Send topic alias maximum from the broker.

man/mosquitto.conf.5.xml

@@ -952,6 +952,16 @@ log_timestamp_format %Y-%m-%dT%H:%M:%S
 						<para>Not reloaded on reload signal.</para>
 					</listitem>
 				</varlistentry>
+				<varlistentry>
+					<term><option>max_topic_alias</option> <replaceable>number</replaceable></term>
+					<listitem>
+						<para>This option sets the maximum number topic aliases
+							that an MQTT v5 client is allowed to create. It
+							applies per listener. Defaults to 10. Set to 0 to
+							disallow topic aliases.</para>
+						<para>Not reloaded on reload signal.</para>
+					</listitem>
+				</varlistentry>
 				<varlistentry>
 					<term><option>mount_point</option> <replaceable>topic prefix</replaceable></term>
 					<listitem>

src/conf.c

@@ -272,6 +272,7 @@ void config__init(struct mosquitto_db *db, struct mosquitto__config *config)
 	config->default_listener.protocol = mp_mqtt;
 	config->default_listener.security_options.allow_anonymous = -1;
 	config->default_listener.maximum_qos = 2;
+	config->default_listener.max_topic_alias = 10;
 }
 
 void config__cleanup(struct mosquitto__config *config)
@@ -507,6 +508,7 @@ int config__parse_args(struct mosquitto_db *db, struct mosquitto__config *config
 		config->listeners[config->listener_count-1].tls_engine = config->default_listener.tls_engine;
 		config->listeners[config->listener_count-1].tls_keyform = config->default_listener.tls_keyform;
 		config->listeners[config->listener_count-1].tls_engine_kpass_sha1 = config->default_listener.tls_engine_kpass_sha1;
+		config->listeners[config->listener_count-1].max_topic_alias = config->default_listener.max_topic_alias;
 		config->listeners[config->listener_count-1].cafile = config->default_listener.cafile;
 		config->listeners[config->listener_count-1].capath = config->default_listener.capath;
 		config->listeners[config->listener_count-1].certfile = config->default_listener.certfile;
@@ -1344,6 +1346,7 @@ int config__read_file_core(struct mosquitto__config *config, bool reload, struct
 						cur_listener->protocol = mp_mqtt;
 						cur_listener->port = tmp_int;
 						cur_listener->maximum_qos = 2;
+						cur_listener->max_topic_alias = 10;
 						token = strtok_r(NULL, " ", &saveptr);
 						if (token != NULL && token[0] == '#'){
 							token = NULL;
@@ -2072,6 +2075,15 @@ int config__read_file_core(struct mosquitto__config *config, bool reload, struct
 #else
 					log__printf(NULL, MOSQ_LOG_WARNING, "Warning: Bridge support not available.");
 #endif
+				}else if(!strcmp(token, "max_topic_alias")){
+					if(reload) continue; // Listeners not valid for reloading.
+					token = strtok_r(NULL, " ", &saveptr);
+					if(token){
+						cur_listener->max_topic_alias = atoi(token);
+						if(cur_listener->max_topic_alias < 0) cur_listener->max_topic_alias = -1;
+					}else{
+						log__printf(NULL, MOSQ_LOG_ERR, "Error: Empty max_topic_alias value in configuration.");
+					}
 				}else if(!strcmp(token, "try_private")){
 #ifdef WITH_BRIDGE
 					if(reload) continue; // FIXME

src/handle_connect.c

@@ -300,6 +300,12 @@ int handle__connect(struct mosquitto_db *db, struct mosquitto *context)
 			goto handle_connect_error;
 		}
 	}
+	if(protocol_version == PROTOCOL_VERSION_v5 && context->listener->max_topic_alias > 0){
+		if(mosquitto_property_add_int16(&connack_props, MQTT_PROP_TOPIC_ALIAS_MAXIMUM, context->listener->max_topic_alias)){
+			rc = MOSQ_ERR_NOMEM;
+			goto handle_connect_error;
+		}
+	}
 
 	if(packet__read_byte(&context->in_packet, &connect_flags)){
 		rc = 1;

src/handle_publish.c

@@ -51,7 +51,7 @@ int handle__publish(struct mosquitto_db *db, struct mosquitto *context)
 	mosquitto_property *p, *p_prev;
 	mosquitto_property *msg_properties = NULL, *msg_properties_last;
 	uint32_t message_expiry_interval = 0;
-	uint16_t topic_alias = 0;
+	int topic_alias = -1;
 	uint8_t reason_code = 0;
 
 #ifdef WITH_BRIDGE
@@ -160,19 +160,20 @@ int handle__publish(struct mosquitto_db *db, struct mosquitto *context)
 	}
 	mosquitto_property_free_all(&properties);
 
-	if(topic && topic_alias){
+	if(topic_alias == 0 || topic_alias > context->listener->max_topic_alias){
+		send__disconnect(context, MQTT_RC_TOPIC_ALIAS_INVALID, NULL);
+		return MOSQ_ERR_PROTOCOL;
+	}else if(topic_alias > 0){
+		if(topic){
 			rc = alias__add(context, topic, topic_alias);
 			if(rc) return rc;
-	}else if(topic == NULL && topic_alias){
+		}else{
 			rc = alias__find(context, &topic, topic_alias);
 			if(rc){
-			if(context->protocol == mosq_p_mqtt5){
 				send__disconnect(context, MQTT_RC_TOPIC_ALIAS_INVALID, NULL);
-			}
 				return rc;
 			}
-	}else if(topic == NULL && topic_alias == 0){
+		}
-		return MOSQ_ERR_PROTOCOL;
 	}
 	if(mosquitto_validate_utf8(topic, slen) != MOSQ_ERR_SUCCESS){
 		log__printf(NULL, MOSQ_LOG_INFO, "Client %s sent topic with invalid UTF-8, disconnecting.", context->id);

src/mosquitto_broker_internal.h

@@ -212,6 +212,7 @@ struct mosquitto__listener {
 	int socket_domain;
 	bool use_username_as_clientid;
 	uint8_t maximum_qos;
+	uint16_t max_topic_alias;
 #ifdef WITH_TLS
 	char *cafile;
 	char *capath;

test/broker/09-auth-bad-method.py

@@ -9,7 +9,7 @@ rc = 1
 keepalive = 10
 props = mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_METHOD, "basic")
 connect_packet = mosq_test.gen_connect("connect-test", proto_ver=5, keepalive=keepalive, properties=props)
-connack_packet = mosq_test.gen_connack(rc=mqtt5_rc.MQTT_RC_BAD_AUTHENTICATION_METHOD, proto_ver=5)
+connack_packet = mosq_test.gen_connack(rc=mqtt5_rc.MQTT_RC_BAD_AUTHENTICATION_METHOD, proto_ver=5, properties=None)
 
 port = mosq_test.get_port()
 broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)

test/broker/12-prop-topic-alias-invalid.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+
+# Test whether the broker handles a topic alias of >max_topic_alias correctly.
+# MQTTv5
+
+from mosq_test_helper import *
+
+def do_test(value):
+    rc = 1
+
+    keepalive = 10
+    connect_packet = mosq_test.gen_connect("test", proto_ver=5, keepalive=keepalive)
+    connack_packet = mosq_test.gen_connack(rc=0, proto_ver=5)
+
+    props = mqtt5_props.gen_uint16_prop(mqtt5_props.PROP_TOPIC_ALIAS, value)
+    publish_packet = mosq_test.gen_publish(topic="test/topic", qos=0, payload="12345678901234567890", proto_ver=5, properties=props)
+
+    disconnect_packet = mosq_test.gen_disconnect(reason_code=mqtt5_rc.MQTT_RC_TOPIC_ALIAS_INVALID, proto_ver=5)
+    port = mosq_test.get_port()
+    broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)
+
+    try:
+        sock = mosq_test.do_client_connect(connect_packet, connack_packet, port=port)
+        sock.send(publish_packet)
+        if mosq_test.expect_packet(sock, "disconnect", disconnect_packet):
+            rc = 0
+    finally:
+        broker.terminate()
+        broker.wait()
+        (stdo, stde) = broker.communicate()
+        if rc:
+            print(stde)
+            exit(rc)
+
+
+do_test(11)
+

test/broker/Makefile

@@ -198,3 +198,4 @@ endif
 	./12-prop-session-expiry-invalid.py
 	./12-prop-subpub-content-type.py
 	./12-prop-subpub-payload-format.py
+	./12-prop-topic-alias-invalid.py

test/broker/test.py

@@ -165,6 +165,7 @@ tests = [
     (1, './12-prop-session-expiry-invalid.py'),
     (1, './12-prop-subpub-content-type.py'),
     (1, './12-prop-subpub-payload-format.py'),
+    (1, './12-prop-topic-alias-invalid.py'),
     ]
 
 ptest.run_tests(tests)

test/mosq_test.py

@@ -389,6 +389,10 @@ def gen_connect(client_id, clean_session=True, keepalive=60, username=None, pass
 
 def gen_connack(flags=0, rc=0, proto_ver=4, properties=""):
     if proto_ver == 5:
+        if properties is not None:
+            properties = mqtt5_props.gen_uint16_prop(mqtt5_props.PROP_TOPIC_ALIAS_MAXIMUM, 10) + properties
+        else:
+            properties = ""
         properties = mqtt5_props.prop_finalise(properties)
 
         packet = struct.pack('!BBBB', 32, 2+len(properties), flags, rc) + properties