# frozen_string_literal: true
require "zlib"
require "time" # for Time.httpdate
require_relative 'constants'
require_relative 'utils'
require_relative 'request'
require_relative 'body_proxy'
module Rack
# 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 Deflater
# Creates Rack::Deflater middleware. Options:
#
# :if :: 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.
# :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+.
def initialize(app, options = {})
@app = app
@condition = options[:if]
@compressible_types = options[:include]
@sync = options.fetch(:sync, true)
end
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(%w(gzip identity),
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)
mtime = headers["last-modified"]
mtime = Time.httpdate(mtime).to_i if mtime
response[2] = GzipStream.new(body, mtime, @sync)
response
when "identity"
response
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]
end
end
# Body class used for gzip encoded responses.
class GzipStream
BUFFER_LENGTH = 128 * 1_024
# Initialize the gzip stream. Arguments:
# body :: Response body to compress with gzip
# mtime :: The modification time of the body, used to set the
# modification time in the gzip header.
# sync :: Whether to flush each gzip chunk as soon as it is ready.
def initialize(body, mtime, sync)
@body = body
@mtime = mtime
@sync = sync
end
# Yield gzip compressed strings to the given block.
def each(&block)
@writer = block
gzip = ::Zlib::GzipWriter.new(self)
gzip.mtime = @mtime if @mtime
# @body.each is equivalent to @body.gets (slow)
if @body.is_a? ::File # XXX: Should probably be ::IO
while part = @body.read(BUFFER_LENGTH)
gzip.write(part)
gzip.flush if @sync
end
else
@body.each { |part|
# Skip empty strings, as they would result in no output,
# and flushing empty parts would raise Zlib::BufError.
next if part.empty?
gzip.write(part)
gzip.flush if @sync
}
end
ensure
gzip.finish
end
# Call the block passed to #each with the gzipped data.
def write(data)
@writer.call(data)
end
# Close the original body if possible.
def close
@body.close if @body.respond_to?(:close)
end
end
private
# Whether the body should be compressed.
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) ||
headers['content-encoding']&.!~(/\bidentity\b/)
return false
end
# 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'
true
end
end
end
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