Hi,
Jernej Tuljak <[email protected]> wrote:
> Hi,
>
> I'm trying to determine who is at fault, our YANG validator
> implementation or the module ietf-netconf-nmda in RFC8526 .
>
> There is a "when" expression at line 193 within this module
>
> when 'derived-from-or-self(datastore, "ds:operational") ';
>
> which is under this pseudo-branch within the module: / get-data
> ("rpc") / input ("input") / origin-filters ("choice").
>
> Our implementation claims that the initial context node of the
> expression does not contain a "datastore" child, resulting in a
> warning for this expression, which seemed like an obvious bug at
> first, but does not anymore.
>
> The accessible tree for this expression is built using the following
> bullet in Section 6.4.1:
>
> o If the XPath expression is defined in a substatement to an "input"
> statement in an "rpc" or "action" statement, the accessible tree
> is the RPC or action operation instance, all state data in the
> server, and the running configuration datastore. The root node
> has top-level data nodes in all modules as children.
> Additionally, for an RPC, the root node also has the node
> representing the RPC operation being defined as a child. The node
> representing the operation being defined has the operation's input
> parameters as children.
>
>
> "origin-filters" for which the "when" expression is defined is clearly
> a substatement to an "input" statement in an "rpc" statement. Pseudo-
> accessible tree below (matches what our implementation does).
>
> <root>
> +- get-data
> +- datastore
> +- // other data node siblings of datastore
> +- // top-level data nodes of all modules
>
> The initial context node is determined by using the following bullet
> in Section 7.21.5:
>
> o If the "when" statement is a child of a "uses", "choice", or
> "case" statement, then the context node is the closest ancestor
> node to the node with the "when" statement that is also a data
> node. If no such node exists, the context node is the root node.
> The accessible tree is tentatively altered during the processing
> of the XPath expression by removing all instances (if any) of the
> nodes added by the "uses", "choice", or "case" statement.
>
>
> The "when" statement in question is clearly a child of a "choice"
> statement without a data node ancestor. Neither "input" nor "rpc"
> represent data nodes, as per Terminology section:
>
> o data node: A node in the schema tree that can be instantiated in a
> data tree. One of container, leaf, leaf-list, list, anydata, and
> anyxml.
>
>
> To our implementation this means that the initial context node is the
> root node of the accessible tree, not the node that represents the
> "rpc". Therefore the expression is attempting to refer to a node that
> is undefined. It is expecting
>
> when 'derived-from-or-self(get-data/datastore, "ds:operational") ';
>
> or something along those lines instead.
>
> Either way, something doesn't add up between RFC7950 and RFC8526.
>
> There is a suspicious verified RFC7950 errata
> (https://www.rfc-editor.org/errata/eid4794) dealing with initial
> context nodes under augments, but there's nothing for the UCC ("uses",
> "choice", "case") corner case. Perhaps there should be? Should Section
> 7.21.5 say
>
> NEW:
>
> o If the "when" statement is a child of a "uses", "choice", or
> "case" statement, then the context node is the closest ancestor
> node to the node with the "when" statement that is also a data
> node, rpc, action or notification. If no such node exists, the
> context node is the root node. The accessible tree is tentatively
> altered during the processing of the XPath expression by removing
> all instances (if any) of the nodes added by the "uses",
> "choice", or "case" statement.
>
> OLD:
>
> o If the "when" statement is a child of a "uses", "choice", or
> "case" statement, then the context node is the closest ancestor
> node to the node with the "when" statement that is also a data
> node. If no such node exists, the context node is the root node.
> The accessible tree is tentatively altered during the processing
> of the XPath expression by removing all instances (if any) of the
> nodes added by the "uses", "choice", or "case" statement.
>
> ?
I think this matches the intent. As you note above, since the
accessible tree is:
<root>
+- get-data
+- datastore
+- // other data node siblings of datastore
+- // top-level data nodes of all modules
the context node for the "when" statement in the "choice" is supposed
to be "get-data".
This also makes it consistent with augment:
augment /get-data/input {
choice origin-filters {
when 'derived-from-or-self(datastore, "ds:operational")';
...
}
}
/martin
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