How do I upload a base64 encoded image (string) directly to a Google Cloud Storage bucket using Node.js?

The solution, I believe, is to use the file.createWriteStream functionality that the bucket.upload function wraps in the Google Cloud Node SDK.

I've got very little experience with streams, so try to bear with me if this doesn't work right off.

First of all, we need take the base64 data and drop it into a stream. For that, we're going to include the stream library, create a buffer from the base64 data, and add the buffer to the end of the stream.

var stream = require('stream');
var bufferStream = new stream.PassThrough();
bufferStream.end(Buffer.from(req.body.base64Image, 'base64'));

More on decoding base64 and creating the stream.

We're then going to pipe the stream into a write stream created by the file.createWriteStream function.

var gcs = require('@google-cloud/storage')({
  projectId: 'grape-spaceship-123',
  keyFilename: '/path/to/keyfile.json'
});

//Define bucket.
var myBucket = gcs.bucket('my-bucket');
//Define file & file name.
var file = myBucket.file('my-file.jpg');
//Pipe the 'bufferStream' into a 'file.createWriteStream' method.
bufferStream.pipe(file.createWriteStream({
    metadata: {
      contentType: 'image/jpeg',
      metadata: {
        custom: 'metadata'
      }
    },
    public: true,
    validation: "md5"
  }))
  .on('error', function(err) {})
  .on('finish', function() {
    // The file upload is complete.
  });

Info on file.createWriteStream, File docs, bucket.upload, and the bucket.upload method code in the Node SDK.

So the way the above code works is to define the bucket you want to put the file in, then define the file and the file name. We don't set upload options here. We then pipe the bufferStream variable we just created into the file.createWriteStream method we discussed before. In these options we define the metadata and other options you want to implement. It was very helpful to look directly at the Node code on Github to figure out how they break down the bucket.upload function, and recommend you do so as well. Finally, we attach a couple events for when the upload finishes and when it errors out.

Posting my version of the answer in response to @krlozadan 's request above:

// Convert the base64 string back to an image to upload into the Google Cloud Storage bucket
var mimeTypes = require('mimetypes');

var image = req.body.profile.image,
    mimeType = image.match(/data:([a-zA-Z0-9]+\/[a-zA-Z0-9-.+]+).*,.*/)[1],
    fileName = req.profile.id + '-original.' + mimeTypes.detectExtension(mimeType),
    base64EncodedImageString = image.replace(/^data:image\/\w+;base64,/, ''),
    imageBuffer = new Buffer(base64EncodedImageString, 'base64');

// Instantiate the GCP Storage instance
var gcs = require('@google-cloud/storage')(),
    bucket = gcs.bucket('my-bucket');

// Upload the image to the bucket
var file = bucket.file('profile-images/' + fileName);

file.save(imageBuffer, {
    metadata: { contentType: mimeType },
    public: true,
    validation: 'md5'
}, function(error) {

    if (error) {
        return res.serverError('Unable to upload the image.');
    }

    return res.ok('Uploaded');
});

This worked just fine for me. Ignore some of the additional logic in the first few lines as they are only relevant to the application I am building.

If you want to save a string as a file in Google Cloud Storage, you can do it easily using the file.save method:

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

const file = myBucket.file('my-file.txt');
const contents = 'This is the contents of the file.';

file.save(contents).then(() => console.log('done'));