Add -1 (oneshot) option to mosquitto_sub.

Thanks to JP Mens.

ChangeLog.txt

@@ -2,6 +2,7 @@
 
 Clients:
 - Both clients can now load default configuration options from a file.
+- Add -1 (oneshot) option to mosquitto_sub.
 
 1.3.2 - 2014xxxx
 ================

client/client_shared.c

@@ -184,6 +184,12 @@ int client_config_line_proc(struct mosq_config *cfg, int pub_or_sub, int argc, c
 				}
 			}
 			i++;
+		}else if(!strcmp(argv[i], "-1") || !strcmp(argv[i], "--oneshot")){
+			if(pub_or_sub == CLIENT_PUB){
+				goto unknown_option;
+			}else{
+				cfg->oneshot = true;
+			}
 		}else if(!strcmp(argv[i], "-A")){
 			if(i==argc-1){
 				fprintf(stderr, "Error: -A argument given but no address specified.\n\n");

client/client_shared.h

@@ -76,6 +76,7 @@ struct mosq_config {
 	int filter_out_count; /* sub */
 	bool verbose; /* sub */
 	bool eol; /* sub */
+	bool oneshot; /* sub */
 #endif
 };
 

client/sub_client.c

@@ -30,12 +30,16 @@ Contributors:
 #include <mosquitto.h>
 #include "client_shared.h"
 
+bool process_messages = true;
+
 void my_message_callback(struct mosquitto *mosq, void *obj, const struct mosquitto_message *message)
 {
 	struct mosq_config *cfg;
 	int i;
 	bool res;
 
+	if(process_messages == false) return;
+
 	assert(obj);
 	cfg = (struct mosq_config *)obj;
 
@@ -69,6 +73,10 @@ void my_message_callback(struct mosquitto *mosq, void *obj, const struct mosquit
 			fflush(stdout);
 		}
 	}
+	if(cfg->oneshot){
+		process_messages = false;
+		mosquitto_disconnect(mosq);
+	}
 }
 
 void my_connect_callback(struct mosquitto *mosq, void *obj, int result)
@@ -118,7 +126,7 @@ void print_usage(void)
 	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("                     [-T filter_out]\n");
+	printf("                     [-1] [-T filter_out]\n");
 	printf("                     [-A bind_address] [-S]\n");
 	printf("                     [-i id] [-I id_prefix]\n");
 	printf("                     [-d] [-N] [--quiet] [-v]\n");
@@ -132,6 +140,7 @@ void print_usage(void)
 #endif
 #endif
 	printf("       mosquitto_sub --help\n\n");
+	printf(" -1 : disconnect and exit after receiving the first message.\n");
 	printf(" -A : bind the outgoing socket to this host/ip address. Use to control which interface\n");
 	printf("      the client communicates over.\n");
 	printf(" -c : disable 'clean session' (store subscription and pending messages when client disconnects).\n");
@@ -229,6 +238,9 @@ int main(int argc, char *argv[])
 	mosquitto_destroy(mosq);
 	mosquitto_lib_cleanup();
 
+	if(cfg.oneshot && rc == MOSQ_ERR_NO_CONN){
+		rc = 0;
+	}
 	if(rc){
 		fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
 	}

man/mosquitto_sub.1.xml

@@ -17,6 +17,7 @@
 	<refsynopsisdiv>
 		<cmdsynopsis>
 			<command>mosquitto_sub</command>
+			<arg><option>-1</option></arg>
 			<arg><option>-A</option> <replaceable>bind_address</replaceable></arg>
 			<arg><option>-c</option></arg>
 			<arg><option>-d</option></arg>
@@ -90,6 +91,19 @@
 			currently some options cannot be negated, e.g.
 			<option>-S</option>.</para>
 		<variablelist>
+			<varlistentry>
+				<term><option>-1</option></term>
+				<listitem>
+					<para>Disconnect and exit the program immediately after the
+						first message is received. This may be useful in shell
+						scripts where on a single status value is required, for
+						example.</para>
+					<para>Combine with <option>-R</option> to print only the
+						first fresh message (i.e. that does not have the
+						retained flag set), or with <option>-T</option> to
+						filter which topics are processed.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>-A</option></term>
 				<listitem>