Fix session expiry with very large expiry intervals.

Closes #1525. Thanks to Christoph Krey.

ChangeLog.txt

@@ -1,3 +1,6 @@
+Broker:
+- Fix session expiry with very large expiry intervals. Closes #1525.
+
 1.6.8 - 20191128
 ================
 

src/session_expiry.c

@@ -31,7 +31,13 @@ static time_t last_check = 0;
 
 static int session_expiry__cmp(struct session_expiry_list *i1, struct session_expiry_list *i2)
 {
-	return i1->context->session_expiry_interval - i2->context->session_expiry_interval;
+	if(i1->context->session_expiry_time == i2->context->session_expiry_time){
+		return 0;
+	}else if(i1->context->session_expiry_time > i2->context->session_expiry_time){
+		return 1;
+	}else{
+		return -1;
+	}
 }
 
 

test/broker/05-session-expiry-v5.py

@@ -7,6 +7,14 @@ from mosq_test_helper import *
 rc = 1
 keepalive = 60
 
+
+# This client exists to test possible fixed size int overflow and sorting of the session intervals
+# https://github.com/eclipse/mosquitto/issues/1525
+props = mqtt5_props.gen_uint32_prop(mqtt5_props.PROP_SESSION_EXPIRY_INTERVAL, 4294967294)
+connect0_packet = mosq_test.gen_connect("overflow", keepalive=keepalive, clean_session=False, proto_ver=5, properties=props)
+connack0_packet = mosq_test.gen_connack(flags=0, rc=0, proto_ver=5)
+
+
 props = mqtt5_props.gen_uint32_prop(mqtt5_props.PROP_SESSION_EXPIRY_INTERVAL, 1)
 connect_packet = mosq_test.gen_connect("clean-qos2-test", keepalive=keepalive, clean_session=False, proto_ver=5, properties=props)
 connack1_packet = mosq_test.gen_connack(flags=0, rc=0, proto_ver=5)
@@ -23,6 +31,12 @@ port = mosq_test.get_port()
 broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)
 
 try:
+    # Connect client with wildly different session expiry, this should impact
+    # on the test if all is well
+    sock0 = mosq_test.do_client_connect(connect0_packet, connack0_packet, port=port, connack_error="connack 0")
+    # Immediately disconnect, this should now be queued to expire
+    sock0.close()
+
     # First connect, clean start is false, we expect a normal connack
     sock = mosq_test.do_client_connect(connect_packet, connack1_packet, port=port, connack_error="connack 1")
     # Forceful disconnect