Treat DESCRIBE as a read

DESCRIBE and DESC only show a table on MySQL/MariaDB. SQLite's PRAGMA
stays out of the read list because it can also change settings.

lib/Service/SqlGuard.php

@@ -32,8 +32,12 @@ class SqlGuard
         '/\bINTO\s+(OUTFILE|DUMPFILE)\b/i' => 'INTO OUTFILE/DUMPFILE',
     ];
 
-    /** Statements that start with one of these only read, unless WRITES_INSIDE_READ matches. */
-    private const READ_ONLY_START = '/^(SELECT|WITH|SHOW|EXPLAIN|SET|VALUES|TABLE)\b/i';
+    /**
+     * Statements that start with one of these only read, unless
+     * WRITES_INSIDE_READ matches. SQLite's PRAGMA is left out on purpose:
+     * it can also change settings, so it asks for confirmation.
+     */
+    private const READ_ONLY_START = '/^(SELECT|WITH|SHOW|EXPLAIN|DESCRIBE|DESC|SET|VALUES|TABLE)\b/i';
 
     /**
      * What makes a statement that starts as a read change something:

tests/Unit/Service/SqlGuardTest.php

@@ -74,6 +74,8 @@ class SqlGuardTest extends TestCase
             ["SELECT \$\$DELETE FROM x\$\$"],
             ["SELECT E'it\\'s delete' FROM t"],
             ['VALUES (1)'],
+            ['DESCRIBE oc_users'],
+            ['DESC oc_users'],
             ["SELECT '/* not a comment */' AS a, '-- nor this' AS b"],
         ];
     }
@@ -113,6 +115,7 @@ class SqlGuardTest extends TestCase
             ["SELECT nextval('seq')"],
             ['MERGE INTO t USING s ON true WHEN MATCHED THEN DELETE'],
             ['VACUUM'],
+            ['PRAGMA journal_mode = WAL'],
             ["WITH a AS (SELECT '/*'), b AS (DELETE FROM t RETURNING 1) SELECT '*/'"],
             ["SELECT '--' AS x FROM t WHERE a IN (SELECT 1) FOR UPDATE"],
             ["WITH a AS (SELECT \$\$/*\$\$), b AS (DELETE FROM t RETURNING 1) SELECT '*/'"],