class Rack::Deflater

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.

Constants

GZIP_MTIME

Public Class Methods

new (app, options = {})

Source

# File lib/rack/deflater.rb, line 45
def initialize(app, options = {})
  @app = app
  @condition = options[:if]
  @compressible_types = options[:include]
  @sync = options.fetch(:sync, true)
  @deflaters = options[:deflaters]
  @available_encodings = %w(gzip)
  @deflaters&.each_key { |key| @available_encodings << key }
  @available_encodings << 'identity'
  @available_encodings.freeze
end

Creates Rack::Deflater middleware. Options:

:if: a lambda enabling / disabling deflation based on returned boolean value (e.g use Rack::Deflater, :if => lambda { |*, body| sum=0; body.each { |i| sum += i.length }; sum > 512 }). 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.
:include: a list of content types that should be compressed. By default, all content types are compressed.
:sync: 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.
:deflaters: a hash of custom deflaters, where keys are encoding names and values are callables

that take (headers, body) and return a deflated body object. When provided, these
custom deflaters will be used if the client's accept-encoding header matches.

Public Instance Methods

call (env)

Source

# File lib/rack/deflater.rb, line 57
def call(env)
  status, headers, body = response = @app.call(env)

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

  request = Request.new(env)
  encoding = Utils.select_best_encoding(@available_encodings,
                                        request.accept_encoding)

  # 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(",")
  end

  case encoding
  when "gzip"
    headers['content-encoding'] = "gzip"
    headers.delete(CONTENT_LENGTH)
    response[2] = GzipStream.new(body, GZIP_MTIME, @sync)
    response
  when "identity"
    response
  else
    if deflater = @deflaters&.[](encoding)
      headers['content-encoding'] = encoding
      headers.delete(CONTENT_LENGTH)
      response[2] = deflater.call(headers, body)
      response
    else
      # 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]
    end
  end
end