Build modified streamline images

The official image from streamline does not currently work for the arm64
platform. As a temporary measure, the source code and docker build scripts
have been lifted from the official images and are used to build locally.

Some additional modifications are made to reduce overall image size, these
are documented in docker/README.md

docker/streamline-src/vendor/symfony/mime/Encoder/AddressEncoderInterface.php

@@ -0,0 +1,28 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+use Symfony\Component\Mime\Exception\AddressEncoderException;
+
+/**
+ * @author Christian Schmidt
+ */
+interface AddressEncoderInterface
+{
+    /**
+     * Encodes an email address.
+     *
+     * @throws AddressEncoderException if the email cannot be represented in
+     *                                 the encoding implemented by this class
+     */
+    public function encodeString(string $address): string;
+}

docker/streamline-src/vendor/symfony/mime/Encoder/Base64ContentEncoder.php

@@ -0,0 +1,45 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+use Symfony\Component\Mime\Exception\RuntimeException;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+final class Base64ContentEncoder extends Base64Encoder implements ContentEncoderInterface
+{
+    public function encodeByteStream($stream, int $maxLineLength = 0): iterable
+    {
+        if (!\is_resource($stream)) {
+            throw new \TypeError(sprintf('Method "%s" takes a stream as a first argument.', __METHOD__));
+        }
+
+        $filter = stream_filter_append($stream, 'convert.base64-encode', \STREAM_FILTER_READ, [
+            'line-length' => 0 >= $maxLineLength || 76 < $maxLineLength ? 76 : $maxLineLength,
+            'line-break-chars' => "\r\n",
+        ]);
+        if (!\is_resource($filter)) {
+            throw new RuntimeException('Unable to set the base64 content encoder to the filter.');
+        }
+
+        while (!feof($stream)) {
+            yield fread($stream, 16372);
+        }
+        stream_filter_remove($filter);
+    }
+
+    public function getName(): string
+    {
+        return 'base64';
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/Base64Encoder.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+class Base64Encoder implements EncoderInterface
+{
+    /**
+     * Takes an unencoded string and produces a Base64 encoded string from it.
+     *
+     * Base64 encoded strings have a maximum line length of 76 characters.
+     * If the first line needs to be shorter, indicate the difference with
+     * $firstLineOffset.
+     */
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        if (0 >= $maxLineLength || 76 < $maxLineLength) {
+            $maxLineLength = 76;
+        }
+
+        $encodedString = base64_encode($string);
+        $firstLine = '';
+        if (0 !== $firstLineOffset) {
+            $firstLine = substr($encodedString, 0, $maxLineLength - $firstLineOffset)."\r\n";
+            $encodedString = substr($encodedString, $maxLineLength - $firstLineOffset);
+        }
+
+        return $firstLine.trim(chunk_split($encodedString, $maxLineLength, "\r\n"));
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/Base64MimeHeaderEncoder.php

@@ -0,0 +1,43 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+final class Base64MimeHeaderEncoder extends Base64Encoder implements MimeHeaderEncoderInterface
+{
+    public function getName(): string
+    {
+        return 'B';
+    }
+
+    /**
+     * Takes an unencoded string and produces a Base64 encoded string from it.
+     *
+     * If the charset is iso-2022-jp, it uses mb_encode_mimeheader instead of
+     * default encodeString, otherwise pass to the parent method.
+     */
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        if ('iso-2022-jp' === strtolower($charset)) {
+            $old = mb_internal_encoding();
+            mb_internal_encoding('utf-8');
+            $newstring = mb_encode_mimeheader($string, 'iso-2022-jp', $this->getName(), "\r\n");
+            mb_internal_encoding($old);
+
+            return $newstring;
+        }
+
+        return parent::encodeString($string, $charset, $firstLineOffset, $maxLineLength);
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/ContentEncoderInterface.php

@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+interface ContentEncoderInterface extends EncoderInterface
+{
+    /**
+     * Encodes the stream to a Generator.
+     *
+     * @param resource $stream
+     */
+    public function encodeByteStream($stream, int $maxLineLength = 0): iterable;
+
+    /**
+     * Gets the MIME name of this content encoding scheme.
+     */
+    public function getName(): string;
+}

docker/streamline-src/vendor/symfony/mime/Encoder/EightBitContentEncoder.php

@@ -0,0 +1,35 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+final class EightBitContentEncoder implements ContentEncoderInterface
+{
+    public function encodeByteStream($stream, int $maxLineLength = 0): iterable
+    {
+        while (!feof($stream)) {
+            yield fread($stream, 16372);
+        }
+    }
+
+    public function getName(): string
+    {
+        return '8bit';
+    }
+
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        return $string;
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/EncoderInterface.php

@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+interface EncoderInterface
+{
+    /**
+     * Encode a given string to produce an encoded string.
+     *
+     * @param int $firstLineOffset if first line needs to be shorter
+     * @param int $maxLineLength   - 0 indicates the default length for this encoding
+     */
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string;
+}

docker/streamline-src/vendor/symfony/mime/Encoder/IdnAddressEncoder.php

@@ -0,0 +1,44 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * An IDN email address encoder.
+ *
+ * Encodes the domain part of an address using IDN. This is compatible will all
+ * SMTP servers.
+ *
+ * Note: It leaves the local part as is. In case there are non-ASCII characters
+ * in the local part then it depends on the SMTP Server if this is supported.
+ *
+ * @author Christian Schmidt
+ */
+final class IdnAddressEncoder implements AddressEncoderInterface
+{
+    /**
+     * Encodes the domain part of an address using IDN.
+     */
+    public function encodeString(string $address): string
+    {
+        $i = strrpos($address, '@');
+        if (false !== $i) {
+            $local = substr($address, 0, $i);
+            $domain = substr($address, $i + 1);
+
+            if (preg_match('/[^\x00-\x7F]/', $domain)) {
+                $address = sprintf('%s@%s', $local, idn_to_ascii($domain, \IDNA_DEFAULT | \IDNA_USE_STD3_RULES | \IDNA_CHECK_BIDI | \IDNA_CHECK_CONTEXTJ | \IDNA_NONTRANSITIONAL_TO_ASCII, \INTL_IDNA_VARIANT_UTS46));
+            }
+        }
+
+        return $address;
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/MimeHeaderEncoderInterface.php

@@ -0,0 +1,23 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+interface MimeHeaderEncoderInterface
+{
+    /**
+     * Get the MIME name of this content encoding scheme.
+     */
+    public function getName(): string;
+}

docker/streamline-src/vendor/symfony/mime/Encoder/QpContentEncoder.php

@@ -0,0 +1,55 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Lars Strojny
+ */
+final class QpContentEncoder implements ContentEncoderInterface
+{
+    public function encodeByteStream($stream, int $maxLineLength = 0): iterable
+    {
+        if (!\is_resource($stream)) {
+            throw new \TypeError(sprintf('Method "%s" takes a stream as a first argument.', __METHOD__));
+        }
+
+        // we don't use PHP stream filters here as the content should be small enough
+        yield $this->encodeString(stream_get_contents($stream), 'utf-8', 0, $maxLineLength);
+    }
+
+    public function getName(): string
+    {
+        return 'quoted-printable';
+    }
+
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        return $this->standardize(quoted_printable_encode($string));
+    }
+
+    /**
+     * Make sure CRLF is correct and HT/SPACE are in valid places.
+     */
+    private function standardize(string $string): string
+    {
+        // transform CR or LF to CRLF
+        $string = preg_replace('~=0D(?!=0A)|(?<!=0D)=0A~', '=0D=0A', $string);
+        // transform =0D=0A to CRLF
+        $string = str_replace(["\t=0D=0A", ' =0D=0A', '=0D=0A'], ["=09\r\n", "=20\r\n", "\r\n"], $string);
+
+        return match (\ord(substr($string, -1))) {
+            0x09 => substr_replace($string, '=09', -1),
+            0x20 => substr_replace($string, '=20', -1),
+            default => $string,
+        };
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/QpEncoder.php

@@ -0,0 +1,192 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+use Symfony\Component\Mime\CharacterStream;
+
+/**
+ * @author Chris Corbyn
+ */
+class QpEncoder implements EncoderInterface
+{
+    /**
+     * Pre-computed QP for HUGE optimization.
+     */
+    private const QP_MAP = [
+        0 => '=00', 1 => '=01', 2 => '=02', 3 => '=03', 4 => '=04',
+        5 => '=05', 6 => '=06', 7 => '=07', 8 => '=08', 9 => '=09',
+        10 => '=0A', 11 => '=0B', 12 => '=0C', 13 => '=0D', 14 => '=0E',
+        15 => '=0F', 16 => '=10', 17 => '=11', 18 => '=12', 19 => '=13',
+        20 => '=14', 21 => '=15', 22 => '=16', 23 => '=17', 24 => '=18',
+        25 => '=19', 26 => '=1A', 27 => '=1B', 28 => '=1C', 29 => '=1D',
+        30 => '=1E', 31 => '=1F', 32 => '=20', 33 => '=21', 34 => '=22',
+        35 => '=23', 36 => '=24', 37 => '=25', 38 => '=26', 39 => '=27',
+        40 => '=28', 41 => '=29', 42 => '=2A', 43 => '=2B', 44 => '=2C',
+        45 => '=2D', 46 => '=2E', 47 => '=2F', 48 => '=30', 49 => '=31',
+        50 => '=32', 51 => '=33', 52 => '=34', 53 => '=35', 54 => '=36',
+        55 => '=37', 56 => '=38', 57 => '=39', 58 => '=3A', 59 => '=3B',
+        60 => '=3C', 61 => '=3D', 62 => '=3E', 63 => '=3F', 64 => '=40',
+        65 => '=41', 66 => '=42', 67 => '=43', 68 => '=44', 69 => '=45',
+        70 => '=46', 71 => '=47', 72 => '=48', 73 => '=49', 74 => '=4A',
+        75 => '=4B', 76 => '=4C', 77 => '=4D', 78 => '=4E', 79 => '=4F',
+        80 => '=50', 81 => '=51', 82 => '=52', 83 => '=53', 84 => '=54',
+        85 => '=55', 86 => '=56', 87 => '=57', 88 => '=58', 89 => '=59',
+        90 => '=5A', 91 => '=5B', 92 => '=5C', 93 => '=5D', 94 => '=5E',
+        95 => '=5F', 96 => '=60', 97 => '=61', 98 => '=62', 99 => '=63',
+        100 => '=64', 101 => '=65', 102 => '=66', 103 => '=67', 104 => '=68',
+        105 => '=69', 106 => '=6A', 107 => '=6B', 108 => '=6C', 109 => '=6D',
+        110 => '=6E', 111 => '=6F', 112 => '=70', 113 => '=71', 114 => '=72',
+        115 => '=73', 116 => '=74', 117 => '=75', 118 => '=76', 119 => '=77',
+        120 => '=78', 121 => '=79', 122 => '=7A', 123 => '=7B', 124 => '=7C',
+        125 => '=7D', 126 => '=7E', 127 => '=7F', 128 => '=80', 129 => '=81',
+        130 => '=82', 131 => '=83', 132 => '=84', 133 => '=85', 134 => '=86',
+        135 => '=87', 136 => '=88', 137 => '=89', 138 => '=8A', 139 => '=8B',
+        140 => '=8C', 141 => '=8D', 142 => '=8E', 143 => '=8F', 144 => '=90',
+        145 => '=91', 146 => '=92', 147 => '=93', 148 => '=94', 149 => '=95',
+        150 => '=96', 151 => '=97', 152 => '=98', 153 => '=99', 154 => '=9A',
+        155 => '=9B', 156 => '=9C', 157 => '=9D', 158 => '=9E', 159 => '=9F',
+        160 => '=A0', 161 => '=A1', 162 => '=A2', 163 => '=A3', 164 => '=A4',
+        165 => '=A5', 166 => '=A6', 167 => '=A7', 168 => '=A8', 169 => '=A9',
+        170 => '=AA', 171 => '=AB', 172 => '=AC', 173 => '=AD', 174 => '=AE',
+        175 => '=AF', 176 => '=B0', 177 => '=B1', 178 => '=B2', 179 => '=B3',
+        180 => '=B4', 181 => '=B5', 182 => '=B6', 183 => '=B7', 184 => '=B8',
+        185 => '=B9', 186 => '=BA', 187 => '=BB', 188 => '=BC', 189 => '=BD',
+        190 => '=BE', 191 => '=BF', 192 => '=C0', 193 => '=C1', 194 => '=C2',
+        195 => '=C3', 196 => '=C4', 197 => '=C5', 198 => '=C6', 199 => '=C7',
+        200 => '=C8', 201 => '=C9', 202 => '=CA', 203 => '=CB', 204 => '=CC',
+        205 => '=CD', 206 => '=CE', 207 => '=CF', 208 => '=D0', 209 => '=D1',
+        210 => '=D2', 211 => '=D3', 212 => '=D4', 213 => '=D5', 214 => '=D6',
+        215 => '=D7', 216 => '=D8', 217 => '=D9', 218 => '=DA', 219 => '=DB',
+        220 => '=DC', 221 => '=DD', 222 => '=DE', 223 => '=DF', 224 => '=E0',
+        225 => '=E1', 226 => '=E2', 227 => '=E3', 228 => '=E4', 229 => '=E5',
+        230 => '=E6', 231 => '=E7', 232 => '=E8', 233 => '=E9', 234 => '=EA',
+        235 => '=EB', 236 => '=EC', 237 => '=ED', 238 => '=EE', 239 => '=EF',
+        240 => '=F0', 241 => '=F1', 242 => '=F2', 243 => '=F3', 244 => '=F4',
+        245 => '=F5', 246 => '=F6', 247 => '=F7', 248 => '=F8', 249 => '=F9',
+        250 => '=FA', 251 => '=FB', 252 => '=FC', 253 => '=FD', 254 => '=FE',
+        255 => '=FF',
+    ];
+
+    private static array $safeMapShare = [];
+
+    /**
+     * A map of non-encoded ascii characters.
+     *
+     * @var string[]
+     *
+     * @internal
+     */
+    protected array $safeMap = [];
+
+    public function __construct()
+    {
+        $id = static::class;
+        if (!isset(self::$safeMapShare[$id])) {
+            $this->initSafeMap();
+            self::$safeMapShare[$id] = $this->safeMap;
+        } else {
+            $this->safeMap = self::$safeMapShare[$id];
+        }
+    }
+
+    protected function initSafeMap(): void
+    {
+        foreach (array_merge([0x09, 0x20], range(0x21, 0x3C), range(0x3E, 0x7E)) as $byte) {
+            $this->safeMap[$byte] = \chr($byte);
+        }
+    }
+
+    /**
+     * Takes an unencoded string and produces a QP encoded string from it.
+     *
+     * QP encoded strings have a maximum line length of 76 characters.
+     * If the first line needs to be shorter, indicate the difference with
+     * $firstLineOffset.
+     */
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        if ($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) {
+                $lines[$lNo] = '';
+                $currentLine = &$lines[$lNo++];
+                $thisLineLength = $maxLineLength;
+                $lineLen = 0;
+            }
+
+            $currentLine .= $enc;
+
+            if (false === $i) {
+                $lineLen += $size;
+            } else {
+                // 6 is the length of '=0D=0A'.
+                $lineLen = $size - strrpos($enc, '=0D=0A') - 6;
+            }
+        }
+
+        return $this->standardize(implode("=\r\n", $lines));
+    }
+
+    /**
+     * Encode the given byte array into a verbatim QP form.
+     */
+    private function encodeByteSequence(array $bytes, int &$size): string
+    {
+        $ret = '';
+        $size = 0;
+        foreach ($bytes as $b) {
+            if (isset($this->safeMap[$b])) {
+                $ret .= $this->safeMap[$b];
+                ++$size;
+            } else {
+                $ret .= self::QP_MAP[$b];
+                $size += 3;
+            }
+        }
+
+        return $ret;
+    }
+
+    /**
+     * Make sure CRLF is correct and HT/SPACE are in valid places.
+     */
+    private function standardize(string $string): string
+    {
+        $string = str_replace(["\t=0D=0A", ' =0D=0A', '=0D=0A'], ["=09\r\n", "=20\r\n", "\r\n"], $string);
+
+        return match ($end = \ord(substr($string, -1))) {
+            0x09,
+            0x20 => substr_replace($string, self::QP_MAP[$end], -1),
+            default => $string,
+        };
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/QpMimeHeaderEncoder.php

@@ -0,0 +1,40 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+final class QpMimeHeaderEncoder extends QpEncoder implements MimeHeaderEncoderInterface
+{
+    protected function initSafeMap(): void
+    {
+        foreach (array_merge(
+            range(0x61, 0x7A), range(0x41, 0x5A),
+            range(0x30, 0x39), [0x20, 0x21, 0x2A, 0x2B, 0x2D, 0x2F]
+        ) as $byte) {
+            $this->safeMap[$byte] = \chr($byte);
+        }
+    }
+
+    public function getName(): string
+    {
+        return 'Q';
+    }
+
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        return str_replace([' ', '=20', "=\r\n"], ['_', '_', "\r\n"],
+            parent::encodeString($string, $charset, $firstLineOffset, $maxLineLength)
+        );
+    }
+}

docker/streamline-src/vendor/symfony/mime/Encoder/Rfc2231Encoder.php

@@ -0,0 +1,50 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+use Symfony\Component\Mime\CharacterStream;
+
+/**
+ * @author Chris Corbyn
+ */
+final class Rfc2231Encoder implements EncoderInterface
+{
+    /**
+     * Takes an unencoded string and produces a string encoded according to RFC 2231 from it.
+     */
+    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;
+        }
+
+        return implode("\r\n", $lines);
+    }
+}