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    <h3>Editing: AbstractMultipartPart.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\Header\Headers;

/**
 * @author Fabien Potencier &lt;fabien@symfony.com&gt;
 */
abstract class AbstractMultipartPart extends AbstractPart
{
    private $boundary;
    private $parts = [];

    public function __construct(AbstractPart ...$parts)
    {
        parent::__construct();

        foreach ($parts as $part) {
            $this-&gt;parts[] = $part;
        }
    }

    /**
     * @return AbstractPart[]
     */
    public function getParts(): array
    {
        return $this-&gt;parts;
    }

    public function getMediaType(): string
    {
        return 'multipart';
    }

    public function getPreparedHeaders(): Headers
    {
        $headers = parent::getPreparedHeaders();
        $headers-&gt;setHeaderParameter('Content-Type', 'boundary', $this-&gt;getBoundary());

        return $headers;
    }

    public function bodyToString(): string
    {
        $parts = $this-&gt;getParts();
        $string = '';
        foreach ($parts as $part) {
            $string .= '--'.$this-&gt;getBoundary().&quot;\r\n&quot;.$part-&gt;toString().&quot;\r\n&quot;;
        }
        $string .= '--'.$this-&gt;getBoundary().&quot;--\r\n&quot;;

        return $string;
    }

    public function bodyToIterable(): iterable
    {
        $parts = $this-&gt;getParts();
        foreach ($parts as $part) {
            yield '--'.$this-&gt;getBoundary().&quot;\r\n&quot;;
            yield from $part-&gt;toIterable();
            yield &quot;\r\n&quot;;
        }
        yield '--'.$this-&gt;getBoundary().&quot;--\r\n&quot;;
    }

    public function asDebugString(): string
    {
        $str = parent::asDebugString();
        foreach ($this-&gt;getParts() as $part) {
            $lines = explode(&quot;\n&quot;, $part-&gt;asDebugString());
            $str .= &quot;\n  └ &quot;.array_shift($lines);
            foreach ($lines as $line) {
                $str .= &quot;\n  |&quot;.$line;
            }
        }

        return $str;
    }

    private function getBoundary(): string
    {
        if (null === $this-&gt;boundary) {
            $this-&gt;boundary = strtr(base64_encode(random_bytes(6)), '+/', '-_');
        }

        return $this-&gt;boundary;
    }
}
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