Node callback style with promisify? "The 'original' argument must be of type function"

Question

I'm using util.promisify in a Google Cloud Function to call IBM Watson Text-to-Speech, which returns a callback. My code works but I get an error message:

TypeError [ERR_INVALID_ARG_TYPE]: The "original" argument must be of type function

The documentation says

Takes a function following the common error-first callback style, i.e. taking a (err, value) => ... callback as the last argument, and returns a version that returns promises.

The IBM Watson callback is complicated and I can't figure out how to refactor it into the Node.js callback style. It's working, should I just ignore the error message? Here's my Google Cloud Function:

exports.IBM_T2S = functions.firestore.document('Users/{userID}/Spanish/IBM_T2S_Request').onUpdate((change) => {

    let word = change.after.data().word;
    let wordFileType = word + '.mp3';

    function getIBMT2S(word, wordFileType) {
      const {Storage} = require('@google-cloud/storage');
      const storage = new Storage();
      const bucket = storage.bucket('myProject.appspot.com');
      const file = bucket.file('Audio/Spanish/Latin_America/' + wordFileType);
      var util = require('util');
      var TextToSpeechV1 = require('watson-developer-cloud/text-to-speech/v1');

      var textToSpeech = new TextToSpeechV1({
        username: 'groucho',
        password: 'swordfish',
        url: 'https://stream.watsonplatform.net/text-to-speech/api'
      });

      var synthesizeParams = {
        text: word,
        accept: 'audio/mpeg',
        voice: 'es-LA_SofiaVoice',
      };

      const options = { // construct the file to write
        metadata: {
          contentType: 'audio/mpeg',
          metadata: {
            source: 'IBM Watson Text-to-Speech',
            languageCode: 'es-LA',
            gender: 'Female'
          }
        }
      };

      textToSpeech.synthesize(synthesizeParams).on('error', function(error) {
        console.log(error);
      }).pipe(file.createWriteStream(options))
      .on('error', function(error) {
        console.error(error);
      })
      .on('finish', function() {
        console.log("Audio file written to Storage.");
      });
    };

var passGetIBMT2S = util.promisify(getIBMT2S(word, wordFileType))
passGetIBMT2S(word, wordFileType)
});

Answer 1

Here's my finished code. There are two functions. getT2S calls IBM Watson Text-to-Speech, then writes the audiofile to Storage, then gets the download URL. writeDownloadURL checks if a Firestore document exists, then either sets or updates the download URL to Firestore.

exports.IBM_T2S = functions.firestore.document('Users/{userID}/Spanish/IBM_T2S_Request').onUpdate((change) => {

if (change.after.data().word != undefined) {
  // get requested word object
  let accent = change.after.data().accent;
  let audioType = change.after.data().audioType;
  let gender = change.after.data().gender;
  let longLanguage = change.after.data().longLanguage;
  let shortLanguage = change.after.data().shortLanguage;
  let shortSource = change.after.data().shortSource;
  let source = change.after.data().source;
  let voice = change.after.data().voice;
  let word = change.after.data().word;
  console.log(word);
  let wordFileType = word + '.' + audioType;
  let pronunciation = `${accent}-${gender}-${shortSource}`;

  const {Storage} = require('@google-cloud/storage');
  const storage = new Storage();
  const bucket = storage.bucket('myProject.appspot.com');
  const file = bucket.file('Audio/' + longLanguage + '/' + pronunciation + '/' + wordFileType);

  var TextToSpeechV1 = require('watson-developer-cloud/text-to-speech/v1');

  var textToSpeech = new TextToSpeechV1({
    username: 'groucho',
    password: 'swordfish',
    url: 'https://stream.watsonplatform.net/text-to-speech/api'
  });

  var synthesizeParams = {
    text: word,
    accept: 'audio/' + audioType,
    voice: voice
  };

  const options = { // construct the file to write
    metadata: {
      contentType: 'audio/' + audioType,
      metadata: {
        accent: accent,
        audioType: audioType,
        gender: gender,
        longLanguage: longLanguage,
        shortLanguage: shortLanguage,
        source: source,
        voice: voice,
        word: word
      }
    }
  };

  // check if Pronunciations collection exists, set or update to not destroy existing data
  function writeDownloadURL(downloadURL) {
    admin.firestore().collection('Dictionaries').doc(longLanguage).collection('Words').doc(word).collection('Pronunciations').doc(pronunciation).get()
    .then(function(doc) {
      if (doc.exists) {
        return admin.firestore().collection('Dictionaries').doc(longLanguage).collection('Words').doc(word).collection('Pronunciations').doc(pronunciation).update({ audioFile: downloadURL })
        .then(result => console.log('DONE'))
        .catch(error => console.error(error));
      } else {
        return admin.firestore().collection('Dictionaries').doc(longLanguage).collection('Words').doc(word).collection('Pronunciations').doc(pronunciation).set({ audioFile: downloadURL })
        .then(result => console.log('DONE'))
        .catch(error => console.error(error));
      } // close else
    })
    .catch(error => console.error(error));
  } // close writeDownloadURL

  // documentation at https://stackoverflow.com/questions/22519784/how-do-i-convert-an-existing-callback-api-to-promises
  function getT2S(synthesizeParams) {
    return new Promise(function(resolve, reject) {
      // documentation at https://cloud.ibm.com/apidocs/text-to-speech?code=node#synthesize-audio-get
      textToSpeech.synthesize(synthesizeParams).on('error', function(error) {
        console.error(error);
        reject(error);
      }).pipe(file.createWriteStream(options))
      .on('error', function(error) {
        console.error(error);
        reject(error);
      })
      .on('finish', function() {
        resolve(file.getSignedUrl({
          action: 'read',
          expires: '03-17-2025'
        }));
      }); // close on finish
    }); // close Promise
  } // close getT2SAsync

  async function getT2SAsync(synthesizeParams) {
    var signedUrls = await getT2S(synthesizeParams);
    var downloadURL = signedUrls[0];
    await writeDownloadURL(downloadURL);
    console.log("All done.");
  }

  return getT2SAsync(synthesizeParams);

} else { // if no word passed to function
  console.error("Error.");
}
}); // close IBM_T2S

I mistakenly wrote

 return file.getSignedUrl({

instead of

 resolve(file.getSignedUrl({

The result was that no data came back from the promise, and the cloud function timed out after six seconds, without finishing execution. You have to do something with resolve. I used reject twice to be sure. :-)

Answer 2

It's working because you are invoking getIBMT2S and passing the return value to util.promisfy and not the function itself.

There are a couple of issues here, firstly your getIBMT2S function doesn't look like it would be compatible with util.promisfy, as you've highlighted from the documents, a compatible function should follow the typical callback-style signature (getIBMT2S does not take a callback parameter).

Secondly, util.promisify expects a function - in your case you are passing the return value of the function instead. If getIBMT2S was updated to support a callback parameter then the correct usage would be

function getIBMT2S(word, wordFileType, cb) {
  ...
  // be sure to invoke cb in here
}
var passGetIBMT2S = util.promisify(getIBMT2S); // <-- don't call getIBMT2S, pass it in directly
passGetIBMT2S(word, wordFileType) // <-- now invoke the wrapped function
  .then(result => console.log('DONE'));
  .catch(e => console.error(e));