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  1. C Driver
  2. CDRIVER-5515

Assertion fails on legacy exhaust cursor with empty results

    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Unknown Unknown
    • 1.26.2
    • Affects Version/s: 1.24.0
    • Component/s: None
    • None
    • C Drivers

      Summary

      An assertion fails when creating a legacy exhaust cursor receiving empty results:

      src/libbson/src/bson/bson-reader.c:526 bson_reader_new_from_data(): precondition failed: data
      

      This applies when creating an exhaust cursor with the legacy op code OP_QUERY. The C driver uses OP_QUERY for exhaust cursor when connected to mongod < 4.2.

      This appears to be a regression introduced in 1.24.0 as part of CDRIVER-4617.

      Additional Information

      Here is a regression test:

      static void
      test_exhaust_cursor_no_match (void *context)
      {
         BSON_UNUSED (context);
         bson_error_t error;
         mongoc_client_t *client = test_framework_new_default_client ();
         mongoc_collection_t *coll = mongoc_client_get_collection (client, "db", "coll");
      
         // Drop collection to remove prior test data.
         mongoc_collection_drop (coll, NULL /* ignore error */);
      
         mongoc_cursor_t *cursor = mongoc_collection_find_with_opts (
            coll, tmp_bson ("{}"), tmp_bson ("{'exhaust': true }"), NULL /* read_prefs */);
         const bson_t *result;
         while (mongoc_cursor_next (cursor, &result)); // Assertion failure!
      
         mongoc_cursor_destroy (cursor);
         mongoc_collection_destroy (coll);
         mongoc_client_destroy (client);
      }
      
      

      Here is a stack trace for the assert:

      #0  bson_reader_new_from_data (data=0x0, length=0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libbson/src/bson/bson-reader.c:526
      #1  0x00005555558c1483 in _mongoc_cursor_op_query_find (cursor=0x5555560556b0, filter=0x555556096c78, response=0x555556096c40) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/src/mongoc/mongoc-cursor-legacy.c:587
      #2  0x00005555558be264 in _prime (cursor=0x5555560556b0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/src/mongoc/mongoc-cursor-find-opquery.c:49
      #3  0x00005555558bdc79 in _prime (cursor=0x5555560556b0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/src/mongoc/mongoc-cursor-find.c:57
      #4  0x00005555558ba91f in _call_transition (cursor=0x5555560556b0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/src/mongoc/mongoc-cursor.c:1145
      #5  0x00005555558bab43 in mongoc_cursor_next (cursor=0x5555560556b0, bson=0x7fffffffd9e0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/src/mongoc/mongoc-cursor.c:1221
      #6  0x00005555556e7031 in test_exhaust_cursor_no_match (context=0x0) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/tests/test-mongoc-exhaust.c:364
      #7  0x00005555557e867c in TestSuite_RunTest (suite=0x7fffffffdf80, test=0x555555efd2d0, count=0x7fffffffdf08) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/tests/TestSuite.c:611
      #8  0x00005555557e98a7 in TestSuite_RunAll (suite=0x7fffffffdf80) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/tests/TestSuite.c:1046
      #9  0x00005555557e99f4 in TestSuite_Run (suite=0x7fffffffdf80) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/tests/TestSuite.c:1091
      #10 0x00005555555665ed in main (argc=4, argv=0x7fffffffe108) at /home/ubuntu/code/tasks/mongo-c-driver-cursor-crash/src/libmongoc/tests/test-libmongoc-main.c:157
      

            Assignee:
            kevin.albertson@mongodb.com Kevin Albertson
            Reporter:
            kevin.albertson@mongodb.com Kevin Albertson
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              Created:
              Updated:
              Resolved: