syscalls.rs

use std::{io, net};

trait RawSysCallsTraitOrSomething {
    fn bind_udp(&self, addr: net::SocketAddr) -> io::Result<UdpSocket> {}
    fn set_ttl_udp(&self, socket: usize, ttl: u32) -> io::Result<()> {}
    fn read(&self, socket: usize, buf: &mut [u8]) -> io::Result<usize> {}
}

cfg_syscall! {

    // When syscall is enabled
    type UdpSocket = udp::UdpSocket;
    struct SysCalls {
        /// This is `DefaultSyscalls` if another `RawSysCallsTraitOrSomething`
        /// is not supplied to the runtime.
        obj: Arc<dyn RawSysCallsTraitOrSomething>
    }

    impl SysCalls {
        fn bind_udp(&self, addr: net::SocketAddr) -> io::Result<UdpSocket> {
            self.obj.bind_udp()
        }
    }

    struct DefaultSyscalls;

    // This is where I get a bit confused and it's unclear that this is less complicated.
    // In order to have a default implementation of RawSysCallsTraitOrSomething, it seems
    // we will need to access real resources like a `UdpSocket` via the `socket: usize`
    impl RawSysCallsTraitOrSomething for DefaultSyscalls {
        fn bind_udp(&self, addr: net::SocketAddr) -> io::Result<UdpSocket> {}
        fn set_ttl_udp(&self, socket: usize, ttl: u32) -> io::Result<()> {}
        fn read(&self, socket: usize, buf: &mut [u8]) -> io::Result<usize> {}
    }


    mod udp {
        struct UpdSocket {
            id: usize,
            obj: Arc<dyn RawSysCallsTraitOrSomething>,
        }

        impl UdpSocket {
            /// These methods on UdpSocket must always match the methods on `mio::net::UdpSocket`.
            fn set_ttl(&self, ttl: u32) -> io::Result<()> {
                self.obj.set_ttl(self.id, ttl)
            }
        }
        impl Read for UdpSocket {...}
        impl Write for UdpSocket {...}
        impl Evented for UdpSocket {...}
    }
}

cfg_not_syscall! {
    type UdpSocket = mio::net::UdpSocket;

    struct SysCalls;
    impl Syscalls {
        fn bind_udp(&self, addr: net::SocketAddr) -> io::Result<UdpSocket> {
            mio::net::UdpSocket::bind(addr)
        }
    }
}