Treat document V1 API visiting timeouts with progress as successful (#2401)

Previously, using a visitor with a selection that did not match any buckets
visited during the session's lifetime would trigger a timeout error to the
client and abort the visiting. With this change, we special case timeouts if
they have successfully visited at least 1 bucket and return a successful
response for these. The client can then use the updated continuation token
for its subsequent request and continue from where the timed out session
left off.

The timeout special cased handling is done _outside_ the session and control
handler to avoid increasing session-internal complexity, and since not all
visitor use cases want this behavior (e.g. streaming search).

1 files changed, 7 insertions, 4 deletions

diff --git a/documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java b/documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java
index 306103f2912..56edc7eb42a 100755
--- a/documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java
+++ b/documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java
@@ -883,8 +883,7 @@ public class MessageBusVisitorSession implements VisitorSession {
 
         if (isFatalError(reply)) {
             if (params.skipBucketsOnFatalErrors()) {
-                progress.getToken().addFailedBucket(bucket, subProgress, message);
-                progress.getIterator().update(bucket, ProgressToken.FINISHED_BUCKET);
+                markBucketProgressAsFailed(bucket, subProgress, message);
             } else {
                 reportVisitorError(message);
                 transitionTo(new StateDescription(State.FAILED, message));
@@ -903,6 +902,11 @@ public class MessageBusVisitorSession implements VisitorSession {
         }
     }
 
+    private void markBucketProgressAsFailed(BucketId bucket, BucketId subProgress, String message) {
+        progress.getToken().addFailedBucket(bucket, subProgress, message);
+        progress.getIterator().update(bucket, ProgressToken.FINISHED_BUCKET);
+    }
+
     private boolean enoughHitsReceived() {
         if (params.getMaxFirstPassHits() != -1
                 && statistics.getDocumentsReturned() >= params.getMaxFirstPassHits())
@@ -1024,7 +1028,6 @@ public class MessageBusVisitorSession implements VisitorSession {
 
     private void handleWrongDistributionReply(WrongDistributionReply reply) {
         try {
-            // Classnames clash with documentapi classes, so be explicit
             ClusterState newState = new ClusterState(reply.getSystemState());
             int stateBits = newState.getDistributionBitCount();
             if (stateBits != progress.getIterator().getDistributionBitCount()) {
@@ -1123,7 +1126,7 @@ public class MessageBusVisitorSession implements VisitorSession {
                 synchronized (completionMonitor) {
                     // If we are destroying the session before it has completed (e.g. because
                     // waitUntilDone timed out or an interactive visiting was interrupted)
-                    // set us to aborted state so that we'll seize
+                    // set us to aborted state so that we'll seize sending new visitors.
                     if (!done) {
                         transitionTo(new StateDescription(State.ABORTED, "Session explicitly destroyed before completion"));
                     }