EXC_FINISH_PENDING. The typical caller is a channel's
       * CHANNEL_CLOSE callback that is called below. */
      break;
      
    case EXC_FINISH_CHANNEL:
      /* NOTE: This type of exception must be handled only once.
       * However, there is at least one case where it is difficult to
       * ensure that the exception is raised only once.
       *
       * For instance, in do_channel_close, the CHANNEL_EOF callback
       * can decide to call close_channel, which might raise this
       * exception. When control gets back to do_channel_close, and
       * CHANNEL_SENT_CLOSE is true, it raises the exception again.
       *
       * To get this right, we set a flag when the channel is
       * deallocated. */
      if (self->dead)
	debug("EXC_FINISH_CHANNEL on dead channel.\n");
      else
	{
	  struct ssh_channel *channel
	    = self->table->channels[self->channel_number];

	  assert(channel);
	  assert(channel->resources->super.alive);

	  if (channel->close)
	    CHANNEL_CLOSE(channel);
	
	  KILL_RESOURCE_LIST(channel->resources);
	
	  dealloc_channel(self->table, self->channel_number);
	  self->dead = 1;

	  if (self->table->pending_close &&
	      !self->table->channel_count)
	    {
	      /* FIXME: Send a SSH_DISCONNECT_BY_APPLICATION message? */
	      EXCEPTION_RAISE(self->table->e, &finish_read_exception);
	    }
	}
      break;
    default:
      EXCEPTION_RAISE(self->super.parent, e);
    }
}

static struct exception_handler *
make_exc_finish_channel_handler(struct channel_table *table,
				uint32_t channel_number,
				struct exception_handler *e,
				const char *context)
{
  NEW(exc_finish_channel_handler, self);
  self->super.parent = e;
  self->super.raise = do_exc_finish_channel_handler;
  self->super.context = context;

  self->table = table;
  self->channel_number = channel_number;
  self->dead = 0;
  
  return &self->super;
}
				

/* Channel objects */

#define INITIAL_CHANNELS 32
/* Arbitrary limit */
#define MAX_CHANNELS (1L<<17)

/* FIXME: Figure out what exceptions really are needed. Perhaps we can
   use some method call instead? */
struct channel_table *
make_channel_table(struct abstract_write *write,
		   struct exception_handler *e)
{
  NEW(channel_table, table);
  table->write = write;
  table->e = e;

  /* FIXME: Really need this? */
  table->chain = NULL;

  /* FIXME: Use an argument for initialization? */
  table->resources = make_resource_list();
  
  table->channels = lsh_space_alloc(sizeof(struct ssh_channel *)
				      * INITIAL_CHANNELS);
  table->in_use = lsh_space_alloc(INITIAL_CHANNELS);
  
  table->allocated_channels = INITIAL_CHANNELS;
  table->used_channels = 0;
  table->next_channel = 0;
  table->channel_count = 0;
  
  table->max_channels = MAX_CHANNELS;

  table->pending_close = 0;

  table->global_requests = make_alist(0, -1);
  table->channel_types = make_alist(0, -1);
  table->open_fallback = NULL;
  
  object_queue_init(&table->local_ports);
  object_queue_init(&table->remote_ports);
  table->x11_display = NULL;
  
  object_queue_init(&table->active_global_requests);
  object_queue_init(&table->pending_global_requests);
  
  return table;
}

/* Returns -1 if allocation fails */
/* NOTE: This function returns locally chosen channel numbers, which
 * are always small integers. So there's no problem fitting them in
 * a signed int. */
int
alloc_channel(struct channel_table *table)
{
  uint32_t i;
  
  for(i = table->next_channel; i < table->used_channels; i++)
    {
      if (table->in_use[i] == CHANNEL_FREE)
	{
	  assert(!table->channels[i]);
	  table->in_use[i] = CHANNEL_RESERVED;
	  table->next_channel = i+1;

	  goto success;
	}
    }
  if (i == table->max_channels)
    return -1;

  if (i == table->allocated_channels) 
    {
      uint32_t new_size = table->allocated_channels * 2;
      struct ssh_channel **new_channels;
      uint8_t *new_in_use;

      new_channels = lsh_space_alloc(sizeof(struct ssh_channel *)
				     * new_size);
      memcpy(new_channels, table->channels,
	     sizeof(struct ssh_channel *) * table->used_channels);
      lsh_space_free(table->channels);
      table->channels = new_channels;

      /* FIXME: Use realloc(). */
      new_in_use = lsh_space_alloc(new_size);
      memcpy(new_in_use, table->in_use, table->used_channels);
      lsh_space_free(table->in_use);
      table->in_use = new_in_use;

      table->allocated_channels = new_size;
    }

  table->next_channel = table->used_channels = i+1;

  table->in_use[i] = CHANNEL_RESERVED;
  table->channels[i] = NULL;
  
 success:
  table->channel_count++;
  verbose("Allocated local channel number %i\n", i);

  return i;
}

void
dealloc_channel(struct channel_table *table, int i)
{
  assert(i >= 0);
  assert( (unsigned) i < table->used_channels);
  assert(table->channel_count);
  
  verbose("Deallocating local channel %i\n", i);
  table->channels[i] = NULL;
  table->in_use[i] = CHANNEL_FREE;

  table->channel_count--;
  
  if ( (unsigned) i < table->next_channel)
    table->next_channel = i;
}

void
use_channel(struct channel_table *table,
	    uint32_t local_channel_number)
{
  struct ssh_channel *channel = table->channels[local_channel_number];

  assert(channel);
  assert(table->in_use[local_channel_number] == CHANNEL_RESERVED);
  
  table->in_use[local_channel_number] = CHANNEL_IN_USE;
  verbose("Taking channel %i in use, (local %i).\n",
	  channel->channel_number, local_channel_number);
}

void
register_channel(struct channel_table *table,
		 uint32_t local_channel_number,
		 struct ssh_channel *channel,
		 int take_into_use)
{
  assert(table->in_use[local_channel_number] == CHANNEL_RESERVED);
  assert(!table->channels[local_channel_number]);

  verbose("Registering local channel %i.\n",
	  local_channel_number);
  
  /* NOTE: Is this the right place to install this exception handler? */
  channel->e =
    make_exc_finish_channel_handler(table,
				    local_channel_number,
				    (channel->e ? channel->e
				     : table->e),
				    HANDLER_CONTEXT);

  table->channels[local_channel_number] = channel;

  if (take_into_use)
    use_channel(table, local_channel_number);
  
  remember_resource(table->resources,
		    &channel->resources->super);
}

struct ssh_channel *
lookup_channel(struct channel_table *table, uint32_t i)
{
  return ( (i < table->used_channels)
	   && (table->in_use[i] == CHANNEL_IN_USE))
    ? table->channels[i] : NULL;
}

struct ssh_channel *
lookup_channel_reserved(struct channel_table *table, uint32_t i)
{
  return ( (i < table->used_channels)
	   && (table->in_use[i] == CHANNEL_RESERVED))
    ? table->channels[i] : NULL;
}

/* FIXME: It seems suboptimal to send a window adjust message for
 * *every* write that we do. A better scheme might be as follows:
 *
 * Delay window adjust messages, keeping track of both the locally
 * maintained window size, which is updated after each write, and the
 * size that has been reported to the remote end. When the difference
 * between these two values gets large enough (say, larger than one
 * half or one third of the maximum window size), we send a
 * window_adjust message to sync them. */
static void
adjust_rec_window(struct flow_controlled *f, uint32_t written)
{
  CAST_SUBTYPE(ssh_channel, channel, f);

  /* NOTE: The channel object (referenced as a flow-control callback)
   * may live longer than the actual channel. */
  if (! (channel->flags & (CHANNEL_RECEIVED_EOF | CHANNEL_RECEIVED_CLOSE
			   | CHANNEL_SENT_CLOSE)))
    A_WRITE(channel->table->write,
	    prepare_window_adjust(channel, written));
}

void
channel_start_receive(struct ssh_channel *channel,
		      uint32_t initial_window_size)
{
  if (channel->rec_window_size < initial_window_size)
    A_WRITE(channel->table->write,
		    prepare_window_adjust
		    (channel, initial_window_size - channel->rec_window_size));
}

/* Channel related messages */

/* GABA:
   (class
     (name request_status)
     (vars
       ; -1 for still active requests,
       ; 0 for failure,
       ; 1 for success
       (status . int)))
*/

static struct request_status *
make_request_status(void)
{
  NEW(request_status, self);
  self->status = -1;

  return self;
}

/* GABA:
   (class
     (name global_request_continuation)
     (super command_continuation)
     (vars
       (table object channel_table)
       (active object request_status)))
*/

static void 
send_global_request_responses(struct channel_table *table, 
			      struct object_queue *q)
{
   for (;;)
     {
       CAST(request_status, n, object_queue_peek_head(q));
       if (!n || (n->status < 0))
	 break;
 
      object_queue_remove_head(q);

      A_WRITE(table->write,
	      (n->status
	       ? format_global_success()
	       : format_global_failure()));
    }
}

static void
do_global_request_response(struct command_continuation *s,
			   struct lsh_object *x UNUSED)
{
  CAST(global_request_continuation, self, s);
  struct object_queue *q = &self->table->active_global_requests;

  assert(self->active->status == -1);
  assert(!object_queue_is_empty(q));
	  
  self->active->status = 1;

  send_global_request_responses(self->table, q);
}

static struct command_continuation *
make_global_request_response(struct channel_table *table,
			     struct request_status *active)
{
  NEW(global_request_continuation, self);

  self->super.c = do_global_request_response;
  self->table = table;
  self->active = active;
   
  return &self->super;
}


/* GABA:
   (class
     (name global_request_exception_handler)
     (super exception_handler)
     (vars
       (table object channel_table)
       (active object request_status)))
*/

/* NOTE: We handle *only* EXC_GLOBAL_REQUEST */
static void 
do_exc_global_request_handler(struct exception_handler *c,
			      const struct exception *e)
{
  CAST(global_request_exception_handler, self, c);
  if (e->type == EXC_GLOBAL_REQUEST)
    {
      struct object_queue *q = &self->table->active_global_requests;
      
      assert(self->active->status == -1);
      assert(!object_queue_is_empty(q));

      self->active->status = 0;
  
      send_global_request_responses(self->table, q);
    }
  else
    EXCEPTION_RAISE(c->parent, e);
}

static struct exception_handler *
make_global_request_exception_handler(struct channel_table *table,
				      struct request_status *active,
				      struct exception_handler *h,
				      const char *context)
{
  NEW(global_request_exception_handler, self);

  self->super.raise = do_exc_global_request_handler;
  self->super.context = context;
  self->super.parent = h;
  self->active = active;
  self->table = table;
  return &self->super;
}

static void
handle_global_request(struct channel_table *table,
		      struct simple_buffer *buffer)
{
  int name;
  int want_reply;
  
  if (parse_atom(buffer, &name)
      && parse_boolean(buffer, &want_reply))
    {
      struct global_request *req = NULL;
      struct command_continuation *c = &discard_continuation;
      struct exception_handler *e = table->e;

      if (name && table->global_requests)
	{
	  CAST_SUBTYPE(global_request, r,
		       ALIST_GET(table->global_requests,
				 name));
	  req = r;
	}
      if (!req)
	{
	  A_WRITE(table->write, format_global_failure());
	  return;
	}
      else
	{
	  if (want_reply)
	    {
	      struct request_status *a = make_request_status();
	      
	      object_queue_add_tail(&table->active_global_requests,
				    &a->super);
	      
	      c = make_global_request_response(table, a);
	      e = make_global_request_exception_handler(table, a, e, HANDLER_CONTEXT);
	    }
	  else
	    {
	      /* We should ignore failures. */
	      static const struct report_exception_info global_req_ignore =
		STATIC_REPORT_EXCEPTION_INFO(EXC_ALL, EXC_GLOBAL_REQUEST,
					     "Ignored:");
	      
	      e = make_report_exception_handler(&global_req_ignore,
						e, HANDLER_CONTEXT);
	    }
	  GLOBAL_REQUEST(req, table, name, want_reply, buffer, c, e);
	}
    }
  else
    PROTOCOL_ERROR(table->e, "Invalid SSH_MSG_GLOBAL_REQUEST message.");
}

static void
handle_global_success(struct channel_table *table,
		      struct simple_buffer *buffer)
{
  if (!parse_eod(buffer))
    {
      PROTOCOL_ERROR(table->e, "Invalid GLOBAL_REQUEST_SUCCESS message.");
      return;
    }

  if (object_queue_is_empty(&table->pending_global_requests))
    {
      werror("do_global_request_success: Unexpected message, ignoring.\n");
      return;
    }
  {
    CAST_SUBTYPE(command_context, ctx,
		 object_queue_remove_head(&table->pending_global_requests));
    COMMAND_RETURN(ctx->c, table);
  }
}

struct exception global_request_exception =
STATIC_EXCEPTION(EXC_GLOBAL_REQUEST, "Global request failed");

static void
handle_global_failure(struct channel_table *table,
		      struct simple_buffer *buffer)
{
  if (!parse_eod(buffer))
    {
      PROTOCOL_ERROR(table->e, "Invalid GLOBAL_REQUEST_FAILURE message.");
      return;
    }

  if (object_queue_is_empty(&table->pending_global_requests))
    {
      werror("do_global_request_failure: Unexpected message, ignoring.\n");
    }
  else
    {
      CAST_SUBTYPE(command_context, ctx,
		   object_queue_remove_head(&table->pending_global_requests));
      EXCEPTION_RAISE(ctx->e, &global_request_exception);
    }
}

/* FIXME: Don't store the channel here, instead have it passed as the
 * argument of the continuation. This might also allow some
 * unification with the handling of global_requests.
 *
 * This won't quite work yet, because not all channel request
 * handlers, in particular gateway_channel_request and
 * x11_req_handler, return the channel in question. */

/* GABA:
   (class
     (name channel_request_continuation)
     (super command_continuation)
     (vars
       (channel object ssh_channel)
       (active object request_status)))
*/

static void
send_channel_request_responses(struct ssh_channel *channel,
			       struct object_queue *q)
{
  for (;;)
    {
      CAST(request_status, n, object_queue_peek_head(q));
      if (!n || (n->status < 0))
	break;

      object_queue_remove_head(q);

      A_WRITE(channel->table->write,
	      (n->status
	       ? format_channel_success(channel->channel_number)
	       : format_channel_failure(channel->channel_number)));
    }
}

static void
do_channel_request_response(struct command_continuation *s,
			    struct lsh_object *x UNUSED)
{
  CAST(channel_request_continuation, self, s);
  struct object_queue *q = &self->channel->active_requests;

  assert(self->active->status == -1);
  assert(!object_queue_is_empty(q));
	  
  self->active->status = 1;

  send_channel_request_responses(self->channel, q);
}

static struct command_continuation *
make_channel_request_response(struct ssh_channel *channel,
			      struct request_status *active)
{
  NEW(channel_request_continuation, self);

  self->super.c = do_channel_request_response;
  self->channel = channel;
  self->active = active;

  return &self->super;
}

/* GABA:
   (class
     (name channel_request_exception_handler)
     (super exception_handler)
     (vars
       (channel object ssh_channel)
       (active object request_status)))
*/

/* NOTE: We handle *only* EXC_CHANNEL_REQUEST */
static void 
do_exc_channel_request_handler(struct exception_handler *c,
			       const struct exception *e)
{
  CAST(channel_request_exception_handler, self, c);
  if (e->type == EXC_CHANNEL_REQUEST)
    {
      struct object_queue *q = &self->channel->active_requests;

      assert(self->active->status == -1);
      assert(!object_queue_is_empty(q));
      
      self->active->status = 0;
      
      send_channel_request_responses(self->channel, q);
    }
  else
    EXCEPTION_RAISE(c->parent, e);
}

static struct exception_handler *
make_channel_request_exception_handler(struct ssh_channel *channel,
				       struct request_status *active,
				       struct exception_handler *h,
				       const char *context)
{
  NEW(channel_request_exception_handler, self);

  self->super.raise = do_exc_channel_request_handler;
  self->super.parent = h;
  self->super.context = context;

  self->channel = channel;
  self->active = active;

  return &self->super;
}

/* FIXME: Inline in caller */
static int
parse_channel_request(struct simple_buffer *buffer,
		      uint32_t *channel_number,
		      struct channel_request_info *info)
{
  if (parse_uint32(buffer, channel_number)
      && parse_string(buffer,
		      &info->type_length, &info->type_data)
      && parse_boolean(buffer, &info->want_reply))
    {
      info->type = lookup_atom(info->type_length, info->type_data);
      return 1;
    }
  else
    return 0;
}

static void
handle_channel_request(struct channel_table *table,
		       struct simple_buffer *buffer)
{
  struct channel_request_info info;
  uint32_t channel_number;
  
  if (parse_channel_request(buffer, &channel_number, &info))
    {
      struct ssh_channel *channel = lookup_channel(table,
						   channel_number);

      /* NOTE: We can't free packet yet, because it is not yet fully
       * parsed. There may be some more arguments, which are parsed by
       * the CHANNEL_REQUEST method below. */

      if (channel)
	{
	  struct channel_request *req = NULL;
	  struct command_continuation *c = &discard_continuation;
	  struct exception_handler *e = channel->e;

	  if (info.type && channel->request_types)
	    {
	      CAST_SUBTYPE(channel_request, r,
			   ALIST_GET(channel->request_types, info.type));
	      req = r;
	    }
	  if (!req)
	    req = channel->request_fallback;
	  
	  if (req)
	    {
	      if (info.want_reply)
		{
		  struct request_status *a = make_request_status();
		  
		  object_queue_add_tail(&channel->active_requests,
					&a->super);
		  
		  c = make_channel_request_response(channel, a);
		  e = make_channel_request_exception_handler(channel, a, e, HANDLER_CONTEXT);
		}
	      else
		{
		  /* We should ignore failures. */
		  static const struct report_exception_info
		    channel_req_ignore =
		    STATIC_REPORT_EXCEPTION_INFO(EXC_ALL, EXC_CHANNEL_REQUEST,
						 "Ignored:");
		  
		  e = make_report_exception_handler(&channel_req_ignore,
						    e, HANDLER_CONTEXT);
		}
	      
	      CHANNEL_REQUEST(req, channel, &info, buffer, c, e);
	    }
	  else
	    {
	      if (info.want_reply)
		A_WRITE(table->write,
			format_channel_failure(channel->channel_number));
	    }
	}
      else
	{
	  werror("SSH_MSG_CHANNEL_REQUEST on nonexistant channel %i: %xs\n",
		 channel_number, buffer->capacity, buffer->pos);
	}
    }
  else
    PROTOCOL_ERROR(table->e, "Invalid SSH_MSG_CHANNEL_REQUEST message.");
}


/* GABA:
   (class
     (name channel_open_continuation)
     (super command_continuation)
     (vars
       (table object channel_table)
       (local_channel_number . uint32_t)
       (remote_channel_number . uint32_t)
       (send_window_size . uint32_t)
       (send_max_packet . uint32_t)))
*/

static void
do_channel_open_continue(struct command_continuation *c,
			 struct lsh_object *value)
{
  CAST(channel_open_continuation, self, c);
  CAST_SUBTYPE(ssh_channel, channel, value);

  assert(channel);

  /* FIXME: This copying could just as well be done by the
   * CHANNEL_OPEN handler? Then we can remove the corresponding fields
   * from the closure as well. */
  channel->send_window_size = self->send_window_size;
  channel->send_max_packet = self->send_max_packet;
  channel->channel_number = self->remote_channel_number;

  channel->table = self->table;
  
  register_channel(self->table, self->local_channel_number,
		   channel,
		   1);

  /* FIXME: Doesn't support sending extra arguments with the
   * confirmation message. */

  A_WRITE(self->table->write,
	  format_open_confirmation(channel,
				   self->local_channel_number, ""));
}

static struct command_continuation *
make_channel_open_continuation(struct channel_table *table,
			       uint32_t local_channel_number,
			       uint32_t remote_channel_number,
			       uint32_t send_window_size,
			       uint32_t send_max_packet)
{
  NEW(channel_open_continuation, self);

  self->super.c = do_channel_open_continue;
  self->table = table;
  self->local_channel_number = local_channel_number;
  self->remote_channel_number = remote_channel_number;
  self->send_window_size = send_window_size;
  self->send_max_packet = send_max_packet;

  return &self->super;
}
			       
/* GABA:
   (class
     (name exc_channel_open_handler)
     (super exception_handler)
     (vars
       (table object channel_table)
       (local_channel_number . uint32_t)
       (remote_channel_number . uint32_t)))
*/

static void
do_exc_channel_open_handler(struct exception_handler *s,
			    const struct exception *e)
{
  CAST(exc_channel_open_handler, self, s);

  switch (e->type)
    {
    case EXC_CHANNEL_OPEN:
      {
	CAST_SUBTYPE(channel_open_exception, exc, e);
	struct channel_table *table = self->table;
	
	assert(table->in_use[self->local_channel_number]);
	assert(!table->channels[self->local_channel_number]);

	dealloc_channel(table, self->local_channel_number);
	
        A_WRITE(table->write,
		format_open_failure(self->remote_channel_number,
				    exc->error_code, e->msg, ""));
	break;
      }
    default:
      EXCEPTION_RAISE(self->super.parent, e);
    }      
}

static struct exception_handler *