Provide and emulate ptsname_r on macOS and iOS by using the TIOCPTYGNAME syscall.

This provides a thread-safe alternative to ptsname() and compatibility
for existing projects using ptsname_r() on macOS.

Author: nelsonjchen

src/pty.rs

@@ -169,6 +169,41 @@ pub fn ptsname_r(fd: &PtyMaster) -> Result<String> {
     Ok(name)
 }
 
+/// (emulated on macOS) Get the name of the slave pseudoterminal (see
+/// [ptsname(3)](http://man7.org/linux/man-pages/man3/ptsname.3.html))
+///
+/// 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()`.
+///
+/// As `ptsname_r()` is Linux-specific, this implementation emulates `ptsname_r()` through
+/// the `TIOCPTYGNAME` syscall on macOS.
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+#[inline]
+pub fn ptsname_r(fd: &PtyMaster) -> Result<String> {
+    // This is based on
+    // https://blog.tarq.io/ptsname-on-osx-with-rust/
+    // and its derivative
+    // https://github.com/philippkeller/rexpect/blob/a71dd02/src/process.rs#L67
+    use libc::{ioctl, TIOCPTYGNAME};
+
+    // the buffer size on OSX is 128, defined by sys/ttycom.h
+    let buf: [i8; 128] = [0; 128];
+
+    unsafe {
+        match ioctl(fd.as_raw_fd(), TIOCPTYGNAME as u64, &buf) {
+            0 => {
+                let res = CStr::from_ptr(buf.as_ptr()).to_string_lossy().into_owned();
+                Ok(res)
+            }
+            _ => Err(Error::last()),
+        }
+    }
+}
+
 /// Unlock a pseudoterminal master/slave pseudoterminal pair (see
 /// [unlockpt(3)](http://man7.org/linux/man-pages/man3/unlockpt.3.html))
 ///
@@ -187,7 +222,7 @@ pub fn unlockpt(fd: &PtyMaster) -> Result<()> {
 
 /// Create a new pseudoterminal, returning the slave and master file descriptors
 /// in `OpenptyResult`
-/// (see [openpty](http://man7.org/linux/man-pages/man3/openpty.3.html)). 
+/// (see [openpty](http://man7.org/linux/man-pages/man3/openpty.3.html)).
 ///
 /// If `winsize` is not `None`, the window size of the slave will be set to
 /// the values in `winsize`. If `termios` is not `None`, the pseudoterminal's

test/test_pty.rs

@@ -25,7 +25,7 @@ fn test_explicit_close() {
 
 /// Test equivalence of `ptsname` and `ptsname_r`
 #[test]
-#[cfg(any(target_os = "android", target_os = "linux"))]
+#[cfg(any(target_os = "android", target_os = "linux", target_os = "macos", target_os = "ios"))]
 fn test_ptsname_equivalence() {
     #[allow(unused_variables)]
     let m = ::PTSNAME_MTX.lock().expect("Mutex got poisoned by another test");
@@ -43,7 +43,7 @@ fn test_ptsname_equivalence() {
 /// Test data copying of `ptsname`
 // TODO need to run in a subprocess, since ptsname is non-reentrant
 #[test]
-#[cfg(any(target_os = "android", target_os = "linux"))]
+#[cfg(any(target_os = "android", target_os = "linux", target_os = "macos", target_os = "ios"))]
 fn test_ptsname_copy() {
     #[allow(unused_variables)]
     let m = ::PTSNAME_MTX.lock().expect("Mutex got poisoned by another test");
@@ -63,7 +63,7 @@ fn test_ptsname_copy() {
 
 /// Test data copying of `ptsname_r`
 #[test]
-#[cfg(any(target_os = "android", target_os = "linux"))]
+#[cfg(any(target_os = "android", target_os = "linux", target_os = "macos", target_os = "ios"))]
 fn test_ptsname_r_copy() {
     // Open a new PTTY master
     let master_fd = posix_openpt(O_RDWR).unwrap();
@@ -78,7 +78,7 @@ fn test_ptsname_r_copy() {
 
 /// Test that `ptsname` returns different names for different devices
 #[test]
-#[cfg(any(target_os = "android", target_os = "linux"))]
+#[cfg(any(target_os = "android", target_os = "linux", target_os = "macos", target_os = "ios"))]
 fn test_ptsname_unique() {
     #[allow(unused_variables)]
     let m = ::PTSNAME_MTX.lock().expect("Mutex got poisoned by another test");