tail: use same-file crate to get a handle of stdin redirected file

Cargo.lock

@@ -2816,6 +2816,7 @@ dependencies = [
  "libc",
  "nix",
  "notify",
+ "same-file",
  "uucore",
  "winapi",
  "winapi-util",

src/uu/tail/Cargo.toml

@@ -20,6 +20,7 @@ clap = { version = "3.2", features = ["wrap_help", "cargo"] }
 libc = "0.2.132"
 notify = { version = "=5.0.0-pre.16", features=["macos_kqueue"]}
 uucore = { version=">=0.0.15", package="uucore", path="../../uucore", features=["ringbuffer", "lines"] }
+same-file = "1.0.6"
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version="0.3", features=["fileapi", "handleapi", "processthreadsapi", "synchapi", "winbase"] }

src/uu/tail/src/chunks.rs

@@ -30,7 +30,11 @@ pub struct ReverseChunks<'a> {
 
 impl<'a> ReverseChunks<'a> {
     pub fn new(file: &'a mut File) -> ReverseChunks<'a> {
-        let current = file.seek(SeekFrom::Current(0)).unwrap();
+        let current = if cfg!(unix) {
+            file.seek(SeekFrom::Current(0)).unwrap()
+        } else {
+            0
+        };
         let size = file.seek(SeekFrom::End(0)).unwrap() - current;
         let max_blocks_to_read = (size as f64 / BLOCK_SIZE as f64).ceil() as usize;
         let block_idx = 0;

src/uu/tail/src/tail.rs

@@ -318,6 +318,18 @@ fn uu_tail(mut settings: Settings) -> UResult<()> {
         ));
     }
 
+    settings.stdin_redirect = dash.handle_redirect();
+    if cfg!(unix) && settings.stdin_is_pipe_or_fifo {
+        // Save the current seek position/offset of a stdin redirected file.
+        // This is needed to pass "gnu/tests/tail-2/start-middle.sh"
+        use same_file::Handle;
+        if let Ok(mut stdin_handle) = Handle::stdin() {
+            if let Ok(offset) = stdin_handle.as_file_mut().seek(SeekFrom::Current(0)) {
+                settings.stdin_offset = offset;
+            }
+        }
+    }
+
     // add '-' to paths
     if !settings.paths.contains(&dash) && settings.stdin_is_pipe_or_fifo
         || settings.paths.is_empty() && !settings.stdin_is_pipe_or_fifo
@@ -325,15 +337,6 @@ fn uu_tail(mut settings: Settings) -> UResult<()> {
         settings.paths.push_front(dash);
     }
 
-    if cfg!(unix) && settings.stdin_is_pipe_or_fifo {
-        settings.stdin_redirect = PathBuf::from(text::STDIN_HEADER).handle_redirect();
-        use std::os::unix::io::FromRawFd;
-        let mut stdin_handle = unsafe { std::fs::File::from_raw_fd(0) };
-        if let Ok(offset) = stdin_handle.seek(SeekFrom::Current(0)) {
-            settings.stdin_offset = offset;
-        }
-    }
-
     // TODO: is there a better way to check for a readable stdin?
     let mut buf = [0; 0]; // empty buffer to check if stdin().read().is_err()
     let stdin_read_possible = settings.stdin_is_pipe_or_fifo && stdin().read(&mut buf).is_ok();
@@ -455,7 +458,7 @@ fn uu_tail(mut settings: Settings) -> UResult<()> {
 
         let metadata = path.metadata().ok();
 
-        if display_name.is_stdin() && path_is_tailable && !path.is_file() {
+        if display_name.is_stdin() && !path.is_file() {
             if settings.verbose {
                 files.print_header(&display_name, !first_header);
                 first_header = false;
@@ -500,11 +503,8 @@ fn uu_tail(mut settings: Settings) -> UResult<()> {
                     }
 
                     let mut reader;
-                    if file.is_seekable(if display_name.is_stdin() {
-                        settings.stdin_offset
-                    } else {
-                        0
-                    }) && metadata.as_ref().unwrap().get_block_size() > 0
+                    if file.is_seekable(settings.stdin_offset)
+                        && metadata.as_ref().unwrap().get_block_size() > 0
                     {
                         bounded_tail(&mut file, &settings);
                         reader = BufReader::new(file);

tests/by-util/test_tail.rs

@@ -107,11 +107,7 @@ fn test_stdin_redirect_offset() {
     let mut fh = std::fs::File::open(at.plus("k")).unwrap();
     fh.seek(SeekFrom::Start(2)).unwrap();
 
-    ts.ucmd()
-        .set_stdin(fh)
-        .run()
-        .stdout_is("2\n")
-        .succeeded();
+    ts.ucmd().set_stdin(fh).run().stdout_is("2\n").succeeded();
 }
 
 #[test]