dd: misc gnu test (#6084)

* dd: check file is a dir for iflag directory

* Improve english

Co-authored-by: Daniel Hofstetter <daniel.hofstetter@42dh.com>

* dd: stderr output checking for "iflag directory" testcase

* dd: replace #[cfg(unix)] with #[test]

---------

Co-authored-by: Sylvestre Ledru <sylvestre@debian.org>
Co-authored-by: Daniel Hofstetter <daniel.hofstetter@42dh.com>

src/uu/dd/src/dd.rs

@@ -310,6 +310,15 @@ impl<'a> Input<'a> {
         };
         #[cfg(unix)]
         let mut src = Source::stdin_as_file();
+        #[cfg(unix)]
+        if let Source::StdinFile(f) = &src {
+            // GNU compatibility:
+            // this will check whether stdin points to a folder or not
+            if f.metadata()?.is_file() && settings.iflags.directory {
+                show_error!("standard input: not a directory");
+                return Err(1.into());
+            }
+        };
         if settings.skip > 0 {
             src.skip(settings.skip)?;
         }

tests/by-util/test_dd.rs

@@ -1715,6 +1715,20 @@ fn test_reading_partial_blocks_from_fifo_unbuffered() {
     assert!(output.stderr.starts_with(expected));
 }
 
+#[test]
+#[cfg(any(target_os = "linux", target_os = "android"))]
+fn test_iflag_directory_fails_when_file_is_passed_via_std_in() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+    at.make_file("input");
+    let filename = at.plus_as_string("input");
+    new_ucmd!()
+        .args(&["iflag=directory", "count=0"])
+        .set_stdin(std::process::Stdio::from(File::open(filename).unwrap()))
+        .fails()
+        .stderr_contains("standard input: not a directory");
+}
+
 #[test]
 fn test_stdin_stdout_not_rewound_even_when_connected_to_seekable_file() {
     use std::process::Stdio;