[getdns-api] Error handling in getdns

Gowri V gmadkat1 at gmail.com
Thu Jan 7 16:25:08 UTC 2016

I strongly agree to this proposed change and have added some comments
inline below...

Also, I would like to propose something analogous to the errno or the
Windows function GetLastError()
where if the user desires, they can get a more detailed description, either
as a string or a dict, in addition to the below.
This would be useful diagnostics for a developer if any of the lower level
socket API calls fail for any reason, currently some of these failures
return a generic error.


On Thu, Jan 7, 2016 at 8:21 AM, Sara Dickinson <sara at sinodun.com> wrote:

> Hi All,
> Willem and I have been discussing the error handling in getdns and would
> like to propose some changes based on our implementation experience.
> 1) Asynchronous error handling
> At the moment the async callbacks are specified as below:
> The response has the requested data in it
> The calling program cancelled the callback; response is NULL
> The requested action timed out; response is filled in with empty structures
> The requested action had an error; response is NULL
> With this approach there is no mechanism to provide any more fine grained
> information to the user when an ERROR is return because the response in the
> callback is NULL.
> When considering a mainly UDP based approach this is probably sufficient,
> but to cater for TCP and TLS (with authentication) we would like to change
> the above so that a variety of errors that can occur that are not timeouts
> can be communicated to the caller.
> We would like to propose that the ERROR case is changed to have the same
> response as the TIMEOUT case i.e:
> The requested action had an error; response is filled in with empty
> structures
> And so the response structure would look similar to this example for a
> {
>   "answer_type": GETDNS_NAMETYPE_DNS,
>   "replies_full": [],
>   "replies_tree": [],
> }
> The new GETDNS_RESPSTATUS_ error cases we would like to add at this time
> are:
> TRANSPORT_SETUP_FAILED - for the case where no connection could be made
> over any specified transport to any upstream (for example, only TLS is
> specified but none of the available upstreams support it).
> TLS_FEATURE_NOT_SUPPORTED  - for the cases where getdns can’t support the
> configured transport/authentication options at runtime because the
> available TLS library doesn’t have the required functionality (for example
> support for TLS 1.2 or hostname verification methods)).

I suggest even more detailed reporting for the above, eg. TLS_FEATURE_NOT
_SUPPORTED_TLS12_NOT AVAILABLE and other errors where possible.

> TLS_AUTH_FAILED  - for the case when using TLS only and authentication is
> required but fails. This is strictly a sub-case of TRANSPORT_SETUP_FAILED
> but seems worthy of a separate status code.
> 3) Synchronous timeouts
> When calling the API synchronously, the return type of the functions is
> getdns_return_t. There is currently no value for GETDNS_RETURN_TIMEOUT and
> the behaviour for the sync calls is not clearly specified for a timeout in
> the spec. So our implementation currently uses GETDNS_RETURN_GOOD (and
> returns the response dict as in 1 above), the best alternative error code
> would be GETDNS_RETURN_GENERIC_ERROR. So we would like to propose adding
> the value GETDNS_RETURN_TIMEOUT to the getdns_return_t type.
> As a future activity we note that the above mechanisms can only relay a
> single error code. Since completing an API call can involve
> - performing multiple DNS queries
> - using multiple upstreams
> - using multiple transports
> - TLS authentication that can fail for various reasons
> - DNSSEC validations
> - TSIG validation
> we are considering adding an ‘error log trail’ utility that would be
> recorded during execution and could be returned in the response dict.
> Feedback on this is welcomed.

The error log trail utility is a good design pattern to implement for
getdns, perhaps add an extension that would return the error log trail in
the response dict similar to the return_call_reporting?

> Sara.
> _______________________________________________
> spec mailing list
> spec at getdnsapi.net
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