@Nullable
    private static SerializationFormat resolveSerializationFormat(HttpRequest req) {
        final MediaType contentType = req.contentType();
        if (contentType == null) {
            return null;
        }
        for (SerializationFormat format : SUPPORTED_SERIALIZATION_FORMATS) {
            if (format.isAccepted(contentType)) {
                return format;
            }
        }
        return null;
    }
Returns an unframed response message to return to the client, given an unframed request message. It is
expected that the implementation has the logic to know how to parse the request and serialize a response
into {@link ByteBuf}. The returned {@link ByteBuf} will be framed and returned to the client.
grpc-protocol/src/main/java/com/linecorp/armeria/server/grpc/protocol/AbstractUnsafeUnaryGrpcService.java