# 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 20
    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 26
    def call(env)
      status, headers, body = @app.call(env)

      headers = Utils::HeaderHash[headers]

      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] = %(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 65
    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 57
    def etag_body?(body)
      !body.respond_to?(:to_path)
    end

etag_status?(status) click to toggle source

    # File lib/rack/etag.rb, line 53
    def etag_status?(status)
      status == 200 || status == 201
    end

skip_caching?(headers) click to toggle source

    # File lib/rack/etag.rb, line 61
    def skip_caching?(headers)
      headers.key?(ETAG_STRING) || headers.key?('Last-Modified')
    end