app_fax.c

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/*
 * Asterisk -- A telephony toolkit for Linux.
 *
 * Simple fax applications
 * 
 * 2007-2008, Dmitry Andrianov <asterisk@dima.spb.ru>
 *
 * Code based on original implementation by Steve Underwood <steveu@coppice.org>
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License
 *
 */

/*** MODULEINFO
    <depend>spandsp</depend>
***/
 
#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 235012 $")

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <pthread.h>
#include <errno.h>
#include <tiffio.h>

#include <spandsp.h>
#ifdef HAVE_SPANDSP_EXPOSE_H
#include <spandsp/expose.h>
#endif
#include <spandsp/version.h>

#include "asterisk/lock.h"
#include "asterisk/file.h"
#include "asterisk/logger.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/app.h"
#include "asterisk/dsp.h"
#include "asterisk/module.h"
#include "asterisk/manager.h"

static char *app_sndfax_name = "SendFAX";
static char *app_sndfax_synopsis = "Send a FAX";
static char *app_sndfax_desc = 
"  SendFAX(filename[|options]):\n"
"Send a given TIFF file to the channel as a FAX.\n"
"The option string may contain zero or more of the following characters:\n"
"     'a' - makes the application behave as an answering machine\n"
"           The default behaviour is to behave as a calling machine.\n"
"\n"
"This application uses following variables:\n"
"     LOCALSTATIONID to identify itself to the remote end.\n"
"     LOCALHEADERINFO to generate a header line on each page.\n"
"\n"
"This application sets the following channel variables upon completion:\n"
"     FAXSTATUS       - status of operation:\n"
"                           SUCCESS | FAILED\n"
"     FAXERROR        - Error when FAILED\n"
"     FAXMODE         - Mode used:\n"
"                           audio | T38\n"
"     REMOTESTATIONID - CSID of the remote side.\n"
"     FAXPAGES        - number of pages sent.\n"
"     FAXBITRATE      - transmition rate.\n"
"     FAXRESOLUTION   - resolution.\n"
"\n"
"Returns -1 in case of user hang up or any channel error.\n"
"Returns 0 on success.\n";

static char *app_rcvfax_name = "ReceiveFAX";
static char *app_rcvfax_synopsis = "Receive a FAX";
static char *app_rcvfax_desc = 
"  ReceiveFAX(filename[|options]):\n"
"Receives a fax from the channel into the given filename overwriting\n"
"the file if it already exists. File created will have TIFF format.\n"
"The option string may contain zero or more of the following characters:\n"
"     'c' -- makes the application behave as a calling machine\n"
"            The default behaviour is to behave as an answering machine.\n"
"\n"
"This application uses following variables:\n"
"     LOCALSTATIONID to identify itself to the remote end.\n"
"     LOCALHEADERINFO to generate a header line on each page.\n"
"\n"
"This application sets the following channel variables upon completion:\n"
"     FAXSTATUS       - status of operation:\n"
"                           SUCCESS | FAILED\n"
"     FAXERROR        - Error when FAILED\n"
"     FAXMODE         - Mode used:\n"
"                           audio | T38\n"
"     REMOTESTATIONID - CSID of the remote side.\n"
"     FAXPAGES        - number of pages sent.\n"
"     FAXBITRATE      - transmition rate.\n"
"     FAXRESOLUTION   - resolution.\n"
"\n"
"Returns -1 in case of user hang up or any channel error.\n"
"Returns 0 on success.\n";

#define MAX_SAMPLES 240

/* Watchdog. I have seen situations when remote fax disconnects (because of poor line
   quality) while SpanDSP continues staying in T30_STATE_IV_CTC state forever.
   To avoid this, we terminate when we see that T30 state does not change for 5 minutes.
   We also terminate application when more than 30 minutes passed regardless of
   state changes. This is just a precaution measure - no fax should take that long */

#define WATCHDOG_TOTAL_TIMEOUT   30 * 60
#define WATCHDOG_STATE_TIMEOUT   5 * 60

typedef struct {
   struct ast_channel *chan;
   enum ast_t38_state t38state;  /* T38 state of the channel */
   int direction;       /* Fax direction: 0 - receiving, 1 - sending */
   int caller_mode;
   char *file_name;
   struct ast_control_t38_parameters t38parameters;
   volatile int finished;
} fax_session;

static void span_message(int level, const char *msg)
{
   if (level == SPAN_LOG_ERROR) {
      ast_log(LOG_ERROR, "%s", msg);
   } else if (level == SPAN_LOG_WARNING) {
      ast_log(LOG_WARNING, "%s", msg);
   } else {
      ast_log(LOG_DEBUG, "%s", msg);
   }
}

static int t38_tx_packet_handler(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count)
{
   struct ast_channel *chan = (struct ast_channel *) user_data;

   struct ast_frame outf = {
      .frametype = AST_FRAME_MODEM,
      .subclass = AST_MODEM_T38,
      .src = __FUNCTION__,
   };

   /* TODO: Asterisk does not provide means of resending the same packet multiple
     times so count is ignored at the moment */

   AST_FRAME_SET_BUFFER(&outf, buf, 0, len);

   if (ast_write(chan, &outf) < 0) {
      ast_log(LOG_WARNING, "Unable to write frame to channel; %s\n", strerror(errno));
      return -1;
   }

   return 0;
}

static void phase_e_handler(t30_state_t *f, void *user_data, int result)
{
   const char *local_ident;
   const char *far_ident;
   char buf[20];
   fax_session *s = (fax_session *) user_data;
   t30_stats_t stat;
   int pages_transferred;

   ast_debug(1, "Fax phase E handler. result=%d\n", result);

   t30_get_transfer_statistics(f, &stat);

   s = (fax_session *) user_data;

   if (result != T30_ERR_OK) {
      s->finished = -1;

      /* FAXSTATUS is already set to FAILED */
      pbx_builtin_setvar_helper(s->chan, "FAXERROR", t30_completion_code_to_str(result));

      ast_log(LOG_WARNING, "Error transmitting fax. result=%d: %s.\n", result, t30_completion_code_to_str(result));

      return;
   }
   
   s->finished = 1; 
   
   local_ident = t30_get_tx_ident(f);
   far_ident = t30_get_rx_ident(f);
   pbx_builtin_setvar_helper(s->chan, "FAXSTATUS", "SUCCESS"); 
   pbx_builtin_setvar_helper(s->chan, "FAXERROR", NULL); 
   pbx_builtin_setvar_helper(s->chan, "REMOTESTATIONID", far_ident);
#if SPANDSP_RELEASE_DATE >= 20090220
   pages_transferred = (s->direction) ? stat.pages_tx : stat.pages_rx;
#else
   pages_transferred = stat.pages_transferred;
#endif
   snprintf(buf, sizeof(buf), "%d", pages_transferred);
   pbx_builtin_setvar_helper(s->chan, "FAXPAGES", buf);
   snprintf(buf, sizeof(buf), "%d", stat.y_resolution);
   pbx_builtin_setvar_helper(s->chan, "FAXRESOLUTION", buf);
   snprintf(buf, sizeof(buf), "%d", stat.bit_rate);
   pbx_builtin_setvar_helper(s->chan, "FAXBITRATE", buf); 
   
   ast_debug(1, "Fax transmitted successfully.\n");
   ast_debug(1, "  Remote station ID: %s\n", far_ident);
   ast_debug(1, "  Pages transferred: %d\n", pages_transferred);
   ast_debug(1, "  Image resolution:  %d x %d\n", stat.x_resolution, stat.y_resolution);
   ast_debug(1, "  Transfer Rate:     %d\n", stat.bit_rate);
   
   manager_event(EVENT_FLAG_CALL,
            s->direction ? "FaxSent" : "FaxReceived", 
            "Channel: %s\r\n"
            "Exten: %s\r\n"
            "CallerID: %s\r\n"
            "RemoteStationID: %s\r\n"
            "LocalStationID: %s\r\n"
            "PagesTransferred: %d\r\n"
            "Resolution: %d\r\n"
            "TransferRate: %d\r\n"
            "FileName: %s\r\n",
            s->chan->name,
            s->chan->exten,
            S_OR(s->chan->cid.cid_num, ""),
            far_ident,
            local_ident,
            pages_transferred,
            stat.y_resolution,
            stat.bit_rate,
            s->file_name);
}

/* === Helper functions to configure fax === */

/* Setup SPAN logging according to Asterisk debug level */
static int set_logging(logging_state_t *state)
{
   int level = SPAN_LOG_WARNING + option_debug;

   span_log_set_message_handler(state, span_message);
   span_log_set_level(state, SPAN_LOG_SHOW_SEVERITY | SPAN_LOG_SHOW_PROTOCOL | level); 

   return 0;
}

static void set_local_info(t30_state_t *state, fax_session *s)
{
   const char *x;

   x = pbx_builtin_getvar_helper(s->chan, "LOCALSTATIONID");
   if (!ast_strlen_zero(x))
      t30_set_tx_ident(state, x);

   x = pbx_builtin_getvar_helper(s->chan, "LOCALHEADERINFO");
   if (!ast_strlen_zero(x))
      t30_set_tx_page_header_info(state, x);
}

static void set_file(t30_state_t *state, fax_session *s)
{
   if (s->direction)
      t30_set_tx_file(state, s->file_name, -1, -1);
   else
      t30_set_rx_file(state, s->file_name, -1);
}

static void set_ecm(t30_state_t *state, int ecm)
{
   t30_set_ecm_capability(state, ecm);
   t30_set_supported_compressions(state, T30_SUPPORT_T4_1D_COMPRESSION | T30_SUPPORT_T4_2D_COMPRESSION | T30_SUPPORT_T6_COMPRESSION);
}

/* === Generator === */

/* This function is only needed to return passed params so
   generator_activate will save it to channel's generatordata */
static void *fax_generator_alloc(struct ast_channel *chan, void *params)
{
   return params;
}

static int fax_generator_generate(struct ast_channel *chan, void *data, int len, int samples)
{
   fax_state_t *fax = (fax_state_t*) data;
   uint8_t buffer[AST_FRIENDLY_OFFSET + MAX_SAMPLES * sizeof(uint16_t)];
   int16_t *buf = (int16_t *) (buffer + AST_FRIENDLY_OFFSET);
    
   struct ast_frame outf = {
      .frametype = AST_FRAME_VOICE,
      .subclass = AST_FORMAT_SLINEAR,
      .src = __FUNCTION__,
   };

   if (samples > MAX_SAMPLES) {
      ast_log(LOG_WARNING, "Only generating %d samples, where %d requested\n", MAX_SAMPLES, samples);
      samples = MAX_SAMPLES;
   }
   
   if ((len = fax_tx(fax, buf, samples)) > 0) {
      outf.samples = len;
      AST_FRAME_SET_BUFFER(&outf, buffer, AST_FRIENDLY_OFFSET, len * sizeof(int16_t));

      if (ast_write(chan, &outf) < 0) {
         ast_log(LOG_WARNING, "Failed to write frame to '%s': %s\n", chan->name, strerror(errno));
         return -1;
      }
   }

   return 0;
}

struct ast_generator generator = {
   alloc:      fax_generator_alloc,
   generate:   fax_generator_generate,
};


/* === Transmission === */

static int transmit_audio(fax_session *s)
{
   int res = -1;
   int original_read_fmt = AST_FORMAT_SLINEAR;
   int original_write_fmt = AST_FORMAT_SLINEAR;
   fax_state_t fax;
   t30_state_t *t30state;
   struct ast_frame *inf = NULL;
   int last_state = 0;
   struct timeval now, start, state_change;
   enum ast_t38_state t38_state;
   struct ast_control_t38_parameters t38_parameters = { .version = 0,
                          .max_ifp = 800,
                          .rate = AST_T38_RATE_14400,
                          .rate_management = AST_T38_RATE_MANAGEMENT_TRANSFERRED_TCF,
                          .fill_bit_removal = 1,
                          .transcoding_mmr = 1,
                          .transcoding_jbig = 1,
   };

   /* if in called party mode, try to use T.38 */
   if (s->caller_mode == FALSE) {
      /* check if we are already in T.38 mode (unlikely), or if we can request
       * a switch... if so, request it now and wait for the result, rather
       * than starting an audio FAX session that will have to be cancelled
       */
      if ((t38_state = ast_channel_get_t38_state(s->chan)) == T38_STATE_NEGOTIATED) {
         return 1;
      } else if ((t38_state != T38_STATE_UNAVAILABLE) &&
            (t38_parameters.request_response = AST_T38_REQUEST_NEGOTIATE,
             (ast_indicate_data(s->chan, AST_CONTROL_T38_PARAMETERS, &t38_parameters, sizeof(t38_parameters)) == 0))) {
         /* wait up to five seconds for negotiation to complete */
         unsigned int timeout = 5000;
         int ms;
         
         ast_debug(1, "Negotiating T.38 for receive on %s\n", s->chan->name);
         while (timeout > 0) {
            ms = ast_waitfor(s->chan, 1000);
            if (ms < 0) {
               ast_log(LOG_WARNING, "something bad happened while channel '%s' was polling.\n", s->chan->name);
               return -1;
            }
            if (!ms) {
               /* nothing happened */
               if (timeout > 0) {
                  timeout -= 1000;
                  continue;
               } else {
                  ast_log(LOG_WARNING, "channel '%s' timed-out during the T.38 negotiation.\n", s->chan->name);
                  break;
               }
            }
            if (!(inf = ast_read(s->chan))) {
               return -1;
            }
            if ((inf->frametype == AST_FRAME_CONTROL) &&
                (inf->subclass == AST_CONTROL_T38_PARAMETERS) &&
                (inf->datalen == sizeof(t38_parameters))) {
               struct ast_control_t38_parameters *parameters = inf->data.ptr;
               
               switch (parameters->request_response) {
               case AST_T38_NEGOTIATED:
                  ast_debug(1, "Negotiated T.38 for receive on %s\n", s->chan->name);
                  res = 1;
                  break;
               case AST_T38_REFUSED:
                  ast_log(LOG_WARNING, "channel '%s' refused to negotiate T.38\n", s->chan->name);
                  break;
               default:
                  ast_log(LOG_ERROR, "channel '%s' failed to negotiate T.38\n", s->chan->name);
                  break;
               }
               ast_frfree(inf);
               if (res == 1) {
                  return 1;
               } else {
                  break;
               }
            }
            ast_frfree(inf);
         }
      }
   }

#if SPANDSP_RELEASE_DATE >= 20080725
        /* for spandsp shaphots 0.0.6 and higher */
        t30state = &fax.t30;
#else
        /* for spandsp release 0.0.5 */
        t30state = &fax.t30_state;
#endif

   original_read_fmt = s->chan->readformat;
   if (original_read_fmt != AST_FORMAT_SLINEAR) {
      res = ast_set_read_format(s->chan, AST_FORMAT_SLINEAR);
      if (res < 0) {
         ast_log(LOG_WARNING, "Unable to set to linear read mode, giving up\n");
         goto done;
      }
   }

   original_write_fmt = s->chan->writeformat;
   if (original_write_fmt != AST_FORMAT_SLINEAR) {
      res = ast_set_write_format(s->chan, AST_FORMAT_SLINEAR);
      if (res < 0) {
         ast_log(LOG_WARNING, "Unable to set to linear write mode, giving up\n");
         goto done;
      }
   }

   /* Initialize T30 terminal */
   fax_init(&fax, s->caller_mode);

   /* Setup logging */
   set_logging(&fax.logging);
   set_logging(&t30state->logging);

   /* Configure terminal */
   set_local_info(t30state, s);
   set_file(t30state, s);
   set_ecm(t30state, TRUE);

   fax_set_transmit_on_idle(&fax, TRUE);

   t30_set_phase_e_handler(t30state, phase_e_handler, s);

   start = state_change = ast_tvnow();

   ast_activate_generator(s->chan, &generator, &fax);

   while (!s->finished) {
      inf = NULL;

      if ((res = ast_waitfor(s->chan, 25)) < 0) {
         ast_debug(1, "Error waiting for a frame\n");
         break;
      }

      /* Watchdog */
      now = ast_tvnow();
      if (ast_tvdiff_sec(now, start) > WATCHDOG_TOTAL_TIMEOUT || ast_tvdiff_sec(now, state_change) > WATCHDOG_STATE_TIMEOUT) {
         ast_log(LOG_WARNING, "It looks like we hung. Aborting.\n");
         res = -1;
         break;
      }

      if (!res) {
         /* There was timeout waiting for a frame. Loop around and wait again */
         continue;
      }

      /* There is a frame available. Get it */
      res = 0;

      if (!(inf = ast_read(s->chan))) {
         ast_debug(1, "Channel hangup\n");
         res = -1;
         break;
      }

      ast_debug(10, "frame %d/%d, len=%d\n", inf->frametype, inf->subclass, inf->datalen);

      /* Check the frame type. Format also must be checked because there is a chance
         that a frame in old format was already queued before we set channel format
         to slinear so it will still be received by ast_read */
      if (inf->frametype == AST_FRAME_VOICE && inf->subclass == AST_FORMAT_SLINEAR) {
         if (fax_rx(&fax, inf->data.ptr, inf->samples) < 0) {
            /* I know fax_rx never returns errors. The check here is for good style only */
            ast_log(LOG_WARNING, "fax_rx returned error\n");
            res = -1;
            break;
         }
         if (last_state != t30state->state) {
            state_change = ast_tvnow();
            last_state = t30state->state;
         }
      } else if ((inf->frametype == AST_FRAME_CONTROL) &&
            (inf->subclass == AST_CONTROL_T38_PARAMETERS)) {
         struct ast_control_t38_parameters *parameters = inf->data.ptr;

         if (parameters->request_response == AST_T38_NEGOTIATED) {
            /* T38 switchover completed */
            s->t38parameters = *parameters;
            ast_debug(1, "T38 negotiated, finishing audio loop\n");
            res = 1;
            break;
         } else if (parameters->request_response == AST_T38_REQUEST_NEGOTIATE) {
            t38_parameters.request_response = AST_T38_NEGOTIATED;
            ast_debug(1, "T38 request received, accepting\n");
            /* Complete T38 switchover */
            ast_indicate_data(s->chan, AST_CONTROL_T38_PARAMETERS, &t38_parameters, sizeof(t38_parameters));
            /* Do not break audio loop, wait until channel driver finally acks switchover
             * with AST_T38_NEGOTIATED
             */
         }
      }

      ast_frfree(inf);
   }

   ast_debug(1, "Loop finished, res=%d\n", res);

   if (inf)
      ast_frfree(inf);

   ast_deactivate_generator(s->chan);

   /* If we are switching to T38, remove phase E handler. Otherwise it will be executed
      by t30_terminate, display diagnostics and set status variables although no transmittion
      has taken place yet. */
   if (res > 0) {
      t30_set_phase_e_handler(t30state, NULL, NULL);
   }

   t30_terminate(t30state);
   fax_release(&fax);

done:
   if (original_write_fmt != AST_FORMAT_SLINEAR) {
      if (ast_set_write_format(s->chan, original_write_fmt) < 0)
         ast_log(LOG_WARNING, "Unable to restore write format on '%s'\n", s->chan->name);
   }

   if (original_read_fmt != AST_FORMAT_SLINEAR) {
      if (ast_set_read_format(s->chan, original_read_fmt) < 0)
         ast_log(LOG_WARNING, "Unable to restore read format on '%s'\n", s->chan->name);
   }

   return res;

}

static int transmit_t38(fax_session *s)
{
   int res = 0;
   t38_terminal_state_t t38;
   struct ast_frame *inf = NULL;
   int last_state = 0;
   struct timeval now, start, state_change, last_frame;
   t30_state_t *t30state;
   t38_core_state_t *t38state;

#if SPANDSP_RELEASE_DATE >= 20080725
   /* for spandsp shaphots 0.0.6 and higher */
   t30state = &t38.t30;
   t38state = &t38.t38_fe.t38;
#else
   /* for spandsp releases 0.0.5 */
   t30state = &t38.t30_state;
   t38state = &t38.t38;
#endif

   /* Initialize terminal */
   memset(&t38, 0, sizeof(t38));
   if (t38_terminal_init(&t38, s->caller_mode, t38_tx_packet_handler, s->chan) == NULL) {
      ast_log(LOG_WARNING, "Unable to start T.38 termination.\n");
      res = -1;
      goto disable_t38;
   }

   t38_set_max_datagram_size(t38state, s->t38parameters.max_ifp);

   if (s->t38parameters.fill_bit_removal) {
      t38_set_fill_bit_removal(t38state, TRUE);
   }
   if (s->t38parameters.transcoding_mmr) {
      t38_set_mmr_transcoding(t38state, TRUE);
   }
   if (s->t38parameters.transcoding_jbig) {
      t38_set_jbig_transcoding(t38state, TRUE);
   }

   /* Setup logging */
   set_logging(&t38.logging);
   set_logging(&t30state->logging);
   set_logging(&t38state->logging);

   /* Configure terminal */
   set_local_info(t30state, s);
   set_file(t30state, s);
   set_ecm(t30state, TRUE);

   t30_set_phase_e_handler(t30state, phase_e_handler, s);

   now = start = state_change = ast_tvnow();

   while (!s->finished) {

      res = ast_waitfor(s->chan, 20);
      if (res < 0)
         break;
      else if (res > 0)
         res = 0;

      last_frame = now;
      now = ast_tvnow();
      t38_terminal_send_timeout(&t38, ast_tvdiff_us(now, last_frame) / (1000000 / 8000));

      inf = ast_read(s->chan);
      if (inf == NULL) {
         ast_debug(1, "Channel hangup\n");
         res = -1;
         break;
      }

      ast_debug(10, "frame %d/%d, len=%d\n", inf->frametype, inf->subclass, inf->datalen);

      if (inf->frametype == AST_FRAME_MODEM && inf->subclass == AST_MODEM_T38) {
         t38_core_rx_ifp_packet(t38state, inf->data.ptr, inf->datalen, inf->seqno);

         /* Watchdog */
         if (last_state != t30state->state) {
            state_change = ast_tvnow();
            last_state = t30state->state;
         }
      } else if (inf->frametype == AST_FRAME_CONTROL && inf->subclass == AST_CONTROL_T38_PARAMETERS) {
         struct ast_control_t38_parameters *parameters = inf->data.ptr;
         if (parameters->request_response == AST_T38_TERMINATED) {
            ast_debug(1, "T38 down, finishing\n");
            break;
         }
      }

      ast_frfree(inf);
      inf = NULL;

      /* Watchdog */
      if (ast_tvdiff_sec(now, start) > WATCHDOG_TOTAL_TIMEOUT || ast_tvdiff_sec(now, state_change) > WATCHDOG_STATE_TIMEOUT) {
         ast_log(LOG_WARNING, "It looks like we hung. Aborting.\n");
         res = -1;
         break;
      }
   }

   ast_debug(1, "Loop finished, res=%d\n", res);

   if (inf)
      ast_frfree(inf);

   t30_terminate(t30state);
   t38_terminal_release(&t38);

disable_t38:
   /* if we are not the caller, it's our job to shut down the T.38
    * session when the FAX transmisson is complete.
    */
   if ((s->caller_mode == FALSE) &&
       (ast_channel_get_t38_state(s->chan) == T38_STATE_NEGOTIATED)) {
      struct ast_control_t38_parameters t38_parameters = { .request_response = AST_T38_REQUEST_TERMINATE, };

      if (ast_indicate_data(s->chan, AST_CONTROL_T38_PARAMETERS, &t38_parameters, sizeof(t38_parameters)) == 0) {
         /* wait up to five seconds for negotiation to complete */
         unsigned int timeout = 5000;
         int ms;
         
         ast_debug(1, "Shutting down T.38 on %s\n", s->chan->name);
         while (timeout > 0) {
            ms = ast_waitfor(s->chan, 1000);
            if (ms < 0) {
               ast_log(LOG_WARNING, "something bad happened while channel '%s' was polling.\n", s->chan->name);
               return -1;
            }
            if (!ms) {
               /* nothing happened */
               if (timeout > 0) {
                  timeout -= 1000;
                  continue;
               } else {
                  ast_log(LOG_WARNING, "channel '%s' timed-out during the T.38 shutdown.\n", s->chan->name);
                  break;
               }
            }
            if (!(inf = ast_read(s->chan))) {
               return -1;
            }
            if ((inf->frametype == AST_FRAME_CONTROL) &&
                (inf->subclass == AST_CONTROL_T38_PARAMETERS) &&
                (inf->datalen == sizeof(t38_parameters))) {
               struct ast_control_t38_parameters *parameters = inf->data.ptr;
               
               switch (parameters->request_response) {
               case AST_T38_TERMINATED:
                  ast_debug(1, "Shut down T.38 on %s\n", s->chan->name);
                  break;
               case AST_T38_REFUSED:
                  ast_log(LOG_WARNING, "channel '%s' refused to disable T.38\n", s->chan->name);
                  break;
               default:
                  ast_log(LOG_ERROR, "channel '%s' failed to disable T.38\n", s->chan->name);
                  break;
               }
               ast_frfree(inf);
               break;
            }
            ast_frfree(inf);
         }
      }
   }

   return res;
}

static int transmit(fax_session *s)
{
   int res = 0;

   /* Clear all channel variables which to be set by the application.
      Pre-set status to error so in case of any problems we can just leave */
   pbx_builtin_setvar_helper(s->chan, "FAXSTATUS", "FAILED"); 
   pbx_builtin_setvar_helper(s->chan, "FAXERROR", "Channel problems"); 

   pbx_builtin_setvar_helper(s->chan, "FAXMODE", NULL);
   pbx_builtin_setvar_helper(s->chan, "REMOTESTATIONID", NULL);
   pbx_builtin_setvar_helper(s->chan, "FAXPAGES", NULL);
   pbx_builtin_setvar_helper(s->chan, "FAXRESOLUTION", NULL);
   pbx_builtin_setvar_helper(s->chan, "FAXBITRATE", NULL); 

   if (s->chan->_state != AST_STATE_UP) {
      /* Shouldn't need this, but checking to see if channel is already answered
       * Theoretically asterisk should already have answered before running the app */
      res = ast_answer(s->chan);
      if (res) {
         ast_log(LOG_WARNING, "Could not answer channel '%s'\n", s->chan->name);
         return res;
      }
   }

   s->t38state = ast_channel_get_t38_state(s->chan);
   if (s->t38state != T38_STATE_NEGOTIATED) {
      /* T38 is not negotiated on the channel yet. First start regular transmission. If it switches to T38, follow */   
      pbx_builtin_setvar_helper(s->chan, "FAXMODE", "audio"); 
      res = transmit_audio(s);
      if (res > 0) {
         /* transmit_audio reports switchover to T38. Update t38state */
         s->t38state = ast_channel_get_t38_state(s->chan);
         if (s->t38state != T38_STATE_NEGOTIATED) {
            ast_log(LOG_ERROR, "Audio loop reports T38 switchover but t38state != T38_STATE_NEGOTIATED\n");
         }
      }
   }

   if (s->t38state == T38_STATE_NEGOTIATED) {
      pbx_builtin_setvar_helper(s->chan, "FAXMODE", "T38"); 
      res = transmit_t38(s);
   }

   if (res) {
      ast_log(LOG_WARNING, "Transmission error\n");
      res = -1;
   } else if (s->finished < 0) {
      ast_log(LOG_WARNING, "Transmission failed\n");
   } else if (s->finished > 0) {
      ast_debug(1, "Transmission finished Ok\n");
   }

   return res;
}

/* === Application functions === */

static int sndfax_exec(struct ast_channel *chan, void *data)
{
   int res = 0;
   char *parse;
   fax_session session = { 0, };

   AST_DECLARE_APP_ARGS(args,
      AST_APP_ARG(file_name);
      AST_APP_ARG(options);
   );

   if (chan == NULL) {
      ast_log(LOG_ERROR, "Fax channel is NULL. Giving up.\n");
      return -1;
   }

   /* The next few lines of code parse out the filename and header from the input string */
   if (ast_strlen_zero(data)) {
      /* No data implies no filename or anything is present */
      ast_log(LOG_ERROR, "SendFAX requires an argument (filename)\n");
      return -1;
   }

   parse = ast_strdupa(data);
   AST_STANDARD_APP_ARGS(args, parse);
   
   session.caller_mode = TRUE;

   if (args.options) {
      if (strchr(args.options, 'a'))
         session.caller_mode = FALSE;
   }

   /* Done parsing */
   session.direction = 1;
   session.file_name = args.file_name;
   session.chan = chan;
   session.finished = 0;

   res = transmit(&session);

   return res;
}

static int rcvfax_exec(struct ast_channel *chan, void *data)
{
   int res = 0;
   char *parse;
   fax_session session;

   AST_DECLARE_APP_ARGS(args,
      AST_APP_ARG(file_name);
      AST_APP_ARG(options);
   );

   if (chan == NULL) {
      ast_log(LOG_ERROR, "Fax channel is NULL. Giving up.\n");
      return -1;
   }

   /* The next few lines of code parse out the filename and header from the input string */
   if (ast_strlen_zero(data)) {
      /* No data implies no filename or anything is present */
      ast_log(LOG_ERROR, "ReceiveFAX requires an argument (filename)\n");
      return -1;
   }

   parse = ast_strdupa(data);
   AST_STANDARD_APP_ARGS(args, parse);
   
   session.caller_mode = FALSE;

   if (args.options) {
      if (strchr(args.options, 'c'))
         session.caller_mode = TRUE;
   }

   /* Done parsing */
   session.direction = 0;
   session.file_name = args.file_name;
   session.chan = chan;
   session.finished = 0;

   res = transmit(&session);

   return res;
}

static int unload_module(void)
{
   int res;

   res = ast_unregister_application(app_sndfax_name); 
   res |= ast_unregister_application(app_rcvfax_name);   

   return res;
}

static int load_module(void)
{
   int res ;

   res = ast_register_application(app_sndfax_name, sndfax_exec, app_sndfax_synopsis, app_sndfax_desc);
   res |= ast_register_application(app_rcvfax_name, rcvfax_exec, app_rcvfax_synopsis, app_rcvfax_desc);

   /* The default SPAN message handler prints to stderr. It is something we do not want */
   span_set_message_handler(NULL);

   return res;
}


AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "Simple FAX Application",
      .load = load_module,
      .unload = unload_module,
      );