[Discussion] TestServer no longer preserves ExecutionContext and AsyncLocals between client and server

Note: This change affects test code using TestServer only.

Starting in ASP.NET Core 3.0 Preview 6, the ExecutionContext will no longer be preserved when making HTTP requests to TestServer.

As a result of this change, the ExecutionContext in the calling code will not be available to the server code. This means the following values which use ExecutionContext as their underlying storage will not be preserved when performing an HTTP request over TestServer:

• Thread.CurrentCulture
• CultureInfo.CurrentCulture
• CultureInfo.CurrentUICulture
• Activity.Current
• Thread.CurrentPrincipal
• Other values which use AsyncLocal<T> for storage.

If the previous behavior is required by your test code, you can restore it by setting the PreserveExecutionContext property on TestServer to true:

var server = new TestServer(webHostBuilder) 
{
	PreserveExecutionContext = true;
};

---

This is the discussion issue for https://github.com/aspnet/Announcements/issues/358.

[analogrelay]

@slang25 Correct, this is about flowing from the client to the server. It’s not a perf thing, it’s a correctness thing. And yeah, it generally makes sense because you are testing an HTTP request, and HTTP requests generally don’t flow AsyncLocal values across them (since they’re cross machine!) 😃.

The specific motivation is that flowing execution context actually breaks IHttpContextAccessor if you have “nested” HTTP calls. Imagine you are testing a multi-app system using TestServer:

Client -> Server A -> Server B

Both servers are hosted in TestServer and you’re giving the HttpClient provided by TestServer to Server A so that it can “call” Server B. Testing authentication flows often requires this, as do some microservice systems.

During an invocation to Server A, both servers are sharing the IHttpContextAccessor value, which makes all kinds of mess 😃.

[msftbot[bot]]

Thank you for contacting us. Due to a lack of activity on this discussion issue we’re closing it in an effort to keep our backlog clean. If you believe there is a concern related to the ASP.NET Core framework, which hasn’t been addressed yet, please file a new issue.

This issue will be locked after 30 more days of inactivity. If you still wish to discuss this subject after then, please create a new issue!