stty: Implement printing assignment of control chars

Part of #3861.

Code comments from sylvestre.

Co-authored-by: Sylvestre Ledru <sledru@mozilla.com>

src/uu/stty/src/flags.rs

@@ -7,6 +7,8 @@
 // spell-checker:ignore ignbrk brkint ignpar parmrk inpck istrip inlcr igncr icrnl ixoff ixon iuclc ixany imaxbel iutf
 // spell-checker:ignore opost olcuc ocrnl onlcr onocr onlret ofill ofdel nldly crdly tabdly bsdly vtdly ffdly
 // 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
 
 use crate::Flag;
 
@@ -19,7 +21,10 @@ use crate::Flag;
     target_os = "openbsd"
 )))]
 use nix::sys::termios::BaudRate;
-use nix::sys::termios::{ControlFlags as C, InputFlags as I, LocalFlags as L, OutputFlags as O};
+use nix::sys::termios::{
+    ControlFlags as C, InputFlags as I, LocalFlags as L, OutputFlags as O,
+    SpecialCharacterIndices as S,
+};
 
 pub const CONTROL_FLAGS: &[Flag<C>] = &[
     Flag::new("parenb", C::PARENB),
@@ -313,3 +318,40 @@ pub const BAUD_RATES: &[(&str, BaudRate)] = &[
     ))]
     ("4000000", BaudRate::B4000000),
 ];
+/// Control characters for the stty command.
+///
+/// This constant provides a mapping between the names of control characters
+/// and their corresponding values in the `S` enum.
+pub const CONTROL_CHARS: &[(&str, S)] = &[
+    // Sends an interrupt signal (SIGINT).
+    ("intr", S::VINTR),
+    // Sends a quit signal (SIGQUIT).
+    ("quit", S::VQUIT),
+    // Deletes the last typed character.
+    ("erase", S::VERASE),
+    // Deletes the current line.
+    ("kill", S::VKILL),
+    // Signals the end of input.
+    ("eof", S::VEOF),
+    // Signals the end of line.
+    ("eol", S::VEOL),
+    // Alternate end-of-line character.
+    ("eol2", S::VEOL2),
+    // Switch character (only on Linux).
+    #[cfg(target_os = "linux")]
+    ("swtch", S::VSWTC),
+    // Starts output after it has been stopped.
+    ("start", S::VSTART),
+    // Stops output.
+    ("stop", S::VSTOP),
+    // Sends a suspend signal (SIGTSTP).
+    ("susp", S::VSUSP),
+    // Reprints the current line.
+    ("rprnt", S::VREPRINT),
+    // Deletes the last word typed.
+    ("werase", S::VWERASE),
+    // Enters literal mode (next character is taken literally).
+    ("lnext", S::VLNEXT),
+    // Discards the current line.
+    ("discard", S::VDISCARD),
+];

src/uu/stty/src/stty.rs

@@ -3,7 +3,7 @@
 // * For the full copyright and license information, please view the LICENSE file
 // * that was distributed with this source code.
 
-// spell-checker:ignore clocal tcgetattr tcsetattr tcsanow tiocgwinsz tiocswinsz cfgetospeed cfsetospeed ushort
+// spell-checker:ignore clocal erange tcgetattr tcsetattr tcsanow tiocgwinsz tiocswinsz cfgetospeed cfsetospeed ushort vmin vtime
 
 mod flags;
 
@@ -11,7 +11,7 @@ use clap::{crate_version, Arg, ArgAction, ArgMatches, Command};
 use nix::libc::{c_ushort, O_NONBLOCK, TIOCGWINSZ, TIOCSWINSZ};
 use nix::sys::termios::{
     cfgetospeed, cfsetospeed, tcgetattr, tcsetattr, ControlFlags, InputFlags, LocalFlags,
-    OutputFlags, Termios,
+    OutputFlags, SpecialCharacterIndices, Termios,
 };
 use nix::{ioctl_read_bad, ioctl_write_ptr_bad};
 use std::io::{self, stdout};
@@ -30,7 +30,7 @@ use uucore::{format_usage, help_about, help_usage};
     target_os = "openbsd"
 )))]
 use flags::BAUD_RATES;
-use flags::{CONTROL_FLAGS, INPUT_FLAGS, LOCAL_FLAGS, OUTPUT_FLAGS};
+use flags::{CONTROL_CHARS, CONTROL_FLAGS, INPUT_FLAGS, LOCAL_FLAGS, OUTPUT_FLAGS};
 
 const USAGE: &str = help_usage!("stty.md");
 const SUMMARY: &str = help_about!("stty.md");
@@ -245,6 +245,52 @@ fn print_terminal_size(termios: &Termios, opts: &Options) -> nix::Result<()> {
     Ok(())
 }
 
+fn control_char_to_string(cc: nix::libc::cc_t) -> nix::Result<String> {
+    if cc == 0 {
+        return Ok("<undef>".to_string());
+    }
+
+    let (meta_prefix, code) = if cc >= 0x80 {
+        ("M-", cc - 0x80)
+    } else {
+        ("", cc)
+    };
+
+    // Determine the '^'-prefix if applicable and character based on the code
+    let (ctrl_prefix, character) = match code {
+        // Control characters in ASCII range
+        0..=0x1f => Ok(("^", (b'@' + code) as char)),
+        // Printable ASCII characters
+        0x20..=0x7e => Ok(("", code as char)),
+        // DEL character
+        0x7f => Ok(("^", '?')),
+        // Out of range (above 8 bits)
+        _ => Err(nix::errno::Errno::ERANGE),
+    }?;
+
+    Ok(format!("{meta_prefix}{ctrl_prefix}{character}"))
+}
+
+fn print_control_chars(termios: &Termios, opts: &Options) -> nix::Result<()> {
+    if !opts.all {
+        // TODO: this branch should print values that differ from defaults
+        return Ok(());
+    }
+
+    for (text, cc_index) in CONTROL_CHARS {
+        print!(
+            "{text} = {}; ",
+            control_char_to_string(termios.control_chars[*cc_index as usize])?
+        );
+    }
+    println!(
+        "min = {}; time = {};",
+        termios.control_chars[SpecialCharacterIndices::VMIN as usize],
+        termios.control_chars[SpecialCharacterIndices::VTIME as usize]
+    );
+    Ok(())
+}
+
 fn print_in_save_format(termios: &Termios) {
     print!(
         "{:x}:{:x}:{:x}:{:x}",
@@ -264,6 +310,7 @@ fn print_settings(termios: &Termios, opts: &Options) -> nix::Result<()> {
         print_in_save_format(termios);
     } else {
         print_terminal_size(termios, opts)?;
+        print_control_chars(termios, opts)?;
         print_flags(termios, opts, CONTROL_FLAGS);
         print_flags(termios, opts, INPUT_FLAGS);
         print_flags(termios, opts, OUTPUT_FLAGS);