Add mqtt documentation from Erik Anderson, rev 4b84fff
diff --git a/doc/mqtt_client.txt b/doc/mqtt_client.txt
new file mode 100644
index 0000000..21e974f
--- /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 11ca6e3..3e3a812 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
*/
/*
