Add max_keepalive, for limiting keepalives of MQTT v5 clients.

ChangeLog.txt

@@ -5,6 +5,8 @@ Broker features:
 - Improved general support for broker generated client ids. Removed libuuid
   dependency.
 - auto_id_prefix now defaults to 'auto-'.
+- Add max_keepalive option, to allow a maximum keepalive value to be set for
+  MQTT v5 clients only.
 
 Client library features:
 - Add mosquitto_subscribe_multiple() for sending subscriptions to multiple

lib/handle_connack.c

@@ -62,6 +62,16 @@ int handle__connack(struct mosquitto *mosq)
 			}
 		}
 	}
+
+	prop = mosquitto_property_get_property(properties, MQTT_PROP_SERVER_KEEP_ALIVE, false);
+	if(prop){
+		rc = mosquitto_property_read_int16(prop, &mosq->keepalive);
+		if(rc){
+			mosquitto_property_free_all(&properties);
+			return rc;
+		}
+	}
+
 	log__printf(mosq, MOSQ_LOG_DEBUG, "Client %s received CONNACK (%d)", mosq->id, reason_code);
 	pthread_mutex_lock(&mosq->callback_mutex);
 	if(mosq->on_connect){

man/mosquitto.conf.5.xml

@@ -435,6 +435,25 @@
 					<para>Reloaded on reload signal.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>max_keepalive</option> <replaceable>value</replaceable></term>
+				<listitem>
+					<para>For MQTT v5 clients, it is possible to have the
+						server send a "server keepalive" value that will
+						override the keepalive value set by the client.  This
+						is intended to be used as a mechanism to say that the
+						server will disconnect the client earlier than it
+						anticipated, and that the client should use the new
+						keepalive value. The max_keepalive option allows you to
+						specify that clients may only connect with keepalive
+						less than or equal to this value, otherwise they will
+						be sent a server keepalive telling them to use
+						max_keepalive. This only applies to MQTT v5 clients.
+						The maximum value allowable, and default value, is
+						65535. Do not set below 10 seconds.</para>
+					<para>Reloaded on reload signal.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>max_queued_bytes</option> <replaceable>count</replaceable></term>
 				<listitem>

mosquitto.conf

@@ -155,6 +155,16 @@
 # false.
 #retain_available true
 
+# For MQTT v5 clients, it is possible to have the server send a "server
+# keepalive" value that will override the keepalive value set by the client.
+# This is intended to be used as a mechanism to say that the server will
+# disconnect the client earlier than it anticipated, and that the client should
+# use the new keepalive value. The max_keepalive option allows you to specify
+# that clients may only connect with keepalive less than or equal to this
+# value, otherwise they will be sent a server keepalive telling them to use
+# max_keepalive. This only applies to MQTT v5 clients. The maximum value
+# allowable is 65535. Do not set below 10.
+#max_keepalive 65535
 
 # =================================================================
 # Default listener

src/conf.c

@@ -212,6 +212,7 @@ static void config__init_reload(struct mosquitto_db *db, struct mosquitto__confi
 	}
 #endif
 	config->log_timestamp = true;
+	config->max_keepalive = 65535;
 	config->persistence = false;
 	mosquitto__free(config->persistence_location);
 	config->persistence_location = NULL;
@@ -1513,6 +1514,13 @@ int config__read_file_core(struct mosquitto__config *config, bool reload, struct
 					}else{
 						log__printf(NULL, MOSQ_LOG_ERR, "Error: Empty max_inflight_messages value in configuration.");
 					}
+				}else if(!strcmp(token, "max_keepalive")){
+					if(conf__parse_int(&token, "max_keepalive", &tmp_int, saveptr)) return MOSQ_ERR_INVAL;
+					if(tmp_int < 10 || tmp_int > 65535){
+						log__printf(NULL, MOSQ_LOG_ERR, "Error: Invalid max_keepalive value (%d).", tmp_int);
+						return MOSQ_ERR_INVAL;
+					}
+					config->max_keepalive = tmp_int;
 				}else if(!strcmp(token, "max_queued_bytes")){
 					token = strtok_r(NULL, " ", &saveptr);
 					if(token){

src/handle_connect.c

@@ -297,11 +297,17 @@ int handle__connect(struct mosquitto_db *db, struct mosquitto *context)
 		rc = 1;
 		goto handle_connect_error;
 	}
+	if(protocol_version == PROTOCOL_VERSION_v5 && context->keepalive > db->config->max_keepalive){
+		context->keepalive = db->config->max_keepalive;
+		if(mosquitto_property_add_int16(&connack_props, MQTT_PROP_SERVER_KEEP_ALIVE, context->keepalive)){
+			rc = MOSQ_ERR_NOMEM;
+			goto handle_connect_error;
+		}
+	}
 
 	if(protocol_version == PROTOCOL_VERSION_v5){
 		rc = property__read_all(CMD_CONNECT, &context->in_packet, &properties);
-		if(rc) return rc;
-		mosquitto_property_free_all(&properties);
+		if(rc) goto handle_connect_error;
 	}
 	property__process_connect(context, properties);
 

src/mosquitto_broker_internal.h

@@ -259,6 +259,7 @@ struct mosquitto__config {
 	bool log_timestamp;
 	char *log_file;
 	FILE *log_fptr;
+	uint16_t max_keepalive;
 	uint32_t message_size_limit;
 	bool persistence;
 	char *persistence_location;

test/broker/12-prop-server-keepalive.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+
+# Test whether sending a non zero session expiry interval in DISCONNECT after
+# having sent a zero session expiry interval is treated correctly in MQTT v5.
+
+from mosq_test_helper import *
+
+def write_config(filename, port):
+    with open(filename, 'w') as f:
+        f.write("port %d\n" % (port))
+        f.write("\n")
+        f.write("max_keepalive 60\n")
+
+port = mosq_test.get_port(1)
+conf_file = os.path.basename(__file__).replace('.py', '.conf')
+write_config(conf_file, port)
+
+
+rc = 1
+
+keepalive = 61
+connect_packet = mosq_test.gen_connect("test", proto_ver=5, keepalive=keepalive)
+
+props = mqtt5_props.gen_uint16_prop(mqtt5_props.PROP_SERVER_KEEP_ALIVE, 60)
+connack_packet = mosq_test.gen_connack(rc=0, proto_ver=5, properties=props)
+
+broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port, use_conf=True)
+
+try:
+    sock = mosq_test.do_client_connect(connect_packet, connack_packet, port=port)
+    sock.close()
+    rc = 0
+finally:
+    os.remove(conf_file)
+    broker.terminate()
+    broker.wait()
+    (stdo, stde) = broker.communicate()
+    if rc:
+        print(stde)
+
+exit(rc)
+

test/broker/Makefile

@@ -140,3 +140,4 @@ endif
 	./12-prop-subpub-payload-format.py
 	./12-prop-subpub-content-type.py
 	./12-prop-assigned-client-identifier.py
+	./12-prop-server-keepalive.py

test/broker/ptest.py

@@ -109,6 +109,7 @@ tests = [
 	(1, './12-prop-subpub-payload-format.py'),
 	(1, './12-prop-subpub-content-type.py'),
 	(1, './12-prop-assigned-client-identifier.py'),
+	(1, './12-prop-server-keepalive.py'),
     ]
 
 minport = 1888