attache

If you're interested in the "why", checkout my slides and the blog post.

Your app can easily support

• dynamic resize of images (no predefined styles in your app)
• all file types since attache let apps display non-image files as icons through <img src...>
• resumeable upload over unreliable (mobile) networks using TUS protocol

You can run your own instance on your own Heroku server

docker run -it -p 9292:5000 --rm attache/attache

Also, see Deploying Attache on Digital Ocean using Docker

You can install the gem and then execute attache command

gem install attache
attache start -c web=1 -p 9292

NOTE: some config files will be written into your current directory

.
├── Procfile
├── config
│   ├── puma.rb
│   └── vhost.yml
└── config.ru

You can also use bundler to manage the gem; add this into your Gemfile

gem 'attache'

then execute

bundle install
bundle exec attache start -c web=1 -p 9292

NOTE: some config files will be written into your current directory (see RubyGems above)

You can checkout the source code and run it like a regular a Procfile-based app:

git clone https://github.com/choonkeat/attache.git
cd attache
bundle install
foreman start -c web=1 -p 9292

See foreman for more details.

LOCAL_DIR is where your local disk cache will be. By default, attache will use a system assigned temporary directory which may not be the same everytime you run attache.

CACHE_SIZE_BYTES determines how much disk space will be used for the local disk cache. If the size of cache exceeds, least recently used files will be evicted after CACHE_EVICTION_INTERVAL_SECONDS duration.

By default attache will delete files from cloud storage using the lightweight, async processing library sucker_punch. This requires no additional setup (read: 1x free dyno).

However if you prefer a more durable queue for reliable uploads, configuring REDIS_PROVIDER or REDIS_URL will switch attache to use a redis queue instead, via sidekiq. Read Sidekiq's documentation for details on these variables.

If for some reason you'd want the cloud storage delete to be synchronous, set INLINE_JOB=1 instead.

attache uses a different config (and backup files into a different cloud service) depending on the request hostname that it was accessed by.

This means a single attache server can be the workhorse for different apps. Refer to config/vhost.example.yml file for configuration details.

At boot time, attache server will first look at VHOST environment variable. If that is missing, it will load the content of config/vhost.yml. If neither exist, the attache server run in development mode; uploaded files are only stored locally and may be evicted to free up disk space.

If you do not want to write down sensitive information like aws access key and secrets into a config/vhost.yml file, you can convert the entire content into json format and assign it to the VHOST environment variable instead.

# bash
export VHOST=$(bundle exec rake attache:vhost)

# heroku
heroku config:set VHOST=$(bundle exec rake attache:vhost)

By default attache will accept uploads and delete requests from any client. Set SECRET_KEY to ensure attache only receives upload (and delete commands) from your own app.

To most app developers using attache in your rails app through a library like attache-rails gem, how this work may not matter. But if you are developing attache itself or writing a client library for attache, then read on.

When SECRET_KEY is set, attache will require a valid hmac parameter in the upload request. Upload and Delete requests will be refused with HTTP 401 error unless the hmac is correct.

The additional parameters required for authorized request are:

• uuid is a uuid string
• expiration is a unix timestamp of a future time. the significance is, if the timestamp has passed, the upload will be regarded as invalid
• hmac is the HMAC-SHA1 of the SECRET_KEY and the concatenated value of uuid and expiration

i.e.

hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha1'), SECRET_KEY, uuid + expiration)

The attache server is a reference implementation of these interfaces. If you write your own server, compatibility can be verified by running a test suite.

Users will upload files directly into the attache server from their browser, bypassing the main app.

PUT /upload?file=image123.jpg

file content is the http request body

The main app front end will receive a unique path for each uploaded file - the only information to store in the main app database.

{"path":"pre/fix/image123.jpg","content_type":"image/jpeg","geometry":"1920x1080"}

json response from attache after upload.

GET /upload_url?url=https://example.com/logo.png

Attache will download the file from url supplied and uploads it through the regular /upload handler. So be expecting the same json response after upload. works with GET, POST, PUT.

Data URIs (aka base64 encoded file binaries) can also be uploaded to the same /upload_url endpoint through the same url parameter.

Whenever the main app wants to display the uploaded file, constrained to a particular size, it will use a helper method provided by the attache lib. e.g. embed_attache(path) which will generate the necessary, barebones markup.

<img src="https://example.com/view/pre/fix/100x100/image123.jpg" />

use the imagemagick resize syntax to specify the desired output.

make sure to escape the geometry string. e.g. for a hard crop of 50x50#, the url should be 50x50%23

<img src="https://example.com/view/pre/fix/50x50%23/image123.jpg" />

requesting for a geometry of original will return the uploaded file. this works well for non-image file uploads. requesting for a geometry of remote will skip the local cache and serve from cloud storage.

• Attache keeps the uploaded file in the local harddisk (a temp directory)
• Attache will also upload the file into cloud storage if FOG_CONFIG is set
• If the local file does not exist for some reason (e.g. cleared cache), it will download from cloud storage and store it locally
• When a specific size is requested, it will generate the resized file based on the local file and serve it in the http response
• If cloud storage is defined, local disk cache will store up to a maximum of CACHE_SIZE_BYTES bytes. By default CACHE_SIZE_BYTES will 80% of available diskspace

DELETE /delete
paths=image1.jpg%0Aprefix2%2Fimage2.jpg%0Aimage3.jpg

Removing 1 or more files from the local cache and remote storage can be done via a http POST or DELETE request to /delete, with a paths parameter in the request body.

The paths value should be delimited by the newline character, aka \n. In the example above, 3 files will be requested for deletion: image1.jpg, prefix2/image2.jpg, and image3.jpg.

POST /backup
paths=image1.jpg%0Aprefix2%2Fimage2.jpg%0Aimage3.jpg

This feature might be known as promote in other file upload solutions. attache allows client app to backup uploaded images to another bucket for longer term storage.

Copying 1 or more files from the default remote storage to the backup remote storage (backup) can be done via a http POST request to /backup, with a paths parameter in the request body.

The paths value should be delimited by the newline character, aka \n. In the example above, 3 files will be requested for backup: image1.jpg, prefix2/image2.jpg, and image3.jpg.

If backup remote storage is not configured, this API call will be a noop. If configured, the backup storage must be accessible by the same credentials as default cloud storage as the system. Please refer to the BACKUP_CONFIG configuration illustrated in config/vhost.example.yml file in this repository.

By default, backup operation is performed synchronously. Set BACKUP_ASYNC environment variable to make it follow the same synchronicity as delete

The main reason to configure a backup storage is to make the default cloud storage auto expire files; mitigating abuse. You should consult the documentation of your cloud storage provider on how to setup auto expiry, e.g. here or here

MIT