diff --git a/doc/mqtt_client.txt b/doc/mqtt_client.txt new file mode 100644 index 00000000..21e974f7 --- /dev/null +++ b/doc/mqtt_client.txt @@ -0,0 +1,162 @@ +MQTT client for lwIP + +Author: Erik Andersson + +Details of the MQTT protocol can be found at: +http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html + +----------------------------------------------------------------- +1. Initial steps, reserve memory and make connection to server: + +1.1: Provide storage + +Static allocation: + mqtt_client_t static_client; + example_do_connect(&static_client); + +Dynamic allocation: + mqtt_client_t *client = mqtt_client_new(); + if(client != NULL) { + example_do_connect(&client); + } + +1.2: Establish Connection with server + +void example_do_connect(mqtt_client_t *client) +{ + struct mqtt_connect_client_info_t ci; + err_t err; + + /* Setup an empty client info structure */ + memset(&ci, 0, sizeof(ci)); + + /* Minimal amount of information required is client identifier, so set it here */ + ci.client_id = "lwip_test"; + + /* Initiate client and connect to server, if this fails immediately an error code is returned + otherwise mqtt_connection_cb will be called with connection result after attempting + to establish a connection with the server. + For now port number 1883 and MQTT version 3.1.1 is always used */ + + err = mqtt_client_connect(client, "192.168.0.55", mqtt_connection_cb, 0, &ci); + + /* For now just print the result code if something goes wrong + if(err != ERR_OK) { + printf("mqtt_connect return %d\n", err); + } +} + +Connection to server can also be probed by calling mqtt_client_is_connected(client) + +----------------------------------------------------------------- +2. Implementing the connection status callback + + +static void mqtt_connection_cb(mqtt_client_t *client, void *arg, mqtt_connection_status_t status) +{ + err_t err; + if(status == MQTT_CONNECT_ACCEPTED) { + printf("mqtt_connection_cb: Successfully connected\n"); + + /* Setup callback for incoming publish requests */ + mqtt_set_inpub_callback(client, mqtt_incoming_publish_cb, mqtt_incoming_data_cb, arg); + + /* Subscribe to a topic named "subtopic" with QoS level 1, call mqtt_sub_request_cb with result */ + err = mqtt_subscribe(client, "subtopic", 1, mqtt_sub_request_cb, arg); + + if(err != ERR_OK) { + printf("mqtt_subscribe return: %d\n", err); + } + } else { + printf("mqtt_connection_cb: Disconnected, reason: %d\n", status); + + /* Its more nice to be connected, so try to reconnect */ + example_do_connect(client); + } +} + +static void mqtt_sub_request_cb(void *arg, err_t result) +{ + /* Just print the result code here for simplicity, + normal behaviour would be to take some action if subscribe fails like + notifying user, retry subscribe or disconnect from server */ + printf("Subscribe result: %d\n", result); +} + +----------------------------------------------------------------- +3. Implementing callbacks for incoming publish and data + +/* The idea is to demultiplex topic and create some reference to be used in data callbacks + Example here uses a global variable, better would be to use a member in arg + If RAM and CPU budget allows it, the easiest implementation might be to just take a copy of + the topic string and use it in mqtt_incoming_data_cb +*/ +static int inpub_id; +static void mqtt_incoming_publish_cb(void *arg, const char *topic, u32_t tot_len) +{ + printf("Incoming publish at topic %s with total length %u\n", topic, (unsigned int)tot_len); + + /* Decode topic string into a user defined reference */ + if(strcmp(topic, "print_payload") == 0) { + inpub_id = 0; + } else if(topic[0] == 'A') { + /* All topics starting with 'A' might be handled at the same way */ + inpub_id = 1; + } else { + /* For all other topics */ + inpub_id = 2; + } +} + +static void mqtt_incoming_data_cb(void *arg, const u8_t *data, u16_t len, u8_t flags) +{ + printf("Incoming publish payload with length %d, flags %u\n", len, (unsigned int)flags); + + if(flags & MQTT_DATA_FLAG_LAST) { + /* Last fragment of payload received (or whole part if payload fits receive buffer + See MQTT_VAR_HEADER_BUFFER_LEN) */ + + /* Call function or do action depending on reference, in this case inpub_id */ + if(inpub_id == 0) { + /* Don't trust the publisher, check zero termination */ + if(data[len-1] == 0) { + printf("mqtt_incoming_data_cb: %s\n", (const char *)data); + } + } else if(inpub_id == 1) { + /* Call an 'A' function... */ + } else { + printf("mqtt_incoming_data_cb: Ignoring payload...\n"); + } + } else { + /* Handle fragmented payload, store in buffer, write to file or whatever */ + } +} + +----------------------------------------------------------------- +4. Using outgoing publish + + +void example_publish(mqtt_client_t *client, void *arg) +{ + const char *pub_payload= "PubSubHubLubJub"; + err_t err; + u8_t qos = 2; /* 0 1 or 2, see MQTT specification */ + u8_t retain = 0; /* No don't retain such crappy payload... */ + err = mqtt_publish(client, "pub_topic", pub_payload, strlen(pub_payload), qos, retain, mqtt_pub_request_cb, arg); + if(err != ERR_OK) { + printf("Publish err: %d\n", err); + } +} + +/* Called when publish is complete either with sucess or failure */ +static void mqtt_pub_request_cb(void *arg, err_t result) +{ + if(result != ERR_OK) { + printf("Publish result: %d\n", result); + } +} + +----------------------------------------------------------------- +5. Disconnecting + +Simply call mqtt_disconnect(client) diff --git a/src/apps/mqtt/mqtt.c b/src/apps/mqtt/mqtt.c index 11ca6e31..3e3a8126 100644 --- a/src/apps/mqtt/mqtt.c +++ b/src/apps/mqtt/mqtt.c @@ -4,6 +4,7 @@ * * @defgroup mqtt MQTT client * @ingroup apps + * @verbinclude mqtt_client.txt */ /*