mesg: Add tool

src/uu/mesg/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "uu_mesg"
+version = "0.0.1"
+edition = "2021"
+
+[lib]
+path = "src/mesg.rs"
+
+[[bin]]
+name = "mesg"
+path = "src/main.rs"
+
+[dependencies]
+clap = { workspace = true }
+nix = { workspace = true }
+uucore = { workspace = true }

src/uu/mesg/mesg.md

@@ -0,0 +1,7 @@
+# mesg
+
+```
+mesg [option] [y|n]
+```
+
+enables or disables displaying messages from other users

src/uu/mesg/src/main.rs

@@ -0,0 +1 @@
+uucore::bin!(uu_mesg);

src/uu/mesg/src/mesg.rs

@@ -0,0 +1,101 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+use clap::{builder::PossibleValuesParser, crate_version, Arg, ArgAction, ArgMatches, Command};
+#[cfg(target_family = "unix")]
+use uucore::error::{set_exit_code, UIoError};
+use uucore::{error::UResult, format_usage, help_about, help_usage};
+
+const ABOUT: &str = help_about!("mesg.md");
+const USAGE: &str = help_usage!("mesg.md");
+
+#[cfg(target_family = "unix")]
+pub fn do_mesg(matches: &ArgMatches) -> UResult<()> {
+    use nix::sys::stat::{fchmod, fstat, Mode};
+    use std::{io, os::fd::AsRawFd};
+    use std::{io::IsTerminal, os::fd::AsFd};
+
+    for fd in &[
+        std::io::stdin().as_fd(),
+        std::io::stdout().as_fd(),
+        std::io::stderr().as_fd(),
+    ] {
+        if fd.is_terminal() {
+            let st = fstat(fd.as_raw_fd())?;
+            if let Some(enable) = matches.get_one::<String>("enable") {
+                // 'mesg y' on the GNU version seems to only modify the group write bit,
+                // but 'mesg n' modifies both group and others write bits.
+                let new_mode = if enable == "y" {
+                    st.st_mode | 0o020
+                } else {
+                    st.st_mode & !0o022
+                };
+                fchmod(fd.as_raw_fd(), Mode::from_bits_retain(new_mode))?;
+                if enable == "n" {
+                    set_exit_code(1);
+                }
+                if matches.get_flag("verbose") {
+                    println!(
+                        "write access to your terminal is {}",
+                        if enable == "y" { "allowed" } else { "denied" }
+                    );
+                }
+            } else if st.st_mode & 0o022 != 0 {
+                println!("is y");
+            } else {
+                set_exit_code(1);
+                println!("is n");
+            }
+            return Ok(());
+        }
+    }
+    Err(UIoError::new(
+        io::ErrorKind::Other,
+        "stdin/stdout/stderr is not a terminal",
+    ))
+}
+
+#[cfg(target_family = "unix")]
+#[uucore::main]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+    let matches = uu_app().try_get_matches_from(args)?;
+    if let Err(e) = do_mesg(&matches) {
+        set_exit_code(2);
+        uucore::show_error!("{}", e);
+    };
+    Ok(())
+}
+
+pub fn uu_app() -> Command {
+    Command::new(uucore::util_name())
+        .version(crate_version!())
+        .about(ABOUT)
+        .override_usage(format_usage(USAGE))
+        .infer_long_args(true)
+        .arg(
+            Arg::new("verbose")
+                .short('v')
+                .long("verbose")
+                .help("Explain what is being done")
+                .action(ArgAction::SetTrue),
+        )
+        .arg(
+            Arg::new("enable")
+                .help("Whether to allow or disallow messages")
+                .value_parser(PossibleValuesParser::new(["y", "n"]))
+                .action(ArgAction::Set),
+        )
+}
+
+#[cfg(not(target_family = "unix"))]
+#[uucore::main]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+    let _matches: ArgMatches = uu_app().try_get_matches_from(args)?;
+
+    Err(uucore::error::USimpleError::new(
+        1,
+        "`mesg` is available only on Unix platforms.",
+    ))
+}