module Shrine::Plugins::PresignEndpoint

  1. lib/shrine/plugins/presign_endpoint.rb

The presign_endpoint plugin provides a Rack endpoint which generates the URL, fields, and headers that can be used to upload files directly to a storage service. It can be used with client-side file upload libraries like [FineUploader], [Dropzone] or [jQuery-File-Upload] for asynchronous uploads. Storage services that support direct uploads include Amazon S3, Google Cloud Storage, Microsoft Azure Storage and more.

plugin :presign_endpoint

The plugin adds a Shrine.presign_endpoint method which accepts a storage identifier and returns a Rack application that accepts GET requests and generates a presign for the specified storage.

Shrine.presign_endpoint(:cache) # rack app

Asynchronous upload is typically meant to replace the caching phase in the default synchronous workflow, so we want to generate parameters for uploads to the temporary (:cache) storage.

We can mount the returned Rack application inside our application:

Rails.application.routes.draw do
  mount Shrine.presign_endpoint(:cache) => "/presign"

The above will create a GET /presign endpoint, which generates presign URL, fields, and headers using the specified storage, and returns it in JSON format.

# GET /presign
  "url": "",
  "fields": {
    "key": "b7d575850ba61b44c8a9ff889dfdb14d88cdc25f8dd121004c8",
    "policy": "eyJleHBpcmF0aW9uIjoiMjAxNS0QwMToxMToyOVoiLCJjb25kaXRpb25zIjpbeyJidWNrZXQiOiJzaHJpbmUtdGVzdGluZyJ9LHsia2V5IjoiYjdkNTc1ODUwYmE2MWI0NGU3Y2M4YTliZmY4OGU5ZGZkYjE2NTQ0ZDk4OGNkYzI1ZjhkZDEyMTAwNGM4In0seyJ4LWFtei1jcmVkZW50aWFsIjoiQUtJQUlKRjU1VE1aWlk0NVVUNlEvMjAxNTEwMjQvZXUtd2VzdC0xL3MzL2F3czRfcmVxdWVzdCJ9LHsieC1hbXotYWxnb3JpdGhtIjoiQVdTNC1ITUFDLVNIQTI1NiJ9LHsieC1hbXotZGF0ZSI6IjIwMTUxMDI0VDAwMTEyOVoifV19",
    "x-amz-credential": "AKIAIJF55TMZYT6Q/20151024/eu-west-1/s3/aws4_request",
    "x-amz-algorithm": "AWS4-HMAC-SHA256",
    "x-amz-date": "20151024T001129Z",
    "x-amz-signature": "c1eb634f83f96b69bd675f535b3ff15ae184b102fcba51e4db5f4959b4ae26f4"
  "headers": {}

This gives the client all the information it needs to make the upload request to the selected file to the storage service. The url field is the request URL, fields are the required POST parameters, and headers are the required request headers.


By default the generated location won't have any file extension, but you can specify one by sending the filename query parameter:

GET /presign?filename=nature.jpg

It's also possible to customize how the presign location is generated:

plugin :presign_endpoint, presign_location: -> (request) do


Some storages accept additional presign options, which you can pass in via :presign_options:

plugin :presign_endpoint, presign_options: -> (request) do
  filename     = request.params["filename"]
  extension    = File.extname(filename)
  content_type = Rack::Mime.mime_type(extension)

    content_length_range: 0..(10*1024*1024),                     # limit filesize to 10MB
    content_disposition: "attachment; filename=\"#{filename}\"", # download with original filename
    content_type:        content_type,                           # set correct content type


You can also customize how the presign itself is generated via the :presign option:

plugin :presign_endpoint, presign: -> (id, options, request) do
  # return an object that responds to #url, #fields, and #headers


The response returned by the endpoint can be customized via the :rack_response option:

plugin :presign_endpoint, rack_response: -> (hash, request) do
  body = { endpoint: hash[:url], params: hash[:fields], headers: hash[:headers] }.to_json
  [201, { "Content-Type" => "application/json" }, [body]]

Ad-hoc options

You can override any of the options above when creating the endpoint:

Shrine.presign_endpoint(:cache, presign_location: "${filename}")


Public Class

  1. configure

Public Class methods

configure (uploader, opts = {})
[show source]
# File lib/shrine/plugins/presign_endpoint.rb, line 114
def self.configure(uploader, opts = {})
  uploader.opts[:presign_endpoint_presign_location] = opts.fetch(:presign_location, uploader.opts[:presign_endpoint_presign_location])
  uploader.opts[:presign_endpoint_presign_options] = opts.fetch(:presign_options, uploader.opts[:presign_endpoint_presign_options])
  uploader.opts[:presign_endpoint_presign] = opts.fetch(:presign, uploader.opts[:presign_endpoint_presign])
  uploader.opts[:presign_endpoint_rack_response] = opts.fetch(:rack_response, uploader.opts[:presign_endpoint_rack_response])