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    use cmp;
    use ffi::CString;
    use fmt;
    use io::{self, Error, ErrorKind};
    use libc::{c_int, c_void};
    use mem;
    use net::{SocketAddr, Shutdown, Ipv4Addr, Ipv6Addr};
    use ptr;
    use sys::net::{cvt, cvt_r, cvt_gai, Socket, init, wrlen_t};
    use sys::net::netc as c;
    use sys_common::{AsInner, FromInner, IntoInner};
    use time::Duration;
    use convert::{TryFrom, TryInto};

    #[cfg(any(target_os = "dragonfly", target_os = "freebsd",
              target_os = "ios", target_os = "macos",
              target_os = "openbsd", target_os = "netbsd",
              target_os = "solaris", target_os = "haiku", target_os = "l4re"))]
    use sys::net::netc::IPV6_JOIN_GROUP as IPV6_ADD_MEMBERSHIP;
    #[cfg(not(any(target_os = "dragonfly", target_os = "freebsd",
                  target_os = "ios", target_os = "macos",
                  target_os = "openbsd", target_os = "netbsd",
                  target_os = "solaris", target_os = "haiku", target_os = "l4re")))]
    use sys::net::netc::IPV6_ADD_MEMBERSHIP;
    #[cfg(any(target_os = "dragonfly", target_os = "freebsd",
              target_os = "ios", target_os = "macos",
              target_os = "openbsd", target_os = "netbsd",
              target_os = "solaris", target_os = "haiku", target_os = "l4re"))]
    use sys::net::netc::IPV6_LEAVE_GROUP as IPV6_DROP_MEMBERSHIP;
    #[cfg(not(any(target_os = "dragonfly", target_os = "freebsd",
                  target_os = "ios", target_os = "macos",
                  target_os = "openbsd", target_os = "netbsd",
                  target_os = "solaris", target_os = "haiku", target_os = "l4re")))]
    use sys::net::netc::IPV6_DROP_MEMBERSHIP;

    #[cfg(any(target_os = "linux", target_os = "android",
              target_os = "dragonfly", target_os = "freebsd",
              target_os = "openbsd", target_os = "netbsd",
              target_os = "haiku", target_os = "bitrig"))]
    use libc::MSG_NOSIGNAL;
    #[cfg(not(any(target_os = "linux", target_os = "android",
                  target_os = "dragonfly", target_os = "freebsd",
                  target_os = "openbsd", target_os = "netbsd",
                  target_os = "haiku", target_os = "bitrig")))]
    const MSG_NOSIGNAL: c_int = 0x0;

    ////////////////////////////////////////////////////////////////////////////////
    // sockaddr and misc bindings
    ////////////////////////////////////////////////////////////////////////////////

    pub fn setsockopt<T>(sock: &Socket, opt: c_int, val: c_int,
                         payload: T) -> io::Result<()> {
        unsafe {
            let payload = &payload as *const T as *const c_void;
            cvt(c::setsockopt(*sock.as_inner(), opt, val, payload,
                              mem::size_of::<T>() as c::socklen_t))?;
            Ok(())
        }
    }

    pub fn getsockopt<T: Copy>(sock: &Socket, opt: c_int,
                           val: c_int) -> io::Result<T> {
        unsafe {
            let mut slot: T = mem::zeroed();
            let mut len = mem::size_of::<T>() as c::socklen_t;
            cvt(c::getsockopt(*sock.as_inner(), opt, val,
                              &mut slot as *mut _ as *mut _,
                              &mut len))?;
            assert_eq!(len as usize, mem::size_of::<T>());
            Ok(slot)
        }
    }

    fn sockname<F>(f: F) -> io::Result<SocketAddr>
        where F: FnOnce(*mut c::sockaddr, *mut c::socklen_t) -> c_int
    {
        unsafe {
            let mut storage: c::sockaddr_storage = mem::zeroed();
            let mut len = mem::size_of_val(&storage) as c::socklen_t;
            cvt(f(&mut storage as *mut _ as *mut _, &mut len))?;
            sockaddr_to_addr(&storage, len as usize)
        }
    }

    pub fn sockaddr_to_addr(storage: &c::sockaddr_storage,
                        len: usize) -> io::Result<SocketAddr> {
        match storage.ss_family as c_int {
            c::AF_INET => {
                assert!(len as usize >= mem::size_of::<c::sockaddr_in>());
                Ok(SocketAddr::V4(FromInner::from_inner(unsafe {
                    *(storage as *const _ as *const c::sockaddr_in)
                })))
            }
            c::AF_INET6 => {
                assert!(len as usize >= mem::size_of::<c::sockaddr_in6>());
                Ok(SocketAddr::V6(FromInner::from_inner(unsafe {
                    *(storage as *const _ as *const c::sockaddr_in6)
                })))
            }
            _ => {
                Err(Error::new(ErrorKind::InvalidInput, "invalid argument"))
            }
        }
    }

    #[cfg(target_os = "android")]
    fn to_ipv6mr_interface(value: u32) -> c_int {
        value as c_int
    }

    #[cfg(not(target_os = "android"))]
    fn to_ipv6mr_interface(value: u32) -> ::libc::c_uint {
        value as ::libc::c_uint
    }

    ////////////////////////////////////////////////////////////////////////////////
    // get_host_addresses
    ////////////////////////////////////////////////////////////////////////////////

    pub struct LookupHost {
        original: *mut c::addrinfo,
        cur: *mut c::addrinfo,
        port: u16
    }

    impl LookupHost {
        pub fn port(&self) -> u16 {
            self.port
        }
    }

    impl Iterator for LookupHost {
        type Item = SocketAddr;
        fn next(&mut self) -> Option<SocketAddr> {
            loop {
                unsafe {
                    let cur = self.cur.as_ref()?;
                    self.cur = cur.ai_next;
                    match sockaddr_to_addr(mem::transmute(cur.ai_addr),
                                           cur.ai_addrlen as usize)
                    {
                        Ok(addr) => return Some(addr),
                        Err(_) => continue,
                    }
                }
            }
        }
    }

    unsafe impl Sync for LookupHost {}
    unsafe impl Send for LookupHost {}

    impl Drop for LookupHost {
        fn drop(&mut self) {
            unsafe { c::freeaddrinfo(self.original) }
        }
    }

    impl<'a> TryFrom<&'a str> for LookupHost {
        type Error = io::Error;

        fn try_from(s: &str) -> io::Result<LookupHost> {
            macro_rules! try_opt {
                ($e:expr, $msg:expr) => (
                    match $e {
                        Some(r) => r,
                        None => return Err(io::Error::new(io::ErrorKind::InvalidInput,
                                                          $msg)),
                    }
                )
            }

            // split the string by ':' and convert the second part to u16
            let mut parts_iter = s.rsplitn(2, ':');
            let port_str = try_opt!(parts_iter.next(), "invalid socket address");
            let host = try_opt!(parts_iter.next(), "invalid socket address");
            let port: u16 = try_opt!(port_str.parse().ok(), "invalid port value");

            (host, port).try_into()
        }
    }

    impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
        type Error = io::Error;

        fn try_from((host, port): (&'a str, u16)) -> io::Result<LookupHost> {
            init();

            let c_host = CString::new(host)?;
            let mut hints: c::addrinfo = unsafe { mem::zeroed() };
            hints.ai_socktype = c::SOCK_STREAM;
            let mut res = ptr::null_mut();
            unsafe {
                cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res)).map(|_| {
                    LookupHost { original: res, cur: res, port }
                })
            }
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // TCP streams
    ////////////////////////////////////////////////////////////////////////////////

    pub struct TcpStream {
        inner: Socket,
    }

    impl TcpStream {
        pub fn connect(addr: io::Result<&SocketAddr>) -> io::Result<TcpStream> {
            let addr = addr?;

            init();

            let sock = Socket::new(addr, c::SOCK_STREAM)?;

            let (addrp, len) = addr.into_inner();
            cvt_r(|| unsafe { c::connect(*sock.as_inner(), addrp, len) })?;
            Ok(TcpStream { inner: sock })
        }

        pub fn connect_timeout(addr: &SocketAddr, timeout: Duration) -> io::Result<TcpStream> {
            init();

            let sock = Socket::new(addr, c::SOCK_STREAM)?;
            sock.connect_timeout(addr, timeout)?;
            Ok(TcpStream { inner: sock })
        }

        pub fn socket(&self) -> &Socket { &self.inner }

        pub fn into_socket(self) -> Socket { self.inner }

        pub fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
            self.inner.set_timeout(dur, c::SO_RCVTIMEO)
        }

        pub fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
            self.inner.set_timeout(dur, c::SO_SNDTIMEO)
        }

        pub fn read_timeout(&self) -> io::Result<Option<Duration>> {
            self.inner.timeout(c::SO_RCVTIMEO)
        }

        pub fn write_timeout(&self) -> io::Result<Option<Duration>> {
            self.inner.timeout(c::SO_SNDTIMEO)
        }

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

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

        pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
            let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
            let ret = cvt(unsafe {
                c::send(*self.inner.as_inner(),
                        buf.as_ptr() as *const c_void,
                        len,
                        MSG_NOSIGNAL)
            })?;
            Ok(ret as usize)
        }

        pub fn peer_addr(&self) -> io::Result<SocketAddr> {
            sockname(|buf, len| unsafe {
                c::getpeername(*self.inner.as_inner(), buf, len)
            })
        }

        pub fn socket_addr(&self) -> io::Result<SocketAddr> {
            sockname(|buf, len| unsafe {
                c::getsockname(*self.inner.as_inner(), buf, len)
            })
        }

        pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
            self.inner.shutdown(how)
        }

        pub fn duplicate(&self) -> io::Result<TcpStream> {
            self.inner.duplicate().map(|s| TcpStream { inner: s })
        }

        pub fn set_nodelay(&self, nodelay: bool) -> io::Result<()> {
            self.inner.set_nodelay(nodelay)
        }

        pub fn nodelay(&self) -> io::Result<bool> {
            self.inner.nodelay()
        }

        pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
        }

        pub fn ttl(&self) -> io::Result<u32> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
            Ok(raw as u32)
        }

        pub fn take_error(&self) -> io::Result<Option<io::Error>> {
            self.inner.take_error()
        }

        pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
            self.inner.set_nonblocking(nonblocking)
        }
    }

    impl FromInner<Socket> for TcpStream {
        fn from_inner(socket: Socket) -> TcpStream {
            TcpStream { inner: socket }
        }
    }

    impl fmt::Debug for TcpStream {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let mut res = f.debug_struct("TcpStream");

            if let Ok(addr) = self.socket_addr() {
                res.field("addr", &addr);
            }

            if let Ok(peer) = self.peer_addr() {
                res.field("peer", &peer);
            }

            let name = if cfg!(windows) {"socket"} else {"fd"};
            res.field(name, &self.inner.as_inner())
                .finish()
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // TCP listeners
    ////////////////////////////////////////////////////////////////////////////////

    pub struct TcpListener {
        inner: Socket,
    }

    impl TcpListener {
        pub fn bind(addr: io::Result<&SocketAddr>) -> io::Result<TcpListener> {
            let addr = addr?;

            init();

            let sock = Socket::new(addr, c::SOCK_STREAM)?;

            // On platforms with Berkeley-derived sockets, this allows
            // to quickly rebind a socket, without needing to wait for
            // the OS to clean up the previous one.
            if !cfg!(windows) {
                setsockopt(&sock, c::SOL_SOCKET, c::SO_REUSEADDR,
                           1 as c_int)?;
            }

            // Bind our new socket
            let (addrp, len) = addr.into_inner();
            cvt(unsafe { c::bind(*sock.as_inner(), addrp, len as _) })?;

            // Start listening
            cvt(unsafe { c::listen(*sock.as_inner(), 128) })?;
            Ok(TcpListener { inner: sock })
        }

        pub fn socket(&self) -> &Socket { &self.inner }

        pub fn into_socket(self) -> Socket { self.inner }

        pub fn socket_addr(&self) -> io::Result<SocketAddr> {
            sockname(|buf, len| unsafe {
                c::getsockname(*self.inner.as_inner(), buf, len)
            })
        }

        pub fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
            let mut storage: c::sockaddr_storage = unsafe { mem::zeroed() };
            let mut len = mem::size_of_val(&storage) as c::socklen_t;
            let sock = self.inner.accept(&mut storage as *mut _ as *mut _,
                                         &mut len)?;
            let addr = sockaddr_to_addr(&storage, len as usize)?;
            Ok((TcpStream { inner: sock, }, addr))
        }

        pub fn duplicate(&self) -> io::Result<TcpListener> {
            self.inner.duplicate().map(|s| TcpListener { inner: s })
        }

        pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
        }

        pub fn ttl(&self) -> io::Result<u32> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
            Ok(raw as u32)
        }

        pub fn set_only_v6(&self, only_v6: bool) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_V6ONLY, only_v6 as c_int)
        }

        pub fn only_v6(&self) -> io::Result<bool> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_V6ONLY)?;
            Ok(raw != 0)
        }

        pub fn take_error(&self) -> io::Result<Option<io::Error>> {
            self.inner.take_error()
        }

        pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
            self.inner.set_nonblocking(nonblocking)
        }
    }

    impl FromInner<Socket> for TcpListener {
        fn from_inner(socket: Socket) -> TcpListener {
            TcpListener { inner: socket }
        }
    }

    impl fmt::Debug for TcpListener {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let mut res = f.debug_struct("TcpListener");

            if let Ok(addr) = self.socket_addr() {
                res.field("addr", &addr);
            }

            let name = if cfg!(windows) {"socket"} else {"fd"};
            res.field(name, &self.inner.as_inner())
                .finish()
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // UDP
    ////////////////////////////////////////////////////////////////////////////////

    pub struct UdpSocket {
        inner: Socket,
    }

    impl UdpSocket {
        pub fn bind(addr: io::Result<&SocketAddr>) -> io::Result<UdpSocket> {
            let addr = addr?;

            init();

            let sock = Socket::new(addr, c::SOCK_DGRAM)?;
            let (addrp, len) = addr.into_inner();
            cvt(unsafe { c::bind(*sock.as_inner(), addrp, len as _) })?;
            Ok(UdpSocket { inner: sock })
        }

        pub fn socket(&self) -> &Socket { &self.inner }

        pub fn into_socket(self) -> Socket { self.inner }

        pub fn socket_addr(&self) -> io::Result<SocketAddr> {
            sockname(|buf, len| unsafe {
                c::getsockname(*self.inner.as_inner(), buf, len)
            })
        }

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

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

        pub fn send_to(&self, buf: &[u8], dst: &SocketAddr) -> io::Result<usize> {
            let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
            let (dstp, dstlen) = dst.into_inner();
            let ret = cvt(unsafe {
                c::sendto(*self.inner.as_inner(),
                          buf.as_ptr() as *const c_void, len,
                          MSG_NOSIGNAL, dstp, dstlen)
            })?;
            Ok(ret as usize)
        }

        pub fn duplicate(&self) -> io::Result<UdpSocket> {
            self.inner.duplicate().map(|s| UdpSocket { inner: s })
        }

        pub fn set_read_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
            self.inner.set_timeout(dur, c::SO_RCVTIMEO)
        }

        pub fn set_write_timeout(&self, dur: Option<Duration>) -> io::Result<()> {
            self.inner.set_timeout(dur, c::SO_SNDTIMEO)
        }

        pub fn read_timeout(&self) -> io::Result<Option<Duration>> {
            self.inner.timeout(c::SO_RCVTIMEO)
        }

        pub fn write_timeout(&self) -> io::Result<Option<Duration>> {
            self.inner.timeout(c::SO_SNDTIMEO)
        }

        pub fn set_broadcast(&self, broadcast: bool) -> io::Result<()> {
            setsockopt(&self.inner, c::SOL_SOCKET, c::SO_BROADCAST, broadcast as c_int)
        }

        pub fn broadcast(&self) -> io::Result<bool> {
            let raw: c_int = getsockopt(&self.inner, c::SOL_SOCKET, c::SO_BROADCAST)?;
            Ok(raw != 0)
        }

        pub fn set_multicast_loop_v4(&self, multicast_loop_v4: bool) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_LOOP, multicast_loop_v4 as c_int)
        }

        pub fn multicast_loop_v4(&self) -> io::Result<bool> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_LOOP)?;
            Ok(raw != 0)
        }

        pub fn set_multicast_ttl_v4(&self, multicast_ttl_v4: u32) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_TTL, multicast_ttl_v4 as c_int)
        }

        pub fn multicast_ttl_v4(&self) -> io::Result<u32> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_MULTICAST_TTL)?;
            Ok(raw as u32)
        }

        pub fn set_multicast_loop_v6(&self, multicast_loop_v6: bool) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_MULTICAST_LOOP, multicast_loop_v6 as c_int)
        }

        pub fn multicast_loop_v6(&self) -> io::Result<bool> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IPV6, c::IPV6_MULTICAST_LOOP)?;
            Ok(raw != 0)
        }

        pub fn join_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr)
                             -> io::Result<()> {
            let mreq = c::ip_mreq {
                imr_multiaddr: *multiaddr.as_inner(),
                imr_interface: *interface.as_inner(),
            };
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_ADD_MEMBERSHIP, mreq)
        }

        pub fn join_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32)
                             -> io::Result<()> {
            let mreq = c::ipv6_mreq {
                ipv6mr_multiaddr: *multiaddr.as_inner(),
                ipv6mr_interface: to_ipv6mr_interface(interface),
            };
            setsockopt(&self.inner, c::IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, mreq)
        }

        pub fn leave_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr)
                              -> io::Result<()> {
            let mreq = c::ip_mreq {
                imr_multiaddr: *multiaddr.as_inner(),
                imr_interface: *interface.as_inner(),
            };
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_DROP_MEMBERSHIP, mreq)
        }

        pub fn leave_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32)
                              -> io::Result<()> {
            let mreq = c::ipv6_mreq {
                ipv6mr_multiaddr: *multiaddr.as_inner(),
                ipv6mr_interface: to_ipv6mr_interface(interface),
            };
            setsockopt(&self.inner, c::IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP, mreq)
        }

        pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
            setsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL, ttl as c_int)
        }

        pub fn ttl(&self) -> io::Result<u32> {
            let raw: c_int = getsockopt(&self.inner, c::IPPROTO_IP, c::IP_TTL)?;
            Ok(raw as u32)
        }

        pub fn take_error(&self) -> io::Result<Option<io::Error>> {
            self.inner.take_error()
        }

        pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
            self.inner.set_nonblocking(nonblocking)
        }

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

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

        pub fn send(&self, buf: &[u8]) -> io::Result<usize> {
            let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
            let ret = cvt(unsafe {
                c::send(*self.inner.as_inner(),
                        buf.as_ptr() as *const c_void,
                        len,
                        MSG_NOSIGNAL)
            })?;
            Ok(ret as usize)
        }

        pub fn connect(&self, addr: io::Result<&SocketAddr>) -> io::Result<()> {
            let (addrp, len) = addr?.into_inner();
            cvt_r(|| unsafe { c::connect(*self.inner.as_inner(), addrp, len) }).map(|_| ())
        }
    }

    impl FromInner<Socket> for UdpSocket {
        fn from_inner(socket: Socket) -> UdpSocket {
            UdpSocket { inner: socket }
        }
    }

    impl fmt::Debug for UdpSocket {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let mut res = f.debug_struct("UdpSocket");

            if let Ok(addr) = self.socket_addr() {
                res.field("addr", &addr);
            }

            let name = if cfg!(windows) {"socket"} else {"fd"};
            res.field(name, &self.inner.as_inner())
                .finish()
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use collections::HashMap;

        #[test]
        fn no_lookup_host_duplicates() {
            let mut addrs = HashMap::new();
            let lh = match LookupHost::try_from(("localhost", 0)) {
                Ok(lh) => lh,
                Err(e) => panic!("couldn't resolve `localhost': {}", e)
            };
            for sa in lh { *addrs.entry(sa).or_insert(0) += 1; };
            assert_eq!(addrs.iter().filter(|&(_, &v)| v > 1).collect::<Vec<_>>(), vec![],
                       "There should be no duplicate localhost entries");
        }
    }

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