HTTP push middleware for Rack powered by Stash.

Need events delivered to an HTTP client in realtime? Perhaps you've investigated solutions like Comet/Bayeux, BOSH, or WebSockets. Not happy with those solutions and just want something simple?

Pistachio provides a simple HTTP long polling middleware for Rack, which is backed by the Stash gem. Stash provides an abstract interface to data structures servers, namely Redis. Servers like Redis provide a list data type, which can easily be used as a message queue. Redis also supports a “blocking pop” from a list, where clients will either receive the next message in the list immediately, or if the list is empty Redis will block until the next message is available (or a timeout occurs).

Pistachio combines this all into a single, easy-to-use Rack middleware for delivering realtime push notification events to HTTP clients like web browsers.

Using Pistachio in your Rack application

Add the following to your config.ru file:

Pistachio.setup :default, :adapter   => :redis, 
                          :namespace => 'myapp_name',
                          :path      => '/message_path'

use Pistachio::Middleware

This will configure Pistachio to talk to Redis, store its messages in the 'myapp_name' Redis namespace, and mount the Pistachio Rack middleware under the /message_path path.

All messages must be sent to a given named endpoint. To send a message via Pistachio within your Rack application, do:

Pistachio[:foobar] << "my totally awesome message"

Messages sent to the 'foobar' endpoint can be retrieved by making an HTTP GET request to /message_path/foobar. This will return one of two HTTP statuses:

  • 200: a message was retrieved successfully

  • 504: the request timed out before a message was received

By default Pistachio uses a 30 second timeout. You can adjust this with the ':timeout' parameter to Pistachio.setup.

It's the responsibility of the client to hit the given message endpoint in a loop. If the client gets a 504 response it should retry. Any other HTTP responses should be considered errors, in which case it'd be good if the client utilized exponential backoff to avoid hammering Pistachio when errors are occurring.

No reference clients are presently available. Pull requests happily accepted!

Copyright © 2010 Tony Arcieri. See file LICENSE for further details.