recovery.cc

// Copyright 2013 The Chromium Authors
// 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 <stddef.h>

#include <memory>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

#include "base/check_op.h"
#include "base/containers/contains.h"
#include "base/dcheck_is_on.h"
#include "base/feature_list.h"
#include "base/files/file_path.h"
#include "base/format_macros.h"
#include "base/functional/bind.h"
#include "base/functional/callback_helpers.h"
#include "base/logging.h"
#include "base/metrics/histogram_functions.h"
#include "base/notreached.h"
#include "base/strings/strcat.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/types/pass_key.h"
#include "build/build_config.h"
#include "sql/database.h"
#include "sql/error_delegate_util.h"
#include "sql/internal_api_token.h"
#include "sql/meta_table.h"
#include "sql/recover_module/module.h"
#include "sql/sql_features.h"
#include "sql/sqlite_result_code.h"
#include "sql/sqlite_result_code_values.h"
#include "sql/statement.h"
#include "third_party/sqlite/sqlite3.h"

namespace sql {

namespace {

constexpr char kMainDatabaseName[] = "main";

}  // namespace

// static
bool BuiltInRecovery::IsSupported() {
  // TODO(https://crbug.com/1385500): `BuiltInRecovery` is not yet supported on
  // Fuchsia.
#if BUILDFLAG(IS_FUCHSIA)
  return false;
#else
  return base::FeatureList::IsEnabled(features::kUseBuiltInRecoveryIfSupported);
#endif  // BUILDFLAG(IS_FUCHSIA)
}

// static
bool BuiltInRecovery::ShouldAttemptRecovery(Database* database,
                                            int extended_error) {
  return BuiltInRecovery::IsSupported() && database && database->is_open() &&
         !database->DbPath(InternalApiToken()).empty() &&
         IsErrorCatastrophic(extended_error);
}

// static
SqliteResultCode BuiltInRecovery::RecoverDatabase(
    Database* database,
    Strategy strategy,
    std::string database_uma_name) {
  if (!BuiltInRecovery::IsSupported()) {
    return SqliteResultCode::kAbort;
  }

  auto recovery =
      BuiltInRecovery(database, strategy, std::move(database_uma_name));
  return recovery.RecoverAndReplaceDatabase();
}

// static
bool BuiltInRecovery::RecoverIfPossible(
    Database* database,
    int extended_error,
    Strategy strategy,
    const base::Feature* const use_builtin_recovery_if_supported_flag,
    std::string database_uma_name) {
  // If `BuiltInRecovery` is supported at all, check the flag for this specific
  // database, provided by the feature team.
  bool use_builtin_recovery =
      BuiltInRecovery::IsSupported() &&
      (!use_builtin_recovery_if_supported_flag ||
       base::FeatureList::IsEnabled(*use_builtin_recovery_if_supported_flag));

  if (use_builtin_recovery
          ? !BuiltInRecovery::ShouldAttemptRecovery(database, extended_error)
          : !database || !database->is_open() ||
                database->DbPath(InternalApiToken()).empty() ||
                !Recovery::ShouldRecover(extended_error)) {
    return false;
  }

  // Recovery should be attempted. Since recovery must only be attempted from
  // within a database error callback, reset the error callback to prevent
  // re-entry.
  database->reset_error_callback();

  if (use_builtin_recovery) {
    CHECK(BuiltInRecovery::IsSupported());
    auto result =
        BuiltInRecovery::RecoverDatabase(database, strategy, database_uma_name);
    if (!IsSqliteSuccessCode(result)) {
      DLOG(ERROR) << "Database recovery failed with result code: " << result;
    }
  } else {
    switch (strategy) {
      case BuiltInRecovery::Strategy::kRecoverOrRaze:
        Recovery::RecoverDatabase(database,
                                  database->DbPath(InternalApiToken()));
        break;
      case BuiltInRecovery::Strategy::kRecoverWithMetaVersionOrRaze:
        Recovery::RecoverDatabaseWithMetaVersion(
            database, database->DbPath(InternalApiToken()));
        break;
    }
  }

  return true;
}

BuiltInRecovery::BuiltInRecovery(Database* database,
                                 Strategy strategy,
                                 std::string database_uma_name)
    : strategy_(strategy),
      database_uma_name_(std::move(database_uma_name)),
      db_(database),
      recover_db_(sql::DatabaseOptions{
          .exclusive_locking = false,
          .page_size = database ? database->page_size() : 0,
          .cache_size = 0,
      }) {
  CHECK(IsSupported());
  CHECK(db_);
  CHECK(db_->is_open());
  // Recovery is likely to be used in error handling. To prevent re-entry due to
  // errors while attempting to recover the database, the error callback must
  // not be set.
  CHECK(!db_->has_error_callback());

  auto db_path = db_->DbPath(InternalApiToken());

  // Corruption recovery for in-memory databases is not supported.
  CHECK(!db_path.empty());

  recovery_database_path_ = db_path.AddExtensionASCII(".recovery");

  // Break any outstanding transactions on the original database, since the
  // recovery module opens a transaction on the database while recovery is in
  // progress.
  db_->RollbackAllTransactions();
}

BuiltInRecovery::~BuiltInRecovery() {
  // Recovery result must be set before we reach this point.
  CHECK_NE(result_, Result::kUnknown);

  base::UmaHistogramEnumeration("Sql.Recovery.Result", result_);
  UmaHistogramSqliteResult("Sql.Recovery.ResultCode",
                           static_cast<int>(sqlite_result_code_));

  if (!database_uma_name_.empty()) {
    base::UmaHistogramEnumeration(
        base::StrCat({"Sql.Recovery.Result.", database_uma_name_}), result_);
    UmaHistogramSqliteResult(
        base::StrCat({"Sql.Recovery.ResultCode.", database_uma_name_}),
        static_cast<int>(sqlite_result_code_));
  }

  if (db_) {
    if (result_ == Result::kSuccess) {
      // Poison the original handle, but don't raze the database.
      db_->Poison();
    } else {
      db_->RazeAndPoison();
    }
  }

  db_ = nullptr;

  if (recover_db_.is_open()) {
    recover_db_.Close();
  }
  // TODO(https://crbug.com/1385500): Don't always delete the recovery db if we
  // are ever to keep around successfully-recovered, but unsuccessfully-restored
  // databases.
  sql::Database::Delete(recovery_database_path_);
}

void BuiltInRecovery::SetRecoverySucceeded() {
  // Recovery result must only be set once.
  CHECK_EQ(result_, Result::kUnknown);

  result_ = Result::kSuccess;
}

void BuiltInRecovery::SetRecoveryFailed(Result failure_result,
                                        SqliteResultCode result_code) {
  // Recovery result must only be set once.
  CHECK_EQ(result_, Result::kUnknown);

  switch (failure_result) {
    case Result::kUnknown:
    case Result::kSuccess:
      NOTREACHED();
      break;
    case Result::kFailedRecoveryInit:
    case Result::kFailedRecoveryRun:
    case Result::kFailedToOpenRecoveredDatabase:
    case Result::kFailedMetaTableDoesNotExist:
    case Result::kFailedMetaTableInit:
    case Result::kFailedMetaTableVersionWasInvalid:
    case Result::kFailedBackupInit:
    case Result::kFailedBackupRun:
      break;
  }

  result_ = failure_result;
  sqlite_result_code_ = result_code;
}

SqliteResultCode BuiltInRecovery::RecoverAndReplaceDatabase() {
  auto sqlite_result_code = AttemptToRecoverDatabaseToBackup();
  if (sqlite_result_code != SqliteResultCode::kOk) {
    return sqlite_result_code;
  }

  // Open a connection to the newly-created recovery database.
  if (!recover_db_.Open(recovery_database_path_)) {
    DVLOG(1) << "Unable to open recovery database.";

    // TODO(https://crbug.com/1385500): It's unfortunate to give up now, after
    // we've successfully recovered the database to a backup. Consider falling
    // back to base::Move().
    SetRecoveryFailed(Result::kFailedToOpenRecoveredDatabase,
                      ToSqliteResultCode(recover_db_.GetErrorCode()));
    return SqliteResultCode::kError;
  }

  if (strategy_ == Strategy::kRecoverWithMetaVersionOrRaze &&
      !RecoveredDbHasValidMetaTable()) {
    DVLOG(1) << "Could not read valid version number from recovery database.";
    return SqliteResultCode::kError;
  }

  return ReplaceOriginalWithRecoveredDb();
}

SqliteResultCode BuiltInRecovery::AttemptToRecoverDatabaseToBackup() {
  CHECK(db_->is_open());
  CHECK(!recover_db_.is_open());

  // See full documentation for the corruption recovery module in
  // https://sqlite.org/src/file/ext/recover/sqlite3recover.h

  // sqlite3_recover_init() create a new sqlite3_recover handle, with data being
  // recovered into a new database. This should very rarely fail - e.g. if
  // memory for the recovery object itself could not be allocated. If it does
  // fail, `recover` will be nullptr and an error code will surface when
  // attempting to configure the recovery object below.
  sqlite3_recover* recover =
      sqlite3_recover_init(db_->db(InternalApiToken()), kMainDatabaseName,
                           recovery_database_path_.AsUTF8Unsafe().c_str());

  // sqlite3_recover_config() configures the sqlite3_recover object.
  //
  // These functions should only fail if the above initialization failed, or if
  // invalid parameters are passed.

  // Don't bother creating a lost-and-found table.
  sqlite3_recover_config(recover, SQLITE_RECOVER_LOST_AND_FOUND, nullptr);
  // Do not attempt to recover records from pages that appear to be linked to
  // the freelist, to avoid "recovering" deleted records.
  int kRecoverFreelist = 0;
  sqlite3_recover_config(recover, SQLITE_RECOVER_FREELIST_CORRUPT,
                         static_cast<void*>(&kRecoverFreelist));
  // Attempt to recover ROWID values that are not INTEGER PRIMARY KEY.
  int kRecoverRowIds = 1;
  sqlite3_recover_config(recover, SQLITE_RECOVER_ROWIDS,
                         static_cast<void*>(&kRecoverRowIds));

  auto sqlite_result_code =
      ToSqliteResultCode(sqlite3_recover_errcode(recover));
  if (sqlite_result_code != SqliteResultCode::kOk) {
    CHECK_NE(sqlite_result_code, SqliteResultCode::kApiMisuse);

    // The recovery could not be configured.
    // TODO(https://crbug.com/1385500): This is likely a transient issue, so we
    // could consider keeping the database intact in case the caller wants to
    // try again later. For now, we'll always raze.
    SetRecoveryFailed(Result::kFailedRecoveryInit, sqlite_result_code);

    DVLOG(1) << "recovery config error: " << sqlite_result_code
             << sqlite3_recover_errcode(recover);

    // Clean up the recovery object.
    sqlite3_recover_finish(recover);
    return sqlite_result_code;
  }

  // sqlite3_recover_run() attempts to construct an copy of the database with
  // data corruption handled. It returns SQLITE_OK if recovery was successful.
  sqlite_result_code = ToSqliteResultCode(sqlite3_recover_run(recover));

  // sqlite3_recover_finish() cleans up the recovery object. It should return
  // the same error code as from sqlite3_recover_run().
  auto finish_result_code = ToSqliteResultCode(sqlite3_recover_finish(recover));
  CHECK_EQ(finish_result_code, sqlite_result_code);

  if (sqlite_result_code != SqliteResultCode::kOk) {
    // Could not recover the database.
    SetRecoveryFailed(Result::kFailedRecoveryRun, sqlite_result_code);

    DVLOG(1) << "recovery error: " << sqlite_result_code
             << sqlite3_recover_errmsg(recover);
  }

  return sqlite_result_code;
}

SqliteResultCode BuiltInRecovery::ReplaceOriginalWithRecoveredDb() {
  CHECK(db_->is_open());
  CHECK(recover_db_.is_open());

  // sqlite3_backup_init() fails if a transaction is ongoing. This should be
  // rare, since we rolled back all transactions in this object's constructor.
  sqlite3_backup* backup = sqlite3_backup_init(
      db_->db(InternalApiToken()), kMainDatabaseName,
      recover_db_.db(InternalApiToken()), kMainDatabaseName);
  if (!backup) {
    // Error code is in the destination database handle.
    DVLOG(1) << "sqlite3_backup_init() failed: "
             << sqlite3_errmsg(db_->db(InternalApiToken()));

    auto result_code =
        ToSqliteResultCode(sqlite3_errcode(db_->db(InternalApiToken())));

    // TODO(https://crbug.com/1385500): It's unfortunate to give up now, after
    // we've successfully recovered the database. Consider falling back to
    // base::Move().
    SetRecoveryFailed(Result::kFailedBackupInit, result_code);
    return result_code;
  }

  // sqlite3_backup_step() copies pages from the source to the destination
  // database. It returns SQLITE_DONE if copying successfully completed, or some
  // other error on failure.
  // TODO(https://crbug.com/1385500): Some of these errors are transient and the
  // operation could feasibly succeed at a later time. Consider keeping around
  // successfully-recovered, but unsuccessfully-restored databases or falling
  // back to base::Move().
  constexpr int kUnlimitedPageCount = -1;  // Back up entire database.
  auto sqlite_result_code =
      ToSqliteResultCode(sqlite3_backup_step(backup, kUnlimitedPageCount));

  // sqlite3_backup_remaining() returns the number of pages still to be backed
  // up, which should be zero if sqlite3_backup_step() completed successfully.
  int pages_remaining = sqlite3_backup_remaining(backup);

  // sqlite3_backup_finish() releases the sqlite3_backup object.
  //
  // It returns an error code only if the backup encountered a permanent error.
  // We use the the sqlite3_backup_step() result instead, because it also tells
  // us about temporary errors, like SQLITE_BUSY.
  //
  // We pass the sqlite3_backup_finish() result code through
  // ToSqliteResultCode() to catch codes that should never occur, like
  // SQLITE_MISUSE.
  std::ignore = ToSqliteResultCode(sqlite3_backup_finish(backup));

  if (sqlite_result_code != SqliteResultCode::kDone) {
    CHECK_NE(sqlite_result_code, SqliteResultCode::kOk)
        << "sqlite3_backup_step() returned SQLITE_OK (instead of SQLITE_DONE) "
        << "when asked to back up the entire database";

    DVLOG(1) << "sqlite3_backup_step() failed: "
             << sqlite3_errmsg(db_->db(InternalApiToken()));
    SetRecoveryFailed(Result::kFailedBackupRun, sqlite_result_code);
    return sqlite_result_code;
  }

  // The original database was successfully recovered and replaced. Hooray!
  SetRecoverySucceeded();

  CHECK_EQ(pages_remaining, 0);
  return SqliteResultCode::kOk;
}

bool BuiltInRecovery::RecoveredDbHasValidMetaTable() {
  CHECK(recover_db_.is_open());

  if (!MetaTable::DoesTableExist(&recover_db_)) {
    DVLOG(1) << "Meta table does not exist in recovery database.";
    SetRecoveryFailed(Result::kFailedMetaTableDoesNotExist,
                      ToSqliteResultCode(recover_db_.GetErrorCode()));
    return false;
  }

  // MetaTable::Init will not create a meta table if one already exists.
  sql::MetaTable meta_table;
  if (!meta_table.Init(&recover_db_, /*version=*/1,
                       /*compatible_version=*/1)) {
    SetRecoveryFailed(Result::kFailedMetaTableInit,
                      ToSqliteResultCode(recover_db_.GetErrorCode()));
    return false;
  }

  // Confirm that we can read a valid version number from the recovered table.
  if (meta_table.GetVersionNumber() <= 0) {
    SetRecoveryFailed(Result::kFailedMetaTableVersionWasInvalid,
                      ToSqliteResultCode(recover_db_.GetErrorCode()));
    return false;
  }

  return true;
}

// static
std::unique_ptr<Recovery> Recovery::Begin(Database* database,
                                          const base::FilePath& db_path) {
  // Recovery is likely to be initiated in an error handler. Since recovery
  // changes the state of the handle, protect against multiple layers attempting
  // the same recovery.
  if (!database->is_open()) {
    // Warn about API mis-use.
    DCHECK(database->poisoned(InternalApiToken()))
        << "Illegal to recover with closed Database";
    return nullptr;
  }

  // Using `new` to access a non-public constructor
  std::unique_ptr<Recovery> recovery(new Recovery(database));
  if (!recovery->Init(db_path)) {
    // TODO(shess): Should Init() failure result in Raze()?
    recovery->Shutdown(POISON);
    return nullptr;
  }

  return recovery;
}

// static
bool Recovery::Recovered(std::unique_ptr<Recovery> r) {
  return r->Backup();
}

// static
void Recovery::Unrecoverable(std::unique_ptr<Recovery> r) {
  CHECK(r->db_);
  // ~Recovery() will RAZE_AND_POISON.
}

// static
void Recovery::Rollback(std::unique_ptr<Recovery> r) {
  // TODO(shess): Crash / crash and dump?
  r->Shutdown(POISON);
}

Recovery::Recovery(Database* connection)
    : db_(connection),
      recover_db_({
          .exclusive_locking = false,
          .page_size = db_->page_size(),
          // The interface to the recovery module is a virtual table.
          .enable_virtual_tables_discouraged = true,
      }) {
  // Files with I/O errors cannot be safely memory-mapped.
  recover_db_.set_mmap_disabled();

  // TODO(shess): This may not handle cases where the default page
  // size is used, but the default has changed.  I do not think this
  // has ever happened.  This could be handled by using "PRAGMA
  // page_size", at the cost of potential additional failure cases.
}

Recovery::~Recovery() {
  Shutdown(RAZE_AND_POISON);
}

bool Recovery::Init(const base::FilePath& db_path) {
#if DCHECK_IS_ON()
  // set_error_callback() will DCHECK if the database already has an error
  // callback. The recovery process is likely to result in SQLite errors, and
  // those shouldn't get surfaced to any callback.
  db_->set_error_callback(base::DoNothing());

  // Undo the set_error_callback() above. We only used it for its DCHECK
  // behavior.
  db_->reset_error_callback();
#endif  // DCHECK_IS_ON()

  // Break any outstanding transactions on the 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 any in-flight changes.  Unfortunately, any attach-based
  // system could not handle that.  A system which manually queried
  // one database and stored to the other possibly could, but would be
  // more complicated.
  db_->RollbackAllTransactions();

  // Disable exclusive locking mode so that the attached database can
  // access things.  The locking_mode change is not active until the
  // next database access, so immediately force an access.  Enabling
  // writable_schema allows processing through certain kinds of
  // corruption.
  // TODO(shess): It would be better to just close the handle, but it
  // is necessary for the final backup which rewrites things.  It
  // might be reasonable to close then re-open the handle.
  std::ignore = db_->Execute("PRAGMA writable_schema=1");
  std::ignore = db_->Execute("PRAGMA locking_mode=NORMAL");
  std::ignore = db_->Execute("SELECT COUNT(*) FROM sqlite_schema");

  // TODO(shess): If this is a common failure case, it might be
  // possible to fall back to a memory database.  But it probably
  // implies that the SQLite tmpdir logic is busted, which could cause
  // a variety of other random issues in our code.
  if (!recover_db_.OpenTemporary(base::PassKey<Recovery>()))
    return false;

  // Enable the recover virtual table for this connection.
  int rc = EnableRecoveryExtension(&recover_db_, InternalApiToken());
  if (rc != SQLITE_OK) {
    LOG(ERROR) << "Failed to initialize recover module: "
               << recover_db_.GetErrorMessage();
    return false;
  }

  // Turn on |SQLITE_RecoveryMode| for the handle, which allows
  // reading certain broken databases.
  if (!recover_db_.Execute("PRAGMA writable_schema=1"))
    return false;

  if (!recover_db_.AttachDatabase(db_path, "corrupt", InternalApiToken()))
    return false;

  return true;
}

bool Recovery::Backup() {
  CHECK(db_);
  CHECK(recover_db_.is_open());

  // TODO(shess): Some of the failure cases here may need further
  // exploration.  Just as elsewhere, persistent problems probably
  // need to be razed, while anything which might succeed on a future
  // run probably should be allowed to try.  But since Raze() uses the
  // same approach, even that wouldn't work when this code fails.
  //
  // The documentation for the backup system indicate a relatively
  // small number of errors are expected:
  // SQLITE_BUSY - cannot lock the destination database.  This should
  //               only happen if someone has another handle to the
  //               database, Chromium generally doesn't do that.
  // SQLITE_LOCKED - someone locked the source database.  Should be
  //                 impossible (perhaps anti-virus could?).
  // SQLITE_READONLY - destination is read-only.
  // SQLITE_IOERR - since source database is temporary, probably
  //                indicates that the destination contains blocks
  //                throwing errors, or gross filesystem errors.
  // SQLITE_NOMEM - out of memory, should be transient.
  //
  // AFAICT, SQLITE_BUSY and SQLITE_NOMEM could perhaps be considered
  // transient, with SQLITE_LOCKED being unclear.
  //
  // SQLITE_READONLY and SQLITE_IOERR are probably persistent, with a
  // strong chance that Raze() would not resolve them.  If Delete()
  // deletes the database file, the code could then re-open the file
  // and attempt the backup again.
  //
  // For now, this code attempts a best effort.

  // Backup the original db from the recovered db.
  sqlite3_backup* backup = sqlite3_backup_init(
      db_->db(InternalApiToken()), kMainDatabaseName,
      recover_db_.db(InternalApiToken()), kMainDatabaseName);
  if (!backup) {
    // Error code is in the destination database handle.
    LOG(ERROR) << "sqlite3_backup_init() failed: "
               << sqlite3_errmsg(db_->db(InternalApiToken()));

    return false;
  }

  // -1 backs up the entire database.
  int rc = sqlite3_backup_step(backup, -1);
  int pages = sqlite3_backup_pagecount(backup);
  // TODO(shess): sqlite3_backup_finish() appears to allow returning a
  // different value from sqlite3_backup_step().  Circle back and
  // figure out if that can usefully inform the decision of whether to
  // retry or not.
  sqlite3_backup_finish(backup);
  DCHECK_GT(pages, 0);

  if (rc != SQLITE_DONE) {
    LOG(ERROR) << "sqlite3_backup_step() failed: "
               << sqlite3_errmsg(db_->db(InternalApiToken()));
  }

  // The destination database was locked.  Give up, but leave the data
  // in place.  Maybe it won't be locked next time.
  if (rc == SQLITE_BUSY || rc == SQLITE_LOCKED) {
    Shutdown(POISON);
    return false;
  }

  // Running out of memory should be transient, retry later.
  if (rc == SQLITE_NOMEM) {
    Shutdown(POISON);
    return false;
  }

  // TODO(shess): For now, leave the original database alone. Some errors should
  // probably route to RAZE_AND_POISON.
  if (rc != SQLITE_DONE) {
    Shutdown(POISON);
    return false;
  }

  // Clean up the recovery db, and terminate the main database
  // connection.
  Shutdown(POISON);
  return true;
}

void Recovery::Shutdown(Recovery::Disposition raze) {
  if (!db_)
    return;

  recover_db_.Close();
  if (raze == RAZE_AND_POISON) {
    db_->RazeAndPoison();
  } else if (raze == POISON) {
    db_->Poison();
  }
  db_ = nullptr;
}

bool Recovery::AutoRecoverTable(const char* table_name,
                                size_t* rows_recovered) {
  // Query the info for the recovered table in database [main].
  std::string query(
      base::StringPrintf("PRAGMA main.table_info(%s)", table_name));
  Statement s(db()->GetUniqueStatement(query.c_str()));

  // The columns of the recover virtual table.
  std::vector<std::string> create_column_decls;

  // The columns to select from the recover virtual table when copying
  // to the recovered table.
  std::vector<std::string> insert_columns;

  // If PRIMARY KEY is a single INTEGER column, then it is an alias
  // for ROWID.  The primary key can be compound, so this can only be
  // determined after processing all column data and tracking what is
  // seen.  |pk_column_count| counts the columns in the primary key.
  // |rowid_decl| stores the ROWID version of the last INTEGER column
  // seen, which is at |rowid_ofs| in |create_column_decls|.
  size_t pk_column_count = 0;
  size_t rowid_ofs = 0;    // Only valid if rowid_decl is set.
  std::string rowid_decl;  // ROWID version of column |rowid_ofs|.

  while (s.Step()) {
    const std::string column_name(s.ColumnString(1));
    const std::string column_type(s.ColumnString(2));
    const ColumnType default_type = s.GetColumnType(4);
    const bool default_is_null = (default_type == ColumnType::kNull);
    const int pk_column = s.ColumnInt(5);

    // http://www.sqlite.org/pragma.html#pragma_table_info documents column 5 as
    // the 1-based index of the column in the primary key, otherwise 0.
    if (pk_column > 0)
      ++pk_column_count;

    // Construct column declaration as "name type [optional constraint]".
    std::string column_decl = column_name;

    // SQLite's affinity detection is documented at:
    // http://www.sqlite.org/datatype3.html#affname
    // The gist of it is that CHAR, TEXT, and INT use substring matches.
    // TODO(shess): It would be nice to unit test the type handling,
    // but it is not obvious to me how to write a test which would
    // fail appropriately when something was broken.  It would have to
    // somehow use data which would allow detecting the various type
    // coercions which happen.  If STRICT could be enabled, type
    // mismatches could be detected by which rows are filtered.
    if (base::Contains(column_type, "INT")) {
      if (pk_column == 1) {
        rowid_ofs = create_column_decls.size();
        rowid_decl = column_name + " ROWID";
      }
      column_decl += " INTEGER";
    } else if (base::Contains(column_type, "CHAR") ||
               base::Contains(column_type, "TEXT")) {
      column_decl += " TEXT";
    } else if (column_type == "BLOB") {
      column_decl += " BLOB";
    } else if (base::Contains(column_type, "DOUB")) {
      column_decl += " FLOAT";
    } else {
      // TODO(shess): AFAICT, there remain:
      // - contains("CLOB") -> TEXT
      // - contains("REAL") -> FLOAT
      // - contains("FLOA") -> FLOAT
      // - other -> "NUMERIC"
      // Just code those in as they come up.
      NOTREACHED() << " Unsupported type " << column_type;
      return false;
    }

    create_column_decls.push_back(column_decl);

    // Per the NOTE in the header file, convert NULL values to the
    // DEFAULT.  All columns could be IFNULL(column_name,default), but
    // the NULL case would require special handling either way.
    if (default_is_null) {
      insert_columns.push_back(column_name);
    } else {
      // The default value appears to be pre-quoted, as if it is
      // literally from the sqlite_schema CREATE statement.
      std::string default_value = s.ColumnString(4);
      insert_columns.push_back(base::StringPrintf(
          "IFNULL(%s,%s)", column_name.c_str(), default_value.c_str()));
    }
  }

  // Receiving no column information implies that the table doesn't exist.
  if (create_column_decls.empty()) {
    return false;
  }

  // If the PRIMARY KEY was a single INTEGER column, convert it to ROWID.
  if (pk_column_count == 1 && !rowid_decl.empty())
    create_column_decls[rowid_ofs] = rowid_decl;

  std::string recover_create(base::StringPrintf(
      "CREATE VIRTUAL TABLE temp.recover_%s USING recover(corrupt.%s, %s)",
      table_name, table_name,
      base::JoinString(create_column_decls, ",").c_str()));

  // INSERT OR IGNORE means that it will drop rows resulting from constraint
  // violations.  INSERT OR REPLACE only handles UNIQUE constraint violations.
  std::string recover_insert(base::StringPrintf(
      "INSERT OR IGNORE INTO main.%s SELECT %s FROM temp.recover_%s",
      table_name, base::JoinString(insert_columns, ",").c_str(), table_name));

  std::string recover_drop(
      base::StringPrintf("DROP TABLE temp.recover_%s", table_name));

  if (!db()->Execute(recover_create.c_str()))
    return false;

  if (!db()->Execute(recover_insert.c_str())) {
    std::ignore = db()->Execute(recover_drop.c_str());
    return false;
  }

  *rows_recovered = db()->GetLastChangeCount();

  // TODO(shess): Is leaving the recover table around a breaker?
  return db()->Execute(recover_drop.c_str());
}

bool Recovery::SetupMeta() {
  // clang-format off
  static const char kCreateSql[] =
      "CREATE VIRTUAL TABLE temp.recover_meta USING recover("
         "corrupt.meta,"
         "key TEXT NOT NULL,"
         "value ANY"  // Whatever is stored.
      ")";
  // clang-format on
  return db()->Execute(kCreateSql);
}

bool Recovery::GetMetaVersionNumber(int* version) {
  DCHECK(version);
  // TODO(shess): DCHECK(db()->DoesTableExist("temp.recover_meta"));
  // Unfortunately, DoesTableExist() queries sqlite_schema, not
  // sqlite_temp_master.

  static const char kVersionSql[] =
      "SELECT value FROM temp.recover_meta WHERE key = 'version'";
  sql::Statement recovery_version(db()->GetUniqueStatement(kVersionSql));
  if (!recovery_version.Step())
    return false;

  *version = recovery_version.ColumnInt(0);
  return true;
}

namespace {

// Collect statements from [corrupt.sqlite_schema.sql] which start with |prefix|
// (which should be a valid SQL string ending with the space before a table
// name), then apply the statements to [main].  Skip any table named
// 'sqlite_sequence', as that table is created on demand by SQLite if any tables
// use AUTOINCREMENT.
//
// Returns |true| if all of the matching items were created in the main
// database.  Returns |false| if an item fails on creation, or if the corrupt
// database schema cannot be queried.
bool SchemaCopyHelper(Database* db, const char* prefix) {
  const size_t prefix_len = strlen(prefix);
  DCHECK_EQ(' ', prefix[prefix_len - 1]);

  sql::Statement s(
      db->GetUniqueStatement("SELECT DISTINCT sql FROM corrupt.sqlite_schema "
                             "WHERE name<>'sqlite_sequence'"));
  while (s.Step()) {
    std::string sql = s.ColumnString(0);

    // Skip statements that don't start with |prefix|.
    if (sql.compare(0, prefix_len, prefix) != 0)
      continue;

    sql.insert(prefix_len, "main.");
    if (!db->Execute(sql.c_str()))
      return false;
  }
  return s.Succeeded();
}

}  // namespace

// This method is derived from SQLite's vacuum.c.  VACUUM operates very
// similarily, creating a new database, populating the schema, then copying the
// data.
//
// TODO(shess): This conservatively uses Rollback() rather than Unrecoverable().
// With Rollback(), it is expected that the database will continue to generate
// errors. Change the failure cases to Unrecoverable().
//
// static
std::unique_ptr<Recovery> Recovery::BeginRecoverDatabase(
    Database* db,
    const base::FilePath& db_path) {
  std::unique_ptr<sql::Recovery> recovery = sql::Recovery::Begin(db, db_path);
  if (!recovery) {
    // Close the underlying sqlite* handle.  Windows does not allow deleting
    // open files, and all platforms block opening a second sqlite3* handle
    // against a database when exclusive locking is set.
    db->Poison();

    // When this code was written, histograms showed that most failures happened
    // while attaching a corrupt database. In this case, a large proportion of
    // attachment failures were SQLITE_NOTADB.
    //
    // We currently only delete the database in that specific failure case.
    {
      Database probe_db;
      if (!probe_db.OpenInMemory() ||
          probe_db.AttachDatabase(db_path, "corrupt", InternalApiToken()) ||
          probe_db.GetErrorCode() != SQLITE_NOTADB) {
        return nullptr;
      }
    }

    // The database has invalid data in the SQLite header, so it is almost
    // certainly not recoverable without manual intervention (and likely not
    // recoverable _with_ manual intervention).  Clear away the broken database.
    if (!sql::Database::Delete(db_path))
      return nullptr;

    // Windows deletion is complicated by file scanners and malware - sometimes
    // Delete() appears to succeed, even though the file remains.  The following
    // attempts to track if this happens often enough to cause concern.
    {
      Database probe_db;
      if (!probe_db.Open(db_path))
        return nullptr;

      if (!probe_db.Execute("PRAGMA auto_vacuum"))
        return nullptr;
    }

    // The rest of the recovery code could be run on the re-opened database, but
    // the database is empty, so there would be no point.
    return nullptr;
  }

#if DCHECK_IS_ON()
  // This code silently fails to recover fts3 virtual tables.  At this time no
  // browser database contain fts3 tables.  Just to be safe, complain loudly if
  // the database contains virtual tables.
  //
  // fts3 has an [x_segdir] table containing a column [end_block INTEGER].  But
  // it actually stores either an integer or a text containing a pair of
  // integers separated by a space.  AutoRecoverTable() trusts the INTEGER tag
  // when setting up the recover vtable, so those rows get dropped.  Setting
  // that column to ANY may work.
  if (db->is_open()) {
    sql::Statement s(db->GetUniqueStatement(
        "SELECT 1 FROM sqlite_schema WHERE sql LIKE 'CREATE VIRTUAL TABLE %'"));
    DCHECK(!s.Step()) << "Recovery of virtual tables not supported";
  }
#endif

  // TODO(shess): vacuum.c turns off checks and foreign keys.

  // TODO(shess): vacuum.c turns synchronous=OFF for the target.  I do not fully
  // understand this, as the temporary db should not have a journal file at all.
  // Perhaps it does in case of cache spill?

  // Copy table schema from [corrupt] to [main].
  if (!SchemaCopyHelper(recovery->db(), "CREATE TABLE ") ||
      !SchemaCopyHelper(recovery->db(), "CREATE INDEX ") ||
      !SchemaCopyHelper(recovery->db(), "CREATE UNIQUE INDEX ")) {
    // No RecordRecoveryEvent() here because SchemaCopyHelper() already did.
    Recovery::Rollback(std::move(recovery));
    return nullptr;
  }

  // Run auto-recover against each table, skipping the sequence table.  This is
  // necessary because table recovery can create the sequence table as a side
  // effect, so recovering that table inline could lead to duplicate data.
  {
    sql::Statement s(recovery->db()->GetUniqueStatement(
        "SELECT name FROM sqlite_schema WHERE sql LIKE 'CREATE TABLE %' "
        "AND name!='sqlite_sequence'"));
    while (s.Step()) {
      const std::string name = s.ColumnString(0);
      size_t rows_recovered;
      if (!recovery->AutoRecoverTable(name.c_str(), &rows_recovered)) {
        Recovery::Rollback(std::move(recovery));
        return nullptr;
      }
    }
    if (!s.Succeeded()) {
      Recovery::Rollback(std::move(recovery));
      return nullptr;
    }
  }

  // Overwrite any sequences created.
  if (recovery->db()->DoesTableExist("corrupt.sqlite_sequence")) {
    std::ignore = recovery->db()->Execute("DELETE FROM main.sqlite_sequence");
    size_t rows_recovered;
    if (!recovery->AutoRecoverTable("sqlite_sequence", &rows_recovered)) {
      Recovery::Rollback(std::move(recovery));
      return nullptr;
    }
  }

  // Copy triggers and views directly to sqlite_schema.  Any tables they refer
  // to should already exist.
  static const char kCreateMetaItemsSql[] =
      "INSERT INTO main.sqlite_schema "
      "SELECT type, name, tbl_name, rootpage, sql "
      "FROM corrupt.sqlite_schema WHERE type='view' OR type='trigger'";
  if (!recovery->db()->Execute(kCreateMetaItemsSql)) {
    Recovery::Rollback(std::move(recovery));
    return nullptr;
  }

  return recovery;
}

void Recovery::RecoverDatabase(Database* db, const base::FilePath& db_path) {
  std::unique_ptr<sql::Recovery> recovery = BeginRecoverDatabase(db, db_path);

  if (recovery)
    std::ignore = Recovery::Recovered(std::move(recovery));
}

void Recovery::RecoverDatabaseWithMetaVersion(Database* db,
                                              const base::FilePath& db_path) {
  std::unique_ptr<sql::Recovery> recovery = BeginRecoverDatabase(db, db_path);
  if (!recovery)
    return;

  int version = 0;
  if (!recovery->SetupMeta() || !recovery->GetMetaVersionNumber(&version)) {
    sql::Recovery::Unrecoverable(std::move(recovery));
    return;
  }

  std::ignore = Recovery::Recovered(std::move(recovery));
}

// static
bool Recovery::ShouldRecover(int extended_error) {
  // Trim extended error codes.
  int error = extended_error & 0xFF;
  switch (error) {
    case SQLITE_NOTADB:
      // SQLITE_NOTADB happens if the SQLite header is broken.  Some earlier
      // versions of SQLite return this where other versions return
      // SQLITE_CORRUPT, which is a recoverable case.  Later versions only
      // return this error only in unrecoverable cases, in which case recovery
      // will fail with no changes to the database, so there's no harm in
      // attempting recovery in this case.
      return true;

    case SQLITE_CORRUPT:
      // SQLITE_CORRUPT generally means that the database is readable as a
      // SQLite database, but some inconsistency has been detected by SQLite.
      // In many cases the inconsistency is relatively trivial, such as if an
      // index refers to a row which was deleted, in which case most or even all
      // of the data can be recovered.  This can also be reported if parts of
      // the file have been overwritten with garbage data, in which recovery
      // should be able to recover partial data.
      return true;

      // TODO(shess): Possible future options for automated fixing:
      // - SQLITE_CANTOPEN - delete the broken symlink or directory.
      // - SQLITE_PERM - permissions could be fixed.
      // - SQLITE_READONLY - permissions could be fixed.
      // - SQLITE_IOERR - rewrite using new blocks.
      // - SQLITE_FULL - recover in memory and rewrite subset of data.

    default:
      return false;
  }
}

// static
int Recovery::EnableRecoveryExtension(Database* db, InternalApiToken) {
  return sql::recover::RegisterRecoverExtension(db->db(InternalApiToken()));
}

}  // namespace sql