consider adding response.originalLength property

[ianstormtaylor]

It would be nice if this added a response.originalLength property to make it easy to send trace information about the "real" response length. This would mimic the existing request.originalUrl that Koa maintains.

[jonathanong]

the primary issue with this is that we don't know the length of streams and finding out means we have to buffer the entire body. might be better done in a downstream middleware

[jonathanong]

actually yeah, should be done downstream