Hi,
What is rack middleware?
Thanks.
A:
First result in Google, first line of text in that result:
Rack middleware is a way to filter a request and response coming into your application.
Source: RailCasts
Charlie Salts
2010-02-13 07:23:40
+9
A:
Rack as design
Rack middleware is more than "a way to filter a request and response" - it's an implementation of the pipeline design pattern for web servers using Rack.
It very cleanly separates out the different stages of processing a request - separation of concerns being a key goal of all well designed software products.
For example with Rack I can have separate stages of the pipleline doing
Authentication - when the request arrives, are the users logon details correct? How do I validate this OAuth, HTTP Basic Authentication, name/password?
Authorisation - is the user authorised to perform this particular task i.e. role-based security
Caching - have I processed this request already, can I return a cached result?
Decoration - how can I enhance the request to make downstream processing better
Performance & Usage Monitoring - what stats can I get from the request & response?
Execution - actually handle the request and provide a response
Being able to separate the different stages (and optionally include them) is a great help in developing well structured applications
Community
There's also a great eco-system developing around Rack Middleware - you should be able to find pre-built rack components to do all of the steps above and more see here
What's middleware?
Middleware is a dreadful term which refers to any software component/library which assists with but is not directly involved in the execution of some task. Very common examples are logging, authentication and the other common, horizontal processing components. These tend to be the things that everyone needs across multiple applications but not too many people are interested (or should be) in building themselves.
More information
The comment about it being a way to filter requests probably comes from this screencast.
Rack middleware evolved out of Rack and there is a great intro here
There's an intro to middleware here
Chris McCauley
2010-02-13 09:08:43
Fantastic answer +1
Sam Saffron
2010-02-14 00:12:18
One thing I'm unclear on: do all the middleware share the same data? Is it possible to separate them (i.e. sandbox one) for security?
Brian Armstrong
2010-03-25 08:00:22
Rack is part of your application so all middleware componets the same copy of the request and each can modify it in any way they want. AFAIK, there's no way to sandbox them the same way there's no way to sandbox one object from another within the same process (attempts at Ruby sandboxing notwithstanding).
Chris McCauley
2010-03-25 08:35:12