# frozen_string_literal: true require 'digest/sha2' require_relative 'constants' require_relative 'utils' module Rack # Automatically sets the etag header on all String bodies. # # The etag header is skipped if etag or last-modified headers are sent or if # a sendfile body (body.responds_to :to_path) is given (since such cases # should be handled by apache/nginx). # # On initialization, you can pass two parameters: a cache-control directive # used when etag is absent and a directive when it is present. The first # defaults to nil, while the second defaults to "max-age=0, private, must-revalidate" class ETag ETAG_STRING = Rack::ETAG DEFAULT_CACHE_CONTROL = "max-age=0, private, must-revalidate" def initialize(app, no_cache_control = nil, cache_control = DEFAULT_CACHE_CONTROL) @app = app @cache_control = cache_control @no_cache_control = no_cache_control end def call(env) status, headers, body = response = @app.call(env) if etag_status?(status) && body.respond_to?(:to_ary) && !skip_caching?(headers) body = body.to_ary digest = digest_body(body) headers[ETAG_STRING] = %(W/"#{digest}") if digest end unless headers[CACHE_CONTROL] if digest headers[CACHE_CONTROL] = @cache_control if @cache_control else headers[CACHE_CONTROL] = @no_cache_control if @no_cache_control end end response end private def etag_status?(status) status == 200 || status == 201 end def skip_caching?(headers) headers.key?(ETAG_STRING) || headers.key?('last-modified') end def digest_body(body) digest = nil body.each do |part| (digest ||= Digest::SHA256.new) << part unless part.empty? end digest && digest.hexdigest.byteslice(0,32) end end end