reconnect_subscriber.c

Same program as simple_subscriber.c, but using the automatic reconnect functionality.

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

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

struct reconnect_state_t {
    const char* hostname;
    const char* port;
    const char* topic;
    uint8_t* sendbuf;
    size_t sendbufsz;
    uint8_t* recvbuf;
    size_t recvbufsz;
};


void reconnect_client(struct mqtt_client* client, void **reconnect_state_vptr);

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";
    }

    /* build the reconnect_state structure which will be passed to reconnect */
    struct reconnect_state_t reconnect_state;
    reconnect_state.hostname = addr;
    reconnect_state.port = port;
    reconnect_state.topic = topic;
    uint8_t sendbuf[2048];
    uint8_t recvbuf[1024];
    reconnect_state.sendbuf = sendbuf;
    reconnect_state.sendbufsz = sizeof(sendbuf);
    reconnect_state.recvbuf = recvbuf;
    reconnect_state.recvbufsz = sizeof(recvbuf);

    /* setup a client */
    struct mqtt_client client;

    mqtt_init_reconnect(&client, 
                        reconnect_client, &reconnect_state, 
                        publish_callback
    );

    /* 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, -1, NULL);

    }

    /* start publishing the time */
    printf("%s listening for '%s' messages.\n", argv[0], topic);
    printf("Press ENTER to inject an error.\n");
    printf("Press CTRL-D to exit.\n\n");
    
    /* block */
    while(fgetc(stdin) != EOF) {
        printf("Injecting error: \"MQTT_ERROR_SOCKET_ERROR\"\n");
        client.error = MQTT_ERROR_SOCKET_ERROR;
    } 
    
    /* disconnect */
    printf("\n%s disconnecting from %s\n", argv[0], addr);
    sleep(1);

    /* exit */ 
    exit_example(EXIT_SUCCESS, client.socketfd, &client_daemon);
}

void reconnect_client(struct mqtt_client* client, void **reconnect_state_vptr)
{
    struct reconnect_state_t *reconnect_state = *((struct reconnect_state_t**) reconnect_state_vptr);

    /* Close the clients socket if this isn't the initial reconnect call */
    if (client->error != MQTT_ERROR_INITIAL_RECONNECT) {
        close(client->socketfd);
    }

    /* Perform error handling here. */
    if (client->error != MQTT_ERROR_INITIAL_RECONNECT) {
        printf("reconnect_client: called while client was in error state \"%s\"\n", 
               mqtt_error_str(client->error)
        );
    }

    /* Open a new socket. */
    int sockfd = open_nb_socket(reconnect_state->hostname, reconnect_state->port);
    if (sockfd == -1) {
        perror("Failed to open socket: ");
        exit_example(EXIT_FAILURE, sockfd, NULL);
    }

    /* Reinitialize the client. */
    mqtt_reinit(client, sockfd, 
                reconnect_state->sendbuf, reconnect_state->sendbufsz,
                reconnect_state->recvbuf, reconnect_state->recvbufsz
    );
    
    /* Send connection request to the broker. */
    mqtt_connect(client, "subscribing_client", NULL, NULL, 0, NULL, NULL, 0, 400);

    /* Subscribe to the topic. */
    mqtt_subscribe(client, reconnect_state->topic, 0);
}

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) 
{
    /* note that published->topic_name is NOT null-terminated (here we'll change it to a c-string) */
    char* topic_name = (char*) malloc(published->topic_name_size + 1);
    memcpy(topic_name, published->topic_name, published->topic_name_size);
    topic_name[published->topic_name_size] = '\0';

    printf("Received publish('%s'): %s\n", topic_name, (const char*) published->application_message);

    free(topic_name);
}

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