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
ETAG_STRING

Public Class Methods

new(app, no_cache_control = nil, cache_control = DEFAULT_CACHE_CONTROL) click to toggle source

# File lib/rack/etag.rb, line 19
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 25
def call(env)
  status, headers, body = @app.call(env)

  if etag_status?(status) && etag_body?(body) && !skip_caching?(headers)
    original_body = body
    digest, new_body = digest_body(body)
    body = Rack::BodyProxy.new(new_body) do
      original_body.close if original_body.respond_to?(:close)
    end
    headers[ETAG_STRING] = %Q(W/"#{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 62
def digest_body(body)
  parts = []
  digest = nil

  body.each do |part|
    parts << part
    (digest ||= Digest::SHA256.new) << part unless part.empty?
  end

  [digest && digest.hexdigest.byteslice(0, 32), parts]
end

etag_body?(body) click to toggle source

# File lib/rack/etag.rb, line 54
def etag_body?(body)
  !body.respond_to?(:to_path)
end

etag_status?(status) click to toggle source

# File lib/rack/etag.rb, line 50
def etag_status?(status)
  status == 200 || status == 201
end

skip_caching?(headers) click to toggle source

# File lib/rack/etag.rb, line 58
def skip_caching?(headers)
  headers.key?(ETAG_STRING) || headers.key?('Last-Modified')
end