stty: baud parsing integration tests and validation (uutils#9454)

* Adding comprehensive gnu suite baud parsing rules

* Adding missing spellcheck words

* Fixed clippy errors and simplified rounding logic

Author: ChrisDryden

src/uu/stty/src/stty.rs

@@ -10,7 +10,7 @@
 // spell-checker:ignore isig icanon iexten echoe crterase echok echonl noflsh xcase tostop echoprt prterase echoctl ctlecho echoke crtkill flusho extproc
 // spell-checker:ignore lnext rprnt susp swtch vdiscard veof veol verase vintr vkill vlnext vquit vreprint vstart vstop vsusp vswtc vwerase werase
 // spell-checker:ignore sigquit sigtstp
-// spell-checker:ignore cbreak decctlq evenp litout oddp tcsadrain
+// spell-checker:ignore cbreak decctlq evenp litout oddp tcsadrain exta extb
 
 mod flags;
 
@@ -23,6 +23,7 @@ use nix::sys::termios::{
     Termios, cfgetospeed, cfsetospeed, tcgetattr, tcsetattr,
 };
 use nix::{ioctl_read_bad, ioctl_write_ptr_bad};
+use std::cmp::Ordering;
 use std::fs::File;
 use std::io::{self, Stdout, stdout};
 use std::num::IntErrorKind;
@@ -563,7 +564,69 @@ fn string_to_combo(arg: &str) -> Option<&str> {
         .map(|_| arg)
 }
 
+/// Parse and round a baud rate value using GNU stty's custom rounding algorithm.
+///
+/// Accepts decimal values with the following rounding rules:
+/// - If first digit after decimal > 5: round up
+/// - If first digit after decimal < 5: round down
+/// - If first digit after decimal == 5:
+///   - If followed by any non-zero digit: round up
+///   - If followed only by zeros (or nothing): banker's rounding (round to nearest even)
+///
+/// Examples: "9600.49" -> 9600, "9600.51" -> 9600, "9600.5" -> 9600 (even), "9601.5" -> 9602 (even)
+/// TODO: there are two special cases "exta" → B19200 and "extb" → B38400
+fn parse_baud_with_rounding(normalized: &str) -> Option<u32> {
+    let (int_part, frac_part) = match normalized.split_once('.') {
+        Some((i, f)) => (i, Some(f)),
+        None => (normalized, None),
+    };
+
+    let mut value = int_part.parse::<u32>().ok()?;
+
+    if let Some(frac) = frac_part {
+        let mut chars = frac.chars();
+        let first_digit = chars.next()?.to_digit(10)?;
+
+        // Validate all remaining chars are digits
+        let rest: Vec<_> = chars.collect();
+        if !rest.iter().all(|c| c.is_ascii_digit()) {
+            return None;
+        }
+
+        match first_digit.cmp(&5) {
+            Ordering::Greater => value += 1,
+            Ordering::Equal => {
+                // Check if any non-zero digit follows
+                if rest.iter().any(|&c| c != '0') {
+                    value += 1;
+                } else {
+                    // Banker's rounding: round to nearest even
+                    value += value & 1;
+                }
+            }
+            Ordering::Less => {} // Round down, already validated
+        }
+    }
+
+    Some(value)
+}
+
 fn string_to_baud(arg: &str) -> Option<AllFlags<'_>> {
+    // Reject invalid formats
+    if arg != arg.trim_end()
+        || arg.trim().starts_with('-')
+        || arg.trim().starts_with("++")
+        || arg.contains('E')
+        || arg.contains('e')
+        || arg.matches('.').count() > 1
+    {
+        return None;
+    }
+
+    let normalized = arg.trim().trim_start_matches('+');
+    let normalized = normalized.strip_suffix('.').unwrap_or(normalized);
+    let value = parse_baud_with_rounding(normalized)?;
+
     // BSDs use a u32 for the baud rate, so any decimal number applies.
     #[cfg(any(
         target_os = "freebsd",
@@ -573,9 +636,7 @@ fn string_to_baud(arg: &str) -> Option<AllFlags<'_>> {
         target_os = "netbsd",
         target_os = "openbsd"
     ))]
-    if let Ok(n) = arg.parse::<u32>() {
-        return Some(AllFlags::Baud(n));
-    }
+    return Some(AllFlags::Baud(value));
 
     #[cfg(not(any(
         target_os = "freebsd",
@@ -585,12 +646,14 @@ fn string_to_baud(arg: &str) -> Option<AllFlags<'_>> {
         target_os = "netbsd",
         target_os = "openbsd"
     )))]
-    for (text, baud_rate) in BAUD_RATES {
-        if *text == arg {
-            return Some(AllFlags::Baud(*baud_rate));
+    {
+        for (text, baud_rate) in BAUD_RATES {
+            if text.parse::<u32>().ok() == Some(value) {
+                return Some(AllFlags::Baud(*baud_rate));
+            }
         }
+        None
     }
-    None
 }
 
 /// return `Some(flag)` if the input is a valid flag, `None` if not

tests/by-util/test_stty.rs

@@ -194,6 +194,24 @@ fn invalid_baud_setting() {
         .args(&["ospeed", "995"])
         .fails()
         .stderr_contains("invalid ospeed '995'");
+
+    for speed in &[
+        "9599..", "9600..", "9600.5.", "9600.50.", "9600.0.", "++9600", "0x2580", "96E2", "9600,0",
+        "9600.0 ",
+    ] {
+        new_ucmd!().args(&["ispeed", speed]).fails();
+    }
+}
+
+#[test]
+#[cfg(unix)]
+fn valid_baud_formats() {
+    let (path, _controller, _replica) = pty_path();
+    for speed in &["  +9600", "9600.49", "9600.50", "9599.51", "  9600."] {
+        new_ucmd!()
+            .args(&["--file", &path, "ispeed", speed])
+            .succeeds();
+    }
 }
 
 #[test]