ljm_j1/modules/transcription/transcriptionServices/SphinxTranscriptionService.js

/* global config */

const TranscriptionService = require('./AbstractTranscriptionService');
const Word = require('../word');
const audioRecorder = require('./../audioRecorder');

/**
 * Implements a TranscriptionService for a Sphinx4 http server
 */
const SphinxService = function() {
    // set the correct url
    this.url = getURL();
};

/**
 * Subclass of AbstractTranscriptionService
 */
SphinxService.prototype = Object.create(TranscriptionService.prototype);

/**
 * Set the right constructor
 */
SphinxService.constructor = SphinxService;

/**
 * Overrides the sendRequest method from AbstractTranscriptionService
 * it will send the audio stream the a Sphinx4 server to get the transcription
 *
 * @param audioFileBlob the recorder audio stream an a single Blob
 * @param callback the callback function retrieving the server response
 */
SphinxService.prototype.sendRequest = function(audioFileBlob, callback) {
    console.log('sending an audio file  to ' + this.url);
    console.log('the audio file being sent: ' + audioFileBlob);
    const request = new XMLHttpRequest();
    request.onreadystatechange = function() {
        if(request.readyState === XMLHttpRequest.DONE
            && request.status === 200) {
            callback(request.responseText);
        } else if (request.readyState === XMLHttpRequest.DONE) {
            throw new Error('unable to accept response from sphinx server.'
                + 'status: ' + request.status);
        }
        // if not ready no point to throw an error
    };
    request.open('POST', this.url);
    request.setRequestHeader('Content-Type',
        audioRecorder.determineCorrectFileType());
    request.send(audioFileBlob);
    console.log('send ' + audioFileBlob);
};

/**
 * Overrides the formatResponse method from AbstractTranscriptionService
 * It will parse the answer from the server in the expected format
 *
 * @param response the JSON body retrieved from the Sphinx4 server
 */
SphinxService.prototype.formatResponse = function(response) {
    const result = JSON.parse(response).objects;
    // make sure to delete the session id object, which is always
    // the first value in the JSON array
    result.shift();
    const array = [];
    result.forEach(function(word) {
        if(!word.filler) {
            array.push(new Word(word.word, word.start, word.end));
        }
    });
    return array;
};

/**
 * checks wether the reply is empty, or doesn't contain a correct JSON object
 * @param response the server response
 * @return {boolean} whether the response is valid
 */
SphinxService.prototype.verify = function(response) {
    console.log('response from server:' + response.toString());
    // test if server responded with a string object
    if(typeof response !== 'string') {
        return false;
    }
    // test if the string can be parsed into valid JSON
    let json;
    try{
        json = JSON.parse(response);
    } catch (error) {
        console.log(error);
        return false;
    }
    // check if the JSON has a "objects" value
    if(json.objects === undefined) {
        return false;
    }
    // get the "objects" value and check for a session ID
    const array = json.objects;
    if(!(array[0] && array[0]['session-id'])) {
        return false;
    }
    // everything seems to be in order
    return true;
};

/**
 * Gets the URL to the Sphinx4 server from the config file. If it's not there,
 * it will throw an error
 *
 * @returns {string} the URL to the sphinx4 server
 */
function getURL() {
    const message = 'config does not contain an url to a '
    + 'Sphinx4 https server';
    if(config.sphinxURL === undefined) {
        console.log(message);
    } else {
        const toReturn = config.sphinxURL;
        if(toReturn.includes !== undefined && toReturn.includes('https://')) {
            return toReturn;
        }
        console.log(message);

    }
}

module.exports = SphinxService;