Automatic rebuild cache on exception, fixes #5213 (#8257)

Try to rebuild cache if an exception is raised, fixes #5213

For now, we catch FileNotFoundError and FileIntegrityError.

Write cache config without manifest to prevent override of manifest_id.
This is needed in order to have an empty manifest_id.
This empty id triggers the re-syncing of the chunks cache by calling sync() inside LocalCache.__init__()

Adapt and extend test_cache_chunks to new behaviour:

- a cache wipe is expected now.
- borg detects the corrupt cache and wipes/rebuilds the cache.
- check if the in-memory and on-disk cache is as expected (a rebuilt chunks cache).

src/borg/cache.py

@@ -488,7 +488,12 @@ def __init__(self, repository, key, manifest, path=None, sync=True, warn_if_unen
             self.security_manager.assert_access_unknown(warn_if_unencrypted, manifest, key)
             self.create()
 
-        self.open()
+        try:
+            self.open()
+        except (FileNotFoundError, FileIntegrityError):
+            self.wipe_cache()
+            self.open()
+
         try:
             self.security_manager.assert_secure(manifest, key, cache_config=self.cache_config)
 
@@ -920,19 +925,31 @@ def check_cache_compatibility(self):
         return True
 
     def wipe_cache(self):
-        logger.warning("Discarding incompatible cache and forcing a cache rebuild")
-        archive_path = os.path.join(self.path, 'chunks.archive.d')
+        logger.warning("Discarding incompatible or corrupted cache and forcing a cache rebuild")
+        archive_path = os.path.join(self.path, "chunks.archive.d")
         if os.path.isdir(archive_path):
             shutil.rmtree(os.path.join(self.path, 'chunks.archive.d'))
             os.makedirs(os.path.join(self.path, 'chunks.archive.d'))
         self.chunks = ChunkIndex()
-        with SaveFile(os.path.join(self.path, files_cache_name()), binary=True):
+        with IntegrityCheckedFile(path=os.path.join(self.path, "chunks"), write=True) as fd:
+            self.chunks.write(fd)
+        self.cache_config.integrity["chunks"] = fd.integrity_data
+        with IntegrityCheckedFile(path=os.path.join(self.path, files_cache_name()), write=True) as fd:
             pass  # empty file
-        self.cache_config.manifest_id = ''
-        self.cache_config._config.set('cache', 'manifest', '')
+        self.cache_config.integrity[files_cache_name()] = fd.integrity_data
+        self.cache_config.manifest_id = ""
+        self.cache_config._config.set("cache", "manifest", "")
+        if not self.cache_config._config.has_section("integrity"):
+            self.cache_config._config.add_section("integrity")
+        for file, integrity_data in self.cache_config.integrity.items():
+            self.cache_config._config.set("integrity", file, integrity_data)
+        # This is needed to pass the integrity check later on inside CacheConfig.load()
+        self.cache_config._config.set("integrity", "manifest", "")
 
         self.cache_config.ignored_features = set()
         self.cache_config.mandatory_features = set()
+        with SaveFile(self.cache_config.config_path) as fd:
+            self.cache_config._config.write(fd)
 
     def update_compatibility(self):
         operation_to_features_map = self.manifest.get_all_mandatory_features()

src/borg/testsuite/archiver.py

@@ -38,6 +38,7 @@
 from ..crypto.key import KeyfileKeyBase, RepoKey, KeyfileKey, Passphrase, TAMRequiredError, ArchiveTAMRequiredError
 from ..crypto.keymanager import RepoIdMismatch, NotABorgKeyFile
 from ..crypto.file_integrity import FileIntegrityError
+from ..hashindex import ChunkIndex
 from ..helpers import Location, get_security_dir
 from ..helpers import Manifest, MandatoryFeatureUnsupported, ArchiveInfo
 from ..helpers import init_ec_warnings
@@ -4361,15 +4362,30 @@ def corrupt(self, file, amount=1):
             fd.seek(-amount, io.SEEK_END)
             fd.write(corrupted)
 
+    @pytest.mark.allow_cache_wipe
     def test_cache_chunks(self):
-        self.corrupt(os.path.join(self.cache_path, 'chunks'))
+        self.create_src_archive("test")
+        chunks_path = os.path.join(self.cache_path, 'chunks')
+        chunks_before_corruption = set(ChunkIndex(path=chunks_path).iteritems())
+        self.corrupt(chunks_path)
 
-        if self.FORK_DEFAULT:
-            out = self.cmd('info', self.repository_location, exit_code=2)
-            assert 'failed integrity check' in out
-        else:
-            with pytest.raises(FileIntegrityError):
-                self.cmd('info', self.repository_location)
+        assert not self.FORK_DEFAULT  # test does not support forking
+
+        chunks_in_memory = None
+        sync_chunks = LocalCache.sync
+
+        def sync_wrapper(cache):
+            nonlocal chunks_in_memory
+            sync_chunks(cache)
+            chunks_in_memory = set(cache.chunks.iteritems())
+
+        with patch.object(LocalCache, "sync", sync_wrapper):
+            out = self.cmd("info", self.repository_location)
+
+        assert chunks_in_memory == chunks_before_corruption
+        assert "forcing a cache rebuild" in out
+        chunks_after_repair = set(ChunkIndex(path=chunks_path).iteritems())
+        assert chunks_after_repair == chunks_before_corruption
 
     def test_cache_files(self):
         self.cmd('create', self.repository_location + '::test', 'input')