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.

JIoT 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.

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, JIoT supports key-value content in JSON. Key is always a string, while value can be either string, boolean, double or long. Using custom binary format or some serialization framework is also possible. See protocol customization for more details. For example:

{"stringKey":"value1", "booleanKey":true, "doubleKey":42.0, "longKey":73}

Telemetry upload API

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

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

The simplest supported data formats are:

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

or

[{"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:

{"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’

Example

# 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 (server-side timestamp will be used)
cat telemetry-data-with-ts.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/telemetry

telemetry-data-as-object.json

{"key1":"value1", "key2":true, "key3": 3.0, "key4": 4}

telemetry-data-as-array.json

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

telemetry-data-with-ts.json

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

Attributes API

JIoT 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 JIoT server node, send POST request to the following URL:

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

Example

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

new-attributes-values.json

{"attribute1":"value1", "attribute2":true, "attribute3":42.0, "attribute4":73}

Request attribute values from the server

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

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

Example

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

Result

{"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:

coap://host:port/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:

Example

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

Result

{"key1":"value1"}

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:

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

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

{
  "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:

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

where $id is an integer request identifier.

Example Subcribe

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

Example Reply

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

Reply Body

{"result":"ok"}

Client-side RPC

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

coap://host:port/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.

Example Request

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

Request Body

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

Response Body

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

Protocol customization

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

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