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/*
* This example shows how to write a client that subscribes to a topic and does
* not do anything other than handle the messages that are received.
*/
#include <mosquitto.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* Callback called when the client receives a CONNACK message from the broker. */
void on_connect(struct mosquitto *mosq, void *obj, int reason_code)
{
int rc;
/* Print out the connection result. mosquitto_connack_string() produces an
* appropriate string for MQTT v3.x clients, the equivalent for MQTT v5.0
* clients is mosquitto_reason_string().
*/
printf("on_connect: %s\n", mosquitto_connack_string(reason_code));
if(reason_code != 0){
/* If the connection fails for any reason, we don't want to keep on
* retrying in this example, so disconnect. Without this, the client
* will attempt to reconnect. */
mosquitto_disconnect(mosq);
}
/* Making subscriptions in the on_connect() callback means that if the
* connection drops and is automatically resumed by the client, then the
* subscriptions will be recreated when the client reconnects. */
rc = mosquitto_subscribe(mosq, NULL, "example/temperature", 1);
if(rc != MOSQ_ERR_SUCCESS){
fprintf(stderr, "Error subscribing: %s\n", mosquitto_strerror(rc));
/* We might as well disconnect if we were unable to subscribe */
mosquitto_disconnect(mosq);
}
}
/* Callback called when the broker sends a SUBACK in response to a SUBSCRIBE. */
void on_subscribe(struct mosquitto *mosq, void *obj, int mid, int qos_count, const int *granted_qos)
{
int i;
bool have_subscription = false;
/* In this example we only subscribe to a single topic at once, but a
* SUBSCRIBE can contain many topics at once, so this is one way to check
* them all. */
for(i=0; i<qos_count; i++){
printf("on_subscribe: %d:granted qos = %d\n", i, granted_qos[i]);
if(granted_qos[i] <= 2){
have_subscription = true;
}
}
if(have_subscription == false){
/* The broker rejected all of our subscriptions, we know we only sent
* the one SUBSCRIBE, so there is no point remaining connected. */
fprintf(stderr, "Error: All subscriptions rejected.\n");
mosquitto_disconnect(mosq);
}
}
/* Callback called when the client receives a message. */
void on_message(struct mosquitto *mosq, void *obj, const struct mosquitto_message *msg)
{
/* This blindly prints the payload, but the payload can be anything so take care. */
printf("%s %d %s\n", msg->topic, msg->qos, (char *)msg->payload);
}
int main(int argc, char *argv[])
{
struct mosquitto *mosq;
int rc;
/* Required before calling other mosquitto functions */
mosquitto_lib_init();
/* Create a new client instance.
* id = NULL -> ask the broker to generate a client id for us
* clean session = true -> the broker should remove old sessions when we connect
* obj = NULL -> we aren't passing any of our private data for callbacks
*/
mosq = mosquitto_new(NULL, true, NULL);
if(mosq == NULL){
fprintf(stderr, "Error: Out of memory.\n");
return 1;
}
/* Configure callbacks. This should be done before connecting ideally. */
mosquitto_connect_callback_set(mosq, on_connect);
mosquitto_subscribe_callback_set(mosq, on_subscribe);
mosquitto_message_callback_set(mosq, on_message);
/* Connect to test.mosquitto.org on port 1883, with a keepalive of 60 seconds.
* This call makes the socket connection only, it does not complete the MQTT
* CONNECT/CONNACK flow, you should use mosquitto_loop_start() or
* mosquitto_loop_forever() for processing net traffic. */
rc = mosquitto_connect(mosq, "test.mosquitto.org", 1883, 60);
if(rc != MOSQ_ERR_SUCCESS){
mosquitto_destroy(mosq);
fprintf(stderr, "Error: %s\n", mosquitto_strerror(rc));
return 1;
}
/* Run the network loop in a blocking call. The only thing we do in this
* example is to print incoming messages, so a blocking call here is fine.
*
* This call will continue forever, carrying automatic reconnections if
* necessary, until the user calls mosquitto_disconnect().
*/
mosquitto_loop_forever(mosq, -1, 1);
mosquitto_lib_cleanup();
return 0;
}
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