.Net 10 Support

[NateRadebaugh]

There was a similar request for 9 via #5022 so I thought it'd be helpful to pin this request to avoid duplicate questions about timeline and consolidate discussions to one issue.

[RicoSuter]

It already supports .NET 10 RC2, so I'd expect it already works, but will release a new version soon...

[NateRadebaugh]

For future reference, seems like after upgrading to latest nuget package, changing from NSwagExe_Net90 to NSwagExe_Net100 is the only fix we'll need.

[pregress]

For those that want to do this dynamically:

<Target Name="GenerateNswagClient" BeforeTargets="Build">
    <PropertyGroup>
        <NSwagRuntime>Net$([System.String]::Copy('$(NETCoreAppMaximumVersion)').Replace('.', ''))</NSwagRuntime>
    </PropertyGroup>
    <Exec Command="dotnet nswag run $(ProjectDir)nswag.json /variables:Runtime=$(NSwagRuntime)" />
</Target>

nswag.json

  "runtime": "$(Runtime)",
  "defaultVariables": "Runtime=Net100",

[patheikkinen]

At least NSWag 14.5.0.0 generates C# code that uses a variable called field:

var field = System.Reflection.IntrospectionExtensions.GetTypeInfo(value.GetType()).GetDeclaredField(name);

if (field != null)
{
   var attribute = System.Reflection.CustomAttributeExtensions.GetCustomAttribute(field, typeof(System.Runtime.Serialization.EnumMemberAttribute)) as System.Runtime.Serialization.EnumMemberAttribute;

In C# 14 that is a keyword and Microsoft advises against using it, and recommends renaming it to something else:

https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-14#the-field-keyword

[TheLastAirsickLowlander]

So i been hitting a problem after upgrading a solution to dotnet 10. I looks like the way nswag is generating the code is not supported in dotnet 10. Have y'all seen this before?

we are using, nswag version 14.6.2

I did end up fixing the issue by overloading my local client with a custom method. I give a brief write up below.

Description
The exception System.NotSupportedException: net_http_synchronous_reads_not_supported occurs because the generated Calamu.Services.SDK.ApiClient performs synchronous JSON deserialization using a StreamReader on the HTTP response stream. In Blazor WebAssembly, synchronous stream reads (Stream.Read, StreamReader.Read*) are not supported; only async APIs (ReadAsStringAsync) work. Newtonsoft.Json is being fed a synchronously read stream, triggering the failure during authentication.

Root cause
SDK’s internal ReadObjectResponseAsync uses a sync StreamReader over response.Content.ReadAsStream()

Fix strategy

namespace Calamu.Services.SDK
{
    public partial class ApiClient
    {
        // Keep visibility aligned with NSwag internal usage
        protected async System.Threading.Tasks.Task<ObjectResponseResult<T>> ReadObjectResponseAsync<T>(
            System.Net.Http.HttpResponseMessage response,
            System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers,
            System.Threading.CancellationToken cancellationToken)
        {
            if (response?.Content == null)
                return new ObjectResponseResult<T>(default(T), string.Empty);

            var responseText = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
            try
            {
                var typedBody = Newtonsoft.Json.JsonConvert.DeserializeObject<T>(responseText, JsonSerializerSettings);
                var textToReturn = ReadResponseAsString ? responseText : string.Empty;
                return new ObjectResponseResult<T>(typedBody, textToReturn);
            }
            catch (Newtonsoft.Json.JsonException ex)
            {
                var message = "Could not deserialize the response body string as " + typeof(T).FullName + ".";
                var textToReturn = ReadResponseAsString ? responseText : string.Empty;
                throw new ApiException(message, (int)response.StatusCode, textToReturn, headers, ex);
            }
        }
    }
}

[RubenPX]

@TheLastAirsickLowlander Same here

[RicoSuter]

@TheLastAirsickLowlander @RubenPX I think this was already an issue before, ie blazor web assembly did not work if i remember correctly. We'd need to correct the template, maybe conditionally using the new JsonLibraryVersion config to avoid breaking changes for older targets:

RicoSuter/NJsonSchema#1865

[RicoSuter]

At least NSWag 14.5.0.0 generates C# code that uses a variable called field:

Fixed in this PR: #5307 (v14.6.3)

[patheikkinen]

At least NSWag 14.5.0.0 generates C# code that uses a variable called field:

Fixed in this PR: #5307 (v14.6.3)

Looks good. Thanks!

[bkzoller]

I'm seeing this error with NSwag 14.6.3 on .NET 10.0.100.

/usr/local/share/dotnet/sdk/10.0.100/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.TargetFrameworkInference.targets(160,5): error MSB4062: The "AllowEmptyTelemetry" task could not be loaded from the assembly /usr/local/share/dotnet/sdk/10.0.100/Sdks/Microsoft.NET.Sdk/targets/../tools/net10.0/Microsoft.NET.Build.Tasks.dll. Could not load file or assembly 'System.Runtime, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
    /usr/local/share/dotnet/sdk/10.0.100/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.TargetFrameworkInference.targets(160,5): error MSB4062: Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
    /Users/user/src/project/BuildEvents.csproj(23,11): error MSB3073: The command "dotnet "/Users/user/.nuget/packages/nswag.msbuild/14.6.3/buildTransitive/../tools/Net100/dotnet-nswag.dll" run ../TBC.TriumphPay.CodeGen/nswag.json /variables:Configuration=Debug,NoBuild=False" exited with code 255.

[RicoSuter]

@bkzoller do you have vs2026 installed or still vs2022 with .NET 10 SDK (not sure whether this is a problem/fix)? Will do more testing with some internal projects tomorrow.

[bkzoller]

@bkzoller do you have vs2026 installed or still vs2022 with .NET 10 SDK (not sure whether this is a problem/fix)? Will do more testing with some internal projects tomorrow.

The IDE is not relevant because this error happens with dotnet build on the command line. However, I'm using JetBrains Rider 2025.3.

[TDroogers]

I am having issues with ReadAsStreamAsync()

I had to add <WasmEnableStreamingResponse>false</WasmEnableStreamingResponse> to my blazor wasm client.

crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
      Unhandled exception rendering component: net_http_synchronous_reads_not_supported
System.NotSupportedException: net_http_synchronous_reads_not_supported
   at System.Net.Http.BrowserHttpReadStream.Read(:6443/Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.DelegatingStream.Read(:6443/Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.StreamReader.ReadBuffer(:6443/Span`1 userBuffer, Boolean& readToUserBuffer)
   at System.IO.StreamReader.ReadSpan(:6443/Span`1 buffer)
   at System.IO.StreamReader.Read(:6443/Char[] buffer, Int32 index, Int32 count)
   at Newtonsoft.Json.JsonTextReader.ReadData(:6443/Boolean append, Int32 charsRequired)
   at Newtonsoft.Json.JsonTextReader.ReadData(:6443/Boolean append)
   at Newtonsoft.Json.JsonTextReader.ParseValue((index))
   at Newtonsoft.Json.JsonTextReader.Read((index))
   at Newtonsoft.Json.JsonReader.ReadAndMoveToContent((index))
   at Newtonsoft.Json.JsonReader.ReadForType(:6443/JsonContract contract, Boolean hasConverter)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(:6443/JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(:6443/JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(:6443/JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize[CurrentUser](:6443/JsonReader reader)
   at :6443/Drogecode.Knrm.Oefenrooster.ClientGenerator.Client.AuthenticationClient.<ReadObjectResponseAsync>d__33`1[[Drogecode.Knrm.Oefenrooster.Shared.Models.User.CurrentUser, Drogecode.Knrm.Oefenrooster.Shared, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].MoveNext() in C:\Users\Taco\source\repos\Drogecode.Knrm.Oefenrooster\src\ClientGenerator\Clients\AuthenticationClient.g.cs:line 753
   at :6443/Drogecode.Knrm.Oefenrooster.ClientGenerator.Client.AuthenticationClient.CurrentUserInfoAsync(CancellationToken cancellationToken) in C:\Users\Taco\source\repos\Drogecode.Knrm.Oefenrooster\src\ClientGenerator\Clients\AuthenticationClient.g.cs:line 424
   at :6443/Drogecode.Knrm.Oefenrooster.Client.Services.CustomStateProvider.GetCurrentUser() in C:\Users\Taco\source\repos\Drogecode.Knrm.Oefenrooster\src\Client\Services\CustomStateProvider.cs:line 122
   at :6443/Drogecode.Knrm.Oefenrooster.Client.Services.CustomStateProvider.GetAuthenticationStateAsync() in C:\Users\Taco\source\repos\Drogecode.Knrm.Oefenrooster\src\Client\Services\CustomStateProvider.cs:line 28
   at Microsoft.AspNetCore.Components.Authorization.AuthorizeViewCore.OnParametersSetAsync((index))
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(:6443/Task task)
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync((index))
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(:6443/Task taskToHandle, ComponentState owningComponentState)

Previous behavior

Previously, in browser environments such as WebAssembly (WASM) and Blazor, the HTTP client buffered the entire response by default. The HttpContent object contained a MemoryStream unless you explicitly opted in to streaming responses using the WebAssemblyEnableStreamingResponse option.
C#

var response = await httpClient.GetAsync("https://example.com");
var contentStream = await response.Content.ReadAsStreamAsync(); // Returns MemoryStream

New behavior

Starting in .NET 10, streaming HTTP responses are enabled by default. The HttpContent no longer contains a MemoryStream. Instead, HttpContent.ReadAsStreamAsync returns a BrowserHttpReadStream, which does not support synchronous operations.
C#

var response = await httpClient.GetAsync("https://example.com");
var contentStream = await response.Content.ReadAsStreamAsync(); // Returns BrowserHttpReadStream

[uladz-zubrycki]

@bkzoller were you able to fix that? Seeing sth similar.

[brianzoller]

@bkzoller were you able to fix that? Seeing sth similar.

No, I have not been able to solve that. I cannot find the reference to AllowEmptyTelemetry task. I suspect it might be coming from OpenTelemetry NuGet packages, but upgrading those did not change the NSwag error.