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    //! Posix Message Queue functions
    //!
    //! [Further reading and details on the C API](http://man7.org/linux/man-pages/man7/mq_overview.7.html)

    use Result;
    use errno::Errno;

    use libc::{self, c_char, c_long, mqd_t, size_t};
    use std::ffi::CString;
    use sys::stat::Mode;
    use std::mem;

    libc_bitflags!{
        pub struct MQ_OFlag: libc::c_int {
            O_RDONLY;
            O_WRONLY;
            O_RDWR;
            O_CREAT;
            O_EXCL;
            O_NONBLOCK;
            O_CLOEXEC;
        }
    }

    libc_bitflags!{
        pub struct FdFlag: libc::c_int {
            FD_CLOEXEC;
        }
    }

    #[repr(C)]
    #[derive(Clone, Copy)]
    #[allow(missing_debug_implementations)]
    pub struct MqAttr {
        mq_attr: libc::mq_attr,
    }

    impl PartialEq<MqAttr> for MqAttr {
        fn eq(&self, other: &MqAttr) -> bool {
            let self_attr = self.mq_attr;
            let other_attr = other.mq_attr;
            self_attr.mq_flags == other_attr.mq_flags && self_attr.mq_maxmsg == other_attr.mq_maxmsg &&
            self_attr.mq_msgsize == other_attr.mq_msgsize &&
            self_attr.mq_curmsgs == other_attr.mq_curmsgs
        }
    }

    impl MqAttr {
        pub fn new(mq_flags: c_long,
                   mq_maxmsg: c_long,
                   mq_msgsize: c_long,
                   mq_curmsgs: c_long)
                   -> MqAttr {
            let mut attr = unsafe { mem::uninitialized::<libc::mq_attr>() };
            attr.mq_flags = mq_flags;
            attr.mq_maxmsg = mq_maxmsg;
            attr.mq_msgsize = mq_msgsize;
            attr.mq_curmsgs = mq_curmsgs;
            MqAttr { mq_attr: attr }
        }

        pub fn flags(&self) -> c_long {
            self.mq_attr.mq_flags
        }
    }

    /// Open a message queue
    ///
    /// See also [`mq_open(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_open.html)
    pub fn mq_open(name: &CString,
                   oflag: MQ_OFlag,
                   mode: Mode,
                   attr: Option<&MqAttr>)
                   -> Result<mqd_t> {
        let res = match attr {
            Some(mq_attr) => unsafe {
                libc::mq_open(name.as_ptr(),
                              oflag.bits(),
                              mode.bits() as libc::c_int,
                              &mq_attr.mq_attr as *const libc::mq_attr)
            },
            None => unsafe { libc::mq_open(name.as_ptr(), oflag.bits()) },
        };
        Errno::result(res)
    }

    /// Remove a message queue
    ///
    /// See also [`mq_unlink(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_unlink.html)
    pub fn mq_unlink(name: &CString) -> Result<()> {
        let res = unsafe { libc::mq_unlink(name.as_ptr()) };
        Errno::result(res).map(drop)
    }

    /// Close a message queue
    ///
    /// See also [`mq_close(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_close.html)
    pub fn mq_close(mqdes: mqd_t) -> Result<()> {
        let res = unsafe { libc::mq_close(mqdes) };
        Errno::result(res).map(drop)
    }

    /// Receive a message from a message queue
    ///
    /// See also [`mq_receive(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_receive.html)
    pub fn mq_receive(mqdes: mqd_t, message: &mut [u8], msg_prio: &mut u32) -> Result<usize> {
        let len = message.len() as size_t;
        let res = unsafe {
            libc::mq_receive(mqdes,
                             message.as_mut_ptr() as *mut c_char,
                             len,
                             msg_prio as *mut u32)
        };
        Errno::result(res).map(|r| r as usize)
    }

    /// Send a message to a message queue
    ///
    /// See also [`mq_send(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_send.html)
    pub fn mq_send(mqdes: mqd_t, message: &[u8], msq_prio: u32) -> Result<()> {
        let res = unsafe {
            libc::mq_send(mqdes,
                          message.as_ptr() as *const c_char,
                          message.len(),
                          msq_prio)
        };
        Errno::result(res).map(drop)
    }

    /// Get message queue attributes
    ///
    /// See also [`mq_getattr(2)`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_getattr.html)
    pub fn mq_getattr(mqd: mqd_t) -> Result<MqAttr> {
        let mut attr = unsafe { mem::uninitialized::<libc::mq_attr>() };
        let res = unsafe { libc::mq_getattr(mqd, &mut attr) };
        Errno::result(res).map(|_| MqAttr { mq_attr: attr })
    }

    /// Set the attributes of the message queue. Only `O_NONBLOCK` can be set, everything else will be ignored
    /// Returns the old attributes
    /// It is recommend to use the `mq_set_nonblock()` and `mq_remove_nonblock()` convenience functions as they are easier to use
    ///
    /// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mq_setattr.html)
    pub fn mq_setattr(mqd: mqd_t, newattr: &MqAttr) -> Result<MqAttr> {
        let mut attr = unsafe { mem::uninitialized::<libc::mq_attr>() };
        let res = unsafe { libc::mq_setattr(mqd, &newattr.mq_attr as *const libc::mq_attr, &mut attr) };
        Errno::result(res).map(|_| MqAttr { mq_attr: attr })
    }

    /// Convenience function.
    /// Sets the `O_NONBLOCK` attribute for a given message queue descriptor
    /// Returns the old attributes
    pub fn mq_set_nonblock(mqd: mqd_t) -> Result<(MqAttr)> {
        let oldattr = mq_getattr(mqd)?;
        let newattr = MqAttr::new(MQ_OFlag::O_NONBLOCK.bits() as c_long,
                                  oldattr.mq_attr.mq_maxmsg,
                                  oldattr.mq_attr.mq_msgsize,
                                  oldattr.mq_attr.mq_curmsgs);
        mq_setattr(mqd, &newattr)
    }

    /// Convenience function.
    /// Removes `O_NONBLOCK` attribute for a given message queue descriptor
    /// Returns the old attributes
    pub fn mq_remove_nonblock(mqd: mqd_t) -> Result<(MqAttr)> {
        let oldattr = mq_getattr(mqd)?;
        let newattr = MqAttr::new(0,
                                  oldattr.mq_attr.mq_maxmsg,
                                  oldattr.mq_attr.mq_msgsize,
                                  oldattr.mq_attr.mq_curmsgs);
        mq_setattr(mqd, &newattr)
    }

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