hashsum: when the filename contains some special chars, escape them

Should fix tests/cksum/md5sum-newline.pl

src/uu/hashsum/src/hashsum.rs

@@ -756,7 +756,9 @@ where
             } else if options.zero {
                 print!("{} {}{}\0", sum, binary_marker, filename.display());
             } else {
-                println!("{} {}{}", sum, binary_marker, filename.display());
+                let (filename, has_prefix) = escape_filename(filename);
+                let prefix = if has_prefix { "\\" } else { "" };
+                println!("{}{} {}{}", prefix, sum, binary_marker, filename);
             }
         }
     }
@@ -781,6 +783,16 @@ where
     Ok(())
 }
 
+fn escape_filename(filename: &Path) -> (String, bool) {
+    let original = filename.as_os_str().to_string_lossy();
+    let escaped = original
+        .replace('\\', "\\\\")
+        .replace('\n', "\\n")
+        .replace('\r', "\\r");
+    let has_changed = escaped != original;
+    (escaped, has_changed)
+}
+
 fn digest_reader<T: Read>(
     digest: &mut Box<dyn Digest>,
     reader: &mut BufReader<T>,

tests/by-util/test_hashsum.rs

@@ -371,3 +371,18 @@ fn test_tag() {
             "SHA256 (foobar) = 1f2ec52b774368781bed1d1fb140a92e0eb6348090619c9291f9a5a3c8e8d151\n",
         );
 }
+
+#[test]
+#[cfg(not(windows))]
+fn test_with_escape_filename() {
+    let scene = TestScenario::new(util_name!());
+
+    let at = &scene.fixtures;
+    let filename = "a\nb";
+    at.touch(filename);
+    let result = scene.ccmd("md5sum").arg("--text").arg(filename).succeeds();
+    let stdout = result.stdout_str();
+    println!("stdout {}", stdout);
+    assert!(stdout.starts_with('\\'));
+    assert!(stdout.trim().ends_with("a\\nb"));
+}