fixup! Rework tail plateform module to tackle uutils#2873

Author: anastygnome

src/uu/tail/src/platform/unix.rs

@@ -8,15 +8,17 @@
  * file that was distributed with this source code.
  */
 
-// spell-checker:ignore (ToDO) stdlib,ctermid
-// spell-checker:ignore (options) GETFD EPERM ENOSYS ISCHR,ISREG,ISFIFO
+// spell-checker:ignore (ToDO) stdlib
+// spell-checker:ignore (options) GETFD EPERM ENOSYS
 
 use std::io::{stdin, Error};
 
 use std::os::unix::prelude::AsRawFd;
 
-use libc::{S_IFIFO, S_IFREG};
 use nix::sys::stat::fstat;
+
+use libc::{S_IFIFO, S_IFSOCK};
+
 pub type Pid = libc::pid_t;
 
 pub struct ProcessChecker {
@@ -49,20 +51,17 @@ fn get_errno() -> i32 {
 }
 
 pub fn stdin_is_pipe_or_fifo() -> bool {
-    // courtesy of Stack Overflow community https://stackoverflow.com/a/7601564 (08/07/2022).
-    // cmd\method             ctermid    open   isatty   fstat
-    // ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
-    // ./test                 /dev/tty   OK     YES      S_ISCHR
-    // ./test < test.cc       /dev/tty   OK     NO       S_ISREG
-    // cat test.cc | ./test   /dev/tty   OK     NO       S_ISFIFO
-    // echo ./test | at now   /dev/tty   FAIL   NO       S_ISREG
-
-    match fstat(libc::STDIN_FILENO) {
-    Ok(m) => { 
-    let mode= m.st_mode as libc::mode_t;
-    (mode & S_IFIFO != 0) || (mode & S_IFREG != 0) }, 
-    Err(err) => panic!("{}",err) 
-    }
+    let fd = libc::STDIN_FILENO;
+    // GNU tail checks fd >= 0
+    fd >= 0
+        && match fstat(fd) {
+            Ok(stat) => {
+                let mode = stat.st_mode as libc::mode_t;
+                // NOTE: This is probably not the most correct way to check this
+                (mode & S_IFIFO != 0) || (mode & S_IFSOCK != 0)
+            }
+            Err(err) => panic!("{}", err),
+        }
 }
 
 // FIXME: Detect a closed file descriptor, e.g.: `tail <&-`