This article is part of the “Better File Uploads with Shrine” series.

So far we were talking about the server side of handling file uploads. However, there is a lot that we can also do on the client side to improve user experience and performance.

Let’s say we have a Photo model with an #image attachment attribute handled by an ImageUploader :

class Photo < Sequel :: Model include ImageUploader :: Attachment ( :image ) end

class ImageUploader < Shrine # ... end

The simplest file upload worfklow is having a vanilla form with a file field for selecting files, and also a hidden field for retaining uploaded files in case of validation errors.

# for retaining selected files across form redisplays Shrine . plugin :cached_attachment_data

<form action= "/photos" method= "post" enctype= "multipart/form-data" > <input type= "hidden" name= "photo[image]" value= " <%= photo . cached_image_data %> " class= "attachment-field" /> <input type= "file" name= "photo[image]" class= "attachment-field" /> <input type= "submit" value= "Submit" /> </form>

This alone provides a basic uploading user experience. There are many obvious limitations with the static approach:

When the user submits the form with selected files, there is no indicator telling them when the upload will finish.

When the user is uploading multiple files at once and the request happens to get aborted, it’s not possible to keep the files that were uploaded so far, because all files are sent in a single request. In other words, multiple uploads are all-or-nothing.

Files are validated only after they have been uploaded, which means the user needs to wait until the upload finishes before they can know whether their file was even valid.

We can improve that by asynchronously starting to upload files on the client side as soon as they’re selected. This also gives users the ability to continue filling in other fields while files are being uploaded, because the UI isn’t blocked during the upload.

There are many popular JavaScript file upload libraries out there – jQuery-File-Upload, Dropzone.js, FineUploader etc. – but the one you should use with Shrine is definitely Uppy . Uppy is a modular library that knows how to upload files to a custom endpoint on your app, to Amazon S3, or even to a resumable endpoint, providing progress bars, drag & drop functionality, image previews, file validations etc, all while making as few assumptions as possible.

var uppy = Uppy . Core ({ /* ... */ }) . use ( Uppy . FileInput , { /* ... */ }) // adds a pretty file field . use ( Uppy . ProgressBar , { /* ... */ }) // displays a progress bar . use ( Uppy . Informer , { /* ... */ }) // displays validation errors // ...

I find using a generic JavaScript library much more future-proof than relying on homegrown solutions such as the ones that Refile and ActiveStorage offer. That’s why Shrine doesn’t come with its own JavaScript; it can be convenient when you want to get up and running quickly, but it could never match the power and stability of a library that’s maintained by the whole JavaScript community.

Theory

The idea is to have a generic endpoint which accepts file uploads and saves the uploads to a temporary storage. The reason for uploading to a separate temporary storage is security; if we allowed users to upload directly to the primary storage, they would be able to flood it if they wanted to, as directly uploaded files don’t have to necessarily end up being attached to a record.

POST http://example.com/upload HTTP / 1.1 [... file content ...]

On the client side we would asynchronously upload selected files to this endpoint, and then send only the information about the cached files on form submission. Once validation has passed and the record has been successfully saved, Shrine would automatically upload the cached file to permanent storage.

In fact, Shrine already handles attachments this way. When a file is attached, Shrine first uploads it to temporary storage, and then once the record has been successfully saved the cached file is uploaded to permanent storage.

photo . image = File . open ( "..." ) # files gets uploaded to temporary storage photo . image # cached file photo . save photo . image # stored file

With direct uploads the only difference is that files are uploaded to temporary storage prior to attachment, and then the information about the cached file is assigned instead of an actual file, in which case Shrine skips the caching step.

photo . image = '{"id":"...","storage":"cache","metadata":{...}}' photo . image # cached file that we assigned photo . save photo . image # stored file

1. Simple upload

The simplest way we could enable direct uploads is to create an upload endpoint in our app. Shrine comes with an upload_endpoint plugin which allows you to create a Rack application that accepts file uploads and forwards them to the specified storage. The only thing we need to do is mount the app to our preferred path:

Shrine . plugin :upload_endpoint

Rails . application . routes . draw do mount Shrine . upload_endpoint ( :cache ) => "/upload" end

The above gives our application a POST /upload endpoint which accepts the file multipart parameter and returns uploaded file data:

POST /upload HTTP / 1.1 Content-Type : multipart/form-data [... file content ...]

HTTP / 1.1 200 OK Content-Type : application/json { "id" : "70be82a657ba9ef892ef5182a1a18bde.jpg" , "storage" : "cache" , "metadata" : { "size" : 3942146 , "filename" : "nature.jpg" , "mime_type" : "image/jpeg" } }

Because Shrine’s upload endpoint is a pure Rack application, it can be run inside any Rack-based Ruby web framework (Sinatra, Roda, Cuba, Hanami, Grape etc), not just Rails. The :cache argument to Shrine.upload_endpoint specifies that incoming files will be uploaded to the configured temporary storage.

Client side

On the client side we just need to add the XHRUpload Uppy plugin and point it to this endpoint.

// ... other plugins ... uppy . use ( Uppy . XHRUpload , { endpoint : ' /upload ' , }) uppy . on ( ' upload-success ' , function ( file , response ) { var uploadedFileData = JSON . stringify ( response . body ) var hiddenField = document . querySelector ( ' .attachment-field[type=hidden] ' ) hiddenField . value = uploadedFileData })

Notice that the response of Shrine’s upload endpoint already contains the uploaded file data in the format that can be assigned, so the only thing left to do is convert it to JSON and write it to the hidden attachment field to be submitted as the attachment.

2. Amazon S3

Uploading files to our app isn’t always the most suitable option. In most cases we don’t want store uploaded files on disk, but rather on a cloud service like Amazon S3, Google Cloud Storage or Microsoft Azure Storage, especially if our app is running on Heroku or on multiple servers. In that case, instead of uploading files to our app and then to the cloud service, it’s more performant to skip the app and upload directly to the cloud.

First we tell Shrine that we’ll be using S3 both for temporary and permanent storage, but specify separate directories:

# Gemfile gem "aws-sdk-s3" , "~> 1.2"

require "shrine/storage/s3" Shrine . storages = { cache: Shrine :: Storage :: S3 . new ( prefix: "cache" , ** options ), store: Shrine :: Storage :: S3 . new ( ** options ), }

The client side flow mostly stays the same, except that the browser now needs to ask the server for the upload URL and request parameters on each upload. Shrine has the presign_endpoint plugin which provides a Rack application that generates direct upload parameters, which we can mount in our application:

Shrine . plugin :presign_endpoint , presign_options: { # Uppy will send these two query parameters filename = request . params [ "filename" ] type = request . params [ "type" ] { content_disposition: ContentDisposition . inline ( filename ), # set download filename content_type: type , # set content type (defaults to "application/octet-stream") content_length_range: 0 .. ( 10 * 1024 * 1024 ), # limit upload size to 10 MB } }

Rails . application . routes . draw do mount Shrine . presign_endpoint ( :cache ) => "/s3/params" end

Our application has now gained the GET /s3/params endpoint which will return URL and parameters for direct upload:

GET /s3/params HTTP / 1.1

HTTP / 1.1 200 OK Content-Type : application/json { "url" : "https://your-bucket.s3.us-east-1.amazonaws.com" , "fields" : { "key" : "cache/df65ee371b42b87463b1840d69331692.jpg" , "policy" : "eyJleHBpcmF0aW9uIjoiMjFrs0wMS0wM1QxNzo0MjoxNloiLCJjb25kaXRpb25zIjpbeyJidWNrZXQiOiJzaHJpbmUtdGVzdGluZy0yIn0seyJrZXkiOiJjYWNoZS9kZjY1ZWUzNzFiNDJiODc0NjNiMTg0MGQ2OTMzMTY5Mi5qcGcifSx7IngtYW16LWNyZWRlbnRpYWwiOiJBS0lBSU1ESDJIVFNCM1JLQjRXUS8yMDE4MDEwMy9ldS1jZW50cmFsLTEvczMvYXdzNF9yZXF1ZXN0In0seyJ4LWFtei1hbGdvcml0aG0iOiJBV1M0LUhNQUMtU0hBMjU2In0seyJ4LWFtei1kYXRlIjoiMjAxODAxMDNUMTY0MjE2WiJ9XX0=" , "x-amz-credential" : "AKIAI8FLFDSB3RKB4WQ/20180103/eu-central-1/s3/aws4_request" , "x-amz-algorithm" : "AWS4-HMAC-SHA256" , "x-amz-date" : "20180103T164216Z" , "x-amz-signature" : "6003f73624724fd2e116620ddc77f1073b434c677ddf7070a67445016c62a263" }, "headers" : {}, "method" : "post" }

Client side

On the client side we have the AwsS3 Uppy plugin (instead of XHRUpload). Note that you’ll need to update your S3 bucket’s CORS configuration to allow client side uploads.

The AwsS3 plugin requires us point it to the Uppy Companion app, which implements GET /s3/params . However, since our configured presign_endpoint will have the same behaviour as Uppy Companion, we can point the AwsS3 plugin to our app, where we’ve already mounted the presign_endpoint to /s3/params .

// ... other plugins ... uppy . use ( Uppy . AwsS3 , { companionUrl : ' / ' , // will call `GET /s3/params` on our app }) uppy . on ( ' upload-success ' , function ( file , response ) { var uploadedFileData = JSON . stringify ({ id : file . meta [ ' key ' ]. match ( /^cache \/( .+ ) / )[ 1 ], // remove the Shrine storage prefix storage : ' cache ' , metadata : { size : file . size , filename : file . name , mime_type : file . type , } }) // ... })

You’ll notice that, unlike our simple upload endpoint which generated the uploaded file data for us, in the S3 case we need to construct the uploaded file data ourselves on the client side.

Fetching direct upload parameters dynamically like this is much more flexible than creating a static S3 upload form on page render, which is the approach that CarrierWave and Paperclip ecosystems seem to prefer. A static S3 form won’t work with multiple uploads, as S3 requires that each file has a new set of upload parameters.

Finally, this approach is not specific to Amazon S3, you can use it with any service that supports direct uploads, such as Google Cloud Storage, Cloudinary, Transloadit and others.

3. Resumable upload

For most use cases, direct upload to a custom endpoint or a cloud service should be everything you need. This is because the majority of applications are dealing only with images, documents, or other small files. If your application happens to deal with large files such as videos, things get a bit more interesting.

If you’ve ever used a service where you needed to upload 500MB, 1GB or 5GB files, you know how frustrating when your upload is 80% complete and then it fails, all because you happened to have lost internet connection for a brief moment, or you had to change locations, or your browser/OS crashed. With slow and/or flaky internet connections it might not even be possible to upload larger files, because every time the upload fails it would have to be retried from the beginning.

Tus.io is an open protocol for resumable file uploads built on HTTP. It specifies the behaviour and communication required between client and the server during file upload so that the upload is resumable in case the request failed. Try their demo to see this in action.

There are many server implementations of the tus protocol out there for various languages; in our case we’re interested in tus-ruby-server.

tus-ruby-server + shrine-tus

Tus-ruby-server is implemented using the Roda web framework, and can be mounted inside any Rack-based web framework (including Rails), but you can also run it standalone. While it can run on classic web servers like Unicorn, Puma or Passenger (with a few gotchas), for best performance it’s recommended to use the Falcon web server.

For attaching files that were uploaded to tus-ruby-server we’ll use shrine-tus.

# Gemfile gem "tus-server" , "~> 2.0" gem "shrine-tus" , "~> 1.0"

require "shrine/storage/tus" require "shrine/storage/s3" Shrine . storages = { cache: Shrine :: Storage :: Tus . new , store: Shrine :: Storage :: S3 . new ( ... ), }

# config/routes.rb Rails . application . routes . draw do mount Tus :: Server => "/files" end

The idea is that on the client side we’ll upload files directly to the tus-ruby-server instance, and afterward submit the resulting tus URL as the attachment. Shrine would then take this file and promote to permanent storage. So, tus-ruby-server would essentially act as a temporary storage.

At first, it might sound pointless to do all that effort of uploading the file to tus-ruby-server only to later move it somewhere else. However, server side uploading will be orders of magnitude faster and more reliable, because servers will have much better internet connection compared to average users. And if that’s not enough, shrine-tus can also do a smart copy directly from the tus storage.

Client side

On the client side, Uppy has our backs again with the Tus plugin (instead of XHRUpload or AwsS3), which internally uses tus-js-client. We need to give the Tus plugin the URL to our tus server, and after the upload we need to construct the uploaded file data as we did with direct uploads to S3.

// ... other plugins ... uppy . use ( Uppy . Tus , { endpoint : ' /files/ ' , }) uppy . on ( ' upload-success ' , function ( file , response ) { var uploadedFileData = JSON . stringify ({ id : response . uploadURL , // Shrine will later use this tus URL to download the file storage : " cache " , metadata : { filename : file . name , size : file . size , mime_type : file . type , } }) // ... })

That’s it, now uploads will be automagically resumed in case of temporary failures, without the user even knowing something happened.

AWS S3 Multipart

The tus approach has the advantages of abstracting away the underlying storage, and the fact that there are lots of client and server implementations in various languages to choose from. But one downside is that you’re receiving the uploads, so you need to ensure any necessary scaling.

If you’re using AWS S3 and would like it to handle the uploads, you can do direct multipart uploads using Uppy’s AwsS3Multipart plugin. It requires certain endpoints to be implemented, which are provided by the Uppy Companion app. However, you can use the uppy-s3_multipart gem which implements these endpoints in Ruby, and allows you to mount them into any Rack app:

# Gemfile gem "uppy-s3_multipart"

require "shrine/storage/s3" Shrine . storages = { cache: Shrine :: Storage :: S3 . new ( prefix: "cache" , ** options ), store: Shrine :: Storage :: S3 . new ( ** options ), } Shrine . plugin :uppy_s3_multipart

Rails . application . routes . draw do mount Shrine . uppy_s3_multipart ( :cache ) => "/s3/multipart" end

We’ll also need to update our S3 bucket’s CORS configuration to allow for client side uploads. Then we can configure Uppy’s AwsS3Multipart plugin:

// ... other plugins ... uppy . use ( Uppy . AwsS3Multipart , { companionUrl : ' / ' , // will call `/s3/multipart/*` endpoints on your app }) uppy . on ( ' upload-success ' , function ( file , response ) { var uploadedFileData = JSON . stringify ({ id : response . uploadURL . match ( / \/ cache \/([^\?] + ) / )[ 1 ], // extract key without prefix storage : ' cache ' , metadata : { size : file . size , filename : file . name , mime_type : file . type , } }) // ... })

Now you have direct uploads to S3 which are also resumable.

Conclusion

Uploading files asynchronously greatly improves the user experience, and there are many ways to do that, each suitable for different requirements (storage, filesize etc). In order to implement direct uploads, both the client and the server side need to do their part.

Regardless of whether you’re just uploading to a simple endpoint in your app, directly to cloud, or doing something as advanced as resumable uploads, with Shrine & Uppy the setup is streamlined and is essentially just a matter of swapping plugins.