Fixed WriteProperty bypass which is only for present-value property of commandable objects. (#984)

src/bacnet/basic/service/h_wp.c

@@ -40,6 +40,12 @@
  *      the property shall not be changed, and the write shall
  *      be considered successful.
  *
+ * @note There was an interpretation request in April 2025 that clarifies
+ *  that the NULL bypass is only for present-value property of objects that
+ *  optionally support a priority array but don't implement it.
+ *  See 135-2024-19.2.1.1 Commandable Properties for the list of commandable
+ *  properties of specific objects.
+ *
  * @param wp_data [in] The WriteProperty data structure
  * @return true if the write shall be considered successful
  */

src/bacnet/proplist.c

@@ -534,3 +534,53 @@ bool property_list_bacnet_list_member(
 
     return property_list_member(Properties_BACnetLIST, object_property);
 }
+
+/**
+ * @brief Determine if the object property is a commandable member
+ *
+ * 19.2.1.1 Commandable Properties
+ * The prioritization scheme is applied to certain properties of objects.
+ * The standard commandable properties and objects are as follows.
+ *
+ * @param object_type - object-type to be checked
+ * @param object_property - object-property to be checked
+ * @return true if the property is a commandable member
+ */
+bool property_list_commandable_member(
+    BACNET_OBJECT_TYPE object_type, BACNET_PROPERTY_ID object_property)
+{
+    bool status = false;
+
+    switch (object_type) {
+        case OBJECT_ACCESS_DOOR:
+        case OBJECT_ANALOG_OUTPUT:
+        case OBJECT_ANALOG_VALUE:
+        case OBJECT_BINARY_LIGHTING_OUTPUT:
+        case OBJECT_BINARY_OUTPUT:
+        case OBJECT_BINARY_VALUE:
+        case OBJECT_BITSTRING_VALUE:
+        case OBJECT_CHANNEL:
+        case OBJECT_CHARACTERSTRING_VALUE:
+        case OBJECT_DATE_VALUE:
+        case OBJECT_DATE_PATTERN_VALUE:
+        case OBJECT_DATETIME_VALUE:
+        case OBJECT_DATETIME_PATTERN_VALUE:
+        case OBJECT_INTEGER_VALUE:
+        case OBJECT_LARGE_ANALOG_VALUE:
+        case OBJECT_LIGHTING_OUTPUT:
+        case OBJECT_MULTI_STATE_OUTPUT:
+        case OBJECT_MULTI_STATE_VALUE:
+        case OBJECT_OCTETSTRING_VALUE:
+        case OBJECT_POSITIVE_INTEGER_VALUE:
+        case OBJECT_TIME_VALUE:
+        case OBJECT_TIME_PATTERN_VALUE:
+            if (object_property == PROP_PRESENT_VALUE) {
+                status = true;
+            }
+            break;
+        default:
+            break;
+    }
+
+    return status;
+}

src/bacnet/proplist.h

@@ -62,6 +62,9 @@ const int *property_list_bacnet_list(void);
 BACNET_STACK_EXPORT
 bool property_list_bacnet_list_member(
     BACNET_OBJECT_TYPE object_type, BACNET_PROPERTY_ID object_property);
+BACNET_STACK_EXPORT
+bool property_list_commandable_member(
+    BACNET_OBJECT_TYPE object_type, BACNET_PROPERTY_ID object_property);
 
 #ifdef __cplusplus
 }

src/bacnet/wp.c

@@ -500,6 +500,12 @@ bool write_property_unsigned_decode(
  *      the property shall not be changed, and the write shall
  *      be considered successful.
  *
+ * @note There was an interpretation request in April 2025 that clarifies
+ *  that the NULL bypass is only for present-value property of objects that
+ *  optionally support a priority array but don't implement it.
+ *  See 135-2024-19.2.1.1 Commandable Properties for the list of commandable
+ *  properties of specific objects.
+ *
  * @param wp_data [in] The WriteProperty data structure
  * @param member_of_object [in] Function to check if a property is a member
   of an object instance
@@ -520,25 +526,25 @@ bool write_property_relinquish_bypass(
         wp_data->application_data, wp_data->application_data_len);
     if ((len > 0) && (len == wp_data->application_data_len)) {
         /* single NULL */
-        /* check to see if this object property is commandable.
-           Does the property list contain a priority-array? */
-        if (member_of_object) {
-            has_priority_array = member_of_object(
-                wp_data->object_type, wp_data->object_instance,
-                PROP_PRIORITY_ARRAY);
-        }
-        if (has_priority_array || (wp_data->object_type == OBJECT_CHANNEL)) {
-            if (wp_data->object_property != PROP_PRESENT_VALUE) {
-                /* this property is not commandable,
+        if (property_list_commandable_member(
+                wp_data->object_type, wp_data->object_property)) {
+            if (member_of_object) {
+                /* check to see if this object property is commandable.
+                Does the property list contain a priority-array? */
+                has_priority_array = member_of_object(
+                    wp_data->object_type, wp_data->object_instance,
+                    PROP_PRIORITY_ARRAY);
+            }
+            if (has_priority_array ||
+                (wp_data->object_type == OBJECT_CHANNEL)) {
+                /* this property is commandable and shall not be bypassed */
+            } else {
+                /* this property that is optionally commandable
+                   is not commandable for this object instance,
                    so it "shall not be changed, and
                    the write shall be considered successful." */
                 bypass = true;
             }
-        } else {
-            /* this object is not commandable, so any property
-               written with a NULL "shall not be changed, and
-               the write shall be considered successful." */
-            bypass = true;
         }
     }