tr: Fix regression causing read error with sockets

.vscode/cspell.dictionaries/workspace.wordlist.txt

@@ -154,6 +154,7 @@ IFSOCK
 IRGRP
 IROTH
 IRUSR
+ISDIR
 ISGID
 ISUID
 ISVTX
@@ -205,6 +206,7 @@ setgid
 setgroups
 settime
 setuid
+socketpair
 socktype
 statfs
 statp

Cargo.toml

@@ -537,7 +537,13 @@ hex-literal = "1.0.0"
 rstest.workspace = true
 
 [target.'cfg(unix)'.dev-dependencies]
-nix = { workspace = true, features = ["process", "signal", "user", "term"] }
+nix = { workspace = true, features = [
+  "process",
+  "signal",
+  "socket",
+  "user",
+  "term",
+] }
 rlimit = "0.10.1"
 xattr.workspace = true
 

src/uucore/src/lib/features/fs.rs

@@ -720,7 +720,9 @@ pub fn is_stdin_directory(stdin: &Stdin) -> bool {
     {
         use nix::sys::stat::fstat;
         let mode = fstat(stdin.as_fd()).unwrap().st_mode as mode_t;
-        has!(mode, S_IFDIR)
+        // We use the S_IFMT mask ala S_ISDIR() to avoid mistaking
+        // sockets for directories.
+        mode & S_IFMT == S_IFDIR
     }
 
     #[cfg(windows)]

tests/by-util/test_tr.rs

@@ -1563,3 +1563,24 @@ fn test_broken_pipe_no_error() {
         .run_stdout_starts_with(b"")
         .fails_silently();
 }
+
+#[cfg(not(windows))]
+#[test]
+fn test_stdin_is_socket() {
+    use nix::sys::socket::{AddressFamily, SockFlag, SockType, socketpair};
+    use nix::unistd::write;
+
+    let (fd1, fd2) = socketpair(
+        AddressFamily::Unix,
+        SockType::Stream,
+        None,
+        SockFlag::empty(),
+    )
+    .unwrap();
+    write(fd1, b"::").unwrap();
+    new_ucmd!()
+        .args(&[":", ";"])
+        .set_stdin(fd2)
+        .succeeds()
+        .stdout_is(";;");
+}