Ndtyjky

I'm trying to write an overload for HttpClient.PutAsJsonAsync<T> which allows headers to be set on each request. Looking at the source code for that method, it creates an ObjectContent<T> internally, which I tried to emulate below.

However, my target server always receives a null body when binding (using [FromBody] Form form).

If I change the request to be a StringContent and manually serialize the body, the request succeeds! What could be the difference between the two implementations?

Even more strangely, if I call await content.ReadAsStringAsync() before SendAsync then it also works!

My thoughts are it could be either:

• The JSON is being serialized differently (But I'm not configuring any Json.NET globals anywhere.) The obvious problem would be different capitalization, but as far as I know, JSON.net is case insensitive when parsing, and my server will be using JSON.net


• I'm not awaiting something and the content is being sent before it serialises fully. I can't spot any un-awaited Tasks in my code though, and the entrypoint is a standard async Main()
  

My environments is:

• Client is a simple netcoreapp2.1 exe, running in a microsoft/dotnet:2.1-sdk-alpine docker image.


• Server is a .NET framework MVC5 WebApi, with many similar APIs which other clients can call fine

The code below is a trimmed down version of what my client is calling.

public static class UserUpdater

{

    public static async Task UpdateAsync(List<string> users)

    {

        using (var client = new HttpClient())

        {

            var form = new { Users = users };

            var headers = new Dictionary<string, string>

            {

                ["Authorization"] = "Bearer " // Real JWT here

            };



            var response = await client.PutAsJsonAsync(new Uri("http://localhost/api/app/v1/gateway-users"), form, headers);

            if (!response.IsSuccessStatusCode)

            {

                throw new InvalidOperationException("Response status code does not indicate success: " +

                                                    response.StatusCode + "nn" +

                                                    await response.Content.ReadAsStringAsync());

            }

        }

    }



    public static async Task<HttpResponseMessage> PutAsJsonAsync<T>(this HttpClient client, Uri requestUri, T value,

        IEnumerable<KeyValuePair<string, string>> headers, CancellationToken cancellationToken = default)

    {

        var content = new ObjectContent<T>(value, new JsonMediaTypeFormatter(), (MediaTypeHeaderValue)null);

        ////var content = new StringContent(JsonConvert.SerializeObject(value), Encoding.UTF8, "application/json"); // This works fine

        var message = MakeRequestMessage(HttpMethod.Put, requestUri, headers, content);

        return await client.SendAsync(message, cancellationToken);

    }



    private static HttpRequestMessage MakeRequestMessage(

        [NotNull] HttpMethod method,

        [NotNull] Uri requestUri,

        [CanBeNull] IEnumerable<KeyValuePair<string, string>> headers,

        [CanBeNull] HttpContent content = null)

    {

        var message = new HttpRequestMessage(method, requestUri);



        if (headers != null)

        {

            foreach (var header in headers)

            {

                message.Headers.Add(header.Key, header.Value);

            }

        }



        if (content != null)

        {

            message.Content = content;

        }



        return message;

    }

If it helps, this is the server side (MVC5 WebApi):

    [Route("")]

    [ValidateModel]

    public IHttpActionResult Put([Required] [FromBody] GatewayUserCollectionForm form)

    {

        Ensure.NotNull(form, nameof(form)); // This throws since form is null



        this.manager.UpdateGatewayUsers(form.Users.ToList());

        return this.Ok();

    }



    public class GatewayUserCollectionForm

    {

        [Required]

        public List<string> Users { get; set; }

    }