Add -U to mosquitto_sub for unsubscribing from topics.

ChangeLog.txt

@@ -33,6 +33,7 @@ Client library:
 
 Client:
 - Add -x to mosquitto_sub for printing the payload in hexadecimal format.
+- Add -U to mosquitto_sub for unsubscribing from topics.
 
 
 1.4.4 - 20150916

client/client_shared.c

@@ -83,6 +83,12 @@ void client_config_cleanup(struct mosq_config *cfg)
 		}
 		free(cfg->filter_outs);
 	}
+	if(cfg->unsub_topics){
+		for(i=0; i<cfg->unsub_topic_count; i++){
+			free(cfg->unsub_topics[i]);
+		}
+		free(cfg->unsub_topics);
+	}
 #ifdef WITH_SOCKS
 	free(cfg->socks5_host);
 	free(cfg->socks5_username);
@@ -556,6 +562,27 @@ int client_config_line_proc(struct mosq_config *cfg, int pub_or_sub, int argc, c
 				cfg->filter_outs[cfg->filter_out_count-1] = strdup(argv[i+1]);
 			}
 			i++;
+		}else if(!strcmp(argv[i], "-U") || !strcmp(argv[i], "--unsubscribe")){
+			if(pub_or_sub == CLIENT_PUB){
+				goto unknown_option;
+			}
+			if(i==argc-1){
+				fprintf(stderr, "Error: -U argument given but no unsubscribe topic specified.\n\n");
+				return 1;
+			}else{
+				if(mosquitto_sub_topic_check(argv[i+1]) == MOSQ_ERR_INVAL){
+					fprintf(stderr, "Error: Invalid unsubscribe topic '%s', are all '+' and '#' wildcards correct?\n", argv[i+1]);
+					return 1;
+				}
+				cfg->unsub_topic_count++;
+				cfg->unsub_topics = realloc(cfg->unsub_topics, cfg->unsub_topic_count*sizeof(char *));
+				if(!cfg->unsub_topics){
+					fprintf(stderr, "Error: Out of memory.\n");
+					return 1;
+				}
+				cfg->unsub_topics[cfg->unsub_topic_count-1] = strdup(argv[i+1]);
+			}
+			i++;
 #ifdef WITH_TLS
 		}else if(!strcmp(argv[i], "--tls-version")){
 			if(i==argc-1){

client/client_shared.h

@@ -77,6 +77,8 @@ struct mosq_config {
 	bool no_retain; /* sub */
 	char **filter_outs; /* sub */
 	int filter_out_count; /* sub */
+	char **unsub_topics; /* sub */
+	int unsub_topic_count; /* sub */
 	bool verbose; /* sub */
 	bool eol; /* sub */
 	bool hex_output; /* sub */

client/sub_client.c

@@ -108,6 +108,9 @@ void my_connect_callback(struct mosquitto *mosq, void *obj, int result)
 		for(i=0; i<cfg->topic_count; i++){
 			mosquitto_subscribe(mosq, NULL, cfg->topics[i], cfg->qos);
 		}
+		for(i=0; i<cfg->unsub_topic_count; i++){
+			mosquitto_unsubscribe(mosq, NULL, cfg->unsub_topics[i]);
+		}
 	}else{
 		if(result && !cfg->quiet){
 			fprintf(stderr, "%s\n", mosquitto_connack_string(result));
@@ -142,7 +145,7 @@ void print_usage(void)
 	mosquitto_lib_version(&major, &minor, &revision);
 	printf("mosquitto_sub is a simple mqtt client that will subscribe to a single topic and print all messages it receives.\n");
 	printf("mosquitto_sub version %s running on libmosquitto %d.%d.%d.\n\n", VERSION, major, minor, revision);
-	printf("Usage: mosquitto_sub [-c] [-h host] [-k keepalive] [-p port] [-q qos] [-R] -t topic ...\n");
+	printf("Usage: mosquitto_sub [-c] [-h host] [-k keepalive] [-p port] [-q qos] [-R] {-t topic ... | -U topic ...}\n");
 	printf("                     [-C msg_count] [-T filter_out]\n");
 #ifdef WITH_SRV
 	printf("                     [-A bind_address] [-S]\n");
@@ -185,6 +188,7 @@ void print_usage(void)
 	printf(" -t : mqtt topic to subscribe to. May be repeated multiple times.\n");
 	printf(" -T : topic string to filter out of results. May be repeated.\n");
 	printf(" -u : provide a username (requires MQTT 3.1 broker)\n");
+	printf(" -U : unsubscribe from a topic. May be repeated.\n");
 	printf(" -v : print published messages verbosely.\n");
 	printf(" -V : specify the version of the MQTT protocol to use when connecting.\n");
 	printf("      Can be mqttv31 or mqttv311. Defaults to mqttv31.\n");

man/mosquitto_sub.1.xml

@@ -63,7 +63,10 @@
 			<arg><option>--proxy</option> <replaceable>socks-url</replaceable></arg>
 			<arg><option>-V</option> <replaceable>protocol-version</replaceable></arg>
 			<arg choice='opt' rep='repeat'><option>-T</option> <replaceable>filter-out</replaceable></arg>
-			<arg choice='plain' rep='repeat'><option>-t</option> <replaceable>message-topic</replaceable></arg>
+			<group choice='req'>
+				<arg choice='plain' rep='repeat'><option>-U</option> <replaceable>unsub-topic</replaceable></arg>
+				<arg choice='plain' rep='repeat'><option>-t</option> <replaceable>message-topic</replaceable></arg>
+			</group>
 		</cmdsynopsis>
 		<cmdsynopsis>
 			<command>mosquitto_sub</command>
@@ -76,8 +79,14 @@
 	<refsect1>
 		<title>Description</title>
 		<para><command>mosquitto_sub</command> is a simple MQTT version 3.1.1
-			client that will subscribe to a topic and print the messages that
+			client that will subscribe to topics and print the messages that
 			it receives.</para>
+		<para>In addition to subscribing to topics,
+			<command>mosquitto_sub</command> can filter out received messages
+			so they are not printed (see the <option>-T</option> option) or
+			unsubscribe from topics (see the <option>-U</option> option).
+			Unsubscribing from topics is useful for clients connecting with
+			clean session set to false. </para>
 	</refsect1>
 
 	<refsect1>
@@ -406,6 +415,40 @@
 						argument.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>-U</option></term>
+				<term><option>--unsubscribe</option></term>
+				<listitem>
+					<para>A topic that will be unsubscribed from. This may be
+						used on its own or in conjunction with the
+						<option>--topic</option> option and only makes sense
+						when used in conjunction with
+						<option>--clean-session</option>.</para>
+					<para>If used with <option>--topic</option> then
+						subscriptions will be processed before
+						unsubscriptions.</para>
+					<para>Note that it is only possible to unsubscribe from
+						subscriptions that have previously been made. It is not
+						possible to punch holes in wildcard subscriptions. For
+						example, subscribing to <option>sensors/#</option> and
+						then unsubscribing from
+						<option>sensors/+/temperature</option> as shown below
+						will still result in messages matching the
+						<option>sensors/+/temperature</option> being delivered
+						to the client.</para>
+					<itemizedlist mark="circle">
+						<listitem><para>mosquitto_sub <literal>-t</literal> sensors/# <literal>-U</literal> sensors/+/temperature <literal>-v</literal></para></listitem>
+					</itemizedlist>
+
+					<para>Note also that because retained messages are
+						published by the broker on receipt of a SUBSCRIBE
+						command, subscribing and unsubscribing to the same
+						topic may result in messages being received at the
+						client.</para>
+
+					<para>This option may be repeated to unsubscribe from multiple topics.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>-v</option></term>
 				<term><option>--verbose</option></term>