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    <h3>Editing: Transports.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\Mailer\Transport;

use Symfony\Component\Mailer\Envelope;
use Symfony\Component\Mailer\Exception\InvalidArgumentException;
use Symfony\Component\Mailer\Exception\LogicException;
use Symfony\Component\Mailer\SentMessage;
use Symfony\Component\Mime\Message;
use Symfony\Component\Mime\RawMessage;

/**
 * @author Fabien Potencier &lt;fabien@symfony.com&gt;
 */
final class Transports implements TransportInterface
{
    /**
     * @var array&lt;string, TransportInterface&gt;
     */
    private array $transports = [];
    private TransportInterface $default;

    /**
     * @param iterable&lt;string, TransportInterface&gt; $transports
     */
    public function __construct(iterable $transports)
    {
        foreach ($transports as $name =&gt; $transport) {
            $this-&gt;default ??= $transport;
            $this-&gt;transports[$name] = $transport;
        }

        if (!$this-&gt;transports) {
            throw new LogicException(sprintf('&quot;%s&quot; must have at least one transport configured.', __CLASS__));
        }
    }

    public function send(RawMessage $message, Envelope $envelope = null): ?SentMessage
    {
        /** @var Message $message */
        if (RawMessage::class === $message::class || !$message-&gt;getHeaders()-&gt;has('X-Transport')) {
            return $this-&gt;default-&gt;send($message, $envelope);
        }

        $headers = $message-&gt;getHeaders();
        $transport = $headers-&gt;get('X-Transport')-&gt;getBody();
        $headers-&gt;remove('X-Transport');

        if (!isset($this-&gt;transports[$transport])) {
            throw new InvalidArgumentException(sprintf('The &quot;%s&quot; transport does not exist (available transports: &quot;%s&quot;).', $transport, implode('&quot;, &quot;', array_keys($this-&gt;transports))));
        }

        try {
            return $this-&gt;transports[$transport]-&gt;send($message, $envelope);
        } catch (\Throwable $e) {
            $headers-&gt;addTextHeader('X-Transport', $transport);

            throw $e;
        }
    }

    public function __toString(): string
    {
        return '['.implode(',', array_keys($this-&gt;transports)).']';
    }
}
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