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require "zlib"
require "stringio"
require "time" # for Time.httpdate

module Rack

class Deflater
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, body = @app.call(env)
    headers = Utils::HeaderHash.new(headers)

    # Skip compressing empty entity body responses and responses with
    # no-transform set.
    if Utils::STATUS_WITH_NO_ENTITY_BODY.include?(status) ||
        headers['Cache-Control'].to_s =~ /\bno-transform\b/
      return [status, headers, body]
    end

    request = Request.new(env)

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

    # 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(",")
    end

    case encoding
    when "gzip"
      mtime = if headers.key?("Last-Modified")
                Time.httpdate(headers["Last-Modified"])
              else
                Time.now
              end
      [status,
       headers.merge("Content-Encoding" => "gzip"),
       self.class.gzip(body, mtime)]
    when "deflate"
      [status,
       headers.merge("Content-Encoding" => "deflate"),
       self.class.deflate(body)]
    when "identity"
      [status, headers, body]
    when nil
      message = ["An acceptable encoding for the requested resource #{request.fullpath} could not be found."]
      [406, {"Content-Type" => "text/plain"}, message]
    end
  end

  def self.gzip(body, mtime)
    io = StringIO.new
    gzip = Zlib::GzipWriter.new(io)
    gzip.mtime = mtime

    # TODO: Add streaming
    body.each { |part| gzip << part }

    gzip.close
    return io.string
  end

  DEFLATE_ARGS = [
    Zlib::DEFAULT_COMPRESSION,
    # drop the zlib header which causes both Safari and IE to choke
   -Zlib::MAX_WBITS,
    Zlib::DEF_MEM_LEVEL,
    Zlib::DEFAULT_STRATEGY
  ]

  # Loosely based on Mongrel's Deflate handler
  def self.deflate(body)
    deflater = Zlib::Deflate.new(*DEFLATE_ARGS)

    # TODO: Add streaming
    body.each { |part| deflater << part }

    return deflater.finish
  end
end

end
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