tar: refuse to write archive to terminal, lock stdout, and buffer output

Cargo.lock

@@ -1681,6 +1681,7 @@ dependencies = [
  "clap",
  "regex",
  "tar",
+ "tempfile",
  "thiserror",
  "uucore",
 ]

src/uu/tar/Cargo.toml

@@ -26,3 +26,6 @@ path = "src/tar.rs"
 [[bin]]
 name = "tar"
 path = "src/main.rs"
+
+[dev-dependencies]
+tempfile = { workspace = true }

src/uu/tar/src/errors.rs

@@ -54,6 +54,10 @@ pub enum TarError {
     /// Cannot finalize the archive
     #[error("tar: Cannot finalize archive: {0}")]
     CannotFinalizeArchive(io::Error),
+
+    /// Refusing to write archive contents to terminal
+    #[error("tar: Refusing to write archive contents to terminal (missing -f option?)")]
+    RefuseWriteArchiveToTerminal,
 }
 
 impl TarError {

src/uu/tar/src/operations/create.rs

@@ -77,8 +77,8 @@ pub fn create_archive(
                     .iter()
                     .collect();
                 writeln!(
-                    status_output,
-                    "Removing leading `{}' from member names",
+                    std::io::stderr(),
+                    "tar: Removing leading `{}' from member names",
                     removed.display()
                 )
                 .map_err(TarError::Io)?;
@@ -146,3 +146,32 @@ fn normalize_path(path: &Path, allow_absolute: bool) -> Option<PathBuf> {
         None
     }
 }
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::{self, Write};
+    use tempfile::TempDir;
+
+    struct FailFlushWriter;
+    impl Write for FailFlushWriter {
+        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+            Ok(buf.len())
+        }
+        fn flush(&mut self) -> io::Result<()> {
+            Err(io::Error::other("flush failed"))
+        }
+    }
+
+    #[test]
+    fn test_create_archive_flush_failed() {
+        let dir = TempDir::new().unwrap();
+        let file_path = dir.path().join("test.txt");
+        fs::write(&file_path, "hello").unwrap();
+
+        let output = FailFlushWriter;
+        let status_output = io::sink();
+
+        let res = create_archive(output, status_output, &[file_path.as_path()], false, false);
+        assert!(res.is_err());
+    }
+}

src/uu/tar/src/tar.rs

@@ -9,7 +9,7 @@ pub mod operations;
 use crate::errors::TarError;
 use clap::{arg, crate_version, ArgAction, Command};
 use std::fs::File;
-use std::io;
+use std::io::{self, IsTerminal};
 use std::path::{Path, PathBuf};
 use uucore::error::UResult;
 use uucore::format_usage;
@@ -171,21 +171,25 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
         let output_is_stdout = archive_path == Path::new("-");
         return if output_is_stdout {
-            let output = io::stdout();
-            let status_output = io::stderr();
-            operations::create::create_archive(
-                output,
-                status_output,
-                &files,
-                allow_absolute,
-                verbose,
-            )
+            if io::stdout().is_terminal() {
+                Err(TarError::RefuseWriteArchiveToTerminal.into())
+            } else {
+                let output = io::stdout().lock();
+                let status_output = io::stderr();
+                operations::create::create_archive(
+                    output,
+                    status_output,
+                    &files,
+                    allow_absolute,
+                    verbose,
+                )
+            }
         } else {
             let output = File::create(archive_path).map_err(|e| TarError::CannotCreateArchive {
                 path: archive_path.clone(),
                 source: e,
             })?;
-            let status_output = io::stdout();
+            let status_output = io::stdout().lock();
             operations::create::create_archive(
                 output,
                 status_output,

tests/by-util/test_tar.rs

@@ -190,7 +190,7 @@ fn test_create_absolute_path() {
         &file_abs_path.display().to_string(),
     ])
     .succeeds()
-    .stdout_contains("Removing leading");
+    .stderr_contains("tar: Removing leading");
 
     assert!(at.file_exists("archive-trimed.tar"));
 
@@ -868,6 +868,10 @@ fn test_create_verbose_to_stdout_keeps_stdout_as_tar_data() {
         "tar header should contain filename"
     );
     assert_eq!(&bytes[..8], b"file.txt");
+    assert_eq!(
+        bytes[8], 0,
+        "stdout should not contain verbose output prefix"
+    );
 }
 
 #[test]