How to retrieve json serializer settings via DI (service collection) in asp netcore 3.1 mvc while using AddNewtonsoftJson

Question

I have an ASP MVC project using .netcore 3.1, where I am overriding serializer options as the following

services
.AddControllers()
.AddNewtonsoftJson(options =>
{
    options.SerializerSettings.DateTimeZoneHandling = DateTimeZoneHandling.RoundtripKind;
    options.SerializerSettings.NullValueHandling = NullValueHandling.Include;
    options.SerializerSettings.Converters.Add(new StringEnumConverter
    {
        NamingStrategy = new CamelCaseNamingStrategy(),
    });
})

This works fine whenever MVC is serialising data (request/response) for me. But now, in one of the Middlewares I need to serialise manually and return some data as a response, like:

public async Task Invoke(HttpContext context)
{
    try
    {
        await _next(context);
    }
    catch (Exception exception)
    {
        ... // removed for simplicity
        await context.Response.WriteAsync(JsonConvert.SerializeObject(errorResponse, _jsonSerializerSettings));
    }
}

Here I want to reuse existing settings for serialization. But old MvcJsonOptions are not available in .netcore 3.1 anymore (please correct if I am wrong). So how can I achieve this, without duplicating json serialization settings?

Answer 1

Here I want to reuse existing settings for serialization.

Since you've configured the NewtonsoftJson Options For Mvc within ConfigureServices() method, just inject a IOptions<MvcNewtonsoftJsonOptions> when you need it. For example, change your middleware to accept an argument of IOptions<MvcNewtonsoftJsonOptions>:

public class MyMiddleware
{
    private readonly RequestDelegate _next;
    private readonly JsonSerializerSettings _jsonSerializerSettings;

    public MyMiddleware(RequestDelegate next,IOptions<MvcNewtonsoftJsonOptions> jsonOptions)
    {
        // ... check null and throw
        this._next = next;
        this._jsonSerializerSettings = jsonOptions.Value.SerializerSettings;
    }

    public async Task Invoke(HttpContext context) 
    {
        try
        {
            await _next(context);
        }
        catch (Exception exception)
        {
            //... removed for simplicity
            await context.Response.WriteAsync(JsonConvert.SerializeObject(errorResponse, _jsonSerializerSettings));
        }
    }
}