sync: Attempt to recover from directory corruption

Sync when sqlite fails to maintain databsae integrity, most likely due
to unexpected shutdowns or flaky storage devices. They can also be
corrupted by logic errors in the sync code, though we hope that's a rare
occurence.

This patch attempts to improve a user's experience in this scenario by
transparently deleting the old directory and re-downloading all their
data. This will be much better than the old behaviours, which included
silently signing a user out of sync, triggering an unrecoverable error,
or crashing.

To help catch sync logic bugs, debug builds are set to crash when they
detect directory corruption.

Also included in this patch is a new test. The
DirectoryBackingStore.MinorCorruption test exercises the code invoked
when the directory is successfully re-created.

BUG=109668, 129825


Review URL: https://chromiumcodereview.appspot.com/10821121

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150465 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 14 insertions, 0 deletions

diff --git a/sync/syncable/on_disk_directory_backing_store.h b/sync/syncable/on_disk_directory_backing_store.h
index f722ef9..0bf720b 100644
--- a/sync/syncable/on_disk_directory_backing_store.h
+++ b/sync/syncable/on_disk_directory_backing_store.h
@@ -17,11 +17,25 @@ class OnDiskDirectoryBackingStore : public DirectoryBackingStore {
  public:
   OnDiskDirectoryBackingStore(const std::string& dir_name,
                               const FilePath& backing_filepath);
+  virtual ~OnDiskDirectoryBackingStore();
   virtual DirOpenResult Load(
       MetahandlesIndex* entry_bucket,
       Directory::KernelLoadInfo* kernel_load_info) OVERRIDE;
 
+  // A helper function that will make one attempt to load the directory.
+  // Unlike Load(), it does not attempt to recover from failure.
+  DirOpenResult TryLoad(
+      MetahandlesIndex* entry_bucket,
+      Directory::KernelLoadInfo* kernel_load_info);
+
+ protected:
+  // Subclasses may override this to avoid a possible DCHECK.
+  virtual void ReportFirstTryOpenFailure();
+
  private:
+  FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MinorCorruption);
+
+  bool allow_failure_for_test_;
   FilePath backing_filepath_;
 };