server.js

'use strict'
require('dotenv').load()

const express = require('express');
const bodyParser = require('body-parser')
const app = express();
const expressWs = require('express-ws')(app);

const Nexmo = require('nexmo');
const { Readable } = require('stream');
const speech = require('@google-cloud/speech');

// this is used with the heroku one-click install.
// if you are running locally, use GOOGLE_APPLICATION_CREDENTIALS to point to the file location
let config = null;

if (process.env.GOOGLE_APPLICATION_CREDENTIALS === undefined) {
  config = {
    projectId: 'nexmo-extend',
    credentials: {
      client_email: process.env.GOOGLE_CLIENT_EMAIL,
      private_key: process.env.GOOGLE_PRIVATE_KEY.replace(/\\n/g, '\n')
    }
  }
}

const client = new speech.SpeechClient(config||null);

const nexmo = new Nexmo({
  apiKey: "dummy",
  apiSecret: "dummy",
  applicationId: process.env.APP_ID,
  privateKey: process.env.PRIVATE_KEY || './private.key'
});

app.use(bodyParser.json());

app.get('/ncco', (req, res) => {

  let nccoResponse = [
    {
      "action": "connect",
      "endpoint": [{
        "type": "websocket",
        "content-type": "audio/l16;rate=16000",
        "uri": `ws://${req.hostname}/socket`
      }]
    }
  ];

  res.status(200).json(nccoResponse);
});

app.post('/event', (req, res) => {
  console.log('EVENT LOG::', req.body)
  res.status(204).end();
});

// Nexmo Websocket Handler
app.ws('/socket', (ws, req) => {

  let request ={
    config: {
      encoding: 'LINEAR16',
      sampleRateHertz: 16000,
      languageCode: process.env.LANG_CODE || 'en-US'
    },
    interimResults: false
  };

  const recognizeStream = client
  .streamingRecognize(request)
  .on('error', console.error)
  .on('data', data => {
    console.log(
      `Transcription: ${data.results[0].alternatives[0].transcript}`
    );
  });

  ws.on('message', (msg) => {
    if (typeof msg === "string") {
      let config = JSON.parse(msg);
    } else {
      recognizeStream.write(msg);
    }

  });

  ws.on('close', () => {
    recognizeStream.destroy();
  })
});

const port = process.env.PORT || 8000;
app.listen(port, () => console.log(`Example app listening on port ${port}!`))