coap_session.[hc]: make message id session-local

The message id in the CoAP header is used for reliability when
transferring a CoAP PDU over a non-reliable transport protocol
such as UDP. For message de-duplication, it is useful to have
a monotonously increasing number space within a session. Therefore,
the context-global value has been moved to coap_session_t.
The function coap_new_message_id() now takes a coap_session_t
object as its argument.

examples/client.c

@@ -148,12 +148,13 @@ coap_new_request(coap_context_t *ctx,
                  size_t length) {
   coap_pdu_t *pdu;
   coap_list_t *opt;
+  (void)ctx;
 
   if ( ! ( pdu = coap_new_pdu(session) ) )
     return NULL;
 
   pdu->hdr->type = msgtype;
-  pdu->hdr->id = coap_new_message_id(ctx);
+  pdu->hdr->id = coap_new_message_id(session);
   pdu->hdr->code = m;
 
   pdu->hdr->token_length = (uint16_t)the_token.length;
@@ -190,11 +191,12 @@ clear_obs(coap_context_t *ctx, coap_session_t *session) {
   coap_list_t *option;
   coap_tid_t tid = COAP_INVALID_TID;
   unsigned char buf[2];
+  (void)ctx;
 
   /* create bare PDU w/o any option  */
   pdu = coap_pdu_init(msgtype,
                       COAP_REQUEST_GET,
-                      coap_new_message_id(ctx),
+                      coap_new_message_id(session),
                       coap_session_max_pdu_size(session));
 
   if (!pdu) {

examples/coap-server.c

@@ -266,7 +266,7 @@ check_async(coap_context_t *ctx,
     return;
   }
 
-  response->hdr->id = coap_new_message_id(ctx);
+  response->hdr->id = coap_new_message_id(async->session);
 
   if (async->tokenlen)
     coap_add_token(response, async->tokenlen, async->token);

include/coap/coap_session.h

@@ -60,6 +60,7 @@ typedef struct coap_session_t {
   struct coap_endpoint_t *endpoint;	  /**< session's endpoint */
   struct coap_context_t *context;	  /**< session's context */
   void *tls;			  /**< security parameters */
+  uint16_t tx_mid;                /**< the last message id that was used in this session */
   struct coap_queue_t *sendqueue; /**< list of messages waiting to be sent */
   coap_tick_t last_rx_tx;
   uint8_t *psk_identity;

include/coap/net.h

@@ -215,13 +215,13 @@ void coap_context_set_psk( coap_context_t *ctx, const char *hint,
  *
  * @return        Incremented message id in network byte order.
  */
-COAP_STATIC_INLINE unsigned short
-coap_new_message_id(coap_context_t *context) {
-  context->message_id++;
+COAP_STATIC_INLINE uint16_t
+coap_new_message_id(coap_session_t *session) {
+  session->tx_mid++;
 #ifndef WITH_CONTIKI
-  return htons(context->message_id);
+  return htons(session->tx_mid);
 #else /* WITH_CONTIKI */
-  return uip_htons(context->message_id);
+  return uip_htons(session->tx_mid);
 #endif
 }
 

src/coap_session.c

@@ -68,6 +68,10 @@ coap_make_session(coap_proto_t proto, coap_session_type_t type, const coap_addre
       coap_log(LOG_ERR, "DTLS overhead exceeds MTU\n");
     }
   }
+
+  /* initialize message id */
+  prng((unsigned char *)&session->tx_mid, sizeof(session->tx_mid));
+
   return session;
 }
 

src/resource.c

@@ -679,7 +679,7 @@ coap_notify_observers(coap_context_t *context, coap_resource_t *r) {
       token.length = obs->token_length;
       token.s = obs->token;
 
-      response->hdr->id = coap_new_message_id(context);
+      response->hdr->id = coap_new_message_id(obs->session);
       if ((r->flags & COAP_RESOURCE_FLAGS_NOTIFY_CON) == 0
 	  && obs->non_cnt < COAP_OBS_MAX_NON) {
 	response->hdr->type = COAP_MESSAGE_NON;