Developer manual

This chapter describes some internals of this extension to let you extend it easily.

Assets such as PDF, images, documents, … are uploaded to TYPO3. Metadata extraction services are called, one after another, based on their advertised priority or quality. These services are the various extraction classes you find under Classes/Service/Extraction/).

The service classes invoke the actual wrappers to the extraction tools (Apache Tika, ExifTool, PHP, …) to be found under Classes/Service/Wrapper/.

In order to map the data format used by the various extraction tools to the FAL metadata structure used by TYPO3, a JSON-based configuration file is used. Those mapping configuration files can be found under Configuration/Services/Wrapper/.

Overview of the workflow of metadata extraction in TYPO3 when using this extension.

JSON mapping configuration file

A mapping configuration file is of the form:

[
  {
    "FAL": "caption",
    "DATA": "CaptionAbstract"
  },
  {
    "FAL": "color_space",
    "DATA": [
      "ColorMode",
      "ColorSpaceData",
      "ColorSpace->Causal\\Extractor\\Utility\\ColorSpace::normalize"
    ]
  }
]

FAL

This is the name (column) of the metadata in FAL.

DATA

This is either a unique key or an array of ordered keys to be checked for content in the extracted metadata. In addition, an arbitrary post-processor may be specified using the -> array notation.

A configuration helper tool is available in Extension Manager.

Hook

The method \Causal\Extractor\Service\Extraction\AbstractExtractionService::getDataMapping() is the central method invoked to map extracted metadata to FAL properties. Developers may dynamically alter the mapping by hooking into the process using $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['extractor']['dataMappingHook'].

Signal after extraction

Once the meta data has been extracted, a signal is emitted, which allows other extensions to process the file further. The Signal can be connected to a Slot as follows (e.g. in file ext_localconf.php of your extension).

// Initiate SignalSlotDispatcher
$signalSlotDispatcher = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(
    'TYPO3\\CMS\\Extbase\\SignalSlot\\Dispatcher'
);

// Connect the Signal "postMetaDataExtraction" to a Slot
$signalSlotDispatcher->connect(
    'Causal\\Extractor\\Service\\AbstractService',
    'postMetaDataExtraction',
    'Vendor\\MyExtension\\Service\\SlotService',
    'dispatch'
);

This requires a PHP class \Vendor\MyExtension\Service\SlotService and a method dispatch() in this class. The FAL $storageRecord is passed as a parameter to the method.