net.c

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/* net.c -- CoAP network interface
 *
 * Copyright (C) 2010--2015 Olaf Bergmann <bergmann@tzi.org>
 *
 * This file is part of the CoAP library libcoap. Please see
 * README for terms of use. 
 */

#include "coap_config.h"

#include <ctype.h>
#include <stdio.h>
#include <errno.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"

#ifndef COAP_DEFAULT_ACK_TIMEOUT

#define COAP_DEFAULT_ACK_TIMEOUT  2 /* see RFC 7252, Section 4.8 */
#endif

#ifndef COAP_DEFAULT_ACK_RANDOM_FACTOR

#define COAP_DEFAULT_ACK_RANDOM_FACTOR  1.5 /* see RFC 7252, Section 4.8 */
#endif

#ifndef COAP_DEFAULT_MAX_RETRANSMIT

#define COAP_DEFAULT_MAX_RETRANSMIT  4 /* see RFC 7252, Section 4.8 */
#endif

#ifndef COAP_DEFAULT_NSTART

#define COAP_DEFAULT_NSTART 1 /* see RFC 7252, Section 4.8 */
#endif

#define FRAC_BITS 6

#define MAX_BITS 8

#if FRAC_BITS > 8
#error FRAC_BITS must be less or equal 8
#endif

#define Q(frac,fval) ((unsigned short)(((1 << (frac)) * (fval))))

#define ACK_RANDOM_FACTOR                   \
  Q(FRAC_BITS, COAP_DEFAULT_ACK_RANDOM_FACTOR)

#define ACK_TIMEOUT Q(FRAC_BITS, COAP_DEFAULT_ACK_TIMEOUT)

#if defined(WITH_POSIX)

time_t clock_offset;

static inline coap_queue_t *
coap_malloc_node(void) {
  return (coap_queue_t *)coap_malloc_type(COAP_NODE, sizeof(coap_queue_t));
}

static inline void
coap_free_node(coap_queue_t *node) {
  coap_free_type(COAP_NODE, 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 "mem.h"
#include "net/ip/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();

unsigned char initialized = 0;
coap_context_t the_coap_context;

PROCESS(coap_retransmit_process, "message retransmit process");

static inline coap_queue_t *
coap_malloc_node() {
  return (coap_queue_t *)coap_malloc_type(COAP_NODE, 0);
}

static inline void
coap_free_node(coap_queue_t *node) {
  coap_free_type(COAP_NODE, node);
}
#endif /* WITH_CONTIKI */

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(void) {
  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) {
  coap_context_t *c;

  if (!listen_addr) {
    coap_log(LOG_EMERG, "no listen address specified\n");
    return NULL;
  }
#ifdef WITH_CONTIKI
  if (initialized)
    return NULL;
#endif /* WITH_CONTIKI */
#ifndef WITH_CONTIKI
  c = coap_malloc_type(COAP_CONTEXT, sizeof(coap_context_t));
#endif /* not WITH_CONTIKI */

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

#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_memory_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));

  c->endpoint = coap_new_endpoint(listen_addr, COAP_ENDPOINT_NOSEC);
  if (c->endpoint == NULL) {
    goto onerror;
  }
#ifdef WITH_LWIP
  c->endpoint->context = c;
#endif

#ifdef WITH_POSIX
  c->sockfd = c->endpoint->handle.fd;
#endif /* WITH_POSIX */

#if defined(WITH_POSIX) || defined(WITH_CONTIKI)
  c->network_send = coap_network_send;
  c->network_read = coap_network_read;
#endif /* WITH_POSIX or WITH_CONTIKI */

#ifdef WITH_CONTIKI
  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);
#endif /* WITH_CONTIKI */

  return c;

 onerror:
  coap_free_type(COAP_CONTEXT, c);
  return NULL;
}

void
coap_free_context(coap_context_t *context) {

  if (!context)
    return;

  coap_delete_all(context->sendqueue);

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

  coap_delete_all_resources(context);

  coap_free_endpoint(context->endpoint);
#ifndef WITH_CONTIKI
  coap_free_type(COAP_CONTEXT, context);
#endif/* not WITH_CONTIKI */
#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) {
      /* first check the built-in critical options */
      switch (opt_iter.type) {
      case COAP_OPTION_IF_MATCH:
      case COAP_OPTION_URI_HOST:
      case COAP_OPTION_IF_NONE_MATCH:
      case COAP_OPTION_URI_PORT:
      case COAP_OPTION_URI_PATH:
      case COAP_OPTION_URI_QUERY:
      case COAP_OPTION_ACCEPT:
      case COAP_OPTION_PROXY_URI:
      case COAP_OPTION_PROXY_SCHEME:
      case COAP_OPTION_BLOCK2:
      case COAP_OPTION_BLOCK1:
    break;
      default:
    if (coap_option_filter_get(ctx->known_options, opt_iter.type) <= 0) {
      debug("unknown critical option %d\n", opt_iter.type);
      ok = 0;

      /* When opt_iter.type is beyond our known option range,
       * coap_option_filter_set() will return -1 and we are safe to leave
       * this loop. */
      if (coap_option_filter_set(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 transport address. */

#ifdef WITH_POSIX
  switch (peer->addr.sa.sa_family) {
  case AF_INET:
    coap_hash((const unsigned char *)&peer->addr.sin.sin_port,
          sizeof(peer->addr.sin.sin_port), h);
    coap_hash((const unsigned char *)&peer->addr.sin.sin_addr,
          sizeof(peer->addr.sin.sin_addr), 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])) & INT_MAX;
}

coap_tid_t
coap_send_ack(coap_context_t *context, 
          const coap_endpoint_t *local_interface,
          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, local_interface, dst, response);
      coap_delete_pdu(response);
    }
  }
  return result;
}

#if defined(WITH_POSIX) || defined(WITH_CONTIKI)
static coap_tid_t
coap_send_impl(coap_context_t *context, 
           const coap_endpoint_t *local_interface,
           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;

  /* Do not send error responses for requests that were received via
   * IP multicast. 
   * FIXME: If No-Response option indicates interest, these responses
   *        must not be dropped. */
  if (coap_is_mcast(&local_interface->addr) &&
      COAP_RESPONSE_CLASS(pdu->hdr->code) > 2) {
    return COAP_DROPPED_RESPONSE;
  }

  bytes_written = context->network_send(context, local_interface, dst, 
                    (unsigned char *)pdu->hdr, pdu->length);

  if (bytes_written >= 0) {
    coap_transaction_id(dst, pdu, &id);
  } else {
    coap_log(LOG_CRIT, "coap_send_impl: %s\n", strerror(errno));
  }

  return id;
}
#endif /* WITH_POSIX */
#ifdef WITH_LWIP
coap_tid_t
coap_send_impl(coap_context_t *context,
           const coap_endpoint_t *local_interface,
           const coap_address_t *dst,
           coap_pdu_t *pdu) {
  coap_tid_t id = COAP_INVALID_TID;

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

  /* 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. */

  pbuf_realloc(pdu->pbuf, pdu->length);

  coap_transaction_id(dst, pdu, &id);

  udp_sendto(context->endpoint->pcb, pdu->pbuf,
            &dst->addr, dst->port);

  return id;
}
#endif /* WITH_LWIP */

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

coap_tid_t
coap_send_error(coap_context_t *context, 
        coap_pdu_t *request,
        const coap_endpoint_t *local_interface,
        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, local_interface, dst, response);
    coap_delete_pdu(response);
  }
  
  return result;
}

coap_tid_t
coap_send_message_type(coap_context_t *context, 
               const coap_endpoint_t *local_interface,
               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, local_interface, dst, response);
      coap_delete_pdu(response);
    }
  }
  return result;
}

static inline unsigned int
calc_timeout(unsigned char r) {
  unsigned int result;

  /* The integer 1.0 as a Qx.FRAC_BITS */
#define FP1 Q(FRAC_BITS, 1)

  /* rounds val up and right shifts by frac positions */
#define SHR_FP(val,frac) (((val) + (1 << ((frac) - 1))) >> (frac))

  /* Inner term: multiply ACK_RANDOM_FACTOR by Q0.MAX_BITS[r] and
   * make the result a rounded Qx.FRAC_BITS */
  result = SHR_FP((ACK_RANDOM_FACTOR - FP1) * r, MAX_BITS);

  /* Add 1 to the inner term and multiply with ACK_TIMEOUT, then
   * make the result a rounded Qx.FRAC_BITS */
  result = SHR_FP(((result + FP1) * ACK_TIMEOUT), FRAC_BITS);

  /* Multiply with COAP_TICKS_PER_SECOND to yield system ticks
   * (yields a Qx.FRAC_BITS) and shift to get an integer */
  return SHR_FP((COAP_TICKS_PER_SECOND * result), FRAC_BITS);

#undef FP1
#undef SHR_FP
}

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

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

  node->id = coap_send_impl(context, local_interface, 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 timeout in range [ACK_TIMEOUT...ACK_TIMEOUT * ACK_RANDOM_FACTOR] */
  node->timeout = calc_timeout(r);

  node->local_if = *local_interface;
  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->local_if, 
                  &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;
}

void coap_dispatch(coap_context_t *context, coap_queue_t *rcvd);

#ifndef WITH_LWIP
/* WITH_LWIP, this is handled by coap_recv in a different way */
int
coap_read( coap_context_t *ctx ) {
  ssize_t bytes_read = -1;
  coap_packet_t *packet;
  coap_address_t src;
  int result = -1;      /* the value to be returned */

  coap_address_init(&src);

  bytes_read = ctx->network_read(ctx->endpoint, &packet);

  if ( bytes_read < 0 ) {
    warn("coap_read: recvfrom");
  } else {
    result = coap_handle_message(ctx, packet);
  }

  coap_free_packet(packet);

  return result;
}
#endif /* not WITH_LWIP */

int
coap_handle_message(coap_context_t *ctx,
            coap_packet_t *packet) {
            /* const coap_address_t *remote,  */
            /* unsigned char *msg, size_t msg_len) { */
  unsigned char *msg;
  size_t msg_len;
  coap_queue_t *node;

  /* the negated result code */
  enum result_t { RESULT_OK, RESULT_ERR_EARLY, RESULT_ERR };
  int result = RESULT_ERR_EARLY;

  coap_packet_get_memmapped(packet, &msg, &msg_len);

  if (msg_len < sizeof(coap_hdr_t)) {
    debug("coap_handle_message: discarded invalid frame\n" );
    goto error_early;
  }

  /* check version identifier */
  if (((*msg >> 6) & 0x03) != COAP_DEFAULT_VERSION) {
    debug("coap_handle_message: unknown protocol version %d\n", (*msg >> 6) & 0x03);
    goto error_early;
  }

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

  /* from this point, the result code indicates that */
  result = RESULT_ERR;
  
#ifdef WITH_LWIP
  node->pdu = coap_pdu_from_pbuf(coap_packet_extract_pbuf(packet));
#else
  node->pdu = coap_pdu_init(0, 0, 0, msg_len);
#endif
  if (!node->pdu) {
    goto error;
  }

  if (!coap_pdu_parse(msg, msg_len, node->pdu)) {
    warn("discard malformed PDU\n");
    goto error;
  }

  coap_ticks(&node->t);

  coap_packet_populate_endpoint(packet, &node->local_if);
  coap_packet_copy_source(packet, &node->remote);

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

#ifndef NDEBUG
  if (LOG_DEBUG <= coap_get_log_level()) {
#ifndef INET6_ADDRSTRLEN
#define INET6_ADDRSTRLEN 40
#endif

    coap_show_pdu(node->pdu);
  }
#endif

  coap_dispatch(ctx, node);
  return -RESULT_OK;

 error:
  /* FIXME: send back RST? */
  coap_delete_node(node);
  return -result;

 error_early:
  return -result;
}

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;
  
  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 (coap_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: coap_print_wellknown() returned %zu\n", len);

  return len;
}

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

coap_pdu_t *
coap_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("coap_wellknown_response: cannot create PDU\n");
    return NULL;
  }
  
  if (!coap_add_token(resp, request->hdr->token_length, request->hdr->token)) {
    debug("coap_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);

  /* The value of some resources is undefined and get_wkc_len will return 0.*/
  if (wkc_len == 0){
    debug("coap_wellknown_response: undefined resource\n");
    /* set error code 4.00 Bad Request*/
    resp->hdr->code = COAP_RESPONSE_CODE(400);
    resp->length = sizeof(coap_hdr_t) + resp->hdr->token_length;
    return resp;
  }

  /* check whether the request contains the Block2 option */
  if (coap_get_block(request, COAP_OPTION_BLOCK2, &block)) {
    debug("create block\n");
    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("coap_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("coap_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("coap_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 = coap_print_wellknown(context, resp->data, &len, offset, query_filter);
  if ((result & COAP_PRINT_STATUS_ERROR) != 0) {
    debug("coap_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;
}

static int
coap_cancel(coap_context_t *context, const coap_queue_t *sent) {
#ifndef WITHOUT_OBSERVE
  str token = { 0, NULL };
  int num_cancelled = 0;    /* the number of observers cancelled */

  /* 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);

  RESOURCES_ITER(context->resources, r) {
    num_cancelled += coap_delete_observer(r, &sent->remote, &token);
    coap_cancel_all_messages(context, &sent->remote, token.s, token.length);
  }

  return num_cancelled;
#else /* WITOUT_OBSERVE */  
  return 0;
#endif /* WITOUT_OBSERVE */  
}

enum respond_t { RESPONSE_DEFAULT, RESPONSE_DROP, RESPONSE_SEND };

static enum respond_t
no_response(coap_pdu_t *request, coap_pdu_t *response) {
  coap_opt_t *nores;
  coap_opt_iterator_t opt_iter;
  uint8_t val = 0;

  assert(request);
  assert(response);

  if (COAP_RESPONSE_CLASS(response->hdr->code) > 0) {
    nores = coap_check_option(request, COAP_OPTION_NORESPONSE, &opt_iter);

    if (nores) {
      val = coap_decode_var_bytes(coap_opt_value(nores), coap_opt_length(nores));

      /* The response should be dropped when the bit corresponding to
       * the response class is set (cf. table in funtion
       * documentation). When a No-Response option is present and the
       * bit is not set, the sender explicitly indicates interest in
       * this response. */
      if (((1 << (COAP_RESPONSE_CLASS(response->hdr->code) - 1)) & val) > 0) {
        return RESPONSE_DROP;
      } else {
        return RESPONSE_SEND;
      }
    }
  }

  /* Default behavior applies when we are not dealing with a response
   * (class == 0) or the request did not contain a No-Response option.
   */
  return RESPONSE_DEFAULT;
}

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

static 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;
  /* The respond field indicates whether a response must be treated
   * specially due to a No-Response option that declares disinterest
   * or interest in a specific response class. DEFAULT indicates that
   * No-Response has not been specified. */
  enum respond_t respond = RESPONSE_DEFAULT;

  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 */

    if (is_wkc(key)) {  /* request for .well-known/core */
      if (node->pdu->hdr->code == COAP_REQUEST_GET) { /* GET */
    info("create default response for %s\n", COAP_DEFAULT_URI_WELLKNOWN);
    response = coap_wellknown_response(context, node->pdu);
      } else {
        debug("method not allowed for .well-known/core\n");
    response = coap_new_error_response(node->pdu, COAP_RESPONSE_CODE(405), 
                       opt_filter);
      }
    } else { /* request for any another resource, return 4.04 */

      debug("request 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);
    }
      
    if (response
        && (no_response(node->pdu, response) != RESPONSE_DROP)
        && (coap_send(context, &node->local_if,
                      &node->remote, response) == COAP_INVALID_TID)) {
      warn("cannot send response for transaction %u\n", node->id);
    }
    coap_delete_pdu(response);
    response = NULL;

    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 };
      coap_opt_iterator_t opt_iter;
      coap_opt_t *observe = NULL;
      int observe_action = COAP_OBSERVE_CANCEL;

      /* check for Observe option */
      if (resource->observable) {
    observe = coap_check_option(node->pdu, COAP_OPTION_OBSERVE, &opt_iter);
    if (observe) {
      observe_action =
        coap_decode_var_bytes(coap_opt_value(observe),
                  coap_opt_length(observe));
     
      if ((observe_action & COAP_OBSERVE_CANCEL) == 0) {
        coap_subscription_t *subscription;

        coap_log(LOG_DEBUG, "create new subscription\n");
        subscription = coap_add_observer(resource, &node->local_if, 
                         &node->remote, &token);
        if (subscription) {
          coap_touch_observer(context, &node->remote, &token);
        }
      } else {
            coap_log(LOG_DEBUG, "removed observer\n");
            coap_delete_observer(resource,  &node->remote, &token);
          }
    }
      }

      h(context, resource, &node->local_if, &node->remote,
    node->pdu, &token, response);

      respond = no_response(node->pdu, response);
      if (respond != RESPONSE_DROP) {
        if (observe && (COAP_RESPONSE_CLASS(response->hdr->code) > 2)) {
          coap_log(LOG_DEBUG, "removed observer\n");
          coap_delete_observer(resource,  &node->remote, &token);
        }

      /* If original request contained a token, and the registered
       * application handler made no changes to the response, then
       * this is an empty ACK with a token, which is a malformed
       * PDU */
      if ((response->hdr->type == COAP_MESSAGE_ACK)
      && (response->hdr->code == 0)) {
    /* Remove token from otherwise-empty acknowledgment PDU */
    response->hdr->token_length = 0;
    response->length = sizeof(coap_hdr_t);
      }

      if ((respond == RESPONSE_SEND)
          || /* RESPOND_DEFAULT */
          (response->hdr->type != COAP_MESSAGE_NON ||
           (response->hdr->code >= 64
            && !coap_mcast_interface(&node->local_if)))) {

    if (coap_send(context, &node->local_if, 
              &node->remote, response) == COAP_INVALID_TID) {
      debug("cannot send response for message %d\n", node->pdu->hdr->id);
      }
      }
      }
      coap_delete_pdu(response);
      response = NULL;
    } 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 = coap_wellknown_response(context, node->pdu);
      debug("have wellknown response %p\n", (void *)response);
    } else
      response = coap_new_error_response(node->pdu, COAP_RESPONSE_CODE(405), 
                     opt_filter);

    if (response && (no_response(node->pdu, response) != RESPONSE_DROP)) {
      if (coap_send(context, &node->local_if, &node->remote,
                    response) == COAP_INVALID_TID) {
        debug("cannot send response for transaction %u\n", node->id);
      }
    }
    coap_delete_pdu(response);
    response = NULL;
  }

  assert(response == NULL);
}

static inline void
handle_response(coap_context_t *context, 
        coap_queue_t *sent, coap_queue_t *rcvd) {

  coap_send_ack(context, &rcvd->local_if, &rcvd->remote, rcvd->pdu);
  
  /* In a lossy context, the ACK of a separate response may have
   * been lost, so we need to stop retransmitting requests with the
   * same token.
   */
  coap_cancel_all_messages(context, &rcvd->remote,
               rcvd->pdu->hdr->token, 
               rcvd->pdu->hdr->token_length);

  /* Call application-specific response handler when available. */
  if (context->response_handler) {
    context->response_handler(context, &rcvd->local_if,
                  &rcvd->remote, sent ? sent->pdu : NULL, 
                  rcvd->pdu, rcvd->id);
  }
}

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;
}

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

  if (!context)
    return;

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

  {
    /* version has been checked in coap_handle_message() */
    /* 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;

      /* 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. */

#ifndef WITH_CONTIKI
      coap_log(LOG_ALERT, "got RST for message %u\n", ntohs(rcvd->pdu->hdr->id));
#else /* WITH_CONTIKI */
      coap_log(LOG_ALERT, "got RST for message %u\n", uip_ntohs(rcvd->pdu->hdr->id));
#endif /* WITH_CONTIKI */

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

      if (sent)
    coap_cancel(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 response\n");
    else {
      if (coap_send(context, &rcvd->local_if, &rcvd->remote, response) 
          == COAP_INVALID_TID) {
        warn("coap_dispatch: error sending response\n");
      }
          coap_delete_pdu(response);
    }    
    
    goto cleanup;
      }
    default: 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 (%d.%02d)\n", 
          COAP_RESPONSE_CLASS(rcvd->pdu->hdr->code),
          rcvd->pdu->hdr->code & 0x1f);

    if (!coap_is_mcast(&rcvd->local_if.addr)) {
      coap_send_message_type(context, &rcvd->local_if, &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->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