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

@@ -531,7 +531,12 @@ def __init__(
             self.security_manager.assert_access_unknown(warn_if_unencrypted, manifest, self.key)
             self.create()
 
-        self.open()
+        try:
+            self.open()
+        except (FileNotFoundError, FileIntegrityError):
+            self.wipe_cache()
+            self.open()
+
         try:
             self.security_manager.assert_secure(manifest, self.key, cache_config=self.cache_config)
 
@@ -924,19 +929,31 @@ def check_cache_compatibility(self):
         return True
 
     def wipe_cache(self):
-        logger.warning("Discarding incompatible cache and forcing a cache rebuild")
+        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.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/corruption.py

@@ -2,13 +2,15 @@
 import json
 import os
 from configparser import ConfigParser
+from unittest.mock import patch
 
 import pytest
 
 from ...constants import *  # NOQA
-from ...crypto.file_integrity import FileIntegrityError
 from ...helpers import bin_to_hex, Error
 from . import cmd, create_src_archive, create_test_files, RK_ENCRYPTION
+from ...hashindex import ChunkIndex
+from ...cache import LocalCache
 
 
 def test_check_corrupted_repository(archiver):
@@ -43,15 +45,31 @@ def corrupt(file, amount=1):
         fd.write(corrupted)
 
 
+@pytest.mark.allow_cache_wipe
 def test_cache_chunks(archiver):
     corrupt_archiver(archiver)
-    corrupt(os.path.join(archiver.cache_path, "chunks"))
-    if archiver.FORK_DEFAULT:
-        out = cmd(archiver, "rinfo", exit_code=2)
-        assert "failed integrity check" in out
-    else:
-        with pytest.raises(FileIntegrityError):
-            cmd(archiver, "rinfo")
+    create_src_archive(archiver, "test")
+    chunks_path = os.path.join(archiver.cache_path, "chunks")
+    chunks_before_corruption = set(ChunkIndex(path=chunks_path).iteritems())
+    corrupt(chunks_path)
+
+    assert not archiver.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 = cmd(archiver, "rinfo")
+
+    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(archiver):