I am working on a project where I want to keep users logged in using access tokens/refresh tokens. I store these values in a cookie and whenever a user visits the site, I want to automatically log him in regardless of the page that he uses to access the site. To do this, I created a BaseController, that all other controllers inherit from. The BaseController looks like this:
public abstract class BaseController : Controller
{
public BaseController()
{
LoginModel.SetUserFromAuthenticationCookie();
}
}
This constructor gets executed every time before an action is executed and is therefore exactly what I want. The problem is that SetUserFromAuthenticationCookie() is an async method, because it has to do calls to other async methods. It looks like this:
public async static Task SetUserFromAuthenticationCookie()
{
// Check if the authentication cookie is set and the User is null
if (AuthenticationRepository != null && User == null)
{
Api api = new Api();
// If a new authentication cookie was successfully created
if (await AuthenticationRepository.CreateNewAuthenticationCookieAsync())
{
var response = await api.Request(HttpMethod.Get, "api/user/mycredentials");
if(response.IsSuccessStatusCode)
{
User = api.serializer.Deserialize<UserViewModel>(await response.Content.ReadAsStringAsync());
}
}
}
}
The problem is that the execution order is not as I anticipated and because of that the user does not get logged in. I tried to work with .Result for the async methods, but that resulted in a deadlock. Besides that I read many threads on SO concerning the issue and eventually also found one that managed to get the login to work: How would I run an async Task<T> method synchronously?. It is somewhat hacky though and works with this helper:
public static class AsyncHelpers
{
/// <summary>
/// Execute's an async Task<T> method which has a void return value synchronously
/// </summary>
/// <param name="task">Task<T> method to execute</param>
public static void RunSync(Func<Task> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
synch.Post(async _ =>
{
try
{
await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
}
/// <summary>
/// Execute's an async Task<T> method which has a T return type synchronously
/// </summary>
/// <typeparam name="T">Return Type</typeparam>
/// <param name="task">Task<T> method to execute</param>
/// <returns></returns>
public static T RunSync<T>(Func<Task<T>> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
T ret = default(T);
synch.Post(async _ =>
{
try
{
ret = await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
return ret;
}
private class ExclusiveSynchronizationContext : SynchronizationContext
{
private bool done;
public Exception InnerException { get; set; }
readonly AutoResetEvent workItemsWaiting = new AutoResetEvent(false);
readonly Queue<Tuple<SendOrPostCallback, object>> items =
new Queue<Tuple<SendOrPostCallback, object>>();
public override void Send(SendOrPostCallback d, object state)
{
throw new NotSupportedException("We cannot send to our same thread");
}
public override void Post(SendOrPostCallback d, object state)
{
lock (items)
{
items.Enqueue(Tuple.Create(d, state));
}
workItemsWaiting.Set();
}
public void EndMessageLoop()
{
Post(_ => done = true, null);
}
public void BeginMessageLoop()
{
while (!done)
{
Tuple<SendOrPostCallback, object> task = null;
lock (items)
{
if (items.Count > 0)
{
task = items.Dequeue();
}
}
if (task != null)
{
task.Item1(task.Item2);
if (InnerException != null) // the method threw an exeption
{
throw new AggregateException("AsyncHelpers.Run method threw an exception.", InnerException);
}
}
else
{
workItemsWaiting.WaitOne();
}
}
}
public override SynchronizationContext CreateCopy()
{
return this;
}
}
If I then change the content of the BaseController constructor to:
AsyncHelpers.RunSync(() => LoginModel.SetUserFromAuthenticationCookie());
the functionality works as anticipated.
I would like to know though if you have any suggestions on how to do this in a nicer manner. Perhaps I should move the call to the SetUserFromAuthenticationCookie() to another location, but at this time I do not know where that would be.
