[esp_event]: fixed and improved docs

* Description of unregistering was incorrect
* Made clear that event loop arg mustn't be NULL
* Added parameter check in create function

Closes https://github.com/espressif/esp-idf/issues/6761
Closes IDFGH-4969

components/esp_event/esp_event.c

@@ -447,7 +447,15 @@ static void inline __attribute__((always_inline)) post_instance_delete(esp_event
 
 esp_err_t esp_event_loop_create(const esp_event_loop_args_t* event_loop_args, esp_event_loop_handle_t* event_loop)
 {
-    assert(event_loop_args);
+    if (event_loop_args == NULL) {
+        ESP_LOGE(TAG, "event_loop_args was NULL");
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    if (event_loop == NULL) {
+        ESP_LOGE(TAG, "event_loop was NULL");
+        return ESP_ERR_INVALID_ARG;
+    }
 
     esp_event_loop_instance_t* loop;
     esp_err_t err = ESP_ERR_NO_MEM; // most likely error

components/esp_event/include/esp_event.h

@@ -48,6 +48,7 @@ typedef struct {
  *
  * @return
  *  - ESP_OK: Success
+ *  - ESP_ERR_INVALID_ARG: event_loop_args or event_loop was NULL
  *  - ESP_ERR_NO_MEM: Cannot allocate memory for event loops list
  *  - ESP_FAIL: Failed to create task loop
  *  - Others: Fail
@@ -57,7 +58,7 @@ esp_err_t esp_event_loop_create(const esp_event_loop_args_t *event_loop_args, es
 /**
  * @brief Delete an existing event loop.
  *
- * @param[in] event_loop event loop to delete
+ * @param[in] event_loop event loop to delete, must not be NULL
  *
  * @return
  *  - ESP_OK: Success
@@ -102,7 +103,7 @@ esp_err_t esp_event_loop_delete_default(void);
  * In cases where waiting on the queue times out, ESP_OK is returned and not ESP_ERR_TIMEOUT, since it is
  * normal behavior.
  *
- * @param[in] event_loop event loop to dispatch posted events from
+ * @param[in] event_loop event loop to dispatch posted events from, must not be NULL
  * @param[in] ticks_to_run number of ticks to run the loop
  *
  * @note encountering an unknown event that has been posted to the loop will only generate a warning, not an error.
@@ -158,7 +159,7 @@ esp_err_t esp_event_handler_register(esp_event_base_t event_base,
  * This function behaves in the same manner as esp_event_handler_register, except the additional
  * specification of the event loop to register the handler to.
  *
- * @param[in] event_loop the event loop to register this handler function to
+ * @param[in] event_loop the event loop to register this handler function to, must not be NULL
  * @param[in] event_base the base id of the event to register the handler for
  * @param[in] event_id the id of the event to register the handler for
  * @param[in] event_handler the handler function which gets called when the event is dispatched
@@ -197,7 +198,7 @@ esp_err_t esp_event_handler_register_with(esp_event_loop_handle_t event_loop,
  * Each registration yields a distinct instance object which identifies it over the registration
  * lifetime.
  *
- * @param[in] event_loop the event loop to register this handler function to
+ * @param[in] event_loop the event loop to register this handler function to, must not be NULL
  * @param[in] event_base the base id of the event to register the handler for
  * @param[in] event_id the id of the event to register the handler for
  * @param[in] event_handler the handler function which gets called when the event is dispatched
@@ -263,15 +264,15 @@ esp_err_t esp_event_handler_instance_register(esp_event_base_t event_base,
  * @note This function is obsolete and will be deprecated soon, please use esp_event_handler_instance_unregister()
  *       instead.
  *
- * This function can be used to unregister a handler so that it no longer gets called during dispatch.
- * Handlers can be unregistered for either: (1) specific events, (2) all events of a certain event base,
- * or (3) all events known by the system event loop
+ * Unregisters a handler so it will no longer be called during dispatch.
+ * Handlers can be unregistered for any combination of event_base and event_id which were previously registered.
+ * To unregister a handler, the event_base and event_id arguments must match exactly the arguments passed to
+ * esp_event_handler_register() when that handler was registered. Passing ESP_EVENT_ANY_BASE and/or ESP_EVENT_ANY_ID
+ * will only unregister handlers that were registered with the same wildcard arguments.
  *
- *  - specific events: specify exact event_base and event_id
- *  - all events of a certain base: specify exact event_base and use ESP_EVENT_ANY_ID as the event_id
- *  - all events known by the loop: use ESP_EVENT_ANY_BASE for event_base and ESP_EVENT_ANY_ID as the event_id
- *
- * This function ignores unregistration of handlers that has not been previously registered.
+ * @note When using ESP_EVENT_ANY_ID, handlers registered to specific event IDs using the same base will not be
+ *       unregistered. When using ESP_EVENT_ANY_BASE, events registered to specific bases will also not be
+ *       unregistered. This avoids accidental unregistration of handlers registered by other users or components.
  *
  * @param[in] event_base the base of the event with which to unregister the handler
  * @param[in] event_id the id of the event with which to unregister the handler
@@ -294,7 +295,7 @@ esp_err_t esp_event_handler_unregister(esp_event_base_t event_base,
  * This function behaves in the same manner as esp_event_handler_unregister, except the additional specification of
  * the event loop to unregister the handler with.
  *
- * @param[in] event_loop the event loop with which to unregister this handler function
+ * @param[in] event_loop the event loop with which to unregister this handler function, must not be NULL
  * @param[in] event_base the base of the event with which to unregister the handler
  * @param[in] event_id the id of the event with which to unregister the handler
  * @param[in] event_handler the handler to unregister
@@ -312,17 +313,18 @@ esp_err_t esp_event_handler_unregister_with(esp_event_loop_handle_t event_loop,
 /**
  * @brief Unregister a handler instance from a specific event loop.
  *
- * This function can be used to unregister a handler so that it no longer gets called during dispatch.
- * Handlers can be unregistered for either: (1) specific events, (2) all events of a certain event base,
- * or (3) all events known by the system event loop
- *
- *  - specific events: specify exact event_base and event_id
- *  - all events of a certain base: specify exact event_base and use ESP_EVENT_ANY_ID as the event_id
- *  - all events known by the loop: use ESP_EVENT_ANY_BASE for event_base and ESP_EVENT_ANY_ID as the event_id
+ * Unregisters a handler instance so it will no longer be called during dispatch.
+ * Handler instances can be unregistered for any combination of event_base and event_id which were previously
+ * registered. To unregister a handler instance, the event_base and event_id arguments must match exactly the
+ * arguments passed to esp_event_handler_instance_register() when that handler instance was registered.
+ * Passing ESP_EVENT_ANY_BASE and/or ESP_EVENT_ANY_ID will only unregister handler instances that were registered
+ * with the same wildcard arguments.
  *
- * This function ignores unregistration of handler instances that have not been previously registered.
+ * @note When using ESP_EVENT_ANY_ID, handlers registered to specific event IDs using the same base will not be
+ *       unregistered. When using ESP_EVENT_ANY_BASE, events registered to specific bases will also not be
+ *       unregistered. This avoids accidental unregistration of handlers registered by other users or components.
  *
- * @param[in] event_loop the event loop with which to unregister this handler function
+ * @param[in] event_loop the event loop with which to unregister this handler function, must not be NULL
  * @param[in] event_base the base of the event with which to unregister the handler
  * @param[in] event_id the id of the event with which to unregister the handler
  * @param[in] instance the instance object of the registration to be unregistered
@@ -388,7 +390,7 @@ esp_err_t esp_event_post(esp_event_base_t event_base,
  * This function behaves in the same manner as esp_event_post_to, except the additional specification of the event loop
  * to post the event to.
  *
- * @param[in] event_loop the event loop to post to
+ * @param[in] event_loop the event loop to post to, must not be NULL
  * @param[in] event_base the event base that identifies the event
  * @param[in] event_id the event id that identifies the event
  * @param[in] event_data the data, specific to the event occurence, that gets passed to the handler
@@ -441,7 +443,7 @@ esp_err_t esp_event_isr_post(esp_event_base_t event_base,
 /**
  * @brief Special variant of esp_event_post_to for posting events from interrupt handlers
  *
- * @param[in] event_loop the event loop to post to
+ * @param[in] event_loop the event loop to post to, must not be NULL
  * @param[in] event_base the event base that identifies the event
  * @param[in] event_id the event id that identifies the event
  * @param[in] event_data the data, specific to the event occurence, that gets passed to the handler

components/esp_event/test/test_event.c

@@ -305,6 +305,14 @@ static void test_teardown(void)
 #define TIMER_SCALE           (TIMER_BASE_CLK / TIMER_DIVIDER)  // convert counter value to seconds
 #define TIMER_INTERVAL0_SEC   (2.0) // sample test interval for the first timer
 
+TEST_CASE("create and event loop with any NULL argument fails", "[event]")
+{
+    esp_event_loop_handle_t loop; // with dedicated task
+    esp_event_loop_args_t loop_args = test_event_get_default_loop_args();
+    TEST_ASSERT_EQUAL(ESP_ERR_INVALID_ARG, esp_event_loop_create(NULL, &loop));
+    TEST_ASSERT_EQUAL(ESP_ERR_INVALID_ARG, esp_event_loop_create(&loop_args, NULL));
+}
+
 TEST_CASE("can create and delete event loops", "[event]")
 {
     /* this test aims to verify that: