Default server configuration prevents the use of server pushes

[thalesfragoso]

https://github.com/hyperium/h2/blob/a8af2358647cd2a68f851dfe3228cc3116654223/src/server.rs#L1378-L1379

This is arguably a bad default, given that it will block any server pushes unless the client explicitly sends a non-zero MAX_CONCURRENT_STREAMS setting.

I don't think we should limit the server that way unless the client explicitly requests that.

[seanmonstar]

Interesting find. I see how that'd be a problem, yea. A PR to change that is welcome.

[thalesfragoso]

Interesting find.

There was some head scratching involved when I couldn't get server push working between a h2 client and server. The workaround is to have the client always send a MAX_CONCURRENT_STREAMS setting, obliviously.

A PR to change that is welcome.

Will do soon. Any opinions on a default value ? I will also add a method to the server Builder, like the one that already exists in the client's.

[seanmonstar]

Unless there's prior art we can copy, an educated guess makes sense.

• On the one hand, how painful is it if the client rejects a bunch of eager push promises?
• On the other, how often do clients even send that setting at all?