I'm using a worker to proxy data from an origin server of mine. I would like to know how many bytes have been streamed from the worker that is proxying my origin server. Any thoughts on how to find the total consumed egress bytes while streaming the response?

The only way I know of is by implementing a transform stream that counts the amount of bytes, but why do you need that? Streaming data from workers is free. Perhaps there is something else that could work better for what you need.