content_length sets the Content-Length to 0

The method content_length creates a header named Content-Length and sets
its value to 0.

lib/zero/response.rb

@@ -38,5 +38,12 @@ module Zero
       [@status, @header, @body]
     end
 
+    # Sets the content length header to the current length of the body
+    # Also creates one, if it does not exists
+    #
+    def content_length
+      header['Content-Length'] = 0
+    end
+
   end
 end

spec/unit/response/response_spec.rb

@@ -16,6 +16,9 @@ describe Zero::Response do
       value[1].should eq({})  # Headers
       value[2].should eq([])  # Body
     end
+
+    it "returns the content length in the header" do
+    end
   end
 
   describe '#status' do
@@ -44,4 +47,12 @@ describe Zero::Response do
     end
   end
 
+  describe '#content_length' do
+    it "sets the content_length to 0, if there is no content" do
+      subject.content_length
+
+      subject.header['Content-Length'].should eq(0)
+    end
+  end
+
 end