Rack::Chain uses fibers to minimize stack depth in Rack applications.
A Rack application assembled with Rack::Chain runs each middleware
#call in a separate fiber, thereby avoiding deep stacks.
The name "chain" comes from javax.servlet.FilterChain, which is the
equivalent pattern to Rack middleware in the Java Servlet API.
Until the Rack API morphs into a before/after pattern which would allow decomposing the request pipeline into a flat sequence of function applications over a request and a response, these kinds of cheeky gyrations may be necessary.
Because Rack::Chain relies on fibers for its operation, Ruby 1.9 is required.
To use Rack::Chain with existing Rack applications, place the
following lines in your config.ru:
require 'rack/chain'
extend Rack::Chain::Linker