# CoAP Device API Reference ### Getting started **CoAP basics** [CoAP](https://en.wikipedia.org/wiki/Constrained_Application_Protocol) is a light-weight IoT protocol for constrained devices. You can find more information about CoAP [here](https://tools.ietf.org/html/rfc7252). CoAP protocol is UDP based, but similar to HTTP it uses request-response model. CoAP observes [option](https://tools.ietf.org/html/rfc7641) 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](https://www.npmjs.com/package/coap-cli). In order to setup this tool, you can use instructions in our [Hello World](https://thingsboard.io/docs/getting-started-guides/helloworld/) 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](https://en.wikipedia.org/wiki/Unix_time) 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/$ACCESS_TOKEN/telemetry ``` telemetry-data-as-object.json ```javascript {"key1":"value1", "key2":true, "key3": 3.0, "key4": 4} ``` telemetry-data-as-array.json ```javascript [{"key1":"value1"}, {"key2":true}] ``` telemetry-data-with-ts.json ```javascript {"ts":1451649600512, "values":{"key1":"value1", "key2":"value2"}} ``` ### Attributes API JIoT attributes API allows devices to * Upload client-side device attributes to the server. * Request client-side and shared device attributes from the server. * Subscribe to shared device attributes from the server. **Publish attribute update to the server** In order to publish client-side device attributes to JIoT server node, send POST request to the following URL: ``` coap://host:port/api/v1/$ACCESS_TOKEN/attributes ``` Example ``` # Publish client-side attributes update cat new-attributes-values.json | coap post coap://localhost/api/v1/$ACCESS_TOKEN/attributes ``` new-attributes-values.json ```javascript {"attribute1":"value1", "attribute2":true, "attribute3":42.0, "attribute4":73} ``` **Request attribute values from the server** In order to request client-side or shared device attributes to JIoT server node, send GET request to the following URL: ``` coap://host:port/api/v1/$ACCESS_TOKEN/attributes?clientKeys=attribute1,attribute2&sharedKeys=shared1,shared2 ``` Example ``` # Send CoAP attributes request coap get coap://localhost/api/v1/$ACCESS_TOKEN/attributes?clientKeys=attribute1,attribute2&sharedKeys=shared1,shared2 ``` Result ```javascript {"key1":"value1"} ``` **Please note**, the intersection of client-side and shared device attribute keys is a bad practice! However, it is still possible to have same keys for client, shared or even server-side attributes. **Subscribe to attribute updates from the server** In order to subscribe to shared device attribute changes, send GET request with Observe option to the following URL: ``` coap://host:port/api/v1/$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/$ACCESS_TOKEN/attributes ``` Result ```javascript {"key1":"value1"} ``` ### RPC API **Server-side RPC** In order to subscribe to RPC commands from the server, send GET request with observe flag to the following URL: ``` coap://host:port/api/v1/$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. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://astian.gitbook.io/jiot/api/coap-device-api-reference.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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