skip attempts to set baud rate of 0 via ioctl (macos)

src/posix/termios.rs

@@ -100,7 +100,13 @@ pub(crate) fn get_termios(fd: RawFd) -> Result<Termios> {
 pub(crate) fn set_termios(fd: RawFd, termios: &libc::termios, baud_rate: u32) -> Result<()> {
     let res = unsafe { libc::tcsetattr(fd, libc::TCSANOW, termios) };
     nix::errno::Errno::result(res)?;
-    crate::posix::ioctl::iossiospeed(fd, &(baud_rate as libc::speed_t))?;
+
+    // Note: attempting to set the baud rate on a pseudo terminal via this ioctl call will faill
+    // with the `ENOTTY` error.
+    if baud_rate > 0 {
+        crate::posix::ioctl::iossiospeed(fd, &(baud_rate as libc::speed_t))?;
+    }
+
     Ok(())
 }
 

src/posix/tty.rs

@@ -37,6 +37,21 @@ fn close(fd: RawFd) {
 /// should not be instantiated directly by using `TTYPort::open()`, instead use
 /// the cross-platform `serialport::open()` or
 /// `serialport::open_with_settings()`.
+///
+/// Note: on macOS, when connecting to a pseudo-terminal (`pty` opened via
+/// `posix_openpt`), the `baud_rate` should be set to 0; this will be used to
+/// explicitly _skip_ an attempt to set the baud rate of the file descriptor
+/// that would otherwise happen via an `ioctl` command.
+///
+/// ```
+/// use serialport::{TTYPort, SerialPort};
+///
+/// let (mut master, slave) = TTYPort::pair().expect("Unable to create ptty pair");
+///
+/// // ... elsewhere
+///
+/// let mut port = TTYPort::open(&serialport::new(slave.name().unwrap(), 0)).expect("unable to open");
+/// ```
 #[derive(Debug)]
 pub struct TTYPort {
     fd: RawFd,

tests/test_tty.rs

@@ -90,6 +90,29 @@ fn test_ttyport_timeout() {
     }
 }
 
+#[test]
+#[cfg(any(target_os = "ios", target_os = "macos"))]
+fn test_osx_pty_pair() {
+    #![allow(unused_variables)]
+    let (mut master, slave) = TTYPort::pair().expect("Unable to create ptty pair");
+    let (output_sink, output_stream) = std::sync::mpsc::sync_channel(1);
+    let name = slave.name().unwrap();
+
+    master.write("12".as_bytes()).expect("");
+
+    let reader_thread = std::thread::spawn(move || {
+        let mut port = TTYPort::open(&serialport::new(&name, 0)).expect("unable to open");
+        let mut buffer = [0u8; 2];
+        let amount = port.read_exact(&mut buffer);
+        output_sink
+            .send(String::from_utf8(buffer.to_vec()).expect("buffer not read as valid utf-8"))
+            .expect("unable to send from thread");
+    });
+
+    reader_thread.join().expect("unable to join sink thread");
+    assert_eq!(output_stream.recv().unwrap(), "12");
+}
+
 // On Mac this should work (in fact used to in b77768a) but now fails. It's not functionality that
 // should be required, and the ptys work otherwise. So going to just diable this test instead.
 #[test]