Add `--random-filter` to mosquitto_sub.

ChangeLog.txt

@@ -42,6 +42,8 @@ Clients:
   option.
 - Add `-x` to all clients to all the session-expiry-interval property to be
   easily set for MQTT v5 clients.
+- Add `--random-filter` to mosquitto_sub, to allow only a certain proportion
+  of received messages to be printed.
 
 
 1.6.9 - 20200227

client/client_shared.c

@@ -149,6 +149,7 @@ void init_config(struct mosq_config *cfg, int pub_or_sub)
 	cfg->repeat_count = 1;
 	cfg->repeat_delay.tv_sec = 0;
 	cfg->repeat_delay.tv_usec = 0;
+	cfg->random_filter = 10000;
 	if(pub_or_sub == CLIENT_RR){
 		cfg->protocol_version = MQTT_PROTOCOL_V5;
 		cfg->msg_count = 1;
@@ -853,6 +854,21 @@ int client_config_line_proc(struct mosq_config *cfg, int pub_or_sub, int argc, c
 			}
 			cfg->no_retain = true;
 			cfg->sub_opts |= MQTT_SUB_OPT_SEND_RETAIN_NEVER;
+		}else if(!strcmp(argv[i], "--random-filter")){
+			if(pub_or_sub != CLIENT_SUB){
+				goto unknown_option;
+			}
+			if(i==argc-1){
+				fprintf(stderr, "Error: --random-filter argument given but no chance specified.\n\n");
+				return 1;
+			}else{
+				cfg->random_filter = 10.0*atof(argv[i+1]);
+				if(cfg->random_filter > 10000 || cfg->random_filter < 1){
+					fprintf(stderr, "Error: --random-filter chance must be between 0.1-100.0\n\n");
+					return 1;
+				}
+			}
+			i++;
 		}else if(!strcmp(argv[i], "--remove-retained")){
 			if(pub_or_sub != CLIENT_SUB){
 				goto unknown_option;

client/client_shared.h

@@ -107,6 +107,7 @@ struct mosq_config {
 	int timeout; /* sub */
 	int sub_opts; /* sub */
 	long session_expiry_interval;
+	int random_filter; /* sub */
 #ifdef WITH_SOCKS
 	char *socks5_host;
 	int socks5_port;

client/sub_client.c

@@ -256,6 +256,9 @@ void print_usage(void)
 	printf(" --pretty : print formatted output rather than minimised output when using the\n");
 	printf("            JSON output format option.\n");
 	printf(" --quiet : don't print error messages.\n");
+	printf(" --random-filter : only print a percentage of received messages. Set to 100 to have all\n");
+	printf("                   messages printed, 50.0 to have half of the messages received on average\n");
+	printf("                   printed, and so on.\n");
 	printf(" --retained-only : only handle messages with the retained flag set, and exit when the\n");
 	printf("                   first non-retained message is received.\n");
 	printf(" --remove-retained : send a message to the server to clear any received retained messages\n");
@@ -307,6 +310,8 @@ int main(int argc, char *argv[])
 
 	mosquitto_lib_init();
 
+	rand_init();
+
 	rc = client_config_load(&cfg, CLIENT_SUB, argc, argv);
 	if(rc){
 		if(rc == 2){

client/sub_client_output.c

@@ -582,8 +582,27 @@ static void formatted_print(const struct mosq_config *lcfg, const struct mosquit
 }
 
 
+void rand_init(void)
+{
+	struct tm *ti = NULL;
+	long ns;
+
+	if(!get_time(&ti, &ns)){
+		srandom(ns);
+	}
+}
+
+
 void print_message(struct mosq_config *cfg, const struct mosquitto_message *message, const mosquitto_property *properties)
 {
+	long r;
+
+	if(cfg->random_filter < 10000){
+		r = random();
+		if((r%10000) >= cfg->random_filter){
+			return;
+		}
+	}
 	if(cfg->format){
 		formatted_print(cfg, message, properties);
 	}else if(cfg->verbose){

client/sub_client_output.h

@@ -20,6 +20,7 @@ Contributors:
 #include "mosquitto.h"
 #include "client_shared.h"
 
+void rand_init(void);
 void print_message(struct mosq_config *cfg, const struct mosquitto_message *message, const mosquitto_property *properties);
 
 #endif

man/mosquitto_sub.1.xml

@@ -44,6 +44,7 @@
 			<arg><option>--nodelay</option></arg>
 			<arg><option>--pretty</option></arg>
 			<arg><option>-q</option> <replaceable>message-QoS</replaceable></arg>
+			<arg><option>--random-filter</option> <replaceable>chance</replaceable></arg>
 			<arg><option>--remove-retained</option></arg>
 			<group choice='opt'>
 				<arg choice='plain'><option>-R</option></arg>
@@ -508,6 +509,17 @@
 						their display.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>--random-filter</option></term>
+				<listitem>
+					<para>This option can be used to reduce the proportion of
+						messages that mosquitto_sub prints. The default behaviour
+						is to print all incoming messages. Setting the
+						<replaceable>chance</replaceable> to a floating point value
+						between 0.1 and 100.0 will ensure that on average that
+						percentage of messages will be printed.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>--remove-retained</option></term>
 				<listitem>