resize and save files to s3 in meteor

Is there any best way to resize and save files to s3 in meteor.

I though about using cfs packages, but they put too much load on server.

To directly upload images to the s3 I'm using slingshot which is very fine.

but slingshot takes only file objects as inputs it doesn't take streams to store the files.

Is there any option to resize the image in client side and pass it to the slingshot package

package: https://github.com/CulturalMe/meteor-slingshot issue: https://github.com/CulturalMe/meteor-slingshot/issues/36

I've found that the following works in order to integrate Clientside Image Manipulation with Slingshot (asynchronous code with ES6 promises):

var uploader;

function b64ToBlob(b64Data, contentType, sliceSize) {
  var byteNumbers, i, slice;
  var offset = 0;
  var byteCharacters = atob(b64Data);
  var byteArrays = [];
  sliceSize = sliceSize || 512;
  byteArrays = [];
  while (offset < byteCharacters.length) {
    slice = byteCharacters.slice(offset, offset + sliceSize);
    byteNumbers = [];
    for (i = 0; i < slice.length; ++i) {
      byteNumbers.push(slice.charCodeAt(i));
    }
    byteArrays.push(new Uint8Array(byteNumbers));
    offset += sliceSize;
  }

  return new Blob(byteArrays, {type: contentType});
}

uploader = new Slingshot.Upload("pictures");

new Promise(function (resolve) {
  processImage(file, 300, 300, resolve);
}).then(function (dataUri) {
  var match = /^data:([^;]+);base64,(.+)$/.exec(dataUri);
  return [file.name, match[1], match[2]];
}).then(function (params) {
  var name = params[0];
  var type = params[1];
  var b64 = params[2];
  return new Promise(function (resolve, reject) {
    var blob = b64ToBlob(b64, type);
    blob.name = name;
    uploader.send(blob, function (error, downloadUrl) {
      if (error != null) {
        reject(error.message);
      } else {
        resolve(downloadUrl);
      }
    });
  });
});

Conversion from Base64 to blob is borrowed from https://stackoverflow.com/a/16245768/1238764.