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Slightly hacky rails middleware for serving up precompiled gzipped assets
require 'action_dispatch/middleware/static'
module Middleware
class FileHandler < ActionDispatch::FileHandler
def initialize(root, assets_path, cache_control)
@assets_path = assets_path.chomp('/') + '/'
super(root, cache_control)
def match?(path)
path.start_with?(@assets_path) && super(path)
class CompressedStaticAssets
def initialize(app, path, assets_path, cache_control=nil)
@app = app
@file_handler =, assets_path, cache_control)
def call(env)
if env['REQUEST_METHOD'] == 'GET'
request =
encoding = Rack::Utils.select_best_encoding(
%w(gzip identity), request.accept_encoding)
if encoding == 'gzip'
pathgz = env['PATH_INFO'] + '.gz'
if match = @file_handler.match?(pathgz)
# Get the filehandler to serve up the gzipped file,
# then strip the .gz suffix
env["PATH_INFO"] = match
status, headers, body =
path = env["PATH_INFO"] = env["PATH_INFO"].chomp('.gz')
# Set the Vary HTTP header.
vary = headers["Vary"].to_s.split(",").map { |v| v.strip }
unless vary.include?("*") || vary.include?("Accept-Encoding")
headers["Vary"] = vary.push("Accept-Encoding").join(",")
headers['Content-Encoding'] = 'gzip'
headers['Content-Type'] =
Rack::Mime.mime_type(File.extname(path), 'text/plain')
return [status, headers, body]
# Serve pre-gzipped static assets
'Rack::Cache', Middleware::CompressedStaticAssets,
paths["public"].first, config.assets.prefix, config.static_cache_control)

This is awesome! Mind if I gemify it?

EduBcn commented Dec 2, 2012

Hi! Newbie question here: Where do I put the first file? I created a folder "app/middleware" but I'm getting an "uninitialized constant error Middleware" in production.rb...

@EduBcn - Try config/initializers/

I have an error when startng the app:
"/app/config/environments/staging.rb:33:in `block in <top (required)>': uninitialized constant Middleware (NameError)"

any idea?

FYI - this functionality can now be achieved by using the heroku-deflater gem.

marcgg commented Feb 26, 2013

@bensheldon the gem doesn't seem very followed and is maintained by a person and not an organization. Are you sure about it? Have you used it in production?

Hey @marcgg, I'm using it in production and yep, it works like a charm. Some pages went from 2mb/1mb when cached to 12kb when properly cached.

@bensheldon @marcgg FYI the heroku-deflater gem is slightly different than this gist. The gem will use Rack::Deflater for every response, but tell it to skip binary files via the no-transform Cache-control directive. This gist takes advantage of the higher compression ratio for precompiled assets by serving up the .gz version, but by itself doesn't do anything with other types of requests. I think a combination of the two approaches is the ideal.

@guyboltonking @neersighted @bensheldon @marcgg @runeroniek I have taken the liberty of gemifying this code (with changes to make it play nice with Rack::Deflate). It is available here. It's been working well for me. Let me know if you have any questions.

Another option for serving gzipped assets using Rack::Rewrite

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