Using HttpClient.GetFromJsonAsync(), how to handle HttpRequestException based on HttpStatusCode without extra SendAsync calls?

You can use:

// return HttpResponseMessage
var res= await httpClient.GetAsync<List<Car>>("/api/cars")

if (res.IsSuccessStatusCode)
   var cars = res.Content.ReadFromJsonAsync<List<Car>>();
else
   // deal with the HttpResponseMessage directly as you used to

I use a base class like this:

using System;
using System.Net.Http;
using System.Net.Http.Json;
using System.Threading.Tasks;


namespace MyProject.ClientAPI
{
    public abstract class ClientAPI
    {
        protected readonly HttpClient Http;
        private readonly string BaseRoute;

        protected ClientAPI(string baseRoute, HttpClient http)
        {
            BaseRoute = baseRoute;
            Http = http;
        }

        protected async Task<TReturn> GetAsync<TReturn>(string relativeUri)
        {
            HttpResponseMessage res = await Http.GetAsync($"{BaseRoute}/{relativeUri}");
            if (res.IsSuccessStatusCode)
            {
                return await res.Content.ReadFromJsonAsync<TReturn>();
            }
            else
            {
                string msg = await res.Content.ReadAsStringAsync();
                Console.WriteLine(msg);
                throw new Exception(msg);
            }
        }
        
        protected async Task<TReturn> PostAsync<TReturn, TRequest>(string relativeUri, TRequest request)
        {
            HttpResponseMessage res = await Http.PostAsJsonAsync<TRequest>($"{BaseRoute}/{relativeUri}", request);
            if (res.IsSuccessStatusCode)
            {
                return await res.Content.ReadFromJsonAsync<TReturn>();
            }
            else
            {
                string msg = await res.Content.ReadAsStringAsync();
                Console.WriteLine(msg);
                throw new Exception(msg);
            }
        }
    }
}

and then from derived class, we’re back to the one-liner

public class MySpecificAPI : ClientAPI
{
    public MySpecificAPI(HttpClient http) : base("api/myspecificapi", http) {}
    
    public async Task<IEnumerable<MyClass>> GetMyClassAsync(int ownerId)
    {
        try
        {
            return GetAsync<IEnumerable<MyClass>>($"apiMethodName?ownerId={ownerId}");
        }
        catch (Exception e)
        {
            // Deal with exception
        }
    }
    
    // repeat for post
}

UPDATE: HANDLING NULL RETURNS

Having encountered a valid scenario where the WebAPI returns null, the line:

return await res.Content.ReadFromJsonAsync<TReturn>();

will throw a Json Deserialization error.

To address this, we need to detect NoContent response (204) and handle accordingly:

if (res.StatusCode == HttpStatusCode.NoContent)
    return default(TReturn);
else if (res.IsSuccessStatusCode)
    return await res.Content.ReadFromJsonAsync<TReturn>();