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    // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use prelude::v1::*;

    use ffi::CStr;
    use io;
    use libc::{self, c_int, size_t, sockaddr, socklen_t};
    use net::{SocketAddr, Shutdown};
    use str;
    use sys::fd::FileDesc;
    use sys_common::{AsInner, FromInner, IntoInner};
    use sys_common::net::{getsockopt, setsockopt};
    use time::Duration;

    pub use sys::{cvt, cvt_r};
    pub extern crate libc as netc;

    pub type wrlen_t = size_t;

    // See below for the usage of SOCK_CLOEXEC, but this constant is only defined on
    // Linux currently (e.g. support doesn't exist on other platforms). In order to
    // get name resolution to work and things to compile we just define a dummy
    // SOCK_CLOEXEC here for other platforms. Note that the dummy constant isn't
    // actually ever used (the blocks below are wrapped in `if cfg!` as well.
    #[cfg(target_os = "linux")]
    use libc::SOCK_CLOEXEC;
    #[cfg(not(target_os = "linux"))]
    const SOCK_CLOEXEC: c_int = 0;

    pub struct Socket(FileDesc);

    pub fn init() {}

    pub fn cvt_gai(err: c_int) -> io::Result<()> {
        if err == 0 { return Ok(()) }

        let detail = unsafe {
            str::from_utf8(CStr::from_ptr(libc::gai_strerror(err)).to_bytes()).unwrap()
                .to_owned()
        };
        Err(io::Error::new(io::ErrorKind::Other,
                           &format!("failed to lookup address information: {}",
                                    detail)[..]))
    }

    impl Socket {
        pub fn new(addr: &SocketAddr, ty: c_int) -> io::Result<Socket> {
            let fam = match *addr {
                SocketAddr::V4(..) => libc::AF_INET,
                SocketAddr::V6(..) => libc::AF_INET6,
            };
            Socket::new_raw(fam, ty)
        }

        pub fn new_raw(fam: c_int, ty: c_int) -> io::Result<Socket> {
            unsafe {
                // On linux we first attempt to pass the SOCK_CLOEXEC flag to
                // atomically create the socket and set it as CLOEXEC. Support for
                // this option, however, was added in 2.6.27, and we still support
                // 2.6.18 as a kernel, so if the returned error is EINVAL we
                // fallthrough to the fallback.
                if cfg!(linux) {
                    match cvt(libc::socket(fam, ty | SOCK_CLOEXEC, 0)) {
                        Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
                        Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {}
                        Err(e) => return Err(e),
                    }
                }

                let fd = cvt(libc::socket(fam, ty, 0))?;
                let fd = FileDesc::new(fd);
                fd.set_cloexec()?;
                Ok(Socket(fd))
            }
        }

        pub fn new_pair(fam: c_int, ty: c_int) -> io::Result<(Socket, Socket)> {
            unsafe {
                let mut fds = [0, 0];

                // Like above, see if we can set cloexec atomically
                if cfg!(linux) {
                    match cvt(libc::socketpair(fam, ty | SOCK_CLOEXEC, 0, fds.as_mut_ptr())) {
                        Ok(_) => {
                            return Ok((Socket(FileDesc::new(fds[0])), Socket(FileDesc::new(fds[1]))));
                        }
                        Err(ref e) if e.raw_os_error() == Some(libc::EINVAL) => {},
                        Err(e) => return Err(e),
                    }
                }

                cvt(libc::socketpair(fam, ty, 0, fds.as_mut_ptr()))?;
                let a = FileDesc::new(fds[0]);
                let b = FileDesc::new(fds[1]);
                a.set_cloexec()?;
                b.set_cloexec()?;
                Ok((Socket(a), Socket(b)))
            }
        }

        pub fn accept(&self, storage: *mut sockaddr, len: *mut socklen_t)
                      -> io::Result<Socket> {
            // Unfortunately the only known way right now to accept a socket and
            // atomically set the CLOEXEC flag is to use the `accept4` syscall on
            // Linux. This was added in 2.6.28, however, and because we support
            // 2.6.18 we must detect this support dynamically.
            if cfg!(target_os = "linux") {
                weak! {
                    fn accept4(c_int, *mut sockaddr, *mut socklen_t, c_int) -> c_int
                }
                if let Some(accept) = accept4.get() {
                    let res = cvt_r(|| unsafe {
                        accept(self.0.raw(), storage, len, SOCK_CLOEXEC)
                    });
                    match res {
                        Ok(fd) => return Ok(Socket(FileDesc::new(fd))),
                        Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {}
                        Err(e) => return Err(e),
                    }
                }
            }

            let fd = cvt_r(|| unsafe {
                libc::accept(self.0.raw(), storage, len)
            })?;
            let fd = FileDesc::new(fd);
            fd.set_cloexec()?;
            Ok(Socket(fd))
        }

        pub fn duplicate(&self) -> io::Result<Socket> {
            self.0.duplicate().map(Socket)
        }

        pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
            self.0.read(buf)
        }

        pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
            self.0.read_to_end(buf)
        }

        pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
            self.0.write(buf)
        }

        pub fn set_timeout(&self, dur: Option<Duration>, kind: libc::c_int) -> io::Result<()> {
            let timeout = match dur {
                Some(dur) => {
                    if dur.as_secs() == 0 && dur.subsec_nanos() == 0 {
                        return Err(io::Error::new(io::ErrorKind::InvalidInput,
                                                  "cannot set a 0 duration timeout"));
                    }

                    let secs = if dur.as_secs() > libc::time_t::max_value() as u64 {
                        libc::time_t::max_value()
                    } else {
                        dur.as_secs() as libc::time_t
                    };
                    let mut timeout = libc::timeval {
                        tv_sec: secs,
                        tv_usec: (dur.subsec_nanos() / 1000) as libc::suseconds_t,
                    };
                    if timeout.tv_sec == 0 && timeout.tv_usec == 0 {
                        timeout.tv_usec = 1;
                    }
                    timeout
                }
                None => {
                    libc::timeval {
                        tv_sec: 0,
                        tv_usec: 0,
                    }
                }
            };
            setsockopt(self, libc::SOL_SOCKET, kind, timeout)
        }

        pub fn timeout(&self, kind: libc::c_int) -> io::Result<Option<Duration>> {
            let raw: libc::timeval = getsockopt(self, libc::SOL_SOCKET, kind)?;
            if raw.tv_sec == 0 && raw.tv_usec == 0 {
                Ok(None)
            } else {
                let sec = raw.tv_sec as u64;
                let nsec = (raw.tv_usec as u32) * 1000;
                Ok(Some(Duration::new(sec, nsec)))
            }
        }

        pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
            let how = match how {
                Shutdown::Write => libc::SHUT_WR,
                Shutdown::Read => libc::SHUT_RD,
                Shutdown::Both => libc::SHUT_RDWR,
            };
            cvt(unsafe { libc::shutdown(self.0.raw(), how) })?;
            Ok(())
        }

        pub fn set_nodelay(&self, nodelay: bool) -> io::Result<()> {
            setsockopt(self, libc::IPPROTO_TCP, libc::TCP_NODELAY, nodelay as c_int)
        }

        pub fn nodelay(&self) -> io::Result<bool> {
            let raw: c_int = getsockopt(self, libc::IPPROTO_TCP, libc::TCP_NODELAY)?;
            Ok(raw != 0)
        }

        pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
            let mut nonblocking = nonblocking as libc::c_ulong;
            cvt(unsafe { libc::ioctl(*self.as_inner(), libc::FIONBIO, &mut nonblocking) }).map(|_| ())
        }

        pub fn take_error(&self) -> io::Result<Option<io::Error>> {
            let raw: c_int = getsockopt(self, libc::SOL_SOCKET, libc::SO_ERROR)?;
            if raw == 0 {
                Ok(None)
            } else {
                Ok(Some(io::Error::from_raw_os_error(raw as i32)))
            }
        }
    }

    impl AsInner<c_int> for Socket {
        fn as_inner(&self) -> &c_int { self.0.as_inner() }
    }

    impl FromInner<c_int> for Socket {
        fn from_inner(fd: c_int) -> Socket { Socket(FileDesc::new(fd)) }
    }

    impl IntoInner<c_int> for Socket {
        fn into_inner(self) -> c_int { self.0.into_raw() }
    }

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