163 lines
5.2 KiB
Plaintext
163 lines
5.2 KiB
Plaintext
MQTT client for lwIP
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Author: Erik Andersson
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Details of the MQTT protocol can be found at:
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http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html
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-----------------------------------------------------------------
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1. Initial steps, reserve memory and make connection to server:
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1.1: Provide storage
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Static allocation:
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mqtt_client_t static_client;
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example_do_connect(&static_client);
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Dynamic allocation:
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mqtt_client_t *client = mqtt_client_new();
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if(client != NULL) {
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example_do_connect(&client);
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}
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1.2: Establish Connection with server
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void example_do_connect(mqtt_client_t *client)
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{
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struct mqtt_connect_client_info_t ci;
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err_t err;
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/* Setup an empty client info structure */
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memset(&ci, 0, sizeof(ci));
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/* Minimal amount of information required is client identifier, so set it here */
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ci.client_id = "lwip_test";
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/* Initiate client and connect to server, if this fails immediately an error code is returned
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otherwise mqtt_connection_cb will be called with connection result after attempting
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to establish a connection with the server.
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For now MQTT version 3.1.1 is always used */
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err = mqtt_client_connect(client, ip_addr, MQTT_PORT, mqtt_connection_cb, 0, &ci);
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/* For now just print the result code if something goes wrong
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if(err != ERR_OK) {
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printf("mqtt_connect return %d\n", err);
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}
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}
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Connection to server can also be probed by calling mqtt_client_is_connected(client)
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-----------------------------------------------------------------
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2. Implementing the connection status callback
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static void mqtt_connection_cb(mqtt_client_t *client, void *arg, mqtt_connection_status_t status)
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{
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err_t err;
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if(status == MQTT_CONNECT_ACCEPTED) {
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printf("mqtt_connection_cb: Successfully connected\n");
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/* Setup callback for incoming publish requests */
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mqtt_set_inpub_callback(client, mqtt_incoming_publish_cb, mqtt_incoming_data_cb, arg);
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/* Subscribe to a topic named "subtopic" with QoS level 1, call mqtt_sub_request_cb with result */
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err = mqtt_subscribe(client, "subtopic", 1, mqtt_sub_request_cb, arg);
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if(err != ERR_OK) {
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printf("mqtt_subscribe return: %d\n", err);
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}
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} else {
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printf("mqtt_connection_cb: Disconnected, reason: %d\n", status);
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/* Its more nice to be connected, so try to reconnect */
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example_do_connect(client);
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}
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}
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static void mqtt_sub_request_cb(void *arg, err_t result)
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{
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/* Just print the result code here for simplicity,
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normal behaviour would be to take some action if subscribe fails like
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notifying user, retry subscribe or disconnect from server */
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printf("Subscribe result: %d\n", result);
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}
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-----------------------------------------------------------------
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3. Implementing callbacks for incoming publish and data
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/* The idea is to demultiplex topic and create some reference to be used in data callbacks
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Example here uses a global variable, better would be to use a member in arg
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If RAM and CPU budget allows it, the easiest implementation might be to just take a copy of
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the topic string and use it in mqtt_incoming_data_cb
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*/
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static int inpub_id;
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static void mqtt_incoming_publish_cb(void *arg, const char *topic, u32_t tot_len)
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{
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printf("Incoming publish at topic %s with total length %u\n", topic, (unsigned int)tot_len);
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/* Decode topic string into a user defined reference */
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if(strcmp(topic, "print_payload") == 0) {
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inpub_id = 0;
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} else if(topic[0] == 'A') {
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/* All topics starting with 'A' might be handled at the same way */
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inpub_id = 1;
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} else {
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/* For all other topics */
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inpub_id = 2;
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}
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}
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static void mqtt_incoming_data_cb(void *arg, const u8_t *data, u16_t len, u8_t flags)
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{
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printf("Incoming publish payload with length %d, flags %u\n", len, (unsigned int)flags);
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if(flags & MQTT_DATA_FLAG_LAST) {
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/* Last fragment of payload received (or whole part if payload fits receive buffer
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See MQTT_VAR_HEADER_BUFFER_LEN) */
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/* Call function or do action depending on reference, in this case inpub_id */
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if(inpub_id == 0) {
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/* Don't trust the publisher, check zero termination */
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if(data[len-1] == 0) {
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printf("mqtt_incoming_data_cb: %s\n", (const char *)data);
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}
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} else if(inpub_id == 1) {
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/* Call an 'A' function... */
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} else {
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printf("mqtt_incoming_data_cb: Ignoring payload...\n");
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}
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} else {
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/* Handle fragmented payload, store in buffer, write to file or whatever */
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}
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}
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-----------------------------------------------------------------
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4. Using outgoing publish
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void example_publish(mqtt_client_t *client, void *arg)
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{
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const char *pub_payload= "PubSubHubLubJub";
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err_t err;
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u8_t qos = 2; /* 0 1 or 2, see MQTT specification */
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u8_t retain = 0; /* No don't retain such crappy payload... */
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err = mqtt_publish(client, "pub_topic", pub_payload, strlen(pub_payload), qos, retain, mqtt_pub_request_cb, arg);
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if(err != ERR_OK) {
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printf("Publish err: %d\n", err);
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}
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}
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/* Called when publish is complete either with sucess or failure */
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static void mqtt_pub_request_cb(void *arg, err_t result)
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{
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if(result != ERR_OK) {
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printf("Publish result: %d\n", result);
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}
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}
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-----------------------------------------------------------------
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5. Disconnecting
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Simply call mqtt_disconnect(client)
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