Add any metadata and serialize it.

gistfile1.php

<?php

$filesystem = new Filesystem(new Local(TMP . DS . 'flytest' . DS), new Predis());
$filesystem->addPlugin(new MetadataSerializer('yourawesomemetadatatag'));
$filesystem->getYourawesomemetadatatag('filename.txt', ['foo' => 'bar'], true);

MetadataSerializer.php

<?php

use Flysystem\FilesystemInterface;
use Flysystem\PluginInterface;

class MetadataSerializer implements PluginInterface {

	protected $filesystem;
	protected $fieldName;

	public function __construct($fieldName) {
		$this->fieldName = $fieldName;
	}

	public function setFilesystem(FilesystemInterface $filesystem)
	{
		$this->filesystem = $filesystem;
	}

	public function getMethod()
	{
		return 'get' . ucfirst($this->fieldName);
	}

	public function handle($path = null, $fieldContents = null, $autosave = false)
	{
		$this->assertPresent($path);

		if ($fieldContents !== null) {
			$data = $this->filesystem->getCache()->updateObject($path, [
				$this->fieldName => serialize($fieldContents),
			], $autosave);

			return $data[$this->fieldName];
		}

		if ($metadata = $this->filesystem->getCache()->getMetadata($path)) {
			if (isset($metadata[$this->fieldName])) {
				return unserialize($metadata[$this->fieldName]);
			}
		}

		return false;
	}

	protected function assertPresent($path)
	{
		if ( ! $this->filesystem->has($path)) {
			throw new FileNotFoundException($path);
		}
	}
}