PERF: send Content-Length from Rails on all requests

config/initializers/300-content_length.rb

@@ -0,0 +1,37 @@
+# Just like Rack except we dont do a to_ary check so we can calculate length
+# on body proxy objects
+# Sets the Content-Length header on responses with fixed-length bodies.
+class ContentLength
+  TRANSFER_ENCODING = "Transfer-Encoding".freeze
+  CONTENT_LENGTH = "Content-Length".freeze
+
+  include Rack::Utils
+
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    status, headers, body = @app.call(env)
+
+    if !STATUS_WITH_NO_ENTITY_BODY.include?(status.to_i) &&
+       !headers[CONTENT_LENGTH] &&
+       !headers[TRANSFER_ENCODING]
+
+      obody = body
+      body, length = [], 0
+      obody.each { |part| body << part; length += part.bytesize }
+
+      body = Rack::BodyProxy.new(body) do
+        obody.close if obody.respond_to?(:close)
+      end
+
+      headers[CONTENT_LENGTH] = length.to_s
+    end
+
+    [status, headers, body]
+  end
+end
+
+# content length helps us instruct NGINX on how to deal with this
+Rails.configuration.middleware.unshift ContentLength