Implement custom baud rates on Apple with the IOSSIOSPEED ioctl.

CHANGELOG

@@ -1,3 +1,6 @@
+# Unlreased
+- [add][minor] Support more custom baud rates on iOS and macOS.
+
 # Version 0.2.25 - 2024-06-13
 - [fix][patch] Fix documentation build failre on http://docs.rs.
 

src/sys/unix/apple.rs

@@ -0,0 +1,58 @@
+use std::path::PathBuf;
+use std::os::unix::io::RawFd;
+
+/// A ioctl to set the baud rate of a serial port.
+///
+/// Value taken from random forum because there is no public documentation.
+/// * https://fpc-pascal.freepascal.narkive.com/oI4b0CM2/non-standard-baud-rates-in-os-x-iossiospeed-ioctl
+/// * https://github.com/dcuddeback/serial-rs/issues/37
+const IOCTL_IOSSIOSPEED: u64 = 0x80045402;
+
+/// Set the baud rate of a serial port using the IOSSIOSPEED ioctl.
+///
+/// The speed set this way applied to the input and the output speed.
+///
+/// According to some source, the speed set this way is *not* reported back in the `termios` struct by `tcgetattr`,
+/// but according to other sources it *is*.
+/// Even the two examples from Apple below contradict each-other on this point.
+///
+/// Testing seems to suggest that the value *is* reported correctly by `tcgetattr`.
+/// So to avoid synchronization problems with other FDs for the same serial port we trust `tcgetattr`.
+/// https://github.com/de-vri-es/serial2-rs/issues/38#issuecomment-2182531900
+///
+/// This is Apple, so there is no public documentation (why would you?).
+/// This is the best I could find:
+/// * https://opensource.apple.com/source/IOSerialFamily/IOSerialFamily-91/tests/IOSerialTestLib.c.auto.html
+/// * https://developer.apple.com/library/archive/samplecode/SerialPortSample/Listings/SerialPortSample_SerialPortSample_c.html
+pub fn ioctl_iossiospeed(fd: RawFd, baud_rate: libc::speed_t) -> Result<(), std::io::Error> {
+	unsafe {
+		super::check(libc::ioctl(fd, IOCTL_IOSSIOSPEED, &baud_rate))?;
+		Ok(())
+	}
+}
+
+pub fn enumerate() -> std::io::Result<Vec<PathBuf>> {
+	use std::os::unix::ffi::OsStrExt;
+	use std::os::unix::fs::FileTypeExt;
+
+	let serial_ports = std::fs::read_dir("/dev")?
+		.filter_map(|entry| {
+			let entry = entry.ok()?;
+			let kind = entry.metadata().ok()?.file_type();
+			if kind.is_char_device() && is_tty_name(entry.file_name().as_bytes()) {
+				Some(entry.path())
+			} else {
+				None
+			}
+		})
+		.collect();
+	Ok(serial_ports)
+}
+
+fn is_tty_name(name: &[u8]) -> bool {
+	// Sigh, closed source doesn't have to mean undocumented.
+	// Anyway:
+	// https://stackoverflow.com/questions/14074413/serial-port-names-on-mac-os-x
+	// https://learn.adafruit.com/ftdi-friend/com-slash-serial-port-name
+	name.starts_with(b"tty.") || name.starts_with(b"cu.")
+}

src/sys/unix/bsd.rs

@@ -1,4 +1,3 @@
-use cfg_if::cfg_if;
 use std::path::PathBuf;
 
 pub fn enumerate() -> std::io::Result<Vec<PathBuf>> {
@@ -20,48 +19,37 @@ pub fn enumerate() -> std::io::Result<Vec<PathBuf>> {
 }
 
 fn is_tty_name(name: &[u8]) -> bool {
-	cfg_if! {
-		if #[cfg(any(target_os = "ios", target_os = "macos"))] {
-			// Sigh, closed source doesn't have to mean undocumented.
-			// Anyway:
-			// https://stackoverflow.com/questions/14074413/serial-port-names-on-mac-os-x
-			// https://learn.adafruit.com/ftdi-friend/com-slash-serial-port-name
-			name.starts_with(b"tty.") || name.starts_with(b"cu.")
-
-		} else {
-			// For BSD variants, we simply report all entries in /dev that look like a TTY.
-			// This may contain a lot of false positives for pseudo-terminals or other fake terminals.
-			// If anyone can improve this for a specific BSD they love, by all means send a PR.
-
-			// https://man.dragonflybsd.org/?command=sio&section=4
-			// https://leaf.dragonflybsd.org/cgi/web-man?command=ucom&section=ANY
-			#[cfg(target_os = "dragonfly")]
-			const PREFIXES: [&[u8]; 4] = [b"ttyd", b"cuaa", b"ttyU", b"cuaU"];
-
-			// https://www.freebsd.org/cgi/man.cgi?query=uart&sektion=4&apropos=0&manpath=FreeBSD+13.0-RELEASE+and+Ports
-			// https://www.freebsd.org/cgi/man.cgi?query=ucom&sektion=4&apropos=0&manpath=FreeBSD+13.0-RELEASE+and+Ports
-			#[cfg(target_os = "freebsd")]
-			const PREFIXES: [&[u8]; 5] = [b"ttyu", b"cuau", b"cuad", b"ttyU", b"cuaU"];
-
-			// https://man.netbsd.org/com.4
-			// https://man.netbsd.org/ucom.4
-			#[cfg(target_os = "netbsd")]
-			const PREFIXES: [&[u8]; 4] = [b"tty", b"dty", b"ttyU", b"dtyU"];
-
-			// https://man.openbsd.org/com
-			// https://man.openbsd.org/ucom
-			#[cfg(target_os = "openbsd")]
-			const PREFIXES: [&[u8]; 4] = [b"tty", b"cua", b"ttyU", b"cuaU"];
-
-			for prefix in PREFIXES {
-				if let Some(suffix) = name.strip_prefix(prefix) {
-					if !suffix.is_empty() && suffix.iter().all(|c| c.is_ascii_digit()) {
-						return true;
-					}
+		// For BSD variants, we simply report all entries in /dev that look like a TTY.
+		// This may contain a lot of false positives for pseudo-terminals or other fake terminals.
+		// If anyone can improve this for a specific BSD they love, by all means send a PR.
+
+		// https://man.dragonflybsd.org/?command=sio&section=4
+		// https://leaf.dragonflybsd.org/cgi/web-man?command=ucom&section=ANY
+		#[cfg(target_os = "dragonfly")]
+		const PREFIXES: [&[u8]; 4] = [b"ttyd", b"cuaa", b"ttyU", b"cuaU"];
+
+		// https://www.freebsd.org/cgi/man.cgi?query=uart&sektion=4&apropos=0&manpath=FreeBSD+13.0-RELEASE+and+Ports
+		// https://www.freebsd.org/cgi/man.cgi?query=ucom&sektion=4&apropos=0&manpath=FreeBSD+13.0-RELEASE+and+Ports
+		#[cfg(target_os = "freebsd")]
+		const PREFIXES: [&[u8]; 5] = [b"ttyu", b"cuau", b"cuad", b"ttyU", b"cuaU"];
+
+		// https://man.netbsd.org/com.4
+		// https://man.netbsd.org/ucom.4
+		#[cfg(target_os = "netbsd")]
+		const PREFIXES: [&[u8]; 4] = [b"tty", b"dty", b"ttyU", b"dtyU"];
+
+		// https://man.openbsd.org/com
+		// https://man.openbsd.org/ucom
+		#[cfg(target_os = "openbsd")]
+		const PREFIXES: [&[u8]; 4] = [b"tty", b"cua", b"ttyU", b"cuaU"];
+
+		for prefix in PREFIXES {
+			if let Some(suffix) = name.strip_prefix(prefix) {
+				if !suffix.is_empty() && suffix.iter().all(|c| c.is_ascii_digit()) {
+					return true;
 				}
 			}
-
-			false
 		}
-	}
+
+		false
 }

src/sys/unix/mod.rs

@@ -13,12 +13,17 @@ pub struct SerialPort {
 
 cfg_if! {
 	if #[cfg(any(
-			target_os = "dragonfly",
-			target_os = "freebsd",
-			target_os = "ios",
-			target_os = "macos",
-			target_os = "netbsd",
-			target_os = "openbsd",
+		target_os = "ios",
+		target_os = "macos",
+	))] {
+		mod apple;
+		pub use apple::*;
+
+	} else if #[cfg(any(
+		target_os = "dragonfly",
+		target_os = "freebsd",
+		target_os = "netbsd",
+		target_os = "openbsd",
 	))] {
 		mod bsd;
 		pub use bsd::*;
@@ -148,8 +153,26 @@ impl SerialPort {
 	}
 
 	pub fn set_configuration(&mut self, settings: &Settings) -> std::io::Result<()> {
+		// On iOS and macOS we set the baud rate with the IOSSIOSPEED ioctl.
+		// But we also need to ensure the `set_on_file()` doesn't fail.
+		// So fill in a safe speed in the termios struct which we will override shortly after.
+		#[cfg(any(target_os = "ios", target_os = "macos"))]
+		let (settings, baud_rate) = {
+			let baud_rate = settings.termios.c_ospeed;
+			let mut settings = settings.clone();
+			settings.termios.c_ispeed = 9600;
+			settings.termios.c_ospeed = 9600;
+			(settings, baud_rate)
+		};
+		#[cfg(any(target_os = "ios", target_os = "macos"))]
+		let settings = &settings;
+
 		settings.set_on_file(&mut self.file)?;
 
+		// On iOS and macOS, override the speed with the IOSSIOSPEED ioctl.
+		#[cfg(any(target_os = "ios", target_os = "macos"))]
+		ioctl_iossiospeed(self.file.as_raw_fd(), baud_rate)?;
+
 		let applied_settings = self.get_configuration()?;
 		if applied_settings != *settings {
 			Err(other_error("failed to apply some or all settings"))