lwIP 2.1.1 Lightweight IP stack

Modules | Data Structures | Macros | Typedefs | Enumerations | Functions
MQTT client
Applications

## Modules
| Options

## Data Structures
struct | mqtt_connect_client_info_t

## Macros
#define | MQTT_PORT LWIP_IANA_PORT_MQTT
#define | MQTT_TLS_PORT LWIP_IANA_PORT_SECURE_MQTT
#define | mqtt_subscribe(client, topic, qos, cb, arg) mqtt_sub_unsub(client, topic, qos, cb, arg, 1)
#define | mqtt_unsubscribe(client, topic, cb, arg) mqtt_sub_unsub(client, topic, 0, cb, arg, 0)

## Typedefs
typedef void(* | mqtt_connection_cb_t) (mqtt_client_t *client, void *arg, mqtt_connection_status_t status)
typedef void(* | mqtt_incoming_data_cb_t) (void *arg, const u8_t *data, u16_t len, u8_t flags)
typedef void(* | mqtt_incoming_publish_cb_t) (void *arg, const char *topic, u32_t tot_len)
typedef void(* | mqtt_request_cb_t) (void *arg, err_t err)

## Enumerations
enum | mqtt_connection_status_t { MQTT_CONNECT_ACCEPTED = 0, MQTT_CONNECT_REFUSED_PROTOCOL_VERSION = 1, MQTT_CONNECT_REFUSED_IDENTIFIER = 2, MQTT_CONNECT_REFUSED_SERVER = 3, MQTT_CONNECT_REFUSED_USERNAME_PASS = 4, MQTT_CONNECT_REFUSED_NOT_AUTHORIZED_ = 5, MQTT_CONNECT_DISCONNECTED = 256, MQTT_CONNECT_TIMEOUT = 257 }
enum | { MQTT_DATA_FLAG_LAST = 1 }

## Functions
err_t | mqtt_publish (mqtt_client_t *client, const char *topic, const void *payload, u16_t payload_length, u8_t qos, u8_t retain, mqtt_request_cb_t cb, void *arg)
err_t | mqtt_sub_unsub (mqtt_client_t *client, const char *topic, u8_t qos, mqtt_request_cb_t cb, void *arg, u8_t sub)
void | mqtt_set_inpub_callback (mqtt_client_t *client, mqtt_incoming_publish_cb_t pub_cb, mqtt_incoming_data_cb_t data_cb, void *arg)
mqtt_client_t * | mqtt_client_new (void)
void | mqtt_client_free (mqtt_client_t *client)
err_t | mqtt_client_connect (mqtt_client_t *client, const ip_addr_t *ip_addr, u16_t port, mqtt_connection_cb_t cb, void *arg, const struct mqtt_connect_client_info_t *client_info)
void | mqtt_disconnect (mqtt_client_t *client)
u8_t | mqtt_client_is_connected (mqtt_client_t *client)

## Detailed Description

    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 MQTT version 3.1.1 is always used */

      err = mqtt_client_connect(client, ip_addr, MQTT_PORT, 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)

## Macro Definition Documentation

## ◆ MQTT_PORT

#define MQTT_PORT LWIP_IANA_PORT_MQTT

Default MQTT port (non-TLS)

## ◆ mqtt_subscribe

#define mqtt_subscribe | ( |  | client,
|  |  | topic,
|  |  | qos,
|  |  | cb,
|  |  | arg
| ) |  | mqtt_sub_unsub(client, topic, qos, cb, arg, 1)

Subscribe to topic

## ◆ MQTT_TLS_PORT

#define MQTT_TLS_PORT LWIP_IANA_PORT_SECURE_MQTT

Default MQTT TLS port

## ◆ mqtt_unsubscribe

#define mqtt_unsubscribe | ( |  | client,
|  |  | topic,
|  |  | cb,
|  |  | arg
| ) |  | mqtt_sub_unsub(client, topic, 0, cb, arg, 0)

Unsubscribe to topic

## Typedef Documentation

## ◆ mqtt_connection_cb_t

typedef void(* mqtt_connection_cb_t) (mqtt_client_t *client, void *arg, mqtt_connection_status_t status)

Function prototype for mqtt connection status callback. Called when client has connected to the server after initiating a mqtt connection attempt by calling mqtt_client_connect() or when connection is closed by server or an error

Parameters

  client | MQTT client itself
  arg | Additional argument to pass to the callback function
  status | Connect result code or disconnection notification

See also
  mqtt_connection_status_t

## ◆ mqtt_incoming_data_cb_t

typedef void(* mqtt_incoming_data_cb_t) (void *arg, const u8_t *data, u16_t len, u8_t flags)

Function prototype for MQTT incoming publish data callback function. Called when data arrives to a subscribed topic

See also
  mqtt_subscribe

Parameters

  arg | Additional argument to pass to the callback function
  data | User data, pointed object, data may not be referenced after callback return, NULL is passed when all publish data are delivered
  len | Length of publish data fragment
  flags | MQTT_DATA_FLAG_LAST set when this call contains the last part of data from publish message

## ◆ mqtt_incoming_publish_cb_t

typedef void(* mqtt_incoming_publish_cb_t) (void *arg, const char *topic, u32_t tot_len)

Function prototype for MQTT incoming publish function. Called when an incoming publish arrives to a subscribed topic

See also
  mqtt_subscribe

Parameters

  arg | Additional argument to pass to the callback function
  topic | Zero terminated Topic text string, topic may not be referenced after callback return
  tot_len | Total length of publish data, if set to 0 (no publish payload) data callback will not be invoked

## ◆ mqtt_request_cb_t

typedef void(* mqtt_request_cb_t) (void *arg, err_t err)

Function prototype for mqtt request callback. Called when a subscribe, unsubscribe or publish request has completed

Parameters

  arg | Pointer to user data supplied when invoking request
  err | ERR_OK on success ERR_TIMEOUT if no response was received within timeout, ERR_ABRT if (un)subscribe was denied

## Enumeration Type Documentation

## ◆ anonymous enum

anonymous enum

Data callback flags

Enumerator
MQTT_DATA_FLAG_LAST | Flag set when last fragment of data arrives in data callback

## ◆ mqtt_connection_status_t

enum mqtt_connection_status_t

Connection status codes

Enumerator
MQTT_CONNECT_ACCEPTED | Accepted
MQTT_CONNECT_REFUSED_PROTOCOL_VERSION | Refused protocol version
MQTT_CONNECT_REFUSED_IDENTIFIER | Refused identifier
MQTT_CONNECT_REFUSED_SERVER | Refused server
MQTT_CONNECT_REFUSED_USERNAME_PASS | Refused user credentials
MQTT_CONNECT_REFUSED_NOT_AUTHORIZED_ | Refused not authorized
MQTT_CONNECT_DISCONNECTED | Disconnected
MQTT_CONNECT_TIMEOUT | Timeout

## Function Documentation

## ◆ mqtt_client_connect()

err_t mqtt_client_connect | ( | mqtt_client_t * | client,
|  | const ip_addr_t * | ip_addr,
|  | u16_t | port,
|  | mqtt_connection_cb_t | cb,
|  | void * | arg,
|  | const struct mqtt_connect_client_info_t * | client_info
| ) |  |

Connect to MQTT server

Parameters

  client | MQTT client
  ip_addr | Server IP
  port | Server port
  cb | Connection state change callback
  arg | User supplied argument to connection callback
  client_info | Client identification and connection options

Returns
  ERR_OK if successful,

See also
  err_t enum for other results

## ◆ mqtt_client_free()

void mqtt_client_free | ( | mqtt_client_t * | client | ) |

Free MQTT client instance

Parameters

  client | Pointer to instance to be freed

## ◆ mqtt_client_is_connected()

u8_t mqtt_client_is_connected | ( | mqtt_client_t * | client | ) |

Check connection with server

Parameters

  client | MQTT client

Returns
  1 if connected to server, 0 otherwise

## ◆ mqtt_client_new()

mqtt_client_t* mqtt_client_new | ( | void |  | ) |

Create a new MQTT client instance

Returns
  Pointer to instance on success, NULL otherwise

## ◆ mqtt_disconnect()

void mqtt_disconnect | ( | mqtt_client_t * | client | ) |

Disconnect from MQTT server

Parameters

  client | MQTT client

## ◆ mqtt_publish()

err_t mqtt_publish | ( | mqtt_client_t * | client,
|  | const char * | topic,
|  | const void * | payload,
|  | u16_t | payload_length,
|  | u8_t | qos,
|  | u8_t | retain,
|  | mqtt_request_cb_t | cb,
|  | void * | arg
| ) |  |

MQTT publish function.

Parameters

  client | MQTT client
  topic | Publish topic string
  payload | Data to publish (NULL is allowed)
  payload_length | Length of payload (0 is allowed)
  qos | Quality of service, 0 1 or 2
  retain | MQTT retain flag
  cb | Callback to call when publish is complete or has timed out
  arg | User supplied argument to publish callback

Returns
  ERR_OK if successful ERR_CONN if client is disconnected ERR_MEM if short on memory

## ◆ mqtt_set_inpub_callback()

void mqtt_set_inpub_callback | ( | mqtt_client_t * | client,
|  | mqtt_incoming_publish_cb_t | pub_cb,
|  | mqtt_incoming_data_cb_t | data_cb,
|  | void * | arg
| ) |  |

Set callback to handle incoming publish requests from server

Parameters

  client | MQTT client
  pub_cb | Callback invoked when publish starts, contain topic and total length of payload
  data_cb | Callback for each fragment of payload that arrives
  arg | User supplied argument to both callbacks

## ◆ mqtt_sub_unsub()

err_t mqtt_sub_unsub | ( | mqtt_client_t * | client,
|  | const char * | topic,
|  | u8_t | qos,
|  | mqtt_request_cb_t | cb,
|  | void * | arg,
|  | u8_t | sub
| ) |  |

MQTT subscribe/unsubscribe function.

Parameters

  client | MQTT client
  topic | topic to subscribe to
  qos | Quality of service, 0 1 or 2 (only used for subscribe)
  cb | Callback to call when subscribe/unsubscribe reponse is received
  arg | User supplied argument to publish callback
  sub | 1 for subscribe, 0 for unsubscribe

Returns
  ERR_OK if successful,

See also
  err_t enum for other results