Web of Things (WoT) Scripting API

Abstract

The Web of Things is made of entities ( Thing s) that can describe their capabilities in a machine-interpretable Thing Description (TD) and expose these capabilities through the WoT Interface , that is, network interactions modeled as Properties (for reading and writing values), Action s (to execute remote procedures with or without return values) and Event s (for signaling notifications).

The main Web of Things (WoT) concepts are described in the Web of Things Architecture 1.1 specification.

Scripting is an optional building block in WoT and it is typically used in gateways or browsers that are able to run a WoT Runtime and script management , providing a convenient way to extend WoT support to new types of endpoints and implement WoT applications such as Thing Directory .

This specification describes an application programming interface (API) representing the WoT Interface that allows scripts to discover, operate Thing s and to expose locally defined Thing s characterized by WoT Interactions specified by a script.

The APIs defined in this document deliberately follow the Web of Things Thing Description 1.1 specification closely. It is possible to implement more abstract APIs on top of them, or implementing directly the WoT network facing interface (i.e. the WoT Interface ).

Editor's note

This specification is implemented at least by the Eclipse Thingweb project also known as node-wot , which is considered the reference open source implementation at the moment. Check its source code , including examples .

5. 6. The `WOT` namespace

Defines the WoT API object as a singleton and contains the API methods, grouped by conformance classes.

WebIDL[SecureContext, Exposed=(Window,Worker)]
namespace WOT {
  // methods defined in UA conformance classes

};

5.1 6.1 The `consume()` method

WebIDLpartial namespace WOT {
  Promise<ConsumedThing> consume(ThingDescription td);
};

Belongs to the WoT Consumer conformance class. Expects an td argument and returns a



Promise

that resolves with a


ConsumedThing

object that represents a client interface to operate with the Thing . The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let thing be a new ConsumedThing object constructed from td.
Set up the WoT Interactions based on introspecting td as explained in [ WOT-TD ] and [ WOT-PROTOCOL-BINDINGS ]. Make a request to the underlying platform to initialize the Protocol Bindings .

Editor's note

Implementations encapsulate the complexity of how to use the Protocol Bindings for implementing WoT interactions . In the future elements of that could be standardized.
Resolve promise with thing.

Editor's note

Note the difference between constructing ConsumedThing and using the consume() method: the latter also initializes the protocol bindings, whereas a simple constructed object will not have WoT Interactions initialized until they are invoked.

5.2 6.2 The `produce()` method

WebIDLtypedef object ExposedThingInit;
partial namespace WOT {
  Promise<ExposedThing> produce(ExposedThingInit init);
};

Belongs to the WoT Producer conformance class. Expects a init argument and returns a



Promise

that resolves with an


ExposedThing

object that extends


ConsumedThing

with a server interface, i.e. the ability to define request handlers. The init object is an instance of the


ExposedThingInit

type. Specifically, an


ExposedThingInit

value is a dictionary used for the initialization of an


ExposedThing

and it represents a Partial TD as described in the [ WOT-ARCHITECTURE ]. As such, it has the same structure of a Thing Description but it may omit some information. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let thing be a new ExposedThing object constructed with init.
Resolve promise with thing.

5.2.1 6.2.1 Expand an ExposedThingInit

To expand an ExposedThingInit given init and obtain a valid td as a result, run the following steps:

Run validate an ExposedThingInit on init. If that fails, throw SyntaxError and abort these steps.
Initialize and empty object called td
For each property key in init copy key and value of key to td recursively.
For each scheme defined in securityDefinitions check if it is supported by at least one Protocol Binding . If not remove scheme
if the value of security is defined but it is not contained in securityDefinitions remove security
For each affordance run the following sub-steps:
1. For each form defined in affordance execute:
  1. if form 's contentType is not recognized by the runtime as valid remove contentType from form
  2. if form 's href has an unknown schema remove href from form.
  3. if form 's href is absolute and its authority it is not recognized by the runtime as a valid remove href from form.
  4. if form 's href is already in use by other ExposedThings remove href from form.
Search for missing required properties in td accordingly to TD JSON Schema .

Editor's note

The editors find this step vague. It will be improved or removed in the next iteration.
For each missing property run these sub-steps:
1. If missing is title generate a runtime unique name and assign to title.
2. If missing is @context assign the latest supported Thing Description context URI.
3. If missing is instance assign the string 1.0.0.
4. If missing is forms generate a list of Forms using the available Protocol Bindings and content types encoders. Then assign the obtained list to forms.
5. If missing is security assign the label of the first supported SecurityScheme in securityDefinitions field. If no SecurityScheme is found generate a NoSecurityScheme called nosec and assing the string nosec to security.
  
  Issue 1
  
  The discussion about how to properly generate a value for security is still open. See issue #299
6. If missing is href define formStub as the partial Form that does not have href. Generate a valid url using the first Protocol Binding that satisfy the requirements of formStub. Assign url to href. If not Protocol Binding can be found remove formStub from td.
7. Add missing to td with value as value
Run validate a TD on td. If that fails re- throw the error and abort these steps
Return td

5.2.2 6.2.2 Validating an ExposedThingInit

To validate an ExposedThingInit given init, run the following steps:

Parse TD JSON Schema and load it in object called exposedThingInitSchema
let optional be a list containing the following strings: title, @context, instance, forms, security, and href.
For each property and sub-property key in exposedThingInitSchema equals to required execute the following steps:
1. if key value is an Array then remove all its elements equal to the elements in optional
2. if key value is a string then if value is equal to one of the elements in optional remove key from exposedThingInitSchema
Return the result of validating an object with JSON Schema given init and exposedThingInitSchema.

Editor's note

The validating an object with JSON Schema steps are still under discussion. Currently this specification reference to the validation process of JSONSchema. Please follow this document when validating init with exposedThingInitSchema. Notice that the working group is evaluating an alternative formal approach.

5.3 6.3 The `discover()` method

WebIDLpartial namespace WOT {
  ThingDiscovery discover(optional ThingFilter filter = null);
};

Belongs to the WoT Discovery conformance class. Starts the discovery process that will provide


ThingDescription

objects for Thing Description s that match an optional filter argument of type


ThingFilter

. The method MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a " SecurityError " and abort these steps.
Construct a ThingDiscovery object discovery with filter.
Invoke the discovery.start() method.
Return discovery.

6. 7. Handling interaction data

As specified in the Web of Things Thing Description 1.1 specification, WoT interactions extend DataSchema and include a number of possible Form s, out of which one is selected for the interaction. The Form contains a contentType to describe the data. For certain content types, a DataSchema is defined, based on JSON Schema , making possible to represent these contents as JavaScript types and eventually set range constraints on the data.

6.1 7.1 The `InteractionInput` type

WebIDLtypedef any DataSchemaValue;
typedef

(

ReadableStream

or


DataSchemaValue


)



InteractionInput


;

Belongs to the WoT Consumer conformance class and represents the WoT Interaction data provided by application scripts to the UA.

DataSchemaValue is an ECMAScript value that is accepted for DataSchema defined in [ WoT-TD ] (i.e. null, boolean, number, string, array, or object).

ReadableStream is meant to be used for WoT Interactions that don't have a DataSchema in the Thing Description , only a Form 's contentType that can be represented by a stream.

In practice, any ECMAScript value may be used for WoT Interactions that have a DataSchema defined in the Thing Description , or which can be mapped by implementations to the Form 's contentType defined in the Thing Description .

The algorithms in this document specify how exactly input data is used in WoT Interactions .

6.2 7.2 The `InteractionOutput` interface

Belongs to the WoT Consumer conformance class. An InteractionOutput object is always created by the implementations and exposes the data returned from WoT Interactions to application scripts.

This interface exposes a convenience function which should cover the vast majority of IoT use cases: the value() function. Its implementation will inspect the data, parse it if adheres to a DataSchema , or otherwise fail early, leaving the underlying stream undisturbed so that application scripts could attempt reading the stream themselves, or handling the data as ArrayBuffer .

WebIDL[SecureContext, Exposed=(Window,Worker)]
interface InteractionOutput {
  readonly attribute ReadableStream? data;
  readonly attribute boolean dataUsed;
  readonly attribute

  readonly attribute Form? form;

  readonly attribute DataSchema? schema;
  Promise<ArrayBuffer> arrayBuffer();
  Promise<DataSchemaValue> value();
};

The data property represents the raw payload in WoT Interactions as a ReadableStream , initially null.

The dataUsed property tells whether the data stream has been disturbed . Initially false.

The form attribute represents the Form selected from the Thing Description for this WoT Interaction , initially null.

The schema attribute represents the DataSchema (defined in [ WoT-TD ]) of the payload as a JSON object, initially null.

The [[value]] internal slot represents the parsed value of the WoT Interaction , initially undefined (note that null is a valid value).

6.2.1 7.2.1 The `value()` function

Parses the data returned by the WoT Interaction and returns a value with the type described by the interaction DataSchema if that exists, or by the


contentType

of the interaction Form . The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If the value of the [[value]] internal slot is not undefined, resolve promise with that value and abort these steps.
If the value of the data property is not a ReadableStream or if dataUsed is true, or if form is null or if schema or its type are null or undefined, reject promise with NotReadableError and abort these steps.
If form 's contentType is not application/json and if a mapping is not available in the Protocol Bindings from form 's contentType to [ JSON-SCHEMA ], reject promise with NotSupportedError and abort these steps.
Let reader be the result of getting a reader from data. If that threw an exception, reject promise with that exception and abort these steps.
Let bytes be the result of reading all bytes from data with reader.
Set dataUsed to true.
If form 's contentType is not application/json and if a mapping is available in the Protocol Bindings from form 's contentType to [ JSON-SCHEMA ], transform bytes with that mapping.
Let json be the result of running parse JSON from bytes on bytes. If that throws, reject promise with that exception and abort these steps.
Set [[value]] to the result of running check data schema on json and schema. If that throws, reject promise with that exception and abort these steps.
Resolve promise with [[value]] .

6.2.2 7.2.2 The `arrayBuffer()` function

When invoked, MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If data is not ReadableStream or if dataUsed is true, reject promise with NotReadableError and abort these steps.
Let reader be the result of getting a reader from data. If that threw an exception, reject promise with that exception and abort these steps.
Let bytes be the result of reading all bytes from data with reader.
Set dataUsed to true.
Let arrayBuffer be a new ArrayBuffer whose contents are bytes. If that throws, reject promise with that exception and abort these steps.
Resolve promise with arrayBuffer.

6.2.3 7.2.3 The check data schema algorithm

To run the check data schema steps on payload and schema,

Let type be schema 's type.
If type is "null" and if payload is not null, throw TypeError and abort these steps, otherwise return null.
If type is "boolean" and payload is a falsey value or its byte length is 0, return false, otherwise return true.
If type is "integer" or "number",
1. If payload is not a number, throw TypeError and abort these steps.
2. If form 's minimum is defined and payload is smaller, or if form 's maximum is defined and payload is bigger, throw RangeError and abort these steps.
If type is "string", return payload.
If type is "array", run these sub-steps:
1. If payload is not an array, throw TypeError and abort these steps.
2. If form 's minItems is defined and payload 's length is less than that, or if form 's maxItems is defined and payload 's length is more than that, throw RangeError and abort these steps.
3. Let payload be an array of items obtained by running the check data schema steps on each element item of payload and schema 's items. If this throws at any stage, re-throw that exception and abort these steps.
If type is "object", run these sub-steps:
1. If payload or schema 's properties is not an object, throw TypeError and abort these steps.
2. For each property key in payload,
  1. Let prop be the value of key.
  2. Let propSchema be the value of key in interaction 's properties.
  3. Let prop be the result of running the check data schema steps on prop and propSchema. If this throws, re-throw that exception and abort these steps.
3. Let required be schema 's required if that is an array or an empty array otherwise.
4. For each key in required, if key is not present in payload, throw SyntaxError and abort these steps.
Return payload.

6.2.4 7.2.4 The create interaction request algorithm

For a given


ConsumedThing

object thing, in order to create interaction request given a source, form and schema, run these steps:

Let idata be a new an InteractionOutput object whose form is set to form, whose schema is set to schema, whose [[value]] internal slot is undefined and whose data is null.
If source is a ReadableStream object, let idata 's data be source, return idata and abort these steps.
If schema and its type are defined and not null, run these sub-steps:
1. If type is "null" and source is not, throw TypeError and abort these steps.
2. If type is "boolean" and source is a falsy value, set idata 's [[value]] value to false, otherwise to true.
3. If type is "integer" or "number" and source is not a number, or if form 's minimum is defined and source is smaller, or if form 's maximum is defined and source is bigger, throw RangeError and abort these steps.
4. If type is "string" and source is not a string, let idata 's [[value]] be the result of running serialize JSON to bytes on source. If that is failure, throw SyntaxError and abort these steps.
5. If type is "array", run these sub-steps:
  1. If source is not an array, throw a TypeError and abort these steps.
  2. Let length be the length of source.
  3. If form 's minItems is defined and length is less than that, or if form 's maxItems is defined and length is more than that, throw RangeError and abort these steps.
  4. For each item in source, let itemschema be schema 's items and let item be the result of running the create interaction request steps on item, form and itemschema. If this throws, re-throw that exception and abort these steps.
  5. Set data 's [[value]] to source.
6. If type is "object", run these sub-steps:
  1. If source is not an object, throw TypeError and abort these steps.
  2. If schema 's properties is not an object, throw TypeError and abort these steps.
  3. For each property key in source,
    1. Let value be the value of key.
    2. Let propschema be the value of key in properties.
    3. Let value be the result of running the create interaction request steps on value, form and propschema. If this throws, re-throw that exception and abort these steps.
  4. If schema 's required is an array, for each item in required check if item is a property name in source. If an item is not found in source, throw SyntaxError and abort these steps.
  5. Set data 's [[value]] to source.
Set idata 's data to a new ReadableStream created from idata 's [[value]] internal slot as its underlying source .
Return idata.

6.2.5 7.2.5 The parse interaction response algorithm

For a given


ConsumedThing

object thing, in order to parse interaction response given response, form and schema, run these steps:

Let result be a new InteractionOutput object.
Let result 's schema be schema.
Let result 's form be form.
Let result 's data be a new ReadableStream with the payload data of response as its underlying source .
Let result 's dataUsed be false.
Return result.

6.3 7.3 Using `InteractionInput` and `InteractionOutput`

As illustrated in the next pictures, the InteractionOutput interface is used every time implementations provide data to scripts, while InteractionInput is used when the scripts pass data to the implementation.

Reading data — Figure 1 Data structures used when reading data

When a ConsumedThing reads data, it receives it from the implementation as an InteractionOutput object.

An ExposedThing read handler provides the read data to the implementation as InteractionInput .

Writing data — Figure 2 Data structures used when writing data

When a ConsumedThing writes data, it provides it to the implementation as InteractionInput .

An ExposedThing write handler receives data from to implementation as an InteractionOutput object.

Invoking action — Figure 3 Data structures used when invoking an Action

When a ConsumedThing invokes an Action data, it provides the parameters as InteractionInput and receives the output of the Action as an InteractionOutput object.

An ExposedThing action handler receives arguments from the implementation as an InteractionOutput object and provides Action output as InteractionInput to the implementation.

6.4 7.4 Error handling

The algorithms in this API define the errors to be reported to application scripts.

The errors reported to the other communication end are mapped and encapsulated by the Protocol Bindings .

Figure 4 Error handling in WoT interactions

Editor's note

This topic is still being discussed in Issue #200 . A standardized error mapping would be needed in order to ensure consistency in mapping script errors to protocol errors and vice versa. In particular, when algorithms say "error received from the Protocol Bindings ", that will be factored out as an explicit error mapping algorithm. Currently, that is encapsulated by implementations.

7. 8. The `ConsumedThing` interface

Represents a client API to operate a Thing . Belongs to the WoT Consumer conformance class.

WebIDL[SecureContext, Exposed=(Window,Worker)]
interface ConsumedThing {
  constructor(ThingDescription td);
  Promise<InteractionOutput> readProperty(DOMString propertyName,
                              optional InteractionOptions options = null);
  Promise<PropertyReadMap> readAllProperties(
                              optional InteractionOptions options = null);
  Promise<PropertyReadMap> readMultipleProperties(
                              sequence<DOMString> propertyNames,
                              optional InteractionOptions options = null);
  Promise<undefined> writeProperty(DOMString propertyName,
                              InteractionInput value,
                              optional InteractionOptions options = null);
  Promise<undefined> writeMultipleProperties(
                              PropertyWriteMap valueMap,
                              optional InteractionOptions options = null);
  /*Promise<undefined> writeAllProperties(
                              PropertyWriteMap valueMap,
                              optional InteractionOptions options = null);*/
  Promise<InteractionOutput> invokeAction(DOMString actionName,
                              optional InteractionInput params = null,
                              optional InteractionOptions options = null);
  Promise<Subscription> observeProperty(DOMString name,
                              InteractionListener listener,
                              optional ErrorListener onerror,
                              optional InteractionOptions options = null);
  Promise<Subscription> subscribeEvent(DOMString name,
                              InteractionListener listener,
                              optional ErrorListener onerror,
                              optional InteractionOptions options = null);
  ThingDescription getThingDescription();
};
dictionary InteractionOptions {
  unsigned long formIndex;
  object uriVariables;
  any data;
};
[SecureContext, Exposed=(Window,Worker)]
interface Subscription {
  readonly attribute boolean active;
  Promise<undefined> stop(optional InteractionOptions options = null);
};
[SecureContext, Exposed=(Window,Worker)]
interface PropertyReadMap {
  readonly maplike<DOMString, InteractionOutput>;
};
[SecureContext, Exposed=(Window,Worker)]
interface PropertyWriteMap {
  readonly maplike<DOMString, InteractionInput>;
};
callback InteractionListener = undefined(InteractionOutput data);
callback


ErrorListener


=


undefined


(


Error



error

);

Editor's note : Where is the writeAllProperties method?

The writeAllProperties() method is still under discussion. Meanwhile, use the writeMultipleProperties() method instead.

7.1 8.1 Internal slots for ConsumedThing

A ConsumedThing object has the following internal slots :

Internal Slot	Initial value	Description ( non-normative )
[[td]]	`null`	The Thing Description of the `ConsumedThing` .

7.2 8.2 Constructing `ConsumedThing`

After fetching a Thing Description as a JSON object, one can create a ConsumedThing object.

To create


ConsumedThing

with the


ThingDescription

td, run the following steps:

Run the validate a TD steps on td. If that fails, throw SyntaxError and abort these steps.
Run the expand a TD steps on td. If that fails, re- throw the error and abort these steps.
Let thing be a new ConsumedThing object.
Set the internal slot [[td]] of thing to td.
Return thing.

7.3 8.3 The `getThingDescription()` method

Returns the internal slot [[td]] of the ConsumedThing object that represents the Thing Description of the ConsumedThing . Applications may consult the Thing metadata stored in [[td]] in order to introspect its capabilities before interacting with it.

7.4 8.4 The `readProperty()` method

Reads a Property value. Takes as arguments propertyName and optionally options. It returns a



Promise

that resolves with a Property value represented as an


InteractionOutput

object or rejects on error. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's propertyName.
If interaction is undefined, reject promise with a NotFoundError and abort this steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in interaction 's forms array, otherwise let form be a Form in interaction 's forms whose op is readproperty, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Make a request to the underlying platform (via the Protocol Bindings ) to retrieve the value of the Property given by propertyName using form and the optional URI templates given in options ' uriVariables.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Let response be the response received to the request.
Let data be the result of running parse interaction response on response, form and interaction. If that fails, reject promise with a SyntaxError and abort these steps.
Resolve promise with data.

7.5 8.5 The `readMultipleProperties()` method

Reads multiple Property values with one request. Takes as arguments propertyNames and optionally options. It returns a



Promise

that resolves with a


PropertyReadMap

object that maps keys from propertyNames to values returned by this algorithm. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in [[td]]'s forms array, otherwise let form be a Form in [[td]]'s forms array whose op is readmultipleproperties, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Let result be an object and for each string name in propertyNames add a property with key name and the value null.
Make a request to the underlying platform (via the Protocol Bindings ) to retrieve the Property values given by propertyNames with form and optional URI templates given in options ' uriVariables.
If this cannot be done with a single request with the Protocol Bindings , reject promise with a NotSupportedError and abort these steps.
Process the response and for each key in result, run the following sub-steps:
1. Let value be the value of result 's key.
2. Let schema be the value of [[td]]'s properties 's key.
3. Let property be the result of running parse interaction response on value, form and schema.
If the above step throws at any point, reject promise with that exception and abort these steps.
Resolve promise with result.

7.6 8.6 The `readAllProperties()` method

Reads all properties of the Thing with one request. Takes options as optional argument. It returns a



Promise

that resolves with a


PropertyReadMap

object that maps keys from Property names to values returned by this algorithm. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in [[td]]'s forms array, otherwise let form be a Form in [[td]]'s forms array whose op is readallproperties, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Make a request to the underlying platform (via the Protocol Bindings ) to retrieve the value of the all the Property definitions from the TD with form and optional URI templates given in options ' uriVariables.
If this cannot be done with a single request with the Protocol Bindings of the Thing , then reject promise with a NotSupportedError and abort these steps.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Process the reply and let result be an object with the keys and values obtained in the reply.
Process the response and for each key in result, run the following sub-steps:
1. Let value be the value of result 's key.
2. Let schema be the value of [[td]]'s properties 's key.
3. Let property be the result of running parse interaction response on value, form and schema.
Resolve promise with result.

7.7 8.7 The `writeProperty()` method

Writes a single Property . Takes as arguments propertyName, value and optionally options. It returns a



Promise

that resolves on success and rejects on failure. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's propertyName.
If interaction is undefined, reject promise with a NotFoundError and abort this steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in interaction 's forms array, otherwise let form be a Form in interaction 's forms whose op is writeproperty, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Let data be the result of running the create interaction request steps on value, form and interaction. If that throws, reject promise with that exception and abort these steps.
Make a request to the underlying platform (via the Protocol Bindings ) to write the Property given by propertyName using data and the optional URI templates given in options ' uriVariables.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Otherwise resolve promise.

Editor's note

As discussed in Issue #193 , the design decision is that write interactions only return success or error, not the written value (optionally). TD s should capture the schema of the Property values, including precision and alternative formats. When a return value is expected from the interaction, an Action should be used instead of a Property .

7.8 8.8 The `writeMultipleProperties()` method

Writes a multiple Property values with one request. Takes as arguments properties - as an object with keys being Property names and values as Property values - and optionally options. It returns a



Promise

that resolves on success and rejects on failure. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in [[td]]'s forms array, otherwise let form be a Form in [[td]]'s forms array whose op is writemultipleproperties, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Let propertyNames be an array of string with as elements the keys of the properties object.
For each name in propertyNames, let property be the value of [[td]]'s properties 's name. If property is null or undefined or is not writeable reject promise with NotSupportedError and abort these steps.
Let result be an object and for each string name in propertyNames add a property with key name and let its value be null.
Let schemas be an object and for each string name in propertyNames add a property with key name and let its value be the value of [[td]]'s properties 's name.
For each key key in properties, take its value as value and run the create interaction request steps on value, form and the value for schema 's key. If that throws for any name, reject promise with that exception and abort these steps.
Make a single request to the underlying platform (via the Protocol Bindings ) to write each Property provided in properties with optional URI templates given in options ' uriVariables.
If this cannot be done with a single request with the Protocol Bindings of the Thing , then reject promise with a NotSupportedError and abort these steps.
If the request fails, return the error received from the Protocol Bindings and abort these steps.
Otherwise resolve promise.

7.9 8.9 The `observeProperty()` method

Makes a request for Property value change notifications. Takes as arguments propertyName, listener and optionally onerror and options. It returns a



Promise

that resolves on success and rejects on failure. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If listener is not a Function , reject promise with a TypeError and abort these steps.
If onerror is not null and is not a Function , reject promise with a TypeError and abort these steps.
Let subscription be a new Subscription object with its internal slots set as follows:
- Let subscription 's [[type]] be "property".
- Let subscription 's [[name]] be the value of propertyName.
- Let subscription 's [[interaction]] be the value of [[td]]'s properties 's propertyName.
- Let subscription 's [[form]] be the Form associated with formIndex in [[interaction]]'s forms array if option 's formIndex is defined, otherwise let [[form]] be a Form in [[interaction]]'s forms array whose op is "observeproperty", selected by the implementation.
- If subscription 's [[form]] is failure, reject promise with a SyntaxError and abort these steps.
- If subscription 's [[interaction]] is undefined, reject promise with a NotFoundError and abort this steps.
Make a request to the underlying platform to observe the Property identified by propertyName with form and optional URI templates given in options ' uriVariables.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Otherwise resolve promise.
Whenever the underlying platform detects a notification for this subscription with a new Property value value, run the following sub-steps:
- Let reply be the result of running parse interaction response with value, [[form]] and [[interaction]]. If that throws, reject promise with that exception and abort these steps.
- Invoke listener with reply.
Whenever the underlying platform detects an error for this subscription, run the following sub-steps:
- If the error is irrecoverable and stops the subscription, set subscription 's active to false and suppress further notifications.
- Let error be a new NetworkError and set its message to reflect the underlying error condition.
- If onerror is a Function , invoke it with error.

7.10 8.10 The `invokeAction()` method

Makes a request for invoking an Action and return the result. Takes as arguments actionName, optionally params and optionally options. It returns a



Promise

that resolves with the result of the Action represented as an


InteractionOutput

object, or rejects with an error. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s actions 's actionName.
If interaction is undefined, reject promise with a NotFoundError and abort this steps.
If option 's formIndex is defined, let form be the Form associated with formIndex in interaction 's forms array, otherwise let form be a Form in interaction 's forms array whose op is invokeaction, selected by the implementation.
If form is failure, reject promise with a SyntaxError and abort these steps.
Let args be the result of running the create interaction request steps on params, form and interaction. If that throws, reject promise with that exception and abort these steps.
Make a request to the underlying platform (via the Protocol Bindings ) to invoke the Action identified by actionName with parameters provided in args and optional URI templates given in options 's uriVariables.
If the request fails locally or returns an error over the network, reject promise with the error received from the Protocol Bindings and abort these steps.
Let value be the reply returned in the reply.
Let result be the result of running parse interaction response with value, form and interaction. If that throws, reject promise with that exception and abort these steps.
Resolve promise with result.

7.11 8.11 The `subscribeEvent()` method

Makes a request for subscribing to Event notifications. Takes as arguments eventName, listener and optionally onerror and options. It returns a



Promise

to signal success or failure. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If listener is not a Function , reject promise with a TypeError and abort these steps.
If onerror is not null and is not a Function , reject promise with a TypeError and abort these steps.
Let subscription be a new Subscription object with its internal slots set as follows:
- Let subscription 's [[type]] be "event".
- Let subscription 's [[name]] be the value of eventName.
- Let subscription 's [[interaction]] be the value of [[td]]'s events 's eventName.
- Let subscription 's [[form]] be the Form associated with formIndex in [[interaction]]'s forms array if option 's formIndex is defined, otherwise let [[form]] be a Form in [[interaction]]'s forms array whose op is "subscribeevent", selected by the implementation.
- If subscription 's [[form]] is failure, reject promise with a SyntaxError and abort these steps.
- If subscription 's [[interaction]] is undefined, reject promise with a NotFoundError and abort this steps.
Make a request to the underlying platform via the Protocol Bindings to subscribe to an Event identified by eventName with [[form]], optional URI templates given in options ' uriVariables and optional subscription data given in options 's data.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Otherwise resolve promise.
Whenever the underlying platform detects a notification for this Event subscription, run the following sub-steps:
1. Invoke listener with the result of running parse interaction response on the data provided with the Event , [[form]] and [[interaction]].
Whenever the underlying platform detects an error for this subscription, run the following sub-steps:
- If the error is irrecoverable and stops the subscription, set subscription 's active to false and suppress further notifications.
- Let error be a new NetworkError and set its message to reflect the underlying error condition.
- If onerror is a Function , invoke it with error.

7.12 8.12 The `InteractionOptions` dictionary

Holds the interaction options that need to be exposed for application scripts according to the Thing Description .

The formIndex property, if defined, represents an application hint for which Form definition, identified by this index, of the TD to use for the given WoT interaction. Implementations SHOULD use the Form with this index for making the interaction, but MAY override this value if the index is not found or not valid. If not defined, implementations SHOULD attempt to use the Form definitions in order of appearance as listed in the TD for the given Wot Interaction.

The uriVariables property if defined, represents the URI template variables to be used with the WoT Interaction that are represented as parsed JSON objects defined in [ WOT-TD ].

Editor's note

The support for URI variables comes from the need, exposed by the Web of Things Thing Description 1.1 specification, to be able to describe existing REST-ful endpoints that use them. However, it should be possible to write a Thing Description that would use Action s for representing this kind of interactions and model the URI variables as action parameters. In that case, implementations can serialize the parameters as URI variables, and therefore, the options parameter could be dismissed.

The data property if defined, represents additional opaque data that needs to be passed to the interaction.

7.13 8.13 The `PropertyReadMap` type

Represents a map of Property names to an InteractionOutput object that represents the value the Property can take. It is used as a property bag for interactions that involve multiple Properties at once.

7.14 8.14 The `PropertyWriteMap` type

Represents a map of Property names to an InteractionInput that represents the value the Property can take. It is used as a property bag for interactions that involve multiple Properties at once.

7.15 8.15 The `InteractionListener` callback

User provided callback that is given an argument of type InteractionOutput and is used for observing Property changes and handling Event notifications. Since subscribing to Events are WoT interactions and might take options or even data, they are not modelled with software events.

7.16 8.16 The `ErrorListener` callback

User provided callback that is given an argument of type Error and is used for conveying critical and non-critical errors from the Protocol Bindings to applications.

7.17 8.17 The `Subscription` interface

Represents a subscription to Property change and Event interactions.

The active boolean property denotes if the subscription is active, i.e. it is not stopped because of an error or because of invocation of the stop() method.

7.17.1 8.17.1 Internal slots for `Subscription`


Subscription

object has the following internal slots :

Internal Slot	Initial value	Description ( non-normative )
[[type]]	`null`	Indicates what WoT Interaction the `Subscription` refers to. The value can be either `"property"` or `"event"` or `null`.
[[name]]	`null`	The Property or Event name.
[[interaction]]	`null`	The Thing Description fragment that describes the WoT interaction .
[[form]]	`null`	The Form associated with the subscription.

7.17.2 8.17.2 The `stop()` method

Stops delivering notifications for the subscription. It takes an optional parameter options and returns a Promise . When invoked, the method MUST execute the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
If options ' formIndex is defined, let unsubscribeForm be the Form associated with formIndex in [[interaction]]'s forms array.
Otherwise let unsubscribeForm be the result of running the find a matching unsubscribe form algorithm given [[form]].
If unsubscribeForm is failure, reject promise with a SyntaxError and abort these steps.
If [[type]] is "property", make a request to the underlying platform via the Protocol Bindings to stop observing the Property identified by [[name]] with unsubscribeForm and optional URI templates given in options ' uriVariables.
Otherwise, if [[type]] is "event", make a request to the underlying platform via the Protocol Bindings to unsubscribe from the Event identified by [[name]] with unsubscribeForm, with optional URI templates given in options ' uriVariables and optional unsubscribe data given in options 's data.
If the request fails, reject promise with the error received from the Protocol Bindings and abort these steps.
Otherwise set active to false and resolve promise.
If the underlying platform receives further notifications for this subscription, implementations SHOULD silently suppress them.

7.17.3 8.17.3 Finding an unsubscribe Form

To find a matching unsubscribe form given subscribeForm in the context of a


Subscription

object, run the following steps:

Note

This algorithm is under development and is non-normative . Implementations MAY choose another algorithm to find a matching unsubscribe Form to a given subscribe Form .

Let results be an empty array.
For each form in [[interaction]]'s forms array,
1. Add an internal slot [[matchLevel]] on form and set its value to 0.
2. If form 's op is "unobserveproperty" if [[type]] is "property" or if form 's op is "unsubscribeevent" if [[type]] is "event",
  1. Set the internal slot [[matchLevel]] on form to 1 and add form to results.
  2. If form 's href and [[subscribeForm]]'s href are same origin-domain , increment form 's [[matchLevel]].
  3. If form 's contentType is equal to [[subscribeForm]]'s contentType and form 's [[matchLevel]] is greater than 2, increment form 's [[matchLevel]].
If results is empty, return null and terminate these steps.
Return the first form in results that has the highest [[matchLevel]] value.

7.18 8.18 ConsumedThing Examples

The next example illustrates how to fetch a TD by URL, create a ConsumedThing , read metadata (title), read property value, subscribe to property change, subscribe to a WoT event, unsubscribe.

Example 2 : Thing Client API example with data value

try {
  let res = await fetch("https://tds.mythings.org/sensor11");
  let td = res.json();
  let thing = new ConsumedThing(td);
  console.log("Thing " + thing.getThingDescription().title + " consumed.");
} catch (e) {
  console.log("TD fetch error: " + e.message);
};
try {
  // subscribe to property change for “temperature”
  await thing.observeProperty("temperature", async (data) => {
    try {
      console.log("Temperature changed to: " + await data.value());
    } catch (error) {
      console.error("Cannot read the observed property temperature");
      console.error(error);
    }
  });
  // subscribe to the “ready” event defined in the TD
  await thing.subscribeEvent("ready", async (eventData) => {
    try {
      console.log("Ready; index: " + await eventData.value());
      // run the “startMeasurement” action defined by TD
      await thing.invokeAction("startMeasurement", { units: "Celsius" });
      console.log("Measurement started.");
    } catch (error) {
      console.error("Cannot read the ready event or startMeasurement failed");
      console.error(error)
    }
  });
} catch (e) {
  console.log("Error starting measurement.");
}
setTimeout(async () => {
  try {
    const temperatureData = await thing.readProperty("temperature")
    const temperature = await temperatureData.value();
    console.log("Temperature: " + temperature);
    await thing.unsubscribe("ready");
    console.log("Unsubscribed from the ‘ready’ event.");
  } catch (error) {
    console.log("Error in the cleanup function");
  }
},

10000

);

The following shows an advance usage of InteractionOutput to read a property without a DataSchema .

Example 3 : Thing Client API example with arrayBuffer

/*
* takePicture affordance form:
* "form": {
*   "op": "invokeaction",
*   "href" : "http://camera.example.com:5683/takePicture",
*   "response": {
*     "contentType": "image/jpeg",
*     "contentCoding": "gzip"
*   }
*}
* See https://www.w3.org/TR/wot-thing-description/#example-23
*/
let response;
let image;
try {
  response = await thing.invokeAction(“takePicture”));
  image = await response.value() // throws NotReadableError --> schema not defined
} catch(ex) {
  image = await response.arrayBuffer();
  // image: ArrayBuffer [0x1 0x2 0x3 0x5 0x15 0x23 ...]
}

Finally, the next two examples shows the usage of a ReadableStream from an InteractionOutput .

Example 4 : Thing Client API example with readable stream (e.g., video stream)

/*{
"video": {
  "description" : "the video stream of this camera",
  "forms": [
    {
      "op": "readproperty",
      "href": "http://camera.example.com/live",
      "subprotocol": "hls"
      "contentType": "video/mp4"
    }
  ]
}}*/
const video = await thing.readProperty("video")
const reader = video.data.getReader()
reader.read().then(function processVideo({ done, value }) {
  if (done) {
    console.log("live video stoped");
    return;
  }
  const decoded = decode(value)
  UI.show(decoded)
  // Read some more, and call this function again
  return reader.read().then(processText);
});

Here consider that the JSON object is too big to be read wholly in the memory. Therefore, we use streaming processing to get the total number of the events recorded by the remote Web Thing.

Example 5 : Thing Client API example with readable stream (e.g., counting json objects)

/*
* "eventHistory":
* {
*   "description" : "A long list of the events recorderd by this thing",
*   "type": "array",
*   "forms": [
*     {
*       "op": "readproperty",
*       "href": "http://recorder.example.com/eventHistory",
*     }
*   ]
* }
*/
// Example of streaming processing: counting json objects
let objectCounter = 0
const parser = new Parser() //User library for json streaming parsing (i.e. https://github.com/uhop/stream-json/wiki/Parser)
parser.on('data', data => data.name === 'startObject' && ++objectCounter);
parser.on('end', () => console.log(`Found ${objectCounter} objects.`));
const response = await thing.readProperty(“eventHistory”)
await response.data.pipeTo(parser);

//
Found
N
objects

8. 9. The `ExposedThing` interface

The ExposedThing interface is the server API to operate the Thing that allows defining request handlers, Property , Action , and Event interactions.

WebIDL[SecureContext, Exposed=(Window,Worker)]
interface ExposedThing {
  ExposedThing setPropertyReadHandler(DOMString name,
          PropertyReadHandler handler);
  ExposedThing setPropertyWriteHandler(DOMString name,
          PropertyWriteHandler handler);
  ExposedThing setPropertyObserveHandler(DOMString name,
          PropertyReadHandler handler);
  ExposedThing setPropertyUnobserveHandler(DOMString name,
          PropertyReadHandler handler);
  Promise<undefined> emitPropertyChange(DOMString name);
  ExposedThing setActionHandler(DOMString name, ActionHandler action);
  ExposedThing setEventSubscribeHandler(DOMString name,
          EventSubscriptionHandler handler);
  ExposedThing setEventUnsubscribeHandler(DOMString name,
          EventSubscriptionHandler handler);
  ExposedThing setEventHandler(DOMString name,
          EventListenerHandler eventHandler);
  Promise<undefined> emitEvent(DOMString name,
          InteractionInput data);
  Promise<undefined> expose();
  Promise<undefined> destroy();
  ThingDescription getThingDescription();
};
callback PropertyReadHandler = Promise<InteractionInput>(
        optional InteractionOptions options = null);
callback PropertyWriteHandler = Promise<undefined>(
        InteractionOutput value,
        optional InteractionOptions options = null);
callback ActionHandler = Promise<InteractionInput>(
        InteractionOutput params,
        optional InteractionOptions options = null);
callback EventSubscriptionHandler = Promise<undefined>(
        optional InteractionOptions options = null);
callback


EventListenerHandler


=


Promise

<


InteractionInput


>

();

8.1 9.1 Internal slots for ExposedThing

An ExposedThing object has the following internal slots :

Internal Slot	Initial value	Description ( non-normative )
*[[td]]*	`null`	The Thing Description of the Thing .

8.2 9.2 Constructing `ExposedThing`

The ExposedThing interface extends ConsumedThing . It is constructed from a full or partial ThingDescription object.

Note

Note that an existing ThingDescription object can be optionally modified (for instance by adding or removing elements on its properties, actions and events internal properties) and the resulting object can used for constructing an ExposedThing object. This is the current way of adding and removing Property , Action and Event definitions, as illustrated in the examples .

Note

Before invoking expose() , the ExposedThing object does not serve any requests. This allows first constructing ExposedThing and then initialize its Properties and service handlers before starting serving requests.

To construct an


ExposedThing

with the


ExposedThingInit

init, run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Run the expand an ExposedThingInit steps on init. if that fails re- throw the error and abort these steps. Otherwise store the obtained td
Run the expand a TD steps on td. If that fails, re- throw the error and abort these steps.
Let thing be a new ExposedThing object.
Set the internal slot [[td]] of thing to td.
Return thing.

8.3 9.3 The `getThingDescription()` method

Returns the internal slot [[td]] of the ExposedThing object that represents the Thing Description of the Thing . Applications may consult the Thing metadata stored in [[td]] in order to introspect its capabilities before interacting with it.

8.4 9.4 The `PropertyReadHandler` callback

A function that is called when an external request for reading a Property is received and defines what to do with such requests. It returns a Promise and resolves with an ReadableStream object or an ECMAScript value conforming to DataSchema , or rejects with an error.

8.5 9.5 The `setPropertyReadHandler()` method

Takes as arguments name and handler. Sets the service handler that defines what to do when a request is received for reading the specified Property matched by name. Throws on error. Returns a reference to this object for supporting chaining.

Editor's note

Note that there is no need to register handlers for handling requests for reading multiple or all Properties . The request and reply are transmitted in a single network request, but the ExposedThing may implement them using multiple calls to the single read handler.

The handler callback function should implement reading a Property and SHOULD be called by implementations when a request for reading a Property is received from the underlying platform.

There MUST be at most one handler for any given Property , so newly added handlers MUST replace the previous handlers. If no handler is initialized for any given Property , implementations SHOULD implement a default property read handler based on the Thing Description provided in the [[td]] internal slot .

When the method is invoked given name and handler, implementations MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If a Property interaction with name is not found, throw NotFoundError and abort these steps.
Add the internal slot [[readHandler]] to interaction and set it to handler.

8.6 9.6 Handling requests for reading a Property

When a network request for reading Property name is received by the implementation with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let value be the result of running the read server property steps with name and options:
1. Let interaction be the value of [[td]]'s properties 's name.
2. If a Property with name does not exist, throw NotFoundError and abort these steps.
3. Let handler be null.
4. If there is a user provided internal slot [[readHandler]] on interaction, let handler be that.
5. Otherwise, if there is a default read handler provided by the implementation, let handler be that.
6. If handler is null, throw NotSupportedError and abort these steps.
7. Let value be the result of invoking handler with options. If that fails, throw the error and abort these steps.
8. Return value.
  
  Note
  
  The value returned here SHOULD either conform to DataSchema or it SHOULD be an ReadableStream object created by the handler.
If the previous step has thrown an error, send the error back with the reply created by following the Protocol Bindings and abort these steps.
Serialize and add the returned value to the reply created by following the Protocol Bindings .

8.7 9.7 Handling requests for reading multiple Properties

When a network request for reading multiple Properties given in an object propertyNames is received with options, run the following read multiple properties steps on propertyNames and options:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
For each property with key name defined in propertyNames,
1. Let value be the result of running the read server property steps on name and options. If that throws, send back the error in the reply created by following the Protocol Bindings and abort these steps.
2. Set the value of propertyNames 's name to value.
Reply to the request by sending a single reply created from propertyNames according to the Protocol Bindings .

8.8 9.8 Handling requests for reading all Properties

When a network request for reading all Properties is received with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let properties be an object created with all properties defined in the Thing with values set to null.
Run the read multiple properties steps on properties and options.

8.9 9.9 The `setPropertyObserveHandler()` method

Takes as arguments name and handler. Sets the service handler that defines what to do when a request is received for observing the specified Property matched by name. Throws on error. Returns a reference to this object for supporting chaining.

The handler callback function should implement reading a Property and resolve with an InteractionOutput object or reject with an error.

When the method is invoked given name and handler, implementations MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If a Property interaction with name is not found, throw NotFoundError and abort these steps.
Set the internal slot [[observeHandler]] on interaction to handler.

8.10 9.10 Handling Property observe requests

When a network request for observing a Property name is received by the implementation with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let property be the value of [[td]]'s properties 's name. If it does not exist, send back a NotFoundError in the reply and abort these steps.
Save the request sender information together with options to property 's internal observer list , in order to be able to notify about Property value changes.

Note

Every time the value of property changes, emitPropertyChange() needs to be explicitly called by the application script.

8.11 9.11 The `setPropertyUnobserveHandler()` method

Takes as arguments name and handler. Sets the service handler that defines what to do when a request is received for unobserving the specified Property matched by name. Throws on error. Returns a reference to this object for supporting chaining.

The handler callback function should implement what to do when an unobserve request is received by the implementation.

When the method is invoked given name and handler, implementations MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If a Property interaction with name is not found, throw NotFoundError and abort these steps.
Set the internal slot [[unobserveHandler]] on interaction to handler.

8.12 9.12 Handling Property unobserve requests

When a network request for unobserving a Property name with options is received by the implementation, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let property be the value of [[td]]'s properties 's name. If it does not exist, send back a NotFoundError in the reply and abort these steps.
If there is an [[unobserveHandler]] of type Function defined for name on property, invoke that with options, send back a reply following the Protocol Bindings and abort these steps.
Let sender be the matching observer found in property 's internal observer list . If not found, send back a NotFoundError in the reply and abort these steps.
Remove sender from property 's internal observer list and send back a reply following the Protocol Bindings .

8.13 9.13 The `emitPropertyChange()` method

Takes the name argument, denoting a Property name. Triggers emitting a notification to all observers of the specified Property with the data obtained from the observe handler or the read handler associated with that Property . The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let property be the value of [[td]]'s properties 's name.
If a Property with the name name is not found, reject promise with NotFoundError and abort these steps.
Let handler be null.
If there is an [[observeHandler]] internal slot on property, let handler be that.
Otherwise, if there is a [[readHandler]] internal slot associated with name on property, let handler be that.
If handler is null, abort these steps.
Let promise be the result of invoking handler wih null.
If promise rejects, abort these steps.
If promise resolves with data, then for each observer in property 's internal observer list , run the following sub-steps:
1. Let options be the interaction options saved with observer.
2. Create a reply from data and options according to the Protocol Bindings .
3. Send reply to observer.

8.14 9.14 The `PropertyWriteHandler` callback

A function that is called when an external request for writing a Property is received and defines what to do with such requests. Takes as argument value and returns a Promise , resolved when the value of the Property - identified by the name provided when setting the handler has been updated -, or rejects with an error if the property is not found or the value cannot be updated.

Editor's note

Note that the code in this callback function can read the property before updating it in order to find out the old value, if needed. Therefore the old value is not provided to this function.

Note

The value is provided by implementations as an InteractionOutput object in order to be able to represent values that are not described by a DataSchema , such as streams.

8.15 9.15 The `setPropertyWriteHandler()` method

Takes as arguments name and handler. Sets the service handler that defines what to do when a request is received for writing the Property matched by name given when setting the handler. Throws on error. Returns a reference to this object for supporting chaining.

Note

Note that even for readonly Properties it is possible to specify a write handler, as explained in Issue 199 . In this case, the write handler may define in an application-specific way to fail the request.

There MUST be at most one write handler for any given Property , so newly added handlers MUST replace the previous handlers. If no write handler is initialized for any given Property , implementations SHOULD implement default property update if the Property is writeable and notifying observers on change if the Property is observable, based on the Thing Description .

When the method is invoked given name and handler, implementations MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If a Property interaction with name is not found, throw NotFoundError and abort these steps.
Set the internal slot [[writeHandler]] on interaction to handler.

8.16 9.16 Handling requests for writing a Property

When a network request for writing a Property name with a new value value and options is received, implementations MUST run the following update property steps , given name, value, options and mode set to


"single"

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If a Property with name does not exist, return a NotFoundError in the reply and abort these steps.
Let handler be null.
If there is a user provided internal slot [[writeHandler]] on interaction, let handler be that.
Otherwise, if there is a default write handler provided by the implementation, let handler be that.
Otherwise, if handler is null, send back a NotSupportedError with the reply and abort these steps.
Let promise be the result of invoking handler with name and options. If it fails, return the error in the reply and abort these steps.
If mode is "single", reply to the request reporting success, following the Protocol Bindings and abort these steps.

8.17 9.17 Handling requests for writing multiple Properties

When a network request for writing multiple Properties given in an object propertyNames is received with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
For each property with key name and value value defined in propertyNames, run the update property steps with name, value, options and mode set to "multiple". If that fails, reply to the request with that error and abort these steps.
Reply to the request by sending a single reply according to the Protocol Bindings .

8.18 9.18 The `ActionHandler` callback

A function that is called when an external request for invoking an Action is received and defines what to do with such requests. It is invoked with params and optionally with an options object. It returns a Promise that rejects with an error or resolves with the value returned by the Action as InteractionInput .

Note

Application scripts MAY return a ReadableStream object from an ActionHandler . Implementations will then use the stream for constructing the Action 's response.

8.19 9.19 The `setActionHandler()` method

Takes as arguments name and action. Sets the handler function that defines what to do when a request is received to invoke the Action matched by name. Throws on error. Returns a reference to this object for supporting chaining.

The action callback function will implement an Action and SHOULD be called by implementations when a request for invoking the Action is received from the underlying platform.

There MUST be at most one handler for any given Action , so newly added handlers MUST replace the previous handlers.

When the method is invoked given name and action, run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s actions 's name.
If an Action with name name is not found, throw a NotFoundError and abort these steps.
Set the internal slot [[actionHandler]] on interaction to action.

8.20 9.20 Handling Action requests

When a network request for invoking the Action identified by name is received with inputs and optionally with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let interaction be the value of [[td]]'s properties 's name.
If an Action identified by name does not exist, return a NotFoundError in the reply and abort these steps.
Let handler be null.
If there is a user provided internal slot [[actionHandler]] on interaction, let handler be its value.
If handler is null, return a NotSupportedError with the reply created by following the Protocol Bindings and abort these steps.
Let promise be the result of invoking handler with name, inputs and options.
If promise rejects, send the error with the reply and abort these steps.
When promise resolves with data, use data to create and send the reply according to the Protocol Bindings .

8.21 9.21 The `EventListenerHandler` callback

A function that is called when an associated Event is triggered and provides the data to be sent with the Event to subscribers. Returns a Promise that resolves with InteractionInput value that represents the Event data, or rejects with an error.

Note

Applications MAY return ReadableStream from an EventListenerHandler Implementations will then use the stream provided in InteractionOutput when constructing the event notification.

8.22 9.22 The `EventSubscriptionHandler` callback

A function that is called when an external request for subscribing to an Event is received and defines what to do with such requests. It is invoked with an options object provided by the implementation and coming from subscribers. It returns a Promise that rejects with an error or resolves when the subscription is accepted.

8.23 9.23 The `setEventSubscribeHandler()` method

Takes as arguments name and handler. Sets the handler function that defines what to do when a subscription request is received for the specified Event matched by name. Throws on error. Returns a reference to this object for supporting chaining.

The handler callback function SHOULD implement what to do when an subscribe request is received, for instance necessary initializations. Note that the handler for emitting Events is set separately.

There MUST be at most one event subscribe handler for any given Event , so newly added handlers MUST replace the previous handlers.

When the method is invoked given name and handler, run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s events 's name.
If an Event with the name name is not found, throw a NotFoundError and abort these steps.
Set the internal slot [[subscribeHandler]] on interaction to handler.
Return this.

8.25 9.25 The `setEventUnsubscribeHandler()` method

Takes as arguments name and handler. Sets the handler function that defines what to do when the specified Event matched by name is unsubscribed from. Throws on error. Returns a reference to this object for supporting chaining.

The handler callback function SHOULD implement what to do when an unsubscribe request is received.

There MUST be at most one handler for any given Event , so newly added handlers MUST replace the previous handlers.

When the method is invoked with name and handler, run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s events 's name.
If an Event with the name name is not found, throw a NotFoundError and abort these steps.
Set the internal slot [[unsubscribeHandler]] on interaction to handler.
Return this.

8.26 9.26 Handling Event unsubscribe requests

When an Event unsubscribe request for name is received by the underlying platform optionally with options, run the following steps:

If this operation is not supported, send back a NotSupportedError according to the Protocol Bindings and abort these steps.
If this operation is not allowed, send back a NotAllowedError according to the Protocol Bindings and abort these steps.
Let interaction be the value of [[td]]'s events 's name.
If an Event with the name name is not found, send back a NotFoundError and abort these steps.
If name has an associated [[unsubscribeHandler]] internal slot that is a function, invoke it with options and abort these steps.
Otherwise let subscriber be the tuple saved in interaction 's internal listener list .
Remove subscriber from interaction 's internal listener list .
Return this.

8.27 9.27 The `setEventHandler()` method

Takes as arguments name and eventHandler. Sets the event handler function for the specified Event matched by name. Throws on error. Returns a reference to this object for supporting chaining.

The eventHandler callback function will implement what to do when the event is emitted. It SHOULD resolve with a value that represents the Event data, or reject with an error.

There MUST be at most one handler for any given Event , so newly added handlers MUST replace the previous handlers.

When the method is invoked with name and eventHandler, run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, throw a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s events 's name.
If an Event with the name name is not found, throw a NotFoundError and abort these steps.
Set the internal slot [[eventHandler]] of interaction to eventHandler.
Return this.

8.28 9.28 Handling Events

When an Event with name name is emitted with data either by the underlying platform or by the emitEvent() method, run the following steps:

Let interaction be the value of [[td]]'s events 's name.
If data is not defined or null,
1. Let eventHandler be the value of the [[eventHandler]] internal slot of interaction.
2. If eventHandler is failure, abort these steps.
3. Let data be the result of awaiting to resolve the invocation of eventHandler. If it rejects, abort these steps.
For each subscriber in the internal listener list of interaction, run the following sub-steps:
1. Create an Event notification response according to the Protocol Bindings from data and subscriber, including its options. If the underlying protocol stack permits conveying event errors and if an error condition has been detected by the UA, create response as an error notification according to the Protocol Bindings , using data, subscriber and its options.
  
  Note
  
  The error reporting is protocol specific and it is encapsulated by implementations. On the client end, the error listener passed with the subscription will be invoked if the client UA detects the error.
2. Send response to the subscriber identified by subscriber.

8.29 9.29 The `emitEvent()` method

Takes as arguments name denoting an Event name and data. Triggers emitting the Event with the given data. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Let interaction be the value of [[td]]'s events 's name.
If an Event with the name name is not found, reject promise with NotFoundError and abort these steps.
Make a request to the underlying platform to emit an Event with data.

Note

This will trigger the handling events steps.

8.30 9.30 The `expose()` method

Start serving external requests for the Thing , so that WoT Interactions using Properties , Action s and Event s will be possible. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Run the expand a TD steps on the internal slot [[td]].
Run the validate a TD on [[td]]. If that fails, reject promise with a TypeError and abort these steps.
For each Property definition in [[td]]'s properties, initialize an | internal observer list | internal slot in order to store observe request data needed to notify the observers on value changes.
For each Event definition is [[td]]'s events, initialize an | internal listener list | internal slot in order to store subscription request data needed to notify the Event listeners.
Set up the WoT Interactions based on introspecting [[td]] as explained in [ WOT-TD ] and [ WOT-PROTOCOL-BINDINGS ]. Make a request to the underlying platform to initialize the Protocol Bindings and then start serving external requests for WoT Interactions (read, write and observe Properties , invoke Action s and manage Event subscriptions), based on the Protocol Bindings . Implementations MAY reject this step for any reason (e.g. if they want to enforce further checks and constraints on interaction forms).
If there was an error during the request, reject promise with an Error object error with error 's message set to the error code seen by the Protocol Bindings and abort these steps.
Otherwise resolve promise and abort these steps.

8.31 9.31 The `destroy()` method

Stop serving external requests for the Thing and destroy the object. Note that eventual unregistering should be done before invoking this method. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If invoking this method is not allowed for the current scripting context for security reasons, reject promise with a SecurityError and abort these steps.
Make a request to the underlying platform to stop serving external requests for WoT Interactions , based on the Protocol Bindings .
If there was an error during the request, reject promise with an Error object error with its message set to the error code seen by the Protocol Bindings and abort these steps.
Otherwise resolve promise and abort these steps.

8.32 9.32 ExposedThing Examples

The next example illustrates how to create an ExposedThing based on a partial TD object constructed beforehands.

Example 6 : Create ExposedThing with a simple Property

try {
  let temperaturePropertyDefinition = {
    type: "number",
    minimum: -50,
    maximum: 10000
  };
  let tdFragment = {
    properties: {
      temperature: temperaturePropertyDefinition
    },
    actions: {
      reset: {
        description: "Reset the temperature sensor",
        input: {
          temperature: temperatureValueDefinition
        },
        output: null,
        forms: []
      },
    },
    events: {
      onchange: temperatureValueDefinition
    }
  };
  let thing1 = await WOT.produce(tdFragment);
  // initialize Properties
  await thing1.writeProperty("temperature", 0);
  // add service handlers
  thing1.setPropertyReadHandler("temperature", () => {
     return readLocalTemperatureSensor();  // Promise
  });
  // start serving requests
  await thing1.expose();
} catch (err) {
   console.log("Error creating ExposedThing: " + err);
}

The next example illustrates how to add or modify a Property definition on an existing ExposedThing : take its td property, add or modify it, then create another ExposedThing with that.

Example 7 : Add an object Property

try {
  // create a deep copy of thing1's TD
  let instance = JSON.parse(JSON.stringify(thing1.td));
  const statusValueDefinition = {
    type: "object",
    properties: {
      brightness: {
        type: "number",
        minimum: 0.0,
        maximum: 100.0,
        required: true
      },
      rgb: {
        type: "array",
        "minItems": 3,
        "maxItems": 3,
        items : {
            "type" : "number",
            "minimum": 0,
            "maximum": 255
        }
      }
  };
  instance["name"] = "mySensor";
  instance.properties["brightness"] = {
    type: "number",
    minimum: 0.0,
    maximum: 100.0,
    required: true,
  };
  instance.properties["status"] = statusValueDefinition;
  instance.actions["getStatus"] = {
    description: "Get status object",
    input: null,
    output: {
      status : statusValueDefinition;
    },
    forms: [...]
  };
  instance.events["onstatuschange"] = statusValueDefinition;
  instance.forms = [...];  // update
  var thing2 = new ExposedThing(instance);
  // TODO: add service handlers
  await thing2.expose();
  });
} catch (err) {
   console.log("Error creating ExposedThing: " + err);
}

The following will cover a set of examples for the generation of a Thing Description from an ExposedThingInit using expand an ExposedThingInit steps. As hypothesis the runtime supports HTTP and COAP protocol bindings and it is hosted at 192.168.0.1.

The next example shows how to exploit a ExposedThingInit to create a simple Thing Description with one Property with the default values.

Example 8 : Create a Thing Description with one Property afforndace

{
  "properties" : {
    "temperature":{}
  }
}

{
  "@context": [
    "https://www.w3.org/2019/wot/td/v1"
  ],
  "title": "Thing-123",
  "securityDefinitions": {
    "no_sec": {
      "scheme": "nosec"
    }
  },
  "security": "no_sec",
  "properties": {
    "temperature": {
      "forms": [{
        "href": "http://192.168.0.1:8080/properties/temperature",
        "contentType": "application/json"
      },
      {
      "href": "coap://192.168.0.1:9090/properties/temperature",
      "contentType": "application/json"
      }]
    }
  }
}

Editor's note

TODO: add more examples where the ExposedThingInit contains suggested values that are replaced by the algorithm.

9. 10. The `ThingDiscovery` interface

Discovery is a distributed application that requires provisioning and support from participating network nodes (clients, servers, directory services). This API models the client side of typical discovery schemes supported by various IoT deployments.

The ThingDiscovery object is constructed given a filter and provides the properties and methods controlling the discovery process.

WebIDL[SecureContext, Exposed=(Window,Worker)]
interface ThingDiscovery {
  constructor(optional ThingFilter filter = null);
  readonly attribute ThingFilter? filter;
  readonly attribute boolean active;
  readonly attribute boolean done;
  readonly attribute Error? error;
  undefined start();
  Promise<ThingDescription> next();
  undefined stop();
};

Editor's note

The ThingDiscovery interface has a next() method and a done property, but it is not an Iterable . Look into Issue 177 for rationale.

The discovery results internal slot is an internal queue for temporarily storing the found ThingDescription objects until they are consumed by the application using the next() method. Implementations MAY optimize the size of this queue based on e.g. the available resources and the frequency of invoking the next() method.

The filter property represents the discovery filter of type ThingFilter specified for the discovery.

The active property is true when the discovery is actively ongoing on protocol level (i.e. new TD s may still arrive) and false otherwise.

The done property is true if the discovery has been completed with no more results to report and discovery results is also empty.

The error property represents the last error that occurred during the discovery process. Typically used for critical errors that stop discovery.

9.1 10.1 Constructing `ThingDiscovery`

To create


ThingDiscovery

with a filter or type


ThingFilter

, run the following steps:

If filter is not an object or null, throw a TypeError and abort these steps.
Let discovery be a new ThingDiscovery object.
Set the filter property to filter.
Set the active and done properties to false. Set the error property to null.
Return discovery.

The start() method sets active to true. The stop() method sets the active property to false, but done may be still false if there are ThingDescription objects in the discovery results not yet consumed with next() .

During successive calls of next() , the active property may be true or false, but the done property is set to false by next() only when both the active property is false and discovery results is empty.

9.2 10.2 The `DiscoveryMethod` enumeration



WebIDL




typedef


DOMString




DiscoveryMethod


;

Represents the discovery type to be used:

"direct" for fetching the Thing Description of a Thing specified by ThingFilter 's url.
"directory" for discovery based on a service provided by a Thing Directory specified by ThingFilter 's url.

9.3 10.3 The `ThingFilter` dictionary

Represents an object containing the constraints for discovering Thing s as key-value pairs.

WebIDLdictionary ThingFilter {
  DiscoveryMethod method = "directory";
  USVString? url;
  object? fragment;
  
};

Editor's note

The DOMString query property was temporarily removed from ThingFilter , until it is standardized in the WoT Discovery task force.

The method property represents the discovery type that should be used in the discovery process. The possible values are defined by the DiscoveryMethod enumeration.

The url property represents the URL of the target entity serving the discovery request, for instance the URL of a Thing Directory (if method is "directory" ), or the URL of a directly targeted Thing (if method is "direct" )

The fragment property represents a template object used for matching property by property against discovered Thing s.

9.4 10.4 The `start()` method

Starts the discovery process. The method MUST run the following steps:

If invoking this method is not allowed for the current scripting context for security reasons, set the error property to a SecurityError and abort these steps.
If discovery is not supported by the implementation, set the error property to NotSupportedError and abort these steps.
Let filter denote the filter property.
Create the discovery results internal slot for storing discovered ThingDescription objects.
Request the underlying platform to start the discovery process, with the following parameters:
- If |filter|s method is not defined or is "directory", use the remote Thing Directory specified in |filter.url|.
- Otherwise if |filter|s method is "direct", use the remote Thing specified in |filter.url|.
When the underlying platform has started the discovery process, set the active property to true.
Whenever a new Thing Description td is discovered by the underlying platform, run the following sub-steps:
1. Fetch td as a JSON object json. If that fails, set the error property to SyntaxError , discard td and continue the discovery process.
2. If filter 's fragment is defined, for each property defined in it, check if that property exists in json 's properties and has the same value. If this is false in any checks, discard td and continue the discovery process.
3. Otherwise add td to the discovery results .
4. At this point implementations MAY control the flow of the discovery process (depending on memory constraints, for instance temporarily stop discovery if the queue is getting too large, or resume discovery when the queue is emptied sufficiently).
Whenever an error occurs during the discovery process,
1. Let error be a new Error object. Set error 's name to "DiscoveryError".
2. If there was an error code or message provided by the Protocol Bindings , set error 's message to that value as string.
3. Set error property to error.
4. If the error is irrecoverable and discovery has been stopped by the underlying platform, set the active property to false.
When the underlying platform reports the discovery process has completed, set the active property to false.

9.5 10.5 The `next()` method

Provides the next discovered


ThingDescription

object. The method MUST run the following steps:

Return a Promise promise and execute the next steps in parallel .
If the active property is true, wait until the discovery results internal slot is not empty.
If discovery results is empty and the active property is false, set the done property to true and reject promise.
Remove the first ThingDescription object td from discovery results .
Resolve promise with td and abort these steps.

9.6 10.6 The `stop()` method

Stops or suppresses the discovery process. It might not be supported by all discovery methods and endpoints, however, any further discovery results or errors will be discarded and the discovery is marked inactive. The method MUST run the following steps:

Request the underlying platform to stop the discovery process. If this returns an error, or if it is not possible, for instance when discovery is based on open ended multicast requests, the implementation SHOULD discard subsequent discovered items.
Set the active property to false.

9.7 10.7 Discovery Examples

The following example finds ThingDescription objects of Thing s that are exposed by local hardware, regardless how many instances of WoT Runtime it is running. Note that the discovery can end (become inactive) before the internal discovery results queue is emptied, so we need to continue reading ThingDescription objects until done. This is typical with local and directory type discoveries.

Example 9 : Fetch the Thing Description of a Thing

let discovery = new ThingDiscovery({ method: "direct" });
do {
  let td = await discovery.next();
  console.log("Found Thing Description for " + td.title);
}

while

(!discovery.done);

The next example finds ThingDescription objects of Thing s listed in a Thing Directory service. We set a timeout for safety.

Example 10 : Discover Things via directory

let discoveryFilter = {
  method: "directory", // default value, no need to specify
  url: "http://directory.wotservice.org"
};
let discovery = new ThingDiscovery(discoveryFilter);
setTimeout( () => {
    discovery.stop();
    console.log("Discovery stopped after timeout.");
  },
  3000);
do {
  let td = await discovery.next();
  console.log("Found Thing Description for " + td.title);
  let thing = new ConsumedThing(td);
  console.log("Thing name: " + thing.getThingDescription().title);
} while (!discovery.done);
if (discovery.error) {
  console.log("Discovery stopped because of an error: " + error.message);
}

Web of Things (WoT) Scripting API

Abstract

Status of This Document

1. Introduction

2. Use Cases

2.1 Consuming a Thing

2.2 Exposing a Thing

2.3 Discovery

3. Conformance

4. Terminology and conventions

5. The ThingDescription type

4.1 5.1 Fetching a Thing Description

4.2 5.2 Expanding a Thing Description

4.3 5.3 Validating a Thing Description

5. 6. The WOT namespace

5.1 6.1 The consume() method

5.2 6.2 The produce() method

5.2.1 6.2.1 Expand an ExposedThingInit

5.2.2 6.2.2 Validating an ExposedThingInit

5.3 6.3 The discover() method

6. 7. Handling interaction data

6.1 7.1 The InteractionInput type

6.2 7.2 The InteractionOutput interface

6.2.1 7.2.1 The value() function

6.2.2 7.2.2 The arrayBuffer() function

6.2.3 7.2.3 The check data schema algorithm

6.2.4 7.2.4 The create interaction request algorithm

6.2.5 7.2.5 The parse interaction response algorithm

6.3 7.3 Using InteractionInput and InteractionOutput

6.4 7.4 Error handling

7. 8. The ConsumedThing interface

7.1 8.1 Internal slots for ConsumedThing

7.2 8.2 Constructing ConsumedThing

7.3 8.3 The getThingDescription() method

7.4 8.4 The readProperty() method

7.5 8.5 The readMultipleProperties() method

7.6 8.6 The readAllProperties() method

7.7 8.7 The writeProperty() method

7.8 8.8 The writeMultipleProperties() method

7.9 8.9 The observeProperty() method

7.10 8.10 The invokeAction() method

7.11 8.11 The subscribeEvent() method

7.12 8.12 The InteractionOptions dictionary

7.13 8.13 The PropertyReadMap type

7.14 8.14 The PropertyWriteMap type

7.15 8.15 The InteractionListener callback

7.16 8.16 The ErrorListener callback

7.17 8.17 The Subscription interface

7.17.1 8.17.1 Internal slots for Subscription

7.17.2 8.17.2 The stop() method

7.17.3 8.17.3 Finding an unsubscribe Form

7.18 8.18 ConsumedThing Examples

8. 9. The ExposedThing interface

8.1 9.1 Internal slots for ExposedThing

8.2 9.2 Constructing ExposedThing

8.3 9.3 The getThingDescription() method

8.4 9.4 The PropertyReadHandler callback

8.5 9.5 The setPropertyReadHandler() method

8.6 9.6 Handling requests for reading a Property

8.7 9.7 Handling requests for reading multiple Properties

8.8 9.8 Handling requests for reading all Properties

8.9 9.9 The setPropertyObserveHandler() method

8.10 9.10 Handling Property observe requests

8.11 9.11 The setPropertyUnobserveHandler() method

8.12 9.12 Handling Property unobserve requests

8.13 9.13 The emitPropertyChange() method

8.14 9.14 The PropertyWriteHandler callback

8.15 9.15 The setPropertyWriteHandler() method

8.16 9.16 Handling requests for writing a Property

8.17 9.17 Handling requests for writing multiple Properties

8.18 9.18 The ActionHandler callback

8.19 9.19 The setActionHandler() method

8.20 9.20 Handling Action requests

8.21 9.21 The EventListenerHandler callback

8.22 9.22 The EventSubscriptionHandler callback

8.23 9.23 The setEventSubscribeHandler() method

8.24 9.24 Handling Event subscribe requests

8.25 9.25 The setEventUnsubscribeHandler() method

8.26 9.26 Handling Event unsubscribe requests

8.27 9.27 The setEventHandler() method

5. The `ThingDescription` type

5. 6. The `WOT` namespace

5.1 6.1 The `consume()` method

5.2 6.2 The `produce()` method

5.3 6.3 The `discover()` method

6.1 7.1 The `InteractionInput` type

6.2 7.2 The `InteractionOutput` interface

6.2.1 7.2.1 The `value()` function

6.2.2 7.2.2 The `arrayBuffer()` function

6.3 7.3 Using `InteractionInput` and `InteractionOutput`

7. 8. The `ConsumedThing` interface

7.2 8.2 Constructing `ConsumedThing`

7.3 8.3 The `getThingDescription()` method

7.4 8.4 The `readProperty()` method

7.5 8.5 The `readMultipleProperties()` method

7.6 8.6 The `readAllProperties()` method

7.7 8.7 The `writeProperty()` method

7.8 8.8 The `writeMultipleProperties()` method

7.9 8.9 The `observeProperty()` method

7.10 8.10 The `invokeAction()` method

7.11 8.11 The `subscribeEvent()` method

7.12 8.12 The `InteractionOptions` dictionary

7.13 8.13 The `PropertyReadMap` type

7.14 8.14 The `PropertyWriteMap` type

7.15 8.15 The `InteractionListener` callback

7.16 8.16 The `ErrorListener` callback

7.17 8.17 The `Subscription` interface

7.17.1 8.17.1 Internal slots for `Subscription`

7.17.2 8.17.2 The `stop()` method

8. 9. The `ExposedThing` interface

8.2 9.2 Constructing `ExposedThing`

8.3 9.3 The `getThingDescription()` method

8.4 9.4 The `PropertyReadHandler` callback

8.5 9.5 The `setPropertyReadHandler()` method

8.9 9.9 The `setPropertyObserveHandler()` method

8.11 9.11 The `setPropertyUnobserveHandler()` method

8.13 9.13 The `emitPropertyChange()` method

8.14 9.14 The `PropertyWriteHandler` callback

8.15 9.15 The `setPropertyWriteHandler()` method

8.18 9.18 The `ActionHandler` callback

8.19 9.19 The `setActionHandler()` method

8.21 9.21 The `EventListenerHandler` callback

8.22 9.22 The `EventSubscriptionHandler` callback

8.23 9.23 The `setEventSubscribeHandler()` method

8.25 9.25 The `setEventUnsubscribeHandler()` method

8.27 9.27 The `setEventHandler()` method

8.29 9.29 The `emitEvent()` method

8.30 9.30 The `expose()` method

8.31 9.31 The `destroy()` method

9. 10. The `ThingDiscovery` interface

9.1 10.1 Constructing `ThingDiscovery`

9.2 10.2 The `DiscoveryMethod` enumeration

9.3 10.3 The `ThingFilter` dictionary

9.4 10.4 The `start()` method

9.5 10.5 The `next()` method

9.6 10.6 The `stop()` method