Peek message before attempting to deserialize ActiveSupport::Message::Metadata using JSON

Rescuing an exception here can be wildly expensive here. We noticed 22ms overhead
on each request when attempting to decode metadata that was serialized using Marshal.

Co-authored-by: Jonathan Hefner <[email protected]>

Author: ianks

activesupport/lib/active_support/messages/metadata.rb

@@ -37,7 +37,10 @@ def pick_expiry(expires_at, expires_in)
           end
 
           def extract_metadata(message)
-            data = JSON.decode(message) rescue nil
+            begin
+              data = JSON.decode(message) if message.start_with?("{")
+            rescue ::JSON::JSONError
+            end
 
             if data.is_a?(Hash) && data.key?("_rails")
               new(decode(data["_rails"]["message"]), data["_rails"]["exp"], data["_rails"]["pur"])