Class: Rack::ConditionalGet

Relationships & Source Files
Inherits: Object
Defined in: lib/rack/conditional_get.rb


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

Class Method Summary

Instance Method Summary

Constructor Details

.new(app) ⇒ ConditionalGet

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 22

def initialize(app)
  @app = app

Instance Method Details


Return empty 304 response if the response has not been modified since the last request.

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 28

def call(env)
  case env[REQUEST_METHOD]
  when "GET", "HEAD"
    status, headers, body = response = @app.call(env)

    if status == 200 && fresh?(env, headers)
      response[0] = 304
      response[2] = Rack::BodyProxy.new([]) do
        body.close if body.respond_to?(:close)

#etag_matches?(none_match, headers) ⇒ Boolean (private)

Whether the etag response header matches the if-none-match request header. If so, the request has not been modified.

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 62

def etag_matches?(none_match, headers)
  headers[ETAG] == none_match

#fresh?(env, headers) ⇒ Boolean (private)

Return whether the response has not been modified since the last request.

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 51

def fresh?(env, headers)
  # if-none-match has priority over if-modified-since per RFC 7232
  if none_match = env['HTTP_IF_NONE_MATCH']
    etag_matches?(none_match, headers)
  elsif (modified_since = env['HTTP_IF_MODIFIED_SINCE']) && (modified_since = to_rfc2822(modified_since))
    modified_since?(modified_since, headers)

#modified_since?(modified_since, headers) ⇒ Boolean (private)

Whether the last-modified response header matches the if-modified-since request header. If so, the request has not been modified.

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 68

def modified_since?(modified_since, headers)
  last_modified = to_rfc2822(headers['last-modified']) and
    modified_since >= last_modified

#to_rfc2822(since) (private)

Return a Time object for the given string (which should be in RFC2822 format), or nil if the string cannot be parsed.

[ GitHub ]

# File 'lib/rack/conditional_get.rb', line 75

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