Class: Rack::Deflater

Relationships & Source Files
Namespace Children
Inherits: Object
Defined in: lib/rack/deflater.rb


This middleware enables content encoding of http responses, usually for purposes of compression.

Currently supported encodings:

  • gzip

  • identity (no transformation)

This middleware automatically detects when encoding is supported and allowed. For example no encoding is made when a cache directive of ‘no-transform’ is present, when the response status code is one that doesn’t allow an entity body, or when the body is empty.

Note that despite the name, Deflater does not support the deflate encoding.

Class Method Summary

Instance Method Summary

Constructor Details

.new(app, options = {}) ⇒ Deflater

Creates Deflater middleware. Options:


a lambda enabling / disabling deflation based on returned boolean value

(e.g <tt>use Rack::Deflater, :if => lambda { |*, body| sum=0; body.each { |i| sum += i.length }; sum > 512 }</tt>).
However, be aware that calling `body.each` inside the block will break cases where `body.each` is not idempotent,
such as when it is an IO instance.

a list of content types that should be compressed. By default, all content types are compressed.


determines if the stream is going to be flushed after every chunk. Flushing after every chunk reduces

latency for time-sensitive streaming applications, but hurts compression and throughput.
Defaults to true.
[ GitHub ]

# File 'lib/rack/deflater.rb', line 39

def initialize(app, options = {})
  @app = app
  @condition = options[:if]
  @compressible_types = options[:include]
  @sync = options.fetch(:sync, true)

Instance Method Details


[ GitHub ]

# File 'lib/rack/deflater.rb', line 46

def call(env)
  status, headers, body = response = @app.call(env)

  unless should_deflate?(env, status, headers, body)
    return response

  request = Request.new(env)

  encoding = Utils.select_best_encoding(%w(gzip identity),

  # Set the Vary HTTP header.
  vary = headers["vary"].to_s.split(",").map(&:strip)
  unless vary.include?("*") || vary.any?{|v| v.downcase == 'accept-encoding'}
    headers["vary"] = vary.push("Accept-Encoding").join(",")

  case encoding
  when "gzip"
    headers['content-encoding'] = "gzip"
    mtime = headers["last-modified"]
    mtime = Time.httpdate(mtime).to_i if mtime
    response[2] = GzipStream.new(body, mtime, @sync)
  when "identity"
  else # when nil
    # Only possible encoding values here are 'gzip', 'identity', and nil
    message = "An acceptable encoding for the requested resource #{request.fullpath} could not be found."
    bp = Rack::BodyProxy.new([message]) { body.close if body.respond_to?(:close) }
    [406, { CONTENT_TYPE => "text/plain", CONTENT_LENGTH => message.length.to_s }, bp]

#should_deflate?(env, status, headers, body) ⇒ Boolean (private)

Whether the body should be compressed.

[ GitHub ]

# File 'lib/rack/deflater.rb', line 136

def should_deflate?(env, status, headers, body)
  # Skip compressing empty entity body responses and responses with
  # no-transform set.
  if Utils::STATUS_WITH_NO_ENTITY_BODY.key?(status.to_i) ||
      /\bno-transform\b/.match?(headers[CACHE_CONTROL].to_s) ||
    return false

  # Skip if @compressible_types are given and does not include request's content type
  return false if @compressible_types && !(headers.has_key?(CONTENT_TYPE) && @compressible_types.include?(headers[CONTENT_TYPE][/[^;]*/]))

  # Skip if @condition lambda is given and evaluates to false
  return false if @condition && !@condition.call(env, status, headers, body)

  # No point in compressing empty body, also handles usage with
  # Rack::Sendfile.
  return false if headers[CONTENT_LENGTH] == '0'