Add plain_hash_response_headers plugin, using a plain hash for respon…

…se headers on Rack 3 for much better performance

This plugin changes behavior on Rack 3 to use a plain hash for
response headers, as Roda has historically done for Rack 2,
instead of the default behavior of using Rack::Headers.
Using this plugin gains back most the performance lost in the
switch to Rack 3.

With Empty Roda App (Roda.route{''}):

Before switch to lower case headers on Rack 3:

* With Rack 2: 190k i/s
* With Rack 3: 120k i/s

After switch to lower case headers on Rack 3:

* With Rack 2: 185k i/s
* With Rack 3:  92k i/s
* With Rack 3 and plain_hash_response_headers plugin: 182k i/s

Support running all of Roda's specs with the
plain_hash_response_headers plugin using the
PLAIN_HASH_RESPONSE_HEADERS environment variable.

CHANGELOG

@@ -1,5 +1,7 @@
 = master
 
+* Add plain_hash_response_headers plugin, using a plain hash for response headers on Rack 3 for much better performance (jeremyevans)
+
 * Use lower case response header keys by default on Rack 3, instead of relying on Rack::Headers conversion (jeremyevans)
 
 = 3.69.0 (2023-06-13)

lib/roda/plugins/plain_hash_response_headers.rb

@@ -0,0 +1,32 @@
+# frozen-string-literal: true
+
+#
+class Roda
+  module RodaPlugins
+    # The response_headers_plain_hash plugin will change Roda to
+    # use a plain hash for response headers.  This is Roda's
+    # default behavior on Rack 2, but on Rack 3+, Roda defaults
+    # to using Rack::Headers for response headers for backwards
+    # compatibility (Rack::Headers automatically lower cases header
+    # keys).
+    #
+    # On Rack 3+, you should use this plugin for better performance
+    # if you are sure all headers in your application and middleware
+    # are already lower case (lower case response header keys are
+    # required by the Rack 3 spec).
+    module PlainHashResponseHeaders
+      if defined?(Rack::Headers) && Rack::Headers.is_a?(Class)
+        module ResponseMethods
+          private
+
+          # Use plain hash for headers
+          def _initialize_headers
+            {}
+          end
+        end
+      end
+    end
+
+    register_plugin(:plain_hash_response_headers, PlainHashResponseHeaders)
+  end
+end

spec/plugin/plain_hash_response_headers_spec.rb

@@ -0,0 +1,23 @@
+require_relative "../spec_helper"
+
+describe "plain_hash_response_headers plugin" do 
+  it "uses plain hashes for response headers" do
+    app(:plain_hash_response_headers) do |r|
+      r.get 'up' do
+        response.headers['UP'] = 'U'
+      end
+
+      response.headers['down'] = 'd'
+    end
+
+    if Rack.release >= '3' && ENV['LINT']
+      proc{req('/up')}.must_raise Rack::Lint::LintError
+    else
+      header('up', '/up').must_be_nil
+      header('UP', '/up').must_equal 'U'
+    end
+    header('down').must_equal 'd'
+    header('DOWN').must_be_nil
+    req[1].must_be_instance_of Hash
+  end
+end

spec/response_spec.rb

@@ -22,6 +22,32 @@
     header('foo').must_equal "bar"
     body.must_equal 'true'
   end
+
+  it "uses plain hash for response headers" do
+    app do |r|
+      response.headers['UP'] = 'U'
+      response.headers['down'] = 'd'
+    end
+
+    req[1].must_be_instance_of Hash
+    header('up').must_be_nil
+    header('UP').must_equal 'U'
+    header('down').must_equal 'd'
+    header('DOWN').must_be_nil
+  end if Rack.release < '3'
+
+  it "uses Rack::Headers for response headers" do
+    app do |r|
+      response.headers['UP'] = 'U'
+      response.headers['down'] = 'd'
+    end
+
+    req[1].must_be_instance_of Rack::Headers
+    header('up').must_equal 'U'
+    header('UP').must_equal 'U'
+    header('down').must_equal 'd'
+    header('DOWN').must_equal 'd'
+  end if Rack.release >= '3'
 end
 
 describe "response #write" do

spec/spec_helper.rb

@@ -48,6 +48,10 @@
   end
 end
 
+if ENV['PLAIN_HASH_RESPONSE_HEADERS']
+  Roda.plugin :plain_hash_response_headers
+end
+
 RodaResponseHeaders = Roda::RodaResponseHeaders
 
 $RODA_WARN = true

www/pages/documentation.erb

@@ -104,6 +104,7 @@
       <li><a href="rdoc/classes/Roda/RodaPlugins/DropBody.html">drop_body</a>: Automatically drops response body and Content-Type/Content-Length headers for response statuses indicating no body.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/Halt.html">halt</a>: Augments request halt method for support for setting response status and/or response body.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/ModuleInclude.html">module_include</a>: Adds request_module and response_module class methods for adding modules/methods to request/response classes.</li>
+      <li><a href="rdoc/classes/Roda/RodaPlugins/PlainHashResponseHeaders.html">plain_hash_response_headers</a>: Uses plain hashes for response headers on Rack 3, for much better performance.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/R.html">r</a>: Adds r method for accessing the request, useful when r local variable is not in scope.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/RequestAref.html">request_aref</a>: Adds configurable handling for [] and []= request methods.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/RequestHeaders.html">request_headers</a>: Adds a headers method to the request object, for easier access to request headers.</li>