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    <h3>Editing: CharacterStream.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;

/**
 * @author Fabien Potencier &lt;fabien@symfony.com&gt;
 * @author Xavier De Cock &lt;xdecock@gmail.com&gt;
 *
 * @internal
 */
final class CharacterStream
{
    /** Pre-computed for optimization */
    private const UTF8_LENGTH_MAP = [
        &quot;\x00&quot; =&gt; 1, &quot;\x01&quot; =&gt; 1, &quot;\x02&quot; =&gt; 1, &quot;\x03&quot; =&gt; 1, &quot;\x04&quot; =&gt; 1, &quot;\x05&quot; =&gt; 1, &quot;\x06&quot; =&gt; 1, &quot;\x07&quot; =&gt; 1,
        &quot;\x08&quot; =&gt; 1, &quot;\x09&quot; =&gt; 1, &quot;\x0a&quot; =&gt; 1, &quot;\x0b&quot; =&gt; 1, &quot;\x0c&quot; =&gt; 1, &quot;\x0d&quot; =&gt; 1, &quot;\x0e&quot; =&gt; 1, &quot;\x0f&quot; =&gt; 1,
        &quot;\x10&quot; =&gt; 1, &quot;\x11&quot; =&gt; 1, &quot;\x12&quot; =&gt; 1, &quot;\x13&quot; =&gt; 1, &quot;\x14&quot; =&gt; 1, &quot;\x15&quot; =&gt; 1, &quot;\x16&quot; =&gt; 1, &quot;\x17&quot; =&gt; 1,
        &quot;\x18&quot; =&gt; 1, &quot;\x19&quot; =&gt; 1, &quot;\x1a&quot; =&gt; 1, &quot;\x1b&quot; =&gt; 1, &quot;\x1c&quot; =&gt; 1, &quot;\x1d&quot; =&gt; 1, &quot;\x1e&quot; =&gt; 1, &quot;\x1f&quot; =&gt; 1,
        &quot;\x20&quot; =&gt; 1, &quot;\x21&quot; =&gt; 1, &quot;\x22&quot; =&gt; 1, &quot;\x23&quot; =&gt; 1, &quot;\x24&quot; =&gt; 1, &quot;\x25&quot; =&gt; 1, &quot;\x26&quot; =&gt; 1, &quot;\x27&quot; =&gt; 1,
        &quot;\x28&quot; =&gt; 1, &quot;\x29&quot; =&gt; 1, &quot;\x2a&quot; =&gt; 1, &quot;\x2b&quot; =&gt; 1, &quot;\x2c&quot; =&gt; 1, &quot;\x2d&quot; =&gt; 1, &quot;\x2e&quot; =&gt; 1, &quot;\x2f&quot; =&gt; 1,
        &quot;\x30&quot; =&gt; 1, &quot;\x31&quot; =&gt; 1, &quot;\x32&quot; =&gt; 1, &quot;\x33&quot; =&gt; 1, &quot;\x34&quot; =&gt; 1, &quot;\x35&quot; =&gt; 1, &quot;\x36&quot; =&gt; 1, &quot;\x37&quot; =&gt; 1,
        &quot;\x38&quot; =&gt; 1, &quot;\x39&quot; =&gt; 1, &quot;\x3a&quot; =&gt; 1, &quot;\x3b&quot; =&gt; 1, &quot;\x3c&quot; =&gt; 1, &quot;\x3d&quot; =&gt; 1, &quot;\x3e&quot; =&gt; 1, &quot;\x3f&quot; =&gt; 1,
        &quot;\x40&quot; =&gt; 1, &quot;\x41&quot; =&gt; 1, &quot;\x42&quot; =&gt; 1, &quot;\x43&quot; =&gt; 1, &quot;\x44&quot; =&gt; 1, &quot;\x45&quot; =&gt; 1, &quot;\x46&quot; =&gt; 1, &quot;\x47&quot; =&gt; 1,
        &quot;\x48&quot; =&gt; 1, &quot;\x49&quot; =&gt; 1, &quot;\x4a&quot; =&gt; 1, &quot;\x4b&quot; =&gt; 1, &quot;\x4c&quot; =&gt; 1, &quot;\x4d&quot; =&gt; 1, &quot;\x4e&quot; =&gt; 1, &quot;\x4f&quot; =&gt; 1,
        &quot;\x50&quot; =&gt; 1, &quot;\x51&quot; =&gt; 1, &quot;\x52&quot; =&gt; 1, &quot;\x53&quot; =&gt; 1, &quot;\x54&quot; =&gt; 1, &quot;\x55&quot; =&gt; 1, &quot;\x56&quot; =&gt; 1, &quot;\x57&quot; =&gt; 1,
        &quot;\x58&quot; =&gt; 1, &quot;\x59&quot; =&gt; 1, &quot;\x5a&quot; =&gt; 1, &quot;\x5b&quot; =&gt; 1, &quot;\x5c&quot; =&gt; 1, &quot;\x5d&quot; =&gt; 1, &quot;\x5e&quot; =&gt; 1, &quot;\x5f&quot; =&gt; 1,
        &quot;\x60&quot; =&gt; 1, &quot;\x61&quot; =&gt; 1, &quot;\x62&quot; =&gt; 1, &quot;\x63&quot; =&gt; 1, &quot;\x64&quot; =&gt; 1, &quot;\x65&quot; =&gt; 1, &quot;\x66&quot; =&gt; 1, &quot;\x67&quot; =&gt; 1,
        &quot;\x68&quot; =&gt; 1, &quot;\x69&quot; =&gt; 1, &quot;\x6a&quot; =&gt; 1, &quot;\x6b&quot; =&gt; 1, &quot;\x6c&quot; =&gt; 1, &quot;\x6d&quot; =&gt; 1, &quot;\x6e&quot; =&gt; 1, &quot;\x6f&quot; =&gt; 1,
        &quot;\x70&quot; =&gt; 1, &quot;\x71&quot; =&gt; 1, &quot;\x72&quot; =&gt; 1, &quot;\x73&quot; =&gt; 1, &quot;\x74&quot; =&gt; 1, &quot;\x75&quot; =&gt; 1, &quot;\x76&quot; =&gt; 1, &quot;\x77&quot; =&gt; 1,
        &quot;\x78&quot; =&gt; 1, &quot;\x79&quot; =&gt; 1, &quot;\x7a&quot; =&gt; 1, &quot;\x7b&quot; =&gt; 1, &quot;\x7c&quot; =&gt; 1, &quot;\x7d&quot; =&gt; 1, &quot;\x7e&quot; =&gt; 1, &quot;\x7f&quot; =&gt; 1,
        &quot;\x80&quot; =&gt; 0, &quot;\x81&quot; =&gt; 0, &quot;\x82&quot; =&gt; 0, &quot;\x83&quot; =&gt; 0, &quot;\x84&quot; =&gt; 0, &quot;\x85&quot; =&gt; 0, &quot;\x86&quot; =&gt; 0, &quot;\x87&quot; =&gt; 0,
        &quot;\x88&quot; =&gt; 0, &quot;\x89&quot; =&gt; 0, &quot;\x8a&quot; =&gt; 0, &quot;\x8b&quot; =&gt; 0, &quot;\x8c&quot; =&gt; 0, &quot;\x8d&quot; =&gt; 0, &quot;\x8e&quot; =&gt; 0, &quot;\x8f&quot; =&gt; 0,
        &quot;\x90&quot; =&gt; 0, &quot;\x91&quot; =&gt; 0, &quot;\x92&quot; =&gt; 0, &quot;\x93&quot; =&gt; 0, &quot;\x94&quot; =&gt; 0, &quot;\x95&quot; =&gt; 0, &quot;\x96&quot; =&gt; 0, &quot;\x97&quot; =&gt; 0,
        &quot;\x98&quot; =&gt; 0, &quot;\x99&quot; =&gt; 0, &quot;\x9a&quot; =&gt; 0, &quot;\x9b&quot; =&gt; 0, &quot;\x9c&quot; =&gt; 0, &quot;\x9d&quot; =&gt; 0, &quot;\x9e&quot; =&gt; 0, &quot;\x9f&quot; =&gt; 0,
        &quot;\xa0&quot; =&gt; 0, &quot;\xa1&quot; =&gt; 0, &quot;\xa2&quot; =&gt; 0, &quot;\xa3&quot; =&gt; 0, &quot;\xa4&quot; =&gt; 0, &quot;\xa5&quot; =&gt; 0, &quot;\xa6&quot; =&gt; 0, &quot;\xa7&quot; =&gt; 0,
        &quot;\xa8&quot; =&gt; 0, &quot;\xa9&quot; =&gt; 0, &quot;\xaa&quot; =&gt; 0, &quot;\xab&quot; =&gt; 0, &quot;\xac&quot; =&gt; 0, &quot;\xad&quot; =&gt; 0, &quot;\xae&quot; =&gt; 0, &quot;\xaf&quot; =&gt; 0,
        &quot;\xb0&quot; =&gt; 0, &quot;\xb1&quot; =&gt; 0, &quot;\xb2&quot; =&gt; 0, &quot;\xb3&quot; =&gt; 0, &quot;\xb4&quot; =&gt; 0, &quot;\xb5&quot; =&gt; 0, &quot;\xb6&quot; =&gt; 0, &quot;\xb7&quot; =&gt; 0,
        &quot;\xb8&quot; =&gt; 0, &quot;\xb9&quot; =&gt; 0, &quot;\xba&quot; =&gt; 0, &quot;\xbb&quot; =&gt; 0, &quot;\xbc&quot; =&gt; 0, &quot;\xbd&quot; =&gt; 0, &quot;\xbe&quot; =&gt; 0, &quot;\xbf&quot; =&gt; 0,
        &quot;\xc0&quot; =&gt; 2, &quot;\xc1&quot; =&gt; 2, &quot;\xc2&quot; =&gt; 2, &quot;\xc3&quot; =&gt; 2, &quot;\xc4&quot; =&gt; 2, &quot;\xc5&quot; =&gt; 2, &quot;\xc6&quot; =&gt; 2, &quot;\xc7&quot; =&gt; 2,
        &quot;\xc8&quot; =&gt; 2, &quot;\xc9&quot; =&gt; 2, &quot;\xca&quot; =&gt; 2, &quot;\xcb&quot; =&gt; 2, &quot;\xcc&quot; =&gt; 2, &quot;\xcd&quot; =&gt; 2, &quot;\xce&quot; =&gt; 2, &quot;\xcf&quot; =&gt; 2,
        &quot;\xd0&quot; =&gt; 2, &quot;\xd1&quot; =&gt; 2, &quot;\xd2&quot; =&gt; 2, &quot;\xd3&quot; =&gt; 2, &quot;\xd4&quot; =&gt; 2, &quot;\xd5&quot; =&gt; 2, &quot;\xd6&quot; =&gt; 2, &quot;\xd7&quot; =&gt; 2,
        &quot;\xd8&quot; =&gt; 2, &quot;\xd9&quot; =&gt; 2, &quot;\xda&quot; =&gt; 2, &quot;\xdb&quot; =&gt; 2, &quot;\xdc&quot; =&gt; 2, &quot;\xdd&quot; =&gt; 2, &quot;\xde&quot; =&gt; 2, &quot;\xdf&quot; =&gt; 2,
        &quot;\xe0&quot; =&gt; 3, &quot;\xe1&quot; =&gt; 3, &quot;\xe2&quot; =&gt; 3, &quot;\xe3&quot; =&gt; 3, &quot;\xe4&quot; =&gt; 3, &quot;\xe5&quot; =&gt; 3, &quot;\xe6&quot; =&gt; 3, &quot;\xe7&quot; =&gt; 3,
        &quot;\xe8&quot; =&gt; 3, &quot;\xe9&quot; =&gt; 3, &quot;\xea&quot; =&gt; 3, &quot;\xeb&quot; =&gt; 3, &quot;\xec&quot; =&gt; 3, &quot;\xed&quot; =&gt; 3, &quot;\xee&quot; =&gt; 3, &quot;\xef&quot; =&gt; 3,
        &quot;\xf0&quot; =&gt; 4, &quot;\xf1&quot; =&gt; 4, &quot;\xf2&quot; =&gt; 4, &quot;\xf3&quot; =&gt; 4, &quot;\xf4&quot; =&gt; 4, &quot;\xf5&quot; =&gt; 4, &quot;\xf6&quot; =&gt; 4, &quot;\xf7&quot; =&gt; 4,
        &quot;\xf8&quot; =&gt; 5, &quot;\xf9&quot; =&gt; 5, &quot;\xfa&quot; =&gt; 5, &quot;\xfb&quot; =&gt; 5, &quot;\xfc&quot; =&gt; 6, &quot;\xfd&quot; =&gt; 6, &quot;\xfe&quot; =&gt; 0, &quot;\xff&quot; =&gt; 0,
    ];

    private $data = '';
    private $dataSize = 0;
    private $map = [];
    private $charCount = 0;
    private $currentPos = 0;
    private $fixedWidth = 0;

    /**
     * @param resource|string $input
     */
    public function __construct($input, ?string $charset = 'utf-8')
    {
        $charset = strtolower(trim($charset)) ?: 'utf-8';
        if ('utf-8' === $charset || 'utf8' === $charset) {
            $this-&gt;fixedWidth = 0;
            $this-&gt;map = ['p' =&gt; [], 'i' =&gt; []];
        } else {
            switch ($charset) {
                // 16 bits
                case 'ucs2':
                case 'ucs-2':
                case 'utf16':
                case 'utf-16':
                    $this-&gt;fixedWidth = 2;
                    break;

                    // 32 bits
                case 'ucs4':
                case 'ucs-4':
                case 'utf32':
                case 'utf-32':
                    $this-&gt;fixedWidth = 4;
                    break;

                    // 7-8 bit charsets: (us-)?ascii, (iso|iec)-?8859-?[0-9]+, windows-?125[0-9], cp-?[0-9]+, ansi, macintosh,
                //                   koi-?7, koi-?8-?.+, mik, (cork|t1), v?iscii
                    // and fallback
                default:
                    $this-&gt;fixedWidth = 1;
            }
        }
        if (\is_resource($input)) {
            $blocks = 16372;
            while (false !== $read = fread($input, $blocks)) {
                $this-&gt;write($read);
            }
        } else {
            $this-&gt;write($input);
        }
    }

    public function read(int $length): ?string
    {
        if ($this-&gt;currentPos &gt;= $this-&gt;charCount) {
            return null;
        }
        $length = ($this-&gt;currentPos + $length &gt; $this-&gt;charCount) ? $this-&gt;charCount - $this-&gt;currentPos : $length;
        if ($this-&gt;fixedWidth &gt; 0) {
            $len = $length * $this-&gt;fixedWidth;
            $ret = substr($this-&gt;data, $this-&gt;currentPos * $this-&gt;fixedWidth, $len);
            $this-&gt;currentPos += $length;
        } else {
            $end = $this-&gt;currentPos + $length;
            $end = $end &gt; $this-&gt;charCount ? $this-&gt;charCount : $end;
            $ret = '';
            $start = 0;
            if ($this-&gt;currentPos &gt; 0) {
                $start = $this-&gt;map['p'][$this-&gt;currentPos - 1];
            }
            $to = $start;
            for (; $this-&gt;currentPos &lt; $end; ++$this-&gt;currentPos) {
                if (isset($this-&gt;map['i'][$this-&gt;currentPos])) {
                    $ret .= substr($this-&gt;data, $start, $to - $start).'?';
                    $start = $this-&gt;map['p'][$this-&gt;currentPos];
                } else {
                    $to = $this-&gt;map['p'][$this-&gt;currentPos];
                }
            }
            $ret .= substr($this-&gt;data, $start, $to - $start);
        }

        return $ret;
    }

    public function readBytes(int $length): ?array
    {
        if (null !== $read = $this-&gt;read($length)) {
            return array_map('ord', str_split($read, 1));
        }

        return null;
    }

    public function setPointer(int $charOffset): void
    {
        if ($this-&gt;charCount &lt; $charOffset) {
            $charOffset = $this-&gt;charCount;
        }
        $this-&gt;currentPos = $charOffset;
    }

    public function write(string $chars): void
    {
        $ignored = '';
        $this-&gt;data .= $chars;
        if ($this-&gt;fixedWidth &gt; 0) {
            $strlen = \strlen($chars);
            $ignoredL = $strlen % $this-&gt;fixedWidth;
            $ignored = $ignoredL ? substr($chars, -$ignoredL) : '';
            $this-&gt;charCount += ($strlen - $ignoredL) / $this-&gt;fixedWidth;
        } else {
            $this-&gt;charCount += $this-&gt;getUtf8CharPositions($chars, $this-&gt;dataSize, $ignored);
        }
        $this-&gt;dataSize = \strlen($this-&gt;data) - \strlen($ignored);
    }

    private function getUtf8CharPositions(string $string, int $startOffset, string &amp;$ignoredChars): int
    {
        $strlen = \strlen($string);
        $charPos = \count($this-&gt;map['p']);
        $foundChars = 0;
        $invalid = false;
        for ($i = 0; $i &lt; $strlen; ++$i) {
            $char = $string[$i];
            $size = self::UTF8_LENGTH_MAP[$char];
            if (0 == $size) {
                /* char is invalid, we must wait for a resync */
                $invalid = true;
                continue;
            }

            if ($invalid) {
                /* We mark the chars as invalid and start a new char */
                $this-&gt;map['p'][$charPos + $foundChars] = $startOffset + $i;
                $this-&gt;map['i'][$charPos + $foundChars] = true;
                ++$foundChars;
                $invalid = false;
            }
            if (($i + $size) &gt; $strlen) {
                $ignoredChars = substr($string, $i);
                break;
            }
            for ($j = 1; $j &lt; $size; ++$j) {
                $char = $string[$i + $j];
                if ($char &gt; &quot;\x7F&quot; &amp;&amp; $char &lt; &quot;\xC0&quot;) {
                    // Valid - continue parsing
                } else {
                    /* char is invalid, we must wait for a resync */
                    $invalid = true;
                    continue 2;
                }
            }
            /* Ok we got a complete char here */
            $this-&gt;map['p'][$charPos + $foundChars] = $startOffset + $i + $size;
            $i += $j - 1;
            ++$foundChars;
        }

        return $foundChars;
    }
}
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