Support sending requests with CancellationToken

[bgold09]

When testing the full server stack, it can be useful to invoke an operation with a CancellationToken other than CancellationToken.None, i.e.

new CancellationToken(canceled: true)

This support can be introduced by modifying ServerTestBuilder:

1. Add a private field CancellationToken cancellationToken to the class, which by default is initialized to CancellationToken.None to preserve the current behavior
2. Add a method IServerTestBuilder WithCancellationToken(CancellationToken cancellationToken) which sets the private field
3. In ServerTestBuilder +124, send the request with the value of this.cancellationToken

What are your thoughts on this idea and its potential implementation? I'd be happy to implement it myself; your library has already been very helpful in testing my WebApi application.

[ivaylokenov]

@bgold09 I believe it will be useful. Will implement it and upload a new version of the library in a few hours.

[ivaylokenov]

@bgold09 I implemented the methods and tried it out but all requests with CancellationToken set to true throw errors that tasks have been canceled. I could not find any proper solution after an hour research.

Do you have any other suggestions?

[bgold09]

@ivaylokenov if you add a custom message handler to the HttpConfiguration used to initialize the server, does the CancellationToken at least flow through to its SendAsync() method?

Does the exception come from the server or the client message invoker?

[ivaylokenov]

@bgold09 I tried with both custom OWIN handler and message handler on the HttpConfiguration and it doest not reach it. The code throws errors on the https://github.com/ivaylokenov/MyTested.WebApi/blob/master/src/MyTested.WebApi/Builders/Servers/ServerTestBuilder.cs#L124 line so I expect the task to throw in the client. The request does not gets processed on the server.

[bgold09]

Is an OperationCanceledException being thrown? If so, I suspect that CancellationToken.ThrowIfCancellationRequested() is being called somewhere in the depths of System.Net.Http.dll.

[ivaylokenov]

@bgold09 Actually it is TaskCanceledException. Looking through this code:

https://www.symbolsource.org/Public/Metadata/NuGet/Project/HttpClient/0.5.0/Release/.NETFramework,Version%3Dv4.0/Microsoft.Net.Http/Microsoft.Net.Http/System/Net/Http/HttpClient.cs?ImageName=Microsoft.Net.Http

There are numerous checks for the cancellation token and I guess it is normal that we receive the exception. I guess it will not be possible to implement this feature? I am out of ideas.

[bgold09]

Hmm, let me do a bit of digging and get back to you. I agree though, it looks like this is less straightforward than I originally thought.

[bgold09]

@ivaylokenov I think I understand what's happening now, as I was misunderstanding part of how CancellationTokens are supposed to be used. We should instead be asking the user to pass a CancellationTokenSource which can be used to get an associated CancellationToken.

What we actually would want here is to create a method IServerTestBuilder WithCancellationTokenSource(CancellationTokenSource cancellationTokenSource) and then do

invoker.SendAsync(this.httpRequestMessage, this.cancellationTokenSource.Token).Result;

For example, the user could then create a new CancellationTokenSource which cancels the operation after a certain amount of time:

var tokenSource = new new CancellationTokenSource(TimeSpan.FromSeconds(30));
MyWebApi.Server().Working().WithCancellationTokenSource(tokenSource);

[ivaylokenov]

@bgold09 Yes, we both misunderstood it obviously. Otherwise, with the CancelationTokenSource it works now and the token is passed through the server.

One final thought before I implement this feature - if the only parameter the developer can use is a TimeSpan value it will be difficult for him/her to determine the exact value to set so that a particular cancelation is tested. It is not very deterministic. Any thoughts?