HeaderMatchingFilter: Gracefully handle missing headers

afew/filters/HeaderMatchingFilter.py

@@ -6,6 +6,8 @@
 
 from afew.filters.BaseFilter import Filter
 
+from notmuch.errors import NullPointerError
+
 import re
 
 
@@ -22,10 +24,13 @@ def __init__(self, database, **kwargs):
     def handle_message(self, message):
         if self.header is not None and self.pattern is not None:
             if not self._tag_blacklist.intersection(message.get_tags()):
-                value = message.get_header(self.header)
-                match = self.pattern.search(value)
-                if match:
-                    tagdict = {k: v.lower() for k, v in match.groupdict().items()}
-                    sub = (lambda tag: tag.format(**tagdict))
-                    self.remove_tags(message, *map(sub, self._tags_to_remove))
-                    self.add_tags(message, *map(sub, self._tags_to_add))
+                try:
+                    value = message.get_header(self.header)
+                    match = self.pattern.search(value)
+                    if match:
+                        tagdict = {k: v.lower() for k, v in match.groupdict().items()}
+                        sub = (lambda tag: tag.format(**tagdict))
+                        self.remove_tags(message, *map(sub, self._tags_to_remove))
+                        self.add_tags(message, *map(sub, self._tags_to_add))
+                except NullPointerError:
+                    pass

afew/tests/test_headermatchingfilter.py

@@ -0,0 +1,84 @@
+"""Test suite for DKIMValidityFilter.
+"""
+import unittest
+from email.utils import make_msgid
+from unittest import mock
+
+from afew.Database import Database
+from afew.filters.HeaderMatchingFilter import HeaderMatchingFilter
+
+from notmuch.errors import NullPointerError
+
+
+class _AddTags:  # pylint: disable=too-few-public-methods
+    """Mock for `add_tags` method of base filter. We need to easily collect
+    tags added by filter for test assertion.
+    """
+    def __init__(self, tags):
+        self._tags = tags
+
+    def __call__(self, message, *tags):
+        self._tags.update(tags)
+
+
+def _make_header_matching_filter():
+    """Make `HeaderMatchingFilter` with mocked `HeaderMatchingFilter.add_tags`
+    method, so in tests we can easily check what tags were added by filter
+    without fiddling with db.
+    """
+    tags = set()
+    add_tags = _AddTags(tags)
+    header_filter = HeaderMatchingFilter(Database(), header="X-test", pattern="")
+    header_filter.add_tags = add_tags
+    return header_filter, tags
+
+
+def _make_message(should_fail):
+    """Make mock email Message.
+
+    Mocked methods:
+
+    - `get_header()` returns non-empty string. When testing with mocked
+      function for verifying DKIM signature, DKIM signature doesn't matter as
+      long as it's non-empty string.
+
+    - `get_filenames()` returns list of non-empty string. When testing with
+    mocked file open, it must just be non-empty string.
+
+    - `get_message_id()` returns some generated message ID.
+    """
+    message = mock.Mock()
+    if should_fail:
+        message.get_header.side_effect = NullPointerError
+    else:
+        message.get_header.return_value = 'header'
+    message.get_filenames.return_value = ['a']
+    message.get_tags.return_value = ['a']
+    message.get_message_id.return_value = make_msgid()
+    return message
+
+
+class TestHeaderMatchingFilter(unittest.TestCase):
+    """Test suite for `HeaderMatchingFilter`.
+    """
+    @mock.patch('afew.filters.HeaderMatchingFilter.open',
+                mock.mock_open(read_data=b''))
+    def test_header_exists(self):
+        """Test message with header that exists.
+        """
+        header_filter, tags = _make_header_matching_filter()
+        message = _make_message(False)
+        header_filter.handle_message(message)
+
+        self.assertSetEqual(tags, set())
+
+    @mock.patch('afew.filters.HeaderMatchingFilter.open',
+                mock.mock_open(read_data=b''))
+    def test_header_doesnt_exist(self):
+        """Test message with header that exists.
+        """
+        header_filter, tags = _make_header_matching_filter()
+        message = _make_message(True)
+        header_filter.handle_message(message)
+
+        self.assertSetEqual(tags, set())