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;
/** @var AuthenticationService $serviceObj */
foreach ($this->getAuthServices($subType, $loginData, $authInfo) as $serviceObj) {
    if ($row = $serviceObj->getUser()) {
        $tempuserArr[] = $row;
        $this->logger->debug('User found', [
            $this->userid_column => $row[$this->userid_column],
            $this->username_column => $row[$this->username_column],
        ]);
        // User found, just stop to search for more if not configured to go on
        if (empty($authConfiguration[$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;
   }
}

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:

foreach ($tempuserArr as $tempuser) {
   // Use 'auth' service to authenticate the user.
   // If one service returns FALSE then authentication fails.
   // A service may return 100 which means there's no reason to stop but the
   // user can't be authenticated by that service.
   $this->logger->debug('Auth user', $tempuser);
   $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.
         // This is 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.