Linux: Support TCP_FASTOPEN

[zonyitoo]

TCP_FASTOPEN requires to replace read and write syscalls to sendto and recvfrom.

I propose to modify the TcpStream and TcpListener in sys::unix like this:

pub enum TcpStream {
    // TCP_FASTOPEN requires this SocketAddr to be passed into sendto and recvfrom
    FastOpen(net::TcpStream, SocketAddr),
    Default(net::TcpStream),
}

[carllerche]

You can use fast open right now w/o mio by managing this state yourself. The goal of Mio is to stay minimal. Could you explain why you think Mio should apply this change?

[zonyitoo]

Well, the Read and Write traits that implemented for TcpStream will call read and write. And the other crates, like tokio, will call Read::read and Write::write in their code. So if I want to use fastopen in my project with tokio, TcpStream in Mio must support reading and writing with sendto and recvfrom.

[zonyitoo]

What's your opinion? @carllerche

[carllerche]

Maybe this should be experimented with first out of crate. I don't think anything in mio/ tokio prevents a tcp-fast-open crate from existing?

[carllerche]

Related to #268

[carllerche]

Closing due to inactivity.