<form method="POST">
    <h3>Editing: DataPart.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\Mime\Part;

use Symfony\Component\Mime\Exception\InvalidArgumentException;
use Symfony\Component\Mime\Header\Headers;
use Symfony\Component\Mime\MimeTypes;

/**
 * @author Fabien Potencier &lt;fabien@symfony.com&gt;
 */
class DataPart extends TextPart
{
    /** @internal */
    protected $_parent;

    private static $mimeTypes;

    private $filename;
    private $mediaType;
    private $cid;
    private $handle;

    /**
     * @param resource|string $body
     */
    public function __construct($body, ?string $filename = null, ?string $contentType = null, ?string $encoding = null)
    {
        unset($this-&gt;_parent);

        if (null === $contentType) {
            $contentType = 'application/octet-stream';
        }
        [$this-&gt;mediaType, $subtype] = explode('/', $contentType);

        parent::__construct($body, null, $subtype, $encoding);

        if (null !== $filename) {
            $this-&gt;filename = $filename;
            $this-&gt;setName($filename);
        }
        $this-&gt;setDisposition('attachment');
    }

    public static function fromPath(string $path, ?string $name = null, ?string $contentType = null): self
    {
        if (null === $contentType) {
            $ext = strtolower(substr($path, strrpos($path, '.') + 1));
            if (null === self::$mimeTypes) {
                self::$mimeTypes = new MimeTypes();
            }
            $contentType = self::$mimeTypes-&gt;getMimeTypes($ext)[0] ?? 'application/octet-stream';
        }

        if ((is_file($path) &amp;&amp; !is_readable($path)) || is_dir($path)) {
            throw new InvalidArgumentException(sprintf('Path &quot;%s&quot; is not readable.', $path));
        }

        if (false === $handle = @fopen($path, 'r', false)) {
            throw new InvalidArgumentException(sprintf('Unable to open path &quot;%s&quot;.', $path));
        }

        if (!is_file($path)) {
            $cache = fopen('php://temp', 'r+');
            stream_copy_to_stream($handle, $cache);
            $handle = $cache;
        }

        $p = new self($handle, $name ?: basename($path), $contentType);
        $p-&gt;handle = $handle;

        return $p;
    }

    /**
     * @return $this
     */
    public function asInline()
    {
        return $this-&gt;setDisposition('inline');
    }

    public function getContentId(): string
    {
        return $this-&gt;cid ?: $this-&gt;cid = $this-&gt;generateContentId();
    }

    public function hasContentId(): bool
    {
        return null !== $this-&gt;cid;
    }

    public function getMediaType(): string
    {
        return $this-&gt;mediaType;
    }

    public function getPreparedHeaders(): Headers
    {
        $headers = parent::getPreparedHeaders();

        if (null !== $this-&gt;cid) {
            $headers-&gt;setHeaderBody('Id', 'Content-ID', $this-&gt;cid);
        }

        if (null !== $this-&gt;filename) {
            $headers-&gt;setHeaderParameter('Content-Disposition', 'filename', $this-&gt;filename);
        }

        return $headers;
    }

    public function asDebugString(): string
    {
        $str = parent::asDebugString();
        if (null !== $this-&gt;filename) {
            $str .= ' filename: '.$this-&gt;filename;
        }

        return $str;
    }

    private function generateContentId(): string
    {
        return bin2hex(random_bytes(16)).'@symfony';
    }

    public function __destruct()
    {
        if (null !== $this-&gt;handle &amp;&amp; \is_resource($this-&gt;handle)) {
            fclose($this-&gt;handle);
        }
    }

    /**
     * @return array
     */
    public function __sleep()
    {
        // converts the body to a string
        parent::__sleep();

        $this-&gt;_parent = [];
        foreach (['body', 'charset', 'subtype', 'disposition', 'name', 'encoding'] as $name) {
            $r = new \ReflectionProperty(TextPart::class, $name);
            $r-&gt;setAccessible(true);
            $this-&gt;_parent[$name] = $r-&gt;getValue($this);
        }
        $this-&gt;_headers = $this-&gt;getHeaders();

        return ['_headers', '_parent', 'filename', 'mediaType'];
    }

    public function __wakeup()
    {
        $r = new \ReflectionProperty(AbstractPart::class, 'headers');
        $r-&gt;setAccessible(true);
        $r-&gt;setValue($this, $this-&gt;_headers);
        unset($this-&gt;_headers);

        if (!\is_array($this-&gt;_parent)) {
            throw new \BadMethodCallException('Cannot unserialize '.__CLASS__);
        }
        foreach (['body', 'charset', 'subtype', 'disposition', 'name', 'encoding'] as $name) {
            if (null !== $this-&gt;_parent[$name] &amp;&amp; !\is_string($this-&gt;_parent[$name])) {
                throw new \BadMethodCallException('Cannot unserialize '.__CLASS__);
            }
            $r = new \ReflectionProperty(TextPart::class, $name);
            $r-&gt;setAccessible(true);
            $r-&gt;setValue($this, $this-&gt;_parent[$name]);
        }
        unset($this-&gt;_parent);
    }
}
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