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 file:ext_localconf.php of your extension).

Registration in TYPO3 v8 and v9

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

// Connect the Signal "postMetaDataExtraction" to a Slot
$signalSlotDispatcher->connect(
    \Causal\Extractor\Service\AbstractService::class,
    'postMetaDataExtraction',
    \VENDOR\MyExtension\Service\Extractor::class,
    'enhanceMetadata'
);

This requires a PHP class \VENDOR\MyExtension\Service\Extractor and a method enhanceMetadata() in this class:

Registration since TYPO3 v10

The signal slot dispatcher is deprecated since TYPO3 v10 and you should instead register a middleware by creating file Configuration/Services.yaml within your extension:

services:
  _defaults:
    autowire: true
    autoconfigure: true
    public: false

  VENDOR\MyExtension\EventListener\ExtractorEventListener:
    tags:
      - name: event.listener
        identifier: 'causal/extractor'
        method: 'postMetaDataExtraction'
        event: Causal\Extractor\Resource\Event\AfterMetadataExtractedEvent

Caution

Be sure to module Admin Tools > Maintenance and to flush the TYPO3 and PHP Cache when you register middlewares.

This requires a PHP class \VENDOR\MyExtension\EventListener\ExtractorEventListener and a method enhanceMetadata() in this class: