channel.c 55.1 KB
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/* channel.c
 *
 * $Id$
 */

/* 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
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 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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 */

#include "channel.h"

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

#include <assert.h>
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#include <string.h>
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#define GABA_DEFINE
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#include "channel.h.x"
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#undef GABA_DEFINE
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#include "channel.c.x"

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struct exception *
make_channel_open_exception(UINT32 error_code, const char *msg)
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{
  NEW(channel_open_exception, self);
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#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
  
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  self->super.type = EXC_CHANNEL_OPEN;
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  self->super.msg = msg ? msg : msgs[error_code];
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  self->error_code = error_code;

  return &self->super;
}

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/* GABA:
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   (class
     (name connection_service)
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     (super command)
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     (vars
       ; Supported global requests 
       (global_requests object alist)

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       (channel_types object alist) ))
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       ; Initialize connection (for instance, request channels to be 
       ; opened or services to be forwarded).

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       ; (start object connection_startup)))
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*/

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

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

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struct lsh_string *
format_open_confirmation(struct ssh_channel *channel,
			 UINT32 channel_number,
			 const char *format, ...)
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{
  va_list args;
  UINT32 l1, l2;
  struct lsh_string *packet;

#define CONFIRM_FORMAT "%c%i%i%i%i"
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#define CONFIRM_ARGS \
  SSH_MSG_CHANNEL_OPEN_CONFIRMATION, channel->channel_number, \
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  channel_number, channel->rec_window_size, channel->rec_max_packet
    
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  debug("format_open_confirmation: rec_window_size = %i,\n"
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	"                          rec_max_packet = %i,\n",
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       channel->rec_window_size,
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       channel->rec_max_packet);
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  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, l1, packet->data, CONFIRM_ARGS);

  va_start(args, format);
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  ssh_vformat_write(format, l2, packet->data+l1, args);
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  va_end(args);

  return packet;
#undef CONFIRM_FORMAT
#undef CONFIRM_ARGS
}

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struct lsh_string *
format_open_failure(UINT32 channel, UINT32 reason,
		    const char *msg, const char *language)
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{
  return ssh_format("%c%i%i%z%z", SSH_MSG_CHANNEL_OPEN_FAILURE,
		    channel, reason, msg, language);
}

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struct lsh_string *
format_channel_success(UINT32 channel)
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{
  return ssh_format("%c%i", SSH_MSG_CHANNEL_SUCCESS, channel);
}

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struct lsh_string *
format_channel_failure(UINT32 channel)
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{
  return ssh_format("%c%i", SSH_MSG_CHANNEL_FAILURE, channel);
}

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struct lsh_string *
prepare_window_adjust(struct ssh_channel *channel,
		      UINT32 add)
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{
  channel->rec_window_size += add;
  
  return ssh_format("%c%i%i",
		    SSH_MSG_CHANNEL_WINDOW_ADJUST,
		    channel->channel_number, add);
}

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/* GABA:
   (class
     (name exc_finish_channel_handler)
     (super exception_handler)
     (vars
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       (connection object ssh_connection)
       ;; (table object channel_table)
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       ; Non-zero if the channel has already been deallocated.
       (dead . int)
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       ; Local channel number 
       (channel_number . UINT32)))
*/

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

  switch (e->type)
    {
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    case EXC_FINISH_PENDING:
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      if (self->dead)
	werror("channel.c: EXC_FINISH_PENDING on dead channel.\n");
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      self->connection->table->pending_close = 1;
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      if (!self->connection->table->next_channel)
	EXCEPTION_RAISE(self->connection->e, &finish_read_exception);
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      break;
      
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    case EXC_FINISH_CHANNEL:
      /* NOTE: This type of exception must be handled only once.
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       * 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
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	    = self->connection->table->channels[self->channel_number];
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	  assert(channel);
	  assert(channel->resources->super.alive);

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

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

static struct exception_handler *
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make_exc_finish_channel_handler(struct ssh_connection *connection,
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				UINT32 channel_number,
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				struct exception_handler *e,
				const char *context)
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{
  NEW(exc_finish_channel_handler, self);
  self->super.parent = e;
  self->super.raise = do_exc_finish_channel_handler;
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  self->super.context = context;
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  self->connection = connection;
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  self->channel_number = channel_number;
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  self->dead = 0;
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  return &self->super;
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}
				

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

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struct channel_table *
make_channel_table(void)
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{
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  NEW(channel_table, table);
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  table->channels = lsh_space_alloc(sizeof(struct ssh_channel *)
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				      * INITIAL_CHANNELS);
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  table->in_use = lsh_space_alloc(INITIAL_CHANNELS);
  
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  table->allocated_channels = INITIAL_CHANNELS;
  table->next_channel = 0;
  table->used_channels = 0;
  table->max_channels = MAX_CHANNELS;
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  table->pending_close = 0;
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  table->global_requests = make_alist(0, -1);
  table->channel_types = make_alist(0, -1);
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  table->open_fallback = NULL;
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  object_queue_init(&table->local_ports);
  object_queue_init(&table->remote_ports);
  
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  object_queue_init(&table->active_global_requests);
  object_queue_init(&table->pending_global_requests);
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  return table;
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}
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/* Returns -1 if allocation fails */
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/* NOTE: This function returns locally chosen channel numbers, which
 * are always small integers. So there's no problem fitting them in
 * a signed int. */
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int
alloc_channel(struct channel_table *table)
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{
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  UINT32 i;
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  for(i = table->next_channel; i < table->used_channels; i++)
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    {
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      if (table->in_use[i] == CHANNEL_FREE)
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	{
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	  assert(!table->channels[i]);
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	  table->in_use[i] = CHANNEL_RESERVED;
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	  table->next_channel = i+1;
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	  verbose("Allocated local channel number %i\n", i);
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	  return i;
	}
    }
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  if (i == table->max_channels)
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    return -1;
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  if (i == table->allocated_channels) 
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    {
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      int new_size = table->allocated_channels * 2;
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      struct ssh_channel **new_channels;
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      UINT8 *new_in_use;
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      new_channels = lsh_space_alloc(sizeof(struct ssh_channel *)
				     * new_size);
      memcpy(new_channels, table->channels,
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	     sizeof(struct ssh_channel *) * table->used_channels);
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      lsh_space_free(table->channels);
      table->channels = new_channels;

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      /* FIXME: Use realloc(). */
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      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;

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      table->allocated_channels = new_size;
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    }

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  table->next_channel = table->used_channels = i+1;
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  table->in_use[i] = CHANNEL_RESERVED;
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  verbose("Allocated local channel number %i\n", i);
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  return i;
}

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

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void
use_channel(struct ssh_connection *connection,
	    UINT32 local_channel_number)
{
  struct channel_table *table = connection->table;
  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);
}
	    
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void
register_channel(struct ssh_connection *connection,
		 UINT32 local_channel_number,
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		 struct ssh_channel *channel,
		 int take_into_use)
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{
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  struct channel_table *table = connection->table;
  
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  assert(table->in_use[local_channel_number] == CHANNEL_RESERVED);
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  assert(!table->channels[local_channel_number]);
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  verbose("Registering local channel %i.\n",
	  local_channel_number);
  
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  /* NOTE: Is this the right place to install this exception handler? */
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  channel->e =
    make_exc_finish_channel_handler(connection,
				    local_channel_number,
				    channel->e ? channel->e : connection->e,
				    HANDLER_CONTEXT);

  table->channels[local_channel_number] = channel;
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  if (take_into_use)
    use_channel(connection, local_channel_number);
  
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  REMEMBER_RESOURCE(connection->resources, &channel->resources->super);
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}

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struct ssh_channel *
lookup_channel(struct channel_table *table, UINT32 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 i)
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{
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  return ( (i < table->used_channels)
	   && (table->in_use[i] == CHANNEL_RESERVED))
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    ? table->channels[i] : NULL;
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}

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/* FIXME: It seems suboptimal to send a window adjust message for
 * *every* write that we do. A better scheme might be as follows:
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 *
 * 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. */
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static void
adjust_rec_window(struct flow_controlled *f, UINT32 written)
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{
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  CAST_SUBTYPE(ssh_channel, channel, f);

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  /* 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->write,
	    prepare_window_adjust(channel, written));
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}

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void
channel_start_receive(struct ssh_channel *channel,
		      UINT32 initial_window_size)
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{
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  if (channel->rec_window_size < initial_window_size)
    A_WRITE(channel->write,
	    prepare_window_adjust
	    (channel, initial_window_size - channel->rec_window_size));
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}

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/* Ugly macros to make it a little simpler to free the input packet at
 * the right time. */

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#define RETURN goto foo_finish
#define END(s) do { foo_finish: \
                    lsh_string_free((s)); \
                    return; } while(0)

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

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

  return self;
}

/* GABA:
   (class
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     (name global_request_continuation)
     (super command_continuation)
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     (vars
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       (connection object ssh_connection)
       (active object request_status)))
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*/

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static void 
send_global_request_responses(struct ssh_connection *connection, 
			      struct object_queue *q)
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{
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   for (;;)
     {
       CAST(request_status, n, object_queue_peek_head(q));
       if (!n || (n->status < 0))
	 break;
 
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      object_queue_remove_head(q);
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      C_WRITE(connection,
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	      (n->status
	       ? format_global_success()
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	       : format_global_failure()));
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    }
}

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static void
do_global_request_response(struct command_continuation *s,
			   struct lsh_object *x UNUSED)
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{
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  CAST(global_request_continuation, self, s);
  struct object_queue *q = &self->connection->table->active_global_requests;
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  assert(self->active->status == -1);
  assert(!object_queue_is_empty(q));
	  
  self->active->status = 1;
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  send_global_request_responses(self->connection, q);
}
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static struct command_continuation *
make_global_request_response(struct ssh_connection *connection,
			     struct request_status *active)
{
  NEW(global_request_continuation, self);

  self->super.c = do_global_request_response;
  self->connection = connection;
  self->active = active;
   
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  return &self->super;
}
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/* GABA:
   (class
     (name global_request_exception_handler)
     (super exception_handler)
     (vars
       (connection object ssh_connection)
       (active object request_status)))
*/

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

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

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

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  self->super.raise = do_exc_global_request_handler;
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  self->super.context = context;
  self->super.parent = h;
  self->active = active;
  self->connection = connection;
  return &self->super;
}
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DEFINE_PACKET_HANDLER(static, global_request_handler, connection, packet)
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{
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  struct simple_buffer buffer;
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  unsigned msg_number;
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  int name;
  int want_reply;
  
  simple_buffer_init(&buffer, packet->length, packet->data);

  if (parse_uint8(&buffer, &msg_number)
      && (msg_number == SSH_MSG_GLOBAL_REQUEST)
      && parse_atom(&buffer, &name)
      && parse_boolean(&buffer, &want_reply))
    {
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      struct global_request *req = NULL;
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      struct command_continuation *c = &discard_continuation;
      struct exception_handler *e = connection->e;
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      if (name && connection->table->global_requests)
	{
	  CAST_SUBTYPE(global_request, r,
		       ALIST_GET(connection->table->global_requests,
				 name));
	  req = r;
	}
      if (!req)
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	{
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	  lsh_string_free(packet);
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	  C_WRITE(connection, format_global_failure());
	  return;
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	}
      else
	{
	  if (want_reply)
	    {
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	      struct request_status *a = make_request_status();
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	      object_queue_add_tail(&connection->table->active_global_requests,
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				    &a->super);
	      
	      c = make_global_request_response(connection, a);
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	      e = make_global_request_exception_handler(connection, a, e, HANDLER_CONTEXT);
	    }
	  else
	    {
	      /* We should ignore failures. */
	      static 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);
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	    }
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	  GLOBAL_REQUEST(req, connection, name, want_reply, &buffer, c, e);
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	}
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    }
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  else
    {
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      PROTOCOL_ERROR(connection->e, "Invalid SSH_MSG_GLOBAL_REQUEST message.");
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    }
  lsh_string_free(packet);
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}

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DEFINE_PACKET_HANDLER(static, global_success_handler,
		      connection, packet)
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{
  if (packet->length != 1)
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    {
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      PROTOCOL_ERROR(connection->e, "Invalid GLOBAL_REQUEST_SUCCESS message.");
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      RETURN;
    }
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  assert(packet->data[0] == SSH_MSG_REQUEST_SUCCESS);

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

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

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DEFINE_PACKET_HANDLER(static, global_failure_handler,
		      connection, packet)
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{
  if (packet->length != 1)
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    {
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      PROTOCOL_ERROR(connection->e, "Invalid GLOBAL_REQUEST_FAILURE message.");
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      RETURN;
    }
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  assert(packet->data[0] == SSH_MSG_REQUEST_FAILURE);

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

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/* 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. */

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

static void
send_channel_request_responses(struct ssh_connection *connection,
			       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);

      C_WRITE(connection,
	      (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->connection, self->channel, q);
}

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

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

  return &self->super;
}

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

/* NOTE: We handle *only* EXC_CHANNEL_REQUEST */
static void 
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do_exc_channel_request_handler(struct exception_handler *c,
			       const struct exception *e)
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{
  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->connection, self->channel, q);
    }
  else
    EXCEPTION_RAISE(c->parent, e);
}

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

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

  return &self->super;
}

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DEFINE_PACKET_HANDLER(static, channel_request_handler,
		      connection, packet)
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{
  struct simple_buffer buffer;
  unsigned msg_number;
  UINT32 channel_number;
  int type;
  int want_reply;
  
  simple_buffer_init(&buffer, packet->length, packet->data);

  if (parse_uint8(&buffer, &msg_number)
      && (msg_number == SSH_MSG_CHANNEL_REQUEST)
      && parse_uint32(&buffer, &channel_number)
      && parse_atom(&buffer, &type)
      && parse_boolean(&buffer, &want_reply))
    {
      struct ssh_channel *channel = lookup_channel(connection->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)
	{
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	  struct channel_request *req = NULL;
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	  struct command_continuation *c = &discard_continuation;
	  struct exception_handler *e = channel->e;

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	  if (type && channel->request_types)
	    {
	      CAST_SUBTYPE(channel_request, r,
			   ALIST_GET(channel->request_types, type));
	      req = r;
	    }
	  if (req)
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	    {
	      if (want_reply)
		{
		  struct request_status *a = make_request_status();
		  
		  object_queue_add_tail(&channel->active_requests,
					&a->super);
		  
		  c = make_channel_request_response(connection, channel, a);
		  e = make_channel_request_exception_handler(connection, channel, a, e, HANDLER_CONTEXT);
		  
		}
	      else
		{
		  /* We should ignore failures. */
		  static 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, connection, type, want_reply, &buffer, c, e);
	    }
	  else
	    {
	      if (want_reply)
		C_WRITE(connection,
			format_channel_failure(channel->channel_number));
	    }
	}
      else
	{
	  werror("SSH_MSG_CHANNEL_REQUEST on nonexistant channel %i\n",
		 channel_number);
	}
    }
  else
    PROTOCOL_ERROR(connection->e, "Invalid SSH_MSG_CHANNEL_REQUEST message.");
  
  lsh_string_free(packet);
}


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/* GABA:
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   (class
     (name channel_open_continuation)
     (super command_continuation)
     (vars
       (connection object ssh_connection)
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       (local_channel_number . UINT32)
       (remote_channel_number . UINT32)
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       (send_window_size . UINT32)
       (send_max_packet . UINT32)))
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*/
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static void
do_channel_open_continue(struct command_continuation *c,
			 struct lsh_object *value)
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{
  CAST(channel_open_continuation, self, c);
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  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. */
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  channel->send_window_size = self->send_window_size;
  channel->send_max_packet = self->send_max_packet;
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  channel->channel_number = self->remote_channel_number;

  /* FIXME: Is the channel->write field really needed? */
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  channel->write = self->connection->write;
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  register_channel(self->connection,
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		   self->local_channel_number, channel,
		   1);
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  /* FIXME: Doesn't support sending extra arguments with the
   * confirmation message. */

  C_WRITE(self->connection,
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	  format_open_confirmation(channel, self->local_channel_number, ""));
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}
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static struct command_continuation *
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make_channel_open_continuation(struct ssh_connection *connection,
			       UINT32 local_channel_number,
			       UINT32 remote_channel_number,
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			       UINT32 send_window_size,
			       UINT32 send_max_packet)
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{
  NEW(channel_open_continuation, self);
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  self->super.c = do_channel_open_continue;
  self->connection = connection;
  self->local_channel_number = local_channel_number;
  self->remote_channel_number = remote_channel_number;
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  self->send_window_size = send_window_size;
  self->send_max_packet = send_max_packet;
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  return &self->super;
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}
			       
/* GABA:
   (class
     (name exc_channel_open_handler)
     (super exception_handler)
     (vars
       (connection object ssh_connection)
       (local_channel_number . UINT32)
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       (remote_channel_number . UINT32)))
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*/

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

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

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

static struct exception_handler *
make_exc_channel_open_handler(struct ssh_connection *connection,
			      UINT32 local_channel_number,