SQLite3::setAuthorizer

Configures a callback to be used as an authorizer to limit what a statement can do

&reftitle.description; public `bool` `SQLite3::setAuthorizer` ``callable``null```callback`

Sets a callback that will be called by SQLite every time an action is performed (reading, deleting, updating, etc.). This is used when preparing a SQL statement from an untrusted source to ensure that the SQL statements do not try to access data they are not allowed to see, or that they do not try to execute malicious statements that damage the database. For example, an application may allow a user to enter arbitrary SQL queries for evaluation by a database. But the application does not want the user to be able to make arbitrary changes to the database. An authorizer could then be put in place while the user-entered SQL is being prepared that disallows everything except SELECT statements.

The authorizer callback may be called multiple times for each statement prepared by SQLite. A `SELECT` or `UPDATE` query will call the authorizer for every column that would be read or updated.

The authorizer is called with up to five parameters. The first parameter is always given, and is an `int` (action code) matching a constant from `SQLite3`. The other parameters are only passed for some actions. The following table describes the second and third parameters according to the action:

## List of action codes and parameters

Action | Second parameter | Third parameter
`SQLite3::CREATE_INDEX` | Index Name | Table Name
`SQLite3::CREATE_TABLE` | Table Name | &null;
`SQLite3::CREATE_TEMP_INDEX` | Index Name | Table Name
`SQLite3::CREATE_TEMP_TABLE` | Table Name | &null;
`SQLite3::CREATE_TEMP_TRIGGER` | Trigger Name | Table Name
`SQLite3::CREATE_TEMP_VIEW` | View Name | &null;
`SQLite3::CREATE_TRIGGER` | Trigger Name | Table Name
`SQLite3::CREATE_VIEW` | View Name | &null;
`SQLite3::DELETE` | Table Name | &null;
`SQLite3::DROP_INDEX` | Index Name | Table Name
`SQLite3::DROP_TABLE` | Table Name | &null;
`SQLite3::DROP_TEMP_INDEX` | Index Name | Table Name
`SQLite3::DROP_TEMP_TABLE` | Table Name | &null;
`SQLite3::DROP_TEMP_TRIGGER` | Trigger Name | Table Name
`SQLite3::DROP_TEMP_VIEW` | View Name | &null;
`SQLite3::DROP_TRIGGER` | Trigger Name | Table Name
`SQLite3::DROP_VIEW` | View Name | &null;
`SQLite3::INSERT` | Table Name | &null;
`SQLite3::PRAGMA` | Pragma Name | First argument passed to the pragma, or &null;
`SQLite3::READ` | Table Name | Column Name
`SQLite3::SELECT` | &null; | &null;
`SQLite3::TRANSACTION` | Operation | &null;
`SQLite3::UPDATE` | Table Name | Column Name
`SQLite3::ATTACH` | Filename | &null;
`SQLite3::DETACH` | Database Name | &null;
`SQLite3::ALTER_TABLE` | Database Name | Table Name
`SQLite3::REINDEX` | Index Name | &null;
`SQLite3::ANALYZE` | Table Name | &null;
`SQLite3::CREATE_VTABLE` | Table Name | Module Name
`SQLite3::DROP_VTABLE` | Table Name | Module Name
`SQLite3::FUNCTION` | &null; | Function Name
`SQLite3::SAVEPOINT` | Operation | Savepoint Name
`SQLite3::RECURSIVE` | &null; | &null;

The 4th parameter will be the name of the database (`"main"`, `"temp"`, etc.) if applicable.

The 5th parameter to the authorizer callback is the name of the inner-most trigger or view that is responsible for the access attempt or &null; if this access attempt is directly from top-level SQL code.

When the callback returns `SQLite3::OK`, that means the operation requested is accepted. When the callback returns `SQLite3::DENY`, the call that triggered the authorizer will fail with an error message explaining that access is denied.

If the action code is `SQLite3::READ` and the callback returns `SQLite3::IGNORE` then the prepared statement is constructed to substitute a &null; value in place of the table column that would have been read if `SQLite3::OK` had been returned. The `SQLite3::IGNORE` return can be used to deny an untrusted user access to individual columns of a table.

When a table is referenced by a `SELECT` but no column values are extracted from that table (for example in a query like `"SELECT count(*) FROM table"`) then the `SQLite3::READ` authorizer callback is invoked once for that table with a column name that is an empty string.

If the action code is `SQLite3::DELETE` and the callback returns `SQLite3::IGNORE` then the DELETE operation proceeds but the truncate optimization is disabled and all rows are deleted individually.

Only a single authorizer can be in place on a database connection at a time. Each call to `SQLite3::setAuthorizer` overrides the previous call. Disable the authorizer by installing a &null; callback. The authorizer is disabled by default.

The authorizer callback must not do anything that will modify the database connection that invoked the authorizer callback.

Note that the authorizer is only called when a statement is prepared, not when it's executed.

More details can be found in the SQLite3 documentation.

&reftitle.parameters;

`callback`

- The `callable` to be called.

  If &null; is passed instead, this will disable the current authorizer callback.

&reftitle.returnvalues;

&return.success;

&reftitle.errors;

This method doesn't throw any error, but if an authorizer is enabled and returns an invalid value, the statement preparation will throw an error (or exception, depending on the use of the `SQLite3::enableExceptions` method).

&reftitle.examples;

### `SQLite3::setAuthorizer` example

This only allows access to reading, and only some columns of the `users` table will be returned. Other columns will be replaced with &null;.

    <?php
    $db = new SQLite3('data.sqlite');
    $db->exec('CREATE TABLE users (id, name, password);');
    $db->exec('INSERT INTO users VALUES (1, \'Pauline\', \'Snails4eva\');');

    $allowed_columns = ['id', 'name'];

    $db->setAuthorizer(function (int $action, ...$args) use ($allowed_columns) {
        if ($action === SQLite3::READ) {
            list($table, $column) = $args;

            if ($table === 'users' && in_array($column, $allowed_columns) {
                return SQLite3::OK;
            }

            return SQLite3::IGNORE;
        }

        return SQLite3::DENY;
    });

    print_r($db->querySingle('SELECT * FROM users WHERE id = 1;'));

&example.outputs;

    Array
    (
        [id] => 1
        [name] => Pauline
        [password] =>
    )