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.conf file.

The 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:

Using west:

west build -b frdm_k64f samples/net/mqtt_publisher
west flash

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=frdm_k64f samples/net/mqtt_publisher
ninja -C build
ninja -C build flash

Open another terminal window and type:

$ sudo mosquitto -v -p 1883

Open another terminal window and type:

$ mosquitto_sub -t sensors

Connecting securely using TLS

While it is possible to set up a local secure MQTT server and update the sample to connect to it, it does require some work on the user’s part to create the certificates and to set them up with the server.

Alternatively, a publicly available Mosquitto MQTT server/broker is available to quickly and easily try this sample with TLS enabled, by following these steps:

  • Download the server’s CA certificate file in DER format from https://test.mosquitto.org
  • In src/test_certs.h, set ca_certificate[] using the certificate contents (or set it to its filename if the socket offloading feature is enabled on your platform and CONFIG_TLS_CREDENTIAL_FILENAMES is set to y).
  • In src/config.h, set SERVER_ADDR to the IP address to connect to, i.e., the IP address of test.mosquitto.org "37.187.106.16"
  • In src/main.c, set TLS_SNI_HOSTNAME to "test.mosquitto.org" to match the Common Name (CN) in the downloaded certificate.
  • Build the sample by specifying -DOVERLAY_CONFIG=overlay-tls.conf when running west build or cmake (or refer to the TLS offloading section below if your platform uses the offloading feature).
  • Flash the binary onto the device to run the sample:
$ ninja flash

TLS offloading

For boards that support this feature, TLS offloading is used by specifying -DOVERLAY_CONFIG=overlay-tls-offload.conf when running west build or cmake.

Using this overlay enables TLS without bringing in mbedtls.

SOCKS5 proxy support

It is also possible to connect to the MQTT broker through a SOCKS5 proxy. To enable it, use -DOVERLAY_CONFIG=overlay-socks5.conf when running west build or cmake.

By default, to make the testing easier, the proxy is expected to run on the same host as the MQTT broker.

To start a proxy server, ssh can be used. Use the following command to run it on your host with the default port:

To connect to a proxy server that is not running under the same IP as the MQTT broker or uses a different port number, modify the following values:

#define SOCKS5_PROXY_ADDR    SERVER_ADDR
#define SOCKS5_PROXY_PORT    1080

Running on cc3220sf_launchxl

Offloading on cc3220sf_launchxl also provides DHCP services, so the sample uses dynamic IP addresses on this board.

By default, the sample is set up to connect to the broker at the address specified by SERVER_ADDR in config.h. If the broker is secured using TLS, users should enable TLS offloading, upload the server’s certificate authority file in DER format to the device filesystem using TI Uniflash, and name it “ca_cert.der”.

In addition, TLS_SNI_HOSTNAME in main.c should be defined to match the Common Name (CN) in the certificate file in order for the TLS domain name verification to succeed.

See the note on Provisioning and Fast Connect in CC3220SF LaunchXL.

The Secure Socket Offload section has information on programming the certificate to flash.

Proceed to test as above.

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