Add MissingHeaders, it will be created in the HeaderSerializer, if the Registry cannot find the headers. It is a collection of missing Headers

Author: DanielBadura

src/Message/MissingHeaders.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Message;
+
+/**
+ * Collects all headers whose names could not be resolved to a registered class,
+ * e.g. because the header class was removed. It keeps the raw names and payloads
+ * so the data is preserved and can be written back without loss.
+ */
+final class MissingHeaders
+{
+    /** @param array<string, array<string, mixed>> $headers */
+    public function __construct(
+        public readonly array $headers,
+    ) {
+    }
+}

src/Message/Serializer/DefaultHeadersSerializer.php

@@ -4,7 +4,9 @@
 
 namespace Patchlevel\EventSourcing\Message\Serializer;
 
+use Patchlevel\EventSourcing\Message\MissingHeaders;
 use Patchlevel\EventSourcing\Metadata\Message\AttributeMessageHeaderRegistryFactory;
+use Patchlevel\EventSourcing\Metadata\Message\HeaderNameNotRegistered;
 use Patchlevel\EventSourcing\Metadata\Message\MessageHeaderRegistry;
 use Patchlevel\EventSourcing\Serializer\Encoder\Encoder;
 use Patchlevel\EventSourcing\Serializer\Encoder\JsonEncoder;
@@ -30,6 +32,14 @@ public function serialize(array $headers, array $options = []): string
     {
         $serializedHeaders = [];
         foreach ($headers as $header) {
+            if ($header instanceof MissingHeaders) {
+                foreach ($header->headers as $name => $payload) {
+                    $serializedHeaders[$name] = $payload;
+                }
+
+                continue;
+            }
+
             $serializedHeaders[$this->messageHeaderRegistry->headerName($header::class)] = $this->hydrator->extract($header);
         }
 
@@ -46,15 +56,24 @@ public function deserialize(string $string, array $options = []): array
         $serializedHeaders = $this->encoder->decode($string, $options);
 
         $headers = [];
+        $missingHeaders = [];
         foreach ($serializedHeaders as $headerName => $headerPayload) {
             if (!is_array($headerPayload)) {
                 throw new InvalidArgument('header payload must be an array');
             }
 
-            $headers[] = $this->hydrator->hydrate(
-                $this->messageHeaderRegistry->headerClass($headerName),
-                $headerPayload,
-            );
+            try {
+                $headers[] = $this->hydrator->hydrate(
+                    $this->messageHeaderRegistry->headerClass($headerName),
+                    $headerPayload,
+                );
+            } catch (HeaderNameNotRegistered) {
+                $missingHeaders[$headerName] = $headerPayload;
+            }
+        }
+
+        if ($missingHeaders !== []) {
+            $headers[] = new MissingHeaders($missingHeaders);
         }
 
         return $headers;

tests/Unit/Message/Serializer/DefaultHeadersSerializerTest.php

@@ -5,6 +5,7 @@
 namespace Patchlevel\EventSourcing\Tests\Unit\Message\Serializer;
 
 use DateTimeImmutable;
+use Patchlevel\EventSourcing\Message\MissingHeaders;
 use Patchlevel\EventSourcing\Message\Serializer\DefaultHeadersSerializer;
 use Patchlevel\EventSourcing\Metadata\Message\AttributeMessageHeaderRegistryFactory;
 use Patchlevel\EventSourcing\Serializer\Encoder\JsonEncoder;
@@ -60,4 +61,52 @@ public function testDeserialize(): void
             $deserializedMessage,
         );
     }
+
+    public function testDeserializeUnknownHeadersAsMissingHeaders(): void
+    {
+        $serializer = new DefaultHeadersSerializer(
+            (new AttributeMessageHeaderRegistryFactory())->create([
+                __DIR__ . '/../../Fixture',
+            ]),
+            new MetadataHydrator(),
+            new JsonEncoder(),
+        );
+
+        $deserializedMessage = $serializer->deserialize('{"streamName":{"streamName":"profile-1"},"removed":{"foo":"bar"},"alsoRemoved":{"baz":1}}');
+
+        self::assertEquals(
+            [
+                new StreamNameHeader('profile-1'),
+                new MissingHeaders([
+                    'removed' => ['foo' => 'bar'],
+                    'alsoRemoved' => ['baz' => 1],
+                ]),
+            ],
+            $deserializedMessage,
+        );
+    }
+
+    public function testSerializeMissingHeadersRoundTrip(): void
+    {
+        $serializer = new DefaultHeadersSerializer(
+            (new AttributeMessageHeaderRegistryFactory())->create([
+                __DIR__ . '/../../Fixture',
+            ]),
+            new MetadataHydrator(),
+            new JsonEncoder(),
+        );
+
+        $content = $serializer->serialize([
+            new StreamNameHeader('profile-1'),
+            new MissingHeaders([
+                'removed' => ['foo' => 'bar'],
+                'alsoRemoved' => ['baz' => 1],
+            ]),
+        ]);
+
+        self::assertEquals(
+            '{"streamName":{"streamName":"profile-1"},"removed":{"foo":"bar"},"alsoRemoved":{"baz":1}}',
+            $content,
+        );
+    }
 }