好文！学习了

• 添加 named json settings

builder.Services.AddControllers().AddJsonOptions("old", options => {});

• 添加 endpoint metadata

public class JsonSettingsNameAttribute : Attribute { }

[JsonSettingsName("old")]
public class OldApiController : ControllerBase {}
}

• 读取 endpoint metadata

public static string? GetJsonSettingsName(this HttpContext context)
{
    return context.GetEndpoint()
        ?.Metadata
        .GetMetadata<JsonSettingsNameAttribute>()
        ?.Name;
}

• 实现 SpecificSystemTextJsonInputFormatter 重写 CanRead

public override bool CanRead(InputFormatterContext context)
{
    if (context.HttpContext.GetJsonSettingsName() != SettingsName)
        return false;

    return base.CanRead(context);
}

• 实现 SpecificSystemTextJsonOutputFormatter 重写 CanWriteResult

public override bool CanWriteResult(OutputFormatterCanWriteContext context)
{
    if (context.HttpContext.GetJsonSettingsName() != SettingsName)
        return false;
        
    return base.CanWriteResult(context);
}

• 实现 ConfigureMvcJsonOptions

public class ConfigureMvcJsonOptions : IConfigureOptions<MvcOptions> {}

• 注册 ConfigureMvcJsonOptions

builder.Services.AddSingleton<IConfigureOptions<MvcOptions>>(sp =>
{
    var options = sp.GetRequiredService<IOptionsMonitor<JsonOptions>>();
    var loggerFactory = sp.GetRequiredService<ILoggerFactory>();
    return new ConfigureMvcJsonOptions(settingsName, options, loggerFactory);
});