Sniff Avro payloads in legacy serializer

Author: durable-workflow-ops

src/Serializers/Serializer.php

@@ -191,6 +191,10 @@ private static function legacyUnserializeClass(string $blob): string
             return Base64::class;
         }
 
+        if (self::looksLikeAvro($blob)) {
+            return Avro::class;
+        }
+
         // JSON blobs always start with "{", "[", a digit, quote, minus, "t"/"f"/"n".
         // PHP-serialized-closure blobs start with "O:".
         if ($blob !== '' && $blob[0] !== 'O' && self::looksLikeJson($blob)) {
@@ -211,6 +215,15 @@ private static function looksLikeJson(string $blob): bool
         }
         return in_array($blob, ['true', 'false', 'null'], true);
     }
+
+    private static function looksLikeAvro(string $blob): bool
+    {
+        $bytes = base64_decode($blob, true);
+
+        return $bytes !== false
+            && $bytes !== ''
+            && in_array($bytes[0], [Avro::PREFIX_GENERIC_WRAPPER, Avro::PREFIX_TYPED_SCHEMA], true);
+    }
 }
 
 /**

tests/Unit/Serializers/SerializeTest.php

@@ -65,6 +65,46 @@ public function testSerializableReturnsFalseForClosure(): void
         }));
     }
 
+    public function testLegacyUnserializeSniffsAvroPayload(): void
+    {
+        config([
+            'workflows.serializer' => 'avro',
+        ]);
+
+        $serialized = Serializer::serialize([
+            'message' => 'hello',
+            'count' => 2,
+        ]);
+
+        config([
+            'workflows.serializer' => Y::class,
+        ]);
+
+        $this->assertSame([
+            'message' => 'hello',
+            'count' => 2,
+        ], Serializer::unserialize($serialized));
+    }
+
+    public function testLegacyYPayloadStillWinsOverAvroDefault(): void
+    {
+        config([
+            'workflows.serializer' => Y::class,
+        ]);
+
+        $serialized = Serializer::serialize([
+            'legacy' => true,
+        ]);
+
+        config([
+            'workflows.serializer' => 'avro',
+        ]);
+
+        $this->assertSame([
+            'legacy' => true,
+        ], Serializer::unserialize($serialized));
+    }
+
     private function testSerializeUnserialize($data, $serializer, $unserializer): void
     {
         config([