Add global_max_connections option.

ChangeLog.txt

@@ -58,6 +58,8 @@ Broker:
 - Add `mosquitto_client_port()` function for plugins.
 - Add `global_max_clients` option to allow limiting client sessions globally
   on the broker.
+- Add `global_max_connections` option to allow limiting client onnections globally
+  on the broker.
 
 Client library:
 - Add MOSQ_OPT_DISABLE_SOCKETPAIR to allow the disabling of the socketpair

man/mosquitto.conf.5.xml

@@ -416,7 +416,7 @@
 					</para>
 
 					<para>
-						See also the max_connections setting, which applies to
+						See also the <option>max_connections</option> setting, which applies to
 						listeners. If you set <option>global_max_clients</option>
 						to 1000 and <option>max_connections</option> on a
 						listener to 10, then that means only 10 simultaneous
@@ -429,6 +429,24 @@
 					<para>Reloaded on reload signal.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>global_max_connections</option> <replaceable>count</replaceable></term>
+				<listitem>
+					<para>
+						The maximum number of currently connected clients to
+						allow across the whole broker.
+					</para>
+
+					<para>
+						See also the <option>global_max_clients</option> and
+						<option>max_connections</option> settings.
+					</para>
+
+					<para>This option applies globally.</para>
+					<para>Defaults to -1 (unlimited)</para>
+					<para>Reloaded on reload signal.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>global_plugin</option> <replaceable>file path</replaceable></term>
 				<listitem>

mosquitto.conf

@@ -65,13 +65,19 @@
 # disconnected, or has disconnected and still hasn't exceeded its session
 # expiry interval (MQTT v5).
 #
-# See also the max_connections setting, which applies to listeners. If you set
+# See also the global_max_connections setting, and the max_connections setting,
-# global_max_clients to 1000 and max_connections on a listener to 10, then that
+# which applies to listeners. If you set global_max_clients to 1000 and
-# means only 10 simultaneous connections will be allowed at once, with an
+# max_connections on a listener to 10, then that means only 10 simultaneous
-# overall maximum of 1000 client sessions.
+# connections will be allowed at once, with an overall maximum of 1000 client
+# sessions.
 #
 #global_max_clients -1
 
+# The maximum number of currently connected clients to allow across the whole
+# broker.
+# See also the global_max_clients and max_connections settings.
+#global_max_connections -1
+
 # QoS 1 and 2 messages will be allowed inflight per client until this limit
 # is exceeded.  Defaults to 0. (No maximum)
 # See also max_inflight_messages

src/conf.c

@@ -193,6 +193,7 @@ static void config__init_reload(struct mosquitto__config *config)
 	mosquitto__free(config->log_timestamp_format);
 	config->log_timestamp_format = NULL;
 	config->global_max_clients = -1;
+	config->global_max_connections = -1;
 	config->max_keepalive = 65535;
 	config->max_packet_size = 0;
 	config->max_inflight_messages = 20;
@@ -1474,6 +1475,8 @@ static int config__read_file_core(struct mosquitto__config *config, bool reload,
 #endif
 				}else if(!strcmp(token, "global_max_clients")){
 					if(conf__parse_int(&token, "global_max_clients", &config->global_max_clients, &saveptr)) return MOSQ_ERR_INVAL;
+				}else if(!strcmp(token, "global_max_connections")){
+					if(conf__parse_int(&token, "global_max_connections", &config->global_max_connections, &saveptr)) return MOSQ_ERR_INVAL;
 				}else if(!strcmp(token, "http_dir")){
 #ifdef WITH_WEBSOCKETS
 					if(reload) continue; /* Listeners not valid for reloading. */

src/mosquitto_broker_internal.h

@@ -274,6 +274,7 @@ struct mosquitto__config {
 	bool daemon;
 	bool enable_control_api;
 	int global_max_clients;
+	int global_max_connections;
 	struct mosquitto__listener default_listener;
 	struct mosquitto__listener *listeners;
 	int listener_count;

src/net.c

@@ -197,7 +197,9 @@ struct mosquitto *net__socket_accept(struct mosquitto__listener_sock *listensock
 	}
 	new_context->listener->client_count++;
 
-	if(new_context->listener->max_connections > 0 && new_context->listener->client_count > new_context->listener->max_connections){
+	if((new_context->listener->max_connections > 0 && new_context->listener->client_count > new_context->listener->max_connections)
+			|| (db.config->global_max_connections > 0 && HASH_CNT(hh_sock, db.contexts_by_sock) > (unsigned int)db.config->global_max_connections)){
+
 		if(db.config->connection_messages == true){
 			log__printf(NULL, MOSQ_LOG_NOTICE, "Client connection from %s denied: max_connections exceeded.", new_context->address);
 		}

src/websockets.c

@@ -164,7 +164,9 @@ static int callback_mqtt(
 				u->mosq = NULL;
 				return -1;
 			}
-			if(mosq->listener->max_connections > 0 && mosq->listener->client_count > mosq->listener->max_connections){
+			if((mosq->listener->max_connections > 0 && mosq->listener->client_count > mosq->listener->max_connections)
+					|| (db.config->global_max_connections > 0 && HASH_CNT(hh_sock, db.contexts_by_sock) > (unsigned int)db.config->global_max_connections)){
+
 				if(db.config->connection_messages == true){
 					log__printf(NULL, MOSQ_LOG_NOTICE, "Client connection from %s denied: max_connections exceeded.", mosq->address);
 				}

test/broker/01-connect-global-max-connections.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+
+# Test whether global_max_connections works
+
+from mosq_test_helper import *
+
+def write_config(filename, port):
+    with open(filename, 'w') as f:
+        f.write("listener %d\n" % (port))
+        f.write("allow_anonymous true\n")
+        f.write("global_max_connections 10\n")
+
+def do_test():
+    rc = 1
+
+    connect_packets_ok = []
+    connack_packets_ok = []
+    for i in range(0, 10):
+        connect_packets_ok.append(mosq_test.gen_connect("max-conn-%d"%i, proto_ver=5))
+        connack_packets_ok.append(mosq_test.gen_connack(rc=0, proto_ver=5))
+
+    connect_packet_bad = mosq_test.gen_connect("max-conn-bad", proto_ver=5)
+    connack_packet_bad = b""
+
+    port = mosq_test.get_port()
+    conf_file = os.path.basename(__file__).replace('.py', '.conf')
+    write_config(conf_file, port)
+    broker = mosq_test.start_broker(filename=os.path.basename(__file__), use_conf=True, port=port)
+
+    socks = []
+    try:
+        # Open all allowed connections, a limit of 10
+        for i in range(0, 10):
+            socks.append(mosq_test.do_client_connect(connect_packets_ok[i], connack_packets_ok[i], port=port))
+
+        # Try to open an 11th connection
+        try:
+            sock_bad = mosq_test.do_client_connect(connect_packet_bad, connack_packet_bad, port=port)
+        except ConnectionResetError:
+            # Expected behaviour
+            pass
+
+        # Close all allowed connections
+        for i in range(0, 10):
+            socks[i].close()
+
+        ## Now repeat - check it works as before
+
+        # Open all allowed connections, a limit of 10
+        for i in range(0, 10):
+            socks.append(mosq_test.do_client_connect(connect_packets_ok[i], connack_packets_ok[i], port=port))
+
+        # Try to open an 11th connection
+        try:
+            sock_bad = mosq_test.do_client_connect(connect_packet_bad, connack_packet_bad, port=port)
+        except ConnectionResetError:
+            # Expected behaviour
+            pass
+
+        # Close all allowed connections
+        for i in range(0, 10):
+            socks[i].close()
+
+        rc = 0
+    except mosq_test.TestError:
+        pass
+    except Exception as err:
+        print(err)
+    finally:
+        os.remove(conf_file)
+        broker.terminate()
+        broker.wait()
+        (stdo, stde) = broker.communicate()
+        if rc:
+            print(stde.decode('utf-8'))
+            exit(rc)
+
+do_test()
+exit(0)

test/broker/Makefile

@@ -27,6 +27,7 @@ msg_sequence_test:
 	./01-connect-allow-anonymous.py
 	./01-connect-disconnect-v5.py
 	./01-connect-global-max-clients.py
+	./01-connect-global-max-connections.py
 	./01-connect-max-connections.py
 	./01-connect-max-keepalive.py
 	./01-connect-uname-no-password-denied.py

test/broker/test.py

@@ -9,6 +9,7 @@ tests = [
     (1, './01-connect-allow-anonymous.py'),
     (1, './01-connect-disconnect-v5.py'),
     (1, './01-connect-global-max-clients.py'),
+    (1, './01-connect-global-max-connections.py'),
     (1, './01-connect-max-connections.py'),
     (1, './01-connect-max-keepalive.py'),
     (1, './01-connect-uname-no-password-denied.py'),