[PATCH 1/3] HeaderHash.new avoids unnecessary object creation

[Eric Wong <normalperson@yhbt.net>]

Creating a new HeaderHash is an O(n) operation in addition to
the cost of allocating a new object.  When using multiple pieces
of middleware, this can lead to unnecessary memory allocation
and iteration overhead.   We now explicitly define the
HeaderHash.new class method to return its original argument if
it is already a HeaderHash to avoid repeating work.
---
 lib/rack/utils.rb       |    4 ++++
 test/spec_rack_utils.rb |    8 ++++++++
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/lib/rack/utils.rb b/lib/rack/utils.rb
index 74303ef..21b58c9 100644
--- a/lib/rack/utils.rb
+++ b/lib/rack/utils.rb
@@ -258,6 +258,10 @@ module Rack
     # A case-insensitive Hash that preserves the original case of a
     # header when set.
     class HeaderHash < Hash
+      def self.new(hash={})
+        HeaderHash === hash ? hash : super(hash)
+      end
+
       def initialize(hash={})
         super()
         @names = {}
diff --git a/test/spec_rack_utils.rb b/test/spec_rack_utils.rb
index c397429..3586f8c 100644
--- a/test/spec_rack_utils.rb
+++ b/test/spec_rack_utils.rb
@@ -268,6 +268,14 @@ context "Rack::Utils::HeaderHash" do
     h = Rack::Utils::HeaderHash.new("foo" => "bar")
     h.delete("Hello").should.be.nil
   end
+
+  specify "should avoid unnecessary object creation if possible" do
+    a = Rack::Utils::HeaderHash.new("foo" => "bar")
+    b = Rack::Utils::HeaderHash.new(a)
+    b.object_id.should.equal(a.object_id)
+    b.should.equal(a)
+  end
+
 end
 
 context "Rack::Utils::Context" do
-- 
1.6.4.2.236.gf324c