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    1338

    //! Socket interface functions
    //!
    //! [Further reading](http://man7.org/linux/man-pages/man7/socket.7.html)
    use {Error, Result};
    use errno::Errno;
    use libc::{self, c_void, c_int, iovec, socklen_t, size_t,
            CMSG_FIRSTHDR, CMSG_NXTHDR, CMSG_DATA, CMSG_LEN};
    use std::{fmt, mem, ptr, slice};
    use std::os::unix::io::RawFd;
    use sys::time::TimeVal;
    use sys::uio::IoVec;

    mod addr;
    pub mod sockopt;

    /*
     *
     * ===== Re-exports =====
     *
     */

    pub use self::addr::{
        AddressFamily,
        SockAddr,
        InetAddr,
        UnixAddr,
        IpAddr,
        Ipv4Addr,
        Ipv6Addr,
        LinkAddr,
    };
    #[cfg(any(target_os = "android", target_os = "linux"))]
    pub use ::sys::socket::addr::netlink::NetlinkAddr;
    #[cfg(any(target_os = "android", target_os = "linux"))]
    pub use sys::socket::addr::alg::AlgAddr;

    pub use libc::{
        cmsghdr,
        msghdr,
        sa_family_t,
        sockaddr,
        sockaddr_in,
        sockaddr_in6,
        sockaddr_storage,
        sockaddr_un,
    };

    // Needed by the cmsg_space macro
    #[doc(hidden)]
    pub use libc::{c_uint, CMSG_SPACE};

    /// These constants are used to specify the communication semantics
    /// when creating a socket with [`socket()`](fn.socket.html)
    #[derive(Clone, Copy, PartialEq, Eq, Debug)]
    #[repr(i32)]
    pub enum SockType {
        /// Provides sequenced, reliable, two-way, connection-
        /// based byte streams.  An out-of-band data transmission
        /// mechanism may be supported.
        Stream = libc::SOCK_STREAM,
        /// Supports datagrams (connectionless, unreliable
        /// messages of a fixed maximum length).
        Datagram = libc::SOCK_DGRAM,
        /// Provides a sequenced, reliable, two-way connection-
        /// based data transmission path for datagrams of fixed
        /// maximum length; a consumer is required to read an
        /// entire packet with each input system call.
        SeqPacket = libc::SOCK_SEQPACKET,
        /// Provides raw network protocol access.
        Raw = libc::SOCK_RAW,
        /// Provides a reliable datagram layer that does not
        /// guarantee ordering.
        Rdm = libc::SOCK_RDM,
    }

    /// Constants used in [`socket`](fn.socket.html) and [`socketpair`](fn.socketpair.html)
    /// to specify the protocol to use.
    #[repr(i32)]
    #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
    pub enum SockProtocol {
        /// TCP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
        Tcp = libc::IPPROTO_TCP,
        /// UDP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
        Udp = libc::IPPROTO_UDP,
        /// Allows applications and other KEXTs to be notified when certain kernel events occur
        /// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
        #[cfg(any(target_os = "ios", target_os = "macos"))]
        KextEvent = libc::SYSPROTO_EVENT,
        /// Allows applications to configure and control a KEXT
        /// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
        #[cfg(any(target_os = "ios", target_os = "macos"))]
        KextControl = libc::SYSPROTO_CONTROL,
    }

    libc_bitflags!{
        /// Additional socket options
        pub struct SockFlag: c_int {
            /// Set non-blocking mode on the new socket
            #[cfg(any(target_os = "android",
                      target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "linux",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            SOCK_NONBLOCK;
            /// Set close-on-exec on the new descriptor
            #[cfg(any(target_os = "android",
                      target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "linux",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            SOCK_CLOEXEC;
            /// Return `EPIPE` instead of raising `SIGPIPE`
            #[cfg(target_os = "netbsd")]
            SOCK_NOSIGPIPE;
            /// For domains `AF_INET(6)`, only allow `connect(2)`, `sendto(2)`, or `sendmsg(2)`
            /// to the DNS port (typically 53)
            #[cfg(target_os = "openbsd")]
            SOCK_DNS;
        }
    }

    libc_bitflags!{
        /// Flags for send/recv and their relatives
        pub struct MsgFlags: c_int {
            /// Sends or requests out-of-band data on sockets that support this notion
            /// (e.g., of type [`Stream`](enum.SockType.html)); the underlying protocol must also
            /// support out-of-band data.
            MSG_OOB;
            /// Peeks at an incoming message. The data is treated as unread and the next
            /// [`recv()`](fn.recv.html)
            /// or similar function shall still return this data.
            MSG_PEEK;
            /// Enables nonblocking operation; if the operation would block,
            /// `EAGAIN` or `EWOULDBLOCK` is returned.  This provides similar
            /// behavior to setting the `O_NONBLOCK` flag
            /// (via the [`fcntl`](../../fcntl/fn.fcntl.html)
            /// `F_SETFL` operation), but differs in that `MSG_DONTWAIT` is a per-
            /// call option, whereas `O_NONBLOCK` is a setting on the open file
            /// description (see [open(2)](http://man7.org/linux/man-pages/man2/open.2.html)),
            /// which will affect all threads in
            /// the calling process and as well as other processes that hold
            /// file descriptors referring to the same open file description.
            MSG_DONTWAIT;
            /// Receive flags: Control Data was discarded (buffer too small)
            MSG_CTRUNC;
            /// For raw ([`Packet`](addr/enum.AddressFamily.html)), Internet datagram
            /// (since Linux 2.4.27/2.6.8),
            /// netlink (since Linux 2.6.22) and UNIX datagram (since Linux 3.4)
            /// sockets: return the real length of the packet or datagram, even
            /// when it was longer than the passed buffer. Not implemented for UNIX
            /// domain ([unix(7)](https://linux.die.net/man/7/unix)) sockets.
            ///
            /// For use with Internet stream sockets, see [tcp(7)](https://linux.die.net/man/7/tcp).
            MSG_TRUNC;
            /// Terminates a record (when this notion is supported, as for
            /// sockets of type [`SeqPacket`](enum.SockType.html)).
            MSG_EOR;
            /// This flag specifies that queued errors should be received from
            /// the socket error queue. (For more details, see
            /// [recvfrom(2)](https://linux.die.net/man/2/recvfrom))
            #[cfg(any(target_os = "android", target_os = "linux"))]
            MSG_ERRQUEUE;
            /// Set the `close-on-exec` flag for the file descriptor received via a UNIX domain
            /// file descriptor using the `SCM_RIGHTS` operation (described in
            /// [unix(7)](https://linux.die.net/man/7/unix)).
            /// This flag is useful for the same reasons as the `O_CLOEXEC` flag of
            /// [open(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html).
            ///
            /// Only used in [`recvmsg`](fn.recvmsg.html) function.
            #[cfg(any(target_os = "android",
                      target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "linux",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            MSG_CMSG_CLOEXEC;
        }
    }

    cfg_if! {
        if #[cfg(any(target_os = "android", target_os = "linux"))] {
            /// Unix credentials of the sending process.
            ///
            /// This struct is used with the `SO_PEERCRED` ancillary message for UNIX sockets.
            #[repr(C)]
            #[derive(Clone, Copy)]
            pub struct UnixCredentials(libc::ucred);

            impl UnixCredentials {
                /// Returns the process identifier
                pub fn pid(&self) -> libc::pid_t {
                    self.0.pid
                }

                /// Returns the user identifier
                pub fn uid(&self) -> libc::uid_t {
                    self.0.uid
                }

                /// Returns the group identifier
                pub fn gid(&self) -> libc::gid_t {
                    self.0.gid
                }
            }

            impl PartialEq for UnixCredentials {
                fn eq(&self, other: &Self) -> bool {
                    self.0.pid == other.0.pid && self.0.uid == other.0.uid && self.0.gid == other.0.gid
                }
            }
            impl Eq for UnixCredentials {}

            impl From<libc::ucred> for UnixCredentials {
                fn from(cred: libc::ucred) -> Self {
                    UnixCredentials(cred)
                }
            }

            impl Into<libc::ucred> for UnixCredentials {
                fn into(self) -> libc::ucred {
                    self.0
                }
            }

            impl fmt::Debug for UnixCredentials {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    f.debug_struct("UnixCredentials")
                        .field("pid", &self.0.pid)
                        .field("uid", &self.0.uid)
                        .field("gid", &self.0.gid)
                        .finish()
                }
            }
        }
    }

    /// Request for multicast socket operations
    ///
    /// This is a wrapper type around `ip_mreq`.
    #[repr(C)]
    #[derive(Clone, Copy)]
    pub struct IpMembershipRequest(libc::ip_mreq);

    impl IpMembershipRequest {
        /// Instantiate a new `IpMembershipRequest`
        ///
        /// If `interface` is `None`, then `Ipv4Addr::any()` will be used for the interface.
        pub fn new(group: Ipv4Addr, interface: Option<Ipv4Addr>) -> Self {
            IpMembershipRequest(libc::ip_mreq {
                imr_multiaddr: group.0,
                imr_interface: interface.unwrap_or_else(Ipv4Addr::any).0,
            })
        }
    }

    impl PartialEq for IpMembershipRequest {
        fn eq(&self, other: &Self) -> bool {
            self.0.imr_multiaddr.s_addr == other.0.imr_multiaddr.s_addr
                && self.0.imr_interface.s_addr == other.0.imr_interface.s_addr
        }
    }
    impl Eq for IpMembershipRequest {}

    impl fmt::Debug for IpMembershipRequest {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let mref = &self.0.imr_multiaddr;
            let maddr = mref.s_addr;
            let iref = &self.0.imr_interface;
            let ifaddr = iref.s_addr;
            f.debug_struct("IpMembershipRequest")
                .field("imr_multiaddr", &maddr)
                .field("imr_interface", &ifaddr)
                .finish()
        }
    }

    /// Request for ipv6 multicast socket operations
    ///
    /// This is a wrapper type around `ipv6_mreq`.
    #[repr(C)]
    #[derive(Clone, Copy)]
    pub struct Ipv6MembershipRequest(libc::ipv6_mreq);

    impl Ipv6MembershipRequest {
        /// Instantiate a new `Ipv6MembershipRequest`
        pub fn new(group: Ipv6Addr) -> Self {
            Ipv6MembershipRequest(libc::ipv6_mreq {
                ipv6mr_multiaddr: group.0,
                ipv6mr_interface: 0,
            })
        }
    }

    impl PartialEq for Ipv6MembershipRequest {
        fn eq(&self, other: &Self) -> bool {
            self.0.ipv6mr_multiaddr.s6_addr == other.0.ipv6mr_multiaddr.s6_addr &&
                self.0.ipv6mr_interface == other.0.ipv6mr_interface
        }
    }
    impl Eq for Ipv6MembershipRequest {}

    impl fmt::Debug for Ipv6MembershipRequest {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("Ipv6MembershipRequest")
                .field("ipv6mr_multiaddr", &self.0.ipv6mr_multiaddr.s6_addr)
                .field("ipv6mr_interface", &self.0.ipv6mr_interface)
                .finish()
        }
    }

    cfg_if! {
        // Darwin and DragonFly BSD always align struct cmsghdr to 32-bit only.
        if #[cfg(any(target_os = "dragonfly", target_os = "ios", target_os = "macos"))] {
            type align_of_cmsg_data = u32;
        } else {
            type align_of_cmsg_data = size_t;
        }
    }

    /// A type that can be used to store ancillary data received by
    /// [`recvmsg`](fn.recvmsg.html)
    pub trait CmsgBuffer {
        fn as_bytes_mut(&mut self) -> &mut [u8];
    }

    /// Create a buffer large enough for storing some control messages as returned
    /// by [`recvmsg`](fn.recvmsg.html).
    ///
    /// # Examples
    ///
    /// ```
    /// # #[macro_use] extern crate nix;
    /// # use nix::sys::time::TimeVal;
    /// # use std::os::unix::io::RawFd;
    /// # fn main() {
    /// // Create a buffer for a `ControlMessageOwned::ScmTimestamp` message
    /// let _ = cmsg_space!(TimeVal);
    /// // Create a buffer big enough for a `ControlMessageOwned::ScmRights` message
    /// // with two file descriptors
    /// let _ = cmsg_space!([RawFd; 2]);
    /// // Create a buffer big enough for a `ControlMessageOwned::ScmRights` message
    /// // and a `ControlMessageOwned::ScmTimestamp` message
    /// let _ = cmsg_space!(RawFd, TimeVal);
    /// # }
    /// ```
    // Unfortunately, CMSG_SPACE isn't a const_fn, or else we could return a
    // stack-allocated array.
    #[macro_export]
    macro_rules! cmsg_space {
        ( $( $x:ty ),* ) => {
            {
                use nix::sys::socket::{c_uint, CMSG_SPACE};
                use std::mem;
                let mut space = 0;
                $(
                    // CMSG_SPACE is always safe
                    space += unsafe {
                        CMSG_SPACE(mem::size_of::<$x>() as c_uint)
                    } as usize;
                )*
                let mut v = Vec::<u8>::with_capacity(space);
                // safe because any bit pattern is a valid u8
                unsafe {v.set_len(space)};
                v
            }
        }
    }

    /// A structure used to make room in a cmsghdr passed to recvmsg. The
    /// size and alignment match that of a cmsghdr followed by a T, but the
    /// fields are not accessible, as the actual types will change on a call
    /// to recvmsg.
    ///
    /// To make room for multiple messages, nest the type parameter with
    /// tuples:
    ///
    /// ```
    /// use std::os::unix::io::RawFd;
    /// use nix::sys::socket::CmsgSpace;
    /// let cmsg: CmsgSpace<([RawFd; 3], CmsgSpace<[RawFd; 2]>)> = CmsgSpace::new();
    /// ```
    #[repr(C)]
    #[allow(missing_debug_implementations)]
    pub struct CmsgSpace<T> {
        _hdr: cmsghdr,
        _pad: [align_of_cmsg_data; 0],
        _data: T,
    }

    impl<T> CmsgSpace<T> {
        /// Create a CmsgSpace<T>. The structure is used only for space, so
        /// the fields are uninitialized.
        #[deprecated( since="0.14.0", note="Use the cmsg_space! macro instead")]
        pub fn new() -> Self {
            // Safe because the fields themselves aren't accessible.
            unsafe { mem::uninitialized() }
        }
    }

    impl<T> CmsgBuffer for CmsgSpace<T> {
        fn as_bytes_mut(&mut self) -> &mut [u8] {
            // Safe because nothing ever attempts to access CmsgSpace's fields
            unsafe {
                slice::from_raw_parts_mut(self as *mut CmsgSpace<T> as *mut u8,
                                          mem::size_of::<Self>())
            }
        }
    }

    impl CmsgBuffer for Vec<u8> {
        fn as_bytes_mut(&mut self) -> &mut [u8] {
            &mut self[..]
        }
    }

    #[allow(missing_debug_implementations)] // msghdr isn't Debug
    pub struct RecvMsg<'a> {
        pub bytes: usize,
        cmsghdr: Option<&'a cmsghdr>,
        pub address: Option<SockAddr>,
        pub flags: MsgFlags,
        mhdr: msghdr,
    }

    impl<'a> RecvMsg<'a> {
        /// Iterate over the valid control messages pointed to by this
        /// msghdr.
        pub fn cmsgs(&self) -> CmsgIterator {
            CmsgIterator {
                cmsghdr: self.cmsghdr,
                mhdr: &self.mhdr
            }
        }
    }

    #[allow(missing_debug_implementations)] // msghdr isn't Debug
    pub struct CmsgIterator<'a> {
        /// Control message buffer to decode from. Must adhere to cmsg alignment.
        cmsghdr: Option<&'a cmsghdr>,
        mhdr: &'a msghdr
    }

    impl<'a> Iterator for CmsgIterator<'a> {
        type Item = ControlMessageOwned;

        fn next(&mut self) -> Option<ControlMessageOwned> {
            match self.cmsghdr {
                None => None,   // No more messages
                Some(hdr) => {
                    // Get the data.
                    // Safe if cmsghdr points to valid data returned by recvmsg(2)
                    let cm = unsafe { Some(ControlMessageOwned::decode_from(hdr))};
                    // Advance the internal pointer.  Safe if mhdr and cmsghdr point
                    // to valid data returned by recvmsg(2)
                    self.cmsghdr = unsafe {
                        let p = CMSG_NXTHDR(self.mhdr as *const _, hdr as *const _);
                        p.as_ref()
                    };
                    cm
                }
            }
        }
    }

    /// A type-safe wrapper around a single control message, as used with
    /// [`recvmsg`](#fn.recvmsg).
    ///
    /// [Further reading](http://man7.org/linux/man-pages/man3/cmsg.3.html)
    //  Nix version 0.13.0 and earlier used ControlMessage for both recvmsg and
    //  sendmsg.  However, on some platforms the messages returned by recvmsg may be
    //  unaligned.  ControlMessageOwned takes those messages by copy, obviating any
    //  alignment issues.
    //
    //  See https://github.com/nix-rust/nix/issues/999
    #[allow(missing_debug_implementations)]
    pub enum ControlMessageOwned {
        /// Received version of
        /// [`ControlMessage::ScmRights`][#enum.ControlMessage.html#variant.ScmRights]
        ScmRights(Vec<RawFd>),
        /// Received version of
        /// [`ControlMessage::ScmCredentials`][#enum.ControlMessage.html#variant.ScmCredentials]
        #[cfg(any(target_os = "android", target_os = "linux"))]
        ScmCredentials(libc::ucred),
        /// A message of type `SCM_TIMESTAMP`, containing the time the
        /// packet was received by the kernel.
        ///
        /// See the kernel's explanation in "SO_TIMESTAMP" of
        /// [networking/timestamping](https://www.kernel.org/doc/Documentation/networking/timestamping.txt).
        ///
        /// # Examples
        ///
        // Disable this test on FreeBSD i386
        // https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=222039
        #[cfg_attr(not(all(target_os = "freebsd", target_arch = "x86")), doc = " ```")]
        #[cfg_attr(all(target_os = "freebsd", target_arch = "x86"), doc = " ```no_run")]
        /// # #[macro_use] extern crate nix;
        /// # use nix::sys::socket::*;
        /// # use nix::sys::uio::IoVec;
        /// # use nix::sys::time::*;
        /// # use std::time::*;
        /// # fn main() {
        /// // Set up
        /// let message = "Ohayō!".as_bytes();
        /// let in_socket = socket(
        ///     AddressFamily::Inet,
        ///     SockType::Datagram,
        ///     SockFlag::empty(),
        ///     None).unwrap();
        /// setsockopt(in_socket, sockopt::ReceiveTimestamp, &true).unwrap();
        /// let localhost = InetAddr::new(IpAddr::new_v4(127, 0, 0, 1), 0);
        /// bind(in_socket, &SockAddr::new_inet(localhost)).unwrap();
        /// let address = getsockname(in_socket).unwrap();
        /// // Get initial time
        /// let time0 = SystemTime::now();
        /// // Send the message
        /// let iov = [IoVec::from_slice(message)];
        /// let flags = MsgFlags::empty();
        /// let l = sendmsg(in_socket, &iov, &[], flags, Some(&address)).unwrap();
        /// assert_eq!(message.len(), l);
        /// // Receive the message
        /// let mut buffer = vec![0u8; message.len()];
        /// let mut cmsgspace = cmsg_space!(TimeVal);
        /// let iov = [IoVec::from_mut_slice(&mut buffer)];
        /// let r = recvmsg(in_socket, &iov, Some(&mut cmsgspace), flags).unwrap();
        /// let rtime = match r.cmsgs().next() {
        ///     Some(ControlMessageOwned::ScmTimestamp(rtime)) => rtime,
        ///     Some(_) => panic!("Unexpected control message"),
        ///     None => panic!("No control message")
        /// };
        /// // Check the final time
        /// let time1 = SystemTime::now();
        /// // the packet's received timestamp should lie in-between the two system
        /// // times, unless the system clock was adjusted in the meantime.
        /// let rduration = Duration::new(rtime.tv_sec() as u64,
        ///                               rtime.tv_usec() as u32 * 1000);
        /// assert!(time0.duration_since(UNIX_EPOCH).unwrap() <= rduration);
        /// assert!(rduration <= time1.duration_since(UNIX_EPOCH).unwrap());
        /// // Close socket
        /// nix::unistd::close(in_socket).unwrap();
        /// # }
        /// ```
        ScmTimestamp(TimeVal),
        #[cfg(any(
            target_os = "android",
            target_os = "ios",
            target_os = "linux",
            target_os = "macos",
            target_os = "netbsd",
        ))]
        Ipv4PacketInfo(libc::in_pktinfo),
        #[cfg(any(
            target_os = "android",
            target_os = "dragonfly",
            target_os = "freebsd",
            target_os = "ios",
            target_os = "linux",
            target_os = "macos",
            target_os = "openbsd",
            target_os = "netbsd",
        ))]
        Ipv6PacketInfo(libc::in6_pktinfo),
        #[cfg(any(
            target_os = "freebsd",
            target_os = "ios",
            target_os = "macos",
            target_os = "netbsd",
            target_os = "openbsd",
        ))]
        Ipv4RecvIf(libc::sockaddr_dl),
        #[cfg(any(
            target_os = "freebsd",
            target_os = "ios",
            target_os = "macos",
            target_os = "netbsd",
            target_os = "openbsd",
        ))]
        Ipv4RecvDstAddr(libc::in_addr),
        /// Catch-all variant for unimplemented cmsg types.
        #[doc(hidden)]
        Unknown(UnknownCmsg),
    }

    impl ControlMessageOwned {
        /// Decodes a `ControlMessageOwned` from raw bytes.
        ///
        /// This is only safe to call if the data is correct for the message type
        /// specified in the header. Normally, the kernel ensures that this is the
        /// case. "Correct" in this case includes correct length, alignment and
        /// actual content.
        ///
        /// Returns `None` if the data may be unaligned.  In that case use
        /// `ControlMessageOwned::decode_from`.
        unsafe fn decode_from(header: &cmsghdr) -> ControlMessageOwned
        {
            let p = CMSG_DATA(header);
            let len = header as *const _ as usize + header.cmsg_len as usize
                - p as usize;
            match (header.cmsg_level, header.cmsg_type) {
                (libc::SOL_SOCKET, libc::SCM_RIGHTS) => {
                    let n = len / mem::size_of::<RawFd>();
                    let mut fds = Vec::with_capacity(n);
                    for i in 0..n {
                        let fdp = (p as *const RawFd).offset(i as isize);
                        fds.push(ptr::read_unaligned(fdp));
                    }
                    let cmo = ControlMessageOwned::ScmRights(fds);
                    cmo
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                (libc::SOL_SOCKET, libc::SCM_CREDENTIALS) => {
                    let cred: libc::ucred = ptr::read_unaligned(p as *const _);
                    ControlMessageOwned::ScmCredentials(cred)
                }
                (libc::SOL_SOCKET, libc::SCM_TIMESTAMP) => {
                    let tv: libc::timeval = ptr::read_unaligned(p as *const _);
                    ControlMessageOwned::ScmTimestamp(TimeVal::from(tv))
                },
                #[cfg(any(
                    target_os = "android",
                    target_os = "freebsd",
                    target_os = "ios",
                    target_os = "linux",
                    target_os = "macos"
                ))]
                (libc::IPPROTO_IPV6, libc::IPV6_PKTINFO) => {
                    let info = ptr::read_unaligned(p as *const libc::in6_pktinfo);
                    ControlMessageOwned::Ipv6PacketInfo(info)
                }
                #[cfg(any(
                    target_os = "android",
                    target_os = "ios",
                    target_os = "linux",
                    target_os = "macos",
                    target_os = "netbsd",
                ))]
                (libc::IPPROTO_IP, libc::IP_PKTINFO) => {
                    let info = ptr::read_unaligned(p as *const libc::in_pktinfo);
                    ControlMessageOwned::Ipv4PacketInfo(info)
                }
                #[cfg(any(
                    target_os = "freebsd",
                    target_os = "ios",
                    target_os = "macos",
                    target_os = "netbsd",
                    target_os = "openbsd",
                ))]
                (libc::IPPROTO_IP, libc::IP_RECVIF) => {
                    let dl = ptr::read_unaligned(p as *const libc::sockaddr_dl);
                    ControlMessageOwned::Ipv4RecvIf(dl)
                },
                #[cfg(any(
                    target_os = "freebsd",
                    target_os = "ios",
                    target_os = "macos",
                    target_os = "netbsd",
                    target_os = "openbsd",
                ))]
                (libc::IPPROTO_IP, libc::IP_RECVDSTADDR) => {
                    let dl = ptr::read_unaligned(p as *const libc::in_addr);
                    ControlMessageOwned::Ipv4RecvDstAddr(dl)
                },
                (_, _) => {
                    let sl = slice::from_raw_parts(p, len);
                    let ucmsg = UnknownCmsg(*header, Vec::<u8>::from(&sl[..]));
                    ControlMessageOwned::Unknown(ucmsg)
                }
            }
        }
    }

    /// A type-safe zero-copy wrapper around a single control message, as used wih
    /// [`sendmsg`](#fn.sendmsg).  More types may be added to this enum; do not
    /// exhaustively pattern-match it.
    ///
    /// [Further reading](http://man7.org/linux/man-pages/man3/cmsg.3.html)
    #[allow(missing_debug_implementations)]
    pub enum ControlMessage<'a> {
        /// A message of type `SCM_RIGHTS`, containing an array of file
        /// descriptors passed between processes.
        ///
        /// See the description in the "Ancillary messages" section of the
        /// [unix(7) man page](http://man7.org/linux/man-pages/man7/unix.7.html).
        ///
        /// Using multiple `ScmRights` messages for a single `sendmsg` call isn't
        /// recommended since it causes platform-dependent behaviour: It might
        /// swallow all but the first `ScmRights` message or fail with `EINVAL`.
        /// Instead, you can put all fds to be passed into a single `ScmRights`
        /// message.
        ScmRights(&'a [RawFd]),
        /// A message of type `SCM_CREDENTIALS`, containing the pid, uid and gid of
        /// a process connected to the socket.
        ///
        /// This is similar to the socket option `SO_PEERCRED`, but requires a
        /// process to explicitly send its credentials. A process running as root is
        /// allowed to specify any credentials, while credentials sent by other
        /// processes are verified by the kernel.
        ///
        /// For further information, please refer to the
        /// [`unix(7)`](http://man7.org/linux/man-pages/man7/unix.7.html) man page.
        // FIXME: When `#[repr(transparent)]` is stable, use it on `UnixCredentials`
        // and put that in here instead of a raw ucred.
        #[cfg(any(target_os = "android", target_os = "linux"))]
        ScmCredentials(&'a libc::ucred),

        /// Set IV for `AF_ALG` crypto API.
        ///
        /// For further information, please refer to the
        /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
        #[cfg(any(
            target_os = "android",
            target_os = "linux",
        ))]
        AlgSetIv(&'a [u8]),
        /// Set crypto operation for `AF_ALG` crypto API. It may be one of
        /// `ALG_OP_ENCRYPT` or `ALG_OP_DECRYPT`
        ///
        /// For further information, please refer to the
        /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
        #[cfg(any(
            target_os = "android",
            target_os = "linux",
        ))]
        AlgSetOp(&'a libc::c_int),
        /// Set the length of associated authentication data (AAD) (applicable only to AEAD algorithms)
        /// for `AF_ALG` crypto API.
        ///
        /// For further information, please refer to the
        /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
        #[cfg(any(
            target_os = "android",
            target_os = "linux",
        ))]
        AlgSetAeadAssoclen(&'a u32),

    }

    // An opaque structure used to prevent cmsghdr from being a public type
    #[doc(hidden)]
    #[allow(missing_debug_implementations)]
    pub struct UnknownCmsg(cmsghdr, Vec<u8>);

    impl<'a> ControlMessage<'a> {
        /// The value of CMSG_SPACE on this message.
        /// Safe because CMSG_SPACE is always safe
        fn space(&self) -> usize {
            unsafe{CMSG_SPACE(self.len() as libc::c_uint) as usize}
        }

        /// The value of CMSG_LEN on this message.
        /// Safe because CMSG_LEN is always safe
        #[cfg(any(target_os = "android",
                  all(target_os = "linux", not(target_env = "musl"))))]
        fn cmsg_len(&self) -> usize {
            unsafe{CMSG_LEN(self.len() as libc::c_uint) as usize}
        }

        #[cfg(not(any(target_os = "android",
                      all(target_os = "linux", not(target_env = "musl")))))]
        fn cmsg_len(&self) -> libc::c_uint {
            unsafe{CMSG_LEN(self.len() as libc::c_uint)}
        }

        /// Return a reference to the payload data as a byte pointer
        fn copy_to_cmsg_data(&self, cmsg_data: *mut u8) {
            let data_ptr = match self {
                &ControlMessage::ScmRights(fds) => {
                    fds as *const _ as *const u8
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::ScmCredentials(creds) => {
                    creds as *const libc::ucred as *const u8
                }
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetIv(iv) => {
                    unsafe {
                        let alg_iv = cmsg_data as *mut libc::af_alg_iv;
                        (*alg_iv).ivlen = iv.len() as u32;
                        ptr::copy_nonoverlapping(
                            iv.as_ptr(),
                            (*alg_iv).iv.as_mut_ptr(),
                            iv.len()
                        );
                    };
                    return
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetOp(op) => {
                    op as *const _ as *const u8
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetAeadAssoclen(len) => {
                    len as *const _ as *const u8
                },
            };
            unsafe {
                ptr::copy_nonoverlapping(
                    data_ptr,
                    cmsg_data,
                    self.len()
                )
            };
        }

        /// The size of the payload, excluding its cmsghdr
        fn len(&self) -> usize {
            match self {
                &ControlMessage::ScmRights(fds) => {
                    mem::size_of_val(fds)
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::ScmCredentials(creds) => {
                    mem::size_of_val(creds)
                }
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetIv(iv) => {
                    mem::size_of::<libc::af_alg_iv>() + iv.len()
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetOp(op) => {
                    mem::size_of_val(op)
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetAeadAssoclen(len) => {
                    mem::size_of_val(len)
                },
            }
        }

        /// Returns the value to put into the `cmsg_level` field of the header.
        fn cmsg_level(&self) -> libc::c_int {
            match self {
                &ControlMessage::ScmRights(_) => libc::SOL_SOCKET,
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::ScmCredentials(_) => libc::SOL_SOCKET,
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetIv(_) | &ControlMessage::AlgSetOp(_) | &ControlMessage::AlgSetAeadAssoclen(_) => {
                    libc::SOL_ALG
                },
            }
        }

        /// Returns the value to put into the `cmsg_type` field of the header.
        fn cmsg_type(&self) -> libc::c_int {
            match self {
                &ControlMessage::ScmRights(_) => libc::SCM_RIGHTS,
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::ScmCredentials(_) => libc::SCM_CREDENTIALS,
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetIv(_) => {
                    libc::ALG_SET_IV
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetOp(_) => {
                    libc::ALG_SET_OP
                },
                #[cfg(any(target_os = "android", target_os = "linux"))]
                &ControlMessage::AlgSetAeadAssoclen(_) => {
                    libc::ALG_SET_AEAD_ASSOCLEN
                },
            }
        }

        // Unsafe: cmsg must point to a valid cmsghdr with enough space to
        // encode self.
        unsafe fn encode_into(&self, cmsg: *mut cmsghdr) {
            (*cmsg).cmsg_level = self.cmsg_level();
            (*cmsg).cmsg_type = self.cmsg_type();
            (*cmsg).cmsg_len = self.cmsg_len();
            self.copy_to_cmsg_data(CMSG_DATA(cmsg));
        }
    }

    /// Send data in scatter-gather vectors to a socket, possibly accompanied
    /// by ancillary data. Optionally direct the message at the given address,
    /// as with sendto.
    ///
    /// Allocates if cmsgs is nonempty.
    pub fn sendmsg(fd: RawFd, iov: &[IoVec<&[u8]>], cmsgs: &[ControlMessage],
                   flags: MsgFlags, addr: Option<&SockAddr>) -> Result<usize>
    {
        let capacity = cmsgs.iter().map(|c| c.space()).sum();

        // First size the buffer needed to hold the cmsgs.  It must be zeroed,
        // because subsequent code will not clear the padding bytes.
        let cmsg_buffer = vec![0u8; capacity];

        // Next encode the sending address, if provided
        let (name, namelen) = match addr {
            Some(addr) => {
                let (x, y) = unsafe { addr.as_ffi_pair() };
                (x as *const _, y)
            },
            None => (ptr::null(), 0),
        };

        // The message header must be initialized before the individual cmsgs.
        let cmsg_ptr = if capacity > 0 {
            cmsg_buffer.as_ptr() as *mut c_void
        } else {
            ptr::null_mut()
        };

        let mhdr = {
            // Musl's msghdr has private fields, so this is the only way to
            // initialize it.
            let mut mhdr: msghdr = unsafe{mem::uninitialized()};
            mhdr.msg_name = name as *mut _;
            mhdr.msg_namelen = namelen;
            // transmute iov into a mutable pointer.  sendmsg doesn't really mutate
            // the buffer, but the standard says that it takes a mutable pointer
            mhdr.msg_iov = iov.as_ptr() as *mut _;
            mhdr.msg_iovlen = iov.len() as _;
            mhdr.msg_control = cmsg_ptr;
            mhdr.msg_controllen = capacity as _;
            mhdr.msg_flags = 0;
            mhdr
        };

        // Encode each cmsg.  This must happen after initializing the header because
        // CMSG_NEXT_HDR and friends read the msg_control and msg_controllen fields.
        // CMSG_FIRSTHDR is always safe
        let mut pmhdr: *mut cmsghdr = unsafe{CMSG_FIRSTHDR(&mhdr as *const msghdr)};
        for cmsg in cmsgs {
            assert_ne!(pmhdr, ptr::null_mut());
            // Safe because we know that pmhdr is valid, and we initialized it with
            // sufficient space
            unsafe { cmsg.encode_into(pmhdr) };
            // Safe because mhdr is valid
            pmhdr = unsafe{CMSG_NXTHDR(&mhdr as *const msghdr, pmhdr)};
        }

        let ret = unsafe { libc::sendmsg(fd, &mhdr, flags.bits()) };

        Errno::result(ret).map(|r| r as usize)
    }

    /// Receive message in scatter-gather vectors from a socket, and
    /// optionally receive ancillary data into the provided buffer.
    /// If no ancillary data is desired, use () as the type parameter.
    ///
    /// # References
    /// [recvmsg(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recvmsg.html)
    pub fn recvmsg<'a>(fd: RawFd, iov: &[IoVec<&mut [u8]>],
                       cmsg_buffer: Option<&'a mut CmsgBuffer>,
                       flags: MsgFlags) -> Result<RecvMsg<'a>>
    {
        let mut address: sockaddr_storage = unsafe { mem::uninitialized() };
        let (msg_control, msg_controllen) = match cmsg_buffer {
            Some(cmsgspace) => {
                let msg_buf = cmsgspace.as_bytes_mut();
                (msg_buf.as_mut_ptr(), msg_buf.len())
            },
            None => (ptr::null_mut(), 0),
        };
        let mut mhdr = {
            // Musl's msghdr has private fields, so this is the only way to
            // initialize it.
            let mut mhdr: msghdr = unsafe{mem::uninitialized()};
            mhdr.msg_name = &mut address as *mut sockaddr_storage as *mut c_void;
            mhdr.msg_namelen = mem::size_of::<sockaddr_storage>() as socklen_t;
            mhdr.msg_iov = iov.as_ptr() as *mut iovec;
            mhdr.msg_iovlen = iov.len() as _;
            mhdr.msg_control = msg_control as *mut c_void;
            mhdr.msg_controllen = msg_controllen as _;
            mhdr.msg_flags = 0;
            mhdr
        };

        let ret = unsafe { libc::recvmsg(fd, &mut mhdr, flags.bits()) };

        Errno::result(ret).map(|r| {
            let cmsghdr = unsafe {
                if mhdr.msg_controllen > 0 {
                    // got control message(s)
                    debug_assert!(!mhdr.msg_control.is_null());
                    debug_assert!(msg_controllen >= mhdr.msg_controllen as usize);
                    CMSG_FIRSTHDR(&mhdr as *const msghdr)
                } else {
                    ptr::null()
                }.as_ref()
            };

            let address = unsafe {
                sockaddr_storage_to_addr(&address, mhdr.msg_namelen as usize).ok()
            };
            RecvMsg {
                bytes: r as usize,
                cmsghdr,
                address,
                flags: MsgFlags::from_bits_truncate(mhdr.msg_flags),
                mhdr,
            }
        })
    }

    /// Create an endpoint for communication
    ///
    /// The `protocol` specifies a particular protocol to be used with the
    /// socket.  Normally only a single protocol exists to support a
    /// particular socket type within a given protocol family, in which case
    /// protocol can be specified as `None`.  However, it is possible that many
    /// protocols may exist, in which case a particular protocol must be
    /// specified in this manner.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socket.html)
    pub fn socket<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, flags: SockFlag, protocol: T) -> Result<RawFd> {
        let protocol = match protocol.into() {
            None => 0,
            Some(p) => p as c_int,
        };

        // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
        // little easier to understand by separating it out. So we have to merge these bitfields
        // here.
        let mut ty = ty as c_int;
        ty |= flags.bits();

        let res = unsafe { libc::socket(domain as c_int, ty, protocol) };

        Errno::result(res)
    }

    /// Create a pair of connected sockets
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socketpair.html)
    pub fn socketpair<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, protocol: T,
                      flags: SockFlag) -> Result<(RawFd, RawFd)> {
        let protocol = match protocol.into() {
            None => 0,
            Some(p) => p as c_int,
        };

        // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
        // little easier to understand by separating it out. So we have to merge these bitfields
        // here.
        let mut ty = ty as c_int;
        ty |= flags.bits();

        let mut fds = [-1, -1];

        let res = unsafe { libc::socketpair(domain as c_int, ty, protocol, fds.as_mut_ptr()) };
        Errno::result(res)?;

        Ok((fds[0], fds[1]))
    }

    /// Listen for connections on a socket
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/listen.html)
    pub fn listen(sockfd: RawFd, backlog: usize) -> Result<()> {
        let res = unsafe { libc::listen(sockfd, backlog as c_int) };

        Errno::result(res).map(drop)
    }

    /// Bind a name to a socket
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/bind.html)
    pub fn bind(fd: RawFd, addr: &SockAddr) -> Result<()> {
        let res = unsafe {
            let (ptr, len) = addr.as_ffi_pair();
            libc::bind(fd, ptr, len)
        };

        Errno::result(res).map(drop)
    }

    /// Accept a connection on a socket
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/accept.html)
    pub fn accept(sockfd: RawFd) -> Result<RawFd> {
        let res = unsafe { libc::accept(sockfd, ptr::null_mut(), ptr::null_mut()) };

        Errno::result(res)
    }

    /// Accept a connection on a socket
    ///
    /// [Further reading](http://man7.org/linux/man-pages/man2/accept.2.html)
    #[cfg(any(target_os = "android",
              target_os = "freebsd",
              target_os = "linux",
              target_os = "openbsd"))]
    pub fn accept4(sockfd: RawFd, flags: SockFlag) -> Result<RawFd> {
        let res = unsafe { libc::accept4(sockfd, ptr::null_mut(), ptr::null_mut(), flags.bits()) };

        Errno::result(res)
    }

    /// Initiate a connection on a socket
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/connect.html)
    pub fn connect(fd: RawFd, addr: &SockAddr) -> Result<()> {
        let res = unsafe {
            let (ptr, len) = addr.as_ffi_pair();
            libc::connect(fd, ptr, len)
        };

        Errno::result(res).map(drop)
    }

    /// Receive data from a connection-oriented socket. Returns the number of
    /// bytes read
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recv.html)
    pub fn recv(sockfd: RawFd, buf: &mut [u8], flags: MsgFlags) -> Result<usize> {
        unsafe {
            let ret = libc::recv(
                sockfd,
                buf.as_ptr() as *mut c_void,
                buf.len() as size_t,
                flags.bits());

            Errno::result(ret).map(|r| r as usize)
        }
    }

    /// Receive data from a connectionless or connection-oriented socket. Returns
    /// the number of bytes read and the socket address of the sender.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recvfrom.html)
    pub fn recvfrom(sockfd: RawFd, buf: &mut [u8]) -> Result<(usize, SockAddr)> {
        unsafe {
            let addr: sockaddr_storage = mem::zeroed();
            let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

            let ret = Errno::result(libc::recvfrom(
                sockfd,
                buf.as_ptr() as *mut c_void,
                buf.len() as size_t,
                0,
                mem::transmute(&addr),
                &mut len as *mut socklen_t))?;

            sockaddr_storage_to_addr(&addr, len as usize)
                .map(|addr| (ret as usize, addr))
        }
    }

    /// Send a message to a socket
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/sendto.html)
    pub fn sendto(fd: RawFd, buf: &[u8], addr: &SockAddr, flags: MsgFlags) -> Result<usize> {
        let ret = unsafe {
            let (ptr, len) = addr.as_ffi_pair();
            libc::sendto(fd, buf.as_ptr() as *const c_void, buf.len() as size_t, flags.bits(), ptr, len)
        };

        Errno::result(ret).map(|r| r as usize)
    }

    /// Send data to a connection-oriented socket. Returns the number of bytes read
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html)
    pub fn send(fd: RawFd, buf: &[u8], flags: MsgFlags) -> Result<usize> {
        let ret = unsafe {
            libc::send(fd, buf.as_ptr() as *const c_void, buf.len() as size_t, flags.bits())
        };

        Errno::result(ret).map(|r| r as usize)
    }

    /*
     *
     * ===== Socket Options =====
     *
     */

    /// The protocol level at which to get / set socket options. Used as an
    /// argument to `getsockopt` and `setsockopt`.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/setsockopt.html)
    #[repr(i32)]
    #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
    pub enum SockLevel {
        Socket = libc::SOL_SOCKET,
        Tcp = libc::IPPROTO_TCP,
        Ip = libc::IPPROTO_IP,
        Ipv6 = libc::IPPROTO_IPV6,
        Udp = libc::IPPROTO_UDP,
        #[cfg(any(target_os = "android", target_os = "linux"))]
        Netlink = libc::SOL_NETLINK,
        #[cfg(any(target_os = "android", target_os = "linux"))]
        Alg = libc::SOL_ALG,
    }

    /// Represents a socket option that can be accessed or set. Used as an argument
    /// to `getsockopt`
    pub trait GetSockOpt : Copy {
        type Val;

        #[doc(hidden)]
        fn get(&self, fd: RawFd) -> Result<Self::Val>;
    }

    /// Represents a socket option that can be accessed or set. Used as an argument
    /// to `setsockopt`
    pub trait SetSockOpt : Clone {
        type Val;

        #[doc(hidden)]
        fn set(&self, fd: RawFd, val: &Self::Val) -> Result<()>;
    }

    /// Get the current value for the requested socket option
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockopt.html)
    pub fn getsockopt<O: GetSockOpt>(fd: RawFd, opt: O) -> Result<O::Val> {
        opt.get(fd)
    }

    /// Sets the value for the requested socket option
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/setsockopt.html)
    ///
    /// # Examples
    ///
    /// ```
    /// use nix::sys::socket::setsockopt;
    /// use nix::sys::socket::sockopt::KeepAlive;
    /// use std::net::TcpListener;
    /// use std::os::unix::io::AsRawFd;
    ///
    /// let listener = TcpListener::bind("0.0.0.0:0").unwrap();
    /// let fd = listener.as_raw_fd();
    /// let res = setsockopt(fd, KeepAlive, &true);
    /// assert!(res.is_ok());
    /// ```
    pub fn setsockopt<O: SetSockOpt>(fd: RawFd, opt: O, val: &O::Val) -> Result<()> {
        opt.set(fd, val)
    }

    /// Get the address of the peer connected to the socket `fd`.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getpeername.html)
    pub fn getpeername(fd: RawFd) -> Result<SockAddr> {
        unsafe {
            let addr: sockaddr_storage = mem::uninitialized();
            let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

            let ret = libc::getpeername(fd, mem::transmute(&addr), &mut len);

            Errno::result(ret)?;

            sockaddr_storage_to_addr(&addr, len as usize)
        }
    }

    /// Get the current address to which the socket `fd` is bound.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockname.html)
    pub fn getsockname(fd: RawFd) -> Result<SockAddr> {
        unsafe {
            let addr: sockaddr_storage = mem::uninitialized();
            let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

            let ret = libc::getsockname(fd, mem::transmute(&addr), &mut len);

            Errno::result(ret)?;

            sockaddr_storage_to_addr(&addr, len as usize)
        }
    }

    /// Return the appropriate `SockAddr` type from a `sockaddr_storage` of a certain
    /// size.  In C this would usually be done by casting.  The `len` argument
    /// should be the number of bytes in the `sockaddr_storage` that are actually
    /// allocated and valid.  It must be at least as large as all the useful parts
    /// of the structure.  Note that in the case of a `sockaddr_un`, `len` need not
    /// include the terminating null.
    pub unsafe fn sockaddr_storage_to_addr(
        addr: &sockaddr_storage,
        len: usize) -> Result<SockAddr> {

        if len < mem::size_of_val(&addr.ss_family) {
            return Err(Error::Sys(Errno::ENOTCONN));
        }

        match addr.ss_family as c_int {
            libc::AF_INET => {
                assert!(len as usize == mem::size_of::<sockaddr_in>());
                let ret = *(addr as *const _ as *const sockaddr_in);
                Ok(SockAddr::Inet(InetAddr::V4(ret)))
            }
            libc::AF_INET6 => {
                assert!(len as usize == mem::size_of::<sockaddr_in6>());
                Ok(SockAddr::Inet(InetAddr::V6(*(addr as *const _ as *const sockaddr_in6))))
            }
            libc::AF_UNIX => {
                let sun = *(addr as *const _ as *const sockaddr_un);
                let pathlen = len - offset_of!(sockaddr_un, sun_path);
                Ok(SockAddr::Unix(UnixAddr(sun, pathlen)))
            }
            #[cfg(any(target_os = "android", target_os = "linux"))]
            libc::AF_NETLINK => {
                use libc::sockaddr_nl;
                Ok(SockAddr::Netlink(NetlinkAddr(*(addr as *const _ as *const sockaddr_nl))))
            }
            #[cfg(any(target_os = "android", target_os = "linux"))]
            libc::AF_ALG => {
                use libc::sockaddr_alg;
                Ok(SockAddr::Alg(AlgAddr(*(addr as *const _ as *const sockaddr_alg))))
            }
            af => panic!("unexpected address family {}", af),
        }
    }

    #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
    pub enum Shutdown {
        /// Further receptions will be disallowed.
        Read,
        /// Further  transmissions will be disallowed.
        Write,
        /// Further receptions and transmissions will be disallowed.
        Both,
    }

    /// Shut down part of a full-duplex connection.
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/shutdown.html)
    pub fn shutdown(df: RawFd, how: Shutdown) -> Result<()> {
        unsafe {
            use libc::shutdown;

            let how = match how {
                Shutdown::Read  => libc::SHUT_RD,
                Shutdown::Write => libc::SHUT_WR,
                Shutdown::Both  => libc::SHUT_RDWR,
            };

            Errno::result(shutdown(df, how)).map(drop)
        }
    }

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