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Last updated: Sat Feb 3 05:00:33 2007

Asterisk developer's documentation :: Codename Pineapple

---

chan_h323.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2005
 *
 * OpenH323 Channel Driver for ASTERISK PBX.
 *       By Jeremy McNamara
 *                      For The NuFone Network
 *
 * chan_h323 has been derived from code created by
 *               Michael Manousos and Mark Spencer
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief This file is part of the chan_h323 driver for Asterisk
 *
 * \author Jeremy McNamara
 *
 * \par See also
 * \arg Config_h323
 *
 * \ingroup channel_drivers
 */

/*** MODULEINFO
   <depend>openh323</depend>
   <defaultenabled>no</defaultenabled>
 ***/

#ifdef __cplusplus
extern "C" {
#endif

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 51637 $")

#ifdef __cplusplus
}
#endif

#include <sys/socket.h>
#include <sys/signal.h>
#include <sys/param.h>
#if defined(BSD)
#ifndef IPTOS_MINCOST
#define IPTOS_MINCOST 0x02
#endif
#endif
#include <arpa/inet.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <unistd.h>
#include <stdlib.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

#ifdef __cplusplus
extern "C" {
#endif

#include "asterisk/lock.h"
#include "asterisk/logger.h"
#include "asterisk/channel.h"
#include "asterisk/config.h"
#include "asterisk/module.h"
#include "asterisk/musiconhold.h"
#include "asterisk/pbx.h"
#include "asterisk/options.h"
#include "asterisk/utils.h"
#include "asterisk/lock.h"
#include "asterisk/sched.h"
#include "asterisk/io.h"
#include "asterisk/rtp.h"
#include "asterisk/acl.h"
#include "asterisk/callerid.h"
#include "asterisk/cli.h"
#include "asterisk/dsp.h"
#include "asterisk/causes.h"
#include "asterisk/stringfields.h"
#include "asterisk/abstract_jb.h"
#include "asterisk/astobj.h"

#ifdef __cplusplus
}
#endif

#include "h323/chan_h323.h"

receive_digit_cb on_receive_digit;
on_rtp_cb on_external_rtp_create;
start_rtp_cb on_start_rtp_channel;
setup_incoming_cb on_incoming_call;
setup_outbound_cb on_outgoing_call;
chan_ringing_cb   on_chan_ringing;
con_established_cb on_connection_established;
clear_con_cb on_connection_cleared;
answer_call_cb on_answer_call;
progress_cb on_progress;
rfc2833_cb on_set_rfc2833_payload;
hangup_cb on_hangup;
setcapabilities_cb on_setcapabilities;
setpeercapabilities_cb on_setpeercapabilities;
onhold_cb on_hold;

/* global debug flag */
int h323debug;

/*! Global jitterbuffer configuration - by default, jb is disabled */
static struct ast_jb_conf default_jbconf =
{
   .flags = 0,
   .max_size = -1,
   .resync_threshold = -1,
   .impl = ""
};
static struct ast_jb_conf global_jbconf;

/** Variables required by Asterisk */
static const char tdesc[] = "The NuFone Network's Open H.323 Channel Driver";
static const char config[] = "h323.conf";
static char default_context[AST_MAX_CONTEXT] = "default";
static struct sockaddr_in bindaddr;

#define GLOBAL_CAPABILITY (AST_FORMAT_G723_1 | AST_FORMAT_GSM | AST_FORMAT_ULAW | AST_FORMAT_ALAW | AST_FORMAT_G729A | AST_FORMAT_G726_AAL2 | AST_FORMAT_H261)

/** H.323 configuration values */
static int h323_signalling_port = 1720;
static char gatekeeper[100];
static int gatekeeper_disable = 1;
static int gatekeeper_discover = 0;
static int gkroute = 0;
/* Find user by alias (h.323 id) is default, alternative is the incomming call's source IP address*/
static int userbyalias = 1;
static int acceptAnonymous = 1;
static int tos = 0;
static char secret[50];
static unsigned int unique = 0;

static call_options_t global_options;

/** Private structure of a OpenH323 channel */
struct oh323_pvt {
   ast_mutex_t lock;             /* Channel private lock */
   call_options_t options;          /* Options to be used during call setup */
   int alreadygone;              /* Whether or not we've already been destroyed by our peer */
   int needdestroy;              /* if we need to be destroyed */
   call_details_t cd;               /* Call details */
   struct ast_channel *owner;       /* Who owns us */
   struct sockaddr_in sa;           /* Our peer */
   struct sockaddr_in redirip;         /* Where our RTP should be going if not to us */
   int nonCodecCapability;          /* non-audio capability */
   int outgoing;                 /* Outgoing or incoming call? */
   char exten[AST_MAX_EXTENSION];      /* Requested extension */
   char context[AST_MAX_CONTEXT];      /* Context where to start */
   char accountcode[256];           /* Account code */
   char rdnis[80];                  /* Referring DNIS, if available */
   int amaflags;                 /* AMA Flags */
   struct ast_rtp *rtp;          /* RTP Session */
   struct ast_dsp *vad;          /* Used for in-band DTMF detection */
   int nativeformats;               /* Codec formats supported by a channel */
   int needhangup;                  /* Send hangup when Asterisk is ready */
   int hangupcause;              /* Hangup cause from OpenH323 layer */
   int newstate;                 /* Pending state change */
   int newcontrol;                  /* Pending control to send */
   int newdigit;                 /* Pending DTMF digit to send */
   int newduration;              /* Pending DTMF digit duration to send */
   int pref_codec;                  /* Preferred codec */
   int peercapability;              /* Capabilities learned from peer */
   int jointcapability;          /* Common capabilities for local and remote side */
   struct ast_codec_pref peer_prefs;   /* Preferenced list of codecs which remote side supports */
   int dtmf_pt[2];                  /* Payload code used for RFC2833/CISCO messages */
   int curDTMF;                  /* DTMF tone being generated to Asterisk side */
   int DTMFsched;                /* Scheduler descriptor for DTMF */
   int update_rtp_info;          /* Configuration of fd's array is pending */
   int recvonly;                 /* Peer isn't wish to receive our voice stream */
   int txDtmfDigit;              /* DTMF digit being to send to H.323 side */
   int noInbandDtmf;             /* Inband DTMF processing by DSP isn't available */
   int connection_established;         /* Call got CONNECT message */
   int got_progress;             /* Call got PROGRESS message, pass inband audio */
   struct oh323_pvt *next;          /* Next channel in list */
} *iflist = NULL;

static struct ast_user_list {
   ASTOBJ_CONTAINER_COMPONENTS(struct oh323_user);
} userl;

static struct ast_peer_list {
   ASTOBJ_CONTAINER_COMPONENTS(struct oh323_peer);
} peerl;

static struct ast_alias_list {
   ASTOBJ_CONTAINER_COMPONENTS(struct oh323_alias);
} aliasl;

/** Asterisk RTP stuff */
static struct sched_context *sched;
static struct io_context *io;

/** Protect the interface list (oh323_pvt) */
AST_MUTEX_DEFINE_STATIC(iflock);

/* Protect the monitoring thread, so only one process can kill or start it, and not
   when it's doing something critical. */
AST_MUTEX_DEFINE_STATIC(monlock);

/* Protect the H.323 capabilities list, to avoid more than one channel to set the capabilities simultaneaously in the h323 stack. */
AST_MUTEX_DEFINE_STATIC(caplock);

/* Protect the reload process */
AST_MUTEX_DEFINE_STATIC(h323_reload_lock);
static int h323_reloading = 0;

/* This is the thread for the monitor which checks for input on the channels
   which are not currently in use. */
static pthread_t monitor_thread = AST_PTHREADT_NULL;
static int restart_monitor(void);
static int h323_do_reload(void);

static struct ast_channel *oh323_request(const char *type, int format, void *data, int *cause);
static int oh323_digit_begin(struct ast_channel *c, char digit);
static int oh323_digit_end(struct ast_channel *c, char digit, unsigned int duration);
static int oh323_call(struct ast_channel *c, char *dest, int timeout);
static int oh323_hangup(struct ast_channel *c);
static int oh323_answer(struct ast_channel *c);
static struct ast_frame *oh323_read(struct ast_channel *c);
static int oh323_write(struct ast_channel *c, struct ast_frame *frame);
static int oh323_indicate(struct ast_channel *c, int condition, const void *data, size_t datalen);
static int oh323_fixup(struct ast_channel *oldchan, struct ast_channel *newchan);

static const struct ast_channel_tech oh323_tech = {
   .type = "H323",
   .description = tdesc,
   .capabilities = ((AST_FORMAT_MAX_AUDIO << 1) - 1),
   .properties = AST_CHAN_TP_WANTSJITTER | AST_CHAN_TP_CREATESJITTER,
   .requester = oh323_request,
   .send_digit_begin = oh323_digit_begin,
   .send_digit_end = oh323_digit_end,
   .call = oh323_call,
   .hangup = oh323_hangup,
   .answer = oh323_answer,
   .read = oh323_read,
   .write = oh323_write,
   .indicate = oh323_indicate,
   .fixup = oh323_fixup,
   /* disable, for now */
#if 0
   .bridge = ast_rtp_bridge,
#endif
};

static const char* redirectingreason2str(int redirectingreason)
{
   switch (redirectingreason) {
   case 0:
      return "UNKNOWN";
   case 1:
      return "BUSY";
   case 2:
      return "NO_REPLY";
   case 0xF:
      return "UNCONDITIONAL";
   default:
      return "NOREDIRECT";
   }
}

static void oh323_destroy_alias(struct oh323_alias *alias)
{
   if (h323debug)
      ast_log(LOG_DEBUG, "Destroying alias '%s'\n", alias->name);
   free(alias);
}

static void oh323_destroy_user(struct oh323_user *user)
{
   if (h323debug)
      ast_log(LOG_DEBUG, "Destroying user '%s'\n", user->name);
   ast_free_ha(user->ha);
   free(user);
}

static void oh323_destroy_peer(struct oh323_peer *peer)
{
   if (h323debug)
      ast_log(LOG_DEBUG, "Destroying peer '%s'\n", peer->name);
   ast_free_ha(peer->ha);
   free(peer);
}

static int oh323_simulate_dtmf_end(void *data)
{
   struct oh323_pvt *pvt = data;

   if (pvt) {
      ast_mutex_lock(&pvt->lock);
      /* Don't hold pvt lock while trying to lock the channel */
      while(pvt->owner && ast_channel_trylock(pvt->owner)) {
         ast_mutex_unlock(&pvt->lock);
         usleep(1);
         ast_mutex_lock(&pvt->lock);
      }

      if (pvt->owner) {
         struct ast_frame f = {
            .frametype = AST_FRAME_DTMF_END,
            .subclass = pvt->curDTMF,
            .samples = 0,
            .src = "SIMULATE_DTMF_END",
         };
         ast_queue_frame(pvt->owner, &f);
         ast_channel_unlock(pvt->owner);
      }

      pvt->DTMFsched = -1;
      ast_mutex_unlock(&pvt->lock);
   }

   return 0;
}

/* Channel and private structures should be already locked */
static void __oh323_update_info(struct ast_channel *c, struct oh323_pvt *pvt)
{
   if (c->nativeformats != pvt->nativeformats) {
      if (h323debug)
         ast_log(LOG_DEBUG, "Preparing %s for new native format\n", c->name);
      c->nativeformats = pvt->nativeformats;
      ast_set_read_format(c, c->readformat);
      ast_set_write_format(c, c->writeformat);
   }
   if (pvt->needhangup) {
      if (h323debug)
         ast_log(LOG_DEBUG, "Process pending hangup for %s\n", c->name);
      c->_softhangup |= AST_SOFTHANGUP_DEV;
      c->hangupcause = pvt->hangupcause;
      ast_queue_hangup(c);
      pvt->needhangup = 0;
      pvt->newstate = pvt->newcontrol = pvt->newdigit = pvt->DTMFsched = -1;
   }
   if (pvt->newstate >= 0) {
      ast_setstate(c, pvt->newstate);
      pvt->newstate = -1;
   }
   if (pvt->newcontrol >= 0) {
      ast_queue_control(c, pvt->newcontrol);
      pvt->newcontrol = -1;
   }
   if (pvt->newdigit >= 0) {
      struct ast_frame f = {
         .frametype = AST_FRAME_DTMF_END,
         .subclass = pvt->newdigit,
         .samples = pvt->newduration * 8,
         .src = "UPDATE_INFO",
      };
      if (pvt->newdigit == ' ') {      /* signalUpdate message */
         f.subclass = pvt->curDTMF;
         if (pvt->DTMFsched >= 0) {
            ast_sched_del(sched, pvt->DTMFsched);
            pvt->DTMFsched = -1;
         }
      } else {                /* Regular input or signal message */
         if (pvt->newduration) {    /* This is a signal, signalUpdate follows */
            f.frametype = AST_FRAME_DTMF_BEGIN;
            if (pvt->DTMFsched >= 0)
               ast_sched_del(sched, pvt->DTMFsched);
            pvt->DTMFsched = ast_sched_add(sched, pvt->newduration, oh323_simulate_dtmf_end, pvt);
            if (h323debug)
               ast_log(LOG_DTMF, "Scheduled DTMF END simulation for %d ms, id=%d\n", pvt->newduration, pvt->DTMFsched);
         }
         pvt->curDTMF = pvt->newdigit;
      }
      ast_queue_frame(c, &f);
      pvt->newdigit = -1;
   }
   if (pvt->update_rtp_info > 0) {
      if (pvt->rtp) {
         ast_jb_configure(c, &global_jbconf);
         c->fds[0] = ast_rtp_fd(pvt->rtp);
         c->fds[1] = ast_rtcp_fd(pvt->rtp);
         ast_queue_frame(pvt->owner, &ast_null_frame);   /* Tell Asterisk to apply changes */
      }
      pvt->update_rtp_info = -1;
   }
}

/* Only channel structure should be locked */
static void oh323_update_info(struct ast_channel *c)
{
   struct oh323_pvt *pvt = c->tech_pvt;

   if (pvt) {
      ast_mutex_lock(&pvt->lock);
      __oh323_update_info(c, pvt);
      ast_mutex_unlock(&pvt->lock);
   }
}

static void cleanup_call_details(call_details_t *cd)
{
   if (cd->call_token) {
      free(cd->call_token);
      cd->call_token = NULL;
   }
   if (cd->call_source_aliases) {
      free(cd->call_source_aliases);
      cd->call_source_aliases = NULL;
   }
   if (cd->call_dest_alias) {
      free(cd->call_dest_alias);
      cd->call_dest_alias = NULL;
   }
   if (cd->call_source_name) {
      free(cd->call_source_name);
      cd->call_source_name = NULL;
   }
   if (cd->call_source_e164) {
      free(cd->call_source_e164);
      cd->call_source_e164 = NULL;
   }
   if (cd->call_dest_e164) {
      free(cd->call_dest_e164);
      cd->call_dest_e164 = NULL;
   }
   if (cd->sourceIp) {
      free(cd->sourceIp);
      cd->sourceIp = NULL;
   }
   if (cd->redirect_number) {
      free(cd->redirect_number);
      cd->redirect_number = NULL;
   }
}

static void __oh323_destroy(struct oh323_pvt *pvt)
{
   struct oh323_pvt *cur, *prev = NULL;

   if (pvt->DTMFsched >= 0) {
      ast_sched_del(sched, pvt->DTMFsched);
      pvt->DTMFsched = -1;
   }

   if (pvt->rtp) {
      ast_rtp_destroy(pvt->rtp);
   }

   /* Free dsp used for in-band DTMF detection */
   if (pvt->vad) {
      ast_dsp_free(pvt->vad);
   }
   cleanup_call_details(&pvt->cd);

   /* Unlink us from the owner if we have one */
   if (pvt->owner) {
      ast_channel_lock(pvt->owner);
      if (h323debug)
         ast_log(LOG_DEBUG, "Detaching from %s\n", pvt->owner->name);
      pvt->owner->tech_pvt = NULL;
      ast_channel_unlock(pvt->owner);
   }
   cur = iflist;
   while(cur) {
      if (cur == pvt) {
         if (prev)
            prev->next = cur->next;
         else
            iflist = cur->next;
         break;
      }
      prev = cur;
      cur = cur->next;
   }
   if (!cur) {
      ast_log(LOG_WARNING, "%p is not in list?!?! \n", cur);
   } else {
      ast_mutex_unlock(&pvt->lock);
      ast_mutex_destroy(&pvt->lock);
      free(pvt);
   }
}

static void oh323_destroy(struct oh323_pvt *pvt)
{
   if (h323debug) {
      ast_log(LOG_DEBUG, "Destroying channel %s\n", (pvt->owner ? pvt->owner->name : "<unknown>"));
   }
   ast_mutex_lock(&iflock);
   ast_mutex_lock(&pvt->lock);
   __oh323_destroy(pvt);
   ast_mutex_unlock(&iflock);
}

static int oh323_digit_begin(struct ast_channel *c, char digit)
{
   struct oh323_pvt *pvt = (struct oh323_pvt *) c->tech_pvt;
   char *token;

   if (!pvt) {
      ast_log(LOG_ERROR, "No private structure?! This is bad\n");
      return -1;
   }
   ast_mutex_lock(&pvt->lock);
   if (pvt->rtp &&
      (((pvt->options.dtmfmode & H323_DTMF_RFC2833) && pvt->dtmf_pt[0])
       /*|| ((pvt->options.dtmfmode & H323_DTMF_CISCO) && pvt->dtmf_pt[1]))*/)) {
      /* out-of-band DTMF */
      if (h323debug) {
         ast_log(LOG_DTMF, "Begin sending out-of-band digit %c on %s\n", digit, c->name);
      }
      ast_rtp_senddigit_begin(pvt->rtp, digit);
      ast_mutex_unlock(&pvt->lock);
   } else if (pvt->txDtmfDigit != digit) {
      /* in-band DTMF */
      if (h323debug) {
         ast_log(LOG_DTMF, "Begin sending inband digit %c on %s\n", digit, c->name);
      }
      pvt->txDtmfDigit = digit;
      token = pvt->cd.call_token ? strdup(pvt->cd.call_token) : NULL;
      ast_mutex_unlock(&pvt->lock);
      h323_send_tone(token, digit);
      if (token) {
         free(token);
      }
   } else
      ast_mutex_unlock(&pvt->lock);
   oh323_update_info(c);
   return 0;
}

/**
 * Send (play) the specified digit to the channel.
 *
 */
static int oh323_digit_end(struct ast_channel *c, char digit, unsigned int duration)
{
   struct oh323_pvt *pvt = (struct oh323_pvt *) c->tech_pvt;
   char *token;

   if (!pvt) {
      ast_log(LOG_ERROR, "No private structure?! This is bad\n");
      return -1;
   }
   ast_mutex_lock(&pvt->lock);
   if (pvt->rtp && (pvt->options.dtmfmode & H323_DTMF_RFC2833) && ((pvt->dtmf_pt[0] > 0) || (pvt->dtmf_pt[0] > 0))) {
      /* out-of-band DTMF */
      if (h323debug) {
         ast_log(LOG_DTMF, "End sending out-of-band digit %c on %s\n", digit, c->name);
      }
      ast_rtp_senddigit_end(pvt->rtp, digit);
      ast_mutex_unlock(&pvt->lock);
   } else {
      /* in-band DTMF */
      if (h323debug) {
         ast_log(LOG_DTMF, "End sending inband digit %c on %s\n", digit, c->name);
      }
      pvt->txDtmfDigit = ' ';
      token = pvt->cd.call_token ? strdup(pvt->cd.call_token) : NULL;
      ast_mutex_unlock(&pvt->lock);
      h323_send_tone(token, ' ');
      if (token) {
         free(token);
      }
   }
   oh323_update_info(c);
   return 0;
}

/**
 * Make a call over the specified channel to the specified
 * destination.
 * Returns -1 on error, 0 on success.
 */
static int oh323_call(struct ast_channel *c, char *dest, int timeout)
{
   int res = 0;
   struct oh323_pvt *pvt = (struct oh323_pvt *)c->tech_pvt;
   const char *addr;
   char called_addr[1024];

   if (h323debug) {
      ast_log(LOG_DEBUG, "Calling to %s on %s\n", dest, c->name);
   }
   if ((c->_state != AST_STATE_DOWN) && (c->_state != AST_STATE_RESERVED)) {
      ast_log(LOG_WARNING, "Line is already in use (%s)\n", c->name);
      return -1;
   }
   ast_mutex_lock(&pvt->lock);
   if (!gatekeeper_disable) {
      if (ast_strlen_zero(pvt->exten)) {
         ast_copy_string(called_addr, dest, sizeof(called_addr));
      } else {
         snprintf(called_addr, sizeof(called_addr), "%s@%s", pvt->exten, dest);
      }
   } else {
      res = htons(pvt->sa.sin_port);
      addr = ast_inet_ntoa(pvt->sa.sin_addr);
      if (ast_strlen_zero(pvt->exten)) {
         snprintf(called_addr, sizeof(called_addr), "%s:%d", addr, res);
      } else {
         snprintf(called_addr, sizeof(called_addr), "%s@%s:%d", pvt->exten, addr, res);
      }
   }
   /* make sure null terminated */
   called_addr[sizeof(called_addr) - 1] = '\0';

   if (c->cid.cid_num)
      ast_copy_string(pvt->options.cid_num, c->cid.cid_num, sizeof(pvt->options.cid_num));

   if (c->cid.cid_name)
      ast_copy_string(pvt->options.cid_name, c->cid.cid_name, sizeof(pvt->options.cid_name));

   if (c->cid.cid_rdnis) {
      ast_copy_string(pvt->options.cid_rdnis, c->cid.cid_rdnis, sizeof(pvt->options.cid_rdnis));
   }

   pvt->options.presentation = c->cid.cid_pres;
   pvt->options.type_of_number = c->cid.cid_ton;

   if ((addr = pbx_builtin_getvar_helper(c, "PRIREDIRECTREASON"))) {
      if (!strcasecmp(addr, "UNKNOWN"))
         pvt->options.redirect_reason = 0;
      else if (!strcasecmp(addr, "BUSY"))
         pvt->options.redirect_reason = 1;
      else if (!strcasecmp(addr, "NO_REPLY"))
         pvt->options.redirect_reason = 2;
      else if (!strcasecmp(addr, "UNCONDITIONAL"))
         pvt->options.redirect_reason = 15;
      else
         pvt->options.redirect_reason = -1;
   } else
      pvt->options.redirect_reason = -1;

   pvt->options.transfer_capability = c->transfercapability;

   /* indicate that this is an outgoing call */
   pvt->outgoing = 1;

   if (option_verbose > 2)
      ast_verbose(VERBOSE_PREFIX_3 "Requested transfer capability: 0x%.2x - %s\n", c->transfercapability, ast_transfercapability2str(c->transfercapability));
   if (h323debug)
      ast_log(LOG_DEBUG, "Placing outgoing call to %s, %d/%d\n", called_addr, pvt->options.dtmfcodec[0], pvt->options.dtmfcodec[1]);
   ast_mutex_unlock(&pvt->lock);
   res = h323_make_call(called_addr, &(pvt->cd), &pvt->options);
   if (res) {
      ast_log(LOG_NOTICE, "h323_make_call failed(%s)\n", c->name);
      return -1;
   }
   oh323_update_info(c);
   return 0;
}

static int oh323_answer(struct ast_channel *c)
{
   int res;
   struct oh323_pvt *pvt = (struct oh323_pvt *) c->tech_pvt;
   char *token;

   if (h323debug)
      ast_log(LOG_DEBUG, "Answering on %s\n", c->name);

   ast_mutex_lock(&pvt->lock);
   token = pvt->cd.call_token ? strdup(pvt->cd.call_token) : NULL;
   ast_mutex_unlock(&pvt->lock);
   res = h323_answering_call(token, 0);
   if (token)
      free(token);

   oh323_update_info(c);
   if (c->_state != AST_STATE_UP) {
      ast_setstate(c, AST_STATE_UP);
   }
   return res;
}

static int oh323_hangup(struct ast_channel *c)
{
   struct oh323_pvt *pvt = (struct oh323_pvt *) c->tech_pvt;
   int q931cause = AST_CAUSE_NORMAL_CLEARING;
   char *call_token;


   if (h323debug)
      ast_log(LOG_DEBUG, "Hanging up and scheduling destroy of call %s\n", c->name);

   if (!c->tech_pvt) {
      ast_log(LOG_WARNING, "Asked to hangup channel not connected\n");
      return 0;
   }
   ast_mutex_lock(&pvt->lock);
   /* Determine how to disconnect */
   if (pvt->owner != c) {
      ast_log(LOG_WARNING, "Huh?  We aren't the owner?\n");
      ast_mutex_unlock(&pvt->lock);
      return 0;
   }

   pvt->owner = NULL;
   c->tech_pvt = NULL;

   if (c->hangupcause) {
      q931cause = c->hangupcause;
   } else {
      const char *cause = pbx_builtin_getvar_helper(c, "DIALSTATUS");
      if (cause) {
         if (!strcmp(cause, "CONGESTION")) {
            q931cause = AST_CAUSE_NORMAL_CIRCUIT_CONGESTION;
         } else if (!strcmp(cause, "BUSY")) {
            q931cause = AST_CAUSE_USER_BUSY;
         } else if (!strcmp(cause, "CHANISUNVAIL")) {
            q931cause = AST_CAUSE_REQUESTED_CHAN_UNAVAIL;
         } else if (!strcmp(cause, "NOANSWER")) {
            q931cause = AST_CAUSE_NO_ANSWER;
         } else if (!strcmp(cause, "CANCEL")) {
            q931cause = AST_CAUSE_CALL_REJECTED;
         }
      }
   }

   /* Start the process if it's not already started */
   if (!pvt->alreadygone && !pvt->hangupcause) {
      call_token = pvt->cd.call_token ? strdup(pvt->cd.call_token) : NULL;
      if (call_token) {
         /* Release lock to eliminate deadlock */
         ast_mutex_unlock(&pvt->lock);
         if (h323_clear_call(call_token, q931cause)) {
            ast_log(LOG_WARNING, "ClearCall failed.\n");
         }
         free(call_token);
         ast_mutex_lock(&pvt->lock);
      }
   }
   pvt->needdestroy = 1;
   ast_mutex_unlock(&pvt->lock);

   /* Update usage counter */
   ast_module_unref(ast_module_info->self);

   return 0;
}

static struct ast_frame *oh323_rtp_read(struct oh323_pvt *pvt)
{
   /* Retrieve audio/etc from channel. Assumes pvt->lock is already held. */
   struct ast_frame *f;

   /* Only apply it for the first packet, we just need the correct ip/port */
   if (pvt->options.nat) {
      ast_rtp_setnat(pvt->rtp, pvt->options.nat);
      pvt->options.nat = 0;
   }

   f = ast_rtp_read(pvt->rtp);
   /* Don't send RFC2833 if we're not supposed to */
   if (f && (f->frametype == AST_FRAME_DTMF) && !(pvt->options.dtmfmode & (H323_DTMF_RFC2833 | H323_DTMF_CISCO))) {
      return &ast_null_frame;
   }
   if (pvt->owner) {
      /* We already hold the channel lock */
      if (f->frametype == AST_FRAME_VOICE) {
         if (f->subclass != pvt->owner->nativeformats) {
            /* Try to avoid deadlock */
            if (ast_channel_trylock(pvt->owner)) {
               ast_log(LOG_NOTICE, "Format changed but channel is locked. Ignoring frame...\n");
               return &ast_null_frame;
            }
            if (h323debug)
               ast_log(LOG_DEBUG, "Oooh, format changed to %d\n", f->subclass);
            pvt->owner->nativeformats = f->subclass;
            pvt->nativeformats = f->subclass;
            ast_set_read_format(pvt->owner, pvt->owner->readformat);
            ast_set_write_format(pvt->owner, pvt->owner->writeformat);
            ast_channel_unlock(pvt->owner);
         }
         /* Do in-band DTMF detection */
         if ((pvt->options.dtmfmode & H323_DTMF_INBAND) && pvt->vad) {
            if ((pvt->nativeformats & (AST_FORMAT_SLINEAR | AST_FORMAT_ALAW | AST_FORMAT_ULAW))) {
               if (!ast_channel_trylock(pvt->owner)) {
                  f = ast_dsp_process(pvt->owner, pvt->vad, f);
                  ast_channel_unlock(pvt->owner);
               }
               else
                  ast_log(LOG_NOTICE, "Unable to process inband DTMF while channel is locked\n");
            } else if (pvt->nativeformats && !pvt->noInbandDtmf) {
               ast_log(LOG_NOTICE, "Inband DTMF is not supported on codec %s. Use RFC2833\n", ast_getformatname(f->subclass));
               pvt->noInbandDtmf = 1;
            }
            if (f &&(f->frametype == AST_FRAME_DTMF)) {
               if (h323debug)
                  ast_log(LOG_DTMF, "Received in-band digit %c.\n", f->subclass);
            }
         }
      }
   }
   return f;
}

static struct ast_frame *oh323_read(struct ast_channel *c)
{
   struct ast_frame *fr;
   struct oh323_pvt *pvt = (struct oh323_pvt *)c->tech_pvt;
   ast_mutex_lock(&pvt->lock);
   __oh323_update_info(c, pvt);
   switch(c->fdno) {
   case 0:
      fr = oh323_rtp_read(pvt);
      break;
   case 1:
      if (pvt->rtp)
         fr = ast_rtcp_read(pvt->rtp);
      else
         fr = &ast_null_frame;
      break;
   default:
      ast_log(LOG_ERROR, "Unable to handle fd %d on channel %s\n", c->fdno, c->name);
      fr = &ast_null_frame;
      break;
   }
   ast_mutex_unlock(&pvt->lock);
   return fr;
}

static int oh323_write(struct ast_channel *c, struct ast_frame *frame)
{
   struct