Remove SessionHash inheritance from Hash

Previous api provided by SessionHash was inconsistent. All methods
provided by Hash which were not rewritten in SessionHash were behaving
incorrectly when session was not loaded yet. For example, #replace, #each,
 #keep_if and many more. So by dropping Hash inheritance we provide
clean api with all methods working without regard to whether session was
loaded or not.

lib/rack/session/abstract/id.rb

@@ -20,20 +20,17 @@ module Abstract
 
       # SessionHash is responsible to lazily load the session from store.
 
-      class SessionHash < Hash
+      class SessionHash
         attr_writer :id
 
         def initialize(by, env)
-          super()
           @by = by
           @env = env
           @loaded = false
-          @id_loaded = false
         end
 
         def id
-          return @id if @loaded or @id_loaded
-          @id_loaded = true
+          return @id if @loaded or instance_variable_defined?(:@id)
           @id = @by.send(:extract_session_id, @env)
         end
 
@@ -43,24 +40,26 @@ def options
 
         def [](key)
           load_for_read!
-          super(key.to_s)
+          @data[key.to_s]
         end
+        alias :fetch :[]
 
         def has_key?(key)
           load_for_read!
-          super(key.to_s)
+          @data.has_key?(key.to_s)
         end
         alias :key? :has_key?
         alias :include? :has_key?
 
         def []=(key, value)
           load_for_write!
-          super(key.to_s, value)
+          @data[key.to_s] = value
         end
+        alias :store :[]=
 
         def clear
           load_for_write!
-          super
+          @data.clear
         end
 
         def destroy
@@ -70,29 +69,36 @@ def destroy
 
         def to_hash
           load_for_read!
-          Hash[self].delete_if { |k,v| v.nil? }
+          @data.dup
         end
 
         def update(hash)
           load_for_write!
-          super(stringify_keys(hash))
+          @data.update(stringify_keys(hash))
+        end
+        alias :merge! :update
+
+        def replace(hash)
+          load_for_write!
+          @data.replace(stringify_keys(hash))
         end
 
         def delete(key)
           load_for_write!
-          super(key.to_s)
+          @data.delete(key.to_s)
         end
 
         def inspect
           if loaded?
-            super
+            @data.inspect
           else
             "#<#{self.class}:0x#{self.object_id.to_s(16)} not yet loaded>"
           end
         end
 
         def exists?
           return @exists if instance_variable_defined?(:@exists)
+          @data = {}
           @exists = @by.send(:session_exists?, @env)
         end
 
@@ -102,7 +108,7 @@ def loaded?
 
         def empty?
           load_for_read!
-          super
+          @data.empty?
         end
 
       private
@@ -117,7 +123,7 @@ def load_for_write!
 
         def load!
           @id, session = @by.send(:load_session, @env)
-          replace(stringify_keys(session))
+          @data = stringify_keys(session)
           @loaded = true
         end
 
@@ -297,7 +303,6 @@ def commit_session(env, status, headers, body)
           options = session.options
 
           if options[:drop] || options[:renew]
-            # if there is no session.id then we have nothing to destroy?!
             session_id = destroy_session(env, session.id || generate_sid, options)
             return [status, headers, body] unless session_id
           end
@@ -306,9 +311,9 @@ def commit_session(env, status, headers, body)
 
           session.send(:load!) unless loaded_session?(session)
           session_id ||= session.id || generate_sid
-          session = session.to_hash
+          session_data = session.to_hash.delete_if { |k,v| v.nil? }
 
-          if not data = set_session(env, session_id, session, options)
+          if not data = set_session(env, session_id, session_data, options)
             env["rack.errors"].puts("Warning! #{self.class.name} failed to save session. Content dropped.")
           elsif options[:defer] and not options[:renew]
             env["rack.errors"].puts("Defering cookie for #{session_id}") if $VERBOSE