exporthistory: guard against repeated continuation tokens in pageable

Author: bachuv

exporthistory/src/main/java/com/microsoft/durabletask/exporthistory/client/ExportJobQueryPageable.java

@@ -57,18 +57,22 @@ public ExportJobDescription next() {
             }
 
             private void fetchNextPage() {
+                String previousToken = this.continuationToken;
                 ExportJobQuery query = new ExportJobQuery(
                         baseQuery != null ? baseQuery.getStatus() : null,
                         baseQuery != null ? baseQuery.getJobIdPrefix() : null,
                         baseQuery != null ? baseQuery.getCreatedFrom() : null,
                         baseQuery != null ? baseQuery.getCreatedTo() : null,
                         baseQuery != null ? baseQuery.getPageSize() : null,
-                        this.continuationToken);
+                        previousToken);
 
                 ExportJobQueryResult result = queryExecutor.apply(query);
                 this.currentPage = result.getJobs().iterator();
                 this.continuationToken = result.getContinuationToken();
-                this.hasMorePages = this.continuationToken != null && !this.continuationToken.isEmpty();
+                boolean hasToken = this.continuationToken != null && !this.continuationToken.isEmpty();
+                // Safety guard: if the backend echoes the same continuation token, treat the
+                // stream as exhausted to avoid an infinite loop in hasNext()'s empty-page loop.
+                this.hasMorePages = hasToken && !this.continuationToken.equals(previousToken);
             }
         };
     }
@@ -92,17 +96,21 @@ public ExportJobQueryResult next() {
                 if (!hasNext()) {
                     throw new java.util.NoSuchElementException();
                 }
+                String previousToken = this.continuationToken;
                 ExportJobQuery query = new ExportJobQuery(
                         baseQuery != null ? baseQuery.getStatus() : null,
                         baseQuery != null ? baseQuery.getJobIdPrefix() : null,
                         baseQuery != null ? baseQuery.getCreatedFrom() : null,
                         baseQuery != null ? baseQuery.getCreatedTo() : null,
                         baseQuery != null ? baseQuery.getPageSize() : null,
-                        this.continuationToken);
+                        previousToken);
 
                 ExportJobQueryResult result = queryExecutor.apply(query);
                 this.continuationToken = result.getContinuationToken();
-                this.hasMorePages = this.continuationToken != null && !this.continuationToken.isEmpty();
+                boolean hasToken = this.continuationToken != null && !this.continuationToken.isEmpty();
+                // Safety guard: if the backend echoes the same continuation token, treat the
+                // stream as exhausted to avoid endless re-fetching of the same page.
+                this.hasMorePages = hasToken && !this.continuationToken.equals(previousToken);
                 return result;
             }
         };