spec/index.html at gh-pages · labthings/spec · GitHub

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<!DOCTYPE html>
<html>

<head>
  <meta charset='utf-8'>
  <title>Lab Things API</title>
  <script src="https://www.w3.org/Tools/respec/respec-w3c" class="remove" defer></script>
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<body>
  <p class="copyright">Copyright © 2017 Mozilla</p>
  <section id='abstract'>
    <p>This document describes a common data model and API for the LabThings devices. The <a
        href="#thing-description">Thing Description</a> provides a vocabulary for describing physical devices
      connected to the World Wide Web in a machine readable format with a default JSON encoding. Common device
      capabilities can be specified using optional <a href="#context-member">semantic annotations</a>. The <a
        href="#rest-api">REST API</a> and <a href="#websocket-api">WebSocket
        API</a> allow a web client to access the properties of devices, request the execution of actions and subscribe
      to events representing a change in state.</p>
  </section>
  <section id='sotd'>
    <p>This document includes a plain JSON serialisation of a <a
        href="https://w3c.github.io/wot-thing-description/">Thing Description</a> and a concrete HTTP and WebSockets <a
        href="https://w3c.github.io/wot-binding-templates/">protocol binding</a> for the Web of Things. This
      implementation is based on <a href="https://iot.mozilla.org/wot/">Mozilla's Web Thing API</a>, which defines
      simple concrete serialisation and protocol binding complementing the current <a
        href="https://www.w3.org/WoT/WG/">W3C Web of Things Working Group</a>'s work on an abstract data model and API
      for the Web of Things</p>

    <p>This implementation is intended to act as an extension to <a href="https://iot.mozilla.org/wot/">Mozilla's Web
        Thing API</a>, with additional provisions for laboratory use based on the project goals of <a
        href="https://labthings.org">LabThings</a>. Ideally, this document should describe a superset of the Mozilla
      implementation.</p>

    <p>While the Web of Things standardisation process continues, this document will continue to be maintained to
      reflect the current API implemented by Mozilla's open source Web of Things implementation through <a
        href="https://iot.mozilla.org/">Project Things</a>. We encourage developers to continue to implement this API to
      build web things compatible with Mozilla's <a href="https://iot.mozilla.org/gateway/">Things Gateway</a>, and
      provide feedback to help us further improve the specification.

    </p>
  </section>
  <section>
    <h2>Introduction</h2>
    <p>Instrumentation control poses a unique set of programming challenges related to resource locking, asynchronous
      execution, experiment planning, and data management. LabThings aims to provide a framework for solving these
      problems in an open, interoperable way using existing standards and technologies. Good solutions to many of these
      problems exist outside of research laboratory development. By utilizing web technologies and standards, labs can
      begin to move away from often prohibitively expensive, proprietary solutions, and modernize lab automation in a
      sustainable and accessible fashion.</p>
    <p>Whilst web technologies are already in widespread use on the Internet of Things, this is currently done with
      mostly proprietary data formats and APIs which require per-vendor integrations to make devices interoperable. In
      order to promote ad-hoc interoperability on the Internet of Things a shared vocabulary and common API is needed.
    </p>
    <p>In this document we outline a common data model and API for networked laboratory instruments based on <a
        href="https://iot.mozilla.org/wot/">Mozilla's Web Thing API</a>.</p>
  </section>
  <section>
    <h2>Thing Description</h2>
    <p>LabThings devices must use a standard W3C Web of Things Thing Description as per [[WOT-THING-DESCRIPTION]].</p>
    <p>The Thing Description provides a vocabulary for describing physical devices connected to the World Wide Web in a
      machine readable format with a default JSON encoding.</p>
    <pre class="example" title="A simple Thing Description" data-include="include/simple-td.json"></pre>
    <pre class="example" title="A more complex Thing Description with semantic annotations"
      data-include="include/complex-td.json"></pre>

    <section>
      <h3><code>@context</code> member</h3>
      <p>
        The <code>@context</code> member is an optional annotation which can be used to provide a URI for a schema repository which defines standard schemas for common "types" of device capabilities. These types can then be referred to
        using <code>@type</code> annotations elsewhere in the Thing Description.
      </p>
      <div class="note">Example experimental schema repositories can be found at <a href="http://iotschema.org/">http://iotschema.org/</a> and <a href="https://iot.mozilla.org/schemas">https://iot.mozilla.org/schemas</a>.</div>
      <div class="note">The Lab Things project will eventually introduce a laboratory-focused schema repository. This specification document will be updated accordingly.</div>
      <pre class="example" title="Example @context member">"@context": ["https://www.w3.org/2019/wot/td/v1", "https://iot.mozilla.org/schemas"]</pre>
    </section>

  </section>
  <section>
    <h2>REST API</h2>
    <p>The Web Thing API provides a web services based programming interface with a RESTful design for applications to
      access the properties of devices, request the execution of actions and access a list of events representing a
      change in state. A default HTTP [[HTTP11]] protocol binding is defined here.</p>
    <p>The Web Thing REST API consists of a number of different types of resources which represent different aspects of
      a device and can be independently referenced by a URL. The specific URLs and URL structure of resources are
      defined by the Thing Description.</p>
    <p>This specification does <strong>not</strong> define a fixed URL structure.</p>
    <section>
      <h3><code>Thing</code> resource</h3>
      <p>A thing Resource provides a <a href="#thing-description">Thing Description</a> for a device. A Thing
        Resource is considered the root resource of a Thing.</p>
      <p>The URL of a Thing Resource may be enumerated by a gateway or directory, or may be discovered by some other
        means.</p>
      <p>A Thing description is usually read only. An HTTP GET request can be used to retrieve a Thing Description for a
        Thing.</p>
      <p><strong>Example: Get a description of a Thing</strong></p>
      <div class="example">
        <div class="example-title marker">
          <span>Request</span>
        </div>
        <pre>GET http://mythingserver.com/things/pi
Accept: application/json</pre>
      </div>
      <div class="example">
        <div class="example-title marker">
          <span>Response</span>
        </div>
        <pre>200 OK
          <div data-include="include/simple-td.json"></div>
        </pre>
      </div>
    </section>

    <section>
      <!--Property resource-->
      <h3><code>Property</code> resource</h3>
      <p>A property resource represents a single property of a device. Some property resources may be read only and some
        may be writable. The value of a property can be retrieved with an HTTP GET request and updated with an HTTP PUT
        request.</p>
      <p>The URL of a Property resource must be defined by the <code>forms</code> section of a Property object in a Thing
        Description.</p>
      <p>If a Property object does not define a primitive <code>type</code> it may not have a JSON serialisation and may
        instead return a binary file or stream in response to an HTTP GET request (e.g. an image file or video stream).
      <p><strong>Example: Get a property</strong></p>
      <div class="example">
        <div class="example-title marker">
          Request
        </div>
        <pre>GET http://mythingserver.com/things/pi/properties/temperature
Accept: application/json</pre>
      </div>
      <div class="example">
        <div class="example-title marker">
          Response
        </div>
        <pre>200 OK
21
</pre>
      </div>
      <p><strong>Example: Set a property</strong></p>
      <div class="example">
        <div class="example-title marker">
          Request
        </div>
        <pre>PUT http://mythingserver.com/things/pi/properties/led
true
Accept: application/json</pre>
      </div>
      <div class="example">
        <div class="example-title marker">
          Response
        </div>
        <pre>200 OK
true
</pre>
      </div>
    </section>
    <section>
      <!--Properties resource-->
      <h3><code>Properties</code> resource</h3>
      <p>A properties resource represents all the properties of a device. The value of all properties can be retrieved
        with an HTTP GET request.</p>
      <p>The URL of a Properties resource can be defined by a <code>properties</code> link relation in the <code>links</code> member of a Thing Description.</p>
      <p><strong>Example: Get all properties</strong></p>
      <div class="example">
        <div class="example-title marker">
          Request
        </div>
        <pre>GET http://mythingserver.com/things/pi/properties
Accept: application/json</pre>
      </div>
      <div class="example">
        <div class="example-title marker">
          Response
        </div>
        <pre>200 OK
{
  "temperature": 21,
  "humidity": 50,
  "led": true
}</pre>
      </div>
    </section>

    <section>
      <!--Action resource-->
      <h3><code>Action</code> resource</h3>
      <p>An action resource represents a queue of actions of a single action type. A new action is created in the queue
        with an HTTP POST request and a list of action requests in the queue can be requested with an HTTP GET request.
      </p>
      <p>The URL of an Action resource must be defined by the <code>links</code> section of an Action object in a Thing Description.</p>
      <p>If a client tries to request an action of another type via this resource, the server should respond with a
        <code>400 Bad Request</code> response.</p>

      <p>If an action request is successful, the server should respond with a <code>201 Created</code>
        response, containing an <a href="#actionrequest-resource">ActionRequest resource</a> in the response body.</p>

      <p><strong>Action Request</strong></p>
      <pre class="example" title="Request an action">
POST https://mythingserver.com/actions/fade
Accept: application/json

{
  "level": 50,
  "duration": 2000
}
      </pre>
      <pre class="example" title="Response to creating an action request">201 Created
        <div data-include="include/action_resource/actionRequest-resource.json"></div>
      </pre>

      <p><strong>Action Queue</strong></p>
      <pre class="example" title="Get a list of all action requests for a given action">
GET /actions/fade
Accept: application/json
      </pre>

      <pre class="example" title="Action list response">200 OK
        <div data-include="include/action_resource/action-queue-resource.json"></div>
      </pre>
    </section>

    <section>
      <!--Action Request resource-->
      <h3><code>ActionRequest</code> resource</h3>
      <p>An action request resource represents an individual action request for a given action. The current status of an
        action request can be retrieved with an HTTP GET request, updated with an HTTP PUT request and deleted with an
        HTTP DELETE request.</p>
      <p>The URL of an Action request resource can be defined by the <code>href</code> member of an action request
        object in an action queue.</p>

      <p>An ActionRequest object should conform to the following JSON schema:</p>
      <pre title="ActionResource schema" data-include="include/action_resource/schema.json"></pre>

      <p><strong>Action Request Status</strong></p>
      <pre class="example" title="Get the status of an action request">
GET /actions/fade/123e4567-e89b-12d3-a456-426655
Accept: application/json
      </pre>

      <pre class="example" title="Action request status response">200 OK
        <div data-include="include/action_resource/actionRequest-resource.json"></div>
      </pre>

      <p><strong>Cancel an Action Request</strong></p>
      <pre class="example" title="Cancel an action request response">
DELETE /actions/fade/123e4567-e89b-12d3-a456-426655
      </pre>
      <pre class="example" title="Action cancellation response">
204 No Content
      </pre>
    </section>
    <section>
      <!--Actions resource-->
      <h3><code>Actions</code> resource</h3>
      <p>An actions resource represents a queue of actions to be executed on a device. A new action is created in the
        queue with an HTTP POST request and a list of action requests in the queue can be requested with an HTTP GET
        request.</p>
      <p>The URL of an actions resource can be defined by an <code>actions</code> link relation in the <code>links</code> member of a Thing Description.</p>
      <p>Any action supported by the thing can be requested via this top level action queue. If an unsupported action
        type is requested, the server should respond with a <code>400 Bad Request</code> response.</p>
      <p><strong>Action Request</strong></p>
      <pre class="example" title="Request an action">
POST https://mythingserver.com/actions/
Accept: application/json

{
  "fade": {
    "input": {
      "level": 50,
      "duration": 2000
    }
  }
}
      </pre>
      <pre class="example" title="Response to creating an action request">201 Created
        <div data-include="include/action_resource/actionRequest-resource.json"></div>
      </pre>
      <p><strong>Actions Queue</strong></p>
      <pre class="example" title="Get a list of all action requests">
GET /actions
Accept: application/json
      </pre>
      <pre class="example" title="Action list response">200 OK
        <div data-include="include/action_resource/actions-queue-resource.json"></div>
      </pre>
    </section>

    <section>
      <!--Event resource-->
      <h3><code>Event</code> resource</h3>
      <p>An event resource provides a log of events recently emitted by a device for a particular event type. An event
        resource is usually read only.</p>
      <p>The URL of an Event resource must be defined by the <code>forms</code> section of an Event object in a Thing Description.</p>
      <p><strong>Event Log</strong></p>
      <pre class="example" title="Event Request">
GET /events/overheated
Accept: application/json
      </pre>
      <pre class="example" title="Event Response">
200 OK
[
  {
    "event": "overheated",
    "data": 102,
    "timestamp": "2017-01-25T15:01:35+00:00"
  },
  {
    "event": "overheated",
    "data": 101,
    "timestamp": "2017-01-24T13:02:45+00:00"
  }
]
</pre>

    </section>
    <section>
      <!--Events resource-->
      <h3><code>Events</code> resource</h3>
      <p>An events resource provides a log of all events recently emitted by a device. An events resource is usually
        read only.</p>
      <p>The URL of an Events resource can be defined by an <code>events</code> link relation in the <code>links</code> member of a Thing Description.</p>
      <p><strong>Event Log</strong></p>
      <pre class="example" title="Events Request">
GET /events
Accept: application/json
      </pre>
      <pre class="example" title="Events Response">
200 OK
[
  {
    "event": "overheated",
    "data": 102,
    "timestamp": "2017-01-25T15:01:35+00:00"
  },
  {
    "event": "reboot",
    "timestamp": "2017-01-24T13:02:45+00:00"
  }
]
</pre>
    </section>
    <section>
      <h3>Alternative Protocol Bindings</h3>
      <p>The default protocol binding for the Web Thing REST API is HTTP(S). Bindings to alternative application
        protocols (e.g. CoAP) may be used, but these bindings are beyond the scope of this specification. A Web Thing
        API protocol binding may also be layered on top of a non-Internet application protocol by use of a gateway.</p>
    </section>
    <section>
      <h3>Alternative Encodings</h3>
      <p>The default content encoding for the Web Thing HTTP(S) REST API is JSON. Alternative content encodings (e.g. CBOR) may be used, but these bindings are beyond the scope of this specification.</p>
    </section>
  </section>
  <section>
    <h2>WebSocket API</h2>
    <p>The Web Thing WebSocket API complements the REST API to provide a realtime mechanism to make multiple requests
      and be notified of events as soon as they happen, by keeping a WebSocket [[WEBSOCKETS-PROTOCOL]] open on the Web
      Thing. The "webthing" WebSocket subprotocol defined here has a simple set of message types and a JSON response
      format consistent with the Web Thing REST API.</p>
    <section>
      <h3>Protocol Handshake</h3>
      <p>To open a WebSocket on a Thing, an HTTP GET request is upgraded to a WebSocket using a standard WebSocket
        protocol handshake [[WEBSOCKETS-PROTOCOL]] and the "webthing" subprotocol. The WebSocket URL for a Web Thing is
        specified in the links member of the Web Thing Description.</p>
      <div class="example">
        <div class="example-title marker">
          Request
        </div>
        <pre>GET wss://mythingserver.com/things/robot
Host: mythingserver.com
Origin: https://mythingserver.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
Sec-WebSocket-Protocol: webthing
Sec-WebSocket-Version: 13</pre>
      </div>
      <div class="example">
        <div class="example-title marker">
          Response
        </div>
        <pre>HTTP 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: webthing</pre>
      </div>
      <p>A WebSocket can be opened from a web page using the JavaScript <a
          href="https://www.w3.org/TR/websockets/">WebSocket API</a> which will take care of the handshake detailed
        above and allow messages to be sent and received.</p>
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>const socket = new WebSocket('wss://mywebthingserver/things/robot', 'webthing');</pre>
      </div>
    </section>
    <section>
      <h3><code>setProperty</code> message</h3>
      <p>The <code>setProperty</code> message type is sent from a web client to a Web Thing in order to set the value of
        one or more of its properties. This is equivalent to a <code>PUT</code> request on a Property resource URL using
        the REST API, but with the WebSocket API a property value can be changed multiple times in quick succession over
        an open socket and multiple properties can be set at the same time.</p>
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "setProperty",
  "data": {
    "leftMotor": 100
  }
}</pre>
      </div>
    </section>
    <section>
      <h3><code>requestAction</code> message</h3>
      <p>The <code>requestAction</code> message type is sent from a web client to a Web Thing to request an action be
        carried out on a Web Thing. This is equivalent to a <code>POST</code> request on an Actions resource URL using
        the REST API, but multiple actions can be requested at the same time or in quick succession over an open socket.
      </p>
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "requestAction",
  "data": {
    "goForward": {
      "steps": 100
    },
  }
}</pre>
      </div>
    </section>
    <section>
      <h3><code>addEventSubscription</code> message</h3>
      <p>The <code>addEventSubscription</code> message type is sent from a web client to a Web Thing to allow a client
        to subscribe to a particular event type, defined by the <code>events</code> member of a Web Thing description.
        This is similar to adding an event listener in JavaScript, but events are received as an <code>event</code>
        message over the Web Thing WebSocket API.</p>
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "addEventSubscription",
  "data": {
    "motion": {}
  }
}</pre>
      </div>
    </section>
    <section>
      <h3><code>propertyStatus</code> message</h3>
      <p>The <code>propertyStatus</code> message type is sent from a Web Thing to a web client whenever a property of a
        Web Thing changes. The payload data of this message is in the same format as a response to a <code>GET</code>
        request on Property resource using the REST API, but the message is pushed to the client whenever a property
        changes and can include multiple properties at the same time.
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "propertyStatus",
  "data": {
    "led": true
  }
}</pre>
      </div>
    </section>
    <section>
      <h3><code>actionStatus</code> message</h3>
      <p>The <code>actionStatus</code> message type is sent from a Web Thing to a web client when the status of a
        requested action changes. The payload data is consistent with the format of an Action resource in the REST API,
        but messages are pushed to the client as soon as the status of an action changes.
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "actionStatus",
  "data": {
    "grab": {
      "action": "goForward",
      "id": "123e4567-e89b-12d3-a456-426655",
      "href": "/actions/go-forward/123e4567-e89b-12d3-a456-426655",
      "timeRequested": "2017-01-24T11:02:45+00:00",
      "timeCompleted": "2017-01-24T11:02:46+00:00",
      "status": "completed",
      "input": {
        "steps": 100
      },
      "output": {},
    }
  }
}</pre>
      </div>
    </section>
    <section>
      <h3><code>event</code> message</h3>
      <p>The <code>event</code> message type is sent from a Web Thing to a web client when an event occurs on the Web
        Thing. The payload data is consistent with the format of an Event resource in the REST API but messages are
        pushed to the client as soon as an event occurs.
      <div class="example">
        <div class="example-title marker">
          Example
        </div>
        <pre>{
  "messageType": "event",
  "data": {
    "motion": {
      "timestamp": "2017-01-24T13:02:45+00:00"
    }
  }
}</pre>
      </div>
    </section>
  </section>

  <section>
    <h2>Thing Discovery</h2>
    <p>
      Web Things can make themselves discoverable to clients via various methods.
    </p>
    <section>
      <h3>mDNS/DNS-SD</h3>
      <p>
        A Web Thing can make itself discoverable on a local network by advertising itself via DNS-SD, with a service type of <code>labthing</code> over TCP, i.e. <code>_labthing._tcp</code>. The service should define a TXT record named
        <code>path</code>, with its value denoting the URI of the thing description on the Web Thing's web server, e.g. <code>path=/api/</code>. Additionally, a TXT record named <code>tls</code> with a value of <code>1</code> should be included if the Web Thing supports connections via HTTPS.
      </p>
    </section>
  </section>

  <section>
    <h2>Further Information</h2>
    <p><a href="https://docs.google.com/document/d/1H3coHbb3Bwd02_NJi4KEBONByUkq92_HsTk1IpfmACY/edit?usp=sharing">Web of
        Things Integration Patterns</a><br />
      Advice on different design patterns for integrating connected devices with the Web of Things.</p>
  </section>
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