attache

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

Upload

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.

Download

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 /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

Configure

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.

Asynchronous upload (and delete)

By default attache will upload to 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 weird reason you'd want the upload to cloud storage to be synchronous, set INLINE_UPLOAD=1 instead.

Cloud Storage Virtual Host

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.

export VHOST=`ruby -ryaml -rjson -e 'puts YAML.load(IO.read("config/vhost.yml")).to_json'`

Virtual Host Authorization

By default attache will accept uploads and delete requests from any client.

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)

This will be transparent to you when using integration libraries like attache_rails gem

Run

attache is a Procfile-based app, to run

foreman start

See foreman for more details.

Todo

Instead of an error, we should "resize" non-image files too. The response should just be a visual representation (image) of the file that was uploaded. i.e. if the file pdf, it is reasonable to respond with a pdf icon (or it's cover page) as an image.

License

MIT