coordinated request observables when aborted could bubble out an UnexpectedElasticsearchClientException or a OperationCancelledException, this normalizes what gets passed to OnError (OperationCancelledException) (#4027)

(cherry picked from commit 6b8c63f)

Author: Mpdreamz

src/Elasticsearch.Net/Transport/Pipeline/RequestPipeline.cs

@@ -290,6 +290,8 @@ public async Task FirstPoolUsageAsync(SemaphoreSlim semaphore, CancellationToken
 		{
 			if (!FirstPoolUsageNeedsSniffing) return;
 
+			// TODO cancellationToken could throw here and will bubble out as OperationCancelledException
+			// everywhere else it would bubble out wrapped in a `UnexpectedElasticsearchClientException`
 			var success = await semaphore.WaitAsync(_settings.RequestTimeout, cancellationToken).ConfigureAwait(false);
 			if (!success)
 			{

src/Elasticsearch.Net/Transport/Transport.cs

@@ -142,6 +142,9 @@ public async Task<TResponse> RequestAsync<TResponse>(HttpMethod method, string p
 					}
 					catch (Exception killerException)
 					{
+						if (killerException is OperationCanceledException && cancellationToken.IsCancellationRequested)
+							pipeline.AuditCancellationRequested();
+
 						throw new UnexpectedElasticsearchClientException(killerException, seenExceptions)
 						{
 							Request = requestData,

src/Nest/CommonAbstractions/Reactive/CoordinatedRequestObserverBase.cs

@@ -1,4 +1,5 @@
 using System;
+using Elasticsearch.Net;
 
 namespace Nest
 {
@@ -27,7 +28,15 @@ protected CoordinatedRequestObserverBase(Action<T> onNext = null, Action<Excepti
 
 		public void OnCompleted() => _completed?.Invoke();
 
-		public void OnError(Exception error) => _onError?.Invoke(error);
+		public void OnError(Exception error)
+		{
+			// This normalizes task cancellation exceptions for observables
+			// If a task cancellation happens in the client it bubbles out as a UnexpectedElasticsearchClientException
+			// where as inside our IObservable implementation we .ThrowIfCancellationRequested() directly.
+			if (error is UnexpectedElasticsearchClientException es && es.InnerException != null && es.InnerException is OperationCanceledException c)
+				_onError?.Invoke(c);
+			else _onError?.Invoke(error);
+		}
 
 		public void OnNext(T value) => _onNext?.Invoke(value);
 	}

src/Tests/Tests/Document/Multiple/BulkAll/BulkAllCancellationTokenApiTests.cs

@@ -46,12 +46,13 @@ public void CancelBulkAll()
 			//when we subscribe the observable becomes hot
 			observableBulk.Subscribe(bulkObserver);
 
-			//we wait Nseconds to see some bulks
+			//we wait N seconds to see some bulks
 			handle.WaitOne(TimeSpan.FromSeconds(3));
 			tokenSource.Cancel();
-			//we wait Nseconds to give in flight request a chance to cancel
+			//we wait N seconds to give in flight request a chance to cancel
 			handle.WaitOne(TimeSpan.FromSeconds(3));
-			if (ex != null && !(ex is TaskCanceledException) && !(ex is OperationCanceledException)) throw ex;
+
+			if (ex != null && !(ex is OperationCanceledException)) throw ex;
 
 			seenPages.Should().BeLessThan(pages).And.BeGreaterThan(0);
 			var count = Client.Count<SmallObject>(f => f.Index(index));

src/Tests/Tests/Document/Multiple/BulkAll/BulkAllDisposeApiTests.cs

@@ -2,6 +2,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Elastic.Xunit.XunitPlumbing;
+using Elasticsearch.Net;
 using FluentAssertions;
 using Nest;
 using Tests.Core.ManagedElasticsearch.Clusters;
@@ -51,7 +52,8 @@ public void DisposingObservableCancelsBulkAll()
 			observableBulk.Dispose();
 			//we wait N seconds to give in flight request a chance to cancel
 			handle.WaitOne(TimeSpan.FromSeconds(3));
-			if (ex != null && !(ex is TaskCanceledException) && !(ex is OperationCanceledException)) throw ex;
+
+			if (ex != null && !(ex is OperationCanceledException)) throw ex;
 
 			seenPages.Should().BeLessThan(pages).And.BeGreaterThan(0);
 			var count = Client.Count<SmallObject>(f => f.Index(index));