add util: mesg

README.md

@@ -104,7 +104,7 @@ https://github.com/jgarzik/posixutils
  - [ ] mailx
  - [ ] make
  - [ ] man
- - [ ] mesg
+ - [x] mesg
  - [ ] mkdir
  - [ ] mkfifo
  - [ ] more

TODO.md

@@ -0,0 +1,16 @@
+# General TODO and future implementation notes
+
+## Translations
+
+* Standard OS error texts must be translated
+
+## OS errors
+
+* OS error messaging: many errors fail to conform to the standard of
+```
+	filename: OS error message
+```
+
+* `from_raw_os_error()` is probably pulling the wrong value and should
+  query errno
+

users/Cargo.toml

@@ -18,6 +18,10 @@ path = "src/logname.rs"
 name = "logger"
 path = "src/logger.rs"
 
+[[bin]]
+name = "mesg"
+path = "src/mesg.rs"
+
 [[bin]]
 name = "tty"
 path = "src/tty.rs"

users/src/mesg.rs

@@ -0,0 +1,129 @@
+//
+// Copyright (c) 2024 Jeff Garzik
+//
+// This file is part of the posixutils-rs project covered under
+// the MIT License.  For the full license text, please see the LICENSE
+// file in the root directory of this project.
+// SPDX-License-Identifier: MIT
+//
+// TODO:
+// - use .metadata() and std::os::unix::fs::PermissionsExt if possible
+// - set process exit code according to spec
+//
+
+extern crate clap;
+extern crate libc;
+extern crate plib;
+
+use clap::Parser;
+use gettextrs::{bind_textdomain_codeset, gettext, textdomain};
+use plib::PROJECT_NAME;
+use std::io::{self, Error, ErrorKind};
+use std::mem;
+
+/// mesg - permit or deny messages
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about)]
+struct Args {
+    /// "y" or "n":  Grant (y) or deny (n) permission to other users to send messages to the terminal device.
+    operand: Option<String>,
+}
+
+fn find_tty() -> Result<i32, &'static str> {
+    let fds = vec![libc::STDIN_FILENO, libc::STDOUT_FILENO, libc::STDERR_FILENO];
+    for fd in fds {
+        unsafe {
+            if libc::isatty(fd) > 0 {
+                return Ok(fd);
+            }
+        }
+    }
+
+    Err("no tty found")
+}
+
+fn stat_tty() -> io::Result<(i32, libc::stat)> {
+    let fd_res = find_tty();
+    if let Err(e) = fd_res {
+        eprintln!("{}", gettext(e));
+        return Err(Error::new(ErrorKind::Other, e));
+    }
+    let fd = fd_res.unwrap();
+
+    unsafe {
+        let mut st: libc::stat = mem::zeroed();
+        let ret = libc::fstat(fd, &mut st);
+        if ret < 0 {
+            eprintln!("{}", gettext("fstat failed"));
+            return Err(io::Error::from_raw_os_error(ret));
+        }
+
+        Ok((fd, st))
+    }
+}
+
+fn show_mesg(st: libc::stat) -> io::Result<()> {
+    if (st.st_mode & (libc::S_IWGRP | libc::S_IWOTH)) != 0 {
+        println!("is y");
+    } else {
+        println!("is n");
+    }
+    Ok(())
+}
+
+fn parse_setting(setting: &str) -> Result<bool, &'static str> {
+    match setting {
+        "y" | "Y" => Ok(true),
+        "n" | "N" => Ok(false),
+        _ => Err("invalid operand"),
+    }
+}
+
+fn set_mesg(fd: i32, st: libc::stat, setting: &str) -> io::Result<()> {
+    let res = parse_setting(setting);
+    if let Err(e) = res {
+        return Err(Error::new(ErrorKind::Other, e));
+    }
+    let affirm = res.unwrap();
+
+    let mut mode = st.st_mode;
+
+    if affirm {
+        if (mode & (libc::S_IWGRP | libc::S_IWOTH)) != 0 {
+            return Ok(());
+        }
+
+        mode = mode | libc::S_IWGRP | libc::S_IWOTH;
+    } else {
+        if (mode & (libc::S_IWGRP | libc::S_IWOTH)) == 0 {
+            return Ok(());
+        }
+
+        mode = mode & !(libc::S_IWGRP | libc::S_IWOTH);
+    }
+
+    let chres = unsafe { libc::fchmod(fd, mode) };
+    if chres < 0 {
+        eprintln!("{}", gettext("failed to change terminal mode"));
+        return Err(io::Error::from_raw_os_error(chres));
+    }
+
+    Ok(())
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // parse command line arguments
+    let args = Args::parse();
+
+    textdomain(PROJECT_NAME)?;
+    bind_textdomain_codeset(PROJECT_NAME, "UTF-8")?;
+
+    let (fd, stat) = stat_tty()?;
+
+    match args.operand {
+        None => show_mesg(stat)?,
+        Some(op) => set_mesg(fd, stat, &op)?,
+    }
+
+    Ok(())
+}