Add the `bridge_max_packet_size` option.

Closes #265.

ChangeLog.txt

@@ -58,6 +58,7 @@ Broker:
 - The broker now sends the receive-maximum property for MQTT v5 CONNACKs.
 - mosquitto_password now forbids the : character. Closes #1833.
 - Fix `log_timestamp_format` not applying to `log_dest topic`. Closes #1862.
+- Add the `bridge_max_packet_size` option. Closes #265.
 
 Client library:
 - Client no longer generates random client ids for v3.1.1 clients, these are

man/mosquitto.conf.5.xml

@@ -1521,6 +1521,20 @@ openssl dhparam -out dhparam.pem 2048</programlisting>
 						<replaceable>true</replaceable>.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>bridge_max_packet_size</option> <replaceable>value</replaceable></term>
+				<listitem>
+					<para>
+						If you wish to restrict the size of messages sent to a
+						remote bridge, use this option. This sets the maximum
+						number of bytes for the total message, including headers
+						and payload. Note that MQTT v5 brokers may provide their
+						own maximum-packet-size property. In this case, the
+						smaller of the two limits will be used. Set to 0 for
+						"unlimited".
+					</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>bridge_outgoing_retain</option> [ true | false ]</term>
 				<listitem>

mosquitto.conf

@@ -786,6 +786,14 @@
 # all outgoing messages to that bridge, regardless of any other setting.
 #bridge_outgoing_retain true
 
+# If you wish to restrict the size of messages sent to a remote bridge, use the
+# bridge_max_packet_size option. This sets the maximum number of bytes for
+# the total message, including headers and payload.
+# Note that MQTT v5 brokers may provide their own maximum-packet-size property.
+# In this case, the smaller of the two limits will be used.
+# Set to 0 for "unlimited".
+#bridge_max_packet_size 0
+
 
 # -----------------------------------------------------------------
 # Certificate based SSL/TLS support

src/bridge.c

@@ -162,6 +162,7 @@ int bridge__connect_step1(struct mosquitto_db *db, struct mosquitto *context)
 	context->in_packet.payload = NULL;
 	context->ping_t = 0;
 	context->bridge->lazy_reconnect = false;
+	context->maximum_packet_size = context->bridge->maximum_packet_size;
 	bridge__packet_cleanup(context);
 	db__message_reconnect_reset(db, context);
 
@@ -339,6 +340,7 @@ int bridge__connect(struct mosquitto_db *db, struct mosquitto *context)
 	context->in_packet.payload = NULL;
 	context->ping_t = 0;
 	context->bridge->lazy_reconnect = false;
+	context->maximum_packet_size = context->bridge->maximum_packet_size;
 	bridge__packet_cleanup(context);
 	db__message_reconnect_reset(db, context);
 

src/conf.c

@@ -1035,6 +1035,19 @@ int config__read_file_core(struct mosquitto__config *config, bool reload, struct
 					if(conf__parse_bool(&token, "bridge_require_ocsp", &cur_bridge->tls_ocsp_required, saveptr)) return MOSQ_ERR_INVAL;
 #else
 					log__printf(NULL, MOSQ_LOG_WARNING, "Warning: TLS support not available.");
+#endif
+				}else if(!strcmp(token, "bridge_max_packet_size")){
+#if defined(WITH_BRIDGE)
+					if(reload) continue; // Bridges not valid for reloading.
+					if(!cur_bridge){
+						log__printf(NULL, MOSQ_LOG_ERR, "Error: Invalid bridge configuration.");
+						return MOSQ_ERR_INVAL;
+					}
+					if(conf__parse_int(&token, "bridge_max_packet_size", &tmp_int, saveptr)) return MOSQ_ERR_INVAL;
+					if(tmp_int < 0) tmp_int = 0;
+					cur_bridge->maximum_packet_size = (uint32_t)tmp_int;
+#else
+					log__printf(NULL, MOSQ_LOG_WARNING, "Warning: Bridge support not available.");
 #endif
 				}else if(!strcmp(token, "bridge_outgoing_retain")){
 #if defined(WITH_BRIDGE)

src/handle_connack.c

@@ -32,6 +32,7 @@ int handle__connack(struct mosquitto_db *db, struct mosquitto *context)
 	uint8_t connect_acknowledge;
 	uint8_t reason_code;
 	mosquitto_property *properties = NULL;
+	uint32_t maximum_packet_size;
 
 	if(!context){
 		return MOSQ_ERR_INVAL;
@@ -55,6 +56,15 @@ int handle__connack(struct mosquitto_db *db, struct mosquitto *context)
 		}
 		rc = property__read_all(CMD_CONNACK, &context->in_packet, &properties);
 		if(rc) return rc;
+
+		if(mosquitto_property_read_int32(properties, MQTT_PROP_MAXIMUM_PACKET_SIZE,
+					&maximum_packet_size, false)){
+
+			if(context->maximum_packet_size == 0 || context->maximum_packet_size > maximum_packet_size){
+				context->maximum_packet_size = maximum_packet_size;
+			}
+		}
+
 		mosquitto_property_free_all(&properties);
 	}
 	mosquitto_property_free_all(&properties); /* FIXME - TEMPORARY UNTIL PROPERTIES PROCESSED */

src/mosquitto_broker_internal.h

@@ -586,6 +586,7 @@ struct mosquitto__bridge{
 	int backoff_base;
 	int backoff_cap;
 	int threshold;
+	uint32_t maximum_packet_size;
 	bool lazy_reconnect;
 	bool attempt_unsubscribe;
 	bool initial_notification_done;