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Since #1046, QETSql::execReadOnly() runs a query with PRAGMA query_only set and switches it off before returning. Switching it off aborts a statement SQLite is still stepping through ("abort due to ROLLBACK"), and QSQLITE has already stepped to the first row by then. A query that produces its rows as it goes -- a UNION ALL without ORDER BY -- therefore came back with its first row only and no error. A sorted query was not affected, because SQLite has read every row before returning the first. Every query from the SQL box of a table, a saved <graphics_table> query and the scripting qet.query() goes through here. The checked run is now finished before query_only is switched off, and a query that passed is run again for the caller. SQLite refuses a write at its first step, so passing that step is what proves a statement reads only; the second run is of a statement already shown to be read-only. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01G2d2Zi8BfrYRPX88zhaoFG
118 lines
4.2 KiB
C++
118 lines
4.2 KiB
C++
/*
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Copyright 2006-2026 The QElectroTech Team
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This file is part of QElectroTech.
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QElectroTech is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 2 of the License, or
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(at your option) any later version.
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QElectroTech is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with QElectroTech. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "sqlreadonly.h"
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#include <QCoreApplication>
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#include <QSqlError>
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namespace QETSql {
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/**
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@brief QETSql::execReadOnly
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Run @p query on @p db with SQLite's query_only pragma set, so that
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SQLite itself refuses anything that would write.
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Why SQLite is asked rather than the text inspected: a check on the
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query's first keyword cannot see what the statement actually does.
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SQLite has allowed a CTE prefix in front of a data-modifying statement
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since 3.8.3, so
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@code
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WITH x AS (SELECT 1) DELETE FROM element
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@endcode
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begins with WITH, contains no semicolon, and deletes every row. With
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query_only set, SQLite fails that statement with SQLITE_READONLY when it
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tries to start writing, before any row is touched, while an ordinary
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WITH ... SELECT still runs.
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Why a pragma rather than sqlite3_stmt_readonly(): that needs the
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driver's native sqlite3 handle passed to the libsqlite3 QElectroTech
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links. The QSQLITE plugin of the Qt online installer carries its own
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private copy of SQLite, so that handle belongs to another library and
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the call crashes (qelectrotech-source-mirror#1045). A pragma goes
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through the driver, whichever SQLite it uses.
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A statement that succeeded here is read-only, so running the returned
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query again, as several callers do, runs a read-only statement again.
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A refused one comes back as an empty query with nothing to run again:
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query_only is only set for the duration of this call.
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Qt's SQLite driver refuses a second statement after the first one, so
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"SELECT 1; DROP TABLE element" is refused too.
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This is a read-only test, NOT a statement-type allowlist: query_only
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does not refuse ATTACH, BEGIN or most PRAGMAs, because none of them
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change the contents of the database. Callers that need to restrict
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which *kind* of statement is acceptable must say so separately --
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projectDataBase::newQuery() keeps isReadOnlySelect() in front of this
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for exactly that reason.
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@param db the connection to run the query on
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@param query the raw SQL text
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@param error set to a human-readable reason when the query is refused
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@return the executed query, or an empty query on @p db if @p query was
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refused or failed
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*/
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QSqlQuery execReadOnly(const QSqlDatabase &db, const QString &query, QString *error)
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{
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if (error) {
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error->clear();
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}
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if (!QSqlQuery(db).exec(QStringLiteral("PRAGMA query_only = ON"))) {
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if (error) {
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*error = QCoreApplication::translate("QETSql",
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"Impossible de vérifier la requête : "
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"la base de données ne peut pas être mise en lecture seule.");
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}
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return QSqlQuery(db);
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}
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QSqlQuery result(db);
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const bool ok = result.exec(query);
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//Switching query_only off aborts a statement SQLite is still
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//stepping through -- an unsorted UNION ALL then ends after its
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//first row. So the checked run is finished first, and a statement
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//that passed is run again for the caller: SQLite refuses a write
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//at its first step, so passing that step proves it read-only.
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result.finish();
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QSqlQuery(db).exec(QStringLiteral("PRAGMA query_only = OFF"));
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if (ok) {
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result.exec(query);
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return result;
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}
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if (error) {
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// SQLITE_READONLY is 8; extended codes keep it in the low byte.
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if ((result.lastError().nativeErrorCode().toInt() & 0xff) == 8) {
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*error = QCoreApplication::translate("QETSql",
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"Seules les requêtes en lecture seule sont autorisées : "
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"cette requête modifierait la base de données.");
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} else {
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*error = QCoreApplication::translate("QETSql",
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"Requête SQL invalide : %1")
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.arg(result.lastError().databaseText());
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}
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}
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return QSqlQuery(db);
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}
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} // namespace QETSql
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