Non-normalizing HeaderHash with case-insensitive lookups

This is a backwards incompatible change that removes header name
normalization while attempting to keep most of its benefits. The
header name case is preserved but the Hash has case insensitive
lookup, replace, delete, and include semantics.

lib/rack/utils.rb

@@ -159,6 +159,7 @@ def pretty_print pp
     # A case-normalizing Hash, adjusting on [] and []=.
     class HeaderHash < Hash
       def initialize(hash={})
+        @names = {}
         hash.each { |k, v| self[k] = v }
       end
 
@@ -167,16 +168,26 @@ def to_hash
       end
 
       def [](k)
-        super capitalize(k)
+        super @names[k.downcase]
       end
 
       def []=(k, v)
-        super capitalize(k), v
+        delete k
+        @names[k.downcase] = k
+        super k, v
       end
 
-      def capitalize(k)
-        k.to_s.downcase.gsub(/^.|[-_\s]./) { |x| x.upcase }
+      def delete(k)
+        super @names.delete(k.downcase)
       end
+
+      def include?(k)
+        @names.has_key? k.downcase
+      end
+
+      alias_method :has_key?, :include?
+      alias_method :member?, :include?
+      alias_method :key?, :include?
     end
 
     # Every standard HTTP code mapped to the appropriate message.

test/spec_rack_utils.rb

@@ -65,28 +65,24 @@
 end
 
 context "Rack::Utils::HeaderHash" do
-  specify "should capitalize on all accesses" do
-    h = Rack::Utils::HeaderHash.new("foo" => "bar")
-    h["foo"].should.equal "bar"
-    h["Foo"].should.equal "bar"
-    h["FOO"].should.equal "bar"
-
-    h.to_hash.should.equal "Foo" => "bar"
-
-    h["bar-zzle"] = "quux"
-
-    h.to_hash.should.equal "Foo" => "bar", "Bar-Zzle" => "quux"
+  specify "should retain header case" do
+    h = Rack::Utils::HeaderHash.new("Content-MD5" => "d5ff4e2a0 ...")
+    h['ETag'] = 'Boo!'
+    h.to_hash.should.equal "Content-MD5" => "d5ff4e2a0 ...", "ETag" => 'Boo!'
   end
 
-  specify "should capitalize correctly" do
-    h = Rack::Utils::HeaderHash.new
+  specify "should check existence of keys case insensitively" do
+    h = Rack::Utils::HeaderHash.new("Content-MD5" => "d5ff4e2a0 ...")
+    h.should.include 'content-md5'
+    h.should.not.include 'ETag'
+  end
 
-    h.capitalize("foo").should.equal "Foo"
-    h.capitalize("foo-bar").should.equal "Foo-Bar"
-    h.capitalize("foo_bar").should.equal "Foo_Bar"
-    h.capitalize("foo bar").should.equal "Foo Bar"
-    h.capitalize("foo-bar-quux").should.equal "Foo-Bar-Quux"
-    h.capitalize("foo-bar-2quux").should.equal "Foo-Bar-2quux"
+  specify "should overwrite case insensitively and assume the new key's case" do
+    h = Rack::Utils::HeaderHash.new("Foo-Bar" => "baz")
+    h["foo-bar"] = "bizzle"
+    h["FOO-BAR"].should.equal "bizzle"
+    h.length.should.equal 1
+    h.to_hash.should.equal "foo-bar" => "bizzle"
   end
 
   specify "should be converted to real Hash" do