Testing message delivery

When sending a message, you may need to verify that it was delivered. A message may fail to reach the MQTT server, e.g., if it is sent:

• To a non-existing device topic.
• From a client with writes to the specified topic disabled.
• From a client that is not authenticated in the system.

The IoT network structure assumes that MQTT clients connect to the MQTT server. It accepts messages sent by publishers and forwards them to subscribers. MQTT does not support notifications that the message has been delivered to subscriber. You can only get a confirmation that a message has been delivered to the MQTT server.

To ascertain that the MQTT server has received the message, specify additional debugging parameters in the send message command. As a result, you will get a detailed command output.

To test the Yandex IoT Core service, use both messaging and device subscription at the same time. If you subscribe a registry to a device topic and send a message to this topic, the registry will receive the message.

In the example below, a device with a light intensity sensor sends the light intensity value of 150 to a permanent device topic. Client authentication is performed through X.509 certificates. The CLI and Mosquitto, an open-source MQTT message broker, are used as tools for sending messages and subscribing to devices.

Getting started

1. If you do not have the Yandex Cloud (CLI) command line interface yet, install and initialize it.

   The folder specified when creating the CLI profile is used by default. To change the default folder, use the yc config set folder-id <folder_ID> command. You can specify a different folder using the --folder-name or --folder-id parameter.

2. Create registry and device certificates.

3. Create a registry.

4. Add a certificate to the registry.

5. Create a device.

6. Add a certificate to the device.

7. (Optional) Download and install Mosquitto if you want to use it for sending messages and subscribing to the device instead of the CLI.

   To connect to the MQTT server via Mosquitto, use the following parameters:

   • Certificate from the certificate authority.
   • Server address: mqtt.cloud.yandex.net.
   • Server port: 8883.
   • Protocol: TLSv1.2.

Send a message with debugging parameters

When sending messages, add the following flags to the command:

• --qos 1 for the CLI or -q 1 for Mosquitto: Quality of service (QoS) level QoS 1: At least once. This level guarantees that the message will be delivered at least once.

  With this QoS level, the MQTT server sends a PUBACK packet to the publisher. This is how the server confirms that it has received the message from the publisher.

• --debug for the CLI and Mosquitto: Command debugging. Outputs the debug log when executing the command, thus helping not only to diagnose the issue but also to learn that the PUBACK packet was received.

Example of sending a message:

yc iot mqtt publish \
   --cert sensor-cert.pem \
   --key sensor-key.pem \
   --topic '$devices/b91qprkvbks9********/state' \
   --message '150' \
   --qos 1 \
   --debug

mosquitto_pub -h mqtt.cloud.yandex.net \
   -p 8883 \
   --cafile rootCA.crt \
   --cert sensor-cert.pem \
   --key sensor-key.pem \
   -t '$devices/b91qprkvbks9********/state' \
   -m '150' \
   -q 1 \
   --debug

Result example:

...
15:02:27.030752   [client]  enter Publish
15:02:27.030797   [client]  sending publish message, topic:$devices/b91qprkvbks9********/state
15:02:27.030923   [net]     obound wrote msg, id:1
15:02:27.030947   [net]     outgoing waiting for an outbound message
15:02:27.261271   [net]     Received Message
15:02:27.261530   [net]     logic got msg on ibound
15:02:27.261587   [store]   memorystore del: message1was deleted
15:02:27.261624   [net]     received puback, id:1
15:02:27.261674   [net]     logic waiting for msg on ibound
15:02:27.261719   [client]  disconnecting
...

Client null sending CONNECT
Client null received CONNACK (0)
Client null sending PUBLISH (d0, q1, r0, m1, '$devices/b91qprkvbks9********/state', ... (6 bytes))
Client null received PUBACK (Mid: 1, RC:0)
Client null sending DISCONNECT

This result indicates that the client has received the PUBACK packet. This is a confirmation from the MQTT server that it has received the message.

Use two clients to work with the same topic

To make sure a sent message has been delivered, subscribe your registry to a device topic. The MQTT server receives messages from topics and forwards them to subscribers. Therefore, if a subscriber has received a message, the MQTT has received it, too.

To use two clients to work with the same topic:

1. Subscribe a registry to a device's permanent topic.
2. Send a message to the device's permanent topic.
3. Make sure the registry has received the message from the device.

Subscribe your registry to the device's permanent topic

Run this command:

yc iot mqtt subscribe \
   --cert registry-cert.pem \
   --key registry-key.pem \
   --topic '$devices/b91qprkvbks9********/state' \
   --qos 1 \
   --debug

mosquitto_sub -h mqtt.cloud.yandex.net \
   -p 8883 \
   --cafile rootCA.crt \
   --cert registry-cert.pem \
   --key registry-key.pem \
   -t '$devices/b91qprkvbks9********/state' \
   -q 1 \
   --debug

Result example:

...
15:46:20.619042   [client]  enter Subscribe
15:46:20.619133   [client]  SUBSCRIBE: dup: false qos: 1 retain: false rLength: 0 MessageID: 0 topics: [$devices/b91qprkvbks9********/state]
15:46:20.619170   [client]  exit Subscribe
15:46:20.619214   [net]     obound priority msg to write, type*packets.SubscribePacket
15:46:20.619385   [net]     outgoing waiting for an outbound message
15:46:20.699795   [net]     Received Message
15:46:20.699959   [net]     logic got msg on ibound
15:46:20.700002   [store]   memorystore del: message1not found
15:46:20.700027   [net]     received suback, id:1
15:46:20.700055   [net]     granted qoss[128]
15:46:20.700092   [net]     logic waiting for msg on ibound

Client null sending CONNECT
Client null received CONNACK (0)
Client null sending SUBSCRIBE (Mid: 1, Topic: $devices/b91qprkvbks9********/state, QoS: 1, Options: 0x00)
Client null received SUBACK
Subscribed (mid: 1): 1

This result indicates that the client has received the SUBACK packet. This is a confirmation from the MQTT server that the subscription is successful.

After the result is output, the command is not terminated. The MQTT client will ping the topic from time to time while awaiting a message:

15:47:45.554570   [pinger]  ping check5
15:47:50.554346   [pinger]  ping check10
15:47:55.554149   [pinger]  ping check15

Client null sending PINGREQ
Client null received PINGRESP

Send a message to the device's permanent topic

Open a new terminal window and run this command:

yc iot mqtt publish \
   --cert sensor-cert.pem \
   --key sensor-key.pem \
   --topic '$devices/b91qprkvbks9********/state' \
   --message '150' \
   --qos 1 \
   --debug

mosquitto_pub -h mqtt.cloud.yandex.net \
   -p 8883 \
   --cafile rootCA.crt \
   --cert sensor-cert.pem \
   --key sensor-key.pem \
   -t '$devices/b91qprkvbks9********/state' \
   -m '150' \
   -q 1 \
   --debug

Result example:

...
15:02:27.030752   [client]  enter Publish
15:02:27.030797   [client]  sending publish message, topic:$devices/b91qprkvbks9********/state
15:02:27.030923   [net]     obound wrote msg, id:1
15:02:27.030947   [net]     outgoing waiting for an outbound message
15:02:27.261271   [net]     Received Message
15:02:27.261530   [net]     logic got msg on ibound
15:02:27.261587   [store]   memorystore del: message1was deleted
15:02:27.261624   [net]     received puback, id:1
15:02:27.261674   [net]     logic waiting for msg on ibound
15:02:27.261719   [client]  disconnecting
...

Client null sending CONNECT
Client null received CONNACK (0)
Client null sending PUBLISH (d0, q1, r0, m1, '$devices/b91qprkvbks9********/state', ... (3 bytes))
Client null received PUBACK (Mid: 1, RC:0)
Client null sending DISCONNECT

Make sure the registry has received the message from the device

If the message is delivered, the subscribe to device command outputs the result. Example:

17:23:26.346405   [net]     Received Message
17:23:26.346493   [net]     logic got msg on ibound
17:23:26.346518   [net]     received publish, msgId:4
17:23:26.346530   [net]     putting msg on onPubChan
17:23:26.346580   [net]     done putting msg on incomingPubChan
17:23:26.346590   [net]     logic waiting for msg on ibound
17:23:26.346591   [net]     putting puback msg on obound
17:23:26.346632   [store]   memorystore del: message4was deleted
17:23:26.346646   [net]     done putting puback msg on obound
150
17:23:26.346656   [net]     obound priority msg to write, type*packets.PubackPacket
17:23:26.346761   [net]     outgoing waiting for an outbound message

Client null received PUBLISH (d0, q1, r0, m3, '$devices/b91qprkvbks9********/state', ... (3 bytes))
Client null sending PUBACK (m3, rc0)
150

The result contains 150, which is the message that was sent.