Close the original body passed to Rack::ETag

The Rack spec states:

> If the Body responds to `close`, it will be called after iteration. If
> the body is replaced by a middleware after action, the original body
> must be closed first, if it responds to close.

After Rack::ETag replaces the response body, close the original body.

Signed-off-by: David Celis <me@davidcel.is>

lib/rack/etag.rb

@@ -62,6 +62,8 @@ def digest_body(body)
           (digest ||= Digest::MD5.new) << part unless part.empty?
         end
 
+        body.close if body.respond_to?(:close)
+
         [digest && digest.hexdigest, parts]
       end
   end

test/spec_etag.rb

@@ -7,17 +7,24 @@
   def etag(app, *args)
     Rack::Lint.new Rack::ETag.new(app, *args)
   end
-  
+
   def request
     Rack::MockRequest.env_for
   end
-  
+
   def sendfile_body
     res = ['Hello World']
     def res.to_path ; "/tmp/hello.txt" ; end
     res
   end
 
+  def closable_body
+    res = ['Hello World']
+    def res.close ; @closed = true ; end
+    def res.closed? ; !!@closed ; end
+    res
+  end
+
   should "set ETag if none is set if status is 200" do
     app = lambda { |env| [200, {'Content-Type' => 'text/plain'}, ["Hello, World!"]] }
     response = etag(app).call(request)
@@ -95,4 +102,11 @@ def res.to_path ; "/tmp/hello.txt" ; end
     response = etag(app).call(request)
     response[1]['ETag'].should.be.nil
   end
+
+  should "close the original body if it responds to close" do
+    body = closable_body
+    app  = lambda { |env| [200, {'Content-Type' => 'text/plain'}, body] }
+    etag(app).call(request)
+    body.should.be.closed
+  end
 end