Add various pty functions

  * grantpt
  * ptsname/ptsname_r
  * posix_openpt
  * unlockpt

Author: Susurrus

CHANGELOG.md

@@ -10,6 +10,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#582](https://github.com/nix-rust/nix/pull/582)
 - Added `nix::unistd::{openat, fstatat, readlink, readlinkat}`
   ([#551](https://github.com/nix-rust/nix/pull/551))
+- Added `nix::pty::{grantpt, posix_openpt, ptsname/ptsname_r, unlockpt}`
+  ([#556](https://github.com/nix-rust/nix/pull/556)
 
 ### Changed
 - Marked `sys::mman::{ mmap, munmap, madvise, munlock, msync }` as unsafe.

src/lib.rs

@@ -44,6 +44,8 @@ pub mod mount;
 #[cfg(target_os = "linux")]
 pub mod mqueue;
 
+pub mod pty;
+
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 pub mod poll;
 

src/pty.rs

@@ -0,0 +1,131 @@
+//! Create master and slave virtual pseudo-terminals (PTTYs)
+
+use std::ffi::CStr;
+use std::os::unix::io::RawFd;
+
+use libc;
+
+use {Error, fcntl, Result};
+
+/// Grant access to a slave pseudoterminal (see
+/// [grantpt(3)](http://man7.org/linux/man-pages/man3/grantpt.3.html))
+///
+/// `grantpt()` changezs the mode and owner of the slave pseudoterminal device corresponding to the
+/// master pseudoterminal referred to by `fd`. This is a necessary step towards opening the slave.
+#[inline]
+pub fn grantpt(fd: RawFd) -> Result<()> {
+    if unsafe { libc::grantpt(fd) } < 0 {
+        return Err(Error::last().into());
+    }
+
+    Ok(())
+}
+
+/// Open a pseudoterminal device (see
+/// [posix_openpt(3)](http://man7.org/linux/man-pages/man3/posix_openpt.3.html))
+///
+/// `posix_openpt()` returns a file descriptor to an existing unused pseuterminal master device.
+///
+/// # Examples
+///
+/// A common use case with this function is to open both a master and slave PTTY pair. This can be
+/// done as follows:
+///
+/// ```
+/// use std::path::Path;
+/// use nix::fcntl::{O_RDWR, open};
+/// use nix::pty::*;
+/// use nix::sys::stat;
+///
+/// # #[allow(dead_code)]
+/// # fn run() -> nix::Result<()> {
+/// // Open a new PTTY master
+/// let master_fd = posix_openpt(O_RDWR)?;
+///
+/// // Allow a slave to be generated for it
+/// grantpt(master_fd)?;
+/// unlockpt(master_fd)?;
+///
+/// // Get the name of the slave
+/// let slave_name = ptsname(master_fd)?;
+///
+/// // Try to open the slave
+/// # #[allow(unused_variables)]
+/// let slave_fd = open(Path::new(&slave_name), O_RDWR, stat::Mode::empty())?;
+/// # Ok(())
+/// # }
+/// ```
+#[inline]
+pub fn posix_openpt(flags: fcntl::OFlag) -> Result<RawFd> {
+    let fd = unsafe {
+        libc::posix_openpt(flags.bits())
+    };
+
+    if fd < 0 {
+        return Err(Error::last().into());
+    }
+
+    Ok(fd)
+}
+
+/// Get the name of the slave pseudoterminal (see
+/// [ptsname(3)](http://man7.org/linux/man-pages/man3/ptsname.3.html))
+///
+/// `ptsname()` returns the name of the slave pseudoterminal device corresponding to the master
+/// referred to by `fd`. Note that this function is *not* threadsafe. For that see `ptsname_r()`.
+///
+/// This value is useful for opening the slave ptty once the master has already been opened with
+/// `posix_openpt()`.
+#[inline]
+pub fn ptsname(fd: RawFd) -> Result<String> {
+    let name_ptr = unsafe { libc::ptsname(fd) };
+    if name_ptr.is_null() {
+        return Err(Error::last().into());
+    }
+
+    let name = unsafe {
+        CStr::from_ptr(name_ptr)
+    };
+    Ok(name.to_string_lossy().into_owned())
+}
+
+/// Get the name of the slave pseudoterminal (see
+/// [ptsname(3)](http://man7.org/linux/man-pages/man3/ptsname.3.html))
+///
+/// `ptsname_r()` returns the name of the slave pseudoterminal device corresponding to the master
+/// referred to by `fd`. This is the threadsafe version of `ptsname()`, but it is not part of the
+/// POSIX standard and is instead a Linux-specific extension.
+///
+/// This value is useful for opening the slave ptty once the master has already been opened with
+/// `posix_openpt()`.
+#[cfg(any(target_os = "linux",
+          target_os = "android",
+          target_os = "emscripten",
+          target_os = "fuchsia"))]
+#[inline]
+pub fn ptsname_r(fd: RawFd) -> Result<String> {
+    let mut name_buf = [0 as libc::c_char; 64];
+    if unsafe { libc::ptsname_r(fd, name_buf.as_mut_ptr(), name_buf.len()) } != 0 {
+        return Err(Error::last().into());
+    }
+
+    let name = unsafe {
+        CStr::from_ptr(name_buf.as_ptr())
+    };
+    Ok(name.to_string_lossy().into_owned())
+}
+
+/// Unlock a pseudoterminal master/slave pseudoterminal pair (see
+/// [unlockpt(3)](http://man7.org/linux/man-pages/man3/unlockpt.3.html))
+///
+/// `unlockpt()` unlocks the slave pseudoterminal device corresponding to the master pseudoterminal
+/// referred to by `fd`. This must be called before trying to open the slave side of a
+/// pseuoterminal.
+#[inline]
+pub fn unlockpt(fd: RawFd) -> Result<()> {
+    if unsafe { libc::unlockpt(fd) } < 0 {
+        return Err(Error::last().into());
+    }
+
+    Ok(())
+}

test/test.rs

@@ -23,6 +23,7 @@ mod test_mq;
 
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 mod test_poll;
+mod test_pty;
 
 use nixtest::assert_size_of;
 

test/test_pty.rs

@@ -0,0 +1,40 @@
+use std::path::Path;
+use nix::fcntl::{O_RDWR, open};
+use nix::pty::*;
+use nix::sys::stat;
+
+/// Test equivalence of `ptsname` and `ptsname_r`
+#[test]
+fn test_ptsname() {
+    // Open a new PTTY master
+    let master_fd = posix_openpt(O_RDWR).unwrap();
+    assert!(master_fd > 0);
+
+    // Get the name of the slave
+    let slave_name = ptsname(master_fd).unwrap();
+    let slave_name_r = ptsname_r(master_fd).unwrap();
+    assert_eq!(slave_name, slave_name_r);
+}
+
+/// Test opening a master/slave PTTY pair
+///
+/// This is a single larger test because much of these functions aren't useful by themselves. So for
+/// this test we perform the basic act of getting a file handle for a connect master/slave PTTY
+/// pair.
+#[test]
+fn test_open_ptty_pair() {
+    // Open a new PTTY master
+    let master_fd = posix_openpt(O_RDWR).unwrap();
+    assert!(master_fd > 0);
+
+    // Allow a slave to be generated for it
+    grantpt(master_fd).unwrap();
+    unlockpt(master_fd).unwrap();
+
+    // Get the name of the slave
+    let slave_name = ptsname(master_fd).unwrap();
+
+    // Open the slave device
+    let slave_fd = open(Path::new(&slave_name), O_RDWR, stat::Mode::empty()).unwrap();
+    assert!(slave_fd > 0);
+}