Add mosquitto_property_command_check()

lib/linker.version

@@ -96,4 +96,5 @@ MOSQ_1.6 {
 	global:
 		mosquitto_subscribe_multiple;
 		mosquitto_property_free_all;
+		mosquitto_property_command_check;
 } MOSQ_1.5;

lib/mosquitto.h

@@ -1897,6 +1897,20 @@ libmosq_EXPORT int mosquitto_validate_utf8(const char *str, int len);
  */
 libmosq_EXPORT void mosquitto_property_free_all(mosquitto_property **properties);
 
+/*
+ * Function: mosquitto_property_command_check
+ *
+ * Check whether a property identifier is valid for the given command.
+ *
+ * Parameters:
+ *   command - MQTT command (e.g. CMD_CONNECT)
+ *   identifier - MQTT property (e.g. MQTT_PROP_USER_PROPERTY)
+ *
+ * Returns:
+ *   MOSQ_ERR_SUCCESS - if the identifier is valid for command
+ *   MOSQ_ERR_PROTOCOL - if the identifier is not valid for use with command.
+ */
+int mosquitto_property_command_check(int command, int identifier);
 
 #ifdef __cplusplus
 }

lib/property_mosq.c

@@ -451,13 +451,9 @@ int property__write_all(struct mosquitto__packet *packet, struct mqtt5__property
 }
 
 
-static int property__command_check(int command, struct mqtt5__property *properties)
+int mosquitto_property_command_check(int command, int identifier)
 {
-	struct mqtt5__property *p;
-
-	p = properties;
-	while(p){
-		switch(p->identifier){
+	switch(identifier){
 		case MQTT_PROP_PAYLOAD_FORMAT_INDICATOR:
 		case MQTT_PROP_MESSAGE_EXPIRY_INTERVAL:
 		case MQTT_PROP_CONTENT_TYPE:
@@ -545,6 +541,18 @@ static int property__command_check(int command, struct mqtt5__property *properti
 		default:
 			return MOSQ_ERR_PROTOCOL;
 	}
+	return MOSQ_ERR_SUCCESS;
+}
+
+static int property__command_check(int command, struct mqtt5__property *properties)
+{
+	struct mqtt5__property *p;
+	int rc;
+
+	p = properties;
+	while(p){
+		rc = mosquitto_property_command_check(command, p->identifier);
+		if(rc) return rc;
 
 		p = p->next;
 	}