net.c

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/* net.c -- CoAP network interface
 *
 * Copyright (C) 2010--2014 Olaf Bergmann <bergmann@tzi.org>
 *
 * This file is part of the CoAP library libcoap. Please see
 * README for terms of use. 
 */

#include "config.h"

#include <ctype.h>
#include <stdio.h>
#ifdef HAVE_LIMITS_H
#include <limits.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#elif HAVE_SYS_UNISTD_H
#include <sys/unistd.h>
#endif
#include <sys/types.h>
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif

#ifdef WITH_LWIP
#include <lwip/pbuf.h>
#include <lwip/udp.h>
#include <lwip/timers.h>
#endif

#include "debug.h"
#include "mem.h"
#include "str.h"
#include "async.h"
#include "resource.h"
#include "option.h"
#include "encode.h"
#include "block.h"
#include "net.h"

#if defined(WITH_POSIX)

time_t clock_offset;

static inline coap_queue_t *
coap_malloc_node() {
  return (coap_queue_t *)coap_malloc(sizeof(coap_queue_t));
}

static inline void
coap_free_node(coap_queue_t *node) {
  coap_free(node);
}
#endif /* WITH_POSIX */
#ifdef WITH_LWIP

#include <lwip/memp.h>

static void coap_retransmittimer_execute(void *arg);
static void coap_retransmittimer_restart(coap_context_t *ctx);

static inline coap_queue_t *
coap_malloc_node() {
    return (coap_queue_t *)memp_malloc(MEMP_COAP_NODE);
}

static inline void
coap_free_node(coap_queue_t *node) {
    memp_free(MEMP_COAP_NODE, node);
}

#endif /* WITH_LWIP */
#ifdef WITH_CONTIKI
# ifndef DEBUG
#  define DEBUG DEBUG_PRINT
# endif /* DEBUG */

#include "memb.h"
#include "net/uip-debug.h"

clock_time_t clock_offset;

#define UIP_IP_BUF   ((struct uip_ip_hdr *)&uip_buf[UIP_LLH_LEN])
#define UIP_UDP_BUF  ((struct uip_udp_hdr *)&uip_buf[UIP_LLIPH_LEN])

void coap_resources_init();
void coap_pdu_resources_init();

unsigned char initialized = 0;
coap_context_t the_coap_context;

MEMB(node_storage, coap_queue_t, COAP_PDU_MAXCNT);

PROCESS(coap_retransmit_process, "message retransmit process");

static inline coap_queue_t *
coap_malloc_node() {
  return (coap_queue_t *)memb_alloc(&node_storage);
}

static inline void
coap_free_node(coap_queue_t *node) {
  memb_free(&node_storage, node);
}
#endif /* WITH_CONTIKI */
#ifdef WITH_LWIP

static void received_package(void *arg, struct udp_pcb *upcb, struct pbuf *p, ip_addr_t *addr, u16_t port)
{
  struct coap_context_t *context = (coap_context_t *)arg;

  LWIP_ASSERT("pending_package was not cleared.", context->pending_package == NULL);

  context->pending_package = p; /* we don't free it, coap_read has to do that */
  context->pending_address.addr = addr->addr; /* FIXME: this has to become address-type independent, probably there'll be an lwip function for that */
  context->pending_port = port;

  coap_read(context);
}

#endif /* WITH_LWIP */

int print_wellknown(coap_context_t *, unsigned char *, size_t *, size_t, coap_opt_t *);

void coap_handle_failed_notify(coap_context_t *, const coap_address_t *, 
                   const str *);

unsigned int
coap_adjust_basetime(coap_context_t *ctx, coap_tick_t now) {
  unsigned int result = 0;
  coap_tick_diff_t delta = now - ctx->sendqueue_basetime;

  if (ctx->sendqueue) {
    /* delta < 0 means that the new time stamp is before the old. */
    if (delta <= 0) {
      ctx->sendqueue->t -= delta;
    } else {
      /* This case is more complex: The time must be advanced forward,
       * thus possibly leading to timed out elements at the queue's
       * start. For every element that has timed out, its relative
       * time is set to zero and the result counter is increased. */

      coap_queue_t *q = ctx->sendqueue;
      coap_tick_t t = 0;
      while (q && (t + q->t < (coap_tick_t)delta)) {
    t += q->t;
    q->t = 0;
    result++;
    q = q->next;
      }

      /* finally adjust the first element that has not expired */
      if (q) {
    q->t = (coap_tick_t)delta - t;
      }
    }
  }

  /* adjust basetime */
  ctx->sendqueue_basetime += delta;

  return result;
}

int
coap_insert_node(coap_queue_t **queue, coap_queue_t *node) {
  coap_queue_t *p, *q;
  if ( !queue || !node )
    return 0;

  /* set queue head if empty */
  if ( !*queue ) {
    *queue = node;
    return 1;
  }

  /* replace queue head if PDU's time is less than head's time */
  q = *queue;
  if (node->t < q->t) {
    node->next = q;
    *queue = node;
    q->t -= node->t;        /* make q->t relative to node->t */
    return 1;
  }

  /* search for right place to insert */
  do {
    node->t -= q->t;        /* make node-> relative to q->t */
    p = q;
    q = q->next;
  } while (q && q->t <= node->t);

  /* insert new item */
  if (q) {
    q->t -= node->t;        /* make q->t relative to node->t */
  }
  node->next = q;
  p->next = node;
  return 1;
}

int
coap_delete_node(coap_queue_t *node) {
  if ( !node )
    return 0;

  coap_delete_pdu(node->pdu);
  coap_free_node(node);

  return 1;
}

void
coap_delete_all(coap_queue_t *queue) {
  if ( !queue )
    return;

  coap_delete_all( queue->next );
  coap_delete_node( queue );
}

coap_queue_t *
coap_new_node() {
  coap_queue_t *node;
  node = coap_malloc_node();

  if ( ! node ) {
#ifndef NDEBUG
    coap_log(LOG_WARNING, "coap_new_node: malloc\n");
#endif
    return NULL;
  }

  memset(node, 0, sizeof *node );
  return node;
}

coap_queue_t *
coap_peek_next( coap_context_t *context ) {
  if ( !context || !context->sendqueue )
    return NULL;

  return context->sendqueue;
}

coap_queue_t *
coap_pop_next( coap_context_t *context ) {
  coap_queue_t *next;

  if ( !context || !context->sendqueue )
    return NULL;

  next = context->sendqueue;
  context->sendqueue = context->sendqueue->next;
  if (context->sendqueue) {
    context->sendqueue->t += next->t;
  }
  next->next = NULL;
  return next;
}

#ifdef COAP_DEFAULT_WKC_HASHKEY

#define is_wkc(Key)                         \
  (memcmp((Key), COAP_DEFAULT_WKC_HASHKEY, sizeof(coap_key_t)) == 0)
#else
/* Implements a singleton to store a hash key for the .wellknown/core
 * resources. */
int
is_wkc(coap_key_t k) {
  static coap_key_t wkc;
  static unsigned char _initialized = 0;
  if (!_initialized) {
    _initialized = coap_hash_path((unsigned char *)COAP_DEFAULT_URI_WELLKNOWN, 
                 sizeof(COAP_DEFAULT_URI_WELLKNOWN) - 1, wkc);
  }
  return memcmp(k, wkc, sizeof(coap_key_t)) == 0;
}
#endif

coap_context_t *
coap_new_context(
  const coap_address_t *listen_addr) {
#ifdef WITH_POSIX
  coap_context_t *c = coap_malloc( sizeof( coap_context_t ) );
  int reuse = 1;
#endif /* WITH_POSIX */
#ifdef WITH_LWIP
  coap_context_t *c = memp_malloc(MEMP_COAP_CONTEXT);
#endif /* WITH_LWIP */
#ifdef WITH_CONTIKI
  coap_context_t *c;

  if (initialized)
    return NULL;
#endif /* WITH_CONTIKI */

  if (!listen_addr) {
    coap_log(LOG_EMERG, "no listen address specified\n");
    return NULL;
  }

  coap_clock_init();
#ifdef WITH_LWIP
  prng_init(LWIP_RAND());
#else /* WITH_LWIP */
  prng_init((unsigned long)listen_addr ^ clock_offset);
#endif /* WITH_LWIP */

#ifndef WITH_CONTIKI
  if ( !c ) {
#ifndef NDEBUG
    coap_log(LOG_EMERG, "coap_init: malloc:\n");
#endif
    return NULL;
  }
#endif /* not WITH_CONTIKI */
#ifdef WITH_CONTIKI
  coap_resources_init();
  coap_pdu_resources_init();

  c = &the_coap_context;
  initialized = 1;
#endif /* WITH_CONTIKI */

  memset(c, 0, sizeof( coap_context_t ) );

  /* initialize message id */
  prng((unsigned char *)&c->message_id, sizeof(unsigned short));

  /* register the critical options that we know */
  coap_register_option(c, COAP_OPTION_IF_MATCH);
  coap_register_option(c, COAP_OPTION_URI_HOST);
  coap_register_option(c, COAP_OPTION_IF_NONE_MATCH);
  coap_register_option(c, COAP_OPTION_URI_PORT);
  coap_register_option(c, COAP_OPTION_URI_PATH);
  coap_register_option(c, COAP_OPTION_URI_QUERY);
  coap_register_option(c, COAP_OPTION_ACCEPT);
  coap_register_option(c, COAP_OPTION_PROXY_URI);
  coap_register_option(c, COAP_OPTION_PROXY_SCHEME);
  coap_register_option(c, COAP_OPTION_BLOCK2);
  coap_register_option(c, COAP_OPTION_BLOCK1);

#ifdef WITH_POSIX
  c->sockfd = socket(listen_addr->addr.sa.sa_family, SOCK_DGRAM, 0);
  if ( c->sockfd < 0 ) {
#ifndef NDEBUG
    coap_log(LOG_EMERG, "coap_new_context: socket\n");
#endif /* WITH_POSIX */
    goto onerror;
  }

  if ( setsockopt( c->sockfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse) ) < 0 ) {
#ifndef NDEBUG
    coap_log(LOG_WARNING, "setsockopt SO_REUSEADDR\n");
#endif
  }

  if (bind(c->sockfd, &listen_addr->addr.sa, listen_addr->size) < 0) {
#ifndef NDEBUG
    coap_log(LOG_EMERG, "coap_new_context: bind\n");
#endif
    goto onerror;
  }

  return c;

 onerror:
  if ( c->sockfd >= 0 )
    close ( c->sockfd );
  coap_free( c );
  return NULL;

#endif /* WITH_POSIX */
#ifdef WITH_CONTIKI
  c->conn = udp_new(NULL, 0, NULL);
  udp_bind(c->conn, listen_addr->port);
  
  process_start(&coap_retransmit_process, (char *)c);

  PROCESS_CONTEXT_BEGIN(&coap_retransmit_process);
#ifndef WITHOUT_OBSERVE
  etimer_set(&c->notify_timer, COAP_RESOURCE_CHECK_TIME * COAP_TICKS_PER_SECOND);
#endif /* WITHOUT_OBSERVE */
  /* the retransmit timer must be initialized to some large value */
  etimer_set(&the_coap_context.retransmit_timer, 0xFFFF);
  PROCESS_CONTEXT_END(&coap_retransmit_process);
  return c;
#endif /* WITH_CONTIKI */
#ifdef WITH_LWIP
  c->pcb = udp_new();
  /* hard assert: this is not expected to fail dynamically */
  LWIP_ASSERT("Failed to allocate PCB for CoAP", c->pcb != NULL);

  udp_recv(c->pcb, received_package, (void*)c);
  udp_bind(c->pcb, &listen_addr->addr, listen_addr->port);

  c->timer_configured = 0;

  return c;
#endif
}

void
coap_free_context( coap_context_t *context ) {
#if defined(WITH_POSIX) || defined(WITH_LWIP)
  coap_resource_t *res;
#ifndef COAP_RESOURCES_NOHASH
  coap_resource_t *rtmp;
#endif
#endif /* WITH_POSIX || WITH_LWIP */
  if ( !context )
    return;

  coap_delete_all(context->recvqueue);
  coap_delete_all(context->sendqueue);

#ifdef WITH_LWIP
  context->sendqueue = NULL;
  coap_retransmittimer_restart(context);
#endif

#if defined(WITH_POSIX) || defined(WITH_LWIP)
#ifdef COAP_RESOURCES_NOHASH
  LL_FOREACH(context->resources, res) {
#else
  HASH_ITER(hh, context->resources, res, rtmp) {
#endif
    coap_delete_resource(context, res->key);
  }
#endif /* WITH_POSIX || WITH_LWIP */

#ifdef WITH_POSIX
  /* coap_delete_list(context->subscriptions); */
  close( context->sockfd );
  coap_free( context );
#endif
#ifdef WITH_LWIP
  udp_remove(context->pcb);
  memp_free(MEMP_COAP_CONTEXT, context);
#endif
#ifdef WITH_CONTIKI
  memset(&the_coap_context, 0, sizeof(coap_context_t));
  initialized = 0;
#endif /* WITH_CONTIKI */
}

int
coap_option_check_critical(coap_context_t *ctx, 
               coap_pdu_t *pdu,
               coap_opt_filter_t unknown) {

  coap_opt_iterator_t opt_iter;
  int ok = 1;
  
  coap_option_iterator_init(pdu, &opt_iter, COAP_OPT_ALL);

  while (coap_option_next(&opt_iter)) {

    /* The following condition makes use of the fact that
     * coap_option_getb() returns -1 if type exceeds the bit-vector
     * filter. As the vector is supposed to be large enough to hold
     * the largest known option, we know that everything beyond is
     * bad.
     */
    if (opt_iter.type & 0x01 && 
    coap_option_getb(ctx->known_options, opt_iter.type) < 1) {
      debug("unknown critical option %d\n", opt_iter.type);
      
      ok = 0;

      /* When opt_iter.type is beyond our known option range,
       * coap_option_setb() will return -1 and we are safe to leave
       * this loop. */
      if (coap_option_setb(unknown, opt_iter.type) == -1)
    break;
    }
  }

  return ok;
}

void
coap_transaction_id(const coap_address_t *peer, const coap_pdu_t *pdu, 
            coap_tid_t *id) {
  coap_key_t h;

  memset(h, 0, sizeof(coap_key_t));

  /* Compare the complete address structure in case of IPv4. For IPv6,
   * we need to look at the transport address only. */

#ifdef WITH_POSIX
  switch (peer->addr.sa.sa_family) {
  case AF_INET:
    coap_hash((const unsigned char *)&peer->addr.sa, peer->size, h);
    break;
  case AF_INET6:
    coap_hash((const unsigned char *)&peer->addr.sin6.sin6_port,
          sizeof(peer->addr.sin6.sin6_port), h);
    coap_hash((const unsigned char *)&peer->addr.sin6.sin6_addr,
          sizeof(peer->addr.sin6.sin6_addr), h);
    break;
  default:
    return;
  }
#endif
#if defined(WITH_LWIP) || defined(WITH_CONTIKI)
    /* FIXME: with lwip, we can do better */
    coap_hash((const unsigned char *)&peer->port, sizeof(peer->port), h);
    coap_hash((const unsigned char *)&peer->addr, sizeof(peer->addr), h);  
#endif /* WITH_LWIP || WITH_CONTIKI */

  coap_hash((const unsigned char *)&pdu->hdr->id, sizeof(unsigned short), h);

  *id = ((h[0] << 8) | h[1]) ^ ((h[2] << 8) | h[3]);
}

coap_tid_t
coap_send_ack(coap_context_t *context, 
          const coap_address_t *dst,
          coap_pdu_t *request) {
  coap_pdu_t *response;
  coap_tid_t result = COAP_INVALID_TID;
  
  if (request && request->hdr->type == COAP_MESSAGE_CON) {
    response = coap_pdu_init(COAP_MESSAGE_ACK, 0, request->hdr->id, 
                 sizeof(coap_pdu_t)); 
    if (response) {
      result = coap_send(context, dst, response);
      coap_delete_pdu(response);
    }
  }
  return result;
}

#ifdef WITH_POSIX
/* releases space allocated by PDU if free_pdu is set */
coap_tid_t
coap_send_impl(coap_context_t *context, 
           const coap_address_t *dst,
           coap_pdu_t *pdu) {
  ssize_t bytes_written;
  coap_tid_t id = COAP_INVALID_TID;

  if ( !context || !dst || !pdu )
    return id;

  bytes_written = sendto( context->sockfd, pdu->hdr, pdu->length, 0,
              &dst->addr.sa, dst->size);

  if (bytes_written >= 0) {
    coap_transaction_id(dst, pdu, &id);
  } else {
    coap_log(LOG_CRIT, "coap_send: sendto\n");
  }

  return id;
}
#endif /* WITH_POSIX */
#ifdef WITH_CONTIKI
/* releases space allocated by PDU if free_pdu is set */
coap_tid_t
coap_send_impl(coap_context_t *context, 
           const coap_address_t *dst,
           coap_pdu_t *pdu) {
  coap_tid_t id = COAP_INVALID_TID;

  if ( !context || !dst || !pdu )
    return id;

  /* FIXME: is there a way to check if send was successful? */
  uip_udp_packet_sendto(context->conn, pdu->hdr, pdu->length,
            &dst->addr, dst->port);

  coap_transaction_id(dst, pdu, &id);

  return id;
}
#endif /* WITH_CONTIKI */
#ifdef WITH_LWIP
coap_tid_t
coap_send_impl(coap_context_t *context,
           const coap_address_t *dst,
           coap_pdu_t *pdu) {
  coap_tid_t id = COAP_INVALID_TID;
  struct pbuf *p;
  uint8_t err;
  char *data_backup;

  if ( !context || !dst || !pdu )
  {
    return id;
  }

  data_backup = pdu->data;

  /* FIXME: we can't check this here with the existing infrastructure, but we
   * should actually check that the pdu is not held by anyone but us. the
   * respective pbuf is already exclusively owned by the pdu. */

  p = pdu->pbuf;
  LWIP_ASSERT("The PDU header is not where it is expected", pdu->hdr == p->payload + sizeof(coap_pdu_t));

  err = pbuf_header(p, -sizeof(coap_pdu_t));
  if (err)
  {
    debug("coap_send_impl: pbuf_header failed\n");
    pbuf_free(p);
    return id;
  }

  coap_transaction_id(dst, pdu, &id);

  pbuf_realloc(p, pdu->length);

  udp_sendto(context->pcb, p,
            &dst->addr, dst->port);

  pbuf_header(p, -(ptrdiff_t)((uint8_t*)pdu - (uint8_t*)p->payload) - sizeof(coap_pdu_t)); /* FIXME hack around udp_sendto not restoring; see http://lists.gnu.org/archive/html/lwip-users/2013-06/msg00008.html. for udp over ip over ethernet, this was -42; as we're doing ppp too, this has to be calculated generically */

  err = pbuf_header(p, sizeof(coap_pdu_t));
  LWIP_ASSERT("Cannot undo pbuf_header", err == 0);

  /* restore destroyed pdu data */
  LWIP_ASSERT("PDU not restored", p->payload == pdu);
  pdu->max_size = p->tot_len - sizeof(coap_pdu_t); /* reduced after pbuf_realloc */
  pdu->hdr = p->payload + sizeof(coap_pdu_t);
  pdu->max_delta = 0; /* won't be used any more */
  pdu->length = pdu->max_size;
  pdu->data = data_backup;
  pdu->pbuf = p;

  return id;
}
#endif /* WITH_LWIP */

coap_tid_t 
coap_send(coap_context_t *context, 
      const coap_address_t *dst, 
      coap_pdu_t *pdu) {
  return coap_send_impl(context, dst, pdu);
}

coap_tid_t
coap_send_error(coap_context_t *context, 
        coap_pdu_t *request,
        const coap_address_t *dst,
        unsigned char code,
        coap_opt_filter_t opts) {
  coap_pdu_t *response;
  coap_tid_t result = COAP_INVALID_TID;

  assert(request);
  assert(dst);

  response = coap_new_error_response(request, code, opts);
  if (response) {
    result = coap_send(context, dst, response);
    coap_delete_pdu(response);
  }
  
  return result;
}

coap_tid_t
coap_send_message_type(coap_context_t *context, 
               const coap_address_t *dst, 
               coap_pdu_t *request,
               unsigned char type) {
  coap_pdu_t *response;
  coap_tid_t result = COAP_INVALID_TID;

  if (request) {
    response = coap_pdu_init(type, 0, request->hdr->id, sizeof(coap_pdu_t)); 
    if (response) {
      result = coap_send(context, dst, response);
      coap_delete_pdu(response);
    }
  }
  return result;
}

coap_tid_t
coap_send_confirmed(coap_context_t *context, 
            const coap_address_t *dst,
            coap_pdu_t *pdu) {
  coap_queue_t *node;
  coap_tick_t now;
  int r;

  node = coap_new_node();
  if (!node) {
    debug("coap_send_confirmed: insufficient memory\n");
    return COAP_INVALID_TID;
  }

  node->id = coap_send_impl(context, dst, pdu);
  if (COAP_INVALID_TID == node->id) {
    debug("coap_send_confirmed: error sending pdu\n");
    coap_free_node(node);
    return COAP_INVALID_TID;
  }
  
  prng((unsigned char *)&r,sizeof(r));

  /* add randomized RESPONSE_TIMEOUT to determine retransmission timeout */
  node->timeout = COAP_DEFAULT_RESPONSE_TIMEOUT * COAP_TICKS_PER_SECOND +
    (COAP_DEFAULT_RESPONSE_TIMEOUT >> 1) *
    ((COAP_TICKS_PER_SECOND * (r & 0xFF)) >> 8);

  memcpy(&node->remote, dst, sizeof(coap_address_t));
  node->pdu = pdu;

  /* Set timer for pdu retransmission. If this is the first element in
   * the retransmission queue, the base time is set to the current
   * time and the retransmission time is node->timeout. If there is
   * already an entry in the sendqueue, we must check if this node is
   * to be retransmitted earlier. Therefore, node->timeout is first
   * normalized to the base time and then inserted into the queue with
   * an adjusted relative time.
   */
  coap_ticks(&now);
  if (context->sendqueue == NULL) {
    node->t = node->timeout;
    context->sendqueue_basetime = now;
  } else {
    /* make node->t relative to context->sendqueue_basetime */
    node->t = (now - context->sendqueue_basetime) + node->timeout;
  }

  coap_insert_node(&context->sendqueue, node);

#ifdef WITH_LWIP
  if (node == context->sendqueue) /* don't bother with timer stuff if there are earlier retransmits */
    coap_retransmittimer_restart(context);
#endif

#ifdef WITH_CONTIKI
  {             /* (re-)initialize retransmission timer */
    coap_queue_t *nextpdu;

    nextpdu = coap_peek_next(context);
    assert(nextpdu);        /* we have just inserted a node */

    /* must set timer within the context of the retransmit process */
    PROCESS_CONTEXT_BEGIN(&coap_retransmit_process);
    etimer_set(&context->retransmit_timer, nextpdu->t);
    PROCESS_CONTEXT_END(&coap_retransmit_process);
  }
#endif /* WITH_CONTIKI */

  return node->id;
}

coap_tid_t
coap_retransmit( coap_context_t *context, coap_queue_t *node ) {
  if ( !context || !node )
    return COAP_INVALID_TID;

  /* re-initialize timeout when maximum number of retransmissions are not reached yet */
  if ( node->retransmit_cnt < COAP_DEFAULT_MAX_RETRANSMIT ) {
    node->retransmit_cnt++;
    node->t = node->timeout << node->retransmit_cnt;
    coap_insert_node(&context->sendqueue, node);
#ifdef WITH_LWIP
    if (node == context->sendqueue) /* don't bother with timer stuff if there are earlier retransmits */
      coap_retransmittimer_restart(context);
#endif

    debug("** retransmission #%d of transaction %d\n",
      node->retransmit_cnt, ntohs(node->pdu->hdr->id));

    node->id = coap_send_impl(context, &node->remote, node->pdu);
    return node->id;
  }

  /* no more retransmissions, remove node from system */

#ifndef WITH_CONTIKI
  debug("** removed transaction %d\n", ntohs(node->id));
#endif

#ifndef WITHOUT_OBSERVE
  /* Check if subscriptions exist that should be canceled after
     COAP_MAX_NOTIFY_FAILURES */
  if (node->pdu->hdr->code >= 64) {
    str token = { 0, NULL };

    token.length = node->pdu->hdr->token_length;
    token.s = node->pdu->hdr->token;

    coap_handle_failed_notify(context, &node->remote, &token);
  }
#endif /* WITHOUT_OBSERVE */

  /* And finally delete the node */
  coap_delete_node( node );
  return COAP_INVALID_TID;
}

static inline int
check_opt_size(coap_opt_t *opt, unsigned char *maxpos) {
  if (opt && opt < maxpos) {
    if (((*opt & 0x0f) < 0x0f) || (opt + 1 < maxpos))
      return opt + COAP_OPT_SIZE(opt) < maxpos;
  }
  return 0;
}

int
coap_read( coap_context_t *ctx ) {
#ifdef WITH_POSIX
  static char buf[COAP_MAX_PDU_SIZE];
#endif
#if defined(WITH_LWIP) || defined(WITH_CONTIKI)
  char *buf;
#endif
  coap_hdr_t *pdu;
  ssize_t bytes_read = -1;
  coap_address_t src, dst;
  coap_queue_t *node;

#ifdef WITH_CONTIKI
  buf = uip_appdata;
#endif /* WITH_CONTIKI */
#ifdef WITH_LWIP
  LWIP_ASSERT("No package pending", ctx->pending_package != NULL);
  LWIP_ASSERT("Can only deal with contiguous PBUFs to read the initial details", ctx->pending_package->tot_len == ctx->pending_package->len);
  buf = ctx->pending_package->payload;
#endif /* WITH_LWIP */

  pdu = (coap_hdr_t *)buf;

  coap_address_init(&src);

#ifdef WITH_POSIX
  bytes_read = recvfrom(ctx->sockfd, buf, sizeof(buf), 0,
            &src.addr.sa, &src.size);
#endif /* WITH_POSIX */
#ifdef WITH_CONTIKI
  if(uip_newdata()) {
    uip_ipaddr_copy(&src.addr, &UIP_IP_BUF->srcipaddr);
    src.port = UIP_UDP_BUF->srcport;
    uip_ipaddr_copy(&dst.addr, &UIP_IP_BUF->destipaddr);
    dst.port = UIP_UDP_BUF->destport;

    bytes_read = uip_datalen();
    ((char *)uip_appdata)[bytes_read] = 0;
    PRINTF("Server received %d bytes from [", (int)bytes_read);
    PRINT6ADDR(&src.addr);
    PRINTF("]:%d\n", uip_ntohs(src.port));
  } 
#endif /* WITH_CONTIKI */
#ifdef WITH_LWIP
  /* FIXME: use lwip address operation functions */
  src.addr.addr = ctx->pending_address.addr;
  src.port = ctx->pending_port;
  bytes_read = ctx->pending_package->tot_len;
#endif /* WITH_LWIP */

  if ( bytes_read < 0 ) {
    warn("coap_read: recvfrom");
    goto error_early;
  }

  if ( (size_t)bytes_read < sizeof(coap_hdr_t) ) {
    debug("coap_read: discarded invalid frame\n" );
    goto error_early;
  }

  if ( pdu->version != COAP_DEFAULT_VERSION ) {
    debug("coap_read: unknown protocol version\n" );
    goto error_early;
  }

  node = coap_new_node();
  if ( !node )
    goto error_early;

#ifdef WITH_LWIP
  node->pdu = coap_pdu_from_pbuf(ctx->pending_package);
  ctx->pending_package = NULL;
#else
  node->pdu = coap_pdu_init(0, 0, 0, bytes_read);
#endif
  if (!node->pdu)
    goto error;

  coap_ticks( &node->t );
  memcpy(&node->local, &dst, sizeof(coap_address_t));
  memcpy(&node->remote, &src, sizeof(coap_address_t));

if (!coap_pdu_parse((unsigned char *)buf, bytes_read, node->pdu)) {
    warn("discard malformed PDU");
    goto error;
  }

  /* and add new node to receive queue */
  coap_transaction_id(&node->remote, node->pdu, &node->id);
  coap_insert_node(&ctx->recvqueue, node);

#ifndef NDEBUG
  if (LOG_DEBUG <= coap_get_log_level()) {
#ifndef INET6_ADDRSTRLEN
#define INET6_ADDRSTRLEN 40
#endif
    unsigned char addr[INET6_ADDRSTRLEN+8];

    if (coap_print_addr(&src, addr, INET6_ADDRSTRLEN+8))
      debug("** received %d bytes from %s:\n", (int)bytes_read, addr);

    coap_show_pdu( node->pdu );
  }
#endif

  return 0;

 error:
  /* FIXME: send back RST? */
  coap_delete_node(node);
  return -1;
 error_early:
#ifdef WITH_LWIP
  /* even if there was an error, clean up */
  pbuf_free(ctx->pending_package);
  ctx->pending_package = NULL;
#endif
  return -1;
}

int
coap_remove_from_queue(coap_queue_t **queue, coap_tid_t id, coap_queue_t **node) {
  coap_queue_t *p, *q;

  if ( !queue || !*queue)
    return 0;

  /* replace queue head if PDU's time is less than head's time */

  if ( id == (*queue)->id ) { /* found transaction */
    *node = *queue;
    *queue = (*queue)->next;
    if (*queue) {     /* adjust relative time of new queue head */
      (*queue)->t += (*node)->t;
    }
    (*node)->next = NULL;
    /* coap_delete_node( q ); */
    debug("*** removed transaction %u\n", id);
    return 1;
  }

  /* search transaction to remove (only first occurence will be removed) */
  q = *queue;
  do {
    p = q;
    q = q->next;
  } while ( q && id != q->id );

  if ( q ) {            /* found transaction */
    p->next = q->next;
    if (p->next) {      /* must update relative time of p->next */
      p->next->t += q->t;
    }
    q->next = NULL;
    *node = q;
    /* coap_delete_node( q ); */
    debug("*** removed transaction %u\n", id);
    return 1;
  }

  return 0;

}

static inline int
token_match(const unsigned char *a, size_t alen, 
        const unsigned char *b, size_t blen) {
  return alen == blen && (alen == 0 || memcmp(a, b, alen) == 0);
}

void
coap_cancel_all_messages(coap_context_t *context, const coap_address_t *dst,
             const unsigned char *token, size_t token_length) {
  /* cancel all messages in sendqueue that are for dst 
   * and use the specified token */
  coap_queue_t *p, *q;
  
  debug("cancel_all_messages\n");
  while (context->sendqueue && 
     coap_address_equals(dst, &context->sendqueue->remote) &&
     token_match(token, token_length, 
             context->sendqueue->pdu->hdr->token, 
             context->sendqueue->pdu->hdr->token_length)) {
    q = context->sendqueue; 
    context->sendqueue = q->next;
    debug("**** removed transaction %d\n", ntohs(q->pdu->hdr->id));
    coap_delete_node(q);
  }

  if (!context->sendqueue)
    return;

  p = context->sendqueue;
  q = p->next;
  
  /* when q is not NULL, it does not match (dst, token), so we can skip it */
  while (q) {
    if (coap_address_equals(dst, &q->remote) &&
    token_match(token, token_length,
            q->pdu->hdr->token, q->pdu->hdr->token_length)) {
      p->next = q->next;
      debug("**** removed transaction %d\n", ntohs(q->pdu->hdr->id));
      coap_delete_node(q);
      q = p->next;
    } else {
      p = q;
      q = q->next;
    }
  }
}

coap_queue_t *
coap_find_transaction(coap_queue_t *queue, coap_tid_t id) {
  while (queue && queue->id != id)
    queue = queue->next;

  return queue;
}

coap_pdu_t *
coap_new_error_response(coap_pdu_t *request, unsigned char code, 
            coap_opt_filter_t opts) {
  coap_opt_iterator_t opt_iter;
  coap_pdu_t *response;
  size_t size = sizeof(coap_hdr_t) + request->hdr->token_length;
  int type; 
  coap_opt_t *option;
  unsigned short opt_type = 0;  /* used for calculating delta-storage */

#if COAP_ERROR_PHRASE_LENGTH > 0
  char *phrase = coap_response_phrase(code);

  /* Need some more space for the error phrase and payload start marker */
  if (phrase)
    size += strlen(phrase) + 1;
#endif

  assert(request);

  /* cannot send ACK if original request was not confirmable */
  type = request->hdr->type == COAP_MESSAGE_CON 
    ? COAP_MESSAGE_ACK
    : COAP_MESSAGE_NON;

  /* Estimate how much space we need for options to copy from
   * request. We always need the Token, for 4.02 the unknown critical
   * options must be included as well. */
  coap_option_clrb(opts, COAP_OPTION_CONTENT_TYPE); /* we do not want this */

  coap_option_iterator_init(request, &opt_iter, opts);

  /* Add size of each unknown critical option. As known critical
     options as well as elective options are not copied, the delta
     value might grow.
   */
  while((option = coap_option_next(&opt_iter))) {
    unsigned short delta = opt_iter.type - opt_type;
    /* calculate space required to encode (opt_iter.type - opt_type) */
    if (delta < 13) {
      size++;
    } else if (delta < 269) {
      size += 2;
    } else {
      size += 3;
    }

    /* add coap_opt_length(option) and the number of additional bytes
     * required to encode the option length */
    
    size += coap_opt_length(option);
    switch (*option & 0x0f) {
    case 0x0e:
      size++;
      /* fall through */
    case 0x0d:
      size++;
      break;
    default:
      ;
    }

    opt_type = opt_iter.type;
  }

  /* Now create the response and fill with options and payload data. */
  response = coap_pdu_init(type, code, request->hdr->id, size);
  if (response) {
    /* copy token */
    if (!coap_add_token(response, request->hdr->token_length, 
            request->hdr->token)) {
      debug("cannot add token to error response\n");
      coap_delete_pdu(response);
      return NULL;
    }

    /* copy all options */
    coap_option_iterator_init(request, &opt_iter, opts);
    while((option = coap_option_next(&opt_iter)))
      coap_add_option(response, opt_iter.type, 
              COAP_OPT_LENGTH(option),
              COAP_OPT_VALUE(option));

#if COAP_ERROR_PHRASE_LENGTH > 0
    /* note that diagnostic messages do not need a Content-Format option. */
    if (phrase)
      coap_add_data(response, strlen(phrase), (unsigned char *)phrase);
#endif
  }

  return response;
}

static inline size_t
get_wkc_len(coap_context_t *context, coap_opt_t *query_filter) {
  unsigned char buf[1];
  size_t len = 0;

  if (print_wellknown(context, buf, &len, UINT_MAX, query_filter)
      & COAP_PRINT_STATUS_ERROR) {
    warn("cannot determine length of /.well-known/core\n");
    return 0;
  }

  debug("get_wkc_len: print_wellknown() returned %zu\n", len);

  return len;
}

#define SZX_TO_BYTES(SZX) ((size_t)(1 << ((SZX) + 4)))

coap_pdu_t *
wellknown_response(coap_context_t *context, coap_pdu_t *request) {
  coap_pdu_t *resp;
  coap_opt_iterator_t opt_iter;
  size_t len, wkc_len;
  unsigned char buf[2];
  int result = 0;
  int need_block2 = 0;     /* set to 1 if Block2 option is required */
  coap_block_t block;
  coap_opt_t *query_filter;
  size_t offset = 0;

  resp = coap_pdu_init(request->hdr->type == COAP_MESSAGE_CON 
               ? COAP_MESSAGE_ACK 
               : COAP_MESSAGE_NON,
               COAP_RESPONSE_CODE(205),
               request->hdr->id, COAP_MAX_PDU_SIZE);
  if (!resp) {
    debug("wellknown_response: cannot create PDU\n");
    return NULL;
  }
  
  if (!coap_add_token(resp, request->hdr->token_length, request->hdr->token)) {
    debug("wellknown_response: cannot add token\n");
    goto error;
  }

  query_filter = coap_check_option(request, COAP_OPTION_URI_QUERY, &opt_iter);
  wkc_len = get_wkc_len(context, query_filter);

  /* check whether the request contains the Block2 option */
  if (coap_get_block(request, COAP_OPTION_BLOCK2, &block)) {
    offset = block.num << (block.szx + 4);
    if (block.szx > 6) {  /* invalid, MUST lead to 4.00 Bad Request */
      resp->hdr->code = COAP_RESPONSE_CODE(400);
      return resp;
    } else if (block.szx > COAP_MAX_BLOCK_SZX) {
      block.szx = COAP_MAX_BLOCK_SZX;
      block.num = offset >> (block.szx + 4);
    }

    need_block2 = 1;
  }

  /* Check if there is sufficient space to add Content-Format option 
   * and data. We do this before adding the Content-Format option to
   * avoid sending error responses with that option but no actual
   * content. */
  if (resp->max_size <= (size_t)resp->length + 3) {
    debug("wellknown_response: insufficient storage space\n");
    goto error;
  }

  /* Add Content-Format. As we have checked for available storage,
   * nothing should go wrong here. */
  assert(coap_encode_var_bytes(buf, 
            COAP_MEDIATYPE_APPLICATION_LINK_FORMAT) == 1);
  coap_add_option(resp, COAP_OPTION_CONTENT_FORMAT,
          coap_encode_var_bytes(buf, 
            COAP_MEDIATYPE_APPLICATION_LINK_FORMAT), buf);

  /* check if Block2 option is required even if not requested */
  if (!need_block2 && (resp->max_size - (size_t)resp->length < wkc_len)) {
    assert(resp->length <= resp->max_size);
    const size_t payloadlen = resp->max_size - resp->length;
    /* yes, need block-wise transfer */
    block.num = 0;
    block.m = 0;      /* the M bit is set by coap_write_block_opt() */
    block.szx = COAP_MAX_BLOCK_SZX;
    while (payloadlen < SZX_TO_BYTES(block.szx)) {
      if (block.szx == 0) {
    debug("wellknown_response: message to small even for szx == 0\n");
    goto error;
      } else {
    block.szx--;
      }
    }

    need_block2 = 1;
  }

  /* write Block2 option if necessary */
  if (need_block2) {
    if (coap_write_block_opt(&block, COAP_OPTION_BLOCK2, resp, wkc_len) < 0) {
      debug("wellknown_response: cannot add Block2 option\n");
      goto error;
    }
  }

  /* Manually set payload of response to let print_wellknown() write,
   * into our buffer without copying data. */

  resp->data = (unsigned char *)resp->hdr + resp->length;
  *resp->data = COAP_PAYLOAD_START;
  resp->data++;
  resp->length++;
  len = need_block2 ? SZX_TO_BYTES(block.szx) : resp->max_size - resp->length;

  result = print_wellknown(context, resp->data, &len, offset, query_filter);
  if ((result & COAP_PRINT_STATUS_ERROR) != 0) {
    debug("print_wellknown failed\n");
    goto error;
  } 
  
  resp->length += COAP_PRINT_OUTPUT_LENGTH(result);
  return resp;

 error:
  /* set error code 5.03 and remove all options and data from response */
  resp->hdr->code = COAP_RESPONSE_CODE(503);
  resp->length = sizeof(coap_hdr_t) + resp->hdr->token_length;
  return resp;
}

#define WANT_WKC(Pdu,Key)                   \
  (((Pdu)->hdr->code == COAP_REQUEST_GET) && is_wkc(Key))

void
handle_request(coap_context_t *context, coap_queue_t *node) {      
  coap_method_handler_t h = NULL;
  coap_pdu_t *response = NULL;
  coap_opt_filter_t opt_filter;
  coap_resource_t *resource;
  coap_key_t key;

  coap_option_filter_clear(opt_filter);
  
  /* try to find the resource from the request URI */
  coap_hash_request_uri(node->pdu, key);
  resource = coap_get_resource_from_key(context, key);
  
  if (!resource) {
    /* The resource was not found. Check if the request URI happens to
     * be the well-known URI. In that case, we generate a default
     * response, otherwise, we return 4.04 */

    switch(node->pdu->hdr->code) {

    case COAP_REQUEST_GET: 
      if (is_wkc(key)) {    /* GET request for .well-known/core */
    info("create default response for %s\n", COAP_DEFAULT_URI_WELLKNOWN);
    response = wellknown_response(context, node->pdu);

      } else { /* GET request for any another resource, return 4.04 */

    debug("GET for unknown resource 0x%02x%02x%02x%02x, return 4.04\n", 
          key[0], key[1], key[2], key[3]);
    response = 
      coap_new_error_response(node->pdu, COAP_RESPONSE_CODE(404), 
                  opt_filter);
      }
      break;

    default:            /* any other request type */

      debug("unhandled request for unknown resource 0x%02x%02x%02x%02x\r\n",
        key[0], key[1], key[2], key[3]);
      if (!coap_is_mcast(&node->local))
    response = coap_new_error_response(node->pdu, COAP_RESPONSE_CODE(405), 
                       opt_filter);
    }
      
    if (response && coap_send(context, &node->remote, response) == COAP_INVALID_TID) {
      warn("cannot send response for transaction %u\n", node->id);
    }
    coap_delete_pdu(response);

    return;
  }
  
  /* the resource was found, check if there is a registered handler */
  if ((size_t)node->pdu->hdr->code - 1 <
      sizeof(resource->handler)/sizeof(coap_method_handler_t))
    h = resource->handler[node->pdu->hdr->code - 1];
  
  if (h) {
    debug("call custom handler for resource 0x%02x%02x%02x%02x\n", 
      key[0], key[1], key[2], key[3]);
    response = coap_pdu_init(node->pdu->hdr->type == COAP_MESSAGE_CON 
                 ? COAP_MESSAGE_ACK
                 : COAP_MESSAGE_NON,
                 0, node->pdu->hdr->id, COAP_MAX_PDU_SIZE);
    
    /* Implementation detail: coap_add_token() immediately returns 0
       if response == NULL */
    if (coap_add_token(response, node->pdu->hdr->token_length,
               node->pdu->hdr->token)) {
      str token = { node->pdu->hdr->token_length, node->pdu->hdr->token };

      h(context, resource, &node->remote, 
    node->pdu, &token, response);
      if (response->hdr->type != COAP_MESSAGE_NON ||
      (response->hdr->code >= 64 
       && !coap_is_mcast(&node->local))) {
    if (coap_send(context, &node->remote, response) == COAP_INVALID_TID) {
      debug("cannot send response for message %d\n", node->pdu->hdr->id);
      }
      }

      coap_delete_pdu(response);
    } else {
      warn("cannot generate response\r\n");
    }
  } else {
    if (WANT_WKC(node->pdu, key)) {
      debug("create default response for %s\n", COAP_DEFAULT_URI_WELLKNOWN);
      response = wellknown_response(context, node->pdu);
    } else
      response = coap_new_error_response(node->pdu, COAP_RESPONSE_CODE(405), 
                     opt_filter);
    
    if (!response || (coap_send(context, &node->remote, response)
              == COAP_INVALID_TID)) {
      debug("cannot send response for transaction %u\n", node->id);
    }
    coap_delete_pdu(response);
  }  
}

static inline void
handle_response(coap_context_t *context, 
        coap_queue_t *sent, coap_queue_t *rcvd) {
  
  /* Call application-specific reponse handler when available.  If
   * not, we must acknowledge confirmable messages. */
  if (context->response_handler) {
    context->response_handler(context, 
                  &rcvd->remote, sent ? sent->pdu : NULL, 
                  rcvd->pdu, rcvd->id);
  } else {
    /* send ACK if rcvd is confirmable (i.e. a separate response) */
    coap_send_ack(context, &rcvd->remote, rcvd->pdu);
  }
}

static inline int
#ifdef __GNUC__
handle_locally(coap_context_t *context __attribute__ ((unused)), 
           coap_queue_t *node __attribute__ ((unused))) {
#else /* not a GCC */
handle_locally(coap_context_t *context, coap_queue_t *node) {
#endif /* GCC */
  /* this function can be used to check if node->pdu is really for us */
  return 1;
}

static void
coap_handle_rst(coap_context_t *context, const coap_queue_t *sent) {
#ifndef WITHOUT_OBSERVE
  coap_resource_t *r;
#ifndef COAP_RESOURCES_NOHASH
  coap_resource_t *tmp;
#endif
  str token = { 0, NULL };

  /* remove observer for this resource, if any 
   * get token from sent and try to find a matching resource. Uh!
   */

  COAP_SET_STR(&token, sent->pdu->hdr->token_length, sent->pdu->hdr->token);

#ifndef WITH_CONTIKI
#ifdef COAP_RESOURCES_NOHASH
  LL_FOREACH(context->resources, r) {
#else
  HASH_ITER(hh, context->resources, r, tmp) {
#endif
    coap_delete_observer(r, &sent->remote, &token);
    coap_cancel_all_messages(context, &sent->remote, token.s, token.length);
  }
#else /* WITH_CONTIKI */
  r = (coap_resource_t *)resource_storage.mem;
  for (i = 0; i < resource_storage.num; ++i, ++r) {
    if (resource_storage.count[i]) {
      coap_delete_observer(r, &sent->remote, &token);
      coap_cancel_all_messages(context, &sent->remote, token.s, token.length);
    }
  }
#endif /* WITH_CONTIKI */
#endif /* WITOUT_OBSERVE */  
}

void
coap_dispatch( coap_context_t *context ) {
  coap_queue_t *rcvd = NULL, *sent = NULL;
  coap_pdu_t *response;
  coap_opt_filter_t opt_filter;

  if (!context)
    return;

  memset(opt_filter, 0, sizeof(coap_opt_filter_t));

  while ( context->recvqueue ) {
    rcvd = context->recvqueue;

    /* remove node from recvqueue */
    context->recvqueue = context->recvqueue->next;
    rcvd->next = NULL;

    if ( rcvd->pdu->hdr->version != COAP_DEFAULT_VERSION ) {
      debug("dropped packet with unknown version %u\n", rcvd->pdu->hdr->version);
      goto cleanup;
    }
    
    switch ( rcvd->pdu->hdr->type ) {
    case COAP_MESSAGE_ACK:
      /* find transaction in sendqueue to stop retransmission */
      coap_remove_from_queue(&context->sendqueue, rcvd->id, &sent);

      if (rcvd->pdu->hdr->code == 0)
    goto cleanup;

      /* FIXME: if sent code was >= 64 the message might have been a 
       * notification. Then, we must flag the observer to be alive
       * by setting obs->fail_cnt = 0. */
      if (sent && COAP_RESPONSE_CLASS(sent->pdu->hdr->code) == 2) {
    const str token = 
      { sent->pdu->hdr->token_length, sent->pdu->hdr->token };
    coap_touch_observer(context, &sent->remote, &token);
      }
      break;

    case COAP_MESSAGE_RST :
      /* We have sent something the receiver disliked, so we remove
       * not only the transaction but also the subscriptions we might
       * have. */

      coap_log(LOG_ALERT, "got RST for message %u\n", ntohs(rcvd->pdu->hdr->id));

      /* find transaction in sendqueue to stop retransmission */
      coap_remove_from_queue(&context->sendqueue, rcvd->id, &sent);

      if (sent)
    coap_handle_rst(context, sent);
      goto cleanup;

    case COAP_MESSAGE_NON : /* check for unknown critical options */
      if (coap_option_check_critical(context, rcvd->pdu, opt_filter) == 0)
    goto cleanup;
      break;

    case COAP_MESSAGE_CON : /* check for unknown critical options */
      if (coap_option_check_critical(context, rcvd->pdu, opt_filter) == 0) {

    /* FIXME: send response only if we have received a request. Otherwise, 
     * send RST. */
    response = 
      coap_new_error_response(rcvd->pdu, COAP_RESPONSE_CODE(402), opt_filter);

    if (!response)
      warn("coap_dispatch: cannot create error reponse\n");
    else {
      if (coap_send(context, &rcvd->remote, response) 
          == COAP_INVALID_TID) {
        warn("coap_dispatch: error sending reponse\n");
      }
          coap_delete_pdu(response);
    }    
    
    goto cleanup;
      }
      break;
    }
   
    /* Pass message to upper layer if a specific handler was
     * registered for a request that should be handled locally. */
    if (handle_locally(context, rcvd)) {
      if (COAP_MESSAGE_IS_REQUEST(rcvd->pdu->hdr))
    handle_request(context, rcvd);
      else if (COAP_MESSAGE_IS_RESPONSE(rcvd->pdu->hdr))
    handle_response(context, sent, rcvd);
      else {
    debug("dropped message with invalid code\n");
    coap_send_message_type(context, &rcvd->remote, rcvd->pdu, 
                 COAP_MESSAGE_RST);
      }
    }
    
  cleanup:
    coap_delete_node(sent);
    coap_delete_node(rcvd);
  }
}

int
coap_can_exit( coap_context_t *context ) {
  return !context || (context->recvqueue == NULL && context->sendqueue == NULL);
}

#ifdef WITH_CONTIKI

/*---------------------------------------------------------------------------*/
/* CoAP message retransmission */
/*---------------------------------------------------------------------------*/
PROCESS_THREAD(coap_retransmit_process, ev, data)
{
  coap_tick_t now;
  coap_queue_t *nextpdu;

  PROCESS_BEGIN();

  debug("Started retransmit process\r\n");

  while(1) {
    PROCESS_YIELD();
    if (ev == PROCESS_EVENT_TIMER) {
      if (etimer_expired(&the_coap_context.retransmit_timer)) {
    
    nextpdu = coap_peek_next(&the_coap_context);
    
    coap_ticks(&now);
    while (nextpdu && nextpdu->t <= now) {
      coap_retransmit(&the_coap_context, coap_pop_next(&the_coap_context));
      nextpdu = coap_peek_next(&the_coap_context);
    }

    /* need to set timer to some value even if no nextpdu is available */
    etimer_set(&the_coap_context.retransmit_timer, 
           nextpdu ? nextpdu->t - now : 0xFFFF);
      } 
#ifndef WITHOUT_OBSERVE
      if (etimer_expired(&the_coap_context.notify_timer)) {
    coap_check_notify(&the_coap_context);
    etimer_reset(&the_coap_context.notify_timer);
      }
#endif /* WITHOUT_OBSERVE */
    }
  }
  
  PROCESS_END();
}
/*---------------------------------------------------------------------------*/

#endif /* WITH_CONTIKI */

#ifdef WITH_LWIP
/* FIXME: retransmits that are not required any more due to incoming packages
 * do *not* get cleared at the moment, the wakeup when the transmission is due
 * is silently accepted. this is mainly due to the fact that the required
 * checks are similar in two places in the code (when receiving ACK and RST)
 * and that they cause more than one patch chunk, as it must be first checked
 * whether the sendqueue item to be dropped is the next one pending, and later
 * the restart function has to be called. nothing insurmountable, but it can
 * also be implemented when things have stabilized, and the performance
 * penality is minimal
 *
 * also, this completely ignores COAP_RESOURCE_CHECK_TIME.
 * */

static void coap_retransmittimer_execute(void *arg)
{
    coap_context_t *ctx = (coap_context_t*)arg;
    coap_tick_t now;
    coap_tick_t elapsed;
    coap_queue_t *nextinqueue;

    ctx->timer_configured = 0;

    coap_ticks(&now);

    elapsed = now - ctx->sendqueue_basetime; /* that's positive for sure, and unless we haven't been called for a complete wrapping cycle, did not wrap */

    nextinqueue = coap_peek_next(ctx);
    while (nextinqueue != NULL)
    {
        if (nextinqueue->t > elapsed) {
            nextinqueue->t -= elapsed;
            break;
        } else {
            elapsed -= nextinqueue->t;
            coap_retransmit(ctx, coap_pop_next(ctx));
            nextinqueue = coap_peek_next(ctx);
        }
    }

    ctx->sendqueue_basetime = now;

    coap_retransmittimer_restart(ctx);
}

static void coap_retransmittimer_restart(coap_context_t *ctx)
{
    coap_tick_t now, elapsed, delay;

    if (ctx->timer_configured)
    {
        printf("clearing\n");
        sys_untimeout(coap_retransmittimer_execute, (void*)ctx);
        ctx->timer_configured = 0;
    }
    if (ctx->sendqueue != NULL)
    {
        coap_ticks(&now);
        elapsed = now - ctx->sendqueue_basetime;
        if (ctx->sendqueue->t >= elapsed) {
            delay = ctx->sendqueue->t - elapsed;
        } else {
            /* a strange situation, but not completely impossible.
             *
             * this happens, for example, right after
             * coap_retransmittimer_execute, when a retransmission
             * was *just not yet* due, and the clock ticked before
             * our coap_ticks was called.
             *
             * not trying to retransmit anything now, as it might
             * cause uncontrollable recursion; let's just try again
             * with the next main loop run.
             * */
            delay = 0;
        }

        printf("scheduling for %d ticks\n", delay);
        sys_timeout(delay, coap_retransmittimer_execute, (void*)ctx);
        ctx->timer_configured = 1;
    }
}
#endif