WCF Data Services Task-based async query API-extension

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Data.Services.Client;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using JetBrains.Annotations;

namespace Blah
{
  public static class DataServiceContextExtensions
  {
    [NotNull]
    public static IEnumerable<Task<List<T>>> QueryAsyncPaged<T>(
      [NotNull] this IQueryable<T> query,
      [NotNull] DataServiceContext context, CancellationToken cancellationToken)
    {
      var registration = new CancellationTokenRegistration();
      var dataServiceQuery = (DataServiceQuery<T>)query;

      DataServiceQueryContinuation<T> queryContinuation = null;
      do
      {
        var completionSource = new TaskCompletionSource<List<T>>();
        try
        {
          AsyncCallback callback = result =>
          {
            // ReSharper disable once AccessToModifiedClosure
            // ReSharper disable once AccessToDisposedClosure
            registration.Dispose();

            try
            {
              var results = context.EndExecute<T>(result);
              var list = new List<T>(results ?? Enumerable.Empty<T>());

              var response = results as QueryOperationResponse<T>;
              if (response != null)
                queryContinuation = response.GetContinuation();

              completionSource.TrySetResult(list);
            }
            catch (Exception exception)
            {
              // DataServices EndExecute() throws IOE if query is cancelled
              if (exception is InvalidOperationException &&
                  cancellationToken.IsCancellationRequested)
                completionSource.TrySetCanceled();
              else
                completionSource.TrySetException(exception);
            }
          };

          var asyncResult = (queryContinuation == null)
            ? context.BeginExecute<T>(dataServiceQuery.RequestUri, callback, null)
            : context.BeginExecute(queryContinuation, callback, null);

          if (cancellationToken != CancellationToken.None)
          {
            registration = cancellationToken.Register(() =>
            {
              try { context.CancelRequest(asyncResult); } catch { }
            });
          }
        }
        catch (Exception exception)
        {
          completionSource.TrySetException(exception);
          registration.Dispose();
        }

        yield return completionSource.Task;

        try
        {
          completionSource.Task.Wait(cancellationToken);
        }
        catch (OperationCanceledException)
        {
          completionSource.TrySetCanceled();
        }
        catch (Exception exception)
        {
          completionSource.TrySetException(exception);
        }
      }
      while (queryContinuation != null);
    }
  }
}

Шо за мрачилова?

Никогда не видел Task-оберток над старыми Begin/End-апишками с маниакальным exception handling'ом и протаскиванием CancellationToken? Счастливый человек :)