Test and fix for subscription identifiers not being updated.

Closes #1169. Thanks to Christoph Krey.

src/subs.c

@@ -263,6 +263,7 @@ static int sub__add_recurse(struct mosquitto_db *db, struct mosquitto *context,
 					 * need to update QoS. Return MOSQ_ERR_SUB_EXISTS to
 					 * indicate this to the calling function. */
 					leaf->qos = qos;
+					leaf->identifier = identifier;
 					if(context->protocol == mosq_p_mqtt31 || context->protocol == mosq_p_mqtt5){
 						return MOSQ_ERR_SUB_EXISTS;
 					}else{

test/broker/02-subpub-qos0-subscription-id.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 
-# Do subscription identifiers work as expected?
+# Does setting and updating subscription identifiers work as expected?
 # MQTT v5
 
 from mosq_test_helper import *
@@ -24,6 +24,24 @@ mid = 3
 subscribe3_packet = mosq_test.gen_subscribe(mid, "subpub/noid", 0, proto_ver=5)
 suback3_packet = mosq_test.gen_suback(mid, 0, proto_ver=5)
 
+# Updated version of subscribe1, now without a subscription identifier
+mid = 4
+subscribe1u_packet = mosq_test.gen_subscribe(mid, "subpub/id1", 0, proto_ver=5)
+suback1u_packet = mosq_test.gen_suback(mid, 0, proto_ver=5)
+
+# Updated version of subscribe2, with a new subscription identifier
+mid = 5
+props = mqtt5_props.gen_varint_prop(mqtt5_props.PROP_SUBSCRIPTION_IDENTIFIER, 19)
+subscribe2u_packet = mosq_test.gen_subscribe(mid, "subpub/+/id2", 0, proto_ver=5, properties=props)
+suback2u_packet = mosq_test.gen_suback(mid, 0, proto_ver=5)
+
+# Updated version of subscribe3, now with a subscription identifier
+mid = 6
+props = mqtt5_props.gen_varint_prop(mqtt5_props.PROP_SUBSCRIPTION_IDENTIFIER, 21)
+subscribe3u_packet = mosq_test.gen_subscribe(mid, "subpub/noid", 0, proto_ver=5, properties=props)
+suback3u_packet = mosq_test.gen_suback(mid, 0, proto_ver=5)
+
+
 publish1_packet = mosq_test.gen_publish("subpub/id1", qos=0, payload="message1", proto_ver=5)
 
 props = mqtt5_props.gen_varint_prop(mqtt5_props.PROP_SUBSCRIPTION_IDENTIFIER, 1)
@@ -36,6 +54,18 @@ publish2r_packet = mosq_test.gen_publish("subpub/test/id2", qos=0, payload="mess
 publish3_packet = mosq_test.gen_publish("subpub/noid", qos=0, payload="message3", proto_ver=5)
 
 
+# Updated version of publish1r, now with no id
+publish1ru_packet = mosq_test.gen_publish("subpub/id1", qos=0, payload="message1", proto_ver=5)
+
+# Updated verison of publish2r, with updated id
+props = mqtt5_props.gen_varint_prop(mqtt5_props.PROP_SUBSCRIPTION_IDENTIFIER, 19)
+publish2ru_packet = mosq_test.gen_publish("subpub/test/id2", qos=0, payload="message2", proto_ver=5, properties=props)
+
+# Updated version of publish3r, now with an id
+props = mqtt5_props.gen_varint_prop(mqtt5_props.PROP_SUBSCRIPTION_IDENTIFIER, 21)
+publish3ru_packet = mosq_test.gen_publish("subpub/noid", qos=0, payload="message3", proto_ver=5, properties=props)
+
+
 port = mosq_test.get_port()
 broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)
 
@@ -50,6 +80,15 @@ try:
     mosq_test.do_send_receive(sock, publish2_packet, publish2r_packet, "publish2")
     mosq_test.do_send_receive(sock, publish1_packet, publish1r_packet, "publish1")
 
+    # Now update the subscription identifiers
+    mosq_test.do_send_receive(sock, subscribe1u_packet, suback1u_packet, "suback1u")
+    mosq_test.do_send_receive(sock, subscribe2u_packet, suback2u_packet, "suback2u")
+    mosq_test.do_send_receive(sock, subscribe3u_packet, suback3u_packet, "suback3u")
+
+    mosq_test.do_send_receive(sock, publish2_packet, publish2ru_packet, "publish2u")
+    mosq_test.do_send_receive(sock, publish3_packet, publish3ru_packet, "publish3u")
+    mosq_test.do_send_receive(sock, publish1_packet, publish1ru_packet, "publish1u")
+
     rc = 0
 
     sock.close()