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    // Copyright 2014-2015 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 os::unix::prelude::*;

    use collections::hash_map::{HashMap, Entry};
    use env;
    use ffi::{OsString, OsStr, CString, CStr};
    use fmt;
    use io::{self, Error, ErrorKind};
    use libc::{self, pid_t, c_int, gid_t, uid_t, c_char};
    use mem;
    use ptr;
    use sys::fd::FileDesc;
    use sys::fs::{File, OpenOptions};
    use sys::pipe::{self, AnonPipe};
    use sys::{self, cvt, cvt_r};

    ////////////////////////////////////////////////////////////////////////////////
    // Command
    ////////////////////////////////////////////////////////////////////////////////

    pub struct Command {
        // Currently we try hard to ensure that the call to `.exec()` doesn't
        // actually allocate any memory. While many platforms try to ensure that
        // memory allocation works after a fork in a multithreaded process, it's
        // been observed to be buggy and somewhat unreliable, so we do our best to
        // just not do it at all!
        //
        // Along those lines, the `argv` and `envp` raw pointers here are exactly
        // what's gonna get passed to `execvp`. The `argv` array starts with the
        // `program` and ends with a NULL, and the `envp` pointer, if present, is
        // also null-terminated.
        //
        // Right now we don't support removing arguments, so there's no much fancy
        // support there, but we support adding and removing environment variables,
        // so a side table is used to track where in the `envp` array each key is
        // located. Whenever we add a key we update it in place if it's already
        // present, and whenever we remove a key we update the locations of all
        // other keys.
        program: CString,
        args: Vec<CString>,
        env: Option<HashMap<OsString, (usize, CString)>>,
        argv: Vec<*const c_char>,
        envp: Option<Vec<*const c_char>>,

        cwd: Option<CString>,
        uid: Option<uid_t>,
        gid: Option<gid_t>,
        saw_nul: bool,
        closures: Vec<Box<FnMut() -> io::Result<()> + Send + Sync>>,
        stdin: Option<Stdio>,
        stdout: Option<Stdio>,
        stderr: Option<Stdio>,
    }

    // passed back to std::process with the pipes connected to the child, if any
    // were requested
    pub struct StdioPipes {
        pub stdin: Option<AnonPipe>,
        pub stdout: Option<AnonPipe>,
        pub stderr: Option<AnonPipe>,
    }

    // passed to do_exec() with configuration of what the child stdio should look
    // like
    struct ChildPipes {
        stdin: ChildStdio,
        stdout: ChildStdio,
        stderr: ChildStdio,
    }

    enum ChildStdio {
        Inherit,
        Explicit(c_int),
        Owned(FileDesc),
    }

    pub enum Stdio {
        Inherit,
        Null,
        MakePipe,
        Fd(FileDesc),
    }

    impl Command {
        pub fn new(program: &OsStr) -> Command {
            let mut saw_nul = false;
            let program = os2c(program, &mut saw_nul);
            Command {
                argv: vec![program.as_ptr(), ptr::null()],
                program: program,
                args: Vec::new(),
                env: None,
                envp: None,
                cwd: None,
                uid: None,
                gid: None,
                saw_nul: saw_nul,
                closures: Vec::new(),
                stdin: None,
                stdout: None,
                stderr: None,
            }
        }

        pub fn arg(&mut self, arg: &OsStr) {
            // Overwrite the trailing NULL pointer in `argv` and then add a new null
            // pointer.
            let arg = os2c(arg, &mut self.saw_nul);
            self.argv[self.args.len() + 1] = arg.as_ptr();
            self.argv.push(ptr::null());

            // Also make sure we keep track of the owned value to schedule a
            // destructor for this memory.
            self.args.push(arg);
        }

        fn init_env_map(&mut self) -> (&mut HashMap<OsString, (usize, CString)>,
                                       &mut Vec<*const c_char>) {
            if self.env.is_none() {
                let mut map = HashMap::new();
                let mut envp = Vec::new();
                for (k, v) in env::vars_os() {
                    let s = pair_to_key(&k, &v, &mut self.saw_nul);
                    envp.push(s.as_ptr());
                    map.insert(k, (envp.len() - 1, s));
                }
                envp.push(ptr::null());
                self.env = Some(map);
                self.envp = Some(envp);
            }
            (self.env.as_mut().unwrap(), self.envp.as_mut().unwrap())
        }

        pub fn env(&mut self, key: &OsStr, val: &OsStr) {
            let new_key = pair_to_key(key, val, &mut self.saw_nul);
            let (map, envp) = self.init_env_map();

            // If `key` is already present then we just update `envp` in place
            // (and store the owned value), but if it's not there we override the
            // trailing NULL pointer, add a new NULL pointer, and store where we
            // were located.
            match map.entry(key.to_owned()) {
                Entry::Occupied(mut e) => {
                    let (i, ref mut s) = *e.get_mut();
                    envp[i] = new_key.as_ptr();
                    *s = new_key;
                }
                Entry::Vacant(e) => {
                    let len = envp.len();
                    envp[len - 1] = new_key.as_ptr();
                    envp.push(ptr::null());
                    e.insert((len - 1, new_key));
                }
            }
        }

        pub fn env_remove(&mut self, key: &OsStr) {
            let (map, envp) = self.init_env_map();

            // If we actually ended up removing a key, then we need to update the
            // position of all keys that come after us in `envp` because they're all
            // one element sooner now.
            if let Some((i, _)) = map.remove(key) {
                envp.remove(i);

                for (_, &mut (ref mut j, _)) in map.iter_mut() {
                    if *j >= i {
                        *j -= 1;
                    }
                }
            }
        }

        pub fn env_clear(&mut self) {
            self.env = Some(HashMap::new());
            self.envp = Some(vec![ptr::null()]);
        }

        pub fn cwd(&mut self, dir: &OsStr) {
            self.cwd = Some(os2c(dir, &mut self.saw_nul));
        }
        pub fn uid(&mut self, id: uid_t) {
            self.uid = Some(id);
        }
        pub fn gid(&mut self, id: gid_t) {
            self.gid = Some(id);
        }

        pub fn before_exec(&mut self,
                           f: Box<FnMut() -> io::Result<()> + Send + Sync>) {
            self.closures.push(f);
        }

        pub fn stdin(&mut self, stdin: Stdio) {
            self.stdin = Some(stdin);
        }
        pub fn stdout(&mut self, stdout: Stdio) {
            self.stdout = Some(stdout);
        }
        pub fn stderr(&mut self, stderr: Stdio) {
            self.stderr = Some(stderr);
        }

        pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                     -> io::Result<(Process, StdioPipes)> {
            const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";

            if self.saw_nul {
                return Err(io::Error::new(ErrorKind::InvalidInput,
                                          "nul byte found in provided data"));
            }

            let (ours, theirs) = self.setup_io(default, needs_stdin)?;
            let (input, output) = sys::pipe::anon_pipe()?;

            let pid = unsafe {
                match cvt(libc::fork())? {
                    0 => {
                        drop(input);
                        let err = self.do_exec(theirs);
                        let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
                        let bytes = [
                            (errno >> 24) as u8,
                            (errno >> 16) as u8,
                            (errno >>  8) as u8,
                            (errno >>  0) as u8,
                            CLOEXEC_MSG_FOOTER[0], CLOEXEC_MSG_FOOTER[1],
                            CLOEXEC_MSG_FOOTER[2], CLOEXEC_MSG_FOOTER[3]
                        ];
                        // pipe I/O up to PIPE_BUF bytes should be atomic, and then
                        // we want to be sure we *don't* run at_exit destructors as
                        // we're being torn down regardless
                        assert!(output.write(&bytes).is_ok());
                        libc::_exit(1)
                    }
                    n => n,
                }
            };

            let mut p = Process { pid: pid, status: None };
            drop(output);
            let mut bytes = [0; 8];

            // loop to handle EINTR
            loop {
                match input.read(&mut bytes) {
                    Ok(0) => return Ok((p, ours)),
                    Ok(8) => {
                        assert!(combine(CLOEXEC_MSG_FOOTER) == combine(&bytes[4.. 8]),
                                "Validation on the CLOEXEC pipe failed: {:?}", bytes);
                        let errno = combine(&bytes[0.. 4]);
                        assert!(p.wait().is_ok(),
                                "wait() should either return Ok or panic");
                        return Err(Error::from_raw_os_error(errno))
                    }
                    Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                    Err(e) => {
                        assert!(p.wait().is_ok(),
                                "wait() should either return Ok or panic");
                        panic!("the CLOEXEC pipe failed: {:?}", e)
                    },
                    Ok(..) => { // pipe I/O up to PIPE_BUF bytes should be atomic
                        assert!(p.wait().is_ok(),
                                "wait() should either return Ok or panic");
                        panic!("short read on the CLOEXEC pipe")
                    }
                }
            }

            fn combine(arr: &[u8]) -> i32 {
                let a = arr[0] as u32;
                let b = arr[1] as u32;
                let c = arr[2] as u32;
                let d = arr[3] as u32;

                ((a << 24) | (b << 16) | (c << 8) | (d << 0)) as i32
            }
        }

        pub fn exec(&mut self, default: Stdio) -> io::Error {
            if self.saw_nul {
                return io::Error::new(ErrorKind::InvalidInput,
                                      "nul byte found in provided data")
            }

            match self.setup_io(default, true) {
                Ok((_, theirs)) => unsafe { self.do_exec(theirs) },
                Err(e) => e,
            }
        }

        // And at this point we've reached a special time in the life of the
        // child. The child must now be considered hamstrung and unable to
        // do anything other than syscalls really. Consider the following
        // scenario:
        //
        //      1. Thread A of process 1 grabs the malloc() mutex
        //      2. Thread B of process 1 forks(), creating thread C
        //      3. Thread C of process 2 then attempts to malloc()
        //      4. The memory of process 2 is the same as the memory of
        //         process 1, so the mutex is locked.
        //
        // This situation looks a lot like deadlock, right? It turns out
        // that this is what pthread_atfork() takes care of, which is
        // presumably implemented across platforms. The first thing that
        // threads to *before* forking is to do things like grab the malloc
        // mutex, and then after the fork they unlock it.
        //
        // Despite this information, libnative's spawn has been witnessed to
        // deadlock on both OSX and FreeBSD. I'm not entirely sure why, but
        // all collected backtraces point at malloc/free traffic in the
        // child spawned process.
        //
        // For this reason, the block of code below should contain 0
        // invocations of either malloc of free (or their related friends).
        //
        // As an example of not having malloc/free traffic, we don't close
        // this file descriptor by dropping the FileDesc (which contains an
        // allocation). Instead we just close it manually. This will never
        // have the drop glue anyway because this code never returns (the
        // child will either exec() or invoke libc::exit)
        unsafe fn do_exec(&mut self, stdio: ChildPipes) -> io::Error {
            macro_rules! t {
                ($e:expr) => (match $e {
                    Ok(e) => e,
                    Err(e) => return e,
                })
            }

            if let Some(fd) = stdio.stdin.fd() {
                t!(cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO)));
            }
            if let Some(fd) = stdio.stdout.fd() {
                t!(cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO)));
            }
            if let Some(fd) = stdio.stderr.fd() {
                t!(cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO)));
            }

            if let Some(u) = self.gid {
                t!(cvt(libc::setgid(u as gid_t)));
            }
            if let Some(u) = self.uid {
                // When dropping privileges from root, the `setgroups` call
                // will remove any extraneous groups. If we don't call this,
                // then even though our uid has dropped, we may still have
                // groups that enable us to do super-user things. This will
                // fail if we aren't root, so don't bother checking the
                // return value, this is just done as an optimistic
                // privilege dropping function.
                let _ = libc::setgroups(0, ptr::null());

                t!(cvt(libc::setuid(u as uid_t)));
            }
            if let Some(ref cwd) = self.cwd {
                t!(cvt(libc::chdir(cwd.as_ptr())));
            }
            if let Some(ref envp) = self.envp {
                *sys::os::environ() = envp.as_ptr();
            }

            // NaCl has no signal support.
            if cfg!(not(target_os = "nacl")) {
                // Reset signal handling so the child process starts in a
                // standardized state. libstd ignores SIGPIPE, and signal-handling
                // libraries often set a mask. Child processes inherit ignored
                // signals and the signal mask from their parent, but most
                // UNIX programs do not reset these things on their own, so we
                // need to clean things up now to avoid confusing the program
                // we're about to run.
                let mut set: libc::sigset_t = mem::uninitialized();
                t!(cvt(libc::sigemptyset(&mut set)));
                t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set,
                                             ptr::null_mut())));
                let ret = super::signal(libc::SIGPIPE, libc::SIG_DFL);
                if ret == libc::SIG_ERR {
                    return io::Error::last_os_error()
                }
            }

            for callback in self.closures.iter_mut() {
                t!(callback());
            }

            libc::execvp(self.argv[0], self.argv.as_ptr());
            io::Error::last_os_error()
        }

        fn setup_io(&self, default: Stdio, needs_stdin: bool)
                    -> io::Result<(StdioPipes, ChildPipes)> {
            let null = Stdio::Null;
            let default_stdin = if needs_stdin {&default} else {&null};
            let stdin = self.stdin.as_ref().unwrap_or(default_stdin);
            let stdout = self.stdout.as_ref().unwrap_or(&default);
            let stderr = self.stderr.as_ref().unwrap_or(&default);
            let (their_stdin, our_stdin) = stdin.to_child_stdio(true)?;
            let (their_stdout, our_stdout) = stdout.to_child_stdio(false)?;
            let (their_stderr, our_stderr) = stderr.to_child_stdio(false)?;
            let ours = StdioPipes {
                stdin: our_stdin,
                stdout: our_stdout,
                stderr: our_stderr,
            };
            let theirs = ChildPipes {
                stdin: their_stdin,
                stdout: their_stdout,
                stderr: their_stderr,
            };
            Ok((ours, theirs))
        }
    }

    fn os2c(s: &OsStr, saw_nul: &mut bool) -> CString {
        CString::new(s.as_bytes()).unwrap_or_else(|_e| {
            *saw_nul = true;
            CString::new("<string-with-nul>").unwrap()
        })
    }

    impl Stdio {
        fn to_child_stdio(&self, readable: bool)
                          -> io::Result<(ChildStdio, Option<AnonPipe>)> {
            match *self {
                Stdio::Inherit => Ok((ChildStdio::Inherit, None)),

                // Make sure that the source descriptors are not an stdio
                // descriptor, otherwise the order which we set the child's
                // descriptors may blow away a descriptor which we are hoping to
                // save. For example, suppose we want the child's stderr to be the
                // parent's stdout, and the child's stdout to be the parent's
                // stderr. No matter which we dup first, the second will get
                // overwritten prematurely.
                Stdio::Fd(ref fd) => {
                    if fd.raw() >= 0 && fd.raw() <= libc::STDERR_FILENO {
                        Ok((ChildStdio::Owned(fd.duplicate()?), None))
                    } else {
                        Ok((ChildStdio::Explicit(fd.raw()), None))
                    }
                }

                Stdio::MakePipe => {
                    let (reader, writer) = pipe::anon_pipe()?;
                    let (ours, theirs) = if readable {
                        (writer, reader)
                    } else {
                        (reader, writer)
                    };
                    Ok((ChildStdio::Owned(theirs.into_fd()), Some(ours)))
                }

                Stdio::Null => {
                    let mut opts = OpenOptions::new();
                    opts.read(readable);
                    opts.write(!readable);
                    let path = unsafe {
                        CStr::from_ptr("/dev/null\0".as_ptr() as *const _)
                    };
                    let fd = File::open_c(&path, &opts)?;
                    Ok((ChildStdio::Owned(fd.into_fd()), None))
                }
            }
        }
    }

    impl ChildStdio {
        fn fd(&self) -> Option<c_int> {
            match *self {
                ChildStdio::Inherit => None,
                ChildStdio::Explicit(fd) => Some(fd),
                ChildStdio::Owned(ref fd) => Some(fd.raw()),
            }
        }
    }

    fn pair_to_key(key: &OsStr, value: &OsStr, saw_nul: &mut bool) -> CString {
        let (key, value) = (key.as_bytes(), value.as_bytes());
        let mut v = Vec::with_capacity(key.len() + value.len() + 1);
        v.extend(key);
        v.push(b'=');
        v.extend(value);
        CString::new(v).unwrap_or_else(|_e| {
            *saw_nul = true;
            CString::new("foo=bar").unwrap()
        })
    }

    impl fmt::Debug for Command {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{:?}", self.program)?;
            for arg in &self.args {
                write!(f, " {:?}", arg)?;
            }
            Ok(())
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // Processes
    ////////////////////////////////////////////////////////////////////////////////

    /// Unix exit statuses
    #[derive(PartialEq, Eq, Clone, Copy, Debug)]
    pub struct ExitStatus(c_int);

    impl ExitStatus {
        fn exited(&self) -> bool {
            unsafe { libc::WIFEXITED(self.0) }
        }

        pub fn success(&self) -> bool {
            self.code() == Some(0)
        }

        pub fn code(&self) -> Option<i32> {
            if self.exited() {
                Some(unsafe { libc::WEXITSTATUS(self.0) })
            } else {
                None
            }
        }

        pub fn signal(&self) -> Option<i32> {
            if !self.exited() {
                Some(unsafe { libc::WTERMSIG(self.0) })
            } else {
                None
            }
        }
    }

    impl From<c_int> for ExitStatus {
        fn from(a: c_int) -> ExitStatus {
            ExitStatus(a)
        }
    }

    impl fmt::Display for ExitStatus {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            if let Some(code) = self.code() {
                write!(f, "exit code: {}", code)
            } else {
                let signal = self.signal().unwrap();
                write!(f, "signal: {}", signal)
            }
        }
    }

    /// The unique id of the process (this should never be negative).
    pub struct Process {
        pid: pid_t,
        status: Option<ExitStatus>,
    }

    impl Process {
        pub fn id(&self) -> u32 {
            self.pid as u32
        }

        pub fn kill(&mut self) -> io::Result<()> {
            // If we've already waited on this process then the pid can be recycled
            // and used for another process, and we probably shouldn't be killing
            // random processes, so just return an error.
            if self.status.is_some() {
                Err(Error::new(ErrorKind::InvalidInput,
                               "invalid argument: can't kill an exited process"))
            } else {
                cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ())
            }
        }

        pub fn wait(&mut self) -> io::Result<ExitStatus> {
            if let Some(status) = self.status {
                return Ok(status)
            }
            let mut status = 0 as c_int;
            cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
            self.status = Some(ExitStatus(status));
            Ok(ExitStatus(status))
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use prelude::v1::*;

        use ffi::OsStr;
        use mem;
        use ptr;
        use libc;
        use sys::cvt;

        macro_rules! t {
            ($e:expr) => {
                match $e {
                    Ok(t) => t,
                    Err(e) => panic!("received error for `{}`: {}", stringify!($e), e),
                }
            }
        }

        #[cfg(not(target_os = "android"))]
        extern {
            #[cfg_attr(target_os = "netbsd", link_name = "__sigaddset14")]
            fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int;
        }

        #[cfg(target_os = "android")]
        unsafe fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int {
            use slice;

            let raw = slice::from_raw_parts_mut(set as *mut u8, mem::size_of::<libc::sigset_t>());
            let bit = (signum - 1) as usize;
            raw[bit / 8] |= 1 << (bit % 8);
            return 0;
        }

        // See #14232 for more information, but it appears that signal delivery to a
        // newly spawned process may just be raced in the OSX, so to prevent this
        // test from being flaky we ignore it on OSX.
        #[test]
        #[cfg_attr(target_os = "macos", ignore)]
        #[cfg_attr(target_os = "nacl", ignore)] // no signals on NaCl.
        fn test_process_mask() {
            unsafe {
                // Test to make sure that a signal mask does not get inherited.
                let mut cmd = Command::new(OsStr::new("cat"));

                let mut set: libc::sigset_t = mem::uninitialized();
                let mut old_set: libc::sigset_t = mem::uninitialized();
                t!(cvt(libc::sigemptyset(&mut set)));
                t!(cvt(sigaddset(&mut set, libc::SIGINT)));
                t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set, &mut old_set)));

                cmd.stdin(Stdio::MakePipe);
                cmd.stdout(Stdio::MakePipe);

                let (mut cat, mut pipes) = t!(cmd.spawn(Stdio::Null, true));
                let stdin_write = pipes.stdin.take().unwrap();
                let stdout_read = pipes.stdout.take().unwrap();

                t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &old_set,
                                             ptr::null_mut())));

                t!(cvt(libc::kill(cat.id() as libc::pid_t, libc::SIGINT)));
                // We need to wait until SIGINT is definitely delivered. The
                // easiest way is to write something to cat, and try to read it
                // back: if SIGINT is unmasked, it'll get delivered when cat is
                // next scheduled.
                let _ = stdin_write.write(b"Hello");
                drop(stdin_write);

                // Either EOF or failure (EPIPE) is okay.
                let mut buf = [0; 5];
                if let Ok(ret) = stdout_read.read(&mut buf) {
                    assert!(ret == 0);
                }

                t!(cat.wait());
            }
        }
    }

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