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CharacterStream example

public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
    {
        $lines = [];
        $lineCount = 0;
        $lines[] = '';
        $currentLine = &$lines[$lineCount++];

        if (0 >= $maxLineLength) {
            $maxLineLength = 75;
        }

        $charStream = new CharacterStream($string, $charset);
        $thisLineLength = $maxLineLength - $firstLineOffset;

        while (null !== $char = $charStream->read(4)) {
            $encodedChar = rawurlencode($char);
            if ('' !== $currentLine && \strlen($currentLine.$encodedChar) > $thisLineLength) {
                $lines[] = '';
                $currentLine = &$lines[$lineCount++];
                $thisLineLength = $maxLineLength;
            }
            $currentLine .= $encodedChar;
        }

if ($maxLineLength > 76 || $maxLineLength <= 0) {
            $maxLineLength = 76;
        }

        $thisLineLength = $maxLineLength - $firstLineOffset;

        $lines = [];
        $lNo = 0;
        $lines[$lNo] = '';
        $currentLine = &$lines[$lNo++];
        $size = $lineLen = 0;
        $charStream = new CharacterStream($string, $charset);

        // Fetching more than 4 chars at one is slower, as is fetching fewer bytes         // Conveniently 4 chars is the UTF-8 safe number since UTF-8 has up to 6         // bytes per char and (6 * 4 * 3 = 72 chars per line) * =NN is 3 bytes         while (null !== $bytes = $charStream->readBytes(4)) {
            $enc = $this->encodeByteSequence($bytes, $size);

            $i = strpos($enc, '=0D=0A');
            $newLineLength = $lineLen + (false === $i ? $size : $i);

            if ($currentLine && $newLineLength >= $thisLineLength) {

namespace Symfony\Component\Mime\Tests;

use PHPUnit\Framework\TestCase;
use Symfony\Component\Mime\CharacterStream;

class CharacterStreamTest extends TestCase
{
    public function testReadCharactersAreInTact()
    {
        $stream = new CharacterStream(pack('C*', 0xD0, 0x94, 0xD0, 0xB6, 0xD0, 0xBE));
        $stream->write(pack('C*',
            0xD0, 0xBB,
            0xD1, 0x8E,
            0xD0, 0xB1,
            0xD1, 0x8B,
            0xD1, 0x85
        ));
        $this->assertSame(pack('C*', 0xD0, 0x94), $stream->read(1));
        $this->assertSame(pack('C*', 0xD0, 0xB6, 0xD0, 0xBE), $stream->read(2));
        $this->assertSame(pack('C*', 0xD0, 0xBB), $stream->read(1));
        $this->assertSame(pack('C*', 0xD1, 0x8E, 0xD0, 0xB1, 0xD1, 0x8B), $stream->read(3));