net: add TcpSocket::set_{send, recv}_buffer_size

[hawkw]

This commit adds methods for setting SO_RECVBUF and SO_SNDBUF to
Mio's TcpSocket type. It would be nice to eventually expose these in
Tokio, so adding them to Mio is the first step.

See tokio-rs/tokio#3082 for details.

Signed-off-by: Eliza Weisman eliza@buoyant.io

[Thomasdezeeuw]

Can you also add the getters and a simple round-trip test?

[hawkw]

Can you also add the getters and a simple round-trip test?

Sure, will do!

[Thomasdezeeuw]

LGTM, see my comment in the test to fix the CI.

[hawkw]

It looks like one of the test is failing on FreeBSD CI:

---- no_events_after_deregister stdout ----
thread 'no_events_after_deregister' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 57, kind: NotConnected, message: "Socket is not connected" }', tests/tcp_stream.rs:492:35
stack backtrace:
   0:  0x110dfb3 - <unknown>
   1:  0x113043e - <unknown>
   2:  0x109c89d - <unknown>
   3:  0x11066b8 - <unknown>
   4:  0x1110020 - <unknown>
   5:  0x110fcb5 - <unknown>
   6:  0x11106c0 - <unknown>
   7:  0x1110271 - <unknown>
   8:  0x110e3fa - <unknown>
   9:  0x1110221 - <unknown>
  10:  0x112ecda - <unknown>
  11:  0x112eb0a - <unknown>
  12:  0x105a0c4 - <unknown>
  13:  0x1055210 - <unknown>
  14:  0x1069573 - <unknown>
  15:  0x106f3f4 - <unknown>
  16:  0x10c1cd3 - <unknown>
  17:  0x10c02ab - <unknown>
  18:  0x109bc43 - <unknown>
  19:  0x10a10b9 - <unknown>
  20:  0x1117090 - <unknown>
  21: 0x211848ab - <unknown>


failures:
    no_events_after_deregister

It seems quite unlikely that the changes in this PR could have actually broken this, since the test that's failing doesn't do anything related to send/recv buffer size:

mio/tests/tcp_stream.rs

Lines 473 to 506 in 7358a31

	#[test]
	fn no_events_after_deregister() {
	let (mut poll, mut events) = init_with_poll();
	let (thread_handle, address) = echo_listener(any_local_address(), 1);
	let mut stream = TcpStream::connect(address).unwrap();
	poll.registry()
	.register(&mut stream, ID1, Interest::WRITABLE.add(Interest::READABLE))
	.expect("unable to register TCP stream");
	poll.registry()
	.deregister(&mut stream)
	.expect("unable to deregister TCP stream");
	expect_no_events(&mut poll, &mut events);
	// We do expect to be connected.
	assert_eq!(stream.peer_addr().unwrap(), address);
	// Also, write should work
	let mut buf = [0; 16];
	assert_would_block(stream.peek(&mut buf));
	assert_would_block(stream.read(&mut buf));
	checked_write!(stream.write(&DATA1));
	stream.flush().unwrap();
	expect_no_events(&mut poll, &mut events);
	drop(stream);
	thread_handle.join().expect("unable to join thread");
	}

I'm guessing this is flaky, so I went ahead and restarted it. @Thomasdezeeuw have you seen this test failing spuriously before?