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empty-codec.js
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empty-codec.js
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/**
* Test/Demo Homebridge-MQTTThing Codec (encoder/decoder)
* Codecs allow custom logic to be applied to accessories in mqttthing, rather like apply() functions,
* but in the convenience of a stand-alone JavaScript file.
*
* empty-codec.js - shows the structure of a codec, but does nothing
*/
'use strict';
// todo: declare any global state
/**
* Initialise codec for accessory
* @param {object} params Initialisation parameters object
* @param {function} params.log Logging function
* @param {object} params.config Configuration
* @param {function} params.publish Function to publish a message directly to MQTT
* @param {function} params.notify Function to send MQTT-Thing a property notification
* @return {object} Encode and/or decode functions
*/
function init( params ) {
// extract parameters for convenience
let { log } = params;
// todo: declare state for accessory instance (available from encode/decode function definitions below)
/**
* Encode message before sending.
* The output function may be called to deliver an encoded value for the property later.
* @param {string} message Message from mqttthing to be published to MQTT
* @param {object} info Object giving contextual information
* @param {string} info.topic MQTT topic to be published
* @param {string} info.property Property associated with publishing operation
* @param {function} output Function which may be called to deliver the encoded value asynchronously
* @returns {string} Processed message (optionally)
*/
function encode( message, info, output ) { // eslint-disable-line no-unused-vars
log( `empty-codec: encode() called for topic [${info.topic}], property [${info.property}] with message [${message}]` );
// todo: manipulate message
return message;
}
/**
* Decode received message, and optionally return decoded value.
* The output function may be called to deliver a decoded value for the property later.
* @param {string} message Message received from MQTT
* @param {object} info Object giving contextual information
* @param {string} info.topic MQTT topic received
* @param {string} info.property Property associated with subscription
* @param {function} output Function which may be called to deliver the decoded value asynchronously
* @returns {string} Processed message (optionally)
*/
function decode( message, info, output ) { // eslint-disable-line no-unused-vars
log( `empty-codec: decode() called for topic [${info.topic}], property [${info.property}] with message [${message}]` );
// todo: manipulate message
return message;
}
// todo: define separate encode/decode functions for specific properties
/**
* The init() function must return an object containing encode and/or decode functions as defined above.
* To define property-specific encode/decode functions, the following syntax may be used:
* {
* properties: {
* targetProp1: {
* encode: encodeFunction1,
* decode: decodeFunction1
* },
* targetProp2: {
* encode: encodeFunction2
* },
* },
* encode: defaultEncodeFunction,
* decode: defaultDecodeFunction
* }
*
* The default encode/decode functions are called for properties for which no property-specific
* entry is specified.
*/
// return encode and decode functions
return {
encode,
decode
};
}
// export initialisation function
module.exports = {
init
};