implement ttyname and ttyname_r

CHANGELOG.md

@@ -33,6 +33,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   (#[1233](https://github.com/nix-rust/nix/pull/1233))
 - Added `EventFilter` bitflags for `EV_DISPATCH` and `EV_RECEIPT` on OpenBSD.
   (#[1252](https://github.com/nix-rust/nix/pull/1252))
+- Added `unistd::ttyname` and `unistd::ttyname_r`.
+  (#[1259](https://github.com/nix-rust/nix/pull/1259))
 
 ### Changed
 - Changed `fallocate` return type from `c_int` to `()` (#[1201](https://github.com/nix-rust/nix/pull/1201))

src/unistd.rs

@@ -2778,3 +2778,42 @@ impl Group {
         })
     }
 }
+
+/// Get the name of the terminal device that is open on file descriptor fd
+/// (see [`ttyname(3)`](http://man7.org/linux/man-pages/man3/ttyname.3.html)).
+///
+/// # Safety
+///
+/// `ttyname()` mutates global variables and is *not* threadsafe.
+/// Mutating global variables is always considered `unsafe` by Rust and this
+/// function is marked as `unsafe` to reflect that.
+///
+/// For a threadsafe and non-`unsafe` alternative, see `ttyname_r()`.
+#[inline]
+pub unsafe fn ttyname(fd: RawFd) -> Result<String> {
+    let buf = libc::ttyname(fd);
+    if buf.is_null() {
+        return Err(Error::Sys(Errno::last()));
+    }
+
+    Ok(CStr::from_ptr(buf).to_string_lossy().into_owned())
+}
+
+/// Get the name of the terminal device that is open on file descriptor fd
+/// (see [`ttyname(3)`](http://man7.org/linux/man-pages/man3/ttyname.3.html)).
+///
+/// This is the threadsafe version of `ttyname()`.
+#[inline]
+pub fn ttyname_r(fd: RawFd) -> Result<String> {
+    const PATH_MAX: usize = libc::PATH_MAX as usize;
+    let mut buf = [0_u8; PATH_MAX];
+    let c_buf = buf.as_mut_ptr() as *mut libc::c_char;
+
+    let ret = unsafe { libc::ttyname_r(fd, c_buf, buf.len()) };
+    if ret != 0 {
+        return Err(Error::Sys(Errno::last()));
+    }
+
+    let nul = buf.iter().position(|c| *c == b'\0').unwrap();
+    Ok(std::string::String::from_utf8_lossy(&buf[..nul]).to_string())
+}

test/test_unistd.rs

@@ -7,6 +7,8 @@ use nix::unistd::ForkResult::*;
 use nix::sys::signal::{SaFlags, SigAction, SigHandler, SigSet, Signal, sigaction};
 use nix::sys::wait::*;
 use nix::sys::stat::{self, Mode, SFlag};
+#[cfg(not(target_os = "redox"))]
+use nix::pty::posix_openpt;
 use nix::errno::Errno;
 #[cfg(not(target_os = "redox"))]
 use nix::Error;
@@ -964,3 +966,13 @@ fn test_setfsuid() {
     // open the temporary file with the current thread filesystem UID
     fs::File::open(temp_path_2).unwrap();
 }
+
+#[test]
+#[cfg(not(target_os = "redox"))]
+fn test_ttyname() {
+    let fd = posix_openpt(OFlag::O_RDWR).expect("posix_openpt failed");
+    assert!(fd.as_raw_fd() > 0);
+    let name_r = ttyname_r(fd.as_raw_fd()).expect("ttyname_r failed");
+    let name = unsafe { ttyname(fd.as_raw_fd()) }.expect("ttyname failed");
+    assert_eq!(name, name_r);
+}