kuma-cp: add generic versioner for xDS resources

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 Changes:
 
+* feature: add a generic versioner for xDS Snapshots
+  [#529](https://github.com/Kong/kuma/pull/529)
 * feature: add a custom version of SnapshotCache that supports arbitrary xDS resources
   [#528](https://github.com/Kong/kuma/pull/528)
 * feature: add proto definition for Monitoring Assignment Discovery Service (MADS)

pkg/util/xds/versioner.go

@@ -0,0 +1,51 @@
+package xds
+
+import (
+	envoy_cache "github.com/envoyproxy/go-control-plane/pkg/cache"
+	"github.com/golang/protobuf/proto"
+)
+
+// SnapshotVersioner assigns versions to xDS resources in a new Snapshot.
+type SnapshotVersioner interface {
+	Version(new, old Snapshot) Snapshot
+}
+
+// SnapshotAutoVersioner assigns versions to xDS resources in a new Snapshot
+// by reusing if possible a version from the old snapshot and
+// generating a new version (UUID) otherwise.
+type SnapshotAutoVersioner struct {
+	UUID func() string
+}
+
+func (v SnapshotAutoVersioner) Version(new, old Snapshot) Snapshot {
+	if new == nil {
+		return nil
+	}
+	for _, typ := range new.GetSupportedTypes() {
+		version := new.GetVersion(typ)
+		if version != "" {
+			// favour a version assigned by resource generator
+			continue
+		}
+		if old != nil && v.equal(new.GetResources(typ), old.GetResources(typ)) {
+			version = old.GetVersion(typ)
+		}
+		if version == "" {
+			version = v.UUID()
+		}
+		new = new.WithVersion(typ, version)
+	}
+	return new
+}
+
+func (_ SnapshotAutoVersioner) equal(new, old map[string]envoy_cache.Resource) bool {
+	if len(new) != len(old) {
+		return false
+	}
+	for key, newValue := range new {
+		if oldValue, hasOldValue := old[key]; !hasOldValue || !proto.Equal(newValue, oldValue) {
+			return false
+		}
+	}
+	return true
+}