.Net Core 3.1 HttpClient Headers.TryAddWithoutValidation Not Working

Question

I am probably missing something really simple but I just cannot find it.

An API I am working with demands the inclusion of a Content-Type header even with GETs.

I am struggling to add the header to my request.

Here is the code that builds the httpclient:

public static async Task<HttpClient> Authenticate(string baseUrl, string clientId, string clientSecret)
    {
        HttpClient httpClient = new HttpClient();
        httpClient.DefaultRequestHeaders.Add("Accept", "application/json");

        string toBeHashed = $"client_id={clientId}&client_secret={clientSecret}";
        string hashed = sha256_hash(toBeHashed);

        AuthRequest request = new AuthRequest
        {
            client_id = clientId,
            hash = hashed
        };

        StringContentWithoutCharset body = new StringContentWithoutCharset(JsonSerializer.Serialize(request), Encoding.UTF8, "application/json");

        HttpResponseMessage response = await httpClient.PostAsync($"{baseUrl}authenticate", body);

        AuthResponse result = await JsonSerializer.DeserializeAsync<AuthResponse>(await response.Content.ReadAsStreamAsync());

        httpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", result.data.token);
        

        return httpClient;
    }

And here is 2 different attempts at making a GET call.

When I look in Fiddler the Content-Type is missing from the headers:

public class Functions
{
    private HttpClient _httpClient;
    private readonly string _baseUrl;

    public Functions(string baseUrl, string clientId, string clientSecret)
    {
        _httpClient = Helpers.Authenticate(baseUrl, clientId, clientSecret).Result;
        _baseUrl = baseUrl;
    }

    public async Task ProductList()
    {
        // this doesn't work
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, $"{_baseUrl}products");
        request.Headers.TryAddWithoutValidation("Content-Type", "application/json");
        HttpResponseMessage response1 = await _httpClient.SendAsync(request);
        ProductList result1 = await JsonSerializer.DeserializeAsync<ProductList>(await response1.Content.ReadAsStreamAsync());

        // nor does this
        _httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "application/json");
        HttpResponseMessage response = await _httpClient.GetAsync($"{_baseUrl}products");
        ProductList result2 = await JsonSerializer.DeserializeAsync<ProductList>(await response.Content.ReadAsStreamAsync());
    }
}

Any help would be greatly appreciated.

Answer 1

Reposting my comment as an answer, so that it's helpful for everyone facing the same.

You can't use Content-Type as request header as godot pointed out, because it's not really that, as far as .NET is concerned. However, it is also a "content header" (which is a request header, technically speaking). Content headers are perfectly valid for POST and PUT requests. Therefore, as a hacky solution (GET requests are not supposed to have content), you can add this line:

request.Content = new StringContent("", Encoding.UTF8, "application/json");

This adds an empty StringRequest, and as the third argument, you can actually specify the Content-Type.

Answer 2

You are using response header as a request header.

TryWithoutValidation method returns false in your example because you are using response header as a request header. If you try to use Add method instead of TryWithoutValidation you see actual reason of error.

request.Headers.Add("content-type", "application/json");

and you receive:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Net.Http.dll: 'Misused header name. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects.'

So use Accept header instead of Content-type

request.Headers.TryAddWithoutValidation("accept", "application/json");