Handling json pretty print parameter in ASP.NET API application

Question

This question is almost verbatim, which is asked in https://stackoverflow.com/a/167012/ ...

But I would like to do it in ASP.NET Core Api. I plan to implement it as a header, and not in the query string. I am struggling with a Json SerializerSettings change set in the ConfigureServices method.

services.AddMvc(config =>
        {
            config.Filters.Add(new WebApiRequireHttps());                
        })
            .AddJsonOptions(options =>
            {
                options.SerializerSettings.Formatting = Formatting.Indented;
            });

What I'm trying to accomplish is changing the Serializer settings to use Formatting.None when I set the header, for example X-MyApi-Pretty: false.

I am trying to create my own ActionFIlterAttribute, as in the above question. Microsoft.AspNetCore.Mvc.Filters uses an ActionExecutedContext, which does not seem to have the obvious equivalent of ActionContext.RequestContext.Configuration.Formatters.JsonFormatter.

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Answer 1

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public class NamedFormatJsonOutputFormatter : JsonOutputFormatter
{
    private readonly IDictionary<string, JsonSerializerSettings> _customJsonSettings;
    private readonly IDictionary<string, JsonSerializer> _customSerializers;
    public NamedFormatJsonOutputFormatter(JsonSerializerSettings defaultSerializerSettings, IDictionary<string, JsonSerializerSettings> customJsonSettings, ArrayPool<char> charPool) : base (defaultSerializerSettings, charPool)
    {
        _customJsonSettings = customJsonSettings;
        _customSerializers = new Dictionary<string, JsonSerializer>();
    }
    protected virtual JsonSerializer CreateCustomJsonSerializer(string serializerName)
    {
        JsonSerializer outputSerializer;
        var exists = _customSerializers.TryGetValue(serializerName, out outputSerializer);
        if (!exists)
        {
            var settings = _customJsonSettings[serializerName];
            outputSerializer = JsonSerializer.Create(settings);
            _customSerializers[serializerName] = outputSerializer;
        }
        return _customSerializers[serializerName];
    }
    public void WriteObjectWithNamedSerializer(TextWriter writer, string serializerName, object value)
    {
        if (writer == null)
        {
            throw new ArgumentNullException(nameof(writer));
        }

        using (var jsonWriter = CreateJsonWriter(writer))
        {
            var jsonSerializer = CreateCustomJsonSerializer(serializerName);
            jsonSerializer.Serialize(jsonWriter, value);
        }
    }
    public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
    {
        var jsonSerializerNameHeader = context.HttpContext.Request.Headers.FirstOrDefault(h => h.Key == "jsonformat" && h.Value.Intersect(_customJsonSettings.Keys).Any());
        if (jsonSerializerNameHeader.Equals(default(KeyValuePair<string, StringValues>)))
        {
            await base.WriteResponseBodyAsync(context, selectedEncoding);
            return;
        }
        var jsonFormatName = jsonSerializerNameHeader.Value.FirstOrDefault();

        var response = context.HttpContext.Response;
        using (var writer = context.WriterFactory(response.Body, selectedEncoding))
        {
            WriteObjectWithNamedSerializer(writer, jsonFormatName, context.Object);
            await writer.FlushAsync();
        }
    }
}

.AddMvc

services.AddMvc(options =>
{
    options.OutputFormatters.RemoveType<JsonOutputFormatter>();
    options.OutputFormatters.Add(new NamedFormatJsonOutputFormatter(new JsonSerializerSettings(),

        new Dictionary<string, JsonSerializerSettings>()
        {
            {
                "pretty", new JsonSerializerSettings()
                {
                    Formatting = Formatting.Indented
                }
            }
        }, ArrayPool<char>.Shared));
});