feat(tcp): add support for custom socket options

[roman-kashitsyn]

This change extends to AddrIncoming API to support setting custom
options before binding the server socket. This change introduces one
such option: reuse_port, which enables the SO_REUSEPORT option on
the socket on UNIX platforms.

Example:

use hyper::server::conn::{AddrIncoming, SocketOptions};
let incoming = AddrIncoming::bind_with_option(
    "0.0.0.0:80".parse().unwrap(),
    SocketOptions::new().reuse_port(true)
);

[seanmonstar]

Thanks for the PR! Is the motivation that you want to make these options more convenient in hyper? Since it's possible to construct a TcpListener and then use AddrIncoming::from_std, it should already be possible to be done outside of hyper, right?

[roman-kashitsyn]

Since it's possible to construct a TcpListener and then use AddrIncoming::from_std, it should already be possible to be done outside of hyper, right?

I don't think so, from_std is private at the moment (pub(super)). But if you're OK with making it public, I'll be totally happy with this solution.

[seanmonstar]

Oh sorry, there's from_listener which is publicly available. It just requires you to convert to a tokio::net::TcpListener first.

[roman-kashitsyn]

Oh sorry, there's from_listener which is publicly available. It just requires you to convert to a tokio::net::TcpListener first.

Indeed! I was using https://docs.rs/hyper/0.14.4/hyper/server/conn/struct.AddrIncoming.html as a reference and didn't think there is a solution to the socket configuring problem already. I can now see that it was merged just 2 weeks ago (#2439).

I'll close this PR and wait for the next release then.

Thanks a lot!