Create a class to represent a DOM Storage Database.

webkit/dom_storage/dom_storage_database.cc

+// Copyright (c) 2012 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 "webkit/dom_storage/dom_storage_database.h"
+
+#include "base/file_util.h"
+#include "base/logging.h"
+#include "sql/diagnostic_error_delegate.h"
+#include "sql/statement.h"
+#include "sql/transaction.h"
+#include "third_party/sqlite/sqlite3.h"
+
+namespace {
+
+class HistogramUniquifier {
+ public:
+  static const char* name() { return "Sqlite.DomStorageDatabase.Error"; }
+};
+
+sql::ErrorDelegate* GetErrorHandlerForDomStorageDatabase() {
+  return new sql::DiagnosticErrorDelegate<HistogramUniquifier>();
+}
+
+}  // anon namespace
+
+namespace dom_storage {
+
+DomStorageDatabase::DomStorageDatabase(const FilePath& file_path)
+    : file_path_(file_path),
+      db_(NULL),
+      failed_to_open_(false),
+      tried_to_recreate_(false) {
+  // Note: in normal use we should never get an empty backing path here.
+  // However, the unit test for this class defines another constructor
+  // that will bypass this check to allow an empty path that signifies
+  // we should operate on an in-memory database for performance/reliability
+  // reasons.
+  DCHECK(!file_path_.empty());
+}
+
+DomStorageDatabase::~DomStorageDatabase() {
+}
+
+void DomStorageDatabase::ReadAllValues(ValuesMap* result) {
+  if (!LazyOpen(false))
+    return;
+
+  sql::Statement statement(db_->GetCachedStatement(SQL_FROM_HERE,
+                                                   "SELECT * from ItemTable"));
+  DCHECK(statement.is_valid());
+
+  while (statement.Step()) {
+    string16 key = statement.ColumnString16(0);
+    string16 value;
+    statement.ColumnBlobAsString16(1, &value);
+    (*result)[key] = NullableString16(value, false);
+  }
+}
+
+bool DomStorageDatabase::CommitChanges(bool clear_all_first,
+                                       const ValuesMap& changes) {
+  if (!LazyOpen(!changes.empty()))
+    return false;
+
+  sql::Transaction transaction(db_.get());
+  if (!transaction.Begin())
+    return false;
+
+  if (clear_all_first) {
+    if (!db_->Execute("DELETE FROM ItemTable"))
+      return false;
+  }
+
+  ValuesMap::const_iterator it = changes.begin();
+  for(; it != changes.end(); ++it) {
+    sql::Statement statement;
+    string16 key = it->first;
+    NullableString16 value = it->second;
+    if (value.is_null()) {
+      statement.Assign(db_->GetCachedStatement(SQL_FROM_HERE,
+         "DELETE FROM ItemTable WHERE key=?"));
+      statement.BindString16(0, key);
+    } else {
+      statement.Assign(db_->GetCachedStatement(SQL_FROM_HERE,
+          "INSERT INTO ItemTable VALUES (?,?)"));
+      statement.BindString16(0, key);
+      statement.BindBlob(1, value.string().data(),
+                         value.string().length() * sizeof(char16));
+    }
+    DCHECK(statement.is_valid());
+    statement.Run();
+  }
+  return transaction.Commit();
+}
+
+bool DomStorageDatabase::LazyOpen(bool create_if_needed) {
+  if (failed_to_open_) {
+    // Don't try to open a database that we know has failed
+    // already.
+    return false;
+  }
+
+  if (IsOpen())
+    return true;
+
+  bool database_exists = file_util::PathExists(file_path_);
+
+  if (!database_exists && !create_if_needed) {
+    // If the file doesn't exist already and we haven't been asked to create
+    // a file on disk, then we don't bother opening the database. This means
+    // we wait until we absolutely need to put something onto disk before we
+    // do so.
+    return false;
+  }
+
+  db_.reset(new sql::Connection());
+  db_->set_error_delegate(GetErrorHandlerForDomStorageDatabase());
+
+  if (file_path_.empty()) {
+    // This code path should only be triggered by unit tests.
+    if (!db_->OpenInMemory()) {
+      LOG(ERROR) << "Unable to open DOM storage database in memory.";

[michaeln, 2012/02/08 06:11:33]

this could probably be a NOTREACHED() instead

[benm (inactive), 2012/02/08 14:59:40]

Done.

+      failed_to_open_ = true;
+      return false;
+    }
+  } else {
+    if (!db_->Open(file_path_)) {
+      LOG(ERROR) << "Unable to open DOM storage database at "
+                 << file_path_.value()
+                 << " error: " << db_->GetErrorMessage();
+      if (database_exists && !tried_to_recreate_)
+        return DeleteFileAndRecreate();
+      failed_to_open_ = true;
+      return false;
+    }
+  }
+
+  // Open() may succeed even if the file we try and open is not a database so
+  // we check here that what we've got is something sensible.
+  // TODO(benm): It might be useful to actually verify the output of the
+  // quick_check too and try to recover in the case errors are detected.
+  // However, in the case that the database is corrupted to the point that
+  // SQLite doesn't actually think it's a database,
+  // sql::Connection::GetCachedStatement will DCHECK.
+  if (db_->ExecuteAndReturnErrorCode("PRAGMA quick_check(1)") != SQLITE_OK) {
+    Close();
+    return DeleteFileAndRecreate();
+  }
+
+  // sql::Connection uses UTF-8 encoding, but WebCore style databases use
+  // UTF-16, so ensure we match.
+  ignore_result(db_->Execute("PRAGMA encoding=\"UTF-16\""));
+
+  // If the table doesn't exist, try to create it at the current version.
+  if (!db_->DoesTableExist("ItemTable")) {
+    if (CreateTable())
+      return true;
+    // Couldn't create the table.
+    Close();
+    return DeleteFileAndRecreate();
+  }
+
+  // Table exists, so ensure we're at the right version, upgrading if
+  // necessary.
+  if (UpgradeVersion1To2IfNeeded())
+    return true;
+
+  // We were not able to verify that the database is at the correct version
+  // so close the connection and attempt to recreate the database from
+  // scratch.
+  Close();
+  return DeleteFileAndRecreate();
+}
+
+bool DomStorageDatabase::CreateTable() {
+  DCHECK(IsOpen());
+  // Current version is 2.
+  return CreateTableV2();

[michaeln, 2012/02/08 06:11:33]

i still don't see the reason for two CreateTable methods and think that one of
them should be removed

[benm (inactive), 2012/02/08 14:59:40]

OK, done.

+}
+
+bool DomStorageDatabase::CreateTableV2() {
+  DCHECK(IsOpen());
+
+  return db_->Execute(
+      "CREATE TABLE IF NOT EXISTS ItemTable ("
+      "key TEXT UNIQUE ON CONFLICT REPLACE, "
+      "value BLOB NOT NULL ON CONFLICT FAIL)");
+}
+
+bool DomStorageDatabase::DeleteFileAndRecreate() {
+  DCHECK(!IsOpen());
+  DCHECK(file_util::PathExists(file_path_));
+
+  // We should only try and do this once.
+  if (tried_to_recreate_)
+    return false;
+
+  tried_to_recreate_ = true;
+
+  // If it's not a directory and we can delete the file, try and open it again.
+  if (!file_util::DirectoryExists(file_path_) &&
+      file_util::Delete(file_path_, false))
+    return LazyOpen(true);
+
+  failed_to_open_ = true;
+  return false;
+}
+
+bool DomStorageDatabase::UpgradeVersion1To2IfNeeded() {
+  DCHECK(IsOpen());
+  sql::Statement statement(db_->GetCachedStatement(SQL_FROM_HERE,
+      "SELECT * FROM ItemTable"));
+  DCHECK(statement.is_valid());
+
+  // Quick check to see if we need to upgrade or not. The single
+  // effect of V1 -> V2 is to change the value column from type
+  // TEXT to type BLOB.
+  sql::ColType value_column_type = statement.DeclaredColumnType(1);
+  if (value_column_type == sql::COLUMN_TYPE_BLOB)
+    return true;
+
+  if (value_column_type != sql::COLUMN_TYPE_TEXT) {
+    // Something is messed up. This is not a V1 database.
+    return false;
+  }
+
+  // Need to migrate from TEXT value column to BLOB.
+  // Store the current database content so we can re-insert
+  // the data into the new V2 table.
+  ValuesMap values;
+  while (statement.Step()) {
+    string16 key = statement.ColumnString16(0);
+    NullableString16 value(statement.ColumnString16(1), false);
+    values[key] = value;
+  }
+
+  sql::Transaction migration(db_.get());
+  if (!migration.Begin())
+    return false;
+
+  if (db_->Execute("DROP TABLE ItemTable")) {
+    CreateTableV2();
+    if (CommitChanges(false, values))
+      return migration.Commit();
+  }
+  return false;
+}
+
+void DomStorageDatabase::Close() {
+  db_.reset(NULL);
+}
+
+}  // namespace dom_storage