coap_resource.c: Make dynamic resource handling thread safe

Let libcoap do the necessary multi-thread locking during resource
generation, lookup and deletion.

Supported using a new handler set up by coap_register_dynamic_resource_handler().

include/coap3/coap_net.h

@@ -106,6 +106,16 @@ typedef void (*coap_pong_handler_t)(coap_session_t *session,
                                     const coap_pdu_t *received,
                                     const coap_mid_t mid);
 
+/**
+ * Definition of resource dynamic creation handler function
+ *
+ * @param session The CoAP session.
+ * @param request The request PDU.
+ *
+ * @return       A pointer to the new resource or @c NULL on error.
+ */
+typedef coap_resource_t *(*coap_resource_dynamic_create_t)(coap_session_t *session,
+                                                           const coap_pdu_t *request);
 /**
  * Registers a new message handler that is called whenever a response is
  * received.
@@ -148,6 +158,24 @@ void coap_register_ping_handler(coap_context_t *context,
 void coap_register_pong_handler(coap_context_t *context,
                                 coap_pong_handler_t handler);
 
+/**
+ * Sets up a handler for calling when an unknown resource is requested.
+ * The @p create_handler is expected to create the required resource to handle
+ * the request which is then used to call the appropriate method handler.
+ *
+ * Doing this stops multiple threads asking for the same unknown resource and
+ * means that a resource unknown handler does not need to be thread safe.
+ *
+ * @param context The context to add this support to.
+ * @param create_handler Called to create a new resource.
+ * @param dynamic_max Maximum number of currently created dynamic resources.  If
+ *                    0, unlimited.
+ *
+ */
+void coap_register_dynamic_resource_handler(coap_context_t *context,
+                                            coap_resource_dynamic_create_t create_handler,
+                                            uint32_t dynamic_max);
+
 /**
  * Registers the option number @p number with the given context object @p context.
  *

include/coap3/coap_net_internal.h

@@ -215,6 +215,9 @@ struct coap_context_t {
   uint8_t testing_cids;            /**< Change client's source port every testing_cids */
 #endif /* COAP_CLIENT_SUPPORT */
   uint32_t block_mode;             /**< Zero or more COAP_BLOCK_ or'd options */
+  coap_resource_dynamic_create_t dyn_create_handler; /**< Dynamc resource create handler */
+  uint32_t dynamic_cur;            /* Current number of dynamic resources */
+  uint32_t dynamic_max;            /* Max number of dynamic resources or 0 is unlimited */
 };
 
 /**

include/coap3/coap_resource_internal.h

@@ -60,7 +60,9 @@ struct coap_resource_t {
   unsigned int is_proxy_uri:1;   /**< resource created for proxy URI handler */
   unsigned int is_reverse_proxy:1; /**< resource created for reverse proxy URI handler */
   unsigned int list_being_traversed:1; /**< resource subscriber list being traversed */
+  unsigned int is_dynamic:1;     /**< create unknown resource dynamically */
 
+  uint32_t ref;                  /**< Resource reference count */
   /**
    * Used to store handlers for the seven coap methods @c GET, @c POST, @c PUT,
    * @c DELETE, @c FETCH, @c PATCH and @c IPATCH.
@@ -147,6 +149,26 @@ int coap_delete_resource_lkd(coap_context_t *context, coap_resource_t *resource)
  */
 void coap_delete_all_resources(coap_context_t *context);
 
+/**
+ * Increment reference counter on a resource.
+ *
+ * Note: This function must be called in the locked state.
+ *
+ * @param resource The CoAP resource.
+ */
+void coap_resource_reference_lkd(coap_resource_t *resource);
+
+/**
+ * Decrement reference counter on a resource.
+ * Note that the resource storage may be deleted as a result and should not be
+ * used after this call.
+ *
+ * Note: This function must be called in the locked state.
+ *
+ * @param resource The CoAP resource.
+ */
+void coap_resource_release_lkd(coap_resource_t *resource);
+
 #define RESOURCES_ADD(r, obj) \
   HASH_ADD(hh, (r), uri_path->s[0], (obj)->uri_path->length, (obj))