Ignore cancellation error when search is cancelled (#64240)

Since #63520, we will cancel a search that hits shard failures and does 
not accept partial results. However, that change can return the wrong
HTTP code for bad requests (from 4xx to 5xx) due to the cancellation.

Relates #63520
Closes #64012
Closes #63702

server/src/main/java/org/elasticsearch/action/search/AbstractSearchAsyncAction.java

@@ -44,6 +44,7 @@
 import org.elasticsearch.search.internal.InternalSearchResponse;
 import org.elasticsearch.search.internal.SearchContext;
 import org.elasticsearch.search.internal.ShardSearchRequest;
+import org.elasticsearch.tasks.TaskCancelledException;
 import org.elasticsearch.transport.Transport;
 
 import java.util.ArrayDeque;
@@ -437,8 +438,9 @@ protected void onShardGroupFailure(int shardIndex, SearchShardTarget shardTarget
      */
     @Override
     public final void onShardFailure(final int shardIndex, @Nullable SearchShardTarget shardTarget, Exception e) {
-        // we don't aggregate shard failures on non active shards (but do keep the header counts right)
-        if (TransportActions.isShardNotAvailableException(e) == false) {
+        // we don't aggregate shard failures on non active shards and failures due to the internal cancellation,
+        // but do keep the header counts right
+        if (TransportActions.isShardNotAvailableException(e) == false && (requestCancelled.get() && isTaskCancelledException(e)) == false) {
             AtomicArray<ShardSearchFailure> shardFailures = this.shardFailures.get();
             // lazily create shard failures, so we can early build the empty shard failure list in most cases (no failures)
             if (shardFailures == null) { // this is double checked locking but it's fine since SetOnce uses a volatile read internally
@@ -469,6 +471,10 @@ public final void onShardFailure(final int shardIndex, @Nullable SearchShardTarg
         results.consumeShardFailure(shardIndex);
     }
 
+    private static boolean isTaskCancelledException(Exception e) {
+        return ExceptionsHelper.unwrapCausesAndSuppressed(e, ex -> ex instanceof TaskCancelledException).isPresent();
+    }
+
     /**
      * Executed once for every successful shard level request.
      * @param result the result returned form the shard

x-pack/plugin/async-search/src/internalClusterTest/java/org/elasticsearch/xpack/search/AsyncSearchActionIT.java

@@ -406,7 +406,6 @@ public void testRemoveAsyncIndex() throws Exception {
         ensureTaskRemoval(newResp.getId());
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/63702")
     public void testSearchPhaseFailureNoCause() throws Exception {
         SubmitAsyncSearchRequest request = new SubmitAsyncSearchRequest(indexName);
         request.setKeepOnCompletion(true);