how to properly perform HTTP Post of a JSON object using C# HttpClient?

Question

I have a very simple C# Http Client console app, which needs to do an HTTP POST of a json object to a WebAPI v2. Currently, My app can do the POST using FormUrlEncodedContent:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Http;
using System.Net.Http.Headers;
using Newtonsoft.Json;
using System.Net.Http.Formatting;


namespace Client1
{
    class Program
    {
        class Product
        {
            public string Name { get; set; }
            public double Price { get; set; }
            public string Category { get; set; }
        }
        static void Main(string[] args)
        {
             RunAsync().Wait();
        }
        static async Task RunAsync()
        {
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri("http://localhost:8888/");
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

                var content = new FormUrlEncodedContent(new[] 
                        {
                            new KeyValuePair<string, string>("Category", "value-1"),
                            new KeyValuePair<string, string>("Name", "value-2")                           
                       });

                var result = client.PostAsync("Incident", content).Result;      
                var r = result;     
            }
        }
    }
}

However, when I try to use JSON in the POST body, I get error 415 - Unsupported media Type:

class Product
{
    public string Name { get; set; }
    public double Price { get; set; }
    public string Category { get; set; }
}

var gizmo = new Product() { Name = "Gizmo", Price = 100, Category = "Widget" };
var  response = await client.PostAsJsonAsync("api/products", gizmo);

Doing explicit JSON serialization does not change the outcome for me:

string json = JsonConvert.SerializeObject(product);
var  response = await client.PostAsJsonAsync("api/products", json);

What is the proper way to handle this, and to be able to POST JSON?

Answer 1

If you expect it to send as FormUrlEncodedContent, then MediaTypeWithQualityHeaderValue("application/json") is wrong. This will set the request content-type to json. Use application/x-www-form-urlencoded instead or just do not set MediaTypeWithQualityHeaderValue at all.