index.js

'use strict';

const config = require('./config.json');

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const {Storage} = require('@google-cloud/storage');
const storage = new Storage();

const Vision = require('@google-cloud/vision');
const vision = new Vision.ImageAnnotatorClient();

const {Translate} = require('@google-cloud/translate');
const translate = new Translate();

const Buffer = require('safe-buffer').Buffer;

/**
 * Publishes the result to the given pubsub topic and returns a Promise.
 *
 * @param {string} topicName Name of the topic on which to publish.
 * @param {object} data The message data to publish.
 */
function publishResult(topicName, data) {
  const dataBuffer = Buffer.from(JSON.stringify(data));

  return pubsub
    .topic(topicName)
    .get({autoCreate: true})
    .then(([topic]) => topic.publisher().publish(dataBuffer));
}

/**
 * Detects the text in an image using the Google Vision API.
 *
 * @param {string} bucketName Cloud Storage bucket name.
 * @param {string} filename Cloud Storage file name.
 * @returns {Promise}
 */
async function detectText(bucketName, filename) {
  console.log(`Scanning for text in image ${filename}`);
  const [detections] = await vision.textDetection(`gs://${bucketName}/${filename}`);
  const [annotation] = detections.textAnnotations;

  const text = annotation ? annotation.description : '';
  console.log(`Extracted text from image (${text.length} chars)`);

  const [d] = await translate.detect(text);
  const detection = Array.isArray(d) ? d[0] : d;
  console.log(`Detected language "${detection.language}" for ${filename}`);

  const tasks = config.TO_LANG.map(lang => {
    const topicName = config[detection.language === lang ? 'RESULT_TOPIC' : 'TRANSLATE_TOPIC'];
    const messageData = {
      text,
      filename,
      lang,
    };
  
   return publishResult(topicName, messageData);
  });

  return Promise.all(tasks);
}

/**
 * Appends a .txt suffix to the image file name.
 *
 * @param {string} filename Name of a file.
 * @param {string} lang Language to append.
 * @returns {string} The new filename.
 */
function renameImageForSave(filename, lang) {
  return `${filename}_to_${lang}.txt`;
}

/**
 * This function is exported by index.js, and is executed when
 * a file is uploaded to the Cloud Storage bucket you created
 * for uploading images.
 *
 * @param {object} event.data (Node 6) A Google Cloud Storage File object.
 * @param {object} event (Node 8+) A Google Cloud Storage File object.
 */
exports.processImage = event => {
  const file = event.data || event;

  if (file.resourceState === 'not_exists') {
    console.log('File does not exist.');
    return Promise.resolve();
  }
  if (!file.bucket)
    return Promise.reject(new Error('Bucket not provided. Make sure you have a "bucket" property in your request'));
  if (!file.name)
    return Promise.reject(new Error('Filename not provided. Make sure you have a "name" property in your request'));

  return detectText(file.bucket, file.name)
    .then(() => {
      console.log(`File ${file.name} processed.`);
    });
};

/**
 * This function is exported by index.js, and is executed when
 * a message is published to the Cloud Pub/Sub topic specified
 * by the TRANSLATE_TOPIC value in the config.json file. The
 * function translates text using the Google Translate API.
 *
 * @param {object} event.data (Node 6) The Cloud Pub/Sub Message object.
 * @param {object} event (Node 8+) The Cloud Pub/Sub Message object.
 * @param {string} {messageObject}.data The "data" property of the Cloud Pub/Sub
 * Message. This property will be a base64-encoded string that you must decode.
 */
exports.translateText = event => {
  const pubsubData = event.data.data || event.data;
  const jsonStr = Buffer.from(pubsubData, 'base64').toString();
  const payload = JSON.parse(jsonStr);

  return Promise.resolve()
    .then(() => {
      if (!payload.text) 
        throw new Error('Text not provided. Make sure you have a "text" property in your request');
      
      if (!payload.filename)
        throw new Error('Filename not provided. Make sure you have a "filename" property in your request');
      
      if (!payload.lang)
        throw new Error('Language not provided. Make sure you have a "lang" property in your request');

      console.log(`Translating text into ${payload.lang}`);
      return translate.translate(payload.text, payload.lang);
    })
    .then(([translation]) => {
      const messageData = {
        text: translation,
        filename: payload.filename,
        lang: payload.lang,
      };

      return publishResult(config.RESULT_TOPIC, messageData);
    })
    .then(() => {
      console.log(`Text translated to ${payload.lang}`);
    });
};

/**
 * This function is exported by index.js, and is executed when
 * a message is published to the Cloud Pub/Sub topic specified
 * by the RESULT_TOPIC value in the config.json file. The
 * function saves the data packet to a file in GCS.
 *
 * @param {object} event.data (Node 6) The Cloud Pub/Sub Message object.
 * @param {object} event (Node 8+) The Cloud Pub/Sub Message object.
 * @param {string} {messageObject}.data The "data" property of the Cloud Pub/Sub
 * Message. This property will be a base64-encoded string that you must decode.
 */
exports.saveResult = event => {
  const pubsubData = event.data.data || event.data;
  const jsonStr = Buffer.from(pubsubData, 'base64').toString();
  const payload = JSON.parse(jsonStr);

  return Promise.resolve()
    .then(() => {
      if (!payload.text)
        throw new Error('Text not provided. Make sure you have a "text" property in your request');
      
      if (!payload.filename)
        throw new Error('Filename not provided. Make sure you have a "filename" property in your request');
      
      if (!payload.lang)
        throw new Error('Language not provided. Make sure you have a "lang" property in your request');
      
      console.log(`Received request to save file ${payload.filename}`);

      const bucketName = config.RESULT_BUCKET;
      const filename = renameImageForSave(payload.filename, payload.lang);
      const file = storage.bucket(bucketName).file(filename);

      console.log(`Saving result to ${filename} in bucket ${bucketName}`);

      return file.save(payload.text);
    })
    .then(() => {
      console.log(`File saved.`);
    });
};