MQTT Publisher¶

Overview¶

MQTT (MQ Telemetry Transport) is a lightweight publish/subscribe messaging protocol optimized for small sensors and mobile devices.

The Zephyr MQTT Publisher sample application is a MQTT v3.1.1 client that sends MQTT PUBLISH messages to a MQTT broker. See the MQTT V3.1.1 spec for more information.

The source code of this sample application can be found at: samples/net/mqtt_publisher.

Requirements¶

Linux machine
Freedom Board (FRDM-K64F)
Mosquitto server: any version that supports MQTT v3.1.1. This sample was tested with mosquitto 1.3.4.
Mosquitto subscriber
LAN for testing purposes (Ethernet)

Build and Running¶

Currently, this sample application only supports static IP addresses. Open the src/config.h file and set the IP addresses according to the LAN environment. Alternatively, set the IP addresses in the prj_frdm_k64f.conf file.

This file src/config.h also contains some variables that may be changed:

MQTT broker TCP port:

#define SERVER_PORT             1883

Application sleep time:

#define APP_SLEEP_MSECS         500

Application RX and TX timeout:

#define APP_TX_RX_TIMEOUT       300

Max number of connection tries:

#define APP_CONNECT_TRIES       10

Max number of MQTT PUBLISH iterations:

#define APP_MAX_ITERATIONS      5

MQTT Client Identifier:

#define MQTT_CLIENTID           "zephyr_publisher"

This sample application supports the IBM Bluemix Watson topic format that can be enabled by changing the default value of APP_BLUEMIX_TOPIC from 0 to 1:

#define APP_BLUEMIX_TOPIC       1

The Bluemix topic may include some parameters like device type, device identifier, event type and message format. This application uses the following macros to specify those values:

#define BLUEMIX_DEVTYPE         "sensor"
#define BLUEMIX_DEVID           "carbon"
#define BLUEMIX_EVENT           "status"
#define BLUEMIX_FORMAT          "json"

On your Linux host computer, open a terminal window, locate the source code of this sample application (i.e. samples/net/mqtt_publisher) and type:

# On Linux/macOS
cd $ZEPHYR_BASE/samples/net/mqtt_publisher
mkdir build && cd build
# On Windows
cd %ZEPHYR_BASE%\samples\net\mqtt_publisher
mkdir build & cd build
cmake -GNinja -DBOARD=frdm_k64f ..
ninja
ninja flash

Open another terminal window and type:

$ sudo mosquitto -v -p 1883

Open another terminal window and type:

$ mosquitto_sub -t sensors

Sample output¶

This is the output from the FRDM UART console, with:

#define APP_MAX_ITERATIONS     5

[dev/eth_mcux] [INF] eth_0_init: Enabled 100M full-duplex mode.
[dev/eth_mcux] [DBG] eth_0_init: MAC 00:04:9f:3e:1a:0a
[publisher:233] network_setup: 0 <OK>
[publisher:258] mqtt_init: 0 <OK>
[connect_cb:81] user_data: CONNECTED
[try_to_connect:212] mqtt_tx_connect: 0 <OK>
[publisher:276] try_to_connect: 0 <OK>
[publisher:285] mqtt_tx_pingreq: 0 <OK>
[publisher:290] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBACK> packet id: 1888, user_data: PUBLISH
[publisher:295] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBREC> packet id: 16356, user_data: PUBLISH
[publish_cb:149] <MQTT_PUBCOMP> packet id: 16356, user_data: PUBLISH
[publisher:300] mqtt_tx_publish: 0 <OK>
[publisher:285] mqtt_tx_pingreq: 0 <OK>
[publisher:290] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBACK> packet id: 45861, user_data: PUBLISH
[publisher:295] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBREC> packet id: 53870, user_data: PUBLISH
[publish_cb:149] <MQTT_PUBCOMP> packet id: 53870, user_data: PUBLISH
[publisher:300] mqtt_tx_publish: 0 <OK>
[publisher:285] mqtt_tx_pingreq: 0 <OK>
[publisher:290] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBACK> packet id: 60144, user_data: PUBLISH
[publisher:295] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBREC> packet id: 6561, user_data: PUBLISH
[publish_cb:149] <MQTT_PUBCOMP> packet id: 6561, user_data: PUBLISH
[publisher:300] mqtt_tx_publish: 0 <OK>
[publisher:285] mqtt_tx_pingreq: 0 <OK>
[publisher:290] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBACK> packet id: 38355, user_data: PUBLISH
[publisher:295] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBREC> packet id: 60656, user_data: PUBLISH
[publish_cb:149] <MQTT_PUBCOMP> packet id: 60656, user_data: PUBLISH
[publisher:300] mqtt_tx_publish: 0 <OK>
[publisher:285] mqtt_tx_pingreq: 0 <OK>
[publisher:290] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBACK> packet id: 28420, user_data: PUBLISH
[publisher:295] mqtt_tx_publish: 0 <OK>
[publish_cb:149] <MQTT_PUBREC> packet id: 49829, user_data: PUBLISH
[publish_cb:149] <MQTT_PUBCOMP> packet id: 49829, user_data: PUBLISH
[publisher:300] mqtt_tx_publish: 0 <OK>
[disconnect_cb:101] user_data: DISCONNECTED
[publisher:304] mqtt_tx_disconnect: 0 <OK>

Bye!

The line:

[try_to_connect:220] mqtt_connect: -5 <ERROR>

means that an error was detected and a new connect message will be sent.

The MQTT API is asynchronous, so messages are displayed as the callbacks are executed.

This is the information that the subscriber will receive:

$ mosquitto_sub -t sensors
DOORS:OPEN_QoS0
DOORS:OPEN_QoS1
DOORS:OPEN_QoS2
DOORS:OPEN_QoS0
DOORS:OPEN_QoS1
DOORS:OPEN_QoS2
DOORS:OPEN_QoS0
DOORS:OPEN_QoS1
DOORS:OPEN_QoS2
DOORS:OPEN_QoS0
DOORS:OPEN_QoS1
DOORS:OPEN_QoS2
DOORS:OPEN_QoS0
DOORS:OPEN_QoS1
DOORS:OPEN_QoS2

This is the output from the MQTT broker:

$ sudo mosquitto -v
1485663791: mosquitto version 1.3.4 (build date 2014-08-17 00:14:52-0300) starting
1485663791: Using default config.
1485663791: Opening ipv4 listen socket on port 1883.
1485663791: Opening ipv6 listen socket on port 1883.
1485663797: New connection from 192.168.1.101 on port 1883.
1485663797: New client connected from 192.168.1.101 as zephyr_publisher (c1, k0).
1485663797: Sending CONNACK to zephyr_publisher (0)
1485663798: Received PINGREQ from zephyr_publisher
1485663798: Sending PINGRESP to zephyr_publisher
1485663798: Received PUBLISH from zephyr_publisher (d0, q0, r0, m0, 'sensors', ... (15 bytes))
1485663799: Received PUBLISH from zephyr_publisher (d0, q1, r0, m1888, 'sensors', ... (15 bytes))
1485663799: Sending PUBACK to zephyr_publisher (Mid: 1888)
1485663799: Received PUBLISH from zephyr_publisher (d0, q2, r0, m16356, 'sensors', ... (15 bytes))
1485663799: Sending PUBREC to zephyr_publisher (Mid: 16356)
1485663799: Received PUBREL from zephyr_publisher (Mid: 16356)
1485663799: Sending PUBCOMP to zephyr_publisher (Mid: 16356)
1485663800: Received PINGREQ from zephyr_publisher
1485663800: Sending PINGRESP to zephyr_publisher
1485663800: Received PUBLISH from zephyr_publisher (d0, q0, r0, m0, 'sensors', ... (15 bytes))
1485663801: Received PUBLISH from zephyr_publisher (d0, q1, r0, m45861, 'sensors', ... (15 bytes))
1485663801: Sending PUBACK to zephyr_publisher (Mid: 45861)
1485663801: Received PUBLISH from zephyr_publisher (d0, q2, r0, m53870, 'sensors', ... (15 bytes))
1485663801: Sending PUBREC to zephyr_publisher (Mid: 53870)
1485663801: Received PUBREL from zephyr_publisher (Mid: 53870)
1485663801: Sending PUBCOMP to zephyr_publisher (Mid: 53870)
1485663802: Received PINGREQ from zephyr_publisher
1485663802: Sending PINGRESP to zephyr_publisher
1485663802: Received PUBLISH from zephyr_publisher (d0, q0, r0, m0, 'sensors', ... (15 bytes))
1485663803: Received PUBLISH from zephyr_publisher (d0, q1, r0, m60144, 'sensors', ... (15 bytes))
1485663803: Sending PUBACK to zephyr_publisher (Mid: 60144)
1485663803: Received PUBLISH from zephyr_publisher (d0, q2, r0, m6561, 'sensors', ... (15 bytes))
1485663803: Sending PUBREC to zephyr_publisher (Mid: 6561)
1485663803: Received PUBREL from zephyr_publisher (Mid: 6561)
1485663803: Sending PUBCOMP to zephyr_publisher (Mid: 6561)
1485663804: Received PINGREQ from zephyr_publisher
1485663804: Sending PINGRESP to zephyr_publisher
1485663804: Received PUBLISH from zephyr_publisher (d0, q0, r0, m0, 'sensors', ... (15 bytes))
1485663805: Received PUBLISH from zephyr_publisher (d0, q1, r0, m38355, 'sensors', ... (15 bytes))
1485663805: Sending PUBACK to zephyr_publisher (Mid: 38355)
1485663805: Received PUBLISH from zephyr_publisher (d0, q2, r0, m60656, 'sensors', ... (15 bytes))
1485663805: Sending PUBREC to zephyr_publisher (Mid: 60656)
1485663805: Received PUBREL from zephyr_publisher (Mid: 60656)
1485663805: Sending PUBCOMP to zephyr_publisher (Mid: 60656)
1485663806: Received PINGREQ from zephyr_publisher
1485663806: Sending PINGRESP to zephyr_publisher
1485663806: Received PUBLISH from zephyr_publisher (d0, q0, r0, m0, 'sensors', ... (15 bytes))
1485663807: Received PUBLISH from zephyr_publisher (d0, q1, r0, m28420, 'sensors', ... (15 bytes))
1485663807: Sending PUBACK to zephyr_publisher (Mid: 28420)
1485663807: Received PUBLISH from zephyr_publisher (d0, q2, r0, m49829, 'sensors', ... (15 bytes))
1485663807: Sending PUBREC to zephyr_publisher (Mid: 49829)
1485663807: Received PUBREL from zephyr_publisher (Mid: 49829)
1485663807: Sending PUBCOMP to zephyr_publisher (Mid: 49829)
1485663808: Received DISCONNECT from zephyr_publisher