mbstring: Make encoding detection stricter

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.0.0] – unreleased
+
+- Mb: Make encoding detection stricter.
+
+
 ## [2.0.0] – 2023-03-07
 
 - Iconv: Fix warning on PHP 8.2 when passing `null` as source encoding.
@@ -23,5 +28,6 @@ The project has been revived and is now available under the name [`fossar/transc
 - Added Nix expression for easier development and sharing the environment with CI.
 - Switched to GitHub Actions for CI and added more PHP versions.
 
-[2.0.0]: https://github.com/fossar/transcoder/compare/1.0.1...v2.0.0
+[3.0.0]: https://github.com/fossar/transcoder/compare/v2.0.0...v3.0.0
+[2.0.0]: https://github.com/fossar/transcoder/compare/v1.0.1...v2.0.0
 [1.0.1]: https://github.com/fossar/transcoder/compare/1.0.0...v1.0.1

src/MbTranscoder.php

@@ -55,34 +55,31 @@ public function transcode(string $string, $from = null, ?string $to = null): str
             } else {
                 $this->assertSupported($from);
             }
+        } else {
+            $from = 'auto';
         }
 
         if ($to) {
             $this->assertSupported($to, false);
         }
 
-        $handleErrors = !$from || 'auto' === $from;
-        if ($handleErrors) {
-            set_error_handler(
-                function ($no, $warning) use ($string): void {
-                    throw new UndetectableEncodingException($string, $warning);
-                },
-                E_WARNING
-            );
+        if ($from === 'auto') {
+            $from = mb_detect_encoding($string, 'auto', true);
         }
 
-        try {
-            $result = mb_convert_encoding(
-                $string,
-                $to ?: $this->defaultEncoding,
-                $from ?: 'auto'
-            );
-        } finally {
-            if ($handleErrors) {
-                restore_error_handler();
-            }
+        if ($from === false) {
+            throw new UndetectableEncodingException($string, 'Unable to detect character encoding');
         }
 
+        $result = mb_convert_encoding(
+            $string,
+            $to ?: $this->defaultEncoding,
+            $from
+        );
+
+        // For PHPStan: We check the encoding is valid.
+        assert($result !== false);
+
         return $result;
     }
 

tests/MbTranscoderTest.php

@@ -55,7 +55,7 @@ public function testUndetectableEncoding(): void
         $this->expectException(\Ddeboer\Transcoder\Exception\UndetectableEncodingException::class);
         $this->expectExceptionMessage('is undetectable');
         $result = $this->transcoder->transcode(
-            '‘curly quotes make this incompatible with 1252’',
+            '‘Windows-1252 encodes curly quotes as 0x91 and 0x92, which are indistinguishable from any other single-byte encoding’',
             null,
             'windows-1252'
         );