class Rack::ETag

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”

Constants

DEFAULT_CACHE_CONTROL

Public Class Methods

new(app, no_cache_control = nil, cache_control = DEFAULT_CACHE_CONTROL) click to toggle source
# File lib/rack/etag.rb, line 16
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

Public Instance Methods

call(env) click to toggle source
# File lib/rack/etag.rb, line 22
def call(env)
  status, headers, body = @app.call(env)

  if etag_status?(status) && etag_body?(body) && !skip_caching?(headers)
    digest, body = digest_body(body)
    headers['ETag'] = %Q("#{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

  [status, headers, body]
end

Private Instance Methods

digest_body(body) click to toggle source
# File lib/rack/etag.rb, line 56
def digest_body(body)
  parts = []
  body.each { |part| parts << part }
  string_body = parts.join
  digest = Digest::MD5.hexdigest(string_body) unless string_body.empty?
  [digest, parts]
end
etag_body?(body) click to toggle source
# File lib/rack/etag.rb, line 47
def etag_body?(body)
  !body.respond_to?(:to_path)
end
etag_status?(status) click to toggle source
# File lib/rack/etag.rb, line 43
def etag_status?(status)
  status == 200 || status == 201
end
skip_caching?(headers) click to toggle source
# File lib/rack/etag.rb, line 51
def skip_caching?(headers)
  (headers['Cache-Control'] && headers['Cache-Control'].include?('no-cache')) ||
    headers.key?('ETag') || headers.key?('Last-Modified')
end