.. include:: /Includes.rst.txt


.. _using-services-service-chain:

Calling a chain of services
^^^^^^^^^^^^^^^^^^^^^^^^^^^

It is also possible to use services in a "chain". This means using all
the available services of a type instead of just one.

The method :code:`\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstanceService()` accepts a third
parameter to exclude a number of services, using a comma-separated
list of service keys. This way you can walk through all available
services of a type by passing the already used service keys. Services
will be called in order of decreasing priority and quality.

The following example is an extract of the user authentication
process:

.. code-block:: php

    // Use 'auth' service to find the user
    // First found user will be used
    $serviceChain = '';
    $subType = 'getUser' . $this->loginType;
    while (is_object($serviceObj = GeneralUtility::makeInstanceService('auth', $subType, $serviceChain))) {
        $serviceChain .= ',' . $serviceObj->getServiceKey();
        $serviceObj->initAuth($subType, $loginData, $authInfo, $this);
        if ($row = $serviceObj->getUser()) {
            ...
            // User found, just stop to search for more if not configured to go on
            if (!$this->svConfig['setup'][$this->loginType . '_fetchAllUsers']) {
                break;
            }
        }
    }


As you see the while loop is exited when a service gives a result.
More sophisticated mechanisms can be imagined. In this next example –
also taken from the authentication process – the loop is exited only
when a certain value is returned by the method called:

.. code-block:: php

    // Use 'auth' service to authenticate the user
    // If one service returns FALSE then authentication failed
    // a service might return 100 which means there's no reason to stop but the user can't be authenticated by that service
    while (is_object($serviceObj = GeneralUtility::makeInstanceService('auth', $subType, $serviceChain))) {
        $serviceChain .= ',' . $serviceObj->getServiceKey();
        $serviceObj->initAuth($subType, $loginData, $authInfo, $this);
        if (($ret = $serviceObj->authUser($tempuser)) > 0) {
            // If the service returns >=200 then no more checking is needed - useful for IP checking without password
            if ((int)$ret >= 200) {
                $authenticated = true;
                break;
            } elseif ((int)$ret >= 100) {
            } else {
                $authenticated = true;
            }
        } else {
            $authenticated = false;
            break;
        }
    }

In the above example the loop will walk through all services of the
given type except if one service returns :code:`false` or a value larger than
or equals to 200, in which case the chain is interrupted.