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 17
def initialize(app)
  @app = app
end

Public Instance Methods

call(env) click to toggle source

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

# File lib/rack/conditional_get.rb, line 23
def call(env)
  case env[REQUEST_METHOD]
  when "GET", "HEAD"
    status, headers, body = @app.call(env)
    headers = Utils::HeaderHash[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

Whether the ETag response header matches the If-None-Match request header. If so, the request has not been modified.

# File lib/rack/conditional_get.rb, line 58
def etag_matches?(none_match, headers)
  headers['ETag'] == none_match
end

fresh?(env, headers) click to toggle source

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

# File lib/rack/conditional_get.rb, line 47
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)
  end
end

modified_since?(modified_since, headers) click to toggle source

Whether the Last-Modified response header matches the If-Modified-Since request header. If so, the request has not been modified.

# File lib/rack/conditional_get.rb, line 64
def modified_since?(modified_since, headers)
  last_modified = to_rfc2822(headers['Last-Modified']) and
    modified_since >= last_modified
end

to_rfc2822(since) click to toggle source

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

# File lib/rack/conditional_get.rb, line 71
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
  end
end