Document cancel safety

[jorendorff]

Would you accept a documentation patch describing Hyper's cancellation behavior?

I think Hyper is largely cancel safe:

• dropping an HTTP/1 request causes the connection to be closed
• dropping an HTTP/2 request leaves the shared connection in a good state and cancels the unwanted response (using RST_STREAM).
• otherwise Hyper doesn't really have a bunch of hidden state to screw up
• well, except the legacy Client support, but actually that's also carefully implemented to do the right thing on cancellation

I don't know about the server side, but that's OK, I can read code. If you're interested.

It doesn't seem like guide material. I was thinking a single # Cancel safety section at the crate level.

[seanmonstar]

Seems fair to document. Though, thinking about where the information would be best to be found... would it be better to have a small section on the relevant futures about cancellation? Or maybe in combination with a small mention at the crate level, "futures are cancel safe, see individual features for behavior when canceled"?