sql/recovery.cc - chromium/src - Git at Google

 // Copyright 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 <stddef.h>

 #include "base/files/file_path.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "sql/connection.h"
 #include "sql/statement.h"
 #include "third_party/sqlite/sqlite3.h"
 #include "third_party/sqlite/src/src/recover.h"

 namespace sql {

 namespace {

 // This enum must match the numbering for Sqlite.RecoveryEvents in
 // histograms.xml.  Do not reorder or remove items, only add new items before
 // RECOVERY_EVENT_MAX.
 enum RecoveryEventType {
   // Init() completed successfully.
   RECOVERY_SUCCESS_INIT = 0,

   // Failed to open temporary database to recover into.
   RECOVERY_FAILED_OPEN_TEMPORARY,

   // Failed to initialize recover vtable system.
   RECOVERY_FAILED_VIRTUAL_TABLE_INIT,

   // System SQLite doesn't support vtable.
   RECOVERY_FAILED_VIRTUAL_TABLE_SYSTEM_SQLITE,

   // Failed attempting to enable writable_schema.
   RECOVERY_FAILED_WRITABLE_SCHEMA,

   // Failed to attach the corrupt database to the temporary database.
   RECOVERY_FAILED_ATTACH,

   // Backup() successfully completed.
   RECOVERY_SUCCESS_BACKUP,

   // Failed sqlite3_backup_init().  Error code in Sqlite.RecoveryHandle.
   RECOVERY_FAILED_BACKUP_INIT,

   // Failed sqlite3_backup_step().  Error code in Sqlite.RecoveryStep.
   RECOVERY_FAILED_BACKUP_STEP,

   // AutoRecoverTable() successfully completed.
   RECOVERY_SUCCESS_AUTORECOVER,

   // The target table contained a type which the code is not equipped
   // to handle.  This should only happen if things are fubar.
   RECOVERY_FAILED_AUTORECOVER_UNRECOGNIZED_TYPE,

   // The target table does not exist.
   RECOVERY_FAILED_AUTORECOVER_MISSING_TABLE,

   // The recovery virtual table creation failed.
   RECOVERY_FAILED_AUTORECOVER_CREATE,

   // Copying data from the recovery table to the target table failed.
   RECOVERY_FAILED_AUTORECOVER_INSERT,

   // Dropping the recovery virtual table failed.
   RECOVERY_FAILED_AUTORECOVER_DROP,

   // SetupMeta() successfully completed.
   RECOVERY_SUCCESS_SETUP_META,

   // Failure creating recovery meta table.
   RECOVERY_FAILED_META_CREATE,

   // GetMetaVersionNumber() successfully completed.
   RECOVERY_SUCCESS_META_VERSION,

   // Failed in querying recovery meta table.
   RECOVERY_FAILED_META_QUERY,

   // No version key in recovery meta table.
   RECOVERY_FAILED_META_NO_VERSION,

   // Automatically recovered entire database successfully.
   RECOVERY_SUCCESS_AUTORECOVERDB,

   // Database was so broken recovery couldn't be entered.
   RECOVERY_FAILED_AUTORECOVERDB_BEGIN,

   // Failed to schema from corrupt database.
   RECOVERY_FAILED_AUTORECOVERDB_SCHEMASELECT,

   // Failed to create copy of schema in recovery database.
   RECOVERY_FAILED_AUTORECOVERDB_SCHEMACREATE,

   // Failed querying tables to recover.  Should be impossible.
   RECOVERY_FAILED_AUTORECOVERDB_NAMESELECT,

   // Failed to recover an individual table.
   RECOVERY_FAILED_AUTORECOVERDB_TABLE,

   // Failed to recover [sqlite_sequence] table.
   RECOVERY_FAILED_AUTORECOVERDB_SEQUENCE,

   // Failed to recover triggers or views or virtual tables.
   RECOVERY_FAILED_AUTORECOVERDB_AUX,

   // After SQLITE_NOTADB failure setting up for recovery, Delete() failed.
   RECOVERY_FAILED_AUTORECOVERDB_NOTADB_DELETE,

   // After SQLITE_NOTADB failure setting up for recovery, Delete() succeeded
   // then Open() failed.
   RECOVERY_FAILED_AUTORECOVERDB_NOTADB_REOPEN,

   // After SQLITE_NOTADB failure setting up for recovery, Delete() and Open()
   // succeeded, then querying the database failed.
   RECOVERY_FAILED_AUTORECOVERDB_NOTADB_QUERY,

   // After SQLITE_NOTADB failure setting up for recovery, the database was
   // successfully deleted.
   RECOVERY_SUCCESS_AUTORECOVERDB_NOTADB_DELETE,

   // Failed to find required [meta.version] information.
   RECOVERY_FAILED_AUTORECOVERDB_META_VERSION,

   // Add new items before this one, always keep this one at the end.
   RECOVERY_EVENT_MAX,
 };

 void RecordRecoveryEvent(RecoveryEventType recovery_event) {
   UMA_HISTOGRAM_ENUMERATION("Sqlite.RecoveryEvents",
                             recovery_event, RECOVERY_EVENT_MAX);
 }

 }  // namespace

 // static
 bool Recovery::FullRecoverySupported() {
   // TODO(shess): See comment in Init().
   return true;
 }

 // static
 std::unique_ptr<Recovery> Recovery::Begin(Connection* connection,
                                           const base::FilePath& db_path) {
   // Recovery is likely to be used in error handling.  Since recovery changes
   // the state of the handle, protect against multiple layers attempting the
   // same recovery.
   if (!connection->is_open()) {
     // Warn about API mis-use.
     DLOG_IF(FATAL, !connection->poisoned_)
         << "Illegal to recover with closed database";
     return std::unique_ptr<Recovery>();
   }

   std::unique_ptr<Recovery> r(new Recovery(connection));
   if (!r->Init(db_path)) {
     // TODO(shess): Should Init() failure result in Raze()?
     r->Shutdown(POISON);
     return std::unique_ptr<Recovery>();
   }

   return r;
 }

 // 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): HISTOGRAM to track?  Or just have people crash out?
   // Crash and dump?
   r->Shutdown(POISON);
 }

 Recovery::Recovery(Connection* connection)
     : db_(connection),
       recover_db_() {
   // Result should keep the page size specified earlier.
   if (db_->page_size_)
     recover_db_.set_page_size(db_->page_size_);

   // 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) {
   // Prevent the possibility of re-entering this code due to errors
   // which happen while executing this code.
   DCHECK(!db_->has_error_callback());

   // 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.
   ignore_result(db_->Execute("PRAGMA writable_schema=1"));
   ignore_result(db_->Execute("PRAGMA locking_mode=NORMAL"));
   ignore_result(db_->Execute("SELECT COUNT(*) FROM sqlite_master"));

   // 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()) {
     RecordRecoveryEvent(RECOVERY_FAILED_OPEN_TEMPORARY);
     return false;
   }

   // Enable the recover virtual table for this connection.
   int rc = recoverVtableInit(recover_db_.db_);
   if (rc != SQLITE_OK) {
     RecordRecoveryEvent(RECOVERY_FAILED_VIRTUAL_TABLE_INIT);
     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")) {
     RecordRecoveryEvent(RECOVERY_FAILED_WRITABLE_SCHEMA);
     return false;
   }

   if (!recover_db_.AttachDatabase(db_path, "corrupt")) {
     RecordRecoveryEvent(RECOVERY_FAILED_ATTACH);
     base::UmaHistogramSparse("Sqlite.RecoveryAttachError",
                              recover_db_.GetErrorCode());
     return false;
   }

   RecordRecoveryEvent(RECOVERY_SUCCESS_INIT);
   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 and records histograms
   // to inform future development.

   // Backup the original db from the recovered db.
   const char* kMain = "main";
   sqlite3_backup* backup = sqlite3_backup_init(db_->db_, kMain,
                                                recover_db_.db_, kMain);
   if (!backup) {
     RecordRecoveryEvent(RECOVERY_FAILED_BACKUP_INIT);

     // Error code is in the destination database handle.
     int err = sqlite3_extended_errcode(db_->db_);
     base::UmaHistogramSparse("Sqlite.RecoveryHandle", err);
     LOG(ERROR) << "sqlite3_backup_init() failed: "
                << sqlite3_errmsg(db_->db_);

     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) {
     RecordRecoveryEvent(RECOVERY_FAILED_BACKUP_STEP);
     base::UmaHistogramSparse("Sqlite.RecoveryStep", rc);
     LOG(ERROR) << "sqlite3_backup_step() failed: "
                << sqlite3_errmsg(db_->db_);
   }

   // 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, pending
   // results from Sqlite.RecoveryStep.  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.
   RecordRecoveryEvent(RECOVERY_SUCCESS_BACKUP);
   Shutdown(POISON);
   return true;
 }

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

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

 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 int default_type = s.ColumnType(4);
     const bool default_is_null = (default_type == COLUMN_TYPE_NULL);
     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 (column_type.find("INT") != std::string::npos) {
       if (pk_column == 1) {
         rowid_ofs = create_column_decls.size();
         rowid_decl = column_name + " ROWID";
       }
       column_decl += " INTEGER";
     } else if (column_type.find("CHAR") != std::string::npos ||
                column_type.find("TEXT") != std::string::npos) {
       column_decl += " TEXT";
     } else if (column_type == "BLOB") {
       column_decl += " BLOB";
     } else if (column_type.find("DOUB") != std::string::npos) {
       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;
       RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVER_UNRECOGNIZED_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_master 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()) {
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVER_MISSING_TABLE);
     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())) {
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVER_CREATE);
     return false;
   }

   if (!db()->Execute(recover_insert.c_str())) {
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVER_INSERT);
     ignore_result(db()->Execute(recover_drop.c_str()));
     return false;
   }

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

   // TODO(shess): Is leaving the recover table around a breaker?
   if (!db()->Execute(recover_drop.c_str())) {
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVER_DROP);
     return false;
   }
   RecordRecoveryEvent(RECOVERY_SUCCESS_AUTORECOVER);
   return true;
 }

 bool Recovery::SetupMeta() {
   const char kCreateSql[] =
       "CREATE VIRTUAL TABLE temp.recover_meta USING recover"
       "("
       "corrupt.meta,"
       "key TEXT NOT NULL,"
       "value ANY"  // Whatever is stored.
       ")";
   if (!db()->Execute(kCreateSql)) {
     RecordRecoveryEvent(RECOVERY_FAILED_META_CREATE);
     return false;
   }
   RecordRecoveryEvent(RECOVERY_SUCCESS_SETUP_META);
   return true;
 }

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

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

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

 namespace {

 // Collect statements from [corrupt.sqlite_master.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(Connection* 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_master "
       "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())) {
       RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_SCHEMACREATE);
       return false;
     }
   }
   if (!s.Succeeded()) {
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_SCHEMASELECT);
     return false;
   }
   return true;
 }

 }  // 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() if/when histogram
 // results indicate that everything is working reasonably.
 //
 // static
 std::unique_ptr<Recovery> Recovery::BeginRecoverDatabase(
     Connection* 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();

     // Histograms from Recovery::Begin() show all current failures are in
     // attaching the corrupt database, with 2/3 being SQLITE_NOTADB.  Don't
     // delete the database except for that specific failure case.
     {
       Connection probe_db;
       if (!probe_db.OpenInMemory() ||
           probe_db.AttachDatabase(db_path, "corrupt") ||
           probe_db.GetErrorCode() != SQLITE_NOTADB) {
         RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_BEGIN);
         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::Connection::Delete(db_path)) {
       RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_NOTADB_DELETE);
       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.
     {
       Connection probe_db;
       if (!probe_db.Open(db_path)) {
         RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_NOTADB_REOPEN);
         return nullptr;
       }
       if (!probe_db.Execute("PRAGMA auto_vacuum")) {
         RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_NOTADB_QUERY);
         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.
     RecordRecoveryEvent(RECOVERY_SUCCESS_AUTORECOVERDB_NOTADB_DELETE);
     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_master 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_master 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)) {
         RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_TABLE);
         Recovery::Rollback(std::move(recovery));
         return nullptr;
       }
     }
     if (!s.Succeeded()) {
       RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_NAMESELECT);
       Recovery::Rollback(std::move(recovery));
       return nullptr;
     }
   }

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

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

   RecordRecoveryEvent(RECOVERY_SUCCESS_AUTORECOVERDB);
   return recovery;
 }

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

   // ignore_result() because BeginRecoverDatabase() and Recovered() already
   // provide suitable histogram coverage.
   if (recovery)
     ignore_result(Recovery::Recovered(std::move(recovery)));
 }

 void Recovery::RecoverDatabaseWithMetaVersion(Connection* 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));
     RecordRecoveryEvent(RECOVERY_FAILED_AUTORECOVERDB_META_VERSION);
     return;
   }

   // ignore_result() because BeginRecoverDatabase() and Recovered() already
   // provide suitable histogram coverage.
   ignore_result(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;
   }
 }

 }  // namespace sql