wekan/models/lib/fsHooks/createOnAfterUpload.js

import { Meteor } from 'meteor/meteor';
import fs from 'fs';

export const createOnAfterUpload = function onAfterUpload(filesCollection, bucket, file, versionName) {
  const self = filesCollection;
  const metadata = { ...file.meta, versionName, fileId: file._id };
  fs.createReadStream(file.versions[versionName].path)

    // this is where we upload the binary to the bucket using bucket.openUploadStream
    // see http://mongodb.github.io/node-mongodb-native/3.2/api/GridFSBucket.html#openUploadStream
    .pipe(
      bucket.openUploadStream(file.name, {
        contentType: file.type || 'binary/octet-stream',
        metadata,
      }),
    )

    // and we unlink the file from the fs on any error
    // that occurred during the upload to prevent zombie files
    .on('error', err => {
      console.error("[createOnAfterUpload error]", err);
      self.unlink(self.collection.findOne(file._id), versionName); // Unlink files from FS
    })

    // once we are finished, we attach the gridFS Object id on the
    // FilesCollection document's meta section and finally unlink the
    // upload file from the filesystem
    .on(
      'finish',
      Meteor.bindEnvironment(ver => {
        const property = `versions.${versionName}.meta.gridFsFileId`;

        self.collection.update(file._id, {
          $set: {
            [property]: ver._id.toHexString(),
          },
        });

        self.unlink(self.collection.findOne(file._id), versionName); // Unlink files from FS
      }),
    );
};