coap_proxy.c

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/* coap_proxy.c -- helper functions for proxy handling
 *
 * Copyright (C) 2024-2025 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.
 */
 
#include "coap3/coap_libcoap_build.h"
 
#if COAP_PROXY_SUPPORT
#include <stdio.h>
 
#if COAP_CLIENT_SUPPORT == 0
#error For Proxy support, COAP_CLIENT_SUPPORT must be set
#endif
#if COAP_SERVER_SUPPORT == 0
#error For Proxy support, COAP_SERVER_SUPPORT must be set
#endif
 
#ifdef _WIN32
#define strcasecmp _stricmp
#define strncasecmp _strnicmp
#endif
 
int
coap_proxy_is_supported(void) {
  return 1;
}
 
static void
coap_proxy_del_req(coap_proxy_list_t *proxy_entry,  coap_proxy_req_t *proxy_req) {
  size_t i;
 
  coap_delete_pdu_lkd(proxy_req->pdu);
  coap_delete_bin_const(proxy_req->token_used);
  coap_delete_cache_key(proxy_req->cache_key);
  if (proxy_req->proxy_cache) {
    assert(proxy_req->proxy_cache->ref);
    proxy_req->proxy_cache->ref--;
    if (proxy_req->proxy_cache->ref == 0) {
      PROXY_CACHE_DELETE(proxy_entry->rsp_cache, proxy_req->proxy_cache);
      coap_delete_pdu_lkd(proxy_req->proxy_cache->req_pdu);
      coap_delete_pdu_lkd(proxy_req->proxy_cache->rsp_pdu);
      coap_free_type(COAP_STRING, proxy_req->proxy_cache);
      proxy_req->proxy_cache = NULL;
    }
  }
 
  for (i = 0; i < proxy_entry->req_count; i++) {
    if (&proxy_entry->req_list[i] == proxy_req) {
      if (proxy_entry->req_count > 1) {
        memmove(&proxy_entry->req_list[i], &proxy_entry->req_list[i+1],
                (proxy_entry->req_count-i-1) * sizeof(proxy_entry->req_list[0]));
      }
      proxy_entry->req_count--;
      break;
    }
  }
}
 
static void
coap_proxy_cleanup_entry(coap_proxy_list_t *proxy_entry, int send_failure) {
  size_t i;
 
  for (i = 0; i < proxy_entry->req_count; i++) {
    coap_proxy_req_t *proxy_req = &proxy_entry->req_list[i];
 
    if (send_failure) {
      coap_pdu_t *response;
      coap_bin_const_t l_token;
 
      /* Need to send back a gateway failure */
      response = coap_pdu_init(proxy_req->pdu->type,
                               COAP_RESPONSE_CODE(502),
                               coap_new_message_id_lkd(proxy_entry->incoming),
                               coap_session_max_pdu_size_lkd(proxy_entry->incoming));
      if (!response) {
        coap_log_info("PDU creation issue\n");
        goto cleanup;
      }
 
      l_token = coap_pdu_get_token(proxy_req->pdu);
      if (!coap_add_token(response, l_token.length,
                          l_token.s)) {
        coap_log_debug("Cannot add token to incoming proxy response PDU\n");
      }
 
      if (coap_send_lkd(proxy_entry->incoming, response) == COAP_INVALID_MID) {
        coap_log_info("Failed to send PDU with 5.02 gateway issue\n");
      }
    }
cleanup:
    coap_proxy_del_req(proxy_entry, proxy_req);
  }
  coap_free_type(COAP_STRING, proxy_entry->req_list);
  coap_free_type(COAP_STRING, proxy_entry->uri_host_keep);
}
 
void
coap_proxy_cleanup(coap_context_t *context) {
  size_t i;
 
  for (i = 0; i < context->proxy_list_count; i++) {
    /* All sessions have now been closed down */
    coap_log_debug("proxy_entry %p cleaned up\n",
                   (void *)&context->proxy_list[i]);
    coap_proxy_cleanup_entry(&context->proxy_list[i], 0);
  }
  coap_free_type(COAP_STRING, context->proxy_list);
}
 
static int
coap_proxy_check_observe(coap_proxy_list_t *proxy_entry) {
  if (proxy_entry && proxy_entry->ongoing) {
    /* Need to see if there are any Observes active */
    coap_lg_crcv_t *lg_crcv;
 
    LL_FOREACH(proxy_entry->ongoing->lg_crcv, lg_crcv) {
      if (lg_crcv->observe_set) {
        return 1;
      }
    }
  }
  return 0;
}
 
/*
 * Return 1 if there is a future expire time, else 0.
 * Update tim_rem with remaining value if return is 1.
 */
int
coap_proxy_check_timeouts(coap_context_t *context, coap_tick_t now,
                          coap_tick_t *tim_rem) {
  size_t i;
  int ret = 0;
 
  *tim_rem = COAP_MAX_DELAY_TICKS;
  for (i = 0; i < context->proxy_list_count; i++) {
    coap_proxy_list_t *proxy_entry = &context->proxy_list[i];
 
    if (coap_proxy_check_observe(proxy_entry))
      continue;
 
    if (proxy_entry->ongoing && proxy_entry->idle_timeout_ticks) {
      if (proxy_entry->last_used + proxy_entry->idle_timeout_ticks <= now) {
        /* Drop session to upstream server (which may remove proxy entry) */
        if (coap_proxy_remove_association(proxy_entry->ongoing, 0))
          i--;
      } else {
        if (*tim_rem > proxy_entry->last_used + proxy_entry->idle_timeout_ticks - now) {
          *tim_rem = proxy_entry->last_used + proxy_entry->idle_timeout_ticks - now;
          ret = 1;
        }
      }
    }
  }
  return ret;
}
 
static int
coap_get_uri_proxy_scheme_info(const coap_pdu_t *request,
                               coap_opt_t *opt,
                               coap_uri_t *uri) {
  const char *opt_val = (const char *)coap_opt_value(opt);
  int opt_len = coap_opt_length(opt);
  coap_opt_iterator_t opt_iter;
 
  if (opt_len == 9 &&
      strncasecmp(opt_val, "coaps+tcp", 9) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAPS_TCP;
    uri->port = COAPS_DEFAULT_PORT;
  } else if (opt_len == 8 &&
             strncasecmp(opt_val, "coap+tcp", 8) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAP_TCP;
    uri->port = COAP_DEFAULT_PORT;
  } else if (opt_len == 5 &&
             strncasecmp(opt_val, "coaps", 5) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAPS;
    uri->port = COAPS_DEFAULT_PORT;
  } else if (opt_len == 4 &&
             strncasecmp(opt_val, "coap", 4) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAP;
    uri->port = COAP_DEFAULT_PORT;
  } else if (opt_len == 7 &&
             strncasecmp(opt_val, "coap+ws", 7) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAP_WS;
    uri->port = 80;
  } else if (opt_len == 8 &&
             strncasecmp(opt_val, "coaps+ws", 8) == 0) {
    uri->scheme = COAP_URI_SCHEME_COAPS_WS;
    uri->port = 443;
  } else {
    coap_log_warn("Unsupported Proxy Scheme '%*.*s'\n",
                  opt_len, opt_len, opt_val);
    return 0;
  }
 
  opt = coap_check_option(request, COAP_OPTION_URI_HOST, &opt_iter);
  if (opt) {
    uri->host.length = coap_opt_length(opt);
    uri->host.s = coap_opt_value(opt);
  } else {
    uri->host.s = NULL;
    uri->host.length = 0;
    coap_log_warn("Proxy Scheme requires Uri-Host\n");
    return 0;
  }
  opt = coap_check_option(request, COAP_OPTION_URI_PORT, &opt_iter);
  if (opt) {
    uri->port =
        coap_decode_var_bytes(coap_opt_value(opt),
                              coap_opt_length(opt));
  }
  return 1;
}
 
int
coap_verify_proxy_scheme_supported(coap_uri_scheme_t scheme) {
 
  /* Sanity check that the connection can be forwarded on */
  switch (scheme) {
  case COAP_URI_SCHEME_HTTP:
  case COAP_URI_SCHEME_HTTPS:
    coap_log_warn("Proxy URI http or https not supported\n");
    return 0;
  case COAP_URI_SCHEME_COAP:
    break;
  case COAP_URI_SCHEME_COAPS:
    if (!coap_dtls_is_supported()) {
      coap_log_warn("coaps URI scheme not supported for proxy\n");
      return 0;
    }
    break;
  case COAP_URI_SCHEME_COAP_TCP:
    if (!coap_tcp_is_supported()) {
      coap_log_warn("coap+tcp URI scheme not supported for proxy\n");
      return 0;
    }
    break;
  case COAP_URI_SCHEME_COAPS_TCP:
    if (!coap_tls_is_supported()) {
      coap_log_warn("coaps+tcp URI scheme not supported for proxy\n");
      return 0;
    }
    break;
  case COAP_URI_SCHEME_COAP_WS:
    if (!coap_ws_is_supported()) {
      coap_log_warn("coap+ws URI scheme not supported for proxy\n");
      return 0;
    }
    break;
  case COAP_URI_SCHEME_COAPS_WS:
    if (!coap_wss_is_supported()) {
      coap_log_warn("coaps+ws URI scheme not supported for proxy\n");
      return 0;
    }
    break;
  case COAP_URI_SCHEME_LAST:
  default:
    coap_log_warn("%d URI scheme not supported\n", scheme);
    return 0;
  }
  return 1;
}
 
static coap_proxy_list_t *
coap_proxy_get_session(coap_session_t *session, const coap_pdu_t *request,
                       coap_pdu_t *response,
                       coap_proxy_server_list_t *server_list,
                       coap_proxy_server_t *server_use, int *proxy_entry_created) {
  size_t i;
  coap_proxy_list_t *new_proxy_list;
  coap_proxy_list_t *proxy_list = session->context->proxy_list;
  size_t proxy_list_count = session->context->proxy_list_count;
  coap_opt_iterator_t opt_iter;
  coap_opt_t *proxy_scheme;
  coap_opt_t *proxy_uri;
 
  *proxy_entry_created = 0;
 
  /*
   * Maintain server stickability. server_use not needed as there is
   * ongoing session in place.
   */
  if (session->proxy_entry) {
    for (i = 0; i < proxy_list_count; i++) {
      if (&proxy_list[i] == session->proxy_entry) {
        if (session->proxy_entry->ongoing) {
          memset(server_use, 0, sizeof(*server_use));
          return session->proxy_entry;
        }
      }
    }
  }
 
  /* Round robin the defined next server list (which usually is just one */
  server_list->next_entry++;
  if (server_list->next_entry >= server_list->entry_count)
    server_list->next_entry = 0;
 
  if (server_list->entry_count) {
    memcpy(server_use, &server_list->entry[server_list->next_entry], sizeof(*server_use));
  } else {
    memset(server_use, 0, sizeof(*server_use));
  }
 
  switch (server_list->type) {
  case COAP_PROXY_REVERSE:
  case COAP_PROXY_REVERSE_STRIP:
  case COAP_PROXY_FORWARD_STATIC:
  case COAP_PROXY_FORWARD_STATIC_STRIP:
    /* Nothing else needs to be done here */
    break;
  case COAP_PROXY_FORWARD_DYNAMIC:
  case COAP_PROXY_FORWARD_DYNAMIC_STRIP:
    /* Need to get actual server from CoAP Proxy-Uri or Proxy-Scheme options */
    /*
     * See if Proxy-Scheme
     */
    proxy_scheme = coap_check_option(request, COAP_OPTION_PROXY_SCHEME, &opt_iter);
    if (proxy_scheme) {
      if (!coap_get_uri_proxy_scheme_info(request, proxy_scheme, &server_use->uri)) {
        response->code = COAP_RESPONSE_CODE(505);
        return NULL;
      }
    }
    /*
     * See if Proxy-Uri
     */
    proxy_uri = coap_check_option(request, COAP_OPTION_PROXY_URI, &opt_iter);
    if (proxy_uri) {
      coap_log_info("Proxy URI '%.*s'\n",
                    (int)coap_opt_length(proxy_uri),
                    (const char *)coap_opt_value(proxy_uri));
      if (coap_split_proxy_uri(coap_opt_value(proxy_uri),
                               coap_opt_length(proxy_uri),
                               &server_use->uri) < 0) {
        /* Need to return a 5.05 RFC7252 Section 5.7.2 */
        coap_log_warn("Proxy URI not decodable\n");
        response->code = COAP_RESPONSE_CODE(505);
        return NULL;
      }
    }
 
    if (!(proxy_scheme || proxy_uri)) {
      response->code = COAP_RESPONSE_CODE(404);
      return NULL;
    }
    break;
  default:
    assert(0);
    return NULL;
  }
 
  if (server_use->uri.host.length == 0) {
    /* Ongoing connection not well formed */
    response->code = COAP_RESPONSE_CODE(505);
    return NULL;
  }
 
  if (!coap_verify_proxy_scheme_supported(server_use->uri.scheme)) {
    response->code = COAP_RESPONSE_CODE(505);
    return NULL;
  }
 
  /* See if we are already connected to the Server */
  for (i = 0; i < proxy_list_count; i++) {
    if (coap_string_equal(&proxy_list[i].uri.host, &server_use->uri.host) &&
        proxy_list[i].uri.port == server_use->uri.port &&
        proxy_list[i].uri.scheme == server_use->uri.scheme) {
      if (!server_list->track_client_session && session->context->proxy_response_handler) {
        coap_ticks(&proxy_list[i].last_used);
        return &proxy_list[i];
      } else {
        if (proxy_list[i].incoming == session) {
          coap_ticks(&proxy_list[i].last_used);
          return &proxy_list[i];
        }
      }
    }
  }
 
  /* Need to create a new forwarding mapping */
  new_proxy_list = coap_realloc_type(COAP_STRING, proxy_list, (i+1)*sizeof(proxy_list[0]));
 
  if (new_proxy_list == NULL) {
    response->code = COAP_RESPONSE_CODE(500);
    return NULL;
  }
  session->context->proxy_list = proxy_list = new_proxy_list;
  memset(&proxy_list[i], 0, sizeof(proxy_list[i]));
 
  /* Keep a copy of the host as server_use->uri pointed to will be going away */
  proxy_list[i].uri = server_use->uri;
  proxy_list[i].uri_host_keep = coap_malloc_type(COAP_STRING,
                                                 server_use->uri.host.length);
  if (!proxy_list[i].uri_host_keep) {
    response->code = COAP_RESPONSE_CODE(500);
    return NULL;
  }
  memcpy(proxy_list[i].uri_host_keep, server_use->uri.host.s,
         server_use->uri.host.length);
  proxy_list[i].uri.host.s = proxy_list[i].uri_host_keep;
  /* Unset uri parts which point to going away information */
  proxy_list[i].uri.path.s = NULL;
  proxy_list[i].uri.path.length = 0;
  proxy_list[i].uri.query.s = NULL;
  proxy_list[i].uri.query.length = 0;
 
  if (server_list->track_client_session) {
    proxy_list[i].incoming = session;
  }
  *proxy_entry_created = 1;
  session->context->proxy_list_count++;
  proxy_list[i].idle_timeout_ticks = server_list->idle_timeout_secs * COAP_TICKS_PER_SECOND;
  coap_ticks(&proxy_list[i].last_used);
  session->proxy_entry = &proxy_list[i];
  return &proxy_list[i];
}
 
int
coap_proxy_remove_association(coap_session_t *session, int send_failure) {
 
  size_t i;
  size_t j;
  coap_proxy_list_t *proxy_list = session->context->proxy_list;
  size_t proxy_list_count = session->context->proxy_list_count;
 
  for (i = 0; i < proxy_list_count; i++) {
    coap_proxy_list_t *proxy_entry = &proxy_list[i];
 
    /* Check for incoming match */
    for (j = 0; j < proxy_entry->req_count; j++) {
      coap_proxy_req_t *proxy_req = &proxy_entry->req_list[j];
 
      if (proxy_req->incoming == session) {
        coap_proxy_del_req(proxy_entry, proxy_req);
        break;
      }
    }
    if (proxy_entry->incoming == session) {
      /* Only if there is a one-to-one tracking */
      coap_session_t *ongoing = proxy_entry->ongoing;
 
      proxy_entry->ongoing = NULL;
      coap_session_release_lkd(ongoing);
      return 0;
    }
 
    /* Check for outgoing match */
    if (proxy_entry->ongoing == session) {
      coap_session_t *ongoing;
 
      coap_proxy_cleanup_entry(proxy_entry, send_failure);
      ongoing = proxy_entry->ongoing;
      coap_log_debug("*  %s: proxy_entry %p released (rem count = %zd)\n",
                     coap_session_str(ongoing),
                     (void *)proxy_entry,
                     session->context->proxy_list_count - 1);
      if (proxy_list_count-i > 1) {
        memmove(&proxy_list[i],
                &proxy_list[i+1],
                (proxy_list_count-i-1) * sizeof(proxy_list[0]));
      }
      session->context->proxy_list_count--;
      coap_session_release_lkd(ongoing);
      return 1;
    }
  }
  return 0;
}
 
static coap_proxy_list_t *
coap_proxy_get_ongoing_session(coap_session_t *session,
                               const coap_pdu_t *request,
                               coap_pdu_t *response,
                               coap_proxy_server_list_t *server_list) {
 
  coap_address_t dst;
  coap_proto_t proto;
  coap_addr_info_t *info_list = NULL;
  coap_proxy_list_t *proxy_entry;
  coap_context_t *context = session->context;
  static char client_sni[256];
  coap_proxy_server_t server_use;
  int proxy_entry_created;
 
  proxy_entry = coap_proxy_get_session(session, request, response, server_list,
                                       &server_use, &proxy_entry_created);
  if (!proxy_entry) {
    /* Error response code already set */
    return NULL;
  }
 
  if (!proxy_entry->ongoing) {
    /* Need to create a new session */
    coap_address_t *local_addr = NULL;
 
    /* resolve destination address where data should be sent */
    info_list = coap_resolve_address_info(&server_use.uri.host,
                                          server_use.uri.port,
                                          server_use.uri.port,
                                          server_use.uri.port,
                                          server_use.uri.port,
                                          0,
                                          1 << server_use.uri.scheme,
                                          COAP_RESOLVE_TYPE_REMOTE);
 
    if (info_list == NULL) {
      response->code = COAP_RESPONSE_CODE(502);
      coap_proxy_remove_association(session, 0);
      return NULL;
    }
    proto = info_list->proto;
    memcpy(&dst, &info_list->addr, sizeof(dst));
    coap_free_address_info(info_list);
 
#if COAP_AF_UNIX_SUPPORT
    coap_address_t bind_addr;
    if (coap_is_af_unix(&dst)) {
      char buf[COAP_UNIX_PATH_MAX];
      coap_tick_t now;
 
      /* Need a unique 'client' address */
      coap_ticks(&now);
      snprintf(buf, COAP_UNIX_PATH_MAX,
               "/tmp/coap-pr-cl-%" PRIu64, (uint64_t)now);
      if (!coap_address_set_unix_domain(&bind_addr, (const uint8_t *)buf,
                                        strlen(buf))) {
        fprintf(stderr, "coap_address_set_unix_domain: %s: failed\n",
                buf);
        remove(buf);
        return NULL;
      }
      (void)remove(buf);
      local_addr = &bind_addr;
    }
#endif /* COAP_AF_UNIX_SUPPORT */
 
    snprintf(client_sni, sizeof(client_sni), "%*.*s", (int)server_use.uri.host.length,
             (int)server_use.uri.host.length, server_use.uri.host.s);
 
    switch (server_use.uri.scheme) {
    case COAP_URI_SCHEME_COAP:
    case COAP_URI_SCHEME_COAP_TCP:
    case COAP_URI_SCHEME_COAP_WS:
#if COAP_OSCORE_SUPPORT
      if (server_use.oscore_conf) {
        proxy_entry->ongoing =
            coap_new_client_session_oscore_lkd(context, local_addr, &dst,
                                               proto, server_use.oscore_conf);
      } else {
#endif /* COAP_OSCORE_SUPPORT */
        proxy_entry->ongoing =
            coap_new_client_session_lkd(context, local_addr, &dst, proto);
#if COAP_OSCORE_SUPPORT
      }
#endif /* COAP_OSCORE_SUPPORT */
      break;
    case COAP_URI_SCHEME_COAPS:
    case COAP_URI_SCHEME_COAPS_TCP:
    case COAP_URI_SCHEME_COAPS_WS:
#if COAP_OSCORE_SUPPORT
      if (server_use.oscore_conf) {
        if (server_use.dtls_pki) {
          server_use.dtls_pki->client_sni = client_sni;
          proxy_entry->ongoing =
              coap_new_client_session_oscore_pki_lkd(context, local_addr, &dst,
                                                     proto, server_use.dtls_pki, server_use.oscore_conf);
        } else if (server_use.dtls_cpsk) {
          server_use.dtls_cpsk->client_sni = client_sni;
          proxy_entry->ongoing =
              coap_new_client_session_oscore_psk_lkd(context, local_addr, &dst,
                                                     proto, server_use.dtls_cpsk, server_use.oscore_conf);
        } else {
          coap_log_warn("Proxy: (D)TLS not configured for secure session\n");
        }
      } else {
#endif /* COAP_OSCORE_SUPPORT */
        /* Not doing OSCORE */
        if (server_use.dtls_pki) {
          server_use.dtls_pki->client_sni = client_sni;
          proxy_entry->ongoing =
              coap_new_client_session_pki_lkd(context, local_addr, &dst,
                                              proto, server_use.dtls_pki);
        } else if (server_use.dtls_cpsk) {
          server_use.dtls_cpsk->client_sni = client_sni;
          proxy_entry->ongoing =
              coap_new_client_session_psk2_lkd(context, local_addr, &dst,
                                               proto, server_use.dtls_cpsk);
        } else {
          /* Using client anonymous PKI */
          proxy_entry->ongoing =
              coap_new_client_session_lkd(context, local_addr, &dst, proto);
        }
#if COAP_OSCORE_SUPPORT
      }
#endif /* COAP_OSCORE_SUPPORT */
      break;
    case COAP_URI_SCHEME_HTTP:
    case COAP_URI_SCHEME_HTTPS:
    case COAP_URI_SCHEME_LAST:
    default:
      assert(0);
      break;
    }
    if (proxy_entry->ongoing == NULL) {
      response->code = COAP_RESPONSE_CODE(505);
      coap_proxy_remove_association(session, 0);
      return NULL;
    }
    if (proxy_entry_created) {
      coap_log_debug("*  %s: proxy_entry %p created (tot count = %zd)\n",
                     coap_session_str(proxy_entry->ongoing),
                     (void *)proxy_entry,
                     session->context->proxy_list_count);
    }
  } else if (proxy_entry->ongoing->session_failed) {
    if (!coap_session_reconnect(proxy_entry->ongoing)) {
      /* Server is not yet back up */
      return NULL;
    }
  }
 
  return proxy_entry;
}
 
static void
coap_proxy_release_body_data(coap_session_t *session COAP_UNUSED,
                             void *app_ptr) {
  coap_delete_binary(app_ptr);
}
 
static coap_proxy_req_t *
coap_proxy_get_req(coap_proxy_list_t *proxy_entry, coap_session_t *session) {
  size_t i;
 
  for (i = 0; i < proxy_entry->req_count; i++) {
    if (proxy_entry->req_list[i].incoming == session) {
      return &proxy_entry->req_list[i];
    }
  }
  return NULL;
}
 
static void
coap_proxy_free_response_data(coap_session_t *session COAP_UNUSED, void *app_ptr) {
  coap_delete_bin_const(app_ptr);
}
 
static coap_response_t
coap_proxy_call_response_handler(coap_session_t *session, const coap_pdu_t *sent,
                                 coap_pdu_t *rcvd, coap_bin_const_t *token,
                                 coap_proxy_req_t *proxy_req, int replace_mid) {
  coap_response_t ret = COAP_RESPONSE_FAIL;
  coap_pdu_t *resp_pdu;
  coap_pdu_t *fwd_pdu = NULL;
  size_t size;
  size_t offset;
  size_t total;
  const uint8_t *data;
  coap_string_t *l_query = NULL;
 
  /* Correct the token */
  resp_pdu = coap_pdu_duplicate_lkd(rcvd, session, token->length, token->s, NULL);
  if (!resp_pdu)
    return COAP_RESPONSE_FAIL;
 
  if (replace_mid)
    resp_pdu->mid = rcvd->mid;
  if (coap_get_data_large(rcvd, &size, &data, &offset, &total)) {
    uint16_t media_type = 0;
    int maxage = -1;
    uint64_t etag = 0;
    coap_opt_t *option;
    coap_opt_iterator_t opt_iter;
    coap_bin_const_t *body;
 
    /* COAP_BLOCK_SINGLE_BODY is set, so single body should be given */
    assert(size == total);
 
    body = coap_new_bin_const(data, size);
    if (!body) {
      coap_log_debug("coap_proxy_call_response_handler: copy data error\n");
      goto failed;
    }
    option = coap_check_option(rcvd, COAP_OPTION_CONTENT_FORMAT, &opt_iter);
    if (option) {
      media_type = coap_decode_var_bytes(coap_opt_value(option),
                                         coap_opt_length(option));
    }
    option = coap_check_option(rcvd, COAP_OPTION_MAXAGE, &opt_iter);
    if (option) {
      maxage = coap_decode_var_bytes(coap_opt_value(option),
                                     coap_opt_length(option));
    }
    option = coap_check_option(rcvd, COAP_OPTION_ETAG, &opt_iter);
    if (option) {
      etag = coap_decode_var_bytes8(coap_opt_value(option),
                                    coap_opt_length(option));
    }
    if (sent)
      l_query = coap_get_query(sent);
    if (!coap_add_data_large_response_lkd(proxy_req->resource, session, sent,
                                          resp_pdu,
                                          l_query,
                                          media_type, maxage, etag, body->length,
                                          body->s,
                                          coap_proxy_free_response_data,
                                          body)) {
      coap_log_debug("coap_proxy_call_response_handler: add data error\n");
      goto failed;
    }
  }
  coap_lock_callback_ret_release(fwd_pdu, session->context,
                                 session->context->proxy_response_handler(session,
                                     sent,
                                     resp_pdu,
                                     proxy_req->cache_key),
                                 /* context is being freed off */
                                 goto failed);
  if (fwd_pdu) {
    ret = COAP_RESPONSE_OK;
    if (coap_send_lkd(session, fwd_pdu) == COAP_INVALID_MID) {
      ret = COAP_RESPONSE_FAIL;
    }
    if (fwd_pdu != resp_pdu) {
      /* Application created a new PDU */
      coap_delete_pdu_lkd(resp_pdu);
    }
  } else {
failed:
    ret = COAP_RESPONSE_FAIL;
    coap_delete_pdu_lkd(resp_pdu);
  }
  coap_delete_string(l_query);
  return ret;
}
 
int COAP_API
coap_proxy_forward_request(coap_session_t *session,
                           const coap_pdu_t *request,
                           coap_pdu_t *response,
                           coap_resource_t *resource,
                           coap_cache_key_t *cache_key,
                           coap_proxy_server_list_t *server_list) {
  int ret;
 
  coap_lock_lock(session->context, return 0);
  ret = coap_proxy_forward_request_lkd(session,
                                       request,
                                       response,
                                       resource,
                                       cache_key,
                                       server_list);
  coap_lock_unlock(session->context);
  return ret;
}
 
/* https://rfc-editor.org/rfc/rfc7641#section-3.6 */
static const uint16_t coap_proxy_ignore_options[] = { COAP_OPTION_ETAG,
                                                      COAP_OPTION_RTAG,
                                                      COAP_OPTION_BLOCK2,
                                                      COAP_OPTION_Q_BLOCK2,
                                                      COAP_OPTION_OSCORE
                                                    };
 
int
coap_proxy_forward_request_lkd(coap_session_t *session,
                               const coap_pdu_t *request,
                               coap_pdu_t *response,
                               coap_resource_t *resource,
                               coap_cache_key_t *cache_key,
                               coap_proxy_server_list_t *server_list) {
  coap_proxy_list_t *proxy_entry;
  size_t size;
  size_t offset;
  size_t total;
  coap_binary_t *body_data = NULL;
  const uint8_t *data;
  coap_pdu_t *pdu = NULL;
  coap_bin_const_t r_token = coap_pdu_get_token(request);
  uint8_t token[8];
  size_t token_len;
  coap_proxy_req_t *proxy_req = NULL;
  coap_optlist_t *optlist = NULL;
  coap_opt_t *option;
  coap_opt_iterator_t opt_iter;
  coap_uri_t uri;
  coap_opt_t *obs_opt = coap_check_option(request,
                                          COAP_OPTION_OBSERVE,
                                          &opt_iter);
  coap_proxy_cache_t *proxy_cache = NULL;
 
  /* Set up ongoing session (if not already done) */
  proxy_entry = coap_proxy_get_ongoing_session(session, request, response,
                                               server_list);
  if (!proxy_entry) {
    /* Error response code already set */
    return 0;
  }
 
  /* Is this a observe cached request? */
  if (obs_opt && session->context->proxy_response_handler) {
    coap_cache_key_t *cache_key_l;
    coap_tick_t now;
 
    cache_key_l = coap_cache_derive_key_w_ignore(session, request,
                                                 COAP_CACHE_NOT_SESSION_BASED,
                                                 coap_proxy_ignore_options,
                                                 sizeof(coap_proxy_ignore_options)/sizeof(coap_proxy_ignore_options[0]));
    if (!cache_key_l) {
      response->code = COAP_RESPONSE_CODE(505);
      return 0;
    }
    PROXY_CACHE_FIND(proxy_entry->rsp_cache, cache_key_l, proxy_cache);
    coap_delete_cache_key(cache_key_l);
    coap_ticks(&now);
    if (proxy_cache && (proxy_cache->expire + COAP_TICKS_PER_SECOND) < now) {
      /* Need to get an updated rsp_pdu */
      proxy_cache = NULL;
    }
  }
 
  if (proxy_cache) {
    proxy_req = coap_proxy_get_req(proxy_entry, session);
    if (proxy_req) {
      if (obs_opt) {
        int observe_action;
 
        observe_action = coap_decode_var_bytes(coap_opt_value(obs_opt),
                                               coap_opt_length(obs_opt));
 
        if (observe_action == COAP_OBSERVE_CANCEL) {
          assert(proxy_cache->ref);
          proxy_cache->ref--;
          if (proxy_cache->ref > 0) {
            goto return_cached_info;
          }
          proxy_cache = NULL;
          if (proxy_req->proxy_cache->ref == 0) {
            PROXY_CACHE_DELETE(proxy_entry->rsp_cache, proxy_req->proxy_cache);
            coap_delete_pdu_lkd(proxy_req->proxy_cache->req_pdu);
            coap_delete_pdu_lkd(proxy_req->proxy_cache->rsp_pdu);
            coap_free_type(COAP_STRING, proxy_req->proxy_cache);
            proxy_req->proxy_cache = NULL;
          }
          /* Last user of proxy_cache.  Need to de-register upstream */
        } else if (observe_action == COAP_OBSERVE_ESTABLISH) {
          /* Client must be re-registering */
          goto return_cached_info;
        }
      } else {
        goto return_cached_info;
      }
    }
  }
 
  if (!proxy_req) {
    coap_proxy_req_t *new_req_list;
 
    new_req_list = coap_realloc_type(COAP_STRING, proxy_entry->req_list,
                                     (proxy_entry->req_count + 1)*sizeof(coap_proxy_req_t));
 
    if (new_req_list == NULL) {
      goto failed;
    }
    proxy_entry->req_list = new_req_list;
    proxy_req = &new_req_list[proxy_entry->req_count];
    memset(proxy_req, 0, sizeof(coap_proxy_req_t));
 
    /* Get a new token for ongoing session */
    coap_session_new_token(proxy_entry->ongoing, &token_len, token);
    proxy_req->token_used = coap_new_bin_const(token, token_len);
    if (proxy_req->token_used == NULL) {
      goto failed;
    }
    proxy_req->pdu = coap_const_pdu_reference_lkd(request);
    proxy_req->resource = resource;
    proxy_req->incoming = session;
    proxy_req->cache_key = cache_key;
    proxy_req->proxy_cache = proxy_cache;
    proxy_entry->req_count++;
  } else if (obs_opt) {
    /* Need to reuse token */
    memcpy(token, proxy_req->token_used->s, proxy_req->token_used->length);
    token_len = proxy_req->token_used->length;
  } else {
    /* Need to refresh used token */
    coap_session_new_token(proxy_entry->ongoing, &token_len, token);
    coap_delete_bin_const(proxy_req->token_used);
    proxy_req->token_used = coap_new_bin_const(token, token_len);
    if (proxy_req->token_used == NULL) {
      goto failed;
    }
  }
 
  if (proxy_cache) {
    if (obs_opt)
      proxy_cache->ref++;
    goto return_cached_info;
  }
 
  /* Need to save the request pdu entry */
  switch (server_list->type) {
  case COAP_PROXY_REVERSE_STRIP:
  case COAP_PROXY_FORWARD_STATIC_STRIP:
  case COAP_PROXY_FORWARD_DYNAMIC_STRIP:
    /*
     * Need to replace Proxy-Uri with Uri-Host (and Uri-Port)
     * and strip out Proxy-Scheme.
     */
 
    /*
     * Build up the ongoing PDU that we are going to send
     */
    pdu = coap_pdu_init(request->type, request->code,
                        coap_new_message_id_lkd(proxy_entry->ongoing),
                        coap_session_max_pdu_size_lkd(proxy_entry->ongoing));
    if (!pdu) {
      goto failed;
    }
 
    if (!coap_add_token(pdu, token_len, token)) {
      goto failed;
    }
 
    /* Copy the remaining options across */
    coap_option_iterator_init(request, &opt_iter, COAP_OPT_ALL);
    while ((option = coap_option_next(&opt_iter))) {
      switch (opt_iter.number) {
      case COAP_OPTION_PROXY_URI:
        if (coap_split_proxy_uri(coap_opt_value(option),
                                 coap_opt_length(option),
                                 &uri) < 0) {
          /* Need to return a 5.05 RFC7252 Section 5.7.2 */
          coap_log_warn("Proxy URI not decodable\n");
          coap_delete_pdu_lkd(pdu);
          return 0;
        }
        if (!coap_uri_into_optlist(&uri, NULL, &optlist, 0)) {
          coap_log_err("Failed to create options for URI\n");
          goto failed;
        }
        break;
      case COAP_OPTION_PROXY_SCHEME:
        break;
      case COAP_OPTION_BLOCK1:
      case COAP_OPTION_BLOCK2:
      case COAP_OPTION_Q_BLOCK1:
      case COAP_OPTION_Q_BLOCK2:
        /* These are not passed on */
        break;
      case COAP_OPTION_URI_HOST:
      case COAP_OPTION_URI_PORT:
        break;
      default:
        coap_insert_optlist(&optlist,
                            coap_new_optlist(opt_iter.number,
                                             coap_opt_length(option),
                                             coap_opt_value(option)));
        break;
      }
    }
 
    /* Update pdu with options */
    coap_add_optlist_pdu(pdu, &optlist);
    coap_delete_optlist(optlist);
    break;
  case COAP_PROXY_REVERSE:
  case COAP_PROXY_FORWARD_STATIC:
  case COAP_PROXY_FORWARD_DYNAMIC:
  default:
    /*
     * Duplicate request PDU for onward transmission (with new token).
     */
    pdu = coap_pdu_duplicate_lkd(request, proxy_entry->ongoing, token_len, token, NULL);
    if (!pdu) {
      coap_log_debug("proxy: PDU generation error\n");
      goto failed;
    }
    break;
  }
 
  if (coap_get_data_large(request, &size, &data, &offset, &total)) {
    /* COAP_BLOCK_SINGLE_BODY is set, so single body should be given */
    assert(size == total);
    /*
     * Need to take a copy of the data as request PDU may go away before
     * all data is transmitted.
     */
    body_data = coap_new_binary(total);
    if (!body_data) {
      coap_log_debug("proxy: body build memory error\n");
      goto failed;
    }
    memcpy(body_data->s, data, size);
    if (!coap_add_data_large_request_lkd(proxy_entry->ongoing, pdu, total, data,
                                         coap_proxy_release_body_data, body_data)) {
      coap_log_debug("proxy: add data error\n");
      goto failed;
    }
  }
 
  if (coap_send_lkd(proxy_entry->ongoing, pdu) == COAP_INVALID_MID) {
    pdu = NULL;
    coap_log_debug("proxy: upstream PDU send error\n");
    goto failed;
  }
 
  /*
   * Do not update the response code (hence empty ACK) as will be sending
   * separate response when response comes back from upstream server
   */
 
  return 1;
 
failed:
  response->code = COAP_RESPONSE_CODE(500);
  coap_delete_pdu_lkd(pdu);
  return 0;
 
return_cached_info:
  coap_proxy_call_response_handler(session, request, proxy_cache->rsp_pdu,
                                   &r_token, proxy_req, 1);
  if (!obs_opt)
    coap_proxy_del_req(proxy_entry, proxy_req);
  return 1;
}
 
struct coap_proxy_req_t *
coap_proxy_map_outgoing_request(coap_session_t *ongoing,
                                const coap_pdu_t *received,
                                coap_proxy_list_t **proxy_entry) {
  coap_proxy_list_t *proxy_list = ongoing->context->proxy_list;
  size_t proxy_list_count = ongoing->context->proxy_list_count;
  size_t i;
  size_t j;
  coap_bin_const_t rcv_token = coap_pdu_get_token(received);
  coap_proxy_list_t *l_proxy_entry = NULL;
 
  for (i = 0; i < proxy_list_count; i++) {
    l_proxy_entry = &proxy_list[i];
    if (l_proxy_entry->ongoing == ongoing) {
      for (j = 0; j < l_proxy_entry->req_count; j++) {
        if (coap_binary_equal(&rcv_token, l_proxy_entry->req_list[j].token_used)) {
          coap_ticks(&l_proxy_entry->last_used);
          if (proxy_entry)
            *proxy_entry = l_proxy_entry;
          return &l_proxy_entry->req_list[j];
        }
      }
    }
  }
  return NULL;
}
 
coap_response_t COAP_API
coap_proxy_forward_response(coap_session_t *session,
                            const coap_pdu_t *received,
                            coap_cache_key_t **cache_key) {
  int ret;
 
  coap_lock_lock(session->context, return 0);
  ret = coap_proxy_forward_response_lkd(session,
                                        received,
                                        cache_key);
  coap_lock_unlock(session->context);
  return ret;
}
 
coap_response_t
coap_proxy_forward_response_lkd(coap_session_t *session,
                                const coap_pdu_t *received,
                                coap_cache_key_t **cache_key) {
  coap_pdu_t *pdu = NULL;
  coap_session_t *incoming = NULL;
  size_t size;
  const uint8_t *data;
  coap_optlist_t *optlist = NULL;
  coap_opt_t *option;
  coap_opt_iterator_t opt_iter;
  size_t offset;
  size_t total;
  coap_proxy_list_t *proxy_entry = NULL;
  uint16_t media_type = COAP_MEDIATYPE_TEXT_PLAIN;
  int maxage = -1;
  uint64_t etag = 0;
  coap_pdu_code_t rcv_code = coap_pdu_get_code(received);
  coap_bin_const_t req_token;
  coap_binary_t *body_data = NULL;
  coap_pdu_t *req_pdu;
  coap_resource_t *resource;
  struct coap_proxy_req_t *proxy_req = NULL;
 
  proxy_req = coap_proxy_map_outgoing_request(session, received, &proxy_entry);
  if (!proxy_req || proxy_req->incoming->server_list) {
    coap_log_warn("Unknown proxy ongoing session response received - ignored\n");
    return COAP_RESPONSE_OK;
  }
 
  req_pdu = proxy_req->pdu;
  req_token = coap_pdu_get_token(req_pdu);
  resource = proxy_req->resource;
  incoming = proxy_req->incoming;
 
  coap_log_debug("** process upstream incoming %d.%02d response:\n",
                 COAP_RESPONSE_CLASS(rcv_code), rcv_code & 0x1F);
 
  if (coap_get_data_large(received, &size, &data, &offset, &total)) {
    /* COAP_BLOCK_SINGLE_BODY is set, so single body should be given */
    assert(size == total);
    body_data = coap_new_binary(total);
    if (!body_data) {
      coap_log_debug("body build memory error\n");
      goto remove_match;
    }
    memcpy(body_data->s, data, size);
    data = body_data->s;
  }
 
  /*
   * Build up the ongoing PDU that we are going to send to proxy originator
   * as separate response
   */
  pdu = coap_pdu_init(req_pdu->type, rcv_code,
                      coap_new_message_id_lkd(incoming),
                      coap_session_max_pdu_size_lkd(incoming));
  if (!pdu) {
    coap_log_debug("Failed to create ongoing proxy response PDU\n");
    goto remove_match;
  }
 
  if (!coap_add_token(pdu, req_token.length, req_token.s)) {
    coap_log_debug("cannot add token to ongoing proxy response PDU\n");
  }
 
  /*
   * Copy the options across, skipping those needed for
   * coap_add_data_response_large()
   */
  coap_option_iterator_init(received, &opt_iter, COAP_OPT_ALL);
  while ((option = coap_option_next(&opt_iter))) {
    switch (opt_iter.number) {
    case COAP_OPTION_CONTENT_FORMAT:
      media_type = coap_decode_var_bytes(coap_opt_value(option),
                                         coap_opt_length(option));
      break;
    case COAP_OPTION_MAXAGE:
      maxage = coap_decode_var_bytes(coap_opt_value(option),
                                     coap_opt_length(option));
      break;
    case COAP_OPTION_ETAG:
      etag = coap_decode_var_bytes8(coap_opt_value(option),
                                    coap_opt_length(option));
      break;
    case COAP_OPTION_BLOCK2:
    case COAP_OPTION_Q_BLOCK2:
    case COAP_OPTION_SIZE2:
      break;
    default:
      coap_insert_optlist(&optlist,
                          coap_new_optlist(opt_iter.number,
                                           coap_opt_length(option),
                                           coap_opt_value(option)));
      break;
    }
  }
  coap_add_optlist_pdu(pdu, &optlist);
  coap_delete_optlist(optlist);
 
  if (size > 0) {
    coap_string_t *l_query = coap_get_query(req_pdu);
 
    coap_add_data_large_response_lkd(resource, incoming, req_pdu, pdu,
                                     l_query,
                                     media_type, maxage, etag, size, data,
                                     coap_proxy_release_body_data,
                                     body_data);
    body_data = NULL;
    coap_delete_string(l_query);
  }
 
  if (cache_key)
    *cache_key = proxy_req->cache_key;
 
  coap_send_lkd(incoming, pdu);
 
remove_match:
  option = coap_check_option(received, COAP_OPTION_OBSERVE, &opt_iter);
  /* Need to remove matching token entry (apart from an Observe response) */
  if (option == NULL && proxy_entry->req_count) {
    /* Do not delete cache key here - caller's responsibility */
    proxy_req->cache_key = NULL;
    coap_proxy_del_req(proxy_entry, proxy_req);
  }
  coap_delete_binary(body_data);
  return COAP_RESPONSE_OK;
}
 
void
coap_proxy_process_incoming(coap_session_t *session,
                            coap_pdu_t *rcvd,
                            void *body_data, coap_proxy_req_t *proxy_req,
                            coap_proxy_list_t *proxy_entry) {
  coap_opt_t *obs_opt;
  coap_opt_t *option;
  coap_opt_iterator_t opt_iter;
  coap_response_t ret = COAP_RESPONSE_FAIL;
  coap_bin_const_t token;
 
  obs_opt = coap_check_option(rcvd, COAP_OPTION_OBSERVE, &opt_iter);
 
  /* See if we are doing proxy caching */
  if (obs_opt) {
    coap_proxy_cache_t *proxy_cache;
    coap_cache_key_t *cache_key_l;
    coap_tick_t now;
    uint64_t expire;
    size_t i;
 
    /* Need to cache the response */
    if (proxy_req->proxy_cache) {
      coap_delete_pdu_lkd(proxy_req->proxy_cache->rsp_pdu);
      proxy_cache = proxy_req->proxy_cache;
    } else {
      proxy_cache = coap_malloc_type(COAP_STRING, sizeof(coap_proxy_cache_t));
      if (proxy_cache == NULL) {
        goto cache_fail;
      }
      memset(proxy_cache, 0, sizeof(coap_proxy_cache_t));
      cache_key_l = coap_cache_derive_key_w_ignore(session, proxy_req->pdu,
                                                   COAP_CACHE_NOT_SESSION_BASED,
                                                   coap_proxy_ignore_options,
                                                   sizeof(coap_proxy_ignore_options)/sizeof(coap_proxy_ignore_options[0]));
      if (!cache_key_l) {
        coap_free_type(COAP_STRING, proxy_cache);
        goto cache_fail;
      }
      memcpy(&proxy_cache->cache_req, cache_key_l,
             sizeof(proxy_cache->cache_req));
      coap_delete_cache_key(cache_key_l);
 
      proxy_cache->req_pdu = coap_pdu_reference_lkd(proxy_req->pdu);
      proxy_req->proxy_cache = proxy_cache;
 
      PROXY_CACHE_ADD(proxy_entry->rsp_cache, proxy_cache);
      proxy_cache->ref++;
    }
    proxy_cache->rsp_pdu = coap_pdu_reference_lkd(rcvd);
    option = coap_check_option(rcvd, COAP_OPTION_ETAG, &opt_iter);
    if (option) {
      proxy_cache->etag = coap_decode_var_bytes8(coap_opt_value(option),
                                                 coap_opt_length(option));
    } else {
      proxy_cache->etag = 0;
    }
    coap_ticks(&now);
    option = coap_check_option(rcvd, COAP_OPTION_MAXAGE, &opt_iter);
    if (option) {
      expire = coap_decode_var_bytes(coap_opt_value(option),
                                     coap_opt_length(option));
    } else {
      /* Default is 60 seconds */
      expire = 60;
    }
    proxy_cache->expire = now + expire * COAP_TICKS_PER_SECOND;
 
    /* Update all the cache listeners */
    for (i = 0; i < proxy_entry->req_count; i++) {
      if (proxy_entry->req_list[i].proxy_cache == proxy_cache) {
        proxy_req = &proxy_entry->req_list[i];
        token = coap_pdu_get_token(proxy_req->pdu);
        if (coap_proxy_call_response_handler(proxy_req->incoming, proxy_req->pdu,
                                             rcvd, &token,
                                             proxy_req, 0) == COAP_RESPONSE_OK) {
          /* At least one success */
          ret = COAP_RESPONSE_OK;
        }
      }
    }
    goto finish;
  }
cache_fail:
  token = coap_pdu_get_token(proxy_req->pdu);
  ret = coap_proxy_call_response_handler(proxy_req->incoming, proxy_req->pdu,
                                         rcvd, &token, proxy_req, 0);
 
finish:
  if (ret == COAP_RESPONSE_FAIL && rcvd->type != COAP_MESSAGE_ACK) {
    coap_send_rst_lkd(session, rcvd);
    session->last_con_handler_res = COAP_RESPONSE_FAIL;
  } else {
    coap_send_ack_lkd(session, rcvd);
    session->last_con_handler_res = COAP_RESPONSE_OK;
  }
  coap_free_type(COAP_STRING, body_data);
}
 
/*
 */
coap_mid_t
coap_proxy_local_write(coap_session_t *session, coap_pdu_t *pdu) {
  coap_pdu_t *response = NULL;
  coap_resource_t *resource;
  coap_mid_t mid = COAP_INVALID_MID;
 
  resource = session->context->unknown_resource ?
             session->context->unknown_resource :
             session->context->proxy_uri_resource;
  if (!resource) {
    coap_log_err("coap_proxy_local_write: Unknown or Proxy resource not defined\n");
    goto fail;
  }
 
  response = coap_pdu_init(pdu->type == COAP_MESSAGE_CON ?
                           COAP_MESSAGE_ACK : COAP_MESSAGE_NON,
                           0, pdu->mid, coap_session_max_pdu_size_lkd(session));
  if (!response) {
    coap_log_err("coap_proxy_local_write: Could not create response PDU\n");
    goto fail;
  }
  response->session = session;
 
  if (!coap_add_token(response, pdu->actual_token.length,
                      pdu->actual_token.s)) {
    goto fail;
  }
 
  coap_log_debug("*  %s: internal: sent %4zd bytes\n",
                 coap_session_str(session),
                 pdu->used_size + coap_pdu_encode_header(pdu, session->proto));
  coap_show_pdu(COAP_LOG_DEBUG, pdu);
 
  mid = pdu->mid;
  if (!coap_proxy_forward_request_lkd(session, pdu, response, resource,
                                      NULL, session->server_list)) {
    coap_log_debug("coap_proxy_local_write: Failed to forward PDU\n");
    mid = COAP_INVALID_MID;
  }
fail:
  coap_delete_pdu_lkd(response);
  coap_delete_pdu_lkd(pdu);
  return mid;
}
 
COAP_API coap_session_t *
coap_new_client_session_proxy(coap_context_t *ctx,
                              coap_proxy_server_list_t *server_list) {
  coap_session_t *session;
 
  coap_lock_lock(ctx, return NULL);
  session = coap_new_client_session_proxy_lkd(ctx, server_list);
  coap_lock_unlock(ctx);
  return session;
}
 
coap_session_t *
coap_new_client_session_proxy_lkd(coap_context_t *ctx,
                                  coap_proxy_server_list_t *server_list) {
  coap_session_t *session;
  coap_addr_info_t *info_list = NULL;
  coap_str_const_t remote;
 
  coap_lock_check_locked(ctx);
 
#if COAP_IPV6_SUPPORT
  remote.s = (const uint8_t *)"::1";
#elif COAP_IPV4_SUPPORT
  remote.s = (const uint8_t *)"127.0.0.1";
#else /* !COAP_IPV6_SUPPORT && ! COAP_IPV4_SUPPORT */
  coap_log_warn("coap_new_client_session_proxy: No IPv4 or IPv6 support\n");
  return NULL;
#endif /* !COAP_IPV6_SUPPORT && ! COAP_IPV4_SUPPORT */
  remote.length = strlen((const char *)remote.s);
  /* resolve internal remote address where proxy session is 'connecting' to */
  info_list = coap_resolve_address_info(&remote, 0, 0, 0, 0,
                                        0,
                                        1 << COAP_URI_SCHEME_COAP,
                                        COAP_RESOLVE_TYPE_REMOTE);
  if (!info_list) {
    coap_log_warn("coap_new_client_session_proxy: Unable to resolve IP address\n");
    return NULL;
  }
 
  session = coap_new_client_session_lkd(ctx, NULL, &info_list->addr, COAP_PROTO_UDP);
 
  if (session) {
    session->server_list = server_list;
  }
  coap_free_address_info(info_list);
  return session;
}
 
#else /* ! COAP_PROXY_SUPPORT */
 
int
coap_proxy_is_supported(void) {
  return 0;
}
 
COAP_API int
coap_proxy_forward_request(coap_session_t *session,
                           const coap_pdu_t *request,
                           coap_pdu_t *response,
                           coap_resource_t *resource,
                           coap_cache_key_t *cache_key,
                           coap_proxy_server_list_t *server_list) {
  (void)session;
  (void)request;
  (void)resource;
  (void)cache_key;
  (void)server_list;
  response->code = COAP_RESPONSE_CODE(500);
  return 0;
}
 
COAP_API coap_response_t
coap_proxy_forward_response(coap_session_t *session,
                            const coap_pdu_t *received,
                            coap_cache_key_t **cache_key) {
  (void)session;
  (void)received;
  (void)cache_key;
  return COAP_RESPONSE_OK;
}
 
int
coap_verify_proxy_scheme_supported(coap_uri_scheme_t scheme) {
  (void)scheme;
  return 0;
}
#endif /* ! COAP_PROXY_SUPPORT */