src/libstd/sys/unix/pipe.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use prelude::v1::*;
  12
  13 use cmp;
  14 use io;
  15 use libc::{self, c_int};
  16 use mem;
  17 use sys::cvt_r;
  18 use sys::fd::FileDesc;
  19
  20 ////////////////////////////////////////////////////////////////////////////////
  21 // Anonymous pipes
  22 ////////////////////////////////////////////////////////////////////////////////
  23
  24 pub struct AnonPipe(FileDesc);
  25
  26 pub fn anon_pipe() -> io::Result<(AnonPipe, AnonPipe)> {
  27     let mut fds = [0; 2];
  28
  29     // Unfortunately the only known way right now to create atomically set the
  30     // CLOEXEC flag is to use the `pipe2` syscall on Linux. This was added in
  31     // 2.6.27, however, and because we support 2.6.18 we must detect this
  32     // support dynamically.
  33     if cfg!(target_os = "linux") {
  34         weak! { fn pipe2(*mut c_int, c_int) -> c_int }
  35         if let Some(pipe) = pipe2.get() {
  36             match cvt_r(|| unsafe { pipe(fds.as_mut_ptr(), libc::O_CLOEXEC) }) {
  37                 Ok(_) => {
  38                     return Ok((AnonPipe(FileDesc::new(fds[0])),
  39                                AnonPipe(FileDesc::new(fds[1]))))
  40                 }
  41                 Err(ref e) if e.raw_os_error() == Some(libc::ENOSYS) => {}
  42                 Err(e) => return Err(e),
  43             }
  44         }
  45     }
  46     if unsafe { libc::pipe(fds.as_mut_ptr()) == 0 } {
  47         Ok((AnonPipe::from_fd(fds[0]), AnonPipe::from_fd(fds[1])))
  48     } else {
  49         Err(io::Error::last_os_error())
  50     }
  51 }
  52
  53 impl AnonPipe {
  54     pub fn from_fd(fd: libc::c_int) -> AnonPipe {
  55         let fd = FileDesc::new(fd);
  56         fd.set_cloexec();
  57         AnonPipe(fd)
  58     }
  59
  60     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
  61         self.0.read(buf)
  62     }
  63
  64     pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
  65         self.0.read_to_end(buf)
  66     }
  67
  68     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
  69         self.0.write(buf)
  70     }
  71
  72     pub fn fd(&self) -> &FileDesc { &self.0 }
  73     pub fn into_fd(self) -> FileDesc { self.0 }
  74 }
  75
  76 pub fn read2(p1: AnonPipe,
  77              v1: &mut Vec<u8>,
  78              p2: AnonPipe,
  79              v2: &mut Vec<u8>) -> io::Result<()> {
  80     // Set both pipes into nonblocking mode as we're gonna be reading from both
  81     // in the `select` loop below, and we wouldn't want one to block the other!
  82     let p1 = p1.into_fd();
  83     let p2 = p2.into_fd();
  84     p1.set_nonblocking(true);
  85     p2.set_nonblocking(true);
  86
  87     let max = cmp::max(p1.raw(), p2.raw());
  88     loop {
  89         // wait for either pipe to become readable using `select`
  90         cvt_r(|| unsafe {
  91             let mut read: libc::fd_set = mem::zeroed();
  92             libc::FD_SET(p1.raw(), &mut read);
  93             libc::FD_SET(p2.raw(), &mut read);
  94             libc::select(max + 1, &mut read, 0 as *mut _, 0 as *mut _,
  95                          0 as *mut _)
  96         })?;
  97
  98         // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
  99         // EAGAIN. If we hit EOF, then this will happen because the underlying
 100         // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
 101         // this case we flip the other fd back into blocking mode and read
 102         // whatever's leftover on that file descriptor.
 103         let read = |fd: &FileDesc, dst: &mut Vec<u8>| {
 104             match fd.read_to_end(dst) {
 105                 Ok(_) => Ok(true),
 106                 Err(e) => {
 107                     if e.raw_os_error() == Some(libc::EWOULDBLOCK) ||
 108                        e.raw_os_error() == Some(libc::EAGAIN) {
 109                         Ok(false)
 110                     } else {
 111                         Err(e)
 112                     }
 113                 }
 114             }
 115         };
 116         if read(&p1, v1)? {
 117             p2.set_nonblocking(false);
 118             return p2.read_to_end(v2).map(|_| ());
 119         }
 120         if read(&p2, v2)? {
 121             p1.set_nonblocking(false);
 122             return p1.read_to_end(v1).map(|_| ());
 123         }
 124     }
 125 }