QUIC: setTargetBufferedAmount & receive window

[aboba]

From w3c/p2p-webtransport#7 (submitted by shampson)

Steps 5/6 of setTargetBufferedAmount:
5. If amount is greater than or equal to stream's [[ReadBufferedAmount]] slot, set stream's maximum receive window to amount.
6. ...then set the maximum receive window to amount.

I discussed this with Peter about the [[TargetReadBufferedAmount]], and we concluded:

• The target read buffered amount shouldn't directly set the backpressure window size. It's more for the app to be able to fill a the read buffer up to a given amount with data while it's busy doing something else.
• It smooths out how data is read in to JavaScript. Without it there would be problems if data came in faster than it could be processed
• We don't want to set the receive window size directly to be the [[TargetReadBufferedAmount]]. The targetReadBufferedAmount attribute should represent the target number of bytes in the receive buffer in addition to the receive window. This allows protocol level control of the receive window separate from the application.

Changes I propose:

• Update definition of targetReadBufferedAmount "represents the target number of bytes in the read buffer" --> "represents the target number of bytes in the receive buffer in addition to the receive window"
  • Update this in setTargetReadBuffered amount as well
• Clarify how setTargetBufferedAmount is for smoothness
• Remove setTargetBufferedAmount steps 5/6
• Do we want [[TargetReadBufferedAmount]] to default to 0? It currently defaults to the maximum read buffer size.