142 lines
4.1 KiB
C
142 lines
4.1 KiB
C
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/**
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* @file
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* A simple program that subscribes to a topic.
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*/
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <mqtt.h>
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#include "templates/posix_sockets.h"
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/**
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* @brief The function will be called whenever a PUBLISH message is received.
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*/
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void publish_callback(void** unused, struct mqtt_response_publish *published);
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/**
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* @brief The client's refresher. This function triggers back-end routines to
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* handle ingress/egress traffic to the broker.
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*
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* @note All this function needs to do is call \ref __mqtt_recv and
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* \ref __mqtt_send every so often. I've picked 100 ms meaning that
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* client ingress/egress traffic will be handled every 100 ms.
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*/
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void* client_refresher(void* client);
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/**
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* @brief Safelty closes the \p sockfd and cancels the \p client_daemon before \c exit.
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*/
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void exit_example(int status, int sockfd, pthread_t *client_daemon);
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int main(int argc, const char *argv[])
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{
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const char* addr;
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const char* port;
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const char* topic;
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/* get address (argv[1] if present) */
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if (argc > 1) {
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addr = argv[1];
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} else {
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addr = "test.mosquitto.org";
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}
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/* get port number (argv[2] if present) */
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if (argc > 2) {
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port = argv[2];
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} else {
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port = "1883";
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}
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/* get the topic name to publish */
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if (argc > 3) {
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topic = argv[3];
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} else {
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topic = "datetime";
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}
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/* open the non-blocking TCP socket (connecting to the broker) */
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int sockfd = open_nb_socket(addr, port);
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if (sockfd == -1) {
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perror("Failed to open socket: ");
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exit_example(EXIT_FAILURE, sockfd, NULL);
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}
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/* setup a client */
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struct mqtt_client client;
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uint8_t sendbuf[2048]; /* sendbuf should be large enough to hold multiple whole mqtt messages */
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uint8_t recvbuf[1024]; /* recvbuf should be large enough any whole mqtt message expected to be received */
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mqtt_init(&client, sockfd, sendbuf, sizeof(sendbuf), recvbuf, sizeof(recvbuf), publish_callback);
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/* Create an anonymous session */
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const char* client_id = NULL;
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/* Ensure we have a clean session */
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uint8_t connect_flags = MQTT_CONNECT_CLEAN_SESSION;
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/* Send connection request to the broker. */
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mqtt_connect(&client, client_id, NULL, NULL, 0, NULL, NULL, connect_flags, 400);
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/* check that we don't have any errors */
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if (client.error != MQTT_OK) {
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fprintf(stderr, "error: %s\n", mqtt_error_str(client.error));
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exit_example(EXIT_FAILURE, sockfd, NULL);
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}
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/* start a thread to refresh the client (handle egress and ingree client traffic) */
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pthread_t client_daemon;
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if(pthread_create(&client_daemon, NULL, client_refresher, &client)) {
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fprintf(stderr, "Failed to start client daemon.\n");
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exit_example(EXIT_FAILURE, sockfd, NULL);
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}
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/* subscribe */
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mqtt_subscribe(&client, topic, 0);
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/* start publishing the time */
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printf("%s listening for '%s' messages.\n", argv[0], topic);
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printf("Press CTRL-D to exit.\n\n");
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/* block */
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while(fgetc(stdin) != EOF);
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/* disconnect */
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printf("\n%s disconnecting from %s\n", argv[0], addr);
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sleep(1);
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/* exit */
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exit_example(EXIT_SUCCESS, sockfd, &client_daemon);
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}
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void exit_example(int status, int sockfd, pthread_t *client_daemon)
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{
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if (sockfd != -1) close(sockfd);
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if (client_daemon != NULL) pthread_cancel(*client_daemon);
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exit(status);
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}
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void publish_callback(void** unused, struct mqtt_response_publish *published)
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{
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/* note that published->topic_name is NOT null-terminated (here we'll change it to a c-string) */
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char* topic_name = (char*) malloc(published->topic_name_size + 1);
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memcpy(topic_name, published->topic_name, published->topic_name_size);
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topic_name[published->topic_name_size] = '\0';
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printf("Received publish('%s'): %s\n", topic_name, (const char*) published->application_message);
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free(topic_name);
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}
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void* client_refresher(void* client)
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{
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while(1)
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{
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mqtt_sync((struct mqtt_client*) client);
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usleep(100000U);
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}
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return NULL;
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} |