getContentTypeHeader example

$context = $this->context;
        /** @var SerializerStamp|null $serializerStamp */
        if ($serializerStamp = $envelope->last(SerializerStamp::class)) {
            $context = $serializerStamp->getContext() + $context;
        }

        /** @var SerializedMessageStamp|null $serializedMessageStamp */
        $serializedMessageStamp = $envelope->last(SerializedMessageStamp::class);

        $envelope = $envelope->withoutStampsOfType(NonSendableStampInterface::class);

        $headers = ['type' => $envelope->getMessage()::class] + $this->encodeStamps($envelope) + $this->getContentTypeHeader();

        return [
            'body' => $serializedMessageStamp
                ? $serializedMessageStamp->getSerializedMessage()
                : $this->serializer->serialize($envelope->getMessage(), $this->format, $context),
            'headers' => $headers,
        ];
    }

    private function decodeStamps(array $encodedEnvelope): array
    {