Add compatibility for legacy bloom filter file naming

src/olympia/blocklist/cron.py

@@ -95,7 +95,7 @@ def _upload_mlbf_to_remote_settings(*, force_base=False):
             or mlbf.should_upload_filter(block_type, base_filter)
         ):
             base_filters_to_update.append(block_type)
-        # Only update the stash if we should AND if we aren't already 
+        # Only update the stash if we should AND if we aren't already
         # re-uploading the filter for this block type.
         elif mlbf.should_upload_stash(block_type, previous_filter or base_filter):
             create_stash = True
@@ -118,6 +118,7 @@ def _upload_mlbf_to_remote_settings(*, force_base=False):
 
     # Until we are ready to enable soft blocking, it should not be possible
     # to create a stash and a filter at the same iteration
+    # This should never happen, but we'll raise an exception just in case.
     if create_stash and len(base_filters_to_update) > 0:
         raise Exception(
             'Cannot upload stash and filter without implementing soft blocking'

src/olympia/blocklist/mlbf.py

@@ -209,9 +209,10 @@ def hash_filter_inputs(cls, input_list):
             for (guid, version) in input_list
         ]
 
-    def filter_path(self, block_type: BlockType):
-        # TODO: explain / test
-        if block_type == BlockType.BLOCKED:
+    def filter_path(self, block_type: BlockType, compat: bool = False):
+        # Override the return value of the BLOCKED filter
+        # to for backwards compatibility with the old file name
+        if block_type == BlockType.BLOCKED and compat:
             return self.storage.path('filter')
         return self.storage.path(f'filter-{BaseMLBFLoader.data_type_key(block_type)}')
 
@@ -233,7 +234,15 @@ def generate_and_write_filter(self, block_type: BlockType = BlockType.BLOCKED):
             not_blocked=self.data.not_blocked_items,
         )
 
-        # write bloomfilter
+        # write bloomfilter to old and new file names
+        mlbf_path = self.filter_path(block_type, compat=True)
+        with self.storage.open(mlbf_path, 'wb') as filter_file:
+            log.info(f'Writing to file {mlbf_path}')
+            bloomfilter.tofile(filter_file)
+            stats['mlbf_filesize'] = os.stat(mlbf_path).st_size
+
+        # also write to the new file name. After the switch is complete,
+        # this file will be used and the old file will be deleted.
         mlbf_path = self.filter_path(block_type)
         with self.storage.open(mlbf_path, 'wb') as filter_file:
             log.info(f'Writing to file {mlbf_path}')

src/olympia/blocklist/tests/test_mlbf.py

@@ -262,6 +262,18 @@ def test_hash_filter_inputs_returns_set_of_hashed_strings(self):
 
 
 class TestMLBF(_MLBFBase):
+    def test_filter_path(self):
+        mlbf = MLBF.generate_from_db('test')
+        assert mlbf.filter_path(BlockType.BLOCKED, compat=True).endswith('filter')
+        assert mlbf.filter_path(BlockType.BLOCKED).endswith('filter-blocked')
+        assert mlbf.filter_path(BlockType.SOFT_BLOCKED).endswith('filter-soft_blocked')
+
+    def test_save_filter_writes_to_both_file_names(self):
+        mlbf = MLBF.generate_from_db('test')
+        mlbf.generate_and_write_filter(BlockType.BLOCKED)
+        assert mlbf.storage.exists('filter')
+        assert mlbf.storage.exists('filter-blocked')
+
     def test_get_data_from_db(self):
         self._blocked_addon()
         mlbf = MLBF.generate_from_db('test')