Send files to Rails Active Storage using direct upload.


Getting Started

First, you instantiate an ActiveStorage object, passing it your Rails' backend url where ActiveStorage::DirectUploadsController (or your customization of it) is responding.

var activeStorage = ActiveStorage(
  directUploadURL: 'http://localhost:3000/rails/active_storage/direct_uploads',

Then, you just have to invoke the upload() method, passing it a File instance along with its info, like this:

DirectUploadResponse response = await activeStorage.upload(
  fileName: 'picture.jpg',
  fileMimeType: 'image/jpeg',
  file: File('my/picture.jpg'),

The returned DirectUploadResponse object provides a signedId getter. You should set that value in the API request attribute that your Rails backend will be setting on the ActiveRecord model attribute "powered by" ActiveStorage (i.e. annotated with has_one_attached).

Custom Headers

It's very likely that your Rails backend's upload endpoint is accessible to authenticated users only. In that case, you'll need to pass an Authorization header together with the upload request. To do so, you just have to invoke the addHeader() method on the ActiveStorage instance, before invoking the upload() method. Like this:

  'Bearer ae38e518bfb4e2b11c2e5cefffe4581e66af07296cfec4b2299ab54a74ef3d8c',

Another case when you might want to set a custom header is for adding User-Agent information to your upload requests.

Upload Progress

When uploading large files, it's important to be able to provide some feedback to your users about the progress. To do so, you have the option to pass a callback function to the upload() method, which would get called as many times as the number of byte chunks that are sent to the server, and every time would receive a double representing the upload progress percentage. Like this:

DirectUploadResponse response = await activeStorage.upload(
  fileName: 'large.jpg',
  fileMimeType: 'image/jpeg',
  file: File('pics/large.jpg'),
  onProgress: (percent) {
    print('Uploaded ${percent.toStringAsFixed(2)}%');