sql/connection.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 "sql/connection.h"

#include <string.h>

#include "base/files/file_path.h"
#include "base/file_util.h"
#include "base/logging.h"
#include "base/metrics/histogram.h"
#include "base/metrics/sparse_histogram.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "sql/statement.h"
#include "third_party/sqlite/sqlite3.h"

namespace {

// Spin for up to a second waiting for the lock to clear when setting
// up the database.
// TODO(shess): Better story on this.  http://crbug.com/56559
const int kBusyTimeoutSeconds = 1;

class ScopedBusyTimeout {
 public:
  explicit ScopedBusyTimeout(sqlite3* db)
      : db_(db) {
  }
  ~ScopedBusyTimeout() {
    sqlite3_busy_timeout(db_, 0);
  }

  int SetTimeout(base::TimeDelta timeout) {
    DCHECK_LT(timeout.InMilliseconds(), INT_MAX);
    return sqlite3_busy_timeout(db_,
                                static_cast<int>(timeout.InMilliseconds()));
  }

 private:
  sqlite3* db_;
};

// Helper to "safely" enable writable_schema.  No error checking
// because it is reasonable to just forge ahead in case of an error.
// If turning it on fails, then most likely nothing will work, whereas
// if turning it off fails, it only matters if some code attempts to
// continue working with the database and tries to modify the
// sqlite_master table (none of our code does this).
class ScopedWritableSchema {
 public:
  explicit ScopedWritableSchema(sqlite3* db)
      : db_(db) {
    sqlite3_exec(db_, "PRAGMA writable_schema=1", NULL, NULL, NULL);
  }
  ~ScopedWritableSchema() {
    sqlite3_exec(db_, "PRAGMA writable_schema=0", NULL, NULL, NULL);
  }

 private:
  sqlite3* db_;
};

}  // namespace

namespace sql {

// static
Connection::ErrorIgnorerCallback* Connection::current_ignorer_cb_ = NULL;

// static
bool Connection::ShouldIgnore(int error) {
  if (!current_ignorer_cb_)
    return false;
  return current_ignorer_cb_->Run(error);
}

// static
void Connection::SetErrorIgnorer(Connection::ErrorIgnorerCallback* cb) {
  CHECK(current_ignorer_cb_ == NULL);
  current_ignorer_cb_ = cb;
}

// static
void Connection::ResetErrorIgnorer() {
  CHECK(current_ignorer_cb_);
  current_ignorer_cb_ = NULL;
}

bool StatementID::operator<(const StatementID& other) const {
  if (number_ != other.number_)
    return number_ < other.number_;
  return strcmp(str_, other.str_) < 0;
}

Connection::StatementRef::StatementRef(Connection* connection,
                                       sqlite3_stmt* stmt,
                                       bool was_valid)
    : connection_(connection),
      stmt_(stmt),
      was_valid_(was_valid) {
  if (connection)
    connection_->StatementRefCreated(this);
}

Connection::StatementRef::~StatementRef() {
  if (connection_)
    connection_->StatementRefDeleted(this);
  Close(false);
}

void Connection::StatementRef::Close(bool forced) {
  if (stmt_) {
    // Call to AssertIOAllowed() cannot go at the beginning of the function
    // because Close() is called unconditionally from destructor to clean
    // connection_. And if this is inactive statement this won't cause any
    // disk access and destructor most probably will be called on thread
    // not allowing disk access.
    // TODO(paivanof@gmail.com): This should move to the beginning
    // of the function. http://crbug.com/136655.
    AssertIOAllowed();
    sqlite3_finalize(stmt_);
    stmt_ = NULL;
  }
  connection_ = NULL;  // The connection may be getting deleted.

  // Forced close is expected to happen from a statement error
  // handler.  In that case maintain the sense of |was_valid_| which
  // previously held for this ref.
  was_valid_ = was_valid_ && forced;
}

Connection::Connection()
    : db_(NULL),
      page_size_(0),
      cache_size_(0),
      exclusive_locking_(false),
      transaction_nesting_(0),
      needs_rollback_(false),
      in_memory_(false),
      poisoned_(false) {
}

Connection::~Connection() {
  Close();
}

bool Connection::Open(const base::FilePath& path) {
  if (!histogram_tag_.empty()) {
    int64 size_64 = 0;
    if (file_util::GetFileSize(path, &size_64)) {
      size_t sample = static_cast<size_t>(size_64 / 1024);
      std::string full_histogram_name = "Sqlite.SizeKB." + histogram_tag_;
      base::HistogramBase* histogram =
          base::Histogram::FactoryGet(
              full_histogram_name, 1, 1000000, 50,
              base::HistogramBase::kUmaTargetedHistogramFlag);
      if (histogram)
        histogram->Add(sample);
    }
  }

#if defined(OS_WIN)
  return OpenInternal(WideToUTF8(path.value()));
#elif defined(OS_POSIX)
  return OpenInternal(path.value());
#endif
}

bool Connection::OpenInMemory() {
  in_memory_ = true;
  return OpenInternal(":memory:");
}

void Connection::CloseInternal(bool forced) {
  // TODO(shess): Calling "PRAGMA journal_mode = DELETE" at this point
  // will delete the -journal file.  For ChromiumOS or other more
  // embedded systems, this is probably not appropriate, whereas on
  // desktop it might make some sense.

  // sqlite3_close() needs all prepared statements to be finalized.

  // Release cached statements.
  statement_cache_.clear();

  // With cached statements released, in-use statements will remain.
  // Closing the database while statements are in use is an API
  // violation, except for forced close (which happens from within a
  // statement's error handler).
  DCHECK(forced || open_statements_.empty());

  // Deactivate any outstanding statements so sqlite3_close() works.
  for (StatementRefSet::iterator i = open_statements_.begin();
       i != open_statements_.end(); ++i)
    (*i)->Close(forced);
  open_statements_.clear();

  if (db_) {
    // Call to AssertIOAllowed() cannot go at the beginning of the function
    // because Close() must be called from destructor to clean
    // statement_cache_, it won't cause any disk access and it most probably
    // will happen on thread not allowing disk access.
    // TODO(paivanof@gmail.com): This should move to the beginning
    // of the function. http://crbug.com/136655.
    AssertIOAllowed();
    // TODO(shess): Histogram for failure.
    sqlite3_close(db_);
    db_ = NULL;
  }
}

void Connection::Close() {
  // If the database was already closed by RazeAndClose(), then no
  // need to close again.  Clear the |poisoned_| bit so that incorrect
  // API calls are caught.
  if (poisoned_) {
    poisoned_ = false;
    return;
  }

  CloseInternal(false);
}

void Connection::Preload() {
  AssertIOAllowed();

  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Cannot preload null db";
    return;
  }

  // A statement must be open for the preload command to work. If the meta
  // table doesn't exist, it probably means this is a new database and there
  // is nothing to preload (so it's OK we do nothing).
  if (!DoesTableExist("meta"))
    return;
  Statement dummy(GetUniqueStatement("SELECT * FROM meta"));
  if (!dummy.Step())
    return;

#if !defined(USE_SYSTEM_SQLITE)
  // This function is only defined in Chromium's version of sqlite.
  // Do not call it when using system sqlite.
  sqlite3_preload(db_);
#endif
}

// Create an in-memory database with the existing database's page
// size, then backup that database over the existing database.
bool Connection::Raze() {
  AssertIOAllowed();

  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Cannot raze null db";
    return false;
  }

  if (transaction_nesting_ > 0) {
    DLOG(FATAL) << "Cannot raze within a transaction";
    return false;
  }

  sql::Connection null_db;
  if (!null_db.OpenInMemory()) {
    DLOG(FATAL) << "Unable to open in-memory database.";
    return false;
  }

  if (page_size_) {
    // Enforce SQLite restrictions on |page_size_|.
    DCHECK(!(page_size_ & (page_size_ - 1)))
        << " page_size_ " << page_size_ << " is not a power of two.";
    const int kSqliteMaxPageSize = 32768;  // from sqliteLimit.h
    DCHECK_LE(page_size_, kSqliteMaxPageSize);
    const std::string sql =
        base::StringPrintf("PRAGMA page_size=%d", page_size_);
    if (!null_db.Execute(sql.c_str()))
      return false;
  }

#if defined(OS_ANDROID)
  // Android compiles with SQLITE_DEFAULT_AUTOVACUUM.  Unfortunately,
  // in-memory databases do not respect this define.
  // TODO(shess): Figure out a way to set this without using platform
  // specific code.  AFAICT from sqlite3.c, the only way to do it
  // would be to create an actual filesystem database, which is
  // unfortunate.
  if (!null_db.Execute("PRAGMA auto_vacuum = 1"))
    return false;
#endif

  // The page size doesn't take effect until a database has pages, and
  // at this point the null database has none.  Changing the schema
  // version will create the first page.  This will not affect the
  // schema version in the resulting database, as SQLite's backup
  // implementation propagates the schema version from the original
  // connection to the new version of the database, incremented by one
  // so that other readers see the schema change and act accordingly.
  if (!null_db.Execute("PRAGMA schema_version = 1"))
    return false;

  // SQLite tracks the expected number of database pages in the first
  // page, and if it does not match the total retrieved from a
  // filesystem call, treats the database as corrupt.  This situation
  // breaks almost all SQLite calls.  "PRAGMA writable_schema" can be
  // used to hint to SQLite to soldier on in that case, specifically
  // for purposes of recovery.  [See SQLITE_CORRUPT_BKPT case in
  // sqlite3.c lockBtree().]
  // TODO(shess): With this, "PRAGMA auto_vacuum" and "PRAGMA
  // page_size" can be used to query such a database.
  ScopedWritableSchema writable_schema(db_);

  sqlite3_backup* backup = sqlite3_backup_init(db_, "main",
                                               null_db.db_, "main");
  if (!backup) {
    DLOG(FATAL) << "Unable to start sqlite3_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);

  // The destination database was locked.
  if (rc == SQLITE_BUSY) {
    return false;
  }

  // The entire database should have been backed up.
  if (rc != SQLITE_DONE) {
    DLOG(FATAL) << "Unable to copy entire null database.";
    return false;
  }

  // Exactly one page should have been backed up.  If this breaks,
  // check this function to make sure assumptions aren't being broken.
  DCHECK_EQ(pages, 1);

  return true;
}

bool Connection::RazeWithTimout(base::TimeDelta timeout) {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Cannot raze null db";
    return false;
  }

  ScopedBusyTimeout busy_timeout(db_);
  busy_timeout.SetTimeout(timeout);
  return Raze();
}

bool Connection::RazeAndClose() {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Cannot raze null db";
    return false;
  }

  // Raze() cannot run in a transaction.
  while (transaction_nesting_) {
    RollbackTransaction();
  }

  bool result = Raze();

  CloseInternal(true);

  // Mark the database so that future API calls fail appropriately,
  // but don't DCHECK (because after calling this function they are
  // expected to fail).
  poisoned_ = true;

  return result;
}

bool Connection::BeginTransaction() {
  if (needs_rollback_) {
    DCHECK_GT(transaction_nesting_, 0);

    // When we're going to rollback, fail on this begin and don't actually
    // mark us as entering the nested transaction.
    return false;
  }

  bool success = true;
  if (!transaction_nesting_) {
    needs_rollback_ = false;

    Statement begin(GetCachedStatement(SQL_FROM_HERE, "BEGIN TRANSACTION"));
    if (!begin.Run())
      return false;
  }
  transaction_nesting_++;
  return success;
}

void Connection::RollbackTransaction() {
  if (!transaction_nesting_) {
    DLOG_IF(FATAL, !poisoned_) << "Rolling back a nonexistent transaction";
    return;
  }

  transaction_nesting_--;

  if (transaction_nesting_ > 0) {
    // Mark the outermost transaction as needing rollback.
    needs_rollback_ = true;
    return;
  }

  DoRollback();
}

bool Connection::CommitTransaction() {
  if (!transaction_nesting_) {
    DLOG_IF(FATAL, !poisoned_) << "Rolling back a nonexistent transaction";
    return false;
  }
  transaction_nesting_--;

  if (transaction_nesting_ > 0) {
    // Mark any nested transactions as failing after we've already got one.
    return !needs_rollback_;
  }

  if (needs_rollback_) {
    DoRollback();
    return false;
  }

  Statement commit(GetCachedStatement(SQL_FROM_HERE, "COMMIT"));
  return commit.Run();
}

int Connection::ExecuteAndReturnErrorCode(const char* sql) {
  AssertIOAllowed();
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return SQLITE_ERROR;
  }
  return sqlite3_exec(db_, sql, NULL, NULL, NULL);
}

bool Connection::Execute(const char* sql) {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return false;
  }

  int error = ExecuteAndReturnErrorCode(sql);
  if (error != SQLITE_OK)
    error = OnSqliteError(error, NULL);

  // This needs to be a FATAL log because the error case of arriving here is
  // that there's a malformed SQL statement. This can arise in development if
  // a change alters the schema but not all queries adjust.  This can happen
  // in production if the schema is corrupted.
  if (error == SQLITE_ERROR)
    DLOG(FATAL) << "SQL Error in " << sql << ", " << GetErrorMessage();
  return error == SQLITE_OK;
}

bool Connection::ExecuteWithTimeout(const char* sql, base::TimeDelta timeout) {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return false;
  }

  ScopedBusyTimeout busy_timeout(db_);
  busy_timeout.SetTimeout(timeout);
  return Execute(sql);
}

bool Connection::HasCachedStatement(const StatementID& id) const {
  return statement_cache_.find(id) != statement_cache_.end();
}

scoped_refptr<Connection::StatementRef> Connection::GetCachedStatement(
    const StatementID& id,
    const char* sql) {
  CachedStatementMap::iterator i = statement_cache_.find(id);
  if (i != statement_cache_.end()) {
    // Statement is in the cache. It should still be active (we're the only
    // one invalidating cached statements, and we'll remove it from the cache
    // if we do that. Make sure we reset it before giving out the cached one in
    // case it still has some stuff bound.
    DCHECK(i->second->is_valid());
    sqlite3_reset(i->second->stmt());
    return i->second;
  }

  scoped_refptr<StatementRef> statement = GetUniqueStatement(sql);
  if (statement->is_valid())
    statement_cache_[id] = statement;  // Only cache valid statements.
  return statement;
}

scoped_refptr<Connection::StatementRef> Connection::GetUniqueStatement(
    const char* sql) {
  AssertIOAllowed();

  // Return inactive statement.
  if (!db_)
    return new StatementRef(NULL, NULL, poisoned_);

  sqlite3_stmt* stmt = NULL;
  int rc = sqlite3_prepare_v2(db_, sql, -1, &stmt, NULL);
  if (rc != SQLITE_OK) {
    // This is evidence of a syntax error in the incoming SQL.
    DLOG(FATAL) << "SQL compile error " << GetErrorMessage();

    // It could also be database corruption.
    OnSqliteError(rc, NULL);
    return new StatementRef(NULL, NULL, false);
  }
  return new StatementRef(this, stmt, true);
}

scoped_refptr<Connection::StatementRef> Connection::GetUntrackedStatement(
    const char* sql) const {
  // Return inactive statement.
  if (!db_)
    return new StatementRef(NULL, NULL, poisoned_);

  sqlite3_stmt* stmt = NULL;
  int rc = sqlite3_prepare_v2(db_, sql, -1, &stmt, NULL);
  if (rc != SQLITE_OK) {
    // This is evidence of a syntax error in the incoming SQL.
    DLOG(FATAL) << "SQL compile error " << GetErrorMessage();
    return new StatementRef(NULL, NULL, false);
  }
  return new StatementRef(NULL, stmt, true);
}

bool Connection::IsSQLValid(const char* sql) {
  AssertIOAllowed();
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return false;
  }

  sqlite3_stmt* stmt = NULL;
  if (sqlite3_prepare_v2(db_, sql, -1, &stmt, NULL) != SQLITE_OK)
    return false;

  sqlite3_finalize(stmt);
  return true;
}

bool Connection::DoesTableExist(const char* table_name) const {
  return DoesTableOrIndexExist(table_name, "table");
}

bool Connection::DoesIndexExist(const char* index_name) const {
  return DoesTableOrIndexExist(index_name, "index");
}

bool Connection::DoesTableOrIndexExist(
    const char* name, const char* type) const {
  const char* kSql = "SELECT name FROM sqlite_master WHERE type=? AND name=?";
  Statement statement(GetUntrackedStatement(kSql));
  statement.BindString(0, type);
  statement.BindString(1, name);

  return statement.Step();  // Table exists if any row was returned.
}

bool Connection::DoesColumnExist(const char* table_name,
                                 const char* column_name) const {
  std::string sql("PRAGMA TABLE_INFO(");
  sql.append(table_name);
  sql.append(")");

  Statement statement(GetUntrackedStatement(sql.c_str()));
  while (statement.Step()) {
    if (!statement.ColumnString(1).compare(column_name))
      return true;
  }
  return false;
}

int64 Connection::GetLastInsertRowId() const {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return 0;
  }
  return sqlite3_last_insert_rowid(db_);
}

int Connection::GetLastChangeCount() const {
  if (!db_) {
    DLOG_IF(FATAL, !poisoned_) << "Illegal use of connection without a db";
    return 0;
  }
  return sqlite3_changes(db_);
}

int Connection::GetErrorCode() const {
  if (!db_)
    return SQLITE_ERROR;
  return sqlite3_errcode(db_);
}

int Connection::GetLastErrno() const {
  if (!db_)
    return -1;

  int err = 0;
  if (SQLITE_OK != sqlite3_file_control(db_, NULL, SQLITE_LAST_ERRNO, &err))
    return -2;

  return err;
}

const char* Connection::GetErrorMessage() const {
  if (!db_)
    return "sql::Connection has no connection.";
  return sqlite3_errmsg(db_);
}

bool Connection::OpenInternal(const std::string& file_name) {
  AssertIOAllowed();

  if (db_) {
    DLOG(FATAL) << "sql::Connection is already open.";
    return false;
  }

  // If |poisoned_| is set, it means an error handler called
  // RazeAndClose().  Until regular Close() is called, the caller
  // should be treating the database as open, but is_open() currently
  // only considers the sqlite3 handle's state.
  // TODO(shess): Revise is_open() to consider poisoned_, and review
  // to see if any non-testing code even depends on it.
  DLOG_IF(FATAL, poisoned_) << "sql::Connection is already open.";

  int err = sqlite3_open(file_name.c_str(), &db_);
  if (err != SQLITE_OK) {
    // Histogram failures specific to initial open for debugging
    // purposes.
    UMA_HISTOGRAM_ENUMERATION("Sqlite.OpenFailure", err & 0xff, 50);

    OnSqliteError(err, NULL);
    Close();
    db_ = NULL;
    return false;
  }

  // SQLite uses a lookaside buffer to improve performance of small mallocs.
  // Chromium already depends on small mallocs being efficient, so we disable
  // this to avoid the extra memory overhead.
  // This must be called immediatly after opening the database before any SQL
  // statements are run.
  sqlite3_db_config(db_, SQLITE_DBCONFIG_LOOKASIDE, NULL, 0, 0);

  // sqlite3_open() does not actually read the database file (unless a
  // hot journal is found).  Successfully executing this pragma on an
  // existing database requires a valid header on page 1.
  // TODO(shess): For now, just probing to see what the lay of the
  // land is.  If it's mostly SQLITE_NOTADB, then the database should
  // be razed.
  err = ExecuteAndReturnErrorCode("PRAGMA auto_vacuum");
  if (err != SQLITE_OK)
    UMA_HISTOGRAM_ENUMERATION("Sqlite.OpenProbeFailure", err & 0xff, 50);

  // Enable extended result codes to provide more color on I/O errors.
  // Not having extended result codes is not a fatal problem, as
  // Chromium code does not attempt to handle I/O errors anyhow.  The
  // current implementation always returns SQLITE_OK, the DCHECK is to
  // quickly notify someone if SQLite changes.
  err = sqlite3_extended_result_codes(db_, 1);
  DCHECK_EQ(err, SQLITE_OK) << "Could not enable extended result codes";

  // If indicated, lock up the database before doing anything else, so
  // that the following code doesn't have to deal with locking.
  // TODO(shess): This code is brittle.  Find the cases where code
  // doesn't request |exclusive_locking_| and audit that it does the
  // right thing with SQLITE_BUSY, and that it doesn't make
  // assumptions about who might change things in the database.
  // http://crbug.com/56559
  if (exclusive_locking_) {
    // TODO(shess): This should probably be a failure.  Code which
    // requests exclusive locking but doesn't get it is almost certain
    // to be ill-tested.
    ignore_result(Execute("PRAGMA locking_mode=EXCLUSIVE"));
  }

  // http://www.sqlite.org/pragma.html#pragma_journal_mode
  // DELETE (default) - delete -journal file to commit.
  // TRUNCATE - truncate -journal file to commit.
  // PERSIST - zero out header of -journal file to commit.
  // journal_size_limit provides size to trim to in PERSIST.
  // TODO(shess): Figure out if PERSIST and journal_size_limit really
  // matter.  In theory, it keeps pages pre-allocated, so if
  // transactions usually fit, it should be faster.
  ignore_result(Execute("PRAGMA journal_mode = PERSIST"));
  ignore_result(Execute("PRAGMA journal_size_limit = 16384"));

  const base::TimeDelta kBusyTimeout =
    base::TimeDelta::FromSeconds(kBusyTimeoutSeconds);

  if (page_size_ != 0) {
    // Enforce SQLite restrictions on |page_size_|.
    DCHECK(!(page_size_ & (page_size_ - 1)))
        << " page_size_ " << page_size_ << " is not a power of two.";
    const int kSqliteMaxPageSize = 32768;  // from sqliteLimit.h
    DCHECK_LE(page_size_, kSqliteMaxPageSize);
    const std::string sql =
        base::StringPrintf("PRAGMA page_size=%d", page_size_);
    ignore_result(ExecuteWithTimeout(sql.c_str(), kBusyTimeout));
  }

  if (cache_size_ != 0) {
    const std::string sql =
        base::StringPrintf("PRAGMA cache_size=%d", cache_size_);
    ignore_result(ExecuteWithTimeout(sql.c_str(), kBusyTimeout));
  }

  if (!ExecuteWithTimeout("PRAGMA secure_delete=ON", kBusyTimeout)) {
    Close();
    return false;
  }

  return true;
}

void Connection::DoRollback() {
  Statement rollback(GetCachedStatement(SQL_FROM_HERE, "ROLLBACK"));
  rollback.Run();
  needs_rollback_ = false;
}

void Connection::StatementRefCreated(StatementRef* ref) {
  DCHECK(open_statements_.find(ref) == open_statements_.end());
  open_statements_.insert(ref);
}

void Connection::StatementRefDeleted(StatementRef* ref) {
  StatementRefSet::iterator i = open_statements_.find(ref);
  if (i == open_statements_.end())
    DLOG(FATAL) << "Could not find statement";
  else
    open_statements_.erase(i);
}

void Connection::AddTaggedHistogram(const std::string& name,
                                    size_t sample) const {
  if (histogram_tag_.empty())
    return;

  // TODO(shess): The histogram macros create a bit of static storage
  // for caching the histogram object.  This code shouldn't execute
  // often enough for such caching to be crucial.  If it becomes an
  // issue, the object could be cached alongside histogram_prefix_.
  std::string full_histogram_name = name + "." + histogram_tag_;
  base::HistogramBase* histogram =
      base::SparseHistogram::FactoryGet(
          full_histogram_name,
          base::HistogramBase::kUmaTargetedHistogramFlag);
  if (histogram)
    histogram->Add(sample);
}

int Connection::OnSqliteError(int err, sql::Statement *stmt) {
  UMA_HISTOGRAM_SPARSE_SLOWLY("Sqlite.Error", err);
  AddTaggedHistogram("Sqlite.Error", err);

  // Always log the error.
  LOG(ERROR) << "sqlite error " << err
             << ", errno " << GetLastErrno()
             << ": " << GetErrorMessage();

  if (!error_callback_.is_null()) {
    error_callback_.Run(err, stmt);
    return err;
  }

  // The default handling is to assert on debug and to ignore on release.
  if (!ShouldIgnore(err))
    DLOG(FATAL) << GetErrorMessage();
  return err;
}

// TODO(shess): Allow specifying integrity_check versus quick_check.
// TODO(shess): Allow specifying maximum results (default 100 lines).
bool Connection::IntegrityCheck(std::vector<std::string>* messages) {
  messages->clear();

  // This has the side effect of setting SQLITE_RecoveryMode, which
  // allows SQLite to process through certain cases of corruption.
  // Failing to set this pragma probably means that the database is
  // beyond recovery.
  const char kWritableSchema[] = "PRAGMA writable_schema = ON";
  if (!Execute(kWritableSchema))
    return false;

  bool ret = false;
  {
    const char kSql[] = "PRAGMA integrity_check";
    sql::Statement stmt(GetUniqueStatement(kSql));

    // The pragma appears to return all results (up to 100 by default)
    // as a single string.  This doesn't appear to be an API contract,
    // it could return separate lines, so loop _and_ split.
    while (stmt.Step()) {
      std::string result(stmt.ColumnString(0));
      base::SplitString(result, '\n', messages);
    }
    ret = stmt.Succeeded();
  }

  // Best effort to put things back as they were before.
  const char kNoWritableSchema[] = "PRAGMA writable_schema = OFF";
  ignore_result(Execute(kNoWritableSchema));

  return ret;
}

}  // namespace sql