class Rack::ConditionalGet

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: github.com/wycats/merb/blob/master/merb-core/lib/merb-core/rack/middleware/conditional_get.rb

Public Class Methods

new(app) click to toggle source
# File lib/rack/conditional_get.rb, line 20
def initialize(app)
  @app = app
end

Public Instance Methods

call(env) click to toggle source
# File lib/rack/conditional_get.rb, line 24
def call(env)
  case env[REQUEST_METHOD]
  when "GET", "HEAD"
    status, headers, body = @app.call(env)
    headers = Utils::HeaderHash.new(headers)
    if status == 200 && fresh?(env, headers)
      status = 304
      headers.delete(CONTENT_TYPE)
      headers.delete(CONTENT_LENGTH)
      original_body = body
      body = Rack::BodyProxy.new([]) do
        original_body.close if original_body.respond_to?(:close)
      end
    end
    [status, headers, body]
  else
    @app.call(env)
  end
end

Private Instance Methods

etag_matches?(none_match, headers) click to toggle source
# File lib/rack/conditional_get.rb, line 58
def etag_matches?(none_match, headers)
  etag = headers['ETag'] and etag == none_match
end
fresh?(env, headers) click to toggle source
# File lib/rack/conditional_get.rb, line 46
def fresh?(env, headers)
  modified_since = env['HTTP_IF_MODIFIED_SINCE']
  none_match     = env['HTTP_IF_NONE_MATCH']

  return false unless modified_since || none_match

  success = true
  success &&= modified_since?(to_rfc2822(modified_since), headers) if modified_since
  success &&= etag_matches?(none_match, headers) if none_match
  success
end
modified_since?(modified_since, headers) click to toggle source
# File lib/rack/conditional_get.rb, line 62
def modified_since?(modified_since, headers)
  last_modified = to_rfc2822(headers['Last-Modified']) and
    modified_since and
    modified_since >= last_modified
end
to_rfc2822(since) click to toggle source
# File lib/rack/conditional_get.rb, line 68
def to_rfc2822(since)
  # shortest possible valid date is the obsolete: 1 Nov 97 09:55 A
  # anything shorter is invalid, this avoids exceptions for common cases
  # most common being the empty string
  if since && since.length >= 16
    # NOTE: there is no trivial way to write this in a non exception way
    #   _rfc2822 returns a hash but is not that usable
    Time.rfc2822(since) rescue nil
  else
    nil
  end
end