require 'rack/utils' module Rack # Middleware that enables conditional GET using If-None-Match and # If-Modified-Since. The application should set either or both of the # Last-Modified or Etag response headers according to RFC 2616. When # either of the conditions is met, the response body is set to be zero # length and the response status is set to 304 Not Modified. # # Applications that defer response body generation until the body's each # message is received will avoid response body generation completely when # a conditional GET matches. # # Adapted from Michael Klishin's Merb implementation: # http://github.com/wycats/merb-core/tree/master/lib/merb-core/rack/middleware/conditional_get.rb class ConditionalGet def initialize(app) @app = app end def call(env) return @app.call(env) unless %w[GET HEAD].include?(env['REQUEST_METHOD']) status, headers, body = @app.call(env) headers = Utils::HeaderHash.new(headers) if etag_matches?(env, headers) || modified_since?(env, headers) status = 304 body = [] end [status, headers, body] end private def etag_matches?(env, headers) etag = headers['Etag'] and etag == env['HTTP_IF_NONE_MATCH'] end def modified_since?(env, headers) last_modified = headers['Last-Modified'] and last_modified == env['HTTP_IF_MODIFIED_SINCE'] end end end