coap_session.c

/* coap_session.c -- Session management for libcoap
 *
 * Copyright (C) 2017      Jean-Claue Michelou <jcm@spinetix.com>
 * Copyright (C) 2022-2024 Jon Shallow <supjps-libcoap@jpshallow.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * This file is part of the CoAP library libcoap. Please see
 * README for terms of use.
 */

/**
 * @file coap_session.c
 * @brief Session handling functions
 */

#include "coap3/coap_libcoap_build.h"

#ifndef COAP_SESSION_C_
#define COAP_SESSION_C_

#include <stdio.h>

#ifdef COAP_EPOLL_SUPPORT
#include <sys/epoll.h>
#include <sys/timerfd.h>
#endif /* COAP_EPOLL_SUPPORT */

coap_fixed_point_t
coap_multi_fixed_fixed(coap_fixed_point_t fp1, coap_fixed_point_t fp2) {
  coap_fixed_point_t res;
  uint32_t fr = fp1.fractional_part * fp2.fractional_part;

  res.integer_part = fp1.integer_part * fp2.integer_part + fr/1000;
  res.fractional_part = fr % 1000;
  return res;
}

coap_fixed_point_t
coap_multi_fixed_uint(coap_fixed_point_t fp1, uint32_t u2) {
  coap_fixed_point_t res;
  uint32_t fr = fp1.fractional_part * u2;

  res.integer_part = fp1.integer_part * u2 + fr/1000;
  res.fractional_part = fr % 1000;
  return res;
}

coap_fixed_point_t
coap_add_fixed_fixed(coap_fixed_point_t fp1, coap_fixed_point_t fp2) {
  coap_fixed_point_t res;
  uint32_t fr = fp1.fractional_part + fp2.fractional_part;

  res.integer_part = fp1.integer_part + fp2.integer_part + fr/1000;
  res.fractional_part = fr % 1000;
  return res;
}

coap_fixed_point_t
coap_add_fixed_uint(coap_fixed_point_t fp1, uint32_t u2) {
  coap_fixed_point_t res = fp1;

  res.integer_part += u2;
  return res;
}

coap_fixed_point_t
coap_sub_fixed_uint(coap_fixed_point_t fp1, uint32_t u2) {
  coap_fixed_point_t res = fp1;

  res.integer_part -= u2;
  return res;
}

coap_fixed_point_t
coap_div_fixed_uint(coap_fixed_point_t fp1, uint32_t u2) {
  coap_fixed_point_t res;
  uint32_t num = (fp1.integer_part * 1000 + fp1.fractional_part) / u2;

  res.integer_part = num / 1000;
  res.fractional_part = num % 1000;
  return res;
}

#if COAP_Q_BLOCK_SUPPORT
coap_fixed_point_t
coap_get_non_timeout_random(coap_session_t *session) {
  coap_fixed_point_t res;
  uint8_t ran;

  coap_prng_lkd(&ran, sizeof(ran));
  res = coap_sub_fixed_uint(COAP_ACK_RANDOM_FACTOR(session), 1);
  res = coap_multi_fixed_uint(res, ran);
  res = coap_div_fixed_uint(res, 0xff);
  res = coap_add_fixed_fixed(COAP_NON_TIMEOUT(session), res);
  return res;
}

coap_tick_t
coap_get_non_timeout_random_ticks(coap_session_t *session) {
  coap_fixed_point_t res = coap_get_non_timeout_random(session);
  coap_tick_t ticks = (res.integer_part * COAP_TICKS_PER_SECOND +
                       res.fractional_part * COAP_TICKS_PER_SECOND / 1000);

  return ticks;
}

/*
 * Save away derived Congestion Control parameters for speed of access.
 * They will get updated whenever a component variable is updated.
 */

/*
 * NON_PROBING_WAIT = NON_TIMEOUT * ((2 ** NON_MAX_RETRANSMIT) - 1) *
 * ACK_RANDOM_FACTOR + (2 * MAX_LATENCY) + NON_TIMEOUT_RANDOM
 *
 * Do not include NON_TIMEOUT_RANDOM as that changes
 */
static void
coap_session_fix_non_probing_wait_base(coap_session_t *s) {
  coap_fixed_point_t res;

  res = coap_multi_fixed_uint(COAP_NON_TIMEOUT(s),
                              ((1 << (COAP_NON_MAX_RETRANSMIT(s) + 1)) -1));
  res = coap_multi_fixed_fixed(res, COAP_ACK_RANDOM_FACTOR(s));
  res = coap_add_fixed_uint(res, 2 * COAP_DEFAULT_MAX_LATENCY);
  COAP_NON_PROBING_WAIT_BASE(s) = res;
}

/*
 * NON_PARTIAL_TIMEOUT = NON_TIMEOUT * ((2 ** NON_MAX_RETRANSMIT) - 1) *
 * ACK_RANDOM_FACTOR + (2 * MAX_LATENCY) + NON_TIMEOUT
 */
static void
coap_session_fix_non_partial_timeout(coap_session_t *s) {
  coap_fixed_point_t res;

  res = coap_multi_fixed_uint(COAP_NON_TIMEOUT(s),
                              ((1 << (COAP_NON_MAX_RETRANSMIT(s) + 1)) -1));
  res = coap_multi_fixed_fixed(res, COAP_ACK_RANDOM_FACTOR(s));
  res = coap_add_fixed_uint(res, 2 * COAP_DEFAULT_MAX_LATENCY);
  res = coap_add_fixed_fixed(res, COAP_NON_TIMEOUT(s));
  COAP_NON_PARTIAL_TIMEOUT(s) = res;
}
#endif /* COAP_Q_BLOCK_SUPPORT */

void
coap_session_set_ack_timeout(coap_session_t *session, coap_fixed_point_t value) {
  if (value.integer_part > 0 && value.fractional_part < 1000) {
    session->ack_timeout = value;
    coap_log_debug("***%s: session ack_timeout set to %u.%03u\n",
                   coap_session_str(session), session->ack_timeout.integer_part,
                   session->ack_timeout.fractional_part);
  }
}

void
coap_session_set_ack_random_factor(coap_session_t *session,
                                   coap_fixed_point_t value) {
  if (value.integer_part > 0 && value.fractional_part < 1000) {
    session->ack_random_factor = value;
    coap_log_debug("***%s: session ack_random_factor set to %u.%03u\n",
                   coap_session_str(session), session->ack_random_factor.integer_part,
                   session->ack_random_factor.fractional_part);
#if COAP_Q_BLOCK_SUPPORT
    coap_session_fix_non_probing_wait_base(session);
    coap_session_fix_non_partial_timeout(session);
#endif /* COAP_Q_BLOCK_SUPPORT */
  }
  return;
}

void
coap_session_set_max_retransmit(coap_session_t *session, uint16_t value) {
  if (value > 0) {
    session->max_retransmit = value;
    coap_log_debug("***%s: session max_retransmit set to %u\n",
                   coap_session_str(session), session->max_retransmit);
  }
}

void
coap_session_set_nstart(coap_session_t *session, uint16_t value) {
  if (value > 0) {
    session->nstart = value;
    coap_log_debug("***%s: session nstart set to %u\n",
                   coap_session_str(session), session->nstart);
  }
}

void
coap_session_set_default_leisure(coap_session_t *session,
                                 coap_fixed_point_t value) {
  if (value.integer_part > 0 && value.fractional_part < 1000) {
    session->default_leisure = value;
    coap_log_debug("***%s: session default_leisure set to %u.%03u\n",
                   coap_session_str(session), session->default_leisure.integer_part,
                   session->default_leisure.fractional_part);
  }
}

void
coap_session_set_probing_rate(coap_session_t *session, uint32_t value) {
  if (value > 0) {
    session->probing_rate = value;
    coap_log_debug("***%s: session probing_rate set to %" PRIu32 "\n",
                   coap_session_str(session), session->probing_rate);
  }
}

void
coap_session_set_max_payloads(coap_session_t *session, uint16_t value) {
#if COAP_Q_BLOCK_SUPPORT
  if (value > 0) {
    session->max_payloads = value;
    coap_log_debug("***%s: session max_payloads set to %u\n",
                   coap_session_str(session), session->max_payloads);
    coap_session_fix_non_probing_wait_base(session);
    coap_session_fix_non_partial_timeout(session);
  }
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  (void)value;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

void
coap_session_set_non_max_retransmit(coap_session_t *session, uint16_t value) {
#if COAP_Q_BLOCK_SUPPORT
  if (value > 0) {
    session->non_max_retransmit = value;
    coap_log_debug("***%s: session non_max_retransmit set to %u\n",
                   coap_session_str(session), session->non_max_retransmit);
    coap_session_fix_non_probing_wait_base(session);
    coap_session_fix_non_partial_timeout(session);
  }
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  (void)value;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

void
coap_session_set_non_timeout(coap_session_t *session,
                             coap_fixed_point_t value) {
#if COAP_Q_BLOCK_SUPPORT
  if (value.integer_part > 0 && value.fractional_part < 1000) {
    session->non_timeout = value;
    coap_log_debug("***%s: session non_timeout set to %u.%03u\n",
                   coap_session_str(session), session->non_timeout.integer_part,
                   session->non_timeout.fractional_part);
    coap_session_fix_non_probing_wait_base(session);
    coap_session_fix_non_partial_timeout(session);
  }
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  (void)value;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

void
coap_session_set_non_receive_timeout(coap_session_t *session,
                                     coap_fixed_point_t value) {
#if COAP_Q_BLOCK_SUPPORT
  if (value.integer_part > 0 && value.fractional_part < 1000)
    session->non_receive_timeout = value;
  coap_log_debug("***%s: session non_receive_timeout set to %u.%03u\n",
                 coap_session_str(session),
                 session->non_receive_timeout.integer_part,
                 session->non_receive_timeout.fractional_part);
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  (void)value;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

coap_fixed_point_t
coap_session_get_ack_timeout(const coap_session_t *session) {
  return session->ack_timeout;
}

coap_fixed_point_t
coap_session_get_ack_random_factor(const coap_session_t *session) {
  return session->ack_random_factor;
}

uint16_t
coap_session_get_max_retransmit(const coap_session_t *session) {
  return session->max_retransmit;
}

uint16_t
coap_session_get_nstart(const coap_session_t *session) {
  return session->nstart;
}

coap_fixed_point_t
coap_session_get_default_leisure(const coap_session_t *session) {
  return session->default_leisure;
}

uint32_t
coap_session_get_probing_rate(const coap_session_t *session) {
  return session->probing_rate;
}

uint16_t
coap_session_get_max_payloads(const coap_session_t *session) {
#if COAP_Q_BLOCK_SUPPORT
  return session->max_payloads;
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  return COAP_DEFAULT_MAX_PAYLOADS;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

uint16_t
coap_session_get_non_max_retransmit(const coap_session_t *session) {
#if COAP_Q_BLOCK_SUPPORT
  return session->non_max_retransmit;
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  return COAP_DEFAULT_NON_MAX_RETRANSMIT;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

coap_fixed_point_t
coap_session_get_non_timeout(const coap_session_t *session) {
#if COAP_Q_BLOCK_SUPPORT
  return session->non_timeout;
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  return COAP_DEFAULT_NON_TIMEOUT;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

coap_fixed_point_t
coap_session_get_non_receive_timeout(const coap_session_t *session) {
#if COAP_Q_BLOCK_SUPPORT
  return session->non_receive_timeout;
#else /* ! COAP_Q_BLOCK_SUPPORT */
  (void)session;
  return COAP_DEFAULT_NON_RECEIVE_TIMEOUT;
#endif /* ! COAP_Q_BLOCK_SUPPORT */
}

COAP_API coap_session_t *
coap_session_reference(coap_session_t *session) {
  coap_lock_lock(session->context, return NULL);
  coap_session_reference_lkd(session);
  coap_lock_unlock(session->context);
  return session;
}

coap_session_t *
coap_session_reference_lkd(coap_session_t *session) {
  ++session->ref;
  return session;
}

COAP_API void
coap_session_release(coap_session_t *session) {
  if (session) {
#if COAP_THREAD_SAFE
    coap_context_t *context = session->context;
    (void)context;
#endif /* COAP_THREAD_SAFE */

    coap_lock_lock(context, return);
    coap_session_release_lkd(session);
    coap_lock_unlock(context);
  }
}

void
coap_session_release_lkd(coap_session_t *session) {
  if (session) {
    coap_lock_check_locked(session->context);
#ifndef __COVERITY__
    assert(session->ref > 0);
    if (session->ref > 0)
      --session->ref;
    if (session->ref == 0 && session->type == COAP_SESSION_TYPE_CLIENT)
      coap_session_free(session);
#else /* __COVERITY__ */
    /* Coverity scan is fooled by the reference counter leading to
     * false positives for USE_AFTER_FREE. */
    --session->ref;
    __coverity_negative_sink__(session->ref);
    /* Indicate that resources are released properly. */
    if (session->ref == 0 && session->type == COAP_SESSION_TYPE_CLIENT) {
      __coverity_free__(session);
    }
#endif /* __COVERITY__ */
  }
}

void
coap_session_set_app_data(coap_session_t *session, void *app_data) {
  assert(session);
  session->app = app_data;
}

void *
coap_session_get_app_data(const coap_session_t *session) {
  assert(session);
  return session->app;
}

static coap_session_t *
coap_make_session(coap_proto_t proto, coap_session_type_t type,
                  const coap_addr_hash_t *addr_hash,
                  const coap_address_t *local_addr,
                  const coap_address_t *remote_addr, int ifindex,
                  coap_context_t *context, coap_endpoint_t *endpoint) {
  coap_session_t *session = (coap_session_t *)coap_malloc_type(COAP_SESSION,
                            sizeof(coap_session_t));
#if ! COAP_SERVER_SUPPORT
  (void)endpoint;
#endif /* ! COAP_SERVER_SUPPORT */
  if (!session)
    return NULL;
  memset(session, 0, sizeof(*session));
  session->proto = proto;
  session->type = type;
  if (addr_hash)
    memcpy(&session->addr_hash, addr_hash, sizeof(session->addr_hash));
  else
    memset(&session->addr_hash, 0, sizeof(session->addr_hash));
  if (local_addr)
    coap_address_copy(&session->addr_info.local, local_addr);
  else
    coap_address_init(&session->addr_info.local);
  if (remote_addr)
    coap_address_copy(&session->addr_info.remote, remote_addr);
  else
    coap_address_init(&session->addr_info.remote);
  session->ifindex = ifindex;
  session->context = context;
#if COAP_SERVER_SUPPORT
  session->endpoint = endpoint;
  if (endpoint)
    session->mtu = endpoint->default_mtu;
  else
#endif /* COAP_SERVER_SUPPORT */
    coap_session_set_mtu(session, COAP_DEFAULT_MTU);
  session->block_mode = context->block_mode;
  if (proto == COAP_PROTO_DTLS) {
    session->tls_overhead = 29;
    if (session->tls_overhead >= session->mtu) {
      session->tls_overhead = session->mtu;
      coap_log_err("DTLS overhead exceeds MTU\n");
    }
  }
  session->ack_timeout = COAP_DEFAULT_ACK_TIMEOUT;
  session->ack_random_factor = COAP_DEFAULT_ACK_RANDOM_FACTOR;
  session->max_retransmit = COAP_DEFAULT_MAX_RETRANSMIT;
  session->nstart = COAP_DEFAULT_NSTART;
  session->default_leisure = COAP_DEFAULT_DEFAULT_LEISURE;
  session->probing_rate = COAP_DEFAULT_PROBING_RATE;
#if COAP_Q_BLOCK_SUPPORT
  session->max_payloads = COAP_DEFAULT_MAX_PAYLOADS;
  session->non_max_retransmit = COAP_DEFAULT_NON_MAX_RETRANSMIT;
  session->non_timeout = COAP_DEFAULT_NON_TIMEOUT;
  session->non_receive_timeout = COAP_DEFAULT_NON_RECEIVE_TIMEOUT;
  coap_session_fix_non_probing_wait_base(session);
  coap_session_fix_non_partial_timeout(session);
#endif /* COAP_Q_BLOCK_SUPPORT */
  session->dtls_event = -1;
  session->last_ping_mid = COAP_INVALID_MID;
  session->last_ack_mid = COAP_INVALID_MID;
  session->last_con_mid = COAP_INVALID_MID;
  session->last_con_handler_res = COAP_RESPONSE_OK;
  session->max_token_size = context->max_token_size; /* RFC8974 */
  if (session->type != COAP_SESSION_TYPE_CLIENT)
    session->max_token_checked = COAP_EXT_T_CHECKED;

  /* Randomly initialize */
  /* TCP/TLS have no notion of mid */
  if (COAP_PROTO_NOT_RELIABLE(session->proto))
    coap_prng_lkd((unsigned char *)&session->tx_mid, sizeof(session->tx_mid));
  coap_prng_lkd((unsigned char *)&session->tx_rtag, sizeof(session->tx_rtag));

  return session;
}

void
coap_session_mfree(coap_session_t *session) {
  coap_queue_t *q, *tmp;
  coap_lg_xmit_t *lq, *ltmp;

#if COAP_CLIENT_SUPPORT
  coap_lg_crcv_t *lg_crcv, *etmp;

  /* Need to do this before (D)TLS and socket is closed down */
  LL_FOREACH_SAFE(session->lg_crcv, lg_crcv, etmp) {
    if (lg_crcv->observe_set && session->no_observe_cancel == 0) {
      /* Need to close down observe */
      if (coap_cancel_observe_lkd(session, lg_crcv->app_token, COAP_MESSAGE_NON)) {
        /* Need to delete node we set up for NON */
        coap_queue_t *queue = session->context->sendqueue;

        while (queue) {
          if (queue->session == session) {
            coap_delete_node_lkd(queue);
            break;
          }
          queue = queue->next;
        }
      }
    }
    LL_DELETE(session->lg_crcv, lg_crcv);
    coap_block_delete_lg_crcv(session, lg_crcv);
  }
#endif /* COAP_CLIENT_SUPPORT */

  if (session->partial_pdu)
    coap_delete_pdu(session->partial_pdu);
  if (session->sock.lfunc[COAP_LAYER_SESSION].l_close)
    session->sock.lfunc[COAP_LAYER_SESSION].l_close(session);
  if (session->psk_identity)
    coap_delete_bin_const(session->psk_identity);
  if (session->psk_key)
    coap_delete_bin_const(session->psk_key);
  if (session->psk_hint)
    coap_delete_bin_const(session->psk_hint);

#if COAP_SERVER_SUPPORT
  coap_cache_entry_t *cp, *ctmp;
  HASH_ITER(hh, session->context->cache, cp, ctmp) {
    /* cp->session is NULL if not session based */
    if (cp->session == session) {
      coap_delete_cache_entry(session->context, cp);
    }
  }
#endif /* COAP_SERVER_SUPPORT */
  LL_FOREACH_SAFE(session->delayqueue, q, tmp) {
    if (q->pdu->type==COAP_MESSAGE_CON) {
      coap_handle_nack(session, q->pdu,
                       session->proto == COAP_PROTO_DTLS ?
                       COAP_NACK_TLS_FAILED : COAP_NACK_NOT_DELIVERABLE,
                       q->id);
    }
    coap_delete_node_lkd(q);
  }
  LL_FOREACH_SAFE(session->lg_xmit, lq, ltmp) {
    LL_DELETE(session->lg_xmit, lq);
    coap_block_delete_lg_xmit(session, lq);
  }
#if COAP_SERVER_SUPPORT
  coap_lg_srcv_t *sq, *stmp;

  LL_FOREACH_SAFE(session->lg_srcv, sq, stmp) {
    LL_DELETE(session->lg_srcv, sq);
    coap_block_delete_lg_srcv(session, sq);
  }
#endif /* COAP_SERVER_SUPPORT */
#if COAP_OSCORE_SUPPORT
  coap_delete_oscore_associations(session);
#endif /* COAP_OSCORE_SUPPORT */
#if COAP_WS_SUPPORT
  coap_free_type(COAP_STRING, session->ws);
  coap_delete_str_const(session->ws_host);
#endif /* COAP_WS_SUPPORT */
}

void
coap_session_free(coap_session_t *session) {
  if (!session)
    return;
  coap_lock_check_locked(session->context);
  assert(session->ref == 0);
  if (session->ref)
    return;
  /* Make sure nothing gets deleted under our feet */
  coap_session_reference_lkd(session);
  coap_session_mfree(session);
#if COAP_SERVER_SUPPORT
  coap_delete_bin_const(session->client_cid);
  if (session->endpoint) {
    if (session->endpoint->sessions)
      SESSIONS_DELETE(session->endpoint->sessions, session);
  } else
#endif /* COAP_SERVER_SUPPORT */
#if COAP_CLIENT_SUPPORT
    if (session->context) {
      if (session->context->sessions)
        SESSIONS_DELETE(session->context->sessions, session);
    }
  coap_delete_bin_const(session->req_token);
#endif /* COAP_CLIENT_SUPPORT */
  coap_delete_bin_const(session->last_token);
  coap_delete_bin_const(session->echo);
  coap_log_debug("***%s: session %p: closed\n", coap_session_str(session),
                 (void *)session);

  assert(session->ref == 1);
  coap_free_type(COAP_SESSION, session);
}

static size_t
coap_session_max_pdu_size_internal(const coap_session_t *session,
                                   size_t max_with_header) {
#if COAP_DISABLE_TCP
  (void)session;
  return max_with_header > COAP_PDU_MAX_UDP_HEADER_SIZE
         ? max_with_header - COAP_PDU_MAX_UDP_HEADER_SIZE
         : 0;
#else /* !COAP_DISABLE_TCP */
  if (COAP_PROTO_NOT_RELIABLE(session->proto))
    return max_with_header > COAP_PDU_MAX_UDP_HEADER_SIZE
           ? max_with_header - COAP_PDU_MAX_UDP_HEADER_SIZE
           : 0;
  /* we must assume there is no token to be on the safe side */
  if (max_with_header <= 2)
    return 0;
  else if (max_with_header <= COAP_MAX_MESSAGE_SIZE_TCP0 + 2)
    return max_with_header - 2;
  else if (max_with_header <= COAP_MAX_MESSAGE_SIZE_TCP8 + 3)
    return max_with_header - 3;
  else if (max_with_header <= COAP_MAX_MESSAGE_SIZE_TCP16 + 4)
    return max_with_header - 4;
  else
    return max_with_header - COAP_PDU_MAX_TCP_HEADER_SIZE;
#endif /* !COAP_DISABLE_TCP */
}

size_t
coap_session_max_pdu_rcv_size(const coap_session_t *session) {
  if (session->csm_rcv_mtu)
    return coap_session_max_pdu_size_internal(session,
                                              (size_t)(session->csm_rcv_mtu));

  return coap_session_max_pdu_size_internal(session,
                                            (size_t)(session->mtu - session->tls_overhead));
}

COAP_API size_t
coap_session_max_pdu_size(const coap_session_t *session) {
  size_t size;
  coap_session_t *session_rw;

  /*
   * Need to do this to not get a compiler warning about const parameters
   * but need to maintain source code backward compatibility
   */
  memcpy(&session_rw, &session, sizeof(session_rw));
  coap_lock_lock(session_rw->context, return 0);
  size = coap_session_max_pdu_size_lkd(session_rw);
  coap_lock_unlock(session_rw->context);
  return size;
}

size_t
coap_session_max_pdu_size_lkd(const coap_session_t *session) {
  size_t max_with_header;

  coap_lock_check_locked(session->context);
#if COAP_CLIENT_SUPPORT
  /*
   * Delay if session->doing_first is set.
   * E.g. Reliable and CSM not in yet for checking block support
   */
  coap_session_t *session_rw;

  /*
   * Need to do this to not get a compiler warning about const parameters
   * but need to maintain source code backward compatibility
   */
  memcpy(&session_rw, &session, sizeof(session_rw));
  if (coap_client_delay_first(session_rw) == 0) {
    coap_log_debug("coap_client_delay_first: timeout\n");
    /* Have to go with the defaults */
  }
#endif /* COAP_CLIENT_SUPPORT */

  max_with_header = (size_t)(session->mtu - session->tls_overhead);

  return coap_session_max_pdu_size_internal(session, max_with_header);
}

void
coap_session_set_mtu(coap_session_t *session, unsigned mtu) {
#if defined(WITH_CONTIKI) || defined(WITH_LWIP)
  if (mtu > COAP_DEFAULT_MAX_PDU_RX_SIZE)
    mtu = COAP_DEFAULT_MAX_PDU_RX_SIZE;
#endif
  if (mtu < 64)
    mtu = 64;
  session->mtu = mtu;
  if (session->tls_overhead >= session->mtu) {
    session->tls_overhead = session->mtu;
    coap_log_err("DTLS overhead exceeds MTU\n");
  }
}

ssize_t
coap_session_delay_pdu(coap_session_t *session, coap_pdu_t *pdu,
                       coap_queue_t *node) {
  if (node) {
    coap_queue_t *removed = NULL;
    coap_remove_from_queue(&session->context->sendqueue, session, node->id, &removed);
    assert(removed == node);
    coap_session_release_lkd(node->session);
    node->session = NULL;
    node->t = 0;
  } else {
    if (COAP_PROTO_NOT_RELIABLE(session->proto)) {
      coap_queue_t *q = NULL;
      /* Check same mid is not getting re-used in violation of RFC7252 */
      LL_FOREACH(session->delayqueue, q) {
        if (q->id == pdu->mid) {
          coap_log_err("**  %s: mid=0x%04x: already in-use - dropped\n",
                       coap_session_str(session), pdu->mid);
          return COAP_INVALID_MID;
        }
      }
    }
    node = coap_new_node();
    if (node == NULL)
      return COAP_INVALID_MID;
    node->id = pdu->mid;
    node->pdu = pdu;
    if (pdu->type == COAP_MESSAGE_CON && COAP_PROTO_NOT_RELIABLE(session->proto)) {
      uint8_t r;
      coap_prng_lkd(&r, sizeof(r));
      /* add timeout in range [ACK_TIMEOUT...ACK_TIMEOUT * ACK_RANDOM_FACTOR] */
      node->timeout = coap_calc_timeout(session, r);
    }
  }
  LL_APPEND(session->delayqueue, node);
  coap_log_debug("** %s: mid=0x%04x: delayed\n",
                 coap_session_str(session), node->id);
  return COAP_PDU_DELAYED;
}

#if !COAP_DISABLE_TCP
void
coap_session_send_csm(coap_session_t *session) {
  coap_pdu_t *pdu;
  uint8_t buf[4];
  assert(COAP_PROTO_RELIABLE(session->proto));
  coap_log_debug("***%s: sending CSM\n", coap_session_str(session));
  session->state = COAP_SESSION_STATE_CSM;
  session->partial_write = 0;
  if (session->mtu == 0)
    coap_session_set_mtu(session, COAP_DEFAULT_MTU);  /* base value */
  pdu = coap_pdu_init(COAP_MESSAGE_CON, COAP_SIGNALING_CODE_CSM, 0, 20);
  if (pdu == NULL
      || coap_add_option_internal(pdu, COAP_SIGNALING_OPTION_MAX_MESSAGE_SIZE,
                                  coap_encode_var_safe(buf, sizeof(buf),
                                                       session->context->csm_max_message_size), buf) == 0
      || coap_add_option_internal(pdu, COAP_SIGNALING_OPTION_BLOCK_WISE_TRANSFER,
                                  coap_encode_var_safe(buf, sizeof(buf),
                                                       0), buf) == 0
      || (session->max_token_size > COAP_TOKEN_DEFAULT_MAX &&
          coap_add_option_internal(pdu,
                                   COAP_SIGNALING_OPTION_EXTENDED_TOKEN_LENGTH,
                                   coap_encode_var_safe(buf, sizeof(buf),
                                                        session->max_token_size),
                                   buf) == 0)
      || coap_pdu_encode_header(pdu, session->proto) == 0
     ) {
    coap_session_disconnected_lkd(session, COAP_NACK_NOT_DELIVERABLE);
  } else {
    ssize_t bytes_written;

    pdu->session = session;
    bytes_written = coap_session_send_pdu(session, pdu);
    if (bytes_written != (ssize_t)pdu->used_size + pdu->hdr_size) {
      coap_session_disconnected_lkd(session, COAP_NACK_NOT_DELIVERABLE);
    } else {
      session->csm_rcv_mtu = session->context->csm_max_message_size;
      if (session->csm_rcv_mtu > COAP_BERT_BASE)
        session->csm_bert_loc_support = 1;
      else
        session->csm_bert_loc_support = 0;
    }
  }
  if (pdu)
    coap_delete_pdu(pdu);
}
#endif /* !COAP_DISABLE_TCP */

COAP_API coap_mid_t
coap_session_send_ping(coap_session_t *session) {
  coap_mid_t mid;

  coap_lock_lock(session->context, return COAP_INVALID_MID);
  mid = coap_session_send_ping_lkd(session);
  coap_lock_unlock(session->context);
  return mid;
}

coap_mid_t
coap_session_send_ping_lkd(coap_session_t *session) {
  coap_pdu_t *ping = NULL;

  coap_lock_check_locked(session->context);
  if (session->state != COAP_SESSION_STATE_ESTABLISHED ||
      session->con_active)
    return COAP_INVALID_MID;
  if (COAP_PROTO_NOT_RELIABLE(session->proto)) {
    uint16_t mid = coap_new_message_id_lkd(session);
    ping = coap_pdu_init(COAP_MESSAGE_CON, 0, mid, 0);
  }
#if !COAP_DISABLE_TCP
  else {
    ping = coap_pdu_init(COAP_MESSAGE_CON, COAP_SIGNALING_CODE_PING, 0, 1);
  }
#endif /* !COAP_DISABLE_TCP */
  if (!ping)
    return COAP_INVALID_MID;
  return coap_send_internal(session, ping);
}

void
coap_session_connected(coap_session_t *session) {
  if (session->state != COAP_SESSION_STATE_ESTABLISHED) {
    coap_log_debug("***%s: session connected\n",
                   coap_session_str(session));
    if (session->state == COAP_SESSION_STATE_CSM) {
      coap_handle_event_lkd(session->context, COAP_EVENT_SESSION_CONNECTED, session);
      if (session->doing_first)
        session->doing_first = 0;
    }
  }

  session->state = COAP_SESSION_STATE_ESTABLISHED;
  session->partial_write = 0;

  if (session->proto==COAP_PROTO_DTLS) {
    session->tls_overhead = coap_dtls_get_overhead(session);
    if (session->tls_overhead >= session->mtu) {
      session->tls_overhead = session->mtu;
      coap_log_err("DTLS overhead exceeds MTU\n");
    }
  }

  while (session->delayqueue && session->state == COAP_SESSION_STATE_ESTABLISHED) {
    ssize_t bytes_written;
    coap_queue_t *q = session->delayqueue;
    if (q->pdu->type == COAP_MESSAGE_CON && COAP_PROTO_NOT_RELIABLE(session->proto)) {
      if (session->con_active >= COAP_NSTART(session))
        break;
      session->con_active++;
    }
    /* Take entry off the queue */
    session->delayqueue = q->next;
    q->next = NULL;

    coap_log_debug("** %s: mid=0x%04x: transmitted after delay\n",
                   coap_session_str(session), (int)q->pdu->mid);
    bytes_written = coap_session_send_pdu(session, q->pdu);
    if (q->pdu->type == COAP_MESSAGE_CON && COAP_PROTO_NOT_RELIABLE(session->proto)) {
      if (coap_wait_ack(session->context, session, q) >= 0)
        q = NULL;
    }
    if (COAP_PROTO_NOT_RELIABLE(session->proto)) {
      if (q)
        coap_delete_node_lkd(q);
      if (bytes_written < 0)
        break;
    } else if (q) {
      if (bytes_written <= 0 || (size_t)bytes_written < q->pdu->used_size + q->pdu->hdr_size) {
        q->next = session->delayqueue;
        session->delayqueue = q;
        if (bytes_written > 0)
          session->partial_write = (size_t)bytes_written;
        break;
      } else {
        coap_delete_node_lkd(q);
      }
    }
  }
}

#if COAP_MAX_LOGGING_LEVEL >= _COAP_LOG_DEBUG
static const char *
coap_nack_name(coap_nack_reason_t reason) {
  switch (reason) {
  case COAP_NACK_TOO_MANY_RETRIES:
    return "COAP_NACK_TOO_MANY_RETRIES";
  case COAP_NACK_NOT_DELIVERABLE:
    return "COAP_NACK_NOT_DELIVERABLE";
  case COAP_NACK_RST:
    return "COAP_NACK_RST";
  case COAP_NACK_TLS_FAILED:
    return "COAP_NACK_TLS_FAILED";
  case COAP_NACK_ICMP_ISSUE:
    return "COAP_NACK_ICMP_ISSUE";
  case COAP_NACK_BAD_RESPONSE:
    return "COAP_NACK_BAD_RESPONSE";
  case COAP_NACK_TLS_LAYER_FAILED:
    return "COAP_NACK_TLS_LAYER_FAILED";
  case COAP_NACK_WS_LAYER_FAILED:
    return "COAP_NACK_WS_LAYER_FAILED";
  case COAP_NACK_WS_FAILED:
    return "COAP_NACK_WS_FAILED";
  default:
    return "???";
  }
}
#endif /* COAP_MAX_LOGGING_LEVEL >= _COAP_LOG_DEBUG */

void
coap_handle_nack(coap_session_t *session,
                 coap_pdu_t *sent,
                 const coap_nack_reason_t reason,
                 const coap_mid_t mid) {
  if (session->context->nack_handler) {
    coap_bin_const_t token;

    if (sent) {
      coap_check_update_token(session, sent);
      token = sent->actual_token;
    }
    coap_lock_callback(session->context,
                       session->context->nack_handler(session, sent, reason, mid));
    if (sent) {
      coap_update_token(sent, token.length, token.s);
    }
  }
#if COAP_CLIENT_SUPPORT
  if (reason != COAP_NACK_ICMP_ISSUE) {
    session->doing_send_recv = 0;
  }
#endif /* COAP_CLIENT_SUPPORT */
}

COAP_API void
coap_session_disconnected(coap_session_t *session, coap_nack_reason_t reason) {
  coap_lock_lock(session->context, return);
  coap_session_disconnected_lkd(session, reason);
  coap_lock_unlock(session->context);
}

void
coap_session_disconnected_lkd(coap_session_t *session, coap_nack_reason_t reason) {
#if !COAP_DISABLE_TCP
  coap_session_state_t state = session->state;
#endif /* !COAP_DISABLE_TCP */
  coap_lg_xmit_t *lq, *ltmp;
#if COAP_SERVER_SUPPORT
  coap_lg_srcv_t *sq, *stmp;
#endif /* COAP_SERVER_SUPPORT */
#if COAP_CLIENT_SUPPORT
  coap_lg_crcv_t *cq, *etmp;
#endif /* COAP_CLIENT_SUPPORT */
  int sent_nack = 0;
  coap_queue_t *q;

  coap_lock_check_locked(session->context);
  q = session->context->sendqueue;

  while (q) {
    if (q->session == session) {
      /* Take the first one */
      coap_handle_nack(session, q->pdu, reason, q->id);
      sent_nack = 1;
      break;
    }
    q = q->next;
  }

  if (reason != COAP_NACK_ICMP_ISSUE) {
    while (session->delayqueue) {
      q = session->delayqueue;
      session->delayqueue = q->next;
      q->next = NULL;
      coap_log_debug("** %s: mid=0x%04x: not transmitted after disconnect\n",
                     coap_session_str(session), q->id);
      if (q->pdu->type == COAP_MESSAGE_CON) {
        coap_handle_nack(session, q->pdu, reason, q->id);
        sent_nack = 1;
      }

#if COAP_CLIENT_SUPPORT
      session->doing_send_recv = 0;
#endif /* COAP_CLIENT_SUPPORT */
      coap_delete_node_lkd(q);
    }
  }
#if COAP_CLIENT_SUPPORT
  if (!sent_nack && session->lg_crcv) {
    /* Take the first one */
    coap_handle_nack(session, &session->lg_crcv->pdu, reason, session->lg_crcv->pdu.mid);
    sent_nack = 1;
  }
#endif /* COAP_CLIENT_SUPPORT */
  if (!sent_nack) {
    /* Unable to determine which request disconnection was for */
    coap_handle_nack(session, NULL, reason, 0);
  }
  if (reason == COAP_NACK_ICMP_ISSUE) {
    coap_log_debug("***%s: session ICMP issue (%s)\n",
                   coap_session_str(session), coap_nack_name(reason));
    return;
  }
  coap_log_debug("***%s: session disconnected (%s)\n",
                 coap_session_str(session), coap_nack_name(reason));
#if COAP_SERVER_SUPPORT
  coap_delete_observers(session->context, session);
#endif /* COAP_SERVER_SUPPORT */

  if (session->proto == COAP_PROTO_UDP)
    session->state = COAP_SESSION_STATE_ESTABLISHED;
  else
    session->state = COAP_SESSION_STATE_NONE;

  session->con_active = 0;

  if (session->partial_pdu) {
    coap_delete_pdu(session->partial_pdu);
    session->partial_pdu = NULL;
  }
  session->partial_read = 0;

  /* Not done if nack handler called above */
  while (session->delayqueue) {
    q = session->delayqueue;
    session->delayqueue = q->next;
    q->next = NULL;
    coap_log_debug("** %s: mid=0x%04x: not transmitted after disconnect\n",
                   coap_session_str(session), q->id);
#if COAP_CLIENT_SUPPORT
    session->doing_send_recv = 0;
#endif /* COAP_CLIENT_SUPPORT */
    coap_delete_node_lkd(q);
  }

#if COAP_CLIENT_SUPPORT
  /* Need to do this before (D)TLS and socket is closed down */
  LL_FOREACH_SAFE(session->lg_crcv, cq, etmp) {
    LL_DELETE(session->lg_crcv, cq);
    coap_block_delete_lg_crcv(session, cq);
  }
#endif /* COAP_CLIENT_SUPPORT */
  LL_FOREACH_SAFE(session->lg_xmit, lq, ltmp) {
    LL_DELETE(session->lg_xmit, lq);
    coap_block_delete_lg_xmit(session, lq);
  }
#if COAP_SERVER_SUPPORT
  LL_FOREACH_SAFE(session->lg_srcv, sq, stmp) {
    LL_DELETE(session->lg_srcv, sq);
    coap_block_delete_lg_srcv(session, sq);
  }
#endif /* COAP_SERVER_SUPPORT */
  coap_cancel_session_messages(session->context, session, reason);

#if !COAP_DISABLE_TCP
  if (COAP_PROTO_RELIABLE(session->proto)) {
    if (coap_netif_available(session)) {
      coap_handle_event_lkd(session->context,
                            state == COAP_SESSION_STATE_CONNECTING ?
                            COAP_EVENT_TCP_FAILED : COAP_EVENT_TCP_CLOSED, session);
    }
    if (state != COAP_SESSION_STATE_NONE) {
      coap_handle_event_lkd(session->context,
                            state == COAP_SESSION_STATE_ESTABLISHED ?
                            COAP_EVENT_SESSION_CLOSED : COAP_EVENT_SESSION_FAILED, session);
    }
    if (session->doing_first)
      session->doing_first = 0;
  }
#endif /* !COAP_DISABLE_TCP */
  session->sock.lfunc[COAP_LAYER_SESSION].l_close(session);
}

#if COAP_SERVER_SUPPORT
static void
coap_make_addr_hash(coap_addr_hash_t *addr_hash, coap_proto_t proto,
                    const coap_addr_tuple_t *addr_info) {
  memset(addr_hash, 0, sizeof(coap_addr_hash_t));
  coap_address_copy(&addr_hash->remote, &addr_info->remote);
  addr_hash->lport = coap_address_get_port(&addr_info->local);
  addr_hash->proto = proto;
}

coap_session_t *
coap_endpoint_get_session(coap_endpoint_t *endpoint,
                          const coap_packet_t *packet, coap_tick_t now) {
  coap_session_t *session;
  coap_session_t *rtmp;
  unsigned int num_idle = 0;
  unsigned int num_hs = 0;
  coap_session_t *oldest = NULL;
  coap_session_t *oldest_hs = NULL;
  coap_addr_hash_t addr_hash;

  coap_make_addr_hash(&addr_hash, endpoint->proto, &packet->addr_info);
  SESSIONS_FIND(endpoint->sessions, addr_hash, session);
  if (session) {
    /* Maybe mcast or unicast IP address which is not in the hash */
    coap_address_copy(&session->addr_info.local, &packet->addr_info.local);
    session->ifindex = packet->ifindex;
    session->last_rx_tx = now;
    return session;
  }

#if COAP_CLIENT_SUPPORT
  if (coap_is_mcast(&packet->addr_info.local)) {
    /* Check if this a proxy client packet we sent on another socket */
    SESSIONS_ITER(endpoint->context->sessions, session, rtmp) {
      if (coap_address_equals(&session->addr_info.remote, &packet->addr_info.local) &&
          coap_address_get_port(&session->addr_info.local) ==
          coap_address_get_port(&packet->addr_info.remote)) {
        /* Drop looped back packet to stop recursion / confusion */
        return NULL;
      }
    }
  }
#endif /* COAP_CLIENT_SUPPORT */
  SESSIONS_ITER(endpoint->sessions, session, rtmp) {
    if (session->ref == 0 && session->delayqueue == NULL) {
      if (session->type == COAP_SESSION_TYPE_SERVER) {
        ++num_idle;
        if (oldest==NULL || session->last_rx_tx < oldest->last_rx_tx)
          oldest = session;

        if (session->state == COAP_SESSION_STATE_HANDSHAKE) {
          ++num_hs;
          /* See if this is a partial (D)TLS session set up
             which needs to be cleared down to prevent DOS */
          if ((session->last_rx_tx + COAP_PARTIAL_SESSION_TIMEOUT_TICKS) < now) {
            if (oldest_hs == NULL ||
                session->last_rx_tx < oldest_hs->last_rx_tx)
              oldest_hs = session;
          }
        }
      } else if (session->type == COAP_SESSION_TYPE_HELLO) {
        ++num_hs;
        /* See if this is a partial (D)TLS session set up for Client Hello
           which needs to be cleared down to prevent DOS */
        if ((session->last_rx_tx + COAP_PARTIAL_SESSION_TIMEOUT_TICKS) < now) {
          if (oldest_hs == NULL ||
              session->last_rx_tx < oldest_hs->last_rx_tx)
            oldest_hs = session;
        }
      }
    }
  }

  if (endpoint->context->max_idle_sessions > 0 &&
      num_idle >= endpoint->context->max_idle_sessions) {
    coap_handle_event_lkd(oldest->context, COAP_EVENT_SERVER_SESSION_DEL, oldest);
    coap_session_free(oldest);
  } else if (oldest_hs) {
    coap_log_warn("***%s: Incomplete session timed out\n",
                  coap_session_str(oldest_hs));
    coap_handle_event_lkd(oldest_hs->context, COAP_EVENT_SERVER_SESSION_DEL, oldest_hs);
    coap_session_free(oldest_hs);
  }

  if (num_hs > (endpoint->context->max_handshake_sessions ?
                endpoint->context->max_handshake_sessions :
                COAP_DEFAULT_MAX_HANDSHAKE_SESSIONS)) {
    /* Maxed out on number of sessions in (D)TLS negotiation state */
    coap_log_debug("Oustanding sessions in COAP_SESSION_STATE_HANDSHAKE too "
                   "large.  New request ignored\n");
    return NULL;
  }

  if (endpoint->proto == COAP_PROTO_DTLS) {
    /*
     * Need to check that this actually is a Client Hello before wasting
     * time allocating and then freeing off session.
     */

    /*
     * Generic header structure of the DTLS record layer.
     * typedef struct __attribute__((__packed__)) {
     *   uint8_t content_type;           content type of the included message
     *   uint16_t version;               Protocol version
     *   uint16_t epoch;                 counter for cipher state changes
     *   uint8_t sequence_number[6];     sequence number
     *   uint16_t length;                length of the following fragment
     *   uint8_t handshake;              If content_type == DTLS_CT_HANDSHAKE
     * } dtls_record_handshake_t;
     */
#define OFF_CONTENT_TYPE      0  /* offset of content_type in dtls_record_handshake_t */
#define DTLS_CT_ALERT        21  /* Content Type Alert */
#define DTLS_CT_HANDSHAKE    22  /* Content Type Handshake */
#define OFF_HANDSHAKE_TYPE   13  /* offset of handshake in dtls_record_handshake_t */
#define DTLS_HT_CLIENT_HELLO  1  /* Client Hello handshake type */
#define DTLS_CT_CID          25  /* Content Type Connection ID */
#define OFF_CID              11  /* offset of CID in dtls_record_handshake_t */
#define OFF_CID_DTLS13        1  /* offset of CID in DTLS1.3 Unified Header */

    const uint8_t *payload = (const uint8_t *)packet->payload;
    size_t length = packet->length;
    if (length < (OFF_HANDSHAKE_TYPE + 1)) {
      coap_log_debug("coap_dtls_hello: ContentType %d Short Packet (%zu < %d) dropped\n",
                     payload[OFF_CONTENT_TYPE], length,
                     OFF_HANDSHAKE_TYPE + 1);
      return NULL;
    }
    if ((payload[OFF_CONTENT_TYPE] & 0x30) == 0x30 ||
        payload[OFF_CONTENT_TYPE] == DTLS_CT_CID) {
      /* Client may have changed its IP address */
      int changed = 0;

      SESSIONS_ITER(endpoint->sessions, session, rtmp) {
        if (session->client_cid) {
          if ((session->is_dtls13 && (payload[OFF_CONTENT_TYPE] & 0x30) == 0x30 &&
               memcmp(session->client_cid->s, &payload[OFF_CID_DTLS13],
                      session->client_cid->length) == 0) ||
              (!session->is_dtls13 && payload[OFF_CONTENT_TYPE] == DTLS_CT_CID &&
               memcmp(session->client_cid->s, &payload[OFF_CID],
                      session->client_cid->length) == 0)) {
            /* Updating IP address */
            coap_log_info("***%s: CID: Old Client Session\n", coap_session_str(session));
            SESSIONS_DELETE(endpoint->sessions, session);
            session->addr_info = packet->addr_info;
            memcpy(&session->addr_hash, &addr_hash, sizeof(session->addr_hash));
            SESSIONS_ADD(endpoint->sessions, session);
            coap_log_info("***%s: CID: New Client Session\n", coap_session_str(session));
            return session;
          }
        }
      }
      if (!changed) {
        coap_log_debug("coap_dtls_hello: ContentType Connection-IS dropped\n");
        return NULL;
      }
    } else if (payload[OFF_CONTENT_TYPE] != DTLS_CT_HANDSHAKE ||
               payload[OFF_HANDSHAKE_TYPE] != DTLS_HT_CLIENT_HELLO) {
      /* only log if not a late alert */
      if (payload[OFF_CONTENT_TYPE] != DTLS_CT_ALERT)
        coap_log_debug("coap_dtls_hello: ContentType %d Handshake %d dropped\n",
                       payload[OFF_CONTENT_TYPE],
                       payload[OFF_HANDSHAKE_TYPE]);
      return NULL;
    }
  }

  session = coap_make_session(endpoint->proto, COAP_SESSION_TYPE_SERVER,
                              &addr_hash, &packet->addr_info.local,
                              &packet->addr_info.remote,
                              packet->ifindex, endpoint->context, endpoint);
  if (session) {
    session->last_rx_tx = now;
    memcpy(session->sock.lfunc, endpoint->sock.lfunc,
           sizeof(session->sock.lfunc));
    if (endpoint->proto == COAP_PROTO_UDP)
      session->state = COAP_SESSION_STATE_ESTABLISHED;
    else if (endpoint->proto == COAP_PROTO_DTLS) {
      session->type = COAP_SESSION_TYPE_HELLO;
    }
    SESSIONS_ADD(endpoint->sessions, session);
    coap_log_debug("***%s: session %p: new incoming session\n",
                   coap_session_str(session), (void *)session);
    coap_handle_event_lkd(session->context, COAP_EVENT_SERVER_SESSION_NEW, session);
  }
  return session;
}

coap_session_t *
coap_session_new_dtls_session(coap_session_t *session,
                              coap_tick_t now) {
  if (session) {
    session->last_rx_tx = now;
    session->type = COAP_SESSION_TYPE_SERVER;
    coap_dtls_establish(session);
  }
  return session;
}
#endif /* COAP_SERVER_SUPPORT */

#if COAP_CLIENT_SUPPORT
static coap_session_t *
coap_session_create_client(coap_context_t *ctx,
                           const coap_address_t *local_if,
                           const coap_address_t *server,
                           coap_proto_t proto) {
  coap_session_t *session = NULL;
  int default_port = COAP_DEFAULT_PORT;

  assert(server);

  switch (proto) {
  case COAP_PROTO_UDP:
    default_port = COAP_DEFAULT_PORT;
    break;
  case COAP_PROTO_DTLS:
    if (!coap_dtls_is_supported()) {
      coap_log_crit("coap_new_client_session*: DTLS not supported\n");
      return NULL;
    }
    default_port = COAPS_DEFAULT_PORT;
    break;
  case COAP_PROTO_TCP:
    if (!coap_tcp_is_supported()) {
      coap_log_crit("coap_new_client_session*: TCP not supported\n");
      return NULL;
    }
    default_port = COAP_DEFAULT_PORT;
    break;
  case COAP_PROTO_TLS:
    if (!coap_tls_is_supported()) {
      coap_log_crit("coap_new_client_session*: TLS not supported\n");
      return NULL;
    }
    default_port = COAPS_DEFAULT_PORT;
    break;
  case COAP_PROTO_WS:
    if (!coap_ws_is_supported()) {
      coap_log_crit("coap_new_client_session*: WS not supported\n");
      return NULL;
    }
    default_port = 80;
    break;
  case COAP_PROTO_WSS:
    if (!coap_wss_is_supported()) {
      coap_log_crit("coap_new_client_session*: WSS not supported\n");
      return NULL;
    }
    default_port = 443;
    break;
  case COAP_PROTO_NONE:
  case COAP_PROTO_LAST:
  default:
    assert(0);
    return NULL;
  }
  session = coap_make_session(proto, COAP_SESSION_TYPE_CLIENT, NULL,
                              local_if, server, 0, ctx, NULL);
  if (!session)
    goto error;

  coap_session_reference_lkd(session);
  session->sock.session = session;
  memcpy(&session->sock.lfunc, coap_layers_coap[proto],
         sizeof(session->sock.lfunc));

  if (COAP_PROTO_NOT_RELIABLE(proto)) {
    coap_session_t *s, *rtmp;
    if (!coap_netif_dgrm_connect(session, local_if, server, default_port)) {
      goto error;
    }
    /* Check that this is not a duplicate 4-tuple */
    SESSIONS_ITER_SAFE(ctx->sessions, s, rtmp) {
      if (COAP_PROTO_NOT_RELIABLE(s->proto) &&
          coap_address_equals(&session->addr_info.local,
                              &s->addr_info.local) &&
          coap_address_equals(&session->addr_info.remote,
                              &s->addr_info.remote)) {
        coap_log_warn("***%s: session %p: duplicate - already exists\n",
                      coap_session_str(session), (void *)session);
        goto error;
      }
    }
#ifdef WITH_CONTIKI
    session->sock.context = ctx;
#endif /* WITH_CONTIKI */
#if !COAP_DISABLE_TCP
  } else if (COAP_PROTO_RELIABLE(proto)) {
    if (!coap_netif_strm_connect1(session, local_if, server, default_port)) {
      goto error;
    }
#endif /* !COAP_DISABLE_TCP */
  }

#ifdef COAP_EPOLL_SUPPORT
  session->sock.session = session;
  coap_epoll_ctl_add(&session->sock,
                     EPOLLIN |
                     ((session->sock.flags & COAP_SOCKET_WANT_CONNECT) ?
                      EPOLLOUT : 0),
                     __func__);
#endif /* COAP_EPOLL_SUPPORT */

  session->sock.flags |= COAP_SOCKET_NOT_EMPTY | COAP_SOCKET_WANT_READ;
  if (local_if)
    session->sock.flags |= COAP_SOCKET_BOUND;
#if COAP_SERVER_SUPPORT
  if (ctx->proxy_uri_resource)
    session->proxy_session = 1;
#endif /* COAP_SERVER_SUPPORT */
  SESSIONS_ADD(ctx->sessions, session);
  return session;

error:
  /*
   * Need to add in the session as coap_session_release_lkd()
   * will call SESSIONS_DELETE in coap_session_free().
   */
  if (session)
    SESSIONS_ADD(ctx->sessions, session);
  coap_session_release_lkd(session);
  return NULL;
}

static void
coap_session_check_connect(coap_session_t *session) {
  if (COAP_PROTO_NOT_RELIABLE(session->proto)) {
    session->sock.lfunc[COAP_LAYER_SESSION].l_establish(session);
  }
#if !COAP_DISABLE_TCP
  if (COAP_PROTO_RELIABLE(session->proto)) {
    if (session->sock.flags & COAP_SOCKET_WANT_CONNECT) {
      session->state = COAP_SESSION_STATE_CONNECTING;
      if (session->state != COAP_SESSION_STATE_ESTABLISHED &&
          session->state != COAP_SESSION_STATE_NONE &&
          session->type == COAP_SESSION_TYPE_CLIENT) {
        session->doing_first = 1;
      }
    } else {
      /* Initial connect worked immediately */
      session->sock.lfunc[COAP_LAYER_SESSION].l_establish(session);
    }
  }
#endif /* !COAP_DISABLE_TCP */
  coap_ticks(&session->last_rx_tx);
}
#endif /* COAP_CLIENT_SUPPORT */

void
coap_session_establish(coap_session_t *session) {
  if (COAP_PROTO_NOT_RELIABLE(session->proto))
    coap_session_connected(session);
#if !COAP_DISABLE_TCP
  if (COAP_PROTO_RELIABLE(session->proto))
    coap_session_send_csm(session);
#endif /* !COAP_DISABLE_TCP */
}

#if COAP_CLIENT_SUPPORT
COAP_API coap_session_t *
coap_new_client_session(coap_context_t *ctx,
                        const coap_address_t *local_if,
                        const coap_address_t *server,
                        coap_proto_t proto) {
  coap_session_t *session;

  coap_lock_lock(ctx, return NULL);
  session = coap_new_client_session_lkd(ctx, local_if, server, proto);
  coap_lock_unlock(ctx);
  return session;
}

coap_session_t *
coap_new_client_session_lkd(coap_context_t *ctx,
                            const coap_address_t *local_if,
                            const coap_address_t *server,
                            coap_proto_t proto) {
  coap_session_t *session;

  coap_lock_check_locked(ctx);
  session = coap_session_create_client(ctx, local_if, server,
                                       proto);
  if (session) {
    coap_log_debug("***%s: session %p: created outgoing session\n",
                   coap_session_str(session), (void *)session);
    coap_session_check_connect(session);
  }
  return session;
}

COAP_API coap_session_t *
coap_new_client_session_psk(coap_context_t *ctx,
                            const coap_address_t *local_if,
                            const coap_address_t *server,
                            coap_proto_t proto, const char *identity,
                            const uint8_t *key, unsigned key_len) {
  coap_session_t *session;

  coap_lock_lock(ctx, return NULL);
  session = coap_new_client_session_psk_lkd(ctx, local_if, server, proto, identity, key, key_len);
  coap_lock_unlock(ctx);
  return session;
}

coap_session_t *
coap_new_client_session_psk_lkd(coap_context_t *ctx,
                                const coap_address_t *local_if,
                                const coap_address_t *server,
                                coap_proto_t proto, const char *identity,
                                const uint8_t *key, unsigned key_len) {
  coap_dtls_cpsk_t setup_data;

  coap_lock_check_locked(ctx);
  memset(&setup_data, 0, sizeof(setup_data));
  setup_data.version = COAP_DTLS_CPSK_SETUP_VERSION;

  if (identity) {
    setup_data.psk_info.identity.s = (const uint8_t *)identity;
    setup_data.psk_info.identity.length = strlen(identity);
  }

  if (key && key_len > 0) {
    setup_data.psk_info.key.s = key;
    setup_data.psk_info.key.length = key_len;
  }

  return coap_new_client_session_psk2_lkd(ctx, local_if, server,
                                          proto, &setup_data);
}

/*
 * Check the validity of the SNI to send to the server.
 *
 * https://datatracker.ietf.org/doc/html/rfc6066#section-3
 *  Literal IPv4 and IPv6 addresses are not permitted in "HostName".
 */
static void
coap_sanitize_client_sni(char **client_sni) {
  char *cp;

  if (*client_sni == NULL)
    return;

  cp = *client_sni;
  switch (*cp) {
  case '0':
  case '1':
  case '2':
  case '3':
  case '4':
  case '5':
  case '6':
  case '7':
  case '8':
  case '9':
  case 'a':
  case 'b':
  case 'c':
  case 'd':
  case 'e':
  case 'f':
  case 'A':
  case 'B':
  case 'C':
  case 'D':
  case 'E':
  case 'F':
  case ':':
    break;
  case '\000':
    /* Empty entry invalid */
    *client_sni = NULL;
    return;
  default:
    /* Does not start with a hex digit or : - not literal IP. */
    return;
  }
  /* Check for IPv4 */
  while (*cp) {
    switch (*cp) {
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
    case '.':
      break;
    default:
      /* Not of format nnn.nnn.nnn.nnn. Could be IPv6 */
      goto check_ipv6;
    }
    cp++;
  }
  /* IPv4 address - not allowed. */
  *client_sni = NULL;
  return;

check_ipv6:
  /* Check for IPv6 */
  cp = *client_sni;
  while (*cp) {
    switch (*cp) {
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
    case 'a':
    case 'b':
    case 'c':
    case 'd':
    case 'e':
    case 'f':
    case 'A':
    case 'B':
    case 'C':
    case 'D':
    case 'E':
    case 'F':
    case ':':
      break;
    case '%':
      /* Start of i/f specification,  Previous is IPv6 */
      *client_sni = NULL;
      return;
    default:
      /* Not of format xx:xx::xx. */
      return;
    }
    cp++;
  }
  *client_sni = NULL;
  return;
}

COAP_API coap_session_t *
coap_new_client_session_psk2(coap_context_t *ctx,
                             const coap_address_t *local_if,
                             const coap_address_t *server,
                             coap_proto_t proto,
                             coap_dtls_cpsk_t *setup_data) {
  coap_session_t *session;

  coap_lock_lock(ctx, return NULL);
  session = coap_new_client_session_psk2_lkd(ctx, local_if, server, proto, setup_data);
  coap_lock_unlock(ctx);
  return session;
}

coap_session_t *
coap_new_client_session_psk2_lkd(coap_context_t *ctx,
                                 const coap_address_t *local_if,
                                 const coap_address_t *server,
                                 coap_proto_t proto,
                                 coap_dtls_cpsk_t *setup_data) {
  coap_session_t *session;

  coap_lock_check_locked(ctx);
  session = coap_session_create_client(ctx, local_if, server, proto);

  if (!session || !setup_data)
    return NULL;

  session->cpsk_setup_data = *setup_data;
  if (setup_data->psk_info.identity.s) {
    session->psk_identity =
        coap_new_bin_const(setup_data->psk_info.identity.s,
                           setup_data->psk_info.identity.length);
    if (!session->psk_identity) {
      coap_log_warn("Cannot store session Identity (PSK)\n");
      coap_session_release_lkd(session);
      return NULL;
    }
  } else if (coap_dtls_is_supported() || coap_tls_is_supported()) {
    coap_log_warn("Identity (PSK) not defined\n");
    coap_session_release_lkd(session);
    return NULL;
  }

  if (setup_data->psk_info.key.s && setup_data->psk_info.key.length > 0) {
    session->psk_key = coap_new_bin_const(setup_data->psk_info.key.s,
                                          setup_data->psk_info.key.length);
    if (!session->psk_key) {
      coap_log_warn("Cannot store session pre-shared key (PSK)\n");
      coap_session_release_lkd(session);
      return NULL;
    }
  } else if (coap_dtls_is_supported() || coap_tls_is_supported()) {
    coap_log_warn("Pre-shared key (PSK) not defined\n");
    coap_session_release_lkd(session);
    return NULL;
  }

  coap_sanitize_client_sni(&session->cpsk_setup_data.client_sni);

  if (coap_dtls_is_supported() || coap_tls_is_supported()) {
    if (!coap_dtls_context_set_cpsk(ctx, &session->cpsk_setup_data)) {
      coap_session_release_lkd(session);
      return NULL;
    }
  }
  coap_log_debug("***%s: new outgoing session\n",
                 coap_session_str(session));
  coap_session_check_connect(session);
  return session;
}
#endif /* COAP_CLIENT_SUPPORT */

int
coap_session_refresh_psk_hint(coap_session_t *session,
                              const coap_bin_const_t *psk_hint
                             ) {
  /* We may be refreshing the hint with the same hint */
  coap_bin_const_t *old_psk_hint = session->psk_hint;

  if (psk_hint && psk_hint->s) {
    if (session->psk_hint) {
      if (coap_binary_equal(session->psk_hint, psk_hint))
        return 1;
    }
    session->psk_hint = coap_new_bin_const(psk_hint->s,
                                           psk_hint->length);
    if (!session->psk_hint) {
      coap_log_err("No memory to store identity hint (PSK)\n");
      if (old_psk_hint)
        coap_delete_bin_const(old_psk_hint);
      return 0;
    }
  } else {
    session->psk_hint = NULL;
  }
  if (old_psk_hint)
    coap_delete_bin_const(old_psk_hint);

  return 1;
}

int
coap_session_refresh_psk_key(coap_session_t *session,
                             const coap_bin_const_t *psk_key
                            ) {
  /* We may be refreshing the key with the same key */
  coap_bin_const_t *old_psk_key = session->psk_key;

  if (psk_key && psk_key->s) {
    if (session->psk_key) {
      if (coap_binary_equal(session->psk_key, psk_key))
        return 1;
    }
    session->psk_key = coap_new_bin_const(psk_key->s, psk_key->length);
    if (!session->psk_key) {
      coap_log_err("No memory to store pre-shared key (PSK)\n");
      if (old_psk_key)
        coap_delete_bin_const(old_psk_key);
      return 0;
    }
  } else {
    session->psk_key = NULL;
  }
  if (old_psk_key)
    coap_delete_bin_const(old_psk_key);

  return 1;
}

int
coap_session_refresh_psk_identity(coap_session_t *session,
                                  const coap_bin_const_t *psk_identity
                                 ) {
  /* We may be refreshing the identity with the same identity */
  coap_bin_const_t *old_psk_identity = session->psk_identity;

  if (psk_identity && psk_identity->s) {
    if (session->psk_identity) {
      if (coap_binary_equal(session->psk_identity, psk_identity))
        return 1;
    }
    session->psk_identity = coap_new_bin_const(psk_identity->s,
                                               psk_identity->length);
    if (!session->psk_identity) {
      coap_log_err("No memory to store pre-shared key identity (PSK)\n");
      if (old_psk_identity)
        coap_delete_bin_const(old_psk_identity);
      return 0;
    }
  } else {
    session->psk_identity = NULL;
  }
  if (old_psk_identity)
    coap_delete_bin_const(old_psk_identity);

  return 1;
}

#if COAP_SERVER_SUPPORT
const coap_bin_const_t *
coap_session_get_psk_hint(const coap_session_t *session) {
  if (session)
    return session->psk_hint;
  return NULL;
}
#endif /* COAP_SERVER_SUPPORT */

const coap_bin_const_t *
coap_session_get_psk_identity(const coap_session_t *session) {
  const coap_bin_const_t *psk_identity = NULL;
  if (session) {
    psk_identity = session->psk_identity;
    if (psk_identity == NULL) {
      psk_identity = &session->cpsk_setup_data.psk_info.identity;
    }
  }
  return psk_identity;
}

const coap_bin_const_t *
coap_session_get_psk_key(const coap_session_t *session) {
  if (session)
    return session->psk_key;
  return NULL;
}

#if COAP_CLIENT_SUPPORT
COAP_API coap_session_t *
coap_new_client_session_pki(coap_context_t *ctx,
                            const coap_address_t *local_if,
                            const coap_address_t *server,
                            coap_proto_t proto,
                            coap_dtls_pki_t *setup_data) {
  coap_session_t *session;

  coap_lock_lock(ctx, return NULL);
  session = coap_new_client_session_pki_lkd(ctx, local_if, server, proto, setup_data);
  coap_lock_unlock(ctx);
  return session;
}

coap_session_t *
coap_new_client_session_pki_lkd(coap_context_t *ctx,
                                const coap_address_t *local_if,
                                const coap_address_t *server,
                                coap_proto_t proto,
                                coap_dtls_pki_t *setup_data) {
  coap_session_t *session;
  coap_dtls_pki_t l_setup_data;

  if (!setup_data)
    return NULL;
  if (setup_data->version != COAP_DTLS_PKI_SETUP_VERSION) {
    coap_log_err("coap_new_client_session_pki: Wrong version of setup_data\n");
    return NULL;
  }

  coap_lock_check_locked(ctx);
  l_setup_data = *setup_data;
  coap_sanitize_client_sni(&l_setup_data.client_sni);

  session = coap_session_create_client(ctx, local_if, server, proto);

  if (!session) {
    return NULL;
  }

  if (coap_dtls_is_supported() || coap_tls_is_supported()) {
    /* we know that setup_data is not NULL */
    if (!coap_dtls_context_set_pki(ctx, &l_setup_data, COAP_DTLS_ROLE_CLIENT)) {
      coap_session_release_lkd(session);
      return NULL;
    }
  }
  coap_log_debug("***%s: new outgoing session\n",
                 coap_session_str(session));
  coap_session_check_connect(session);
  return session;
}
#endif /* ! COAP_CLIENT_SUPPORT */

#if COAP_SERVER_SUPPORT
#if !COAP_DISABLE_TCP
coap_session_t *
coap_new_server_session(coap_context_t *ctx, coap_endpoint_t *ep, void *extra) {
  coap_session_t *session;
  session = coap_make_session(ep->proto, COAP_SESSION_TYPE_SERVER,
                              NULL, NULL, NULL, 0, ctx, ep);
  if (!session)
    goto error;

  memcpy(session->sock.lfunc, ep->sock.lfunc, sizeof(session->sock.lfunc));
  if (!coap_netif_strm_accept(ep, session, extra))
    goto error;

  coap_make_addr_hash(&session->addr_hash, session->proto, &session->addr_info);

#ifdef COAP_EPOLL_SUPPORT
  session->sock.session = session;
  coap_epoll_ctl_add(&session->sock,
                     EPOLLIN,
                     __func__);
#endif /* COAP_EPOLL_SUPPORT */
  SESSIONS_ADD(ep->sessions, session);
  if (session) {
    coap_log_debug("***%s: session %p: new incoming session\n",
                   coap_session_str(session), (void *)session);
    coap_handle_event_lkd(session->context, COAP_EVENT_TCP_CONNECTED, session);
    coap_handle_event_lkd(session->context, COAP_EVENT_SERVER_SESSION_NEW, session);
    session->state = COAP_SESSION_STATE_CONNECTING;
    session->sock.lfunc[COAP_LAYER_SESSION].l_establish(session);
  }
  return session;

error:
  /*
   * Need to add in the session as coap_session_release_lkd()
   * will call SESSIONS_DELETE in coap_session_free().
   */
  if (session) {
    SESSIONS_ADD(ep->sessions, session);
    coap_session_free(session);
  }
  return NULL;
}
#endif /* !COAP_DISABLE_TCP */
#endif /* COAP_SERVER_SUPPORT */

void
coap_session_init_token(coap_session_t *session, size_t len,
                        const uint8_t *data) {
  session->tx_token = coap_decode_var_bytes8(data, len);
  /*
   * Decrement as when first used by coap_session_new_token() it will
   * get incremented
   */
  session->tx_token--;
}

void
coap_session_new_token(coap_session_t *session, size_t *len,
                       uint8_t *data) {
  *len = coap_encode_var_safe8(data,
                               sizeof(session->tx_token), ++session->tx_token);
}

COAP_API uint16_t
coap_new_message_id(coap_session_t *session) {
  uint16_t mid;

  coap_lock_lock(session->context, return 0);
  mid = coap_new_message_id_lkd(session);
  coap_lock_unlock(session->context);
  return mid;
}

uint16_t
coap_new_message_id_lkd(coap_session_t *session) {
  coap_lock_check_locked(session->context);
  if (COAP_PROTO_NOT_RELIABLE(session->proto))
    return ++session->tx_mid;
  /* TCP/TLS have no notion of mid */
  return 0;
}

const coap_address_t *
coap_session_get_addr_remote(const coap_session_t *session) {
  if (session)
    return &session->addr_info.remote;
  return NULL;
}

const coap_address_t *
coap_session_get_addr_local(const coap_session_t *session) {
  if (session)
    return &session->addr_info.local;
  return NULL;
}

const coap_address_t *
coap_session_get_addr_mcast(const coap_session_t *session) {
#if COAP_CLIENT_SUPPORT
  if (session && session->type == COAP_SESSION_TYPE_CLIENT &&
      session->sock.flags & COAP_SOCKET_MULTICAST)
    return &session->sock.mcast_addr;
#else /* ! COAP_CLIENT_SUPPORT */
  (void)session;
#endif /* ! COAP_CLIENT_SUPPORT */
  return NULL;
}

coap_context_t *
coap_session_get_context(const coap_session_t *session) {
  if (session)
    return session->context;
  return NULL;
}

coap_proto_t
coap_session_get_proto(const coap_session_t *session) {
  if (session)
    return session->proto;
  return 0;
}

coap_session_type_t
coap_session_get_type(const coap_session_t *session) {
  if (session)
    return session->type;
  return 0;
}

COAP_API int
coap_session_set_type_client(coap_session_t *session) {
  int ret;

  coap_lock_lock(session->context, return 0);
  ret = coap_session_set_type_client_lkd(session);
  coap_lock_unlock(session->context);
  return ret;
}

int
coap_session_set_type_client_lkd(coap_session_t *session) {
#if COAP_SERVER_SUPPORT
  if (session && session->type == COAP_SESSION_TYPE_SERVER) {
    coap_session_reference_lkd(session);
    session->type = COAP_SESSION_TYPE_CLIENT;
    return 1;
  }
#else /* ! COAP_SERVER_SUPPORT */
  (void)session;
#endif /* ! COAP_SERVER_SUPPORT */
  return 0;
}

coap_session_state_t
coap_session_get_state(const coap_session_t *session) {
  if (session)
    return session->state;
  return 0;
}

int
coap_session_get_ifindex(const coap_session_t *session) {
  if (session)
    return session->ifindex;
  return -1;
}

void *
coap_session_get_tls(const coap_session_t *session,
                     coap_tls_library_t *tls_lib) {
  if (session)
    return coap_dtls_get_tls(session, tls_lib);
  return NULL;
}

static const char *
coap_proto_name(coap_proto_t proto) {
  switch (proto) {
  case COAP_PROTO_UDP:
    return "UDP ";
  case COAP_PROTO_DTLS:
    return "DTLS";
  case COAP_PROTO_TCP:
    return "TCP ";
  case COAP_PROTO_TLS:
    return "TLS ";
  case COAP_PROTO_WS:
    return "WS  ";
  case COAP_PROTO_WSS:
    return "WSS ";
  case COAP_PROTO_NONE:
  case COAP_PROTO_LAST:
  default:
    return "????" ;
    break;
  }
  return NULL;
}

#if COAP_SERVER_SUPPORT
COAP_API coap_endpoint_t *
coap_new_endpoint(coap_context_t *context, const coap_address_t *listen_addr, coap_proto_t proto) {
  coap_endpoint_t *endpoint;

  coap_lock_lock(context, return NULL);
  endpoint = coap_new_endpoint_lkd(context, listen_addr, proto);
  coap_lock_unlock(context);
  return endpoint;
}

coap_endpoint_t *
coap_new_endpoint_lkd(coap_context_t *context, const coap_address_t *listen_addr,
                      coap_proto_t proto) {
  coap_endpoint_t *ep = NULL;

  assert(context);
  assert(listen_addr);
  assert(proto != COAP_PROTO_NONE);

  coap_lock_check_locked(context);

  if (proto == COAP_PROTO_DTLS && !coap_dtls_is_supported()) {
    coap_log_crit("coap_new_endpoint: DTLS not supported\n");
    goto error;
  }

  if (proto == COAP_PROTO_TLS && !coap_tls_is_supported()) {
    coap_log_crit("coap_new_endpoint: TLS not supported\n");
    goto error;
  }

  if (proto == COAP_PROTO_TCP && !coap_tcp_is_supported()) {
    coap_log_crit("coap_new_endpoint: TCP not supported\n");
    goto error;
  }

  if (proto == COAP_PROTO_WS && !coap_ws_is_supported()) {
    coap_log_crit("coap_new_endpoint: WS not supported\n");
    goto error;
  }

  if (proto == COAP_PROTO_WSS && !coap_wss_is_supported()) {
    coap_log_crit("coap_new_endpoint: WSS not supported\n");
    goto error;
  }

  if (proto == COAP_PROTO_DTLS || proto == COAP_PROTO_TLS ||
      proto == COAP_PROTO_WSS) {
    if (!coap_dtls_context_check_keys_enabled(context)) {
      coap_log_info("coap_new_endpoint: one of coap_context_set_psk() or "
                    "coap_context_set_pki() not called\n");
      goto error;
    }
  }

  ep = coap_malloc_endpoint();
  if (!ep) {
    coap_log_warn("coap_new_endpoint: malloc");
    goto error;
  }

  memset(ep, 0, sizeof(coap_endpoint_t));
  ep->context = context;
  ep->proto = proto;
  ep->sock.endpoint = ep;
  assert(proto < COAP_PROTO_LAST);
  memcpy(&ep->sock.lfunc, coap_layers_coap[proto], sizeof(ep->sock.lfunc));

  if (COAP_PROTO_NOT_RELIABLE(proto)) {
    if (!coap_netif_dgrm_listen(ep, listen_addr))
      goto error;
#ifdef WITH_CONTIKI
    ep->sock.context = context;
#endif /* WITH_CONTIKI */
#if !COAP_DISABLE_TCP
  } else if (COAP_PROTO_RELIABLE(proto)) {
    if (!coap_netif_strm_listen(ep, listen_addr))
      goto error;
#endif /* !COAP_DISABLE_TCP */
  } else {
    coap_log_crit("coap_new_endpoint: protocol not supported\n");
    goto error;
  }

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

    if (coap_print_addr(&ep->bind_addr, addr_str, INET6_ADDRSTRLEN + 8)) {
      coap_log_debug("created %s endpoint %s\n", coap_proto_name(ep->proto),
                     addr_str);
    }
  }

  ep->default_mtu = COAP_DEFAULT_MTU;

#ifdef COAP_EPOLL_SUPPORT
  ep->sock.endpoint = ep;
  coap_epoll_ctl_add(&ep->sock,
                     EPOLLIN,
                     __func__);
#endif /* COAP_EPOLL_SUPPORT */

  LL_PREPEND(context->endpoint, ep);
  return ep;

error:
  coap_free_endpoint_lkd(ep);
  return NULL;
}

void
coap_endpoint_set_default_mtu(coap_endpoint_t *ep, unsigned mtu) {
  ep->default_mtu = (uint16_t)mtu;
}

COAP_API void
coap_free_endpoint(coap_endpoint_t *ep) {
  if (ep) {
    coap_context_t *context = ep->context;
    if (context) {
      coap_lock_lock(context, return);
    }
    coap_free_endpoint_lkd(ep);
    if (context) {
      coap_lock_unlock(context);
    }
  }
}

void
coap_free_endpoint_lkd(coap_endpoint_t *ep) {
  if (ep) {
    coap_session_t *session, *rtmp;

    if (ep->context) {
      /* If fully allocated and inserted */
      coap_lock_check_locked(ep->context);
      SESSIONS_ITER_SAFE(ep->sessions, session, rtmp) {
        assert(session->ref == 0);
        if (session->ref == 0) {
          coap_handle_event_lkd(ep->context, COAP_EVENT_SERVER_SESSION_DEL, session);
          coap_session_free(session);
        }
      }
      if (coap_netif_available_ep(ep)) {
        /*
         * ep->sock.endpoint is set in coap_new_endpoint().
         * ep->sock.session is never set.
         *
         * session->sock.session is set for both clients and servers (when a
         * new session is accepted), but does not affect the endpoint.
         *
         * So, it is safe to call coap_netif_close_ep() after all the sessions
         * have been freed above as we are only working with the endpoint sock.
         */
#ifdef COAP_EPOLL_SUPPORT
        assert(ep->sock.session == NULL);
#endif /* COAP_EPOLL_SUPPORT */
        coap_netif_close_ep(ep);
      }

      if (ep->context->endpoint) {
        LL_DELETE(ep->context->endpoint, ep);
      }
    }
    coap_mfree_endpoint(ep);
  }
}
#endif /* COAP_SERVER_SUPPORT */

coap_session_t *
coap_session_get_by_peer(const coap_context_t *ctx,
                         const coap_address_t *remote_addr,
                         int ifindex) {
  coap_session_t *s, *rtmp;
#if COAP_CLIENT_SUPPORT
  SESSIONS_ITER(ctx->sessions, s, rtmp) {
    if (s->ifindex == ifindex) {
      if (s->sock.flags & COAP_SOCKET_MULTICAST) {
        if (coap_address_equals(&s->sock.mcast_addr, remote_addr))
          return s;
      } else if (coap_address_equals(&s->addr_info.remote, remote_addr))
        return s;
    }
  }
#endif /* COAP_CLIENT_SUPPORT */
#if COAP_SERVER_SUPPORT
  coap_endpoint_t *ep;

  LL_FOREACH(ctx->endpoint, ep) {
    SESSIONS_ITER(ep->sessions, s, rtmp) {
      if (s->ifindex == ifindex && coap_address_equals(&s->addr_info.remote,
                                                       remote_addr))
        return s;
    }
  }
#endif /* COAP_SERVER_SUPPORT */
  return NULL;
}

#ifndef INET6_ADDRSTRLEN
#define INET6_ADDRSTRLEN 46
#endif
const char *
coap_session_str(const coap_session_t *session) {
  static char szSession[2 * (INET6_ADDRSTRLEN + 8) + 24];
  char *p = szSession, *end = szSession + sizeof(szSession);
  if (coap_print_addr(&session->addr_info.local,
                      (unsigned char *)p, end - p) > 0)
    p += strlen(p);
  if (p + 6 < end) {
    strcpy(p, " <-> ");
    p += 5;
  }
  if (p + 1 < end) {
    if (coap_print_addr(&session->addr_info.remote,
                        (unsigned char *)p, end - p) > 0)
      p += strlen(p);
  }
  if (session->ifindex > 0 && p + 1 < end)
    p += snprintf(p, end - p, " (if%d)", session->ifindex);
  if (p + 6 < end) {
    strcpy(p, " ");
    p++;
    strcpy(p, coap_proto_name(session->proto));
  }

  return szSession;
}

#if COAP_SERVER_SUPPORT
const char *
coap_endpoint_str(const coap_endpoint_t *endpoint) {
  static char szEndpoint[128];
  char *p = szEndpoint, *end = szEndpoint + sizeof(szEndpoint);
  if (coap_print_addr(&endpoint->bind_addr, (unsigned char *)p, end - p) > 0)
    p += strlen(p);
  if (p + 6 < end) {
    if (endpoint->proto == COAP_PROTO_UDP) {
      strcpy(p, " UDP");
    } else if (endpoint->proto == COAP_PROTO_DTLS) {
      strcpy(p, " DTLS");
    } else {
      strcpy(p, " NONE");
    }
  }

  return szEndpoint;
}
#endif /* COAP_SERVER_SUPPORT */
#if COAP_CLIENT_SUPPORT
void
coap_session_set_no_observe_cancel(coap_session_t *session) {
  session->no_observe_cancel = 1;
}
#endif /* COAP_CLIENT_SUPPORT */
#endif  /* COAP_SESSION_C_ */