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    use libc::{gid_t, pid_t, uid_t};

    /// Credentials of a process
    #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
    pub struct UCred {
        /// PID (process ID) of the process
        pid: Option<pid_t>,
        /// UID (user ID) of the process
        uid: uid_t,
        /// GID (group ID) of the process
        gid: gid_t,
    }

    impl UCred {
        /// Gets UID (user ID) of the process.
        pub fn uid(&self) -> uid_t {
            self.uid
        }

        /// Gets GID (group ID) of the process.
        pub fn gid(&self) -> gid_t {
            self.gid
        }

        /// Gets PID (process ID) of the process.
        ///
        /// This is only implemented under Linux, Android, iOS, macOS, Solaris and
        /// Illumos. On other plaforms this will always return `None`.
        pub fn pid(&self) -> Option<pid_t> {
            self.pid
        }
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub(crate) use self::impl_linux::get_peer_cred;

    #[cfg(any(
        target_os = "dragonfly",
        target_os = "freebsd",
        target_os = "netbsd",
        target_os = "openbsd"
    ))]
    pub(crate) use self::impl_bsd::get_peer_cred;

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    pub(crate) use self::impl_macos::get_peer_cred;

    #[cfg(any(target_os = "solaris", target_os = "illumos"))]
    pub(crate) use self::impl_solaris::get_peer_cred;

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub(crate) mod impl_linux {
        use crate::net::unix::UnixStream;

        use libc::{c_void, getsockopt, socklen_t, SOL_SOCKET, SO_PEERCRED};
        use std::{io, mem};

        use libc::ucred;

        pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
            use std::os::unix::io::AsRawFd;

            unsafe {
                let raw_fd = sock.as_raw_fd();

                let mut ucred = ucred {
                    pid: 0,
                    uid: 0,
                    gid: 0,
                };

                let ucred_size = mem::size_of::<ucred>();

                // These paranoid checks should be optimized-out
                assert!(mem::size_of::<u32>() <= mem::size_of::<usize>());
                assert!(ucred_size <= u32::max_value() as usize);

                let mut ucred_size = ucred_size as socklen_t;

                let ret = getsockopt(
                    raw_fd,
                    SOL_SOCKET,
                    SO_PEERCRED,
                    &mut ucred as *mut ucred as *mut c_void,
                    &mut ucred_size,
                );
                if ret == 0 && ucred_size as usize == mem::size_of::<ucred>() {
                    Ok(super::UCred {
                        uid: ucred.uid,
                        gid: ucred.gid,
                        pid: Some(ucred.pid),
                    })
                } else {
                    Err(io::Error::last_os_error())
                }
            }
        }
    }

    #[cfg(any(
        target_os = "dragonfly",
        target_os = "freebsd",
        target_os = "netbsd",
        target_os = "openbsd"
    ))]
    pub(crate) mod impl_bsd {
        use crate::net::unix::UnixStream;

        use libc::getpeereid;
        use std::io;
        use std::mem::MaybeUninit;
        use std::os::unix::io::AsRawFd;

        pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
            unsafe {
                let raw_fd = sock.as_raw_fd();

                let mut uid = MaybeUninit::uninit();
                let mut gid = MaybeUninit::uninit();

                let ret = getpeereid(raw_fd, uid.as_mut_ptr(), gid.as_mut_ptr());

                if ret == 0 {
                    Ok(super::UCred {
                        uid: uid.assume_init(),
                        gid: gid.assume_init(),
                        pid: None,
                    })
                } else {
                    Err(io::Error::last_os_error())
                }
            }
        }
    }

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    pub(crate) mod impl_macos {
        use crate::net::unix::UnixStream;

        use libc::{c_void, getpeereid, getsockopt, pid_t, LOCAL_PEEREPID, SOL_LOCAL};
        use std::io;
        use std::mem::size_of;
        use std::mem::MaybeUninit;
        use std::os::unix::io::AsRawFd;

        pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
            unsafe {
                let raw_fd = sock.as_raw_fd();

                let mut uid = MaybeUninit::uninit();
                let mut gid = MaybeUninit::uninit();
                let mut pid: MaybeUninit<pid_t> = MaybeUninit::uninit();
                let mut pid_size: MaybeUninit<u32> = MaybeUninit::new(size_of::<pid_t>() as u32);

                if getsockopt(
                    raw_fd,
                    SOL_LOCAL,
                    LOCAL_PEEREPID,
                    pid.as_mut_ptr() as *mut c_void,
                    pid_size.as_mut_ptr(),
                ) != 0
                {
                    return Err(io::Error::last_os_error());
                }

                assert!(pid_size.assume_init() == (size_of::<pid_t>() as u32));

                let ret = getpeereid(raw_fd, uid.as_mut_ptr(), gid.as_mut_ptr());

                if ret == 0 {
                    Ok(super::UCred {
                        uid: uid.assume_init(),
                        gid: gid.assume_init(),
                        pid: Some(pid.assume_init()),
                    })
                } else {
                    Err(io::Error::last_os_error())
                }
            }
        }
    }

    #[cfg(any(target_os = "solaris", target_os = "illumos"))]
    pub(crate) mod impl_solaris {
        use crate::net::unix::UnixStream;
        use std::io;
        use std::os::unix::io::AsRawFd;
        use std::ptr;

        pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
            unsafe {
                let raw_fd = sock.as_raw_fd();

                let mut cred = ptr::null_mut();
                let ret = libc::getpeerucred(raw_fd, &mut cred);

                if ret == 0 {
                    let uid = libc::ucred_geteuid(cred);
                    let gid = libc::ucred_getegid(cred);
                    let pid = libc::ucred_getpid(cred);

                    libc::ucred_free(cred);

                    Ok(super::UCred {
                        uid,
                        gid,
                        pid: Some(pid),
                    })
                } else {
                    Err(io::Error::last_os_error())
                }
            }
        }
    }