CoAP Device API Reference

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CoAP Device API Reference

Getting started

CoAP basics

CoAP is a light-weight IoT protocol for constrained devices. You can find more information about CoAP here. CoAP protocol is UDP based, but similar to HTTP it uses request-response model. CoAP observes option allows to subscribe to resources and receive notifications on resource change.

IoT Hub server nodes act as a CoAP Server that supports both regular and observe requests.

Client libraries setup

You can find CoAP client libraries for different programming languages on the web. Examples in this article will be based on CoAP cli. In order to setup this tool, you can use instructions in our Hello World guide.

NOTE: CoAP cli does not support query parameters. If you require to use query parameters, you should use coap client instead. To install the coap-client please execute:

  • Ubuntu 20.04: sudo apt install libcoap2-bin
  • Ubuntu 18.04: sudo apt install libcoap1-bin
CoAP Authentication and error codes

We will use access token device credentials in this article and they will be referred to later as $ACCESS_TOKEN. The application needs to include $ACCESS_TOKEN as a path parameter into each CoAP request. Possible error codes and their reasons:

  • 4.00 Bad Request - Invalid URL, request parameters or body.
  • 4.01 Unauthorized - Invalid $ACCESS_TOKEN.
  • 4.04 Not Found - Resource not found.

Key-value format

By default, IoT Hub supports key-value content in JSON. Key is always a string, while value can be either string, boolean, double, long or JSON. For example:

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{
 "stringKey":"value1", 
 "booleanKey":true, 
 "doubleKey":42.0, 
 "longKey":73, 
 "jsonKey": {
    "someNumber": 42,
    "someArray": [1,2,3],
    "someNestedObject": {"key": "value"}
 }
}

However, it is also possible to send data via Protocol Buffers. Please refer to the CoAP transport type configuration section in device profile article for more details.

Using custom binary format or some serialization framework is also possible. See protocol customization for more details.

Telemetry upload API

In order to publish telemetry data to IoT Hub server node, send POST request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/telemetry

The simplest supported data formats are:

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{"key1":"value1", "key2":"value2"}

or

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[{"key1":"value1"}, {"key2":"value2"}]

Please note that in this case, the server-side timestamp will be assigned to uploaded data!

In case your device is able to get the client-side timestamp, you can use following format:

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{"ts":1451649600512, "values":{"key1":"value1", "key2":"value2"}}

In the example above, we assume that “1451649600512” is a unix timestamp with milliseconds precision. For example, the value ‘1451649600512’ corresponds to ‘Fri, 01 Jan 2016 12:00:00.512 GMT’

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# for IoT Hub

# Publish data as an object without timestamp (server-side timestamp will be used)
cat telemetry-data-as-object.json | coap post coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/telemetry
# Publish data as an array of objects without timestamp (server-side timestamp will be used)
cat telemetry-data-as-array.json | coap post coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/telemetry
# Publish data as an object with timestamp (telemetry timestamp will be used)
cat telemetry-data-with-ts.json | coap post coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/telemetry

# for local IoT Hub

# Publish data as an object without timestamp (server-side timestamp will be used)
cat telemetry-data-as-object.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/telemetry
# Publish data as an array of objects without timestamp (server-side timestamp will be used)
cat telemetry-data-as-array.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/telemetry
# Publish data as an object with timestamp (telemetry timestamp will be used)
cat telemetry-data-with-ts.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/telemetry

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{
  "stringKey": "value1",
  "booleanKey": true,
  "doubleKey": 42.0,
  "longKey": 73,
  "jsonKey": {
    "someNumber": 42,
    "someArray": [1,2,3],
    "someNestedObject": {"key": "value"}
  }
}

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[{"key1":"value1"}, {"key2":true}]

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{
  "ts": 1451649600512,
  "values": {
    "stringKey": "value1",
    "booleanKey": true,
    "doubleKey": 42.0,
    "longKey": 73,
    "jsonKey": {
      "someNumber": 42,
      "someArray": [1, 2, 3],
      "someNestedObject": {
        "key": "value"
      }
    }
  }
}

Attributes API

IoT Hub attributes API allows devices to

  • Upload client-side device attributes to the server.
  • Request client-side and shared device attributes from the server.
  • Subscribe to shared device attributes from the server.
Publish attribute update to the server

In order to publish client-side device attributes to IoT Hub server node, send POST request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/attributes

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# for IoT Hub

# Publish client-side attributes update
cat new-attributes-values.json | coap post coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/attributes

# for local IoT Hub

# Publish client-side attributes update
cat new-attributes-values.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/attributes

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{
  "attribute1": "value1",
  "attribute2": true,
  "attribute3": 42.0,
  "attribute4": 73,
  "attribute5": {
    "someNumber": 42,
    "someArray": [1,2,3],
    "someNestedObject": {"key": "value"}
  }
}
Request attribute values from the server

In order to request client-side or shared device attributes to IoT Hub server node, send GET request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/attributes?clientKeys=attribute1,attribute2&sharedKeys=shared1,shared2

NOTE: This example shown with the coap-client instead of CoAP cli since CoAP cli does not support query parameters. Please refer to Client libraries setup.

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# for IoT Hub

# Send CoAP attributes request
coap-client -m get "coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/attributes?clientKeys=attribute1,attribute2&sharedKeys=shared1,shared2"

# for local IoT Hub

# Send CoAP attributes request
coap-client -m get "coap://localhost/api/v1/$ACCESS_TOKEN/attributes?clientKeys=attribute1,attribute2&sharedKeys=shared1,shared2"

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{"key1":"value1"}

Please note, the intersection of client-side and shared device attribute keys is a bad practice! However, it is still possible to have same keys for client, shared or even server-side attributes.

Subscribe to attribute updates from the server

In order to subscribe to shared device attribute changes, send GET request with Observe option to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/attributes

Once shared attribute will be changed by one of the server-side components (REST API or Rule Chain) the client will receive the following update:

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# for IoT Hub

# Subscribe to attribute updates
coap get -o coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/attributes

# for local IoT Hub

# Subscribe to attribute updates
coap get -o coap://localhost/api/v1/$ACCESS_TOKEN/attributes

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{"key1":"value1"}

JSON value support

We added support of JSON data structures to telemetry and attributes API to simplify work with device configuration. JSON support allows you to both upload from the device, and push to device nested objects. You can store one configuration JSON as a shared attribute and push it to the device. You can also process the JSON data in the rule engine and raise alarms, etc.

Therefore, this improvement minimizes the number of Database operations when IoT Hub stores the data. For example, “temperature” and “humidity” would be stored as separate rows in SQL or NoSQL databases in order to efficiently aggregate this data for visualization. Since there is no need to aggregate JSON data, we can store all the content as one row instead of separate rows for each configuration item. In some of our environments, it is possible to decrease the number of database operations more than 10 times by aggregating multiple parameters within one JSON.

Learn more about JSON value support with the video.

RPC API

Server-side RPC

In order to subscribe to RPC commands from the server, send GET request with observe flag to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/rpc

Once subscribed, a client may receive rpc requests. An example of RPC request body is shown below:

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{
  "id": "1",
  "method": "setGpio",
  "params": {
    "pin": "23",
    "value": 1
  }
}

where

  • id - request id, integer request identifier
  • method - RPC method name, string
  • params - RPC method params, custom json object

and can reply to them using POST request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/rpc/{$id}

where $id is an integer request identifier.

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# for IoT Hub

# Subscribe to RPC requests
coap get -o coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/rpc

# for local IoT Hub

# Subscribe to RPC requests
coap get -o coap://localhost/api/v1/$ACCESS_TOKEN/rpc

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# Publish response to RPC request
cat rpc-response.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/rpc/1

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{"result":"ok"}
Client-side RPC

In order to send RPC commands to the server, send POST request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/rpc

Both request and response body should be valid JSON documents. The content of the documents is specific to the rule node that will handle your request.

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# for IoT Hub

# Post client-side rpc request
cat rpc-client-request.json | coap post coap://coap-device.iothub.magenta.at/api/v1/$ACCESS_TOKEN/rpc

# for local IoT Hub

# Post client-side rpc request
cat rpc-client-request.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/rpc

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{"method": "getTime", "params":{}}

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{"time":"2016 11 21 12:54:44.287"}

Claiming devices

Please see the corresponding article to get more information about the Claiming devices feature.

In order to initiate claiming device, send POST request to the following URL:

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coap://host/api/v1/$ACCESS_TOKEN/claim

The supported data format is:

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{"secretKey":"value", "durationMs":60000}

Please note that the above fields are optional. In case the secretKey is not specified, the empty string as a default value is used. In case the durationMs is not specified, the system parameter device.claim.duration is used (in the file /etc/thingsboard/conf/thingsboard.yml).

Device provisioning

Please see the corresponding article to get more information about the Device provisioning feature.

In order to initiate device provisioning, send POST request to the following URL:

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coap://host/api/v1/provision

The supported data format is:

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{
  "deviceName": "DEVICE_NAME",
  "provisionDeviceKey": "u7piawkboq8v32dmcmpp",
  "provisionDeviceSecret": "jpmwdn8ptlswmf4m29bw"
}

Firmware API

The CoAP client has to issue the GET request to

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 coap get coap://host/api/v1/${access_token}/firmware?title=${title}&version=${version}

Where
host - your localhost, or the platform address;
${access_token} - device access token;
${title} - the firmware title;
${version} - the version of the target firmware.

Protocol customization

CoAP transport can be fully customized for specific use-case by changing the corresponding module.

Next steps