sync: Attempt to recover from directory corruption

sync/syncable/on_disk_directory_backing_store.cc

Index: sync/syncable/on_disk_directory_backing_store.cc
diff --git a/sync/syncable/on_disk_directory_backing_store.cc b/sync/syncable/on_disk_directory_backing_store.cc
index 1f43da6ada6744be7eacba8293c0801d12b7c730..f844f38c4293d2552143b94d1aeba619a582f96f 100644
--- a/sync/syncable/on_disk_directory_backing_store.cc
+++ b/sync/syncable/on_disk_directory_backing_store.cc
@@ -5,19 +5,35 @@
 #include "sync/syncable/on_disk_directory_backing_store.h"
 
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
+#include "sync/syncable/syncable-inl.h"
 
 namespace syncer {
 namespace syncable {
 
+namespace {
+
+enum HistogramResultEnum {
+  FIRST_TRY_SUCCESS,
+  SECOND_TRY_SUCCESS,
+  SECOND_TRY_FAILURE,
+  RESULT_COUNT
+};
+
+}  // namespace
+
 OnDiskDirectoryBackingStore::OnDiskDirectoryBackingStore(
     const std::string& dir_name, const FilePath& backing_filepath)
     : DirectoryBackingStore(dir_name),
+      allow_failure_for_test_(false),
       backing_filepath_(backing_filepath) {
   db_->set_exclusive_locking();
   db_->set_page_size(4096);
 }
 
-DirOpenResult OnDiskDirectoryBackingStore::Load(
+OnDiskDirectoryBackingStore::~OnDiskDirectoryBackingStore() { }
+
+DirOpenResult OnDiskDirectoryBackingStore::TryLoad(
     MetahandlesIndex* entry_bucket,
     Directory::KernelLoadInfo* kernel_load_info) {
   DCHECK(CalledOnValidThread());
@@ -35,8 +51,53 @@ DirOpenResult OnDiskDirectoryBackingStore::Load(
     return FAILED_DATABASE_CORRUPT;
   if (!LoadInfo(kernel_load_info))
     return FAILED_DATABASE_CORRUPT;
+  if (!VerifyReferenceIntegrity(*entry_bucket))
+    return FAILED_DATABASE_CORRUPT;
 
   return OPENED;
+
+}
+
+DirOpenResult OnDiskDirectoryBackingStore::Load(
+    MetahandlesIndex* entry_bucket,
+    Directory::KernelLoadInfo* kernel_load_info) {
+  DirOpenResult result = TryLoad(entry_bucket, kernel_load_info);
+  if (result == OPENED) {
+    HISTOGRAM_ENUMERATION(
+        "Sync.DirectoryOpenResult", FIRST_TRY_SUCCESS, RESULT_COUNT);
+    return OPENED;
+  }
+
+  ReportFirstTryOpenFailure();
+
+  // The fallback: delete the current database and return a fresh one.  We can
+  // fetch the user's data from the could.
+  entry_bucket->clear();
+  db_.reset(new sql::Connection);
+  file_util::Delete(backing_filepath_, false);
+
+  result = TryLoad(entry_bucket, kernel_load_info);
+  if (result == OPENED) {
+    HISTOGRAM_ENUMERATION(
+        "Sync.DirectoryOpenResult", SECOND_TRY_SUCCESS, RESULT_COUNT);
+  } else {
+    HISTOGRAM_ENUMERATION(
+        "Sync.DirectoryOpenResult", SECOND_TRY_FAILURE, RESULT_COUNT);
+  }
+
+  return result;
+}
+
+void OnDiskDirectoryBackingStore::ReportFirstTryOpenFailure() {
+  // In debug builds, the last thing we want is to silently clear the database.
+  // It's full of evidence that might help us determine what went wrong.  It
+  // might be sqlite's fault, but it could also be a bug in sync.  We crash
+  // immediately so a developer can investigate.
+  //
+  // Developers: If you're not interested in debugging this right now, just move
+  // aside the 'Sync Data' directory in your profile.  This is similar to what
+  // the code would do if this DCHECK were disabled.
+  NOTREACHED() << "Crashing to preserve corrupt sync database";
 }
 
 }  // namespace syncable