From 55a8b06b10805339d376003d6428ce0acf09afcd Mon Sep 17 00:00:00 2001
From: "Samani G. Gikandi" <samani@gojulas.com>
Date: Wed, 3 Sep 2025 07:51:58 -0700
Subject: [PATCH] xpath: adds support for prefixes in list keys

This diff adds support for prefixes in list keys as well as some unit
tests.

**Context**

Where an identifier is something like `interfaces`, an identifier with a
prefix might be `openconfig-interfaces:interface`. The ABNF in the YANG
RFCs refers to these as `node-identifier` rules.

The current xpath implementation does not allow prefixed identifiers in
list keys, however per [RFC 6020](https://datatracker.ietf.org/doc/html/rfc6020#section-12) and [RFC 7950](https://datatracker.ietf.org/doc/html/rfc7950#section-14) these
are valid.

We can look to openconfig for a [real world example](https://github.com/openconfig/public/blob/edf48ec7092fc2be9775937512dac8a1115483fb/release/models/interfaces/openconfig-interfaces.yang#L237-L242).

For completeness I've lifted some relevant grammar snippets from the YANG RFCs:

```
   identifier          = (ALPHA / "_")
                         *(ALPHA / DIGIT / "_" / "-" / ".")

   prefix              = identifier

   node-identifier     = [prefix ":"] identifier

   absolute-path       = 1*("/" (node-identifier *path-predicate))

   relative-path       = 1*(".." "/") descendant-path

   descendant-path     = node-identifier
                         [*path-predicate absolute-path]

   key-arg             = node-identifier *(sep node-identifier)

   key-arg-str         = < a string that matches the rule
                           key-arg >

   key-stmt            = key-keyword sep key-arg-str stmtend
```
---
 utils/xpath/xpath.go      |  7 ++++---
 utils/xpath/xpath_test.go | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/utils/xpath/xpath.go b/utils/xpath/xpath.go
index f18f02fe..c7618b4e 100644
--- a/utils/xpath/xpath.go
+++ b/utils/xpath/xpath.go
@@ -23,16 +23,17 @@ import (
 )
 
 var (
-	idPattern = `[a-zA-Z_][a-zA-Z\d\_\-\.]*`
+	idPattern     = `[a-zA-Z_][a-zA-Z\d\_\-\.]*`
+	nodeIdPattern = `(?:` + idPattern + `:)?` + idPattern
 	// YANG identifiers must follow RFC 6020:
 	// https://tools.ietf.org/html/rfc6020#section-6.2.
-	idRe = regexp.MustCompile(`^(?:`+idPattern+`:)?` + idPattern + `$`)
+	idRe = regexp.MustCompile(`^` + nodeIdPattern + `$`)
 	// The sting representation of List key value pairs must follow the
 	// following pattern: [key=value], where key is the List key leaf name,
 	// and value is the string representation of key leaf value.
 	kvRe = regexp.MustCompile(`^\[` +
 		// Key leaf name must be a valid YANG identifier.
-		idPattern + `=` +
+		nodeIdPattern + `=` +
 		// Key leaf value must be a non-empty string, which may contain
 		// newlines. Use (?s) to turn on s flag to match newlines.
 		`((?s).+)` +
diff --git a/utils/xpath/xpath_test.go b/utils/xpath/xpath_test.go
index ae844278..a4bbdd47 100644
--- a/utils/xpath/xpath_test.go
+++ b/utils/xpath/xpath_test.go
@@ -277,6 +277,11 @@ func TestParseElement(t *testing.T) {
 		elem:     "a[k1=v1][k2=v2]",
 		expectOK: true,
 		want:     []interface{}{"a", map[string]string{"k1": "v1", "k2": "v2"}},
+	}, {
+		desc:     "test list with xpath expression in key",
+		elem:     "interface[name=current()]",
+		expectOK: true,
+		want:     []interface{}{"interface", map[string]string{"name": "current()"}},
 	}}
 
 	for _, test := range tests {
@@ -360,6 +365,16 @@ func TestParseStringPath(t *testing.T) {
 	}, {
 		desc: "test path containing a multi-key List, second key-value pair without [ and ]",
 		path: "/a/b[k1=10]k2=abc/c",
+	}, {
+		desc:     "test path containing prefix",
+		path:     "/openconfig-interfaces:interface",
+		expectOK: true,
+		want:     []interface{}{"openconfig-interfaces:interface"},
+	}, {
+		desc:     "test path containing prefix in path and List",
+		path:     "/oc-if:interfaces/oc-if:interface[oc-if:name=current()/../interface]/oc-if:subinterfaces",
+		expectOK: true,
+		want:     []interface{}{"oc-if:interfaces", "oc-if:interface", map[string]string{"oc-if:name": "current()/../interface"}, "oc-if:subinterfaces"},
 	}}
 
 	for _, test := range tests {