simple_publisher.c

A simple program to that publishes the current time whenever ENTER is pressed.

Usage:

./bin/simple_publisher [address [port [topic]]]

Where address is the address of the MQTT broker, port is the port number the MQTT broker is running on, and topic is the name of the topic to publish with. Note that all these arguments are optional and the defaults are address = "test.mosquitto.org", port = "1883", and topic = "datetime".

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

#include <mqtt.h>
#include "templates/posix_sockets.h"


void publish_callback(void** unused, struct mqtt_response_publish *published);

void* client_refresher(void* client);

void exit_example(int status, int sockfd, pthread_t *client_daemon);

int main(int argc, const char *argv[]) 
{
    const char* addr;
    const char* port;
    const char* topic;

    /* get address (argv[1] if present) */
    if (argc > 1) {
        addr = argv[1];
    } else {
        addr = "test.mosquitto.org";
    }

    /* get port number (argv[2] if present) */
    if (argc > 2) {
        port = argv[2];
    } else {
        port = "1883";
    }

    /* get the topic name to publish */
    if (argc > 3) {
        topic = argv[3];
    } else {
        topic = "datetime";
    }

    /* open the non-blocking TCP socket (connecting to the broker) */
    int sockfd = open_nb_socket(addr, port);

    if (sockfd == -1) {
        perror("Failed to open socket: ");
        exit_example(EXIT_FAILURE, sockfd, NULL);
    }

    /* setup a client */
    struct mqtt_client client;
    uint8_t sendbuf[2048]; /* sendbuf should be large enough to hold multiple whole mqtt messages */
    uint8_t recvbuf[1024]; /* recvbuf should be large enough any whole mqtt message expected to be received */
    mqtt_init(&client, sockfd, sendbuf, sizeof(sendbuf), recvbuf, sizeof(recvbuf), publish_callback);
    mqtt_connect(&client, "publishing_client", NULL, NULL, 0, NULL, NULL, 0, 400);

    /* check that we don't have any errors */
    if (client.error != MQTT_OK) {
        fprintf(stderr, "error: %s\n", mqtt_error_str(client.error));
        exit_example(EXIT_FAILURE, sockfd, NULL);
    }

    /* start a thread to refresh the client (handle egress and ingree client traffic) */
    pthread_t client_daemon;
    if(pthread_create(&client_daemon, NULL, client_refresher, &client)) {
        fprintf(stderr, "Failed to start client daemon.\n");
        exit_example(EXIT_FAILURE, sockfd, NULL);

    }

    /* start publishing the time */
    printf("%s is ready to begin publishing the time.\n", argv[0]);
    printf("Press ENTER to publish the current time.\n");
    printf("Press CTRL-D (or any other key) to exit.\n\n");
    while(fgetc(stdin) == '\n') {
        /* get the current time */
        time_t timer;
        time(&timer);
        struct tm* tm_info = localtime(&timer);
        char timebuf[26];
        strftime(timebuf, 26, "%Y-%m-%d %H:%M:%S", tm_info);

        /* print a message */
        char application_message[256];
        snprintf(application_message, sizeof(application_message), "The time is %s", timebuf);
        printf("%s published : \"%s\"", argv[0], application_message);

        /* publish the time */
        mqtt_publish(&client, topic, application_message, strlen(application_message) + 1, MQTT_PUBLISH_QOS_0);

        /* check for errors */
        if (client.error != MQTT_OK) {
            fprintf(stderr, "error: %s\n", mqtt_error_str(client.error));
            exit_example(EXIT_FAILURE, sockfd, &client_daemon);
        }
    }   

    /* disconnect */
    printf("\n%s disconnecting from %s\n", argv[0], addr);
    sleep(1);

    /* exit */ 
    exit_example(EXIT_SUCCESS, sockfd, &client_daemon);
}

void exit_example(int status, int sockfd, pthread_t *client_daemon)
{
    if (sockfd != -1) close(sockfd);
    if (client_daemon != NULL) pthread_cancel(*client_daemon);
    exit(status);
}



void publish_callback(void** unused, struct mqtt_response_publish *published) 
{
    /* not used in this example */
}

void* client_refresher(void* client)
{
    while(1) 
    {
        mqtt_sync((struct mqtt_client*) client);
        usleep(100000U);
    }
    return NULL;
}