将DefaultHttpContext.Response.Body初始化为MemoryStream会引发NullReferencePointer

Question

我正在研究全局异常中间件的实现，我想用单元测试介绍中间件。在下面您可以看到我走了多远。

这是单元测试的代码。

    [Fact]
    public async Task MethodName_StateUnderTest_ExpectedBehavior()
    {
        //Arrange
        IExceptionHandlerFeature exceptionHandlerFeature = new ExceptionHandlerFeature {Error = new NotFoundException()};

        IFeatureCollection features = new FeatureCollection();
        features.Set(exceptionHandlerFeature);

        var context = new DefaultHttpContext(features);
        context.Response.Body = new MemoryStream();
        //Act
        await ExceptionMiddleware.HandleException(context);

        //Assert
        context.Response.StatusCode.Should().Be((int) HttpStatusCode.NotFound);
    }

这是ExceptionMiddleware.Handle方法的代码

public static async Task HandleException(HttpContext context)
{
    var contextFeature = context.Features.Get<IExceptionHandlerFeature>();

    if (contextFeature == null)
    {
        return;
    }

    if (contextFeature.Error is AppValidationException validationException)
    {
        context.Response.StatusCode = (int) HttpStatusCode.BadRequest;

        var failures = JsonConvert.SerializeObject(validationException.Failures);

        await context.Response.WriteAsync(
            new ErrorDetails
            {
                StatusCode = context.Response.StatusCode,
                Message = contextFeature.Error.Message,
                StackTrace = contextFeature.Error.StackTrace,
                Detail = failures
            }.ToString());

        return;
    }

    context.Response.StatusCode = (int) ResolveStatusCodeFromExceptionType(contextFeature.Error);
    context.Response.ContentType = "application/json";

    await context.Response.WriteAsync(
        new ErrorDetails
        {
            StatusCode = context.Response.StatusCode,
            Message = contextFeature.Error.Message,
            StackTrace = contextFeature.Error.StackTrace
        }.ToString());
}

测试正在压碎线上

context.Response.Body = new MemoryStream();

据此question，一切都应该没问题，但我仍然无法初始化属性Body。

测试项目的目标框架是.Net Core 3.0。ExceptionMiddleware.cs在具有已设置目标框架.NET Standard 2.1的项目中，它是类库。

StackTrace异常确实很短：

在Microsoft.AspNetCore.Http.Internal.DefaultHttpResponse.set_Body（Stream价值）Itixis.Shared.API.Tests.ExceptionMiddlewareTests.d__0.MoveNext（）在C：\ Users \ daniel.rusnok \ source \ repos \ Itixis \ Itixis.Shared \ Tests \ Itixis.Shared.API.Tests \ ExceptionMiddlewareTests.cs：line35

Answer 1

通过手动设置功能，您将删除默认设置的功能，这将导致空错误。

    public DefaultHttpContext()
        : this(new FeatureCollection())
    {
        Features.Set<IHttpRequestFeature>(new HttpRequestFeature());
        Features.Set<IHttpResponseFeature>(new HttpResponseFeature());
        Features.Set<IHttpResponseBodyFeature>(new StreamResponseBodyFeature(Stream.Null));
    }

    public DefaultHttpContext(IFeatureCollection features)
    {
        _features.Initalize(features);
        _request = new DefaultHttpRequest(this);
        _response = new DefaultHttpResponse(this);
    }

Source

请注意默认构造函数中添加的请求，响应和响应主体功能。

通过添加必需的功能，尝试重新创建默认构造函数中的内容，

IExceptionHandlerFeature exceptionHandlerFeature = new ExceptionHandlerFeature {Error = new NotFoundException()};

IFeatureCollection features = new FeatureCollection();
features.Set(exceptionHandlerFeature);
features.Set<IHttpRequestFeature>(new HttpRequestFeature());
features.Set<IHttpResponseFeature>(new HttpResponseFeature());
features.Set<IHttpResponseBodyFeature>(new StreamResponseBodyFeature(Stream.Null));

var context = new DefaultHttpContext(features);

//...

或删除手动功能，它应该可以正常工作。

[Fact]
public async Task MethodName_StateUnderTest_ExpectedBehavior() {
    //Arrange
    var context = new DefaultHttpContext();
    context.Response.Body = new MemoryStream();
    //Act
    await ExceptionMiddleware.HandleException(context);

    //Assert
    context.Response.StatusCode.Should().Be((int) HttpStatusCode.NotFound);
}