Goal of this lesson is to understand what middlewares in Rack are good for.

Rack

Start with these articles:

• Rails on Rack Show archive.org snapshot
• Introduction to Rack Middleware Show archive.org snapshot
• Short Screencast to a sample Middleware Show archive.org snapshot

You should be able to answer the following questions:

• What is Rack?
• How does Rack relate to Ruby on Rails?
• What is Rack middleware?
• What are some advantages of implementing functionality as a middleware as opposed to e.g. a before_filter in ApplicationController?

Rails middleware

Now look at the middleware stack of a freshly installed Rails application Show archive.org snapshot . For each middleware in the stack:

• What does it do?
• What would happen if we removed it from the stack?
• Can you find the code that implements it?

Exception Notification

We are using the exception_notification gem to receive an e-mail whenever one of our apps raises an unhandled exception.

Look through the repo Show archive.org snapshot and understand how it does this (hint: it’s a middleware!).

Excercises

• Write a Middleware that makes a Rails application respond to GET /hello when added to the middleware stack. The path would simply print HI WORLD with a text/plain content type.
• Write a Middleware that prints OUCH to the screen whenever the Rails application raises an unhandled error.