Scoped recovery module for sql/

sql/recovery.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sql/recovery.h"
+
+#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "sql/connection.h"
+#include "third_party/sqlite/sqlite3.h"
+
+namespace sql {
+
+Recovery::Recovery(Connection* connection)
+    : db_(connection),
+      recover_db_(),
+      attach_(&recover_db_) {
+  // TODO(shess): Consider only applying this for small databases.
+
+  // Result should keep the page size specified earlier.
+  if (db_->page_size_)
+    recover_db_.set_page_size(db_->page_size_);
+}
+
+Recovery::~Recovery() {
+  if (db_)
+    Unrecoverable();
+}
+
+bool Recovery::Open(const base::FilePath& db_path) {
+  // Prevent re-entrancy if some call to db_ happens to fail.
+  // TODO(shess): Should this be scoped?  Should the caller manage it?
+  db_->reset_error_callback();
+
+  if (!recover_db_.OpenTemporary())
+    return false;
+
+  // Turn on |SQLITE_RecoveryMode|, which allows reading certain
+  // broken databases.
+  // TODO(shess): Double-check that this works for attached dbs.
+  if (!recover_db_.Execute("PRAGMA writable_schema=1")) {
+    recover_db_.Close();
+    return false;
+  }
+
+  // Break any outstanding transactions on original database to
+  // prevent deadlocks reading through the attached version.
+  // TODO(shess): A client may legitimately wish to recover from
+  // within the transaction context, because it would potentially
+  // preserve the in-process changes.  Unfortunately, any attach-based
+  // system could not handle that.  A system which manually queried
+  // one database and stored to the other could.
+  db_->RollbackAllTransactions();
+
+  if (!attach_.Attach(db_path, "corrupt")) {
+    recover_db_.Close();
+    return false;
+  }
+
+  return true;
+}
+
+void Recovery::Unrecoverable() {
+  CHECK(db_);
+  attach_.Detach();
+  recover_db_.Close();
+  db_->RazeAndClose();
+  db_ = NULL;
+}
+
+bool Recovery::Recovered() {
+  CHECK(db_);
+  CHECK(recover_db_.is_open());
+
+  sqlite3_backup* backup = sqlite3_backup_init(db_->db_, "main",
+                                               recover_db_.db_, "main");
+  if (!backup) {
+    LOG(ERROR) << "Failed to make backup?";
+    return false;
+  }
+
+  // -1 backs up the entire database.
+  int rc = sqlite3_backup_step(backup, -1);
+  int pages = sqlite3_backup_pagecount(backup);
+  sqlite3_backup_finish(backup);
+  DCHECK_GT(pages, 0);
+
+  // The destination database was locked.
+  if (rc == SQLITE_BUSY) {
+    // TODO(shess): Ignore it?  What if it's ALWAYS locked?  If it's
+    // locked, it probably can't be deleted, either, and Raze() will
+    // fail the same way.
+    attach_.Detach();
+    recover_db_.Close();
+    db_->CloseAndPoison();
+    db_ = NULL;
+    return false;
+  }
+
+  // It is unclear what errors are possible at this point, and how to
+  // handle them.  Some could perhaps be resolved with a future retry,
+  // but it is unclear how that could possibly work.
+  // TODO(shess): I wonder about try/sleep/try :-).
+  if (rc != SQLITE_DONE) {
+    attach_.Detach();
+    recover_db_.Close();
+    db_->RazeAndClose();
+    db_ = NULL;
+    return false;
+  }
+
+  // Clean up the recovery db, and terminate the main database
+  // connection.
+  attach_.Detach();
+  recover_db_.Close();
+  db_->CloseAndPoison();
+  db_ = NULL;
+  return true;
+}
+
+}  // namespace sql