cat: add error handling in write_fast function (#8091)

src/uu/cat/src/cat.rs

@@ -496,12 +496,17 @@ fn write_fast<R: FdReadable>(handle: &mut InputHandle<R>) -> CatResult<()> {
     // If we're not on Linux or Android, or the splice() call failed,
     // fall back on slower writing.
     let mut buf = [0; 1024 * 64];
-    while let Ok(n) = handle.reader.read(&mut buf) {
+    loop {
+        match handle.reader.read(&mut buf) {
+            Ok(n) => {
                 if n == 0 {
                     break;
                 }
                 stdout_lock.write_all(&buf[..n])?;
             }
+            Err(e) => return Err(e.into()),
+        }
+    }
 
     // If the splice() call failed and there has been some data written to
     // stdout via while loop above AND there will be second splice() call

tests/by-util/test_cat.rs

@@ -713,6 +713,26 @@ fn test_u_ignored() {
     }
 }
 
+#[test]
+#[cfg(unix)]
+fn test_write_fast_read_error() {
+    use std::os::unix::fs::PermissionsExt;
+
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    // Create a file with content
+    at.write("foo", "content");
+
+    // Remove read permissions to cause a read error
+    let file_path = at.plus_as_string("foo");
+    let mut perms = std::fs::metadata(&file_path).unwrap().permissions();
+    perms.set_mode(0o000); // No permissions
+    std::fs::set_permissions(&file_path, perms).unwrap();
+
+    // Test that cat fails with permission denied
+    ucmd.arg("foo").fails().stderr_contains("Permission denied");
+}
+
 #[test]
 #[cfg(target_os = "linux")]
 fn test_appending_same_input_output() {