Allow the Rack handler to be configured via Capybara.server {|app, port| ...}

For example, to use mongrel rather than thin or webrick:

    Capybara.server do |app, port|
      require 'rack/handler/mongrel'
      Rack::Handler::Mongrel.run(app, :Port => port)
    end

lib/capybara.rb

@@ -108,6 +108,38 @@ module Capybara
       @drivers ||= {}
     end
 
+    ##
+    #
+    # Register a proc that Capybara will call to run the Rack application.
+    #
+    #     Capybara.server do |app, port|
+    #       require 'rack/handler/mongrel'
+    #       Rack::Handler::Mongrel.run(app, :Port => port)
+    #     end
+    #
+    # By default, Capybara will try to run thin, falling back to webrick.
+    #
+    # @yield [app, port]                      This block recieves a rack app and port and should run a Rack handler
+    #
+    def server(&block)
+      if block_given?
+        @server = block
+      else
+        @server
+      end
+    end
+
+    def run_default_server(app, port)
+      begin
+        require 'rack/handler/thin'
+        Thin::Logging.silent = true
+        Rack::Handler::Thin.run(app, :Port => port)
+      rescue LoadError
+        require 'rack/handler/webrick'
+        Rack::Handler::WEBrick.run(app, :Port => port, :AccessLog => [], :Logger => WEBrick::Log::new(nil, 0))
+      end
+    end
+
     def deprecate(method, alternate_method)
       warn "DEPRECATED: ##{method} is deprecated, please use ##{alternate_method} instead"
     end
@@ -133,6 +165,7 @@ end
 
 Capybara.configure do |config|
   config.run_server = true
+  config.server {|app, port| Capybara.run_default_server(app, port)}
   config.default_selector = :css
   config.default_wait_time = 2
   config.ignore_hidden_elements = false

lib/capybara/server.rb

@@ -62,14 +62,7 @@ module Capybara
           Capybara::Server.ports[@app.object_id] = @port
 
           Thread.new do
-            begin
-              require 'rack/handler/thin'
-              Thin::Logging.silent = true
-              Rack::Handler::Thin.run(Identify.new(@app), :Port => @port)
-            rescue LoadError
-              require 'rack/handler/webrick'
-              Rack::Handler::WEBrick.run(Identify.new(@app), :Port => @port, :AccessLog => [], :Logger => WEBrick::Log::new(nil, 0))
-            end
+            Capybara.server.call(Identify.new(@app), @port)
           end
 
           Capybara.timeout(10) { if responsive? then true else sleep(0.5) and false end }

spec/capybara_spec.rb

@@ -25,4 +25,22 @@ describe Capybara do
     end
   end
 
+  describe ".server" do
+    after do
+      Capybara.server {|app, port| Capybara.run_default_server(app, port)}
+    end
+
+    it "should default to a proc that calls run_default_server" do
+      mock_app = mock('app')
+      Capybara.should_receive(:run_default_server).with(mock_app, 8000)
+      Capybara.server.call(mock_app, 8000)
+    end
+
+    it "should return a custom server proc" do
+      server = lambda {|app, port|}
+      Capybara.server(&server)
+      Capybara.server.should == server
+    end
+  end
+
 end