[NXOS] Diff PIM multicast group bindings individually per RP

Replacing entire StaticRP entries when their multicast group lists
change fails on NX-OS with "child (Rn) cannot be added to deleted
object Rn=rpgrplist-[...], Commit Failed".

Make StaticRPGrp implement Configurable so individual group entries
can be added or removed through gNMI. The EnsurePIM reconciliation
now diffs RPGrpListList entries per RP: only new groups are created,
only removed groups are deleted, and unchanged bindings stay in place.

Co-authored-by: i521907 <weneghawi@gmail.com>

Author: felix-kaestner

internal/provider/cisco/nxos/pim.go

@@ -9,6 +9,8 @@ var (
 	_ gnmiext.Configurable = (*PIM)(nil)
 	_ gnmiext.Configurable = (*PIMDom)(nil)
 	_ gnmiext.Configurable = (*StaticRPItems)(nil)
+	_ gnmiext.Configurable = (*StaticRP)(nil)
+	_ gnmiext.Configurable = (*StaticRPGrp)(nil)
 	_ gnmiext.Configurable = (*AnycastPeerItems)(nil)
 	_ gnmiext.Configurable = (*PIMIfItems)(nil)
 )
@@ -63,10 +65,18 @@ type StaticRPGrp struct {
 	Bidir       bool   `json:"bidir"`
 	GrpListName string `json:"grpListName"`
 	Override    bool   `json:"override"`
+
+	// RpAddr is the parent StaticRP address, used to construct the XPath.
+	// It is not serialized to JSON.
+	RpAddr string `json:"-"`
 }
 
 func (g *StaticRPGrp) Key() string { return g.GrpListName }
 
+func (g *StaticRPGrp) XPath() string {
+	return "System/pim-items/inst-items/dom-items/Dom-list[name=default]/staticrp-items/rp-items/StaticRP-list[addr=" + g.RpAddr + "]/rpgrplist-items/RPGrpList-list[grpListName=" + g.GrpListName + "]"
+}
+
 type AnycastPeerItems struct {
 	AcastRPPeerList gnmiext.List[AnycastPeerAddr, *AnycastPeerAddr] `json:"AcastRPPeer-list,omitzero"`
 }

internal/provider/cisco/nxos/provider.go

@@ -1705,7 +1705,39 @@ func (p *Provider) EnsurePIM(ctx context.Context, req *provider.EnsurePIMRequest
 	del := make([]gnmiext.Configurable, 0, 3)
 
 	if len(rpItems.StaticRPList) > 0 {
-		conf = append(conf, rpItems)
+		// Diff group-to-RP bindings individually; replacing entire StaticRP entries fails on NX-OS
+		// with "child (Rn) cannot be added to deleted object Rn=rpgrplist-[...], Commit Failed".
+		current := new(StaticRPItems)
+		if err := p.client.GetConfig(ctx, current); err != nil && !errors.Is(err, gnmiext.ErrNil) {
+			return err
+		}
+		for _, rp := range rpItems.StaticRPList {
+			got, ok := current.StaticRPList.Get(rp.Key())
+			if !ok {
+				// StaticRP does not exist yet — add the entire entry.
+				conf = append(conf, rp)
+				continue
+			}
+			for _, grp := range rp.RpgrplistItems.RPGrpListList {
+				if gotGrp, ok := got.RpgrplistItems.RPGrpListList.Get(grp.Key()); !ok || !reflect.DeepEqual(gotGrp, grp) {
+					g := *grp
+					g.RpAddr = rp.Addr
+					conf = append(conf, &g)
+				}
+			}
+			for _, grp := range got.RpgrplistItems.RPGrpListList {
+				if _, ok := rp.RpgrplistItems.RPGrpListList.Get(grp.Key()); !ok {
+					g := *grp
+					g.RpAddr = rp.Addr
+					del = append(del, &g)
+				}
+			}
+		}
+		for _, rp := range current.StaticRPList {
+			if _, ok := rpItems.StaticRPList.Get(rp.Key()); !ok {
+				del = append(del, rp)
+			}
+		}
 	} else {
 		del = append(del, rpItems)
 	}