Italo Busi <[email protected]> wrote:
> We have found some issues with RPC XPaths when developing the YANG
> code for
> https://tools.ietf.org/html/draft-ietf-teas-yang-path-computation
>
> As discussed during the TEAS WG session in IETF 108, this issue has
> been raised on pyang github:
> https://github.com/mbj4668/pyang/issues/662
>
> It was also suggested to check with Netmod WG what should be the
> correct behavior according to RFC7950.
>
> The following code is accepted by pyang 1.75 but not by pyang 2.1:
>
> type leafref {
> path "/te:tunnels-path-compute/te:input/"
> + "te:path-compute-info/"
> + "te-pc:tunnel-attributes/te-pc:tunnel-name";
> }
>
> The following code instead is accepted by pyang 2.1 but not by pyang
> 1.7.5:
>
> type leafref {
> path "/te:tunnels-path-compute/"
> + "te:path-compute-info/"
> + "te-pc:tunnel-attributes/te-pc:tunnel-name";
> }
The leafref path is an XPath expression, which operates on the data
tree (instance data). The "input" node is not present in the instance
data / data tree. See section 6.4.1 of RFC 7950.
So the latter path (as verfied by pyang 2.1) is correct.
> Moreover the following when statement, which is quite useful to
> constraint which information is provided by the RPC output based on
> some attributes in the RPC input, is accepted by pyang 1.7.5 but not
> accepted by pyang 2.1;
>
> augment "/te:tunnels-actions/te:output" {
> description
> "Augment Tunnels Action RPC input with path delete result";
>
> container path-computed-delete-result {
> when "derived-from-or-self(../../te:input/te:action-info/"
> + "te:action, 'tunnel-action-path-compute-delete')";
> description "Path Delete RPC output";
> leaf-list path-compute-transaction-id {
> type string;
> description
> "The list of the transaction-id values of the
> transient states that have been successfully deleted";
> }
> } // container path-computed-delete-result
> } // path-delete rpc output
>
>
> Could you please help us to understand what is the correct behavior?
>
> In case the correct behavior is the one of pyang 2.1, our
> understanding is that it would not be possible to provide in YANG when
> constraints for the data nodes in the RPC output depending on specific
> values of the data nodes used in the RPC input. Therefore these
> constraints should be specified as behavior and implemented in the
> back-end.
>
> Is our understanding correct?
Yes, this is correct. It is not possible to refer to the
corresponding "input" instance data in the XPath expressions for the
"output".
/martin
>
> Thanks for your help
>
> Sergio and Italo (on behalf of co-authors/contributors)
>
> Italo Busi
> Principal Optical Transport Network Research Engineer
>
> [cid:[email protected]]
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