feat: support custom encoders in mime parts

Author: KDederichs

src/Symfony/Component/Mime/Part/TextPart.php

@@ -23,6 +23,8 @@
  */
 class TextPart extends AbstractPart
 {
+    private const DEFAULT_ENCODERS = ['quoted-printable', 'base64', '8bit'];
+
     /** @internal */
     protected Headers $_headers;
 
@@ -63,8 +65,8 @@ public function __construct($body, ?string $charset = 'utf-8', string $subtype =
         if (null === $encoding) {
             $this->encoding = $this->chooseEncoding();
         } else {
-            if ('quoted-printable' !== $encoding && 'base64' !== $encoding && '8bit' !== $encoding) {
-                throw new InvalidArgumentException(sprintf('The encoding must be one of "quoted-printable", "base64", or "8bit" ("%s" given).', $encoding));
+            if (!\in_array($encoding, self::DEFAULT_ENCODERS, true) && !\array_key_exists($encoding, self::$encoders)) {
+                throw new InvalidArgumentException(sprintf('The encoding must be one of "%s" ("%s" given).', implode('", "', array_unique(array_merge(self::DEFAULT_ENCODERS, array_keys(self::$encoders)))), $encoding));
             }
             $this->encoding = $encoding;
         }
@@ -207,7 +209,20 @@ private function getEncoder(): ContentEncoderInterface
             return self::$encoders[$this->encoding] ??= new QpContentEncoder();
         }
 
-        return self::$encoders[$this->encoding] ??= new Base64ContentEncoder();
+        if ('base64' === $this->encoding) {
+            return self::$encoders[$this->encoding] ??= new Base64ContentEncoder();
+        }
+
+        return self::$encoders[$this->encoding];
+    }
+
+    public static function addEncoder(string $name, ContentEncoderInterface $encoder): void
+    {
+        if (\in_array($name, self::DEFAULT_ENCODERS, true)) {
+            throw new InvalidArgumentException('You are not allowed to change the default encoders ("quoted-printable","base64","8bit"). If you want to modify their behaviour please register and use a new encoder.');
+        }
+
+        self::$encoders[$name] = $encoder;
     }
 
     private function chooseEncoding(): string

src/Symfony/Component/Mime/Tests/Part/TextPartTest.php

@@ -12,6 +12,9 @@
 namespace Symfony\Component\Mime\Tests\Part;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mime\Encoder\ContentEncoderInterface;
+use Symfony\Component\Mime\Exception\InvalidArgumentException;
+use Symfony\Component\Mime\Exception\RuntimeException;
 use Symfony\Component\Mime\Header\Headers;
 use Symfony\Component\Mime\Header\ParameterizedHeader;
 use Symfony\Component\Mime\Header\UnstructuredHeader;
@@ -87,6 +90,57 @@ public function testEncoding()
         ), $p->getPreparedHeaders());
     }
 
+    public function testCustomEncoderNeedsToRegisterFirst()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('The encoding must be one of "quoted-printable", "base64", "8bit", "exception_test" ("upper_encoder" given).');
+        TextPart::addEncoder('exception_test', $this->createMock(ContentEncoderInterface::class));
+        new TextPart('content', 'utf-8', 'plain', 'upper_encoder');
+    }
+
+    public function testOverwriteDefaultEncoder()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('You are not allowed to change the default encoders ("quoted-printable","base64","8bit"). If you want to modify their behaviour please register and use a new encoder.');
+        TextPart::addEncoder('8bit', $this->createMock(ContentEncoderInterface::class));
+    }
+
+    public function testCustomEncoding()
+    {
+        TextPart::addEncoder('upper_encoder', new class() implements ContentEncoderInterface {
+            public function encodeByteStream($stream, int $maxLineLength = 0): iterable
+            {
+                $filter = stream_filter_append($stream, 'string.toupper', \STREAM_FILTER_READ);
+                if (!\is_resource($filter)) {
+                    throw new RuntimeException('Unable to set the upper content encoder to the filter.');
+                }
+
+                while (!feof($stream)) {
+                    yield fread($stream, 16372);
+                }
+                stream_filter_remove($filter);
+            }
+
+            public function getName(): string
+            {
+                return 'upper_encoder';
+            }
+
+            public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+            {
+                return strtoupper($string);
+            }
+        });
+
+        $p = new TextPart('content', 'utf-8', 'plain', 'upper_encoder');
+        $this->assertEquals('CONTENT', $p->bodyToString());
+        $this->assertEquals('CONTENT', implode('', iterator_to_array($p->bodyToIterable())));
+        $this->assertEquals(new Headers(
+            new ParameterizedHeader('Content-Type', 'text/plain', ['charset' => 'utf-8']),
+            new UnstructuredHeader('Content-Transfer-Encoding', 'upper_encoder')
+        ), $p->getPreparedHeaders());
+    }
+
     public function testSerialize()
     {
         $r = fopen('php://memory', 'r+', false);