ljm_j1/modules/transcription/transcriptionServices/SphinxTranscriptionService.js

/* global config,  XMLHttpRequest, console, APP, JSON */

var TranscriptionService = require("./AbstractTranscriptionService");
var Word = require( "../word");
var audioRecorder = require("./../audioRecorder");

/**
 * Implements a TranscriptionService for a Sphinx4 http server
 */
var 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);
    var 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) {
    var 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();
    var 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
    var 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
    var 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() {
    var message = "config does not contain an url to a " +
    "Sphinx4 https server";
    if(config.sphinxURL === undefined){
        console.log(message);
    }
    else {
        var toReturn = config.sphinxURL;
        if(toReturn.includes !== undefined && toReturn.includes("https://")){
            return toReturn;
        }
        else{
            console.log(message);
        }
    }
}

module.exports = SphinxService;