Enable gzip compression by default

If someone is using ActionDispatch::Static to serve assets and makes it past the `match?` then the file exists on disk and it will be served. This PR adds in logic that checks to see if the file being served is already compressed (via gzip) and on disk, if it is it will be served as long as the client can handle gzip encoding. If not, then a non gzip file will be served.

This additional logic slows down an individual asset request but should speed up the consumer experience as compressed files are served and production applications should be delivered with a CDN. This PR allows a CDN to cache a gzip file by setting the `Vary` header appropriately. In net this should speed up a production application that are using Rails as an origin for a CDN. Non-asset request speed is not affected in this PR.

actionpack/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Requests that hit `ActionDispatch::Static` can now take advantage
+    of gzipped assets on disk. By default a gzip asset will be served if
+    the client supports gzip and a compressed file is on disk.
+
+    *Richard Schneeman*
+
 *   `ActionController::Parameters` will stop inheriting from `Hash` and
     `HashWithIndifferentAccess` in the next major release. If you use any method
     that is not available on `ActionController::Parameters` you should consider

actionpack/lib/action_dispatch/middleware/static.rb

@@ -16,8 +16,9 @@ module ActionDispatch
     def initialize(root, cache_control)
       @root          = root.chomp('/')
       @compiled_root = /^#{Regexp.escape(root)}/
-      headers = cache_control && { 'Cache-Control' => cache_control }
-      @file_server   = ::Rack::File.new(@root, headers)
+      headers        = {}
+      headers['Cache-Control'] = cache_control if cache_control
+      @file_server = ::Rack::File.new(@root, headers)
     end
 
     def match?(path)
@@ -36,23 +37,48 @@ module ActionDispatch
     end
 
     def call(env)
-      @file_server.call(env)
-    end
-
-    def ext
-      @ext ||= begin
-        ext = ::ActionController::Base.default_static_extension
-        "{,#{ext},/index#{ext}}"
+      path             = env['PATH_INFO']
+      gzip_file_exists = gzip_file_exists?(path)
+      if gzip_file_exists && gzip_encoding_accepted?(env)
+        env['PATH_INFO'] = "#{path}.gz"
+        status, headers, body       = @file_server.call(env)
+        headers['Content-Encoding'] = 'gzip'
+        headers['Content-Type']     = content_type(path)
+      else
+        status, headers, body = @file_server.call(env)
       end
+
+      headers['Vary'] = 'Accept-Encoding' if gzip_file_exists
+      return [status, headers, body]
     end
 
-    def unescape_path(path)
-      URI.parser.unescape(path)
-    end
+    private
+      def ext
+        @ext ||= begin
+          ext = ::ActionController::Base.default_static_extension
+          "{,#{ext},/index#{ext}}"
+        end
+      end
 
-    def escape_glob_chars(path)
-      path.gsub(/[*?{}\[\]]/, "\\\\\\&")
-    end
+      def unescape_path(path)
+        URI.parser.unescape(path)
+      end
+
+      def escape_glob_chars(path)
+        path.gsub(/[*?{}\[\]]/, "\\\\\\&")
+      end
+
+      def content_type(path)
+        ::Rack::Mime.mime_type(::File.extname(path), 'text/plain')
+      end
+
+      def gzip_encoding_accepted?(env)
+        env['HTTP_ACCEPT_ENCODING'] =~ /\bgzip\b/
+      end
+
+      def gzip_file_exists?(path)
+        File.exist?(File.join(@root, "#{::Rack::Utils.unescape(path)}.gz"))
+      end
   end
 
   # This middleware will attempt to return the contents of a file's body from

actionpack/test/dispatch/static_test.rb

@@ -1,6 +1,7 @@
 # encoding: utf-8
 require 'abstract_unit'
 require 'rbconfig'
+require 'zlib'
 
 module StaticTests
   def test_serves_dynamic_content
@@ -106,6 +107,18 @@ module StaticTests
     end
   end
 
+  def test_serves_gzip_files_when_header_set
+    file_name = "/gzip/application-a71b3024f80aea3181c09774ca17e712.js"
+    response  = get(file_name, 'HTTP_ACCEPT_ENCODING' => 'gzip')
+    assert_gzip  file_name, response
+    assert_equal 'application/javascript', response.headers['Content-Type']
+    assert_equal 'Accept-Encoding',        response.headers["Vary"]
+    assert_equal 'gzip',                   response.headers["Content-Encoding"]
+
+    response  = get(file_name, 'HTTP_ACCEPT_ENCODING' => '')
+    refute_equal 'gzip', response.headers["Content-Encoding"]
+  end
+
   # Windows doesn't allow \ / : * ? " < > | in filenames
   unless RbConfig::CONFIG['host_os'] =~ /mswin|mingw/
     def test_serves_static_file_with_colon
@@ -125,13 +138,20 @@ module StaticTests
 
   private
 
+    def assert_gzip(file_name, response)
+      expected = File.read("#{FIXTURE_LOAD_PATH}/#{public_path}" + file_name)
+      actual   = Zlib::GzipReader.new(StringIO.new(response.body)).read
+      assert_equal expected, actual
+    end
+
     def assert_html(body, response)
       assert_equal body, response.body
       assert_equal "text/html", response.headers["Content-Type"]
+      refute response.headers.key?("Vary")
     end
 
-    def get(path)
-      Rack::MockRequest.new(@app).request("GET", path)
+    def get(path, headers = {})
+      Rack::MockRequest.new(@app).request("GET", path, headers)
     end
 
     def with_static_file(file)