Fails to read response content twice

[di97mni]

public class MockHttpMessageHandlerTests
{
    //this test is OK and copied from tests in this repo
    [Fact]
    public void Should_respond_with_basic_requests()
    {
        var mockHandler = new MockHttpMessageHandler();

        mockHandler
            .When("/test")
            .Respond("application/json", "{'Status' : 'OK'}");

        var httpClient = new HttpClient(mockHandler);
        var result = httpClient.GetAsync("http://invalid/test").Result;

        Assert.Equal(System.Net.HttpStatusCode.OK, result.StatusCode);
        Assert.Equal("application/json", result.Content.Headers.ContentType.MediaType);
        var responseDto = result.Content.ReadAsAsync<ResponseDto>().Result;
        Assert.Equal("OK", responseDto.Status);
    }

    //this test fails
    [Fact]
    public void Should_respond_with_basic_requests_2()
    {
        var mockHandler = new MockHttpMessageHandler();

        mockHandler
            .When("/test")
            .Respond("application/json", "{'Status' : 'OK'}");

        var httpClient = new HttpClient(mockHandler);
        var result = httpClient.GetAsync("http://invalid/test").Result;

        Assert.Equal(System.Net.HttpStatusCode.OK, result.StatusCode);
        Assert.Equal("application/json", result.Content.Headers.ContentType.MediaType);
        var responseDto = result.Content.ReadAsAsync<ResponseDto>().Result;
        Assert.Equal("OK", responseDto.Status);

        result = httpClient.GetAsync("http://invalid/test").Result;
        Assert.Equal(System.Net.HttpStatusCode.OK, result.StatusCode);
        Assert.Equal("application/json", result.Content.Headers.ContentType.MediaType);
        responseDto = result.Content.ReadAsAsync<ResponseDto>().Result;

        //this fails due to responseDto is null. 
        Assert.Equal("OK", responseDto.Status);
    }
}

public class ResponseDto
{
    public string Status { get; set; }
}

[di97mni]

If I change to this

mockHandler
  .When("/test")
  .Respond(HttpStatusCode.OK, new ObjectContent<ResponseDto>(new ResponseDto("OK"), new JsonMediaTypeFormatter()));

Then response content is not null the second time. But it would be good if the json string would work because that's the format I have in my expected payloads. I would like to avoid creating the Dtos before the mocks.

[richardszalay]

Hi Martin,

This is actually a limitation with how ReadAsAsync<T> uses HttpContent, and has nothing to do with MockHttp.

HttpContentExtensions.ReadAsAsync<T> calls HttpContent.ReadAsStreamAsync, which reuses the existing memory buffer without resetting it's position, which causes ReadAsAsync<T> to return null since it thinks there's no data.

There's not much point attempting to workaroud this in my opinion, so I'd advise simply limiting your application to only call ReadAsAsync<T> once.

Cheers,
Richard

[richardszalay]

It just occurred to me that you are actually making the request twice, so the real HttpClient would actually send back two different responses. This is definitely a bug in MockHttp's behavior. Thanks for bringing it to my attention.

I'll look at fixing this behavior, but in the meantime you can workaround it by using a different Respond overload that creates a new HttpConent each time:

mockHandler
    .When("/test")
    .Respond(req => new HttpResponseMessage(HttpStatusCode.OK)
    {
        Content = new StringContent("{'Status' : 'OK'}", Encoding.UTF8, "application/json")
    });

[richardszalay]

This has been resolved in v1.3.1, now available on NuGet.