Reaper

Reaper picks the correct media-type for a resource based on a request's Accept header and what the resource or server supports.

It also allows the registration of serializers / deserializers for automatic serialization and deserialization of any formats that might be automatically serializable/deserializable.

var reaper = new Reaper();
reaper.register('application/json', 
                function(str){ return JSON.parse(str); },
                function(obj){ return JSON.stringify(obj); });

reaper.isAcceptable('application/json');   // returns true
reaper.isAcceptable('*/*');   // returns true
reaper.isAcceptable('application/xml');   // returns false

reaper.isRegistered('application/json');  // returns true
reaper.isRegistered('application/xml');  // returns false

reaper.input("application/json", '{"hello" : "world"}');  // returns {hello : "world"}
reaper.output("application/json", {hello : "world"});   // returns '{"hello" : "world"}'

Additionally Reaper comes with a connect-compatible middleware that attaches a body and rawBody object to your request object that automatically uses any deserializer you may have configured for the content-type to populate the body property. The middleware will return errors in the case of bad deserialization, or unacceptable Accept / Content-Type headers.