<form method="POST">
    <h3>Editing: TextPart.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\Encoder\Base64ContentEncoder;
use Symfony\Component\Mime\Encoder\ContentEncoderInterface;
use Symfony\Component\Mime\Encoder\EightBitContentEncoder;
use Symfony\Component\Mime\Encoder\QpContentEncoder;
use Symfony\Component\Mime\Exception\InvalidArgumentException;
use Symfony\Component\Mime\Header\Headers;

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

    private static $encoders = [];

    private $body;
    private $charset;
    private $subtype;
    /**
     * @var ?string
     */
    private $disposition;
    private $name;
    private $encoding;
    private $seekable;

    /**
     * @param resource|string|File $body Use a File instance to defer loading the file until rendering
     */
    public function __construct($body, ?string $charset = 'utf-8', string $subtype = 'plain', string $encoding = null)
    {
        unset($this-&gt;_headers);

        parent::__construct();

        if (!\is_string($body) &amp;&amp; !\is_resource($body) &amp;&amp; !$body instanceof File) {
            throw new \TypeError(sprintf('The body of &quot;%s&quot; must be a string, a resource, or an instance of &quot;%s&quot; (got &quot;%s&quot;).', self::class, File::class, get_debug_type($body)));
        }

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

        $this-&gt;body = $body;
        $this-&gt;charset = $charset;
        $this-&gt;subtype = $subtype;
        $this-&gt;seekable = \is_resource($body) ? stream_get_meta_data($body)['seekable'] &amp;&amp; 0 === fseek($body, 0, \SEEK_CUR) : null;

        if (null === $encoding) {
            $this-&gt;encoding = $this-&gt;chooseEncoding();
        } else {
            if ('quoted-printable' !== $encoding &amp;&amp; 'base64' !== $encoding &amp;&amp; '8bit' !== $encoding) {
                throw new InvalidArgumentException(sprintf('The encoding must be one of &quot;quoted-printable&quot;, &quot;base64&quot;, or &quot;8bit&quot; (&quot;%s&quot; given).', $encoding));
            }
            $this-&gt;encoding = $encoding;
        }
    }

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

    public function getMediaSubtype(): string
    {
        return $this-&gt;subtype;
    }

    /**
     * @param string $disposition one of attachment, inline, or form-data
     *
     * @return $this
     */
    public function setDisposition(string $disposition): static
    {
        $this-&gt;disposition = $disposition;

        return $this;
    }

    /**
     * Sets the name of the file (used by FormDataPart).
     *
     * @return $this
     */
    public function setName(string $name): static
    {
        $this-&gt;name = $name;

        return $this;
    }

    /**
     * Gets the name of the file.
     */
    public function getName(): ?string
    {
        return $this-&gt;name;
    }

    public function getBody(): string
    {
        if ($this-&gt;body instanceof File) {
            return file_get_contents($this-&gt;body-&gt;getPath());
        }

        if (null === $this-&gt;seekable) {
            return $this-&gt;body;
        }

        if ($this-&gt;seekable) {
            rewind($this-&gt;body);
        }

        return stream_get_contents($this-&gt;body) ?: '';
    }

    public function bodyToString(): string
    {
        return $this-&gt;getEncoder()-&gt;encodeString($this-&gt;getBody(), $this-&gt;charset);
    }

    public function bodyToIterable(): iterable
    {
        if ($this-&gt;body instanceof File) {
            $path = $this-&gt;body-&gt;getPath();
            if (false === $handle = @fopen($path, 'r', false)) {
                throw new InvalidArgumentException(sprintf('Unable to open path &quot;%s&quot;.', $path));
            }

            yield from $this-&gt;getEncoder()-&gt;encodeByteStream($handle);
        } elseif (null !== $this-&gt;seekable) {
            if ($this-&gt;seekable) {
                rewind($this-&gt;body);
            }
            yield from $this-&gt;getEncoder()-&gt;encodeByteStream($this-&gt;body);
        } else {
            yield $this-&gt;getEncoder()-&gt;encodeString($this-&gt;body);
        }
    }

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

        $headers-&gt;setHeaderBody('Parameterized', 'Content-Type', $this-&gt;getMediaType().'/'.$this-&gt;getMediaSubtype());
        if ($this-&gt;charset) {
            $headers-&gt;setHeaderParameter('Content-Type', 'charset', $this-&gt;charset);
        }
        if ($this-&gt;name &amp;&amp; 'form-data' !== $this-&gt;disposition) {
            $headers-&gt;setHeaderParameter('Content-Type', 'name', $this-&gt;name);
        }
        $headers-&gt;setHeaderBody('Text', 'Content-Transfer-Encoding', $this-&gt;encoding);

        if (!$headers-&gt;has('Content-Disposition') &amp;&amp; null !== $this-&gt;disposition) {
            $headers-&gt;setHeaderBody('Parameterized', 'Content-Disposition', $this-&gt;disposition);
            if ($this-&gt;name) {
                $headers-&gt;setHeaderParameter('Content-Disposition', 'name', $this-&gt;name);
            }
        }

        return $headers;
    }

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

        return $str;
    }

    private function getEncoder(): ContentEncoderInterface
    {
        if ('8bit' === $this-&gt;encoding) {
            return self::$encoders[$this-&gt;encoding] ??= new EightBitContentEncoder();
        }

        if ('quoted-printable' === $this-&gt;encoding) {
            return self::$encoders[$this-&gt;encoding] ??= new QpContentEncoder();
        }

        return self::$encoders[$this-&gt;encoding] ??= new Base64ContentEncoder();
    }

    private function chooseEncoding(): string
    {
        if (null === $this-&gt;charset) {
            return 'base64';
        }

        return 'quoted-printable';
    }

    public function __sleep(): array
    {
        // convert resources to strings for serialization
        if (null !== $this-&gt;seekable || $this-&gt;body instanceof File) {
            $this-&gt;body = $this-&gt;getBody();
            $this-&gt;seekable = null;
        }

        $this-&gt;_headers = $this-&gt;getHeaders();

        return ['_headers', 'body', 'charset', 'subtype', 'disposition', 'name', 'encoding'];
    }

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