udptl.c

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/*
 * Asterisk -- A telephony toolkit for Linux.
 *
 * UDPTL support for T.38
 * 
 * Copyright (C) 2005, Steve Underwood, partly based on RTP code which is
 * Copyright (C) 1999-2006, Digium, Inc.
 *
 * Steve Underwood <steveu@coppice.org>
 *
 * 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.
 *
 * A license has been granted to Digium (via disclaimer) for the use of
 * this code.
 */

/*! 
 * \file 
 *
 * \brief UDPTL support for T.38 faxing
 * 
 *
 * \author Mark Spencer <markster@digium.com>,  Steve Underwood <steveu@coppice.org>
 * 
 * \page T38fax_udptl T.38 support :: UDPTL
 *
 * Asterisk supports T.38 fax passthrough, origination and termination. It does
 * not support gateway operation. The only channel driver that supports T.38 at
 * this time is chan_sip.
 *
 * UDPTL is handled very much like RTP. It can be reinvited to go directly between
 * the endpoints, without involving Asterisk in the media stream.
 * 
 * \b References:
 * - chan_sip.c
 * - udptl.c
 * - app_fax.c
 */


#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 210994 $")

#include <sys/time.h>
#include <signal.h>
#include <fcntl.h>

#include "asterisk/udptl.h"
#include "asterisk/frame.h"
#include "asterisk/channel.h"
#include "asterisk/acl.h"
#include "asterisk/config.h"
#include "asterisk/lock.h"
#include "asterisk/utils.h"
#include "asterisk/netsock.h"
#include "asterisk/cli.h"
#include "asterisk/unaligned.h"

#define UDPTL_MTU    1200

#if !defined(FALSE)
#define FALSE 0
#endif
#if !defined(TRUE)
#define TRUE (!FALSE)
#endif

static int udptlstart = 4500;
static int udptlend = 4599;
static int udptldebug;                      /*!< Are we debugging? */
static struct sockaddr_in udptldebugaddr;   /*!< Debug packets to/from this host */
#ifdef SO_NO_CHECK
static int nochecksums;
#endif
static enum ast_t38_ec_modes udptlfectype;
static int udptlfecentries;
static int udptlfecspan;
static int udptlmaxdatagram;
static int use_even_ports;

#define LOCAL_FAX_MAX_DATAGRAM      1400
#define MAX_FEC_ENTRIES             5
#define MAX_FEC_SPAN                5

#define UDPTL_BUF_MASK              15

typedef struct {
   int buf_len;
   uint8_t buf[LOCAL_FAX_MAX_DATAGRAM];
} udptl_fec_tx_buffer_t;

typedef struct {
   int buf_len;
   uint8_t buf[LOCAL_FAX_MAX_DATAGRAM];
   unsigned int fec_len[MAX_FEC_ENTRIES];
   uint8_t fec[MAX_FEC_ENTRIES][LOCAL_FAX_MAX_DATAGRAM];
   unsigned int fec_span;
   unsigned int fec_entries;
} udptl_fec_rx_buffer_t;

/*! \brief Structure for an UDPTL session */
struct ast_udptl {
   int fd;
   char resp;
   struct ast_frame f[16];
   unsigned char rawdata[8192 + AST_FRIENDLY_OFFSET];
   unsigned int lasteventseqn;
   int nat;
   int flags;
   struct sockaddr_in us;
   struct sockaddr_in them;
   int *ioid;
   struct sched_context *sched;
   struct io_context *io;
   void *data;
   ast_udptl_callback callback;

   /*! This option indicates the error correction scheme used in transmitted UDPTL
    *    packets and expected in received UDPTL packets.
    */
   enum ast_t38_ec_modes error_correction_scheme;

   /*! This option indicates the number of error correction entries transmitted in
    *  UDPTL packets and expected in received UDPTL packets.
    */
   unsigned int error_correction_entries;

   /*! This option indicates the span of the error correction entries in transmitted
    *  UDPTL packets (FEC only).
    */
   unsigned int error_correction_span;

   /*! The maximum size UDPTL packet that can be accepted by
    *  the remote device.
    */
   unsigned int far_max_datagram;

   /*! The maximum size UDPTL packet that we are prepared to
    *  accept.
    */
   unsigned int local_max_datagram;

   /*! The maximum IFP that can be submitted for sending
    * to the remote device. Calculated from far_max_datagram,
    * error_correction_scheme and error_correction_entries.
    */
   unsigned int far_max_ifp;

   /*! The maximum IFP that the local endpoint is prepared
    * to accept. Along with error_correction_scheme and
    * error_correction_entries, used to calculate local_max_datagram.
    */
   unsigned int local_max_ifp;

   int verbose;

   struct sockaddr_in far;

   unsigned int tx_seq_no;
   unsigned int rx_seq_no;
   unsigned int rx_expected_seq_no;

   udptl_fec_tx_buffer_t tx[UDPTL_BUF_MASK + 1];
   udptl_fec_rx_buffer_t rx[UDPTL_BUF_MASK + 1];
};

static AST_RWLIST_HEAD_STATIC(protos, ast_udptl_protocol);

static inline int udptl_debug_test_addr(const struct sockaddr_in *addr)
{
   if (udptldebug == 0)
      return 0;
   if (udptldebugaddr.sin_addr.s_addr) {
      if (((ntohs(udptldebugaddr.sin_port) != 0) &&
           (udptldebugaddr.sin_port != addr->sin_port)) ||
          (udptldebugaddr.sin_addr.s_addr != addr->sin_addr.s_addr))
         return 0;
   }
   return 1;
}

static int decode_length(uint8_t *buf, unsigned int limit, unsigned int *len, unsigned int *pvalue)
{
   if (*len >= limit)
      return -1;
   if ((buf[*len] & 0x80) == 0) {
      *pvalue = buf[*len];
      (*len)++;
      return 0;
   }
   if ((buf[*len] & 0x40) == 0) {
      if (*len == limit - 1)
         return -1;
      *pvalue = (buf[*len] & 0x3F) << 8;
      (*len)++;
      *pvalue |= buf[*len];
      (*len)++;
      return 0;
   }
   *pvalue = (buf[*len] & 0x3F) << 14;
   (*len)++;
   /* Indicate we have a fragment */
   return 1;
}
/*- End of function --------------------------------------------------------*/

static int decode_open_type(uint8_t *buf, unsigned int limit, unsigned int *len, const uint8_t **p_object, unsigned int *p_num_octets)
{
   unsigned int octet_cnt;
   unsigned int octet_idx;
   unsigned int length;
   unsigned int i;
   const uint8_t **pbuf;

   for (octet_idx = 0, *p_num_octets = 0; ; octet_idx += octet_cnt) {
      octet_cnt = 0;
      if ((length = decode_length(buf, limit, len, &octet_cnt)) < 0)
         return -1;
      if (octet_cnt > 0) {
         *p_num_octets += octet_cnt;

         pbuf = &p_object[octet_idx];
         i = 0;
         /* Make sure the buffer contains at least the number of bits requested */
         if ((*len + octet_cnt) > limit)
            return -1;

         *pbuf = &buf[*len];
         *len += octet_cnt;
      }
      if (length == 0)
         break;
   }
   return 0;
}
/*- End of function --------------------------------------------------------*/

static unsigned int encode_length(uint8_t *buf, unsigned int *len, unsigned int value)
{
   unsigned int multiplier;

   if (value < 0x80) {
      /* 1 octet */
      buf[*len] = value;
      (*len)++;
      return value;
   }
   if (value < 0x4000) {
      /* 2 octets */
      /* Set the first bit of the first octet */
      buf[*len] = ((0x8000 | value) >> 8) & 0xFF;
      (*len)++;
      buf[*len] = value & 0xFF;
      (*len)++;
      return value;
   }
   /* Fragmentation */
   multiplier = (value < 0x10000) ? (value >> 14) : 4;
   /* Set the first 2 bits of the octet */
   buf[*len] = 0xC0 | multiplier;
   (*len)++;
   return multiplier << 14;
}
/*- End of function --------------------------------------------------------*/

static int encode_open_type(uint8_t *buf, unsigned int buflen, unsigned int *len, const uint8_t *data, unsigned int num_octets)
{
   unsigned int enclen;
   unsigned int octet_idx;
   uint8_t zero_byte;

   /* If open type is of zero length, add a single zero byte (10.1) */
   if (num_octets == 0) {
      zero_byte = 0;
      data = &zero_byte;
      num_octets = 1;
   }
   /* Encode the open type */
   for (octet_idx = 0; ; num_octets -= enclen, octet_idx += enclen) {
      if ((enclen = encode_length(buf, len, num_octets)) < 0)
         return -1;
      if (enclen + *len > buflen) {
         ast_log(LOG_ERROR, "Buffer overflow detected (%d + %d > %d)\n", enclen, *len, buflen);
         return -1;
      }
      if (enclen > 0) {
         memcpy(&buf[*len], &data[octet_idx], enclen);
         *len += enclen;
      }
      if (enclen >= num_octets)
         break;
   }

   return 0;
}
/*- End of function --------------------------------------------------------*/

static int udptl_rx_packet(struct ast_udptl *s, uint8_t *buf, unsigned int len)
{
   int stat1;
   int stat2;
   int i;
   int j;
   int k;
   int l;
   int m;
   int x;
   int limit;
   int which;
   unsigned int ptr;
   unsigned int count;
   int total_count;
   int seq_no;
   const uint8_t *ifp;
   const uint8_t *data;
   unsigned int ifp_len;
   int repaired[16];
   const uint8_t *bufs[16];
   unsigned int lengths[16];
   int span;
   int entries;
   int ifp_no;

   ptr = 0;
   ifp_no = 0;
   memset(&s->f[0], 0, sizeof(s->f[0]));

   /* Decode seq_number */
   if (ptr + 2 > len)
      return -1;
   seq_no = (buf[0] << 8) | buf[1];
   ptr += 2;

   /* Break out the primary packet */
   if ((stat1 = decode_open_type(buf, len, &ptr, &ifp, &ifp_len)) != 0)
      return -1;
   /* Decode error_recovery */
   if (ptr + 1 > len)
      return -1;
   if ((buf[ptr++] & 0x80) == 0) {
      /* Secondary packet mode for error recovery */
      if (seq_no > s->rx_seq_no) {
         /* We received a later packet than we expected, so we need to check if we can fill in the gap from the
            secondary packets. */
         total_count = 0;
         do {
            if ((stat2 = decode_length(buf, len, &ptr, &count)) < 0)
               return -1;
            for (i = 0; i < count; i++) {
               if ((stat1 = decode_open_type(buf, len, &ptr, &bufs[total_count + i], &lengths[total_count + i])) != 0)
                  return -1;
            }
            total_count += count;
         }
         while (stat2 > 0);
         /* Step through in reverse order, so we go oldest to newest */
         for (i = total_count; i > 0; i--) {
            if (seq_no - i >= s->rx_seq_no) {
               /* This one wasn't seen before */
               /* Decode the secondary IFP packet */
               //fprintf(stderr, "Secondary %d, len %d\n", seq_no - i, lengths[i - 1]);
               s->f[ifp_no].frametype = AST_FRAME_MODEM;
               s->f[ifp_no].subclass = AST_MODEM_T38;

               s->f[ifp_no].mallocd = 0;
               s->f[ifp_no].seqno = seq_no - i;
               s->f[ifp_no].datalen = lengths[i - 1];
               s->f[ifp_no].data.ptr = (uint8_t *) bufs[i - 1];
               s->f[ifp_no].offset = 0;
               s->f[ifp_no].src = "UDPTL";
               if (ifp_no > 0)
                  AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
               AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;
               ifp_no++;
            }
         }
      }
   }
   else
   {
      /* FEC mode for error recovery */
      /* Our buffers cannot tolerate overlength IFP packets in FEC mode */
      if (ifp_len > LOCAL_FAX_MAX_DATAGRAM)
         return -1;
      /* Update any missed slots in the buffer */
      for ( ; seq_no > s->rx_seq_no; s->rx_seq_no++) {
         x = s->rx_seq_no & UDPTL_BUF_MASK;
         s->rx[x].buf_len = -1;
         s->rx[x].fec_len[0] = 0;
         s->rx[x].fec_span = 0;
         s->rx[x].fec_entries = 0;
      }

      x = seq_no & UDPTL_BUF_MASK;

      memset(repaired, 0, sizeof(repaired));

      /* Save the new IFP packet */
      memcpy(s->rx[x].buf, ifp, ifp_len);
      s->rx[x].buf_len = ifp_len;
      repaired[x] = TRUE;

      /* Decode the FEC packets */
      /* The span is defined as an unconstrained integer, but will never be more
         than a small value. */
      if (ptr + 2 > len)
         return -1;
      if (buf[ptr++] != 1)
         return -1;
      span = buf[ptr++];
      s->rx[x].fec_span = span;

      /* The number of entries is defined as a length, but will only ever be a small
         value. Treat it as such. */
      if (ptr + 1 > len)
         return -1;
      entries = buf[ptr++];
      s->rx[x].fec_entries = entries;

      /* Decode the elements */
      for (i = 0; i < entries; i++) {
         if ((stat1 = decode_open_type(buf, len, &ptr, &data, &s->rx[x].fec_len[i])) != 0)
            return -1;
         if (s->rx[x].fec_len[i] > LOCAL_FAX_MAX_DATAGRAM)
            return -1;

         /* Save the new FEC data */
         memcpy(s->rx[x].fec[i], data, s->rx[x].fec_len[i]);
#if 0
         fprintf(stderr, "FEC: ");
         for (j = 0; j < s->rx[x].fec_len[i]; j++)
            fprintf(stderr, "%02X ", data[j]);
         fprintf(stderr, "\n");
#endif
      }

      /* See if we can reconstruct anything which is missing */
      /* TODO: this does not comprehensively hunt back and repair everything that is possible */
      for (l = x; l != ((x - (16 - span*entries)) & UDPTL_BUF_MASK); l = (l - 1) & UDPTL_BUF_MASK) {
         if (s->rx[l].fec_len[0] <= 0)
            continue;
         for (m = 0; m < s->rx[l].fec_entries; m++) {
            limit = (l + m) & UDPTL_BUF_MASK;
            for (which = -1, k = (limit - s->rx[l].fec_span * s->rx[l].fec_entries) & UDPTL_BUF_MASK; k != limit; k = (k + s->rx[l].fec_entries) & UDPTL_BUF_MASK) {
               if (s->rx[k].buf_len <= 0)
                  which = (which == -1) ? k : -2;
            }
            if (which >= 0) {
               /* Repairable */
               for (j = 0; j < s->rx[l].fec_len[m]; j++) {
                  s->rx[which].buf[j] = s->rx[l].fec[m][j];
                  for (k = (limit - s->rx[l].fec_span * s->rx[l].fec_entries) & UDPTL_BUF_MASK; k != limit; k = (k + s->rx[l].fec_entries) & UDPTL_BUF_MASK)
                     s->rx[which].buf[j] ^= (s->rx[k].buf_len > j) ? s->rx[k].buf[j] : 0;
               }
               s->rx[which].buf_len = s->rx[l].fec_len[m];
               repaired[which] = TRUE;
            }
         }
      }
      /* Now play any new packets forwards in time */
      for (l = (x + 1) & UDPTL_BUF_MASK, j = seq_no - UDPTL_BUF_MASK; l != x; l = (l + 1) & UDPTL_BUF_MASK, j++) {
         if (repaired[l]) {
            //fprintf(stderr, "Fixed packet %d, len %d\n", j, l);
            s->f[ifp_no].frametype = AST_FRAME_MODEM;
            s->f[ifp_no].subclass = AST_MODEM_T38;
         
            s->f[ifp_no].mallocd = 0;
            s->f[ifp_no].seqno = j;
            s->f[ifp_no].datalen = s->rx[l].buf_len;
            s->f[ifp_no].data.ptr = s->rx[l].buf;
            s->f[ifp_no].offset = 0;
            s->f[ifp_no].src = "UDPTL";
            if (ifp_no > 0)
               AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
            AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;
            ifp_no++;
         }
      }
   }

   /* If packets are received out of sequence, we may have already processed this packet from the error
      recovery information in a packet already received. */
   if (seq_no >= s->rx_seq_no) {
      /* Decode the primary IFP packet */
      s->f[ifp_no].frametype = AST_FRAME_MODEM;
      s->f[ifp_no].subclass = AST_MODEM_T38;
      
      s->f[ifp_no].mallocd = 0;
      s->f[ifp_no].seqno = seq_no;
      s->f[ifp_no].datalen = ifp_len;
      s->f[ifp_no].data.ptr = (uint8_t *) ifp;
      s->f[ifp_no].offset = 0;
      s->f[ifp_no].src = "UDPTL";
      if (ifp_no > 0)
         AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
      AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;

      ifp_no++;
   }

   s->rx_seq_no = seq_no + 1;
   return ifp_no;
}
/*- End of function --------------------------------------------------------*/

static int udptl_build_packet(struct ast_udptl *s, uint8_t *buf, unsigned int buflen, uint8_t *ifp, unsigned int ifp_len)
{
   uint8_t fec[LOCAL_FAX_MAX_DATAGRAM * 2];
   int i;
   int j;
   int seq;
   int entry;
   int entries;
   int span;
   int m;
   unsigned int len;
   int limit;
   int high_tide;

   seq = s->tx_seq_no & 0xFFFF;

   /* Map the sequence number to an entry in the circular buffer */
   entry = seq & UDPTL_BUF_MASK;

   /* We save the message in a circular buffer, for generating FEC or
      redundancy sets later on. */
   s->tx[entry].buf_len = ifp_len;
   memcpy(s->tx[entry].buf, ifp, ifp_len);
   
   /* Build the UDPTLPacket */

   len = 0;
   /* Encode the sequence number */
   buf[len++] = (seq >> 8) & 0xFF;
   buf[len++] = seq & 0xFF;

   /* Encode the primary IFP packet */
   if (encode_open_type(buf, buflen, &len, ifp, ifp_len) < 0)
      return -1;

   /* Encode the appropriate type of error recovery information */
   switch (s->error_correction_scheme)
   {
   case UDPTL_ERROR_CORRECTION_NONE:
      /* Encode the error recovery type */
      buf[len++] = 0x00;
      /* The number of entries will always be zero, so it is pointless allowing
         for the fragmented case here. */
      if (encode_length(buf, &len, 0) < 0)
         return -1;
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      /* Encode the error recovery type */
      buf[len++] = 0x00;
      if (s->tx_seq_no > s->error_correction_entries)
         entries = s->error_correction_entries;
      else
         entries = s->tx_seq_no;
      /* The number of entries will always be small, so it is pointless allowing
         for the fragmented case here. */
      if (encode_length(buf, &len, entries) < 0)
         return -1;
      /* Encode the elements */
      for (i = 0; i < entries; i++) {
         j = (entry - i - 1) & UDPTL_BUF_MASK;
         if (encode_open_type(buf, buflen, &len, s->tx[j].buf, s->tx[j].buf_len) < 0) {
            if (option_debug) {
               ast_log(LOG_DEBUG, "Encoding failed at i=%d, j=%d\n", i, j);
            }
            return -1;
         }
      }
      break;
   case UDPTL_ERROR_CORRECTION_FEC:
      span = s->error_correction_span;
      entries = s->error_correction_entries;
      if (seq < s->error_correction_span*s->error_correction_entries) {
         /* In the initial stages, wind up the FEC smoothly */
         entries = seq/s->error_correction_span;
         if (seq < s->error_correction_span)
            span = 0;
      }
      /* Encode the error recovery type */
      buf[len++] = 0x80;
      /* Span is defined as an inconstrained integer, which it dumb. It will only
         ever be a small value. Treat it as such. */
      buf[len++] = 1;
      buf[len++] = span;
      /* The number of entries is defined as a length, but will only ever be a small
         value. Treat it as such. */
      buf[len++] = entries;
      for (m = 0; m < entries; m++) {
         /* Make an XOR'ed entry the maximum length */
         limit = (entry + m) & UDPTL_BUF_MASK;
         high_tide = 0;
         for (i = (limit - span*entries) & UDPTL_BUF_MASK; i != limit; i = (i + entries) & UDPTL_BUF_MASK) {
            if (high_tide < s->tx[i].buf_len) {
               for (j = 0; j < high_tide; j++)
                  fec[j] ^= s->tx[i].buf[j];
               for ( ; j < s->tx[i].buf_len; j++)
                  fec[j] = s->tx[i].buf[j];
               high_tide = s->tx[i].buf_len;
            } else {
               for (j = 0; j < s->tx[i].buf_len; j++)
                  fec[j] ^= s->tx[i].buf[j];
            }
         }
         if (encode_open_type(buf, buflen, &len, fec, high_tide) < 0)
            return -1;
      }
      break;
   }

   if (s->verbose)
      fprintf(stderr, "\n");

   s->tx_seq_no++;
   return len;
}

int ast_udptl_fd(const struct ast_udptl *udptl)
{
   return udptl->fd;
}

void ast_udptl_set_data(struct ast_udptl *udptl, void *data)
{
   udptl->data = data;
}

void ast_udptl_set_callback(struct ast_udptl *udptl, ast_udptl_callback callback)
{
   udptl->callback = callback;
}

void ast_udptl_setnat(struct ast_udptl *udptl, int nat)
{
   udptl->nat = nat;
}

static int udptlread(int *id, int fd, short events, void *cbdata)
{
   struct ast_udptl *udptl = cbdata;
   struct ast_frame *f;

   if ((f = ast_udptl_read(udptl))) {
      if (udptl->callback)
         udptl->callback(udptl, f, udptl->data);
   }
   return 1;
}

struct ast_frame *ast_udptl_read(struct ast_udptl *udptl)
{
   int res;
   struct sockaddr_in sin;
   socklen_t len;
   uint16_t seqno = 0;
   uint16_t *udptlheader;

   len = sizeof(sin);
   
   /* Cache where the header will go */
   res = recvfrom(udptl->fd,
         udptl->rawdata + AST_FRIENDLY_OFFSET,
         sizeof(udptl->rawdata) - AST_FRIENDLY_OFFSET,
         0,
         (struct sockaddr *) &sin,
         &len);
   udptlheader = (uint16_t *)(udptl->rawdata + AST_FRIENDLY_OFFSET);
   if (res < 0) {
      if (errno != EAGAIN)
         ast_log(LOG_WARNING, "UDPTL read error: %s\n", strerror(errno));
      ast_assert(errno != EBADF);
      return &ast_null_frame;
   }

   /* Ignore if the other side hasn't been given an address yet. */
   if (!udptl->them.sin_addr.s_addr || !udptl->them.sin_port)
      return &ast_null_frame;

   if (udptl->nat) {
      /* Send to whoever sent to us */
      if ((udptl->them.sin_addr.s_addr != sin.sin_addr.s_addr) ||
         (udptl->them.sin_port != sin.sin_port)) {
         memcpy(&udptl->them, &sin, sizeof(udptl->them));
         ast_debug(1, "UDPTL NAT: Using address %s:%d\n", ast_inet_ntoa(udptl->them.sin_addr), ntohs(udptl->them.sin_port));
      }
   }

   if (udptl_debug_test_addr(&sin)) {
      ast_verb(1, "Got UDPTL packet from %s:%d (type %d, seq %d, len %d)\n",
            ast_inet_ntoa(sin.sin_addr), ntohs(sin.sin_port), 0, seqno, res);
   }
#if 0
   printf("Got UDPTL packet from %s:%d (seq %d, len = %d)\n", ast_inet_ntoa(sin.sin_addr), ntohs(sin.sin_port), seqno, res);
#endif
   if (udptl_rx_packet(udptl, udptl->rawdata + AST_FRIENDLY_OFFSET, res) < 1)
      return &ast_null_frame;

   return &udptl->f[0];
}

static void calculate_local_max_datagram(struct ast_udptl *udptl)
{
   unsigned int new_max = 200;

   /* calculate the amount of space required to receive an IFP
    * using the current error correction mode, and ensure that our
    * local max datagram size is at least that big
    */
   switch (udptl->error_correction_scheme) {
   case UDPTL_ERROR_CORRECTION_NONE:
      /* only need room for sequence number and length indicators */
      new_max = 6 + udptl->local_max_ifp;
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      /* need room for sequence number, length indicators and the
       * configured number of redundant packets
       */
      new_max = 6 + udptl->local_max_ifp + 2 + (udptl->error_correction_entries * udptl->local_max_ifp);
      break;
   case UDPTL_ERROR_CORRECTION_FEC:
      /* need room for sequence number, length indicators and a
       * a single IFP of the maximum size expected
       */
      new_max = 6 + udptl->local_max_ifp + 4 + udptl->local_max_ifp;
      break;
   }
   /* add 25% of extra space for insurance, but no larger than LOCAL_FAX_MAX_DATAGRAM */
   udptl->local_max_datagram = MIN(new_max * 1.25, LOCAL_FAX_MAX_DATAGRAM);
}

static void calculate_far_max_ifp(struct ast_udptl *udptl)
{
   unsigned new_max = 60;

   /* calculate the maximum IFP the local endpoint should
    * generate based on the far end's maximum datagram size
    * and the current error correction mode. some endpoints
    * bogus 'max datagram' values that would result in unusable
    * (too small) maximum IFP values, so we have a a reasonable
    * minimum value to ensure that we can actually construct
    * UDPTL packets.
    */
   switch (udptl->error_correction_scheme) {
   case UDPTL_ERROR_CORRECTION_NONE:
      /* only need room for sequence number and length indicators */
      new_max = MAX(new_max, udptl->far_max_datagram - 6);
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      /* need room for sequence number, length indicators and the
       * configured number of redundant packets
       */
      new_max = MAX(new_max, (udptl->far_max_datagram - 8) / (udptl->error_correction_entries + 1));
      break;
   case UDPTL_ERROR_CORRECTION_FEC:
      /* need room for sequence number, length indicators and a
       * a single IFP of the maximum size expected
       */
      new_max = MAX(new_max, (udptl->far_max_datagram - 10) / 2);
      break;
   }
   /* subtract 25% of space for insurance */
   udptl->far_max_ifp = new_max * 0.75;
}

enum ast_t38_ec_modes ast_udptl_get_error_correction_scheme(const struct ast_udptl *udptl)
{
   if (udptl)
      return udptl->error_correction_scheme;
   else {
      ast_log(LOG_WARNING, "udptl structure is null\n");
      return -1;
   }
}

void ast_udptl_set_error_correction_scheme(struct ast_udptl *udptl, enum ast_t38_ec_modes ec)
{
   if (udptl) {
      udptl->error_correction_scheme = ec;
      switch (ec) {
      case UDPTL_ERROR_CORRECTION_FEC:
         udptl->error_correction_scheme = UDPTL_ERROR_CORRECTION_FEC;
         if (udptl->error_correction_entries == 0) {
            udptl->error_correction_entries = 3;
         }
         if (udptl->error_correction_span == 0) {
            udptl->error_correction_span = 3;
         }
         break;
      case UDPTL_ERROR_CORRECTION_REDUNDANCY:
         udptl->error_correction_scheme = UDPTL_ERROR_CORRECTION_REDUNDANCY;
         if (udptl->error_correction_entries == 0) {
            udptl->error_correction_entries = 3;
         }
         break;
      default:
         /* nothing to do */
         break;
      };
      calculate_local_max_datagram(udptl);
      calculate_far_max_ifp(udptl);
   } else
      ast_log(LOG_WARNING, "udptl structure is null\n");
}

unsigned int ast_udptl_get_local_max_datagram(const struct ast_udptl *udptl)
{
   if (udptl)
      return udptl->local_max_datagram;
   else {
      ast_log(LOG_WARNING, "udptl structure is null\n");
      return 0;
   }
}

unsigned int ast_udptl_get_far_max_datagram(const struct ast_udptl *udptl)
{
   if (udptl)
      return udptl->far_max_datagram;
   else {
      ast_log(LOG_WARNING, "udptl structure is null\n");
      return 0;
   }
}

void ast_udptl_set_far_max_datagram(struct ast_udptl *udptl, unsigned int max_datagram)
{
   if (udptl) {
      udptl->far_max_datagram = max_datagram;
      calculate_far_max_ifp(udptl);
   } else {
      ast_log(LOG_WARNING, "udptl structure is null\n");
   }
}

void ast_udptl_set_local_max_ifp(struct ast_udptl *udptl, unsigned int max_ifp)
{
   udptl->local_max_ifp = max_ifp;
   calculate_local_max_datagram(udptl);
}

unsigned int ast_udptl_get_far_max_ifp(const struct ast_udptl *udptl)
{
   return udptl->far_max_ifp;
}

struct ast_udptl *ast_udptl_new_with_bindaddr(struct sched_context *sched, struct io_context *io, int callbackmode, struct in_addr addr)
{
   struct ast_udptl *udptl;
   int x;
   int startplace;
   int i;
   long int flags;

   if (!(udptl = ast_calloc(1, sizeof(*udptl))))
      return NULL;

   udptl->error_correction_scheme = udptlfectype;
   udptl->error_correction_span = udptlfecspan;
   udptl->error_correction_entries = udptlfecentries;
   
   udptl->far_max_datagram = udptlmaxdatagram;
   udptl->local_max_datagram = udptlmaxdatagram;

   for (i = 0; i <= UDPTL_BUF_MASK; i++) {
      udptl->rx[i].buf_len = -1;
      udptl->tx[i].buf_len = -1;
   }

   udptl->them.sin_family = AF_INET;
   udptl->us.sin_family = AF_INET;

   if ((udptl->fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
      ast_free(udptl);
      ast_log(LOG_WARNING, "Unable to allocate socket: %s\n", strerror(errno));
      return NULL;
   }
   flags = fcntl(udptl->fd, F_GETFL);
   fcntl(udptl->fd, F_SETFL, flags | O_NONBLOCK);
#ifdef SO_NO_CHECK
   if (nochecksums)
      setsockopt(udptl->fd, SOL_SOCKET, SO_NO_CHECK, &nochecksums, sizeof(nochecksums));
#endif
   /* Find us a place */
   x = (udptlstart == udptlend) ? udptlstart : (ast_random() % (udptlend - udptlstart)) + udptlstart;
   if (use_even_ports && (x & 1)) {
      ++x;
   }
   startplace = x;
   for (;;) {
      udptl->us.sin_port = htons(x);
      udptl->us.sin_addr = addr;
      if (bind(udptl->fd, (struct sockaddr *) &udptl->us, sizeof(udptl->us)) == 0)
         break;
      if (errno != EADDRINUSE) {
         ast_log(LOG_WARNING, "Unexpected bind error: %s\n", strerror(errno));
         close(udptl->fd);
         ast_free(udptl);
         return NULL;
      }
      if (use_even_ports) {
         x += 2;
      } else {
         ++x;
      }
      if (x > udptlend)
         x = udptlstart;
      if (x == startplace) {
         ast_log(LOG_WARNING, "No UDPTL ports remaining\n");
         close(udptl->fd);
         ast_free(udptl);
         return NULL;
      }
   }
   if (io && sched && callbackmode) {
      /* Operate this one in a callback mode */
      udptl->sched = sched;
      udptl->io = io;
      udptl->ioid = ast_io_add(udptl->io, udptl->fd, udptlread, AST_IO_IN, udptl);
   }
   return udptl;
}

struct ast_udptl *ast_udptl_new(struct sched_context *sched, struct io_context *io, int callbackmode)
{
   struct in_addr ia;
   memset(&ia, 0, sizeof(ia));
   return ast_udptl_new_with_bindaddr(sched, io, callbackmode, ia);
}

int ast_udptl_setqos(struct ast_udptl *udptl, unsigned int tos, unsigned int cos)
{
   return ast_netsock_set_qos(udptl->fd, tos, cos, "UDPTL");
}

void ast_udptl_set_peer(struct ast_udptl *udptl, const struct sockaddr_in *them)
{
   udptl->them.sin_port = them->sin_port;
   udptl->them.sin_addr = them->sin_addr;
}

void ast_udptl_get_peer(const struct ast_udptl *udptl, struct sockaddr_in *them)
{
   memset(them, 0, sizeof(*them));
   them->sin_family = AF_INET;
   them->sin_port = udptl->them.sin_port;
   them->sin_addr = udptl->them.sin_addr;
}

void ast_udptl_get_us(const struct ast_udptl *udptl, struct sockaddr_in *us)
{
   memcpy(us, &udptl->us, sizeof(udptl->us));
}

void ast_udptl_stop(struct ast_udptl *udptl)
{
   memset(&udptl->them.sin_addr, 0, sizeof(udptl->them.sin_addr));
   memset(&udptl->them.sin_port, 0, sizeof(udptl->them.sin_port));
}

void ast_udptl_destroy(struct ast_udptl *udptl)
{
   if (udptl->ioid)
      ast_io_remove(udptl->io, udptl->ioid);
   if (udptl->fd > -1)
      close(udptl->fd);
   ast_free(udptl);
}

int ast_udptl_write(struct ast_udptl *s, struct ast_frame *f)
{
   unsigned int seq;
   unsigned int len;
   int res;
   uint8_t buf[s->far_max_datagram];

   /* If we have no peer, return immediately */ 
   if (s->them.sin_addr.s_addr == INADDR_ANY)
      return 0;

   /* If there is no data length, return immediately */
   if (f->datalen == 0)
      return 0;
   
   if ((f->frametype != AST_FRAME_MODEM) ||
       (f->subclass != AST_MODEM_T38)) {
      ast_log(LOG_WARNING, "UDPTL can only send T.38 data.\n");
      return -1;
   }

   if (f->datalen > s->far_max_ifp) {
      ast_log(LOG_WARNING, "UDPTL asked to send %d bytes of IFP when far end only prepared to accept %d bytes; data loss may occur.\n", f->datalen, s->far_max_ifp);
   }

   /* Save seq_no for debug output because udptl_build_packet increments it */
   seq = s->tx_seq_no & 0xFFFF;

   /* Cook up the UDPTL packet, with the relevant EC info. */
   len = udptl_build_packet(s, buf, sizeof(buf), f->data.ptr, f->datalen);

   if (len > 0 && s->them.sin_port && s->them.sin_addr.s_addr) {
      if ((res = sendto(s->fd, buf, len, 0, (struct sockaddr *) &s->them, sizeof(s->them))) < 0)
         ast_log(LOG_NOTICE, "UDPTL Transmission error to %s:%d: %s\n", ast_inet_ntoa(s->them.sin_addr), ntohs(s->them.sin_port), strerror(errno));
#if 0
      printf("Sent %d bytes of UDPTL data to %s:%d\n", res, ast_inet_ntoa(udptl->them.sin_addr), ntohs(udptl->them.sin_port));
#endif
      if (udptl_debug_test_addr(&s->them))
         ast_verb(1, "Sent UDPTL packet to %s:%d (type %d, seq %d, len %d)\n",
               ast_inet_ntoa(s->them.sin_addr),
               ntohs(s->them.sin_port), 0, seq, len);
   }
      
   return 0;
}

void ast_udptl_proto_unregister(struct ast_udptl_protocol *proto)
{
   AST_RWLIST_WRLOCK(&protos);
   AST_RWLIST_REMOVE(&protos, proto, list);
   AST_RWLIST_UNLOCK(&protos);
}

int ast_udptl_proto_register(struct ast_udptl_protocol *proto)
{
   struct ast_udptl_protocol *cur;

   AST_RWLIST_WRLOCK(&protos);
   AST_RWLIST_TRAVERSE(&protos, cur, list) {
      if (cur->type == proto->type) {
         ast_log(LOG_WARNING, "Tried to register same protocol '%s' twice\n", cur->type);
         AST_RWLIST_UNLOCK(&protos);
         return -1;
      }
   }
   AST_RWLIST_INSERT_TAIL(&protos, proto, list);
   AST_RWLIST_UNLOCK(&protos);
   return 0;
}

static struct ast_udptl_protocol *get_proto(struct ast_channel *chan)
{
   struct ast_udptl_protocol *cur = NULL;

   AST_RWLIST_RDLOCK(&protos);
   AST_RWLIST_TRAVERSE(&protos, cur, list) {
      if (cur->type == chan->tech->type)
         break;
   }
   AST_RWLIST_UNLOCK(&protos);

   return cur;
}

int ast_udptl_bridge(struct ast_channel *c0, struct ast_channel *c1, int flags, struct ast_frame **fo, struct ast_channel **rc)
{
   struct ast_frame *f;
   struct ast_channel *who;
   struct ast_channel *cs[3];
   struct ast_udptl *p0;
   struct ast_udptl *p1;
   struct ast_udptl_protocol *pr0;
   struct ast_udptl_protocol *pr1;
   struct sockaddr_in ac0;
   struct sockaddr_in ac1;
   struct sockaddr_in t0;
   struct sockaddr_in t1;
   void *pvt0;
   void *pvt1;
   int to;
   
   ast_channel_lock(c0);
   while (ast_channel_trylock(c1)) {
      ast_channel_unlock(c0);
      usleep(1);
      ast_channel_lock(c0);
   }
   pr0 = get_proto(c0);
   pr1 = get_proto(c1);
   if (!pr0) {
      ast_log(LOG_WARNING, "Can't find native functions for channel '%s'\n", c0->name);
      ast_channel_unlock(c0);
      ast_channel_unlock(c1);
      return -1;
   }
   if (!pr1) {
      ast_log(LOG_WARNING, "Can't find native functions for channel '%s'\n", c1->name);
      ast_channel_unlock(c0);
      ast_channel_unlock(c1);
      return -1;
   }
   pvt0 = c0->tech_pvt;
   pvt1 = c1->tech_pvt;
   p0 = pr0->get_udptl_info(c0);
   p1 = pr1->get_udptl_info(c1);
   if (!p0 || !p1) {
      /* Somebody doesn't want to play... */
      ast_channel_unlock(c0);
      ast_channel_unlock(c1);
      return -2;
   }
   if (pr0->set_udptl_peer(c0, p1)) {
      ast_log(LOG_WARNING, "Channel '%s' failed to talk to '%s'\n", c0->name, c1->name);
      memset(&ac1, 0, sizeof(ac1));
   } else {
      /* Store UDPTL peer */
      ast_udptl_get_peer(p1, &ac1);
   }
   if (pr1->set_udptl_peer(c1, p0)) {
      ast_log(LOG_WARNING, "Channel '%s' failed to talk back to '%s'\n", c1->name, c0->name);
      memset(&ac0, 0, sizeof(ac0));
   } else {
      /* Store UDPTL peer */
      ast_udptl_get_peer(p0, &ac0);
   }
   ast_channel_unlock(c0);
   ast_channel_unlock(c1);
   cs[0] = c0;
   cs[1] = c1;
   cs[2] = NULL;
   for (;;) {
      if ((c0->tech_pvt != pvt0) ||
         (c1->tech_pvt != pvt1) ||
         (c0->masq || c0->masqr || c1->masq || c1->masqr)) {
            ast_debug(1, "Oooh, something is weird, backing out\n");
            /* Tell it to try again later */
            return -3;
      }
      to = -1;
      ast_udptl_get_peer(p1, &t1);
      ast_udptl_get_peer(p0, &t0);
      if (inaddrcmp(&t1, &ac1)) {
         ast_debug(1, "Oooh, '%s' changed end address to %s:%d\n", 
            c1->name, ast_inet_ntoa(t1.sin_addr), ntohs(t1.sin_port));
         ast_debug(1, "Oooh, '%s' was %s:%d\n", 
            c1->name, ast_inet_ntoa(ac1.sin_addr), ntohs(ac1.sin_port));
         memcpy(&ac1, &t1, sizeof(ac1));
      }
      if (inaddrcmp(&t0, &ac0)) {
         ast_debug(1, "Oooh, '%s' changed end address to %s:%d\n", 
            c0->name, ast_inet_ntoa(t0.sin_addr), ntohs(t0.sin_port));
         ast_debug(1, "Oooh, '%s' was %s:%d\n", 
            c0->name, ast_inet_ntoa(ac0.sin_addr), ntohs(ac0.sin_port));
         memcpy(&ac0, &t0, sizeof(ac0));
      }
      who = ast_waitfor_n(cs, 2, &to);
      if (!who) {
         ast_debug(1, "Ooh, empty read...\n");
         /* check for hangup / whentohangup */
         if (ast_check_hangup(c0) || ast_check_hangup(c1))
            break;
         continue;
      }
      f = ast_read(who);
      if (!f) {
         *fo = f;
         *rc = who;
         ast_debug(1, "Oooh, got a %s\n", f ? "digit" : "hangup");
         /* That's all we needed */
         return 0;
      } else {
         if (f->frametype == AST_FRAME_MODEM) {
            /* Forward T.38 frames if they happen upon us */
            if (who == c0) {
               ast_write(c1, f);
            } else if (who == c1) {
               ast_write(c0, f);
            }
         }
         ast_frfree(f);
      }
      /* Swap priority. Not that it's a big deal at this point */
      cs[2] = cs[0];
      cs[0] = cs[1];
      cs[1] = cs[2];
   }
   return -1;
}

static char *handle_cli_udptl_debug_deprecated(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct hostent *hp;
   struct ast_hostent ahp;
   int port;
   char *p;
   char *arg;

   switch (cmd) {
   case CLI_INIT:
      e->command = "udptl debug [off|ip]";
      e->usage = 
         "Usage: udptl debug [off]|[ip host[:port]]\n"
         "       Enable or disable dumping of UDPTL packets.\n"
         "       If ip is specified, limit the dumped packets to those to and from\n"
         "       the specified 'host' with optional port.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc < 2 || a->argc > 4)
      return CLI_SHOWUSAGE;

   if (a->argc == 2) { 
      udptldebug = 1;
      memset(&udptldebugaddr, 0, sizeof(udptldebugaddr));
      ast_cli(a->fd, "UDPTL Debugging Enabled\n");
   } else if (a->argc == 3) {
      if (strncasecmp(a->argv[2], "off", 3))
         return CLI_SHOWUSAGE;
      udptldebug = 0;
      ast_cli(a->fd, "UDPTL Debugging Disabled\n");
   } else {
      if (strncasecmp(a->argv[2], "ip", 2))
         return CLI_SHOWUSAGE;
      port = 0;
      arg = a->argv[3];
      p = strstr(arg, ":");
      if (p) {
         *p = '\0';
         p++;
         port = atoi(p);
      }
      hp = ast_gethostbyname(arg, &ahp);
      if (hp == NULL)
         return CLI_SHOWUSAGE;
      udptldebugaddr.sin_family = AF_INET;
      memcpy(&udptldebugaddr.sin_addr, hp->h_addr, sizeof(udptldebugaddr.sin_addr));
      udptldebugaddr.sin_port = htons(port);
      if (port == 0)
         ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s\n", ast_inet_ntoa(udptldebugaddr.sin_addr));
      else
         ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s:%d\n", ast_inet_ntoa(udptldebugaddr.sin_addr), port);
      udptldebug = 1;
   }

   return CLI_SUCCESS;
}

static char *handle_cli_udptl_set_debug(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct hostent *hp;
   struct ast_hostent ahp;
   int port;
   char *p;
   char *arg;

   switch (cmd) {
   case CLI_INIT:
      e->command = "udptl set debug {on|off|ip}";
      e->usage = 
         "Usage: udptl set debug {on|off|ip host[:port]}\n"
         "       Enable or disable dumping of UDPTL packets.\n"
         "       If ip is specified, limit the dumped packets to those to and from\n"
         "       the specified 'host' with optional port.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc < 4 || a->argc > 5)
      return CLI_SHOWUSAGE;

   if (a->argc == 4) {
      if (!strncasecmp(a->argv[3], "on", 2)) {
         udptldebug = 1;
         memset(&udptldebugaddr, 0, sizeof(udptldebugaddr));
         ast_cli(a->fd, "UDPTL Debugging Enabled\n");
      } else if (!strncasecmp(a->argv[3], "off", 3)) {
         udptldebug = 0;
         ast_cli(a->fd, "UDPTL Debugging Disabled\n");
      } else {
         return CLI_SHOWUSAGE;
      }
   } else {
      if (strncasecmp(a->argv[3], "ip", 2))
         return CLI_SHOWUSAGE;
      port = 0;
      arg = a->argv[4];
      p = strstr(arg, ":");
      if (p) {
         *p = '\0';
         p++;
         port = atoi(p);
      }
      hp = ast_gethostbyname(arg, &ahp);
      if (hp == NULL)
         return CLI_SHOWUSAGE;
      udptldebugaddr.sin_family = AF_INET;
      memcpy(&udptldebugaddr.sin_addr, hp->h_addr, sizeof(udptldebugaddr.sin_addr));
      udptldebugaddr.sin_port = htons(port);
      if (port == 0)
         ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s\n", ast_inet_ntoa(udptldebugaddr.sin_addr));
      else
         ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s:%d\n", ast_inet_ntoa(udptldebugaddr.sin_addr), port);
      udptldebug = 1;
   }

   return CLI_SUCCESS;
}

static struct ast_cli_entry cli_handle_udptl_debug_deprecated = AST_CLI_DEFINE(handle_cli_udptl_debug_deprecated, "Enable/Disable UDPTL debugging");

static struct ast_cli_entry cli_udptl[] = {
   AST_CLI_DEFINE(handle_cli_udptl_set_debug, "Enable/Disable UDPTL debugging", .deprecate_cmd = &cli_handle_udptl_debug_deprecated)
};

static void __ast_udptl_reload(int reload)
{
   struct ast_config *cfg;
   const char *s;
   struct ast_flags config_flags = { reload ? CONFIG_FLAG_FILEUNCHANGED : 0 };

   if ((cfg = ast_config_load2("udptl.conf", "udptl", config_flags)) == CONFIG_STATUS_FILEUNCHANGED)
      return;

   udptlstart = 4500;
   udptlend = 4999;
   udptlfectype = UDPTL_ERROR_CORRECTION_NONE;
   udptlfecentries = 0;
   udptlfecspan = 0;
   udptlmaxdatagram = 0;
   use_even_ports = 0;

   if (cfg) {
      if ((s = ast_variable_retrieve(cfg, "general", "udptlstart"))) {
         udptlstart = atoi(s);
         if (udptlstart < 1024) {
            ast_log(LOG_WARNING, "Ports under 1024 are not allowed for T.38.\n");
            udptlstart = 1024;
         }
         if (udptlstart > 65535) {
            ast_log(LOG_WARNING, "Ports over 65535 are invalid.\n");
            udptlstart = 65535;
         }
      }
      if ((s = ast_variable_retrieve(cfg, "general", "udptlend"))) {
         udptlend = atoi(s);
         if (udptlend < 1024) {
            ast_log(LOG_WARNING, "Ports under 1024 are not allowed for T.38.\n");
            udptlend = 1024;
         }
         if (udptlend > 65535) {
            ast_log(LOG_WARNING, "Ports over 65535 are invalid.\n");
            udptlend = 65535;
         }
      }
      if ((s = ast_variable_retrieve(cfg, "general", "udptlchecksums"))) {
#ifdef SO_NO_CHECK
         if (ast_false(s))
            nochecksums = 1;
         else
            nochecksums = 0;
#else
         if (ast_false(s))
            ast_log(LOG_WARNING, "Disabling UDPTL checksums is not supported on this operating system!\n");
#endif
      }
      if ((s = ast_variable_retrieve(cfg, "general", "T38FaxUdpEC"))) {
         if (strcmp(s, "t38UDPFEC") == 0)
            udptlfectype = UDPTL_ERROR_CORRECTION_FEC;
         else if (strcmp(s, "t38UDPRedundancy") == 0)
            udptlfectype = UDPTL_ERROR_CORRECTION_REDUNDANCY;
      }
      if ((s = ast_variable_retrieve(cfg, "general", "T38FaxMaxDatagram"))) {
         udptlmaxdatagram = atoi(s);
         if (udptlmaxdatagram < 100) {
            ast_log(LOG_WARNING, "Too small T38FaxMaxDatagram size.  Defaulting to 100.\n");
            udptlmaxdatagram = 100;
         }
         if (udptlmaxdatagram > LOCAL_FAX_MAX_DATAGRAM) {
            ast_log(LOG_WARNING, "Too large T38FaxMaxDatagram size.  Defaulting to %d.\n", LOCAL_FAX_MAX_DATAGRAM);
            udptlmaxdatagram = LOCAL_FAX_MAX_DATAGRAM;
         }
      }
      if ((s = ast_variable_retrieve(cfg, "general", "UDPTLFECentries"))) {
         udptlfecentries = atoi(s);
         if (udptlfecentries < 1) {
            ast_log(LOG_WARNING, "Too small UDPTLFECentries value.  Defaulting to 1.\n");
            udptlfecentries = 1;
         }
         if (udptlfecentries > MAX_FEC_ENTRIES) {
            ast_log(LOG_WARNING, "Too large UDPTLFECentries value.  Defaulting to %d.\n", MAX_FEC_ENTRIES);
            udptlfecentries = MAX_FEC_ENTRIES;
         }
      }
      if ((s = ast_variable_retrieve(cfg, "general", "UDPTLFECspan"))) {
         udptlfecspan = atoi(s);
         if (udptlfecspan < 1) {
            ast_log(LOG_WARNING, "Too small UDPTLFECspan value.  Defaulting to 1.\n");
            udptlfecspan = 1;
         }
         if (udptlfecspan > MAX_FEC_SPAN) {
            ast_log(LOG_WARNING, "Too large UDPTLFECspan value.  Defaulting to %d.\n", MAX_FEC_SPAN);
            udptlfecspan = MAX_FEC_SPAN;
         }
      }
      if ((s = ast_variable_retrieve(cfg, "general", "use_even_ports"))) {
         use_even_ports = ast_true(s);
      }
      ast_config_destroy(cfg);
   }
   if (udptlstart >= udptlend) {
      ast_log(LOG_WARNING, "Unreasonable values for UDPTL start/end\n");
      udptlstart = 4500;
      udptlend = 4999;
   }
   if (use_even_ports && (udptlstart & 1)) {
      ++udptlstart;
      ast_log(LOG_NOTICE, "Odd numbered udptlstart specified but use_even_ports enabled. udptlstart is now %d\n", udptlstart);
   }
   if (use_even_ports && (udptlend & 1)) {
      --udptlend;
      ast_log(LOG_NOTICE, "Odd numbered udptlend specified but use_event_ports enabled. udptlend is now %d\n", udptlend);
   }
   ast_verb(2, "UDPTL allocating from port range %d -> %d\n", udptlstart, udptlend);
}

int ast_udptl_reload(void)
{
   __ast_udptl_reload(1);
   return 0;
}

void ast_udptl_init(void)
{
   ast_cli_register_multiple(cli_udptl, sizeof(cli_udptl) / sizeof(struct ast_cli_entry));
   __ast_udptl_reload(0);
}