Exception for status code 204 using TypeSpec

[AnReZa]

I'm generating my server code with TypeSpec as a basis. For example the following method:

  @route("/{productionOrderNumber}")
  @get getOrderData(
    @path productionOrderNumber: string
  ): ProductionOrder | NoContentResponse | ProblemDetail;

The c# implementation will return 204, if no content could be found under this key. However, the code that Visual Studio's code generator generates looks as follows:

public virtual async System.Threading.Tasks.Task<ProductionOrder> GetOrderDataAsync(string productionOrderNumber, System.Threading.CancellationToken cancellationToken)
{
    if (productionOrderNumber == null)
        throw new System.ArgumentNullException("productionOrderNumber");

    var client_ = _httpClient;
    var disposeClient_ = false;
    try
    {
        using (var request_ = new System.Net.Http.HttpRequestMessage())
        {
            request_.Method = new System.Net.Http.HttpMethod("GET");
            request_.Headers.Accept.Add(System.Net.Http.Headers.MediaTypeWithQualityHeaderValue.Parse("application/json"));

            var urlBuilder_ = new System.Text.StringBuilder();
            if (!string.IsNullOrEmpty(_baseUrl)) urlBuilder_.Append(_baseUrl);
            // Operation Path: "productionOrders/{productionOrderNumber}"
            urlBuilder_.Append("productionOrders/");
            urlBuilder_.Append(System.Uri.EscapeDataString(ConvertToString(productionOrderNumber, System.Globalization.CultureInfo.InvariantCulture)));

            PrepareRequest(client_, request_, urlBuilder_);

            var url_ = urlBuilder_.ToString();
            request_.RequestUri = new System.Uri(url_, System.UriKind.RelativeOrAbsolute);

            PrepareRequest(client_, request_, url_);

            var response_ = await client_.SendAsync(request_, System.Net.Http.HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
            var disposeResponse_ = true;
            try
            {
                var headers_ = new System.Collections.Generic.Dictionary<string, System.Collections.Generic.IEnumerable<string>>();
                foreach (var item_ in response_.Headers)
                    headers_[item_.Key] = item_.Value;
                if (response_.Content != null && response_.Content.Headers != null)
                {
                    foreach (var item_ in response_.Content.Headers)
                        headers_[item_.Key] = item_.Value;
                }

                ProcessResponse(client_, response_);

                var status_ = (int)response_.StatusCode;
                if (status_ == 200)
                {
                    var objectResponse_ = await ReadObjectResponseAsync<ProductionOrder>(response_, headers_, cancellationToken).ConfigureAwait(false);
                    if (objectResponse_.Object == null)
                    {
                        throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                    }
                    return objectResponse_.Object;
                }
                else
                if (status_ == 204)
                {
                    string responseText_ = ( response_.Content == null ) ? string.Empty : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                    throw new ApiException("There is no content to send for this request, but the headers may be useful.", status_, responseText_, headers_, null);
                }
                else
                if (status_ == 500)
                {
                    var objectResponse_ = await ReadObjectResponseAsync<ProblemDetail>(response_, headers_, cancellationToken).ConfigureAwait(false);
                    if (objectResponse_.Object == null)
                    {
                        throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                    }
                    throw new ApiException<ProblemDetail>("Server error", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                }
                else
                {
                    var responseData_ = response_.Content == null ? null : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                    throw new ApiException("The HTTP status code of the response was not expected (" + status_ + ").", status_, responseData_, headers_, null);
                }
            }
            finally
            {
                if (disposeResponse_)
                    response_.Dispose();
            }
        }
    }
    finally
    {
        if (disposeClient_)
            client_.Dispose();
    }
}

As you can see, it'll always throw an exception for status 204 instead of simply returning null, which would be the expected behavior. I also tried to modify the TypeSpec return type definition to ProductionOrder | null | ProblemDetail to allow returning null, but that lead to a similar result with an exception.

How can I fix that weird behavior without workarounds? Is there a flag that I can set for the generator? I read that people have been having similar problems for years now. Is there a solution that I missed? Am I doing something wrong?

[vvdb-architecture]

Same problem with C#, solvable with response "nullable" annotation. See GFlisch/Arc4u.Guidance.Doc#88

[ErikPilsits-RJW]

You could vote for my PR to be merged...

#4257

Otherwise you can use a local override of the template file which is what our org is doing right now.

[AnReZa]

As this repository seems to be pretty much dead, using the local override seems to be the way to go.