This library provides support for Google.Protobuf types to System.Text.Json.

By default classes generated from *.proto files don't work well with System.Text.Json. You can properly serialize and deserialize only very simple contracts (only scalar value types work properly). When your schema contains some more advanced structures like repeated fields, maps, oneofs, or optional fields the results are far from acceptable.

You may try to write a custom JsonConverter that will utilize JsonFormatter and JsonParser from Google.Protobuf package to do all the heavy lifting. Unfortunately, this solution falls short in terms of performance. This library provides high-performance and low-allocating types that serialize Google.Protobuf objects to JavaScript Object Notation (JSON) text and deserialize JSON text to Google.Protobuf objects.

Add Protobuf.System.Text.Json NuGet package to your project using dotnet CLI:

dotnet add package Protobuf.System.Text.Json

To enable Protobuf support you need to register it on JsonSerializerOptions:

var jsonSerializerOptions = new JsonSerializerOptions();
jsonSerializerOptions.PropertyNamingPolicy = new JsonLowerCaseNamingPolicy();
jsonSerializerOptions.AddProtobufSupport();

You need to pass the options each time you want to serialize:

var msg = new SimpleMessage
{
    DoubleProperty = 2.5d
};
var payload = JsonSerializer.Serialize(msg, options: jsonSerializerOptions);

or deserialize Google.Protobuf objects:

var deserialized = JsonSerializer.Deserialize<SimpleMessage>(payload, jsonSerializerOptions);

BenchmarkDotNet=v0.13.1, OS=macOS Monterey 12.3 (21E230) [Darwin 21.4.0]
Apple M1 Pro, 1 CPU, 10 logical and 10 physical cores
.NET SDK=6.0.101
  [Host]     : .NET 6.0.1 (6.0.121.56705), Arm64 RyuJIT
  DefaultJob : .NET 6.0.1 (6.0.121.56705), Arm64 RyuJIT

This project uses MIT licence. Long story short - you are more than welcome to use it anywhere you like, completely free of charge and without oppressive obligations.