Fix empty `url_cache_thumbnails/yyyy-mm-dd/` directories being left behind (#10924)

3 files changed, 75 insertions, 31 deletions

diff --git a/changelog.d/10924.bugfix b/changelog.d/10924.bugfix
new file mode 100644
index 0000000000..c73a51e32f
--- /dev/null
+++ b/changelog.d/10924.bugfix
@@ -0,0 +1 @@
+Fix a bug where empty `yyyy-mm-dd/` directories would be left behind in the media store's `url_cache_thumbnails/` directory.
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 79a42b2455..044f44a397 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -73,6 +73,7 @@ OG_TAG_VALUE_MAXLEN = 1000
 
 ONE_HOUR = 60 * 60 * 1000
 ONE_DAY = 24 * ONE_HOUR
+IMAGE_CACHE_EXPIRY_MS = 2 * ONE_DAY
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
@@ -496,6 +497,27 @@ class PreviewUrlResource(DirectServeJsonResource):
             logger.info("Still running DB updates; skipping expiry")
             return
 
+        def try_remove_parent_dirs(dirs: Iterable[str]) -> None:
+            """Attempt to remove the given chain of parent directories
+
+            Args:
+                dirs: The list of directory paths to delete, with children appearing
+                    before their parents.
+            """
+            for dir in dirs:
+                try:
+                    os.rmdir(dir)
+                except FileNotFoundError:
+                    # Already deleted, continue with deleting the rest
+                    pass
+                except OSError as e:
+                    # Failed, skip deleting the rest of the parent dirs
+                    if e.errno != errno.ENOTEMPTY:
+                        logger.warning(
+                            "Failed to remove media directory: %r: %s", dir, e
+                        )
+                    break
+
         # First we delete expired url cache entries
         media_ids = await self.store.get_expired_url_cache(now)
 
@@ -504,20 +526,16 @@ class PreviewUrlResource(DirectServeJsonResource):
             fname = self.filepaths.url_cache_filepath(media_id)
             try:
                 os.remove(fname)
+            except FileNotFoundError:
+                pass  # If the path doesn't exist, meh
             except OSError as e:
-                # If the path doesn't exist, meh
-                if e.errno != errno.ENOENT:
-                    logger.warning("Failed to remove media: %r: %s", media_id, e)
-                    continue
+                logger.warning("Failed to remove media: %r: %s", media_id, e)
+                continue
 
             removed_media.append(media_id)
 
-            try:
-                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
-                for dir in dirs:
-                    os.rmdir(dir)
-            except Exception:
-                pass
+            dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
+            try_remove_parent_dirs(dirs)
 
         await self.store.delete_url_cache(removed_media)
 
@@ -530,7 +548,7 @@ class PreviewUrlResource(DirectServeJsonResource):
         # These may be cached for a bit on the client (i.e., they
         # may have a room open with a preview url thing open).
         # So we wait a couple of days before deleting, just in case.
-        expire_before = now - 2 * ONE_DAY
+        expire_before = now - IMAGE_CACHE_EXPIRY_MS
         media_ids = await self.store.get_url_cache_media_before(expire_before)
 
         removed_media = []
@@ -538,36 +556,30 @@ class PreviewUrlResource(DirectServeJsonResource):
             fname = self.filepaths.url_cache_filepath(media_id)
             try:
                 os.remove(fname)
+            except FileNotFoundError:
+                pass  # If the path doesn't exist, meh
             except OSError as e:
-                # If the path doesn't exist, meh
-                if e.errno != errno.ENOENT:
-                    logger.warning("Failed to remove media: %r: %s", media_id, e)
-                    continue
+                logger.warning("Failed to remove media: %r: %s", media_id, e)
+                continue
 
-            try:
-                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
-                for dir in dirs:
-                    os.rmdir(dir)
-            except Exception:
-                pass
+            dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
+            try_remove_parent_dirs(dirs)
 
             thumbnail_dir = self.filepaths.url_cache_thumbnail_directory(media_id)
             try:
                 shutil.rmtree(thumbnail_dir)
+            except FileNotFoundError:
+                pass  # If the path doesn't exist, meh
             except OSError as e:
-                # If the path doesn't exist, meh
-                if e.errno != errno.ENOENT:
-                    logger.warning("Failed to remove media: %r: %s", media_id, e)
-                    continue
+                logger.warning("Failed to remove media: %r: %s", media_id, e)
+                continue
 
             removed_media.append(media_id)
 
-            try:
-                dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id)
-                for dir in dirs:
-                    os.rmdir(dir)
-            except Exception:
-                pass
+            dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id)
+            # Note that one of the directories to be deleted has already been
+            # removed by the `rmtree` above.
+            try_remove_parent_dirs(dirs)
 
         await self.store.delete_url_cache_media(removed_media)
 
diff --git a/tests/rest/media/v1/test_url_preview.py b/tests/rest/media/v1/test_url_preview.py
index 4d09b5d07e..ce43de780b 100644
--- a/tests/rest/media/v1/test_url_preview.py
+++ b/tests/rest/media/v1/test_url_preview.py
@@ -21,11 +21,13 @@ from twisted.internet.error import DNSLookupError
 from twisted.test.proto_helpers import AccumulatingProtocol
 
 from synapse.config.oembed import OEmbedEndpointConfig
+from synapse.rest.media.v1.preview_url_resource import IMAGE_CACHE_EXPIRY_MS
 from synapse.util.stringutils import parse_and_validate_mxc_uri
 
 from tests import unittest
 from tests.server import FakeTransport
 from tests.test_utils import SMALL_PNG
+from tests.utils import MockClock
 
 try:
     import lxml
@@ -851,3 +853,32 @@ class URLPreviewTests(unittest.HomeserverTestCase):
             404,
             "URL cache thumbnail was unexpectedly retrieved from a storage provider",
         )
+
+    def test_cache_expiry(self):
+        """Test that URL cache files and thumbnails are cleaned up properly on expiry."""
+        self.preview_url.clock = MockClock()
+
+        _host, media_id = self._download_image()
+
+        file_path = self.preview_url.filepaths.url_cache_filepath(media_id)
+        file_dirs = self.preview_url.filepaths.url_cache_filepath_dirs_to_delete(
+            media_id
+        )
+        thumbnail_dir = self.preview_url.filepaths.url_cache_thumbnail_directory(
+            media_id
+        )
+        thumbnail_dirs = self.preview_url.filepaths.url_cache_thumbnail_dirs_to_delete(
+            media_id
+        )
+
+        self.assertTrue(os.path.isfile(file_path))
+        self.assertTrue(os.path.isdir(thumbnail_dir))
+
+        self.preview_url.clock.advance_time_msec(IMAGE_CACHE_EXPIRY_MS + 1)
+        self.get_success(self.preview_url._expire_url_cache_data())
+
+        for path in [file_path] + file_dirs + [thumbnail_dir] + thumbnail_dirs:
+            self.assertFalse(
+                os.path.exists(path),
+                f"{os.path.relpath(path, self.media_store_path)} was not deleted",
+            )