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 \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstanceService() accepts a third parameter to exclude a number of services, using an array 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:

// Use 'auth' service to find the user
// First found user will be used
$subType = 'getUser' . $this->loginType;
foreach ($this->getAuthServices($subType, $loginData, $authInfo) as $serviceObj) {
    if ($row = $serviceObj->getUser()) {
        $tempuserArr[] = $row;
        if ($this->writeDevLog) {
            GeneralUtility::devLog('User found: ' . GeneralUtility::arrayToLogString($row, [$this->userid_column, $this->username_column]), self::class, 0);
        }
        // User found, just stop to search for more if not configured to go on
        if (!$this->svConfig['setup'][$this->loginType . '_fetchAllUsers']) {
            break;
        }
    }
}

protected function getAuthServices(string $subType, array $loginData, array $authInfo): \Traversable
{
    $serviceChain = '';
    while (is_object($serviceObj = GeneralUtility::makeInstanceService('auth', $subType, $serviceChain))) {
        $serviceChain .= ',' . $serviceObj->getServiceKey();
        $serviceObj->initAuth($subType, $loginData, $authInfo, $this);
        yield $serviceObj;
    }
    if ($this->writeDevLog && $serviceChain) {
        GeneralUtility::devLog($subType . ' auth services called: ' . $serviceChain, self::class);
    }
}

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:

// 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
if ($this->writeDevLog) {
    GeneralUtility::devLog('Auth user: ' . GeneralUtility::arrayToLogString($tempuser), self::class);
}
$subType = 'authUser' . $this->loginType;

foreach ($this->getAuthServices($subType, $loginData, $authInfo) as $serviceObj) {
    if (($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) {
            $authenticated = true;
            break;
        }
        if ((int)$ret >= 100) {
        } else {
            $authenticated = true;
        }
    } else {
        $authenticated = false;
        break;
    }
}

if ($authenticated) {
    // Leave foreach() because a user is authenticated
    break;
}

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