Ability to strictly prioritize streams, defaulting to round-robin

[kixelated]

Only applies when the congestion window is full. This gives applications a way to specify which streams should be sent first under poor network conditions.

[kixelated]

I didn't actually meant to submit a PR upstream; just to my fork. Oh well.

Priority could be replaced with Order or Precedence, seeing as it's an often overloaded term. There's a sort that could be removed with a bit of a refactoring but I suppose it doesn't matter.

[marten-seemann]

Only applies when the congestion window is full.

Why?

[kixelated]

Only applies when the congestion window is full.

Why?

Or when rate limited by a pacer.

I'm currently working on sample code for a new live video protocol. The idea is that we prioritize newer media during congestion, skipping over old media instead of buffering. This either requires cancelling streams when we're network bound or more elegantly, prioritizing streams. The lowest priority streams will be starved until the network recovers or they are cancelled.

This code review adds the ability to specify which streams take strict priority instead of using round-robin. A future implementation might use weights instead.

[marten-seemann]

For video you probably want to do a lot more than just use a different prioritisation scheme. fyi, there's a MoQ (Media over QUIC) working group at the IETF now.