ASP.NET Core 3.0 / Swashbuckle : restrict responses content types globally

Question

This is basically the same question as How do I set or remove the Default Response Content Type Using SwashBuckle, but for .NET Core 3.0

By default in .NET Core 3.0, you configure a web api with services.AddControllers() and then you configure swagger with swashbuckle with services.AddSwaggerGen() + app.UseSwagger()

That is working fine, however the swagger.json contains multiple response content types for every operation (text/plain + application/json + text/json)

I know I can restrict these response content types by adding [Produces] and [Consumes] to my operations, but I'd like to avoid that for each and every operation (i.e I want to do that globally)

Please note that I preferably want to use System.Text.Json but if you have a solution that works only with Newtonsoft.JSON then it's better than nothing ;)

Answer 1

Swashbuckle.AspNetCore.SwaggerGen 5.0 uses the OpenApiOperation to describe API operations.

using System.Collections.Generic;
using Microsoft.OpenApi.Models;
using Swashbuckle.AspNetCore.SwaggerGen;

public class AssignContentTypeFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if (operation.Responses.ContainsKey("200"))
        {
            operation.Responses.Clear();
        }

        var data = new OpenApiResponse
        {
            Description = "Ok",
            Content = new Dictionary<string, OpenApiMediaType>
            {
                ["application/json"] = new OpenApiMediaType(),
                ["application/xml"] = new OpenApiMediaType(),
            }
        };

        operation.Responses.Add("200", data);
    }
}

In Startup.cs

        services.AddSwaggerGen(q =>
        {
            q.SwaggerDoc("v1", new OpenApiInfo
            {
                Title = "mytitle",
                Version = "v1",
            });
            q.OperationFilter<AssignContentTypeFilter>();  
        });