测试Refit实现的接口时的NullReferenceException

Question

我正在尝试测试一些错误响应(BadRequest，未授权，...)使用Refit等，我实现了一个返回任何所需响应的TestHandler。使用"OK“(HTTP状态代码200)响应时，响应可以正常工作：

public class Program
{
    private static async Task Main()
    {
        var api = RestService.For<ITest>(
            new HttpClient(new TestHandler(HttpStatusCode.OK))
                {
                    BaseAddress = new Uri("https://example.com")
                }
            );
        Console.WriteLine(await api.Test("foo").ConfigureAwait(false));
    }
}

public interface ITest
{
    [Get("/foo/{bar}")]
    Task<string> Test(string bar);
}

public class TestHandler : HttpMessageHandler
{
    private readonly HttpResponseMessage _response;

    public TestHandler(HttpStatusCode httpStatusCode)
        => _response = new HttpResponseMessage(httpStatusCode) { Content = new StringContent("Yay!") };

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        => Task.FromResult(_response);
}

但是，每当我将响应状态代码更改为(例如) BadRequest (400)、NotFound (404)或未授权(401) Refit时，都会抛出NullReferenceException

Object reference not set to an instance of an object.
   at Refit.DefaultApiExceptionFactory.<CreateExceptionAsync>d__4.MoveNext() in /_/Refit/RefitSettings.cs:line 183
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at Refit.RequestBuilderImplementation.<>c__DisplayClass14_0`2.<<BuildCancellableTaskFuncForMethod>b__0>d.MoveNext() in /_/Refit/RequestBuilderImplementation.cs:line 313
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at RefitTest.Program.<Main>d__0.MoveNext() in C:\Users\Rob\Source\Repos\RefitTest\RefitTest\Program.cs:line 18

这指向RefitSettings.cs line 183。但我不明白为什么200OK可以工作，而其他任何响应都不行？我做错了什么？

编辑:为了进一步调试，我克隆了Refit，并用Refit NuGet包替换了对Refit项目的项目引用。这会产生一个InvalidOperationException: ITest doesn't look like a Refit interface. Make sure it has at least one method with a Refit HTTP method attribute and Refit is installed in the project。此外，返回几个版本(我已经转到5.2.4)也没有帮助。

Answer 1

在同事的帮助下找到了！事实证明HttpResponseMessage需要一些/任何RequestMessage。

变化

public TestHandler(HttpStatusCode httpStatusCode)
    => _response = new HttpResponseMessage(httpStatusCode)
    { 
        Content = new StringContent("Yay!") 
    };

至：

public TestHandler(HttpStatusCode httpStatusCode)
    => _response = new HttpResponseMessage(httpStatusCode)
    {
        RequestMessage = new(),  // <-- This one here...
        Content = new StringContent("Yay!")
    };

它的工作方式和预期的一样。正如问题(和评论)中所说，我很接近，但显然是半睡半醒，因为这正是它指向我的地方。

我已经提交了一个问题here。