tty_ptsname is a safe function that builds a CStr from a possibly null ptsname() #1953

teletypewriter::tty_ptsname is a public safe function. Its comment says it is unsafe because it calls libc::ptsname, but the function is not unsafe fn.

ptsname returns a null pointer when fd is not a pty master. The function passes that pointer straight to CStr::from_ptr:

pub fn tty_ptsname(fd: libc::c_int) -> Result<String, String> {
    let c_str: &CStr = unsafe {
        let name_ptr = ptsname(fd as *mut _);
        CStr::from_ptr(name_ptr)
    };
    ...
}

CStr::from_ptr requires a non-null, NUL-terminated string. A null pointer is immediate undefined behavior, not a Result::Err. Safe Rust can call tty_ptsname(-1) with no unsafe block.

Current file: teletypewriter/src/unix/mod.rs, tty_ptsname (around line 962 on main).

Suggested fix: if name_ptr is null, return Err (and read errno if you want a message). Do that before CStr::from_ptr. Marking the function unsafe would also match the comment, but the null check is the useful fix because the signature already returns Result.

I did not find an existing issue for ptsname / tty_ptsname.