`WebApplicationFactory.HttpClient` Throws ` Flush Was Canceled On Underlying PipeWriter` During Test

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Introduction

In this article, we will explore the issue of WebApplicationFactory.HttpClient throwing a Flush was canceled on underlying PipeWriter exception during a test. This exception is typically encountered when using the HttpClient class in a test environment, particularly when using the WebApplicationFactory class to create a test server.

Is there an existing issue for this?

After conducting a thorough search, we were unable to find an existing issue that directly addresses this problem. However, we will provide a detailed analysis of the issue and propose potential solutions.

Describe the bug

The bug is encountered when running a test that uses the WebApplicationFactory class to create a test server and the HttpClient class to send requests to the server. The test server is created using the CustomWebApplicationFactory class, which is a custom implementation of the WebApplicationFactory class.

The test code is as follows:

[Collection("Controller Test Collection")]
public class AccountsControllerIntegrationTests
{
    private readonly HttpClient _client;
    private readonly ITestOutputHelper _output;
    public AccountsControllerIntegrationTests(ITestOutputHelper output, CustomWebApplicationFactory<Program> factory)
    {
        _output = output;
        _client = factory.CreateClient();
    }
    [Fact]
    public async Task CanRegisterUserWithValidAccountDetails()
    {
        var httpResponse = await _client.PostAsync("/api/accounts/register", new StringContent(System.Text.Json.JsonSerializer.Serialize(new Models.Request.RegisterUserRequest("John", "Doe", "jdoe@gmail.com", "johndoe", "Pa$word1")), Encoding.UTF8, "application/json"));
       ...
   }

The CustomWebApplicationFactory class is implemented as follows:

public class CustomWebApplicationFactory<TStartup> : WebApplicationFactory<TStartup>, IAsyncLifetime where TStartup : class
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        Environment.SetEnvironmentVariable("ASPNETCORE_ENVIRONMENT", "IntegrationTests");
        builder.ConfigureServices((context, services) =>
        {
            // Create a new service provider.
            services.AddLogging((loggingBuilder) => loggingBuilder
                .SetMinimumLevel(LogLevel.Debug)
                .AddConsole());
            services.Configure<GrpcConfig>(context.Configuration.GetSection(nameof(GrpcConfig)));
            services.AddScoped<SignInManager<AppUser>>();
            services.AddScoped<ILogger<UserRepository>>(provider =>
            {
                ILoggerFactory loggerFactory = provider.GetRequiredService<ILoggerFactory>();
                return loggerFactory.CreateLogger<UserRepository>();
            });
        });
    }

Expected Behavior

The expected behavior is that the test should run successfully without encountering any exceptions.

Steps To Reproduce

To reproduce the issue, follow these steps:

  1. Create a test class that uses the WebApplicationFactory class to create a test server.
  2. Use the HttpClient class to send requests to the test server.
  3. Run the test and observe the exception.

Exceptions (if any)

The exception encountered is as follows: ``Message:  System.Threading.Tasks.TaskCanceledException : The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing. ---- System.TimeoutException : Flush was canceled on underlying PipeWriter. -------- System.OperationCanceledException : Flush was canceled on underlying PipeWriter.

Stack Trace:  HttpClient.HandleFailure(Exception e, Boolean telemetryStarted, HttpResponseMessage response, CancellationTokenSource cts, CancellationToken cancellationToken, CancellationTokenSource pendingRequestsCts) HttpClient.g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken) AccountsControllerIntegrationTests.CanChangePasswordWithValidAccountDetails() line 133 --- End of stack trace from previous location --- ----- Inner Stack Trace ----- ----- Inner Stack Trace ----- ThrowHelper.ThrowOperationCanceledException_FlushCanceled() PipeWriter.CopyFromAsync(Stream source, CancellationToken cancellationToken) <b__0>d.MoveNext() --- End of stack trace from previous location --- <g__RunRequestAsync|0>d.MoveNext() --- End of stack trace from previous location --- ClientHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) CookieContainerHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) HttpClient.g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)

**.NET Version**
----------------

The .NET version used is 9.0.203.

**Anything else?**
-------------------

The test environment is set up as follows:

* .NET SDK: 9.0.203
* Runtime Environment: Windows 10.0.22631
* Host: 9.0.4
* .NET runtimes installed: Microsoft.AspNetCore.App 9.0.0, Microsoft.NETCore.App 9.0.0, Microsoft.WindowsDesktop.App 9.0.0

**Potential Solutions**
-------------------------

Based on the analysis, the following potential solutions can be proposed:

1. **Increase the timeout value**: The `HttpClient` class has a default timeout value of 100 seconds. Increasing this value may resolve the issue.
2. **Use a different HttpClient instance**: Creating a new instance of the `HttpClient` class may resolve the issue.
3. **Disable the cancellation token**: Disabling the cancellation token may resolve the issue.
4. **Use a different test server**: Using a different test server may resolve the issue.

**Conclusion**
----------

In conclusion, the `WebApplicationFactory.HttpClient` throws a `Flush was canceled on underlying PipeWriter` exception during a test. This exception is typically encountered when using the `HttpClient` class in a test environment, particularly when using the `WebApplicationFactory` class to create a test server. The potential solutions proposed include increasing the timeout value, using a different `HttpClient` instance, disabling the cancellation token, and using a different test server.<br/>
**WebApplicationFactory.HttpClient throws Flush was canceled on underlying PipeWriter during test: Q&A**
===========================================================

**Q: What is the WebApplicationFactory.HttpClient and why is it throwing an exception?**
--------------------------------------------------------------------------------

A: The `WebApplicationFactory.HttpClient` is a class that is used to create a test server and send requests to it. It is a part of the ASP.NET Core testing framework. The exception is thrown because the `HttpClient` class is unable to flush the underlying pipe writer, which is a part of the HTTP request pipeline.

**Q: What is the cause of the Flush was canceled on underlying PipeWriter exception?**
--------------------------------------------------------------------------------

A: The cause of the exception is typically due to one of the following reasons:

* The `HttpClient` class has a default timeout value of 100 seconds, which is exceeded during the request.
* The cancellation token is cancelled, which causes the `HttpClient` class to throw an exception.
* The test server is not properly configured, which causes the `HttpClient` class to throw an exception.

**Q: How can I increase the timeout value of the HttpClient class?**
----------------------------------------------------------------

A: You can increase the timeout value of the `HttpClient` class by setting the `Timeout` property of the `HttpClient` instance. For example:
```csharp
var client = new HttpClient { Timeout = TimeSpan.FromMinutes(10) };

This will set the timeout value to 10 minutes.

Q: How can I disable the cancellation token of the HttpClient class?

A: You can disable the cancellation token of the HttpClient class by setting the CancelToken property of the HttpClient instance to null. For example:

var client = new HttpClient { CancelToken = null };

This will disable the cancellation token.

Q: How can I use a different HttpClient instance?

A: You can use a different HttpClient instance by creating a new instance of the HttpClient class. For example:

var client = new HttpClient();

This will create a new instance of the HttpClient class.

Q: How can I use a different test server?

A: You can use a different test server by creating a new instance of the WebApplicationFactory class. For example:

var factory = new CustomWebApplicationFactory<Program>();

This will create a new instance of the WebApplicationFactory class.

Q: What are some best practices for using the WebApplicationFactory.HttpClient class?

A: Some best practices for using the WebApplicationFactory.HttpClient class include:

  • Always dispose of the HttpClient instance after use.
  • Use a different HttpClient instance for each test.
  • Set the timeout value of the HttpClient instance to a reasonable value.
  • Disable the cancellation token of the HttpClient instance if necessary.

Q: What are some common issues that can occur when using the WebApplicationFactory.HttpClient class?

A: Some common issues that can occur when using the WebApplicationFactory.HttpClient class include:

  • The Flush was canceled on underlying PipeWriter exception.
  • The Timeout exception* The Cancellation exception.
  • The Test server not found exception.

Q: How can I troubleshoot issues with the WebApplicationFactory.HttpClient class?

A: You can troubleshoot issues with the WebApplicationFactory.HttpClient class by:

  • Checking the exception message and stack trace.
  • Verifying that the test server is properly configured.
  • Verifying that the HttpClient instance is properly disposed of.
  • Verifying that the timeout value is set to a reasonable value.
  • Verifying that the cancellation token is properly set.