mhtml: Sanitize default filename suggestion

qutebrowser/browser/commands.py

@@ -1187,6 +1187,7 @@ class CommandDispatcher:
         tab_id = self._current_index()
         if dest is None:
             suggested_fn = self._current_title() + ".mht"
+            suggested_fn = utils.sanitize_filename(suggested_fn)
             q = usertypes.Question()
             q.text = "Save page to: "
             q.mode = usertypes.PromptMode.text

qutebrowser/browser/mhtml.py

@@ -458,7 +458,7 @@ def start_download_checked(dest, win_id, tab_id):
     # The default name is 'page title.mht'
     title = (objreg.get('webview', scope='tab', window=win_id, tab=tab_id)
              .title())
-    default_name = title + '.mht'
+    default_name = utils.sanitize_filename(title + '.mht')
 
     # Remove characters which cannot be expressed in the file system encoding
     encoding = sys.getfilesystemencoding()

qutebrowser/utils/utils.py

@@ -611,6 +611,27 @@ def force_encoding(text, encoding):
     return text.encode(encoding, errors='replace').decode(encoding)
 
 
+def sanitize_filename(name, replacement='_'):
+    """Replace invalid filename characters.
+
+    Note: This should be used for the basename, as it also removes the path
+    separator.
+
+    Args:
+        name: The filename.
+        replacement: The replacement character (or None).
+    """
+    if replacement is None:
+        replacement = ''
+    # Bad characters taken from Windows, there are even fewer on Linux
+    # See also
+    # https://en.wikipedia.org/wiki/Filename#Reserved_characters_and_words
+    bad_chars = '\\/:*?"<>|'
+    for bad_char in bad_chars:
+        name = name.replace(bad_char, replacement)
+    return name
+
+
 def newest_slice(iterable, count):
     """Get an iterable for the n newest items of the given iterable.
 

tests/unit/utils/test_utils.py

@@ -839,6 +839,20 @@ def test_force_encoding(inp, enc, expected):
     assert utils.force_encoding(inp, enc) == expected
 
 
+@pytest.mark.parametrize('inp, expected', [
+    ('normal.txt', 'normal.txt'),
+    ('user/repo issues.mht', 'user_repo issues.mht'),
+    ('<Test\\File> - "*?:|', '_Test_File_ - _____'),
+])
+def test_sanitize_filename(inp, expected):
+    assert utils.sanitize_filename(inp) == expected
+
+
+def test_sanitize_filename_empty_replacement():
+    name = '/<Bad File>/'
+    assert utils.sanitize_filename(name, replacement=None) == 'Bad File'
+
+
 class TestNewestSlice:
 
     """Test newest_slice."""