Ensure that resumeToken is included on resume attempts

driver-core/src/main/com/mongodb/internal/operation/ChangeStreamBatchCursor.java

@@ -64,7 +64,11 @@ public boolean hasNext() {
         return resumeableOperation(new Function<AggregateResponseBatchCursor<RawBsonDocument>, Boolean>() {
             @Override
             public Boolean apply(final AggregateResponseBatchCursor<RawBsonDocument> queryBatchCursor) {
-                return queryBatchCursor.hasNext();
+                try {
+                    return queryBatchCursor.hasNext();
+                } finally {
+                    cachePostBatchResumeToken(queryBatchCursor);
+                }
             }
         });
     }
@@ -74,9 +78,11 @@ public List<T> next() {
         return resumeableOperation(new Function<AggregateResponseBatchCursor<RawBsonDocument>, List<T>>() {
             @Override
             public List<T> apply(final AggregateResponseBatchCursor<RawBsonDocument> queryBatchCursor) {
-                List<T> results = convertResults(queryBatchCursor.next());
-                cachePostBatchResumeToken(queryBatchCursor);
-                return results;
+                try {
+                    return convertResults(queryBatchCursor.next());
+                } finally {
+                    cachePostBatchResumeToken(queryBatchCursor);
+                }
             }
         });
     }
@@ -86,9 +92,11 @@ public List<T> tryNext() {
         return resumeableOperation(new Function<AggregateResponseBatchCursor<RawBsonDocument>, List<T>>() {
             @Override
             public List<T> apply(final AggregateResponseBatchCursor<RawBsonDocument> queryBatchCursor) {
-                List<T> results = convertResults(queryBatchCursor.tryNext());
-                cachePostBatchResumeToken(queryBatchCursor);
-                return results;
+                try {
+                    return convertResults(queryBatchCursor.tryNext());
+                } finally {
+                    cachePostBatchResumeToken(queryBatchCursor);
+                }
             }
         });
     }

driver-core/src/main/com/mongodb/internal/operation/QueryBatchCursor.java

@@ -100,6 +100,7 @@ class QueryBatchCursor<T> implements AggregateResponseBatchCursor<T> {
         this.decoder = notNull("decoder", decoder);
         if (result != null) {
             this.operationTime = result.getTimestamp(OPERATION_TIME, null);
+            this.postBatchResumeToken = getPostBatchResumeTokenFromResponse(result);
         }
         if (firstQueryResult.getCursor() != null) {
             notNull("connectionSource", connectionSource);

driver-core/src/test/functional/com/mongodb/OperationFunctionalSpecification.groovy

@@ -157,21 +157,32 @@ class OperationFunctionalSpecification extends Specification {
     }
 
     def next(cursor, boolean async, int minimumCount) {
+        next(cursor, async, false, minimumCount)
+    }
+
+    def next(cursor, boolean async, boolean callHasNextBeforeNext, int minimumCount) {
         List<BsonDocument> retVal = []
 
         while (retVal.size() < minimumCount) {
-            retVal.addAll(next(cursor, async))
+            retVal.addAll(doNext(cursor, async, callHasNextBeforeNext))
         }
 
         retVal
     }
 
     def next(cursor, boolean async) {
+        doNext(cursor, async, false)
+    }
+
+    def doNext(cursor, boolean async, boolean callHasNextBeforeNext) {
         if (async) {
             def futureResultCallback = new FutureResultCallback<List<BsonDocument>>()
             cursor.next(futureResultCallback)
             futureResultCallback.get(TIMEOUT, TimeUnit.SECONDS)
         } else {
+            if (callHasNextBeforeNext) {
+                cursor.hasNext()
+            }
             cursor.next()
         }
     }

driver-core/src/test/functional/com/mongodb/internal/operation/ChangeStreamOperationProseTestSpecification.groovy

@@ -96,7 +96,7 @@ class ChangeStreamOperationProseTestSpecification extends OperationFunctionalSpe
         setFailPoint(failPointDocument)
 
         then:
-        def result = next(cursor, async, 2)
+        def result = next(cursor, async, callHasNext, 2)
 
         then:
         result.size() == 2
@@ -107,7 +107,10 @@ class ChangeStreamOperationProseTestSpecification extends OperationFunctionalSpe
         waitForLastRelease(async ? getAsyncCluster() : getCluster())
 
         where:
-        async << [true, false]
+        async  | callHasNext
+        true   | false
+        false  | false
+        false  | true
     }
 
     //

driver-sync/src/test/functional/com/mongodb/client/ChangeStreamProseTest.java

@@ -370,8 +370,10 @@ public void testGetResumeTokenReturnsPostBatchResumeTokenAfterGetMore()
             // use reflection to access the postBatchResumeToken
             AggregateResponseBatchCursor<?> batchCursor = getBatchCursor(cursor);
 
-            // check equality in the case where the batch has not been iterated at all
-            assertEquals(cursor.getResumeToken(), batchCursor.getPostBatchResumeToken());
+            assertNotNull(batchCursor.getPostBatchResumeToken());
+
+            // resume token should be null before iteration
+            assertNull(cursor.getResumeToken());
 
             cursor.next();
             assertEquals(cursor.getResumeToken(), batchCursor.getPostBatchResumeToken());

driver-sync/src/test/functional/com/mongodb/client/unified/UnifiedTestValidator.java

@@ -33,7 +33,6 @@
 import java.util.Collection;
 import java.util.List;
 
-import static org.junit.Assume.assumeTrue;
 import static util.JsonPoweredTestHelper.getTestDocument;
 import static util.JsonPoweredTestHelper.getTestFiles;
 
@@ -51,8 +50,6 @@ public UnifiedTestValidator(final String fileDescription, final String testDescr
 
     @Before
     public void setUp() {
-        // TODO: remove after https://jira.mongodb.org/browse/JAVA-3871 is fixed
-        assumeTrue(!(fileDescription.equals("poc-change-streams") && testDescription.equals("Test consecutive resume")));
         super.setUp();
     }