1 files changed, 39 insertions, 15 deletions
diff --git a/actionpack/lib/action_dispatch/http/headers.rb b/actionpack/lib/action_dispatch/http/headers.rb
index dc04d4577b..2666cd4b0a 100644
--- a/actionpack/lib/action_dispatch/http/headers.rb
+++ b/actionpack/lib/action_dispatch/http/headers.rb
@@ -1,38 +1,62 @@
 module ActionDispatch
   module Http
     class Headers
+      CGI_VARIABLES = %w(
+        CONTENT_TYPE CONTENT_LENGTH
+        HTTPS AUTH_TYPE GATEWAY_INTERFACE
+        PATH_INFO PATH_TRANSLATED QUERY_STRING
+        REMOTE_ADDR REMOTE_HOST REMOTE_IDENT REMOTE_USER
+        REQUEST_METHOD SCRIPT_NAME
+        SERVER_NAME SERVER_PORT SERVER_PROTOCOL SERVER_SOFTWARE
+      )
+      HTTP_HEADER = /\A[A-Za-z0-9-]+\z/
+
       include Enumerable
+      attr_reader :env
 
       def initialize(env = {})
-        @headers = env
+        @env = env
+      end
+
+      def [](key)
+        @env[env_name(key)]
       end
 
-      def [](header_name)
-        @headers[env_name(header_name)]
+      def []=(key, value)
+        @env[env_name(key)] = value
       end
 
-      def []=(k,v); @headers[k] = v; end
-      def key?(k); @headers.key? k; end
+      def key?(key); @env.key? key; end
       alias :include? :key?
 
-      def fetch(header_name, *args, &block)
-        @headers.fetch env_name(header_name), *args, &block
+      def fetch(key, *args, &block)
+        @env.fetch env_name(key), *args, &block
       end
 
       def each(&block)
-        @headers.each(&block)
+        @env.each(&block)
       end
 
-      private
+      def merge(headers_or_env)
+        headers = Http::Headers.new(env.dup)
+        headers.merge!(headers_or_env)
+        headers
+      end
 
-      # Converts a HTTP header name to an environment variable name if it is
-      # not contained within the headers hash.
-      def env_name(header_name)
-        @headers.include?(header_name) ? header_name : cgi_name(header_name)
+      def merge!(headers_or_env)
+        headers_or_env.each do |key, value|
+          self[env_name(key)] = value
+        end
       end
 
-      def cgi_name(k)
-        "HTTP_#{k.upcase.gsub(/-/, '_')}"
+      private
+      def env_name(key)
+        key = key.to_s
+        if key =~ HTTP_HEADER
+          key = key.upcase.tr('-', '_')
+          key = "HTTP_" + key unless CGI_VARIABLES.include?(key)
+        end
+        key
       end
     end
   end