Add rack.response_finished to Rack::Lint

This updates Rack::Lint to validate that `rack.response_finished` is an
array of callables when present in the `env`. e.g. procs, lambdas, or
objects that respond to `call`.

This validates that:

* `rack.response_finished` is an array
* The contents of the array all respond to `call`

SPEC.rdoc

@@ -137,6 +137,7 @@ There are the following restrictions:
   set. <tt>PATH_INFO</tt> should be <tt>/</tt> if
   <tt>SCRIPT_NAME</tt> is empty.
   <tt>SCRIPT_NAME</tt> never should be <tt>/</tt>, but instead be empty.
+<tt>rack.response_finished</tt>:: An array of callables run after the HTTP response has been sent.
 
 === The Input Stream
 

lib/rack.rb

@@ -59,6 +59,7 @@ module Rack
   RACK_HIJACK                         = 'rack.hijack'
   RACK_IS_HIJACK                      = 'rack.hijack?'
   RACK_HIJACK_IO                      = 'rack.hijack_io'
+  RACK_RESPONSE_FINISHED              = 'rack.response_finished'
   RACK_RECURSIVE_INCLUDE              = 'rack.recursive.include'
   RACK_MULTIPART_BUFFER_SIZE          = 'rack.multipart.buffer_size'
   RACK_MULTIPART_TEMPFILE_FACTORY     = 'rack.multipart.tempfile_factory'

lib/rack/lint.rb

@@ -356,6 +356,15 @@ def check_environment(env)
         unless env[SCRIPT_NAME] != "/"
           raise LintError, "SCRIPT_NAME cannot be '/', make it '' and PATH_INFO '/'"
         end
+
+        ## <tt>rack.response_finished</tt>:: An array of callables run after the HTTP response has been sent.
+        if callables = env[RACK_RESPONSE_FINISHED]
+          raise LintError, "rack.response_finished must be an array of callable objects" unless callables.is_a?(Array)
+
+          callables.each do |callable|
+            raise LintError, "rack.response_finished values must respond to call" unless callable.respond_to?(:call)
+          end
+        end
       end
 
       ##

test/spec_lint.rb

@@ -204,6 +204,16 @@ def obj.error(*) end
       Rack::Lint.new(nil).call(env("SCRIPT_NAME" => "/"))
     }.must_raise(Rack::Lint::LintError).
       message.must_match(/cannot be .* make it ''/)
+
+    lambda {
+      Rack::Lint.new(nil).call(env("rack.response_finished" => "not a callable"))
+    }.must_raise(Rack::Lint::LintError).
+    message.must_match(/rack.response_finished must be an array of callable objects/)
+
+    lambda {
+      Rack::Lint.new(nil).call(env("rack.response_finished" => [->{}, "not a callable"]))
+    }.must_raise(Rack::Lint::LintError).
+    message.must_match(/rack.response_finished values must respond to call/)
   end
 
   it "notice input errors" do
@@ -731,6 +741,12 @@ def assert_lint(*args)
                      }).call(env({}))[1]['rack.hijack'].call(StringIO.new).read.must_equal ''
   end
 
+  it "pass valid rack.response_finished" do
+    Rack::Lint.new(lambda { |env|
+                     [200, { "rack.response_finished" => [-> {}, lambda {}], "Content-length" => "3" }, ["foo"]]
+                   }).call(env({})).first.must_equal 200
+  end
+
 end
 
 describe "Rack::Lint::Wrapper::InputWrapper" do