Document that chunking boundaries aren't preserved in streams

[martinthomson]

A stream of datagrams will preserve boundaries between each chunk, even as those chunks traverse the network.

However, unidirectional and bidirectional streams won't preserve the boundaries between chunks.

Write that down so that people understand this, otherwise they might be surprised: one thing that can happen in local testing is that with small writes, the chunks are preserved, but this isn't a guarantee and once you add load, latency, and loss, people might be surprised at the outcome.

[jan-ivar]

with small writes, the chunks are preserved, but this isn't a guarantee and once you add load, latency, and loss, people might be surprised at the outcome.

For example, a simple text-chat app over a bidirectional bytestream may appear chunked by message, until after a network blip when you may receive a backlog of text all at once. You'll need to rely on some other message separator, like newlines, or a notation like JSON.

[aboba]

@jan-ivar Is it always true that a stream of datagrams will preserve boundaries between chunks? For example, what happens if datagram transport is emulated over a reliable transport (e.g. emulated datagram transport over HTTP/2)? Can we assume that we are only talking about HTTP/3 datagrams (which are not on the standards track) for now?

[martinthomson]

My expectation is that any emulation would add framing so that boundaries could be preserved.

[jan-ivar]

This 2021 TPAC slide has some illustrations that might prove useful.