TTS with a websocket:Creating a WAV from binary data fails - node.js

Question

I try to create a WAV from binary data using the websocket connection on a node.js server. I use the BluemixTTS to create the speech. Here is my current code:
'use strict';
const WebSocket = require('ws');
var express = require('express');
var watson = require('watson-developer-cloud');
var vcapServices = require('vcap_services');
var extend = (extend = require('util')._extend);
var fs = require('fs');
var ttsConfig = extend(
{
version: 'v1',
url: 'https://stream.watsonplatform.net/text-to-speech/api',
username: 'myusernamehere',
password: "mypasswordhere"
},
vcapServices.getCredentials('text_to_speech')
);
var ttsAuthService = watson.authorization(ttsConfig);
var websocket;
ttsAuthService.getToken({ url: ttsConfig.url }, function(err, token) {
if (err) {
console.log('Error retrieving token: ', err);
return;
}
var voice = 'en-US_AllisonVoice';
var wsURI = 'wss://stream.watsonplatform.net/text-to-speech/api/v1/synthesize?voice=' +
voice + '&watson-token=' + token;
websocket = new WebSocket(wsURI);
websocket.onopen = function(evt) { onOpen(evt) };
websocket.onclose = function(evt) { onClose(evt) };
websocket.onmessage = function(evt) { onMessage(evt) };
websocket.onerror = function(evt) { onError(evt) };
});
function onOpen(evt) {
var message = {
text: 'Hello world',
accept: 'audio/wav',
timings: ['words']
};
websocket.send(JSON.stringify(message));
}
var messages;
var audioStream = null;
function onMessage(evt) {
if (typeof evt.data === 'string') {
messages += evt.data;
} else {
if(audioStream == null){
audioStream = evt.data;
}else{
audioStream += evt.data;
}
}
}
function onClose(evt) {
console.log(messages);
var wstream = fs.createWriteStream('test.wav');
wstream.write((audioStream));
wstream.end();
}
function onError(evt) {
}
I get the token, trigger the TTS specifying audio/wav, build my buffer in the onMessage method and then write it into a .wav file. Everything seems fine.
However the file is somehow broken, and cannot be opened with any music-player. Do I miss some special encoding ?
Any help is appreciated
Regards,
Rambazamba

Answer 1

As the data contains a buffer one has to write the buffer in the file directly each time you get a message and then close the file stream in the onClose event. Like this:
var messages;
var wstream = fs.createWriteStream('test.wav');
function onMessage(evt) {
if (typeof evt.data === 'string') {
messages += evt.data;
} else {
wstream.write(evt.data)
}
}
function onClose(evt) {
console.log(messages);
wstream.end();
}
function onError(evt) {
}