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) 1999-2009, Digium, Inc.
 *
 * Steve Underwood <steveu@coppice.org>
 * Kevin P. Fleming <kpfleming@digium.com>
 *
 * 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>
 * \author Steve Underwood <steveu@coppice.org>
 * \author Kevin P. Fleming <kpfleming@digium.com>
 *
 * \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
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 406934 $")

#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_options.h"
#include "asterisk/lock.h"
#include "asterisk/utils.h"
#include "asterisk/netsock2.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

#define LOG_TAG(u) S_OR(u->tag, "no tag")

#define DEFAULT_UDPTLSTART 4000
#define DEFAULT_UDPTLEND 4999

static int udptldebug;                      /*!< Are we debugging? */
static struct ast_sockaddr udptldebugaddr;   /*!< Debug packets to/from this host */

#define LOCAL_FAX_MAX_DATAGRAM      1400
#define DEFAULT_FAX_MAX_DATAGRAM    400
#define FAX_MAX_DATAGRAM_LIMIT      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 ast_sockaddr us;
   struct ast_sockaddr them;
   int *ioid;
   struct ast_sched_context *sched;
   struct io_context *io;
   void *data;
   char *tag;
   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.
    */
   int far_max_datagram;

   /*! The maximum size UDPTL packet that we are prepared to
    * accept, or -1 if it hasn't been calculated since the last
    * changes were applied to the UDPTL structure.
    */
   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,
    * or -1 if it hasn't been calculated since the last
    * changes were applied to the UDPTL structure.
    */
   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.
    */
   int local_max_ifp;

   unsigned int tx_seq_no;
   unsigned int rx_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);

struct udptl_global_options {
   unsigned int start; /*< The UDPTL start port */
   unsigned int end;   /*< The UDPTL end port */
   unsigned int fecentries;
   unsigned int fecspan;
   unsigned int nochecksums;
   unsigned int use_even_ports;
};

static AO2_GLOBAL_OBJ_STATIC(globals);

struct udptl_config {
   struct udptl_global_options *general;
};

static void *udptl_snapshot_alloc(void);
static int udptl_pre_apply_config(void);

static struct aco_type general_option = {
   .type = ACO_GLOBAL,
   .category_match = ACO_WHITELIST,
   .item_offset = offsetof(struct udptl_config, general),
   .category = "^general$",
};

static struct aco_type *general_options[] = ACO_TYPES(&general_option);

static struct aco_file udptl_conf = {
   .filename = "udptl.conf",
   .types = ACO_TYPES(&general_option),
};

CONFIG_INFO_STANDARD(cfg_info, globals, udptl_snapshot_alloc,
   .files = ACO_FILES(&udptl_conf),
   .pre_apply_config = udptl_pre_apply_config,
);

static inline int udptl_debug_test_addr(const struct ast_sockaddr *addr)
{
   if (udptldebug == 0)
      return 0;

   if (ast_sockaddr_isnull(&udptldebugaddr)) {
      return 1;
   }

   if (ast_sockaddr_port(&udptldebugaddr)) {
      return !ast_sockaddr_cmp(&udptldebugaddr, addr);
   } else {
      return !ast_sockaddr_cmp_addr(&udptldebugaddr, addr);
   }
}

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)++;
   /* We have a fragment.  Currently we don't process fragments. */
   ast_debug(1, "UDPTL packet with length greater than 16K received, decoding will fail\n");
   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 = 0;

   if (decode_length(buf, limit, len, &octet_cnt) != 0)
      return -1;

   if (octet_cnt > 0) {
      /* Make sure the buffer contains at least the number of bits requested */
      if ((*len + octet_cnt) > limit)
         return -1;

      *p_num_octets = octet_cnt;
      *p_object = &buf[*len];
      *len += octet_cnt;
   }

   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(const struct ast_udptl *udptl, 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, "UDPTL (%s): Buffer overflow detected (%d + %d > %d)\n",
            LOG_TAG(udptl), 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;
   unsigned int ptr; /* an index that keeps track of how much of the UDPTL packet has been processed */
   int seq_no;
   const uint8_t *ifp = NULL;
   const uint8_t *data = NULL;
   unsigned int ifp_len = 0;
   int repaired[16];
   const uint8_t *bufs[ARRAY_LEN(s->f) - 1];
   unsigned int lengths[ARRAY_LEN(s->f) - 1];
   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. */
         int total_count = 0;
         do {
            unsigned int count;
            if ((stat2 = decode_length(buf, len, &ptr, &count)) < 0)
               return -1;
            for (i = 0; i < count && total_count + i < ARRAY_LEN(bufs); i++) {
               if ((stat1 = decode_open_type(buf, len, &ptr, &bufs[total_count + i], &lengths[total_count + i])) != 0) {
                  return -1;
               }
               /* valid secondaries can contain zero-length packets that should be ignored */
               if (!bufs[total_count + i] || !lengths[total_count + i]) {
                  /* drop the count of items to process and reuse the buffers that were just set */
                  i--;
                  count--;
               }
            }
            total_count += i;
         }
         while (stat2 > 0 && total_count < ARRAY_LEN(bufs));
         /* 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 */
               ast_debug(3, "Recovering lost packet via secondary %d, len %d\n", seq_no - i, lengths[i - 1]);
               s->f[ifp_no].frametype = AST_FRAME_MODEM;
               s->f[ifp_no].subclass.integer = 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
   {
      int j;
      int l;
      int x;
      /* 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++];
      if (entries > MAX_FEC_ENTRIES) {
         return -1;
      }
      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) {
         int m;
         if (s->rx[l].fec_len[0] <= 0)
            continue;
         for (m = 0; m < s->rx[l].fec_entries; m++) {
            int k;
            int which;
            int 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.integer = 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.integer = 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] = { 0, };
   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(s, 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(s, buf, buflen, &len, s->tx[j].buf, s->tx[j].buf_len) < 0) {
            ast_debug(1, "UDPTL (%s): Encoding failed at i=%d, j=%d\n",
                 LOG_TAG(s), 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(s, buf, buflen, &len, fec, high_tide) < 0)
            return -1;
      }
      break;
   }

   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 ast_sockaddr addr;
   uint8_t *buf;

   buf = udptl->rawdata + AST_FRIENDLY_OFFSET;

   /* Cache where the header will go */
   res = ast_recvfrom(udptl->fd,
         buf,
         sizeof(udptl->rawdata) - AST_FRIENDLY_OFFSET,
         0,
         &addr);
   if (res < 0) {
      if (errno != EAGAIN)
         ast_log(LOG_WARNING, "UDPTL (%s): read error: %s\n",
            LOG_TAG(udptl), strerror(errno));
      ast_assert(errno != EBADF);
      return &ast_null_frame;
   }

   /* Ignore if the other side hasn't been given an address yet. */
   if (ast_sockaddr_isnull(&udptl->them)) {
      return &ast_null_frame;
   }

   if (udptl->nat) {
      /* Send to whoever sent to us */
      if (ast_sockaddr_cmp(&udptl->them, &addr)) {
         ast_sockaddr_copy(&udptl->them, &addr);
         ast_debug(1, "UDPTL (%s): NAT, Using address %s\n",
              LOG_TAG(udptl), ast_sockaddr_stringify(&udptl->them));
      }
   }

   if (udptl_debug_test_addr(&addr)) {
      int seq_no;

      /* Decode sequence number just for verbose message. */
      if (res < 2) {
         /* Short packet. */
         seq_no = -1;
      } else {
         seq_no = (buf[0] << 8) | buf[1];
      }

      ast_verb(1, "UDPTL (%s): packet from %s (seq %d, len %d)\n",
         LOG_TAG(udptl), ast_sockaddr_stringify(&addr), seq_no, res);
   }
   if (udptl_rx_packet(udptl, buf, res) < 1) {
      return &ast_null_frame;
   }

   return &udptl->f[0];
}

static void calculate_local_max_datagram(struct ast_udptl *udptl)
{
   unsigned int new_max = 0;

   if (udptl->local_max_ifp == -1) {
      ast_log(LOG_WARNING, "UDPTL (%s): Cannot calculate local_max_datagram before local_max_ifp has been set.\n",
         LOG_TAG(udptl));
      udptl->local_max_datagram = -1;
      return;
   }

   /* calculate the amount of space required to receive an IFP
    * of the maximum size supported by the application/endpoint
    * that we are delivering them to (local endpoint), and add
    * the amount of space required to support the selected
    * error correction mode
    */
   switch (udptl->error_correction_scheme) {
   case UDPTL_ERROR_CORRECTION_NONE:
      /* need room for sequence number, length indicator, redundancy
       * indicator and following length indicator
       */
      new_max = 5 + udptl->local_max_ifp;
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      /* need room for sequence number, length indicators, plus
       * room for up to 3 redundancy packets
       */
      new_max = 5 + udptl->local_max_ifp + 2 + (3 * 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 = 5 + udptl->local_max_ifp + 4 + udptl->local_max_ifp;
      break;
   }
   /* add 5% extra space for insurance, but no larger than LOCAL_FAX_MAX_DATAGRAM */
   udptl->local_max_datagram = MIN(new_max * 1.05, LOCAL_FAX_MAX_DATAGRAM);
}

static void calculate_far_max_ifp(struct ast_udptl *udptl)
{
   unsigned new_max = 0;

   if (udptl->far_max_datagram == -1) {
      ast_log(LOG_WARNING, "UDPTL (%s): Cannot calculate far_max_ifp before far_max_datagram has been set.\n",
         LOG_TAG(udptl));
      udptl->far_max_ifp = -1;
      return;
   }

   /* the goal here is to supply the local endpoint (application
    * or bridged channel) a maximum IFP value that will allow it
    * to effectively and efficiently transfer image data at its
    * selected bit rate, taking into account the selected error
    * correction mode, but without overrunning the far endpoint's
    * datagram buffer. this is complicated by the fact that some
    * far endpoints send us bogus (small) max datagram values,
    * which would result in either buffer overrun or no error
    * correction. we try to accomodate those, but if the supplied
    * value is too small to do so, we'll emit warning messages and
    * the user will have to use configuration options to override
    * the max datagram value supplied by the far endpoint.
    */
   switch (udptl->error_correction_scheme) {
   case UDPTL_ERROR_CORRECTION_NONE:
      /* need room for sequence number, length indicator, redundancy
       * indicator and following length indicator
       */
      new_max = udptl->far_max_datagram - 5;
      break;
   case UDPTL_ERROR_CORRECTION_REDUNDANCY:
      /* for this case, we'd like to send as many error correction entries
       * as possible (up to the number we're configured for), but we'll settle
       * for sending fewer if the configured number would cause the
       * calculated max IFP to be too small for effective operation
       *
       * need room for sequence number, length indicators and the
       * configured number of redundant packets
       *
       * note: we purposely don't allow error_correction_entries to drop to
       * zero in this loop; we'd rather send smaller IFPs (and thus reduce
       * the image data transfer rate) than sacrifice redundancy completely
       */
      for (;;) {
         new_max = (udptl->far_max_datagram - 8) / (udptl->error_correction_entries + 1);

         if ((new_max < 80) && (udptl->error_correction_entries > 1)) {
            /* the max ifp is not large enough, subtract an
             * error correction entry and calculate again
             * */
            --udptl->error_correction_entries;
         } else {
            break;
         }
      }
      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 = (udptl->far_max_datagram - 10) / 2;
      break;
   }
   /* subtract 5% of space for insurance */
   udptl->far_max_ifp = new_max * 0.95;
}

enum ast_t38_ec_modes ast_udptl_get_error_correction_scheme(const struct ast_udptl *udptl)
{
   return udptl->error_correction_scheme;
}

void ast_udptl_set_error_correction_scheme(struct ast_udptl *udptl, enum ast_t38_ec_modes ec)
{
   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;
   };
   /* reset calculated values so they'll be computed again */
   udptl->local_max_datagram = -1;
   udptl->far_max_ifp = -1;
}

void ast_udptl_set_local_max_ifp(struct ast_udptl *udptl, unsigned int max_ifp)
{
   /* make sure max_ifp is a positive value since a cast will take place when
    * when setting local_max_ifp */
   if ((signed int) max_ifp > 0) {
      udptl->local_max_ifp = max_ifp;
      /* reset calculated values so they'll be computed again */
      udptl->local_max_datagram = -1;
   }
}

unsigned int ast_udptl_get_local_max_datagram(struct ast_udptl *udptl)
{
   if (udptl->local_max_datagram == -1) {
      calculate_local_max_datagram(udptl);
   }

   /* this function expects a unsigned value in return. */
   if (udptl->local_max_datagram < 0) {
      return 0;
   }
   return udptl->local_max_datagram;
}

void ast_udptl_set_far_max_datagram(struct ast_udptl *udptl, unsigned int max_datagram)
{
   if (!max_datagram || (max_datagram > FAX_MAX_DATAGRAM_LIMIT)) {
      udptl->far_max_datagram = DEFAULT_FAX_MAX_DATAGRAM;
   } else {
      udptl->far_max_datagram = max_datagram;
   }
   /* reset calculated values so they'll be computed again */
   udptl->far_max_ifp = -1;
}

unsigned int ast_udptl_get_far_max_datagram(const struct ast_udptl *udptl)
{
   if (udptl->far_max_datagram < 0) {
      return 0;
   }
   return udptl->far_max_datagram;
}

unsigned int ast_udptl_get_far_max_ifp(struct ast_udptl *udptl)
{
   if (udptl->far_max_ifp == -1) {
      calculate_far_max_ifp(udptl);
   }

   if (udptl->far_max_ifp < 0) {
      return 0;
   }
   return udptl->far_max_ifp;
}

struct ast_udptl *ast_udptl_new_with_bindaddr(struct ast_sched_context *sched, struct io_context *io, int callbackmode, struct ast_sockaddr *addr)
{
   struct ast_udptl *udptl;
   int x;
   int startplace;
   int i;
   long int flags;
   RAII_VAR(struct udptl_config *, cfg, ao2_global_obj_ref(globals), ao2_cleanup);

   if (!cfg || !cfg->general) {
      ast_log(LOG_ERROR, "Could not access global udptl options!\n");
      return NULL;
   }

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

   udptl->error_correction_span = cfg->general->fecspan;
   udptl->error_correction_entries = cfg->general->fecentries;

   udptl->far_max_datagram = -1;
   udptl->far_max_ifp = -1;
   udptl->local_max_ifp = -1;
   udptl->local_max_datagram = -1;

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

   if ((udptl->fd = socket(ast_sockaddr_is_ipv6(addr) ?
               AF_INET6 : 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 (cfg->general->nochecksums)
      setsockopt(udptl->fd, SOL_SOCKET, SO_NO_CHECK, &cfg->general->nochecksums, sizeof(cfg->general->nochecksums));
#endif

   /* Find us a place */
   x = (cfg->general->start == cfg->general->end) ? cfg->general->start : (ast_random() % (cfg->general->end - cfg->general->start)) + cfg->general->start;
   if (cfg->general->use_even_ports && (x & 1)) {
      ++x;
   }
   startplace = x;
   for (;;) {
      ast_sockaddr_copy(&udptl->us, addr);
      ast_sockaddr_set_port(&udptl->us, x);
      if (ast_bind(udptl->fd, &udptl->us) == 0) {
         break;
      }
      if (errno != EADDRINUSE && errno != EACCES) {
         ast_log(LOG_WARNING, "Unexpected bind error: %s\n", strerror(errno));
         close(udptl->fd);
         ast_free(udptl);
         return NULL;
      }
      if (cfg->general->use_even_ports) {
         x += 2;
      } else {
         ++x;
      }
      if (x > cfg->general->end)
         x = cfg->general->start;
      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;
}

void ast_udptl_set_tag(struct ast_udptl *udptl, const char *format, ...)
{
   va_list ap;

   ast_free(udptl->tag);
   udptl->tag = NULL;
   va_start(ap, format);
   if (ast_vasprintf(&udptl->tag, format, ap) == -1) {
      udptl->tag = NULL;
   }
   va_end(ap);
}

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

void ast_udptl_set_peer(struct ast_udptl *udptl, const struct ast_sockaddr *them)
{
   ast_sockaddr_copy(&udptl->them, them);
}

void ast_udptl_get_peer(const struct ast_udptl *udptl, struct ast_sockaddr *them)
{
   ast_sockaddr_copy(them, &udptl->them);
}

void ast_udptl_get_us(const struct ast_udptl *udptl, struct ast_sockaddr *us)
{
   ast_sockaddr_copy(us, &udptl->us);
}

void ast_udptl_stop(struct ast_udptl *udptl)
{
   ast_sockaddr_setnull(&udptl->them);
}

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);
   if (udptl->tag)
      ast_free(udptl->tag);
   ast_free(udptl);
}

int ast_udptl_write(struct ast_udptl *s, struct ast_frame *f)
{
   unsigned int seq;
   unsigned int len = f->datalen;
   /* if no max datagram size is provided, use default value */
   const int bufsize = (s->far_max_datagram > 0) ? s->far_max_datagram : DEFAULT_FAX_MAX_DATAGRAM;
   uint8_t buf[bufsize];

   memset(buf, 0, sizeof(buf));

   /* If we have no peer, return immediately */
   if (ast_sockaddr_isnull(&s->them)) {
      return 0;
   }

   /* If there is no data length, return immediately */
   if (f->datalen == 0)
      return 0;

   if ((f->frametype != AST_FRAME_MODEM) ||
       (f->subclass.integer != AST_MODEM_T38)) {
      ast_log(LOG_WARNING, "UDPTL (%s): UDPTL can only send T.38 data.\n",
         LOG_TAG(s));
      return -1;
   }

   if (len > s->far_max_ifp) {
      ast_log(LOG_WARNING,
         "UDPTL (%s): UDPTL asked to send %d bytes of IFP when far end only prepared to accept %d bytes; data loss will occur."
         "You may need to override the T38FaxMaxDatagram value for this endpoint in the channel driver configuration.\n",
         LOG_TAG(s), len, s->far_max_ifp);
      len = 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, len);

   if ((signed int) len > 0 && !ast_sockaddr_isnull(&s->them)) {
      if (ast_sendto(s->fd, buf, len, 0, &s->them) < 0) {
         ast_log(LOG_NOTICE, "UDPTL (%s): Transmission error to %s: %s\n",
            LOG_TAG(s), ast_sockaddr_stringify(&s->them), strerror(errno));
      }
      if (udptl_debug_test_addr(&s->them)) {
         ast_verb(1, "UDPTL (%s): packet to %s (seq %d, len %d)\n",
            LOG_TAG(s), ast_sockaddr_stringify(&s->them), 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 == ast_channel_tech(chan)->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 ast_sockaddr ac0;
   struct ast_sockaddr ac1;
   struct ast_sockaddr t0;
   struct ast_sockaddr 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", ast_channel_name(c0));
      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", ast_channel_name(c1));
      ast_channel_unlock(c0);
      ast_channel_unlock(c1);
      return -1;
   }
   pvt0 = ast_channel_tech_pvt(c0);
   pvt1 = ast_channel_tech_pvt(c1);
   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", ast_channel_name(c0), ast_channel_name(c1));
      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", ast_channel_name(c1), ast_channel_name(c0));
      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 ((ast_channel_tech_pvt(c0) != pvt0) ||
         (ast_channel_tech_pvt(c1) != pvt1) ||
         (ast_channel_masq(c0) || ast_channel_masqr(c0) || ast_channel_masq(c1) || ast_channel_masqr(c1))) {
            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 (ast_sockaddr_cmp(&t1, &ac1)) {
         ast_debug(1, "Oooh, '%s' changed end address to %s\n",
            ast_channel_name(c1), ast_sockaddr_stringify(&t1));
         ast_debug(1, "Oooh, '%s' was %s\n",
            ast_channel_name(c1), ast_sockaddr_stringify(&ac1));
         ast_sockaddr_copy(&ac1, &t1);
      }
      if (ast_sockaddr_cmp(&t0, &ac0)) {
         ast_debug(1, "Oooh, '%s' changed end address to %s\n",
            ast_channel_name(c0), ast_sockaddr_stringify(&t0));
         ast_debug(1, "Oooh, '%s' was %s\n",
            ast_channel_name(c0), ast_sockaddr_stringify(&ac0));
         ast_sockaddr_copy(&ac0, &t0);
      }
      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_set_debug(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   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 {
      struct ast_sockaddr *addrs;
      if (strncasecmp(a->argv[3], "ip", 2))
         return CLI_SHOWUSAGE;
      if (!ast_sockaddr_resolve(&addrs, a->argv[4], 0, 0)) {
         return CLI_SHOWUSAGE;
      }
      ast_sockaddr_copy(&udptldebugaddr, &addrs[0]);
         ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s\n", ast_sockaddr_stringify(&udptldebugaddr));
      udptldebug = 1;
      ast_free(addrs);
   }

   return CLI_SUCCESS;
}

static char *handle_cli_show_config(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   RAII_VAR(struct udptl_config *, cfg, NULL, ao2_cleanup);

   switch (cmd) {
   case CLI_INIT:
      e->command = "udptl show config";
      e->usage =
         "Usage: udptl show config\n"
         "       Display UDPTL configuration options\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (!(cfg = ao2_global_obj_ref(globals))) {
      return CLI_FAILURE;
   }

   ast_cli(a->fd, "UDPTL Global options\n");
   ast_cli(a->fd, "--------------------\n");
   ast_cli(a->fd, "udptlstart:      %u\n", cfg->general->start);
   ast_cli(a->fd, "udptlend:        %u\n", cfg->general->end);
   ast_cli(a->fd, "udptlfecentries: %u\n", cfg->general->fecentries);
   ast_cli(a->fd, "udptlfecspan:    %u\n", cfg->general->fecspan);
   ast_cli(a->fd, "use_even_ports:  %s\n", AST_CLI_YESNO(cfg->general->use_even_ports));
   ast_cli(a->fd, "udptlchecksums: %s\n", AST_CLI_YESNO(!cfg->general->nochecksums));

   return CLI_SUCCESS;
}

static struct ast_cli_entry cli_udptl[] = {
   AST_CLI_DEFINE(handle_cli_udptl_set_debug, "Enable/Disable UDPTL debugging"),
   AST_CLI_DEFINE(handle_cli_show_config, "Show UDPTL config options"),
};

static void udptl_config_destructor(void *obj)
{
   struct udptl_config *cfg = obj;
   ao2_cleanup(cfg->general);
}

static void *udptl_snapshot_alloc(void)
{
   struct udptl_config *cfg;

   if (!(cfg = ao2_alloc(sizeof(*cfg), udptl_config_destructor))) {
      return NULL;
   }
   if (!(cfg->general = ao2_alloc(sizeof(*cfg->general), NULL))) {
      ao2_ref(cfg, -1);
      return NULL;
   }

   return cfg;
}

static int removed_options_handler(const struct aco_option *opt, struct ast_variable *var, void *obj)
{
   if (!strcasecmp(var->name, "t38faxudpec")) {
      ast_log(LOG_WARNING, "t38faxudpec in udptl.conf is no longer supported; use the t38pt_udptl configuration option in sip.conf instead.\n");
   } else if (!strcasecmp(var->name, "t38faxmaxdatagram")) {
      ast_log(LOG_WARNING, "t38faxmaxdatagram in udptl.conf is no longer supported; value is now supplied by T.38 applications.\n");
   }
   return 0;
}

static void __ast_udptl_reload(int reload)
{
   if (aco_process_config(&cfg_info, reload) == ACO_PROCESS_ERROR) {
      if (!reload) {
         RAII_VAR(struct udptl_config *, udptl_cfg, udptl_snapshot_alloc(), ao2_cleanup);

         if (aco_set_defaults(&general_option, "general", udptl_cfg->general)) {
            ast_log(LOG_ERROR, "Failed to load udptl.conf and failed to initialize defaults.\n");
            return;
         }

         ast_log(LOG_NOTICE, "Could not load udptl config; using defaults\n");
         ao2_global_obj_replace_unref(globals, udptl_cfg);
      }
   }
}

static int udptl_pre_apply_config(void) {
   struct udptl_config *cfg = aco_pending_config(&cfg_info);

   if (!cfg->general) {
      return -1;
   }

#ifndef SO_NO_CHECK
   if (cfg->general->nochecksums) {
      ast_log(LOG_WARNING, "Disabling UDPTL checksums is not supported on this operating system!\n");
      cfg->general->nochecksums = 0;
   }
#endif

   /* Fix up any global config values that we can handle before replacing the config */
   if (cfg->general->use_even_ports && (cfg->general->start & 1)) {
      ++cfg->general->start;
      ast_log(LOG_NOTICE, "Odd numbered udptlstart specified but use_even_ports enabled. udptlstart is now %d\n", cfg->general->start);
   }
   if (cfg->general->start > cfg->general->end) {
      ast_log(LOG_WARNING, "Unreasonable values for UDPTL start/end ports; defaulting to %s-%s.\n", __stringify(DEFAULT_UDPTLSTART), __stringify(DEFAULT_UDPTLEND));
      cfg->general->start = DEFAULT_UDPTLSTART;
      cfg->general->end = DEFAULT_UDPTLEND;
   }
   if (cfg->general->use_even_ports && (cfg->general->end & 1)) {
      --cfg->general->end;
      ast_log(LOG_NOTICE, "Odd numbered udptlend specified but use_even_ports enabled. udptlend is now %d\n", cfg->general->end);
   }

   return 0;
}

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

/*!
 * \internal
 * \brief Clean up resources on Asterisk shutdown
 */
static void udptl_shutdown(void)
{
   ast_cli_unregister_multiple(cli_udptl, ARRAY_LEN(cli_udptl));
   ao2_t_global_obj_release(globals, "Unref udptl global container in shutdown");
   aco_info_destroy(&cfg_info);
}

void ast_udptl_init(void)
{
   if (aco_info_init(&cfg_info)) {
      return;
   }

   aco_option_register(&cfg_info, "udptlstart", ACO_EXACT, general_options, __stringify(DEFAULT_UDPTLSTART),
      OPT_UINT_T, PARSE_IN_RANGE | PARSE_DEFAULT,
      FLDSET(struct udptl_global_options, start), DEFAULT_UDPTLSTART, 1024, 65535);

   aco_option_register(&cfg_info, "udptlend", ACO_EXACT, general_options, __stringify(DEFAULT_UDPTLEND),
      OPT_UINT_T, PARSE_IN_RANGE | PARSE_DEFAULT,
      FLDSET(struct udptl_global_options, end), DEFAULT_UDPTLEND, 1024, 65535);

   aco_option_register(&cfg_info, "udptlfecentries", ACO_EXACT, general_options, NULL,
      OPT_UINT_T, PARSE_IN_RANGE | PARSE_RANGE_DEFAULTS,
      FLDSET(struct udptl_global_options, fecentries), 1, MAX_FEC_ENTRIES);

   aco_option_register(&cfg_info, "udptlfecspan", ACO_EXACT, general_options, NULL,
      OPT_UINT_T, PARSE_IN_RANGE | PARSE_RANGE_DEFAULTS,
      FLDSET(struct udptl_global_options, fecspan), 1, MAX_FEC_SPAN);

   aco_option_register(&cfg_info, "udptlchecksums", ACO_EXACT, general_options, "yes",
      OPT_BOOL_T, 0, FLDSET(struct udptl_global_options, nochecksums));

   aco_option_register(&cfg_info, "use_even_ports", ACO_EXACT, general_options, "no",
      OPT_BOOL_T, 1, FLDSET(struct udptl_global_options, use_even_ports));

   aco_option_register_custom(&cfg_info, "t38faxudpec", ACO_EXACT, general_options, NULL, removed_options_handler, 0);
   aco_option_register_custom(&cfg_info, "t38faxmaxdatagram", ACO_EXACT, general_options, NULL, removed_options_handler, 0);

   __ast_udptl_reload(0);

   ast_cli_register_multiple(cli_udptl, ARRAY_LEN(cli_udptl));

   ast_register_atexit(udptl_shutdown);
}