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  1. C Driver
  2. CDRIVER-4028

Wrong error message printed when DNS resolution fails

    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Major - P3 Major - P3
    • 1.17.7
    • Affects Version/s: None
    • Component/s: None
    • None

      While investigating HELP-25377, I noticed that _mongoc_get_rr_search uses strerror to print an error message from h_errno. The latter is set when an error occurs in the res_nsearch or res_search calls earlier. However, h_errno is not designed to be run through strerror, and the actual error is different from what we see in the error message. In HELP-25377 in particular, the error message seen was "Interrupted system call". We can see its mapping:

      #define	EINTR		 4	/* Interrupted system call */
      

      Looking at the error section for h_errno in the manual, this is not at all what's happening:

      Errors

      The variable h_errno can have the following values:

      HOST_NOT_FOUND
      The specified host is unknown.
      NO_ADDRESS or NO_DATA
      The requested name is valid but does not have an IP address.
      NO_RECOVERY
      A nonrecoverable name server error occurred.
      TRY_AGAIN
      A temporary error occurred on an authoritative name server. Try again later.

      h_errno.h also defines hstrerror to retrieve the error string for a given error code, but this has been marked obsolete. With that in mind, I'd suggest adding _mongoc_hstrerror to get an error string for an error, taken from the list above.

      I'll note that whether on purpose or by oversight, the function also ignores the TRY_AGAIN error. One could argue that "Try again later" does not suggest retrying the lookup right away, and it also wouldn't have fixed the problem in HELP-25377 as h_errno is set to NO_DATA. However, it might be beneficial to try again to protect against transient failures.

            Assignee:
            andreas.braun@mongodb.com Andreas Braun
            Reporter:
            andreas.braun@mongodb.com Andreas Braun
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              Created:
              Updated:
              Resolved: