Added the JSONP middleware and specs.

lib/rack/jsonp.rb

@@ -0,0 +1,38 @@
+module Rack
+
+  # A Rack middleware for providing JSON-P support.
+  # 
+  # Full credit to Flinn Mueller (http://actsasflinn.com/) for this contribution.
+  # 
+  class JSONP
+
+    def initialize(app)
+      @app = app
+    end
+
+    # Proxies the request to the application, stripping out the JSON-P callback
+    # method and padding the response with the appropriate callback format.
+    # 
+    # Changes nothing if no <tt>callback</tt> param is specified.
+    # 
+    def call(env)
+      status, headers, response = @app.call(env)
+      request = Rack::Request.new(env)
+      response = pad(request.params.delete('callback'), response) if request.params.include?('callback')
+      [status, headers, response]
+    end
+
+    # Pads the response with the appropriate callback format according to the
+    # JSON-P spec/requirements.
+    # 
+    # The Rack response spec indicates that it should be enumerable. The method
+    # of combining all of the data into a sinle string makes sense since JSON
+    # is returned as a full string.
+    # 
+    def pad(callback, response, body = "")
+      response.each{ |s| body << s }
+      "#{callback}(#{body})"
+    end
+
+  end
+end

test/spec_rack_jsonp.rb

@@ -0,0 +1,20 @@
+# require 'rack/mock'
+require 'rack/jsonp'
+
+context "Rack::JSONP" do
+
+  specify "should wrap the response body in the Javascript callback when provided" do
+    app = lambda { |env| [200, {'Content-Type' => 'text/plain'}, '{"bar":"foo"}'] }
+    request = Rack::MockRequest.env_for("/", :input => "foo=bar&callback=foo")
+    body = Rack::JSONP.new(app).call(request).last
+    body.should == 'foo({"bar":"foo"})'
+  end
+
+  specify "should not change anything if no :callback param is provided" do
+    app = lambda { |env| [200, {'Content-Type' => 'text/plain'}, '{"bar":"foo"}'] }
+    request = Rack::MockRequest.env_for("/", :input => "foo=bar")
+    body = Rack::JSONP.new(app).call(request).last
+    body.should == '{"bar":"foo"}'
+  end
+
+end