Protobuf serializer for Azure Cosmos DB

ProtobufCosmosSerializer.cs

using System;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Text;
using System.Text.Json;
using Google.Protobuf;
using Google.Protobuf.Reflection;
using Microsoft.Azure.Cosmos;

public class ProtobufCosmosSerializer : CosmosSerializer
{
    private readonly JsonParser _parser = new(JsonParser.Settings.Default.WithIgnoreUnknownFields(true));

    public override T FromStream<T>(Stream stream) {
        using (stream) {
            if (typeof(Stream).IsAssignableFrom(typeof(T))) {
                return (T)(object)stream;
            }

            var descriptor = GetDescriptor<T>();
            var document = JsonDocument.Parse(stream);

            if (document.RootElement.ValueKind == JsonValueKind.Array) {
                var size = document.RootElement.GetArrayLength();
                var result = Array.CreateInstance(typeof(T).GetElementType()!, size);

                for (var i = 0; i < size; i++) {
                    var message = _parser.Parse(document.RootElement[i].GetRawText(), descriptor);
                    result.SetValue(message, i);
                }
                return (T)(object)result;
            }

            using StreamReader reader = new(stream);
            // rewind stream to 0 because the document parser moved it to the end
            reader.BaseStream.Position = 0;
            return (T)_parser.Parse(reader, descriptor);
        }
    }

    public override Stream ToStream<T>(T input)
    {
        if (input is not IMessage) throw new Exception("input message must be 'IMessage'");

        MemoryStream streamPayload = new();
        using StreamWriter streamWriter = new(streamPayload, new UTF8Encoding(false, true), 1024, true);
        JsonFormatter.Default.Format((IMessage) input, streamWriter);

        streamWriter.Flush();
        streamPayload.Position = 0;
        return streamPayload;
    }
    
    private static MessageDescriptor GetDescriptor<T>() {
        var messageType = typeof(T).IsArray ? typeof(T).GetElementType()! : typeof(T);
        if (!messageType.IsAssignableTo(typeof(IMessage))) {
            throw new Exception($"requested type must be IMessage, found {messageType.Name}");
        }
        return (MessageDescriptor)messageType.GetProperty("Descriptor")!.GetValue(null)!;
    }
}