MonitorScopeSelector with optional NetworkService?

[zolug]

I'd be interested in NSM connections around the cluster that belong to a particular Network Service. The concept would be similar to cmd-dashboard-backend.
However, MonitorScopeSelector only allows PathSegment based filtering/subscription.

The processes doing the monitoring would have NO knowledge on the path segments involved (might come and go over time). Using an empty selector does work, but the reason why I'd be interested in Network Service based filtering is mostly due to performance considerations.

I've attached a rudimentary patch with the proposed changes.
api.txt

[zolug]

diff --git a/pkg/api/networkservice/connection.pb.go b/pkg/api/networkservice/connection.pb.go
index 1b1122b..bc01690 100644
--- a/pkg/api/networkservice/connection.pb.go
+++ b/pkg/api/networkservice/connection.pb.go
@@ -46,9 +46,18 @@ const (
 type State int32
 
 const (
-	State_UP                 State = 0
-	State_DOWN               State = 1
-	State_REFRESH_REQUESTED  State = 2
+	// UP - Endpoint sets the connection state to UP when it successfully
+	// establishes the connection.
+	State_UP State = 0
+	// DOWN - Monitor Connection Server sets the connection state to DOWN
+	// when the connection is broken (for example, one of the NSM components is dead).
+	// Monitor Connection Server also sets the DOWN state for the deleted connections.
+	State_DOWN State = 1
+	// REFRESH_REQUESTED - This state indicates the server's connection parameters have
+	// been changed and the client should make a refresh to get them.
+	State_REFRESH_REQUESTED State = 2
+	// RESELECT_REQUESTED - This state indicates the client wants to use another endpoint
+	// for the connection. The client can set this state when it loses the connection.
 	State_RESELECT_REQUESTED State = 3
 )
 
@@ -98,9 +107,17 @@ func (State) EnumDescriptor() ([]byte, []int) {
 type ConnectionEventType int32
 
 const (
+	// INITIAL_STATE_TRANSFER - Monitor Connection Server immediately sends event
+	// with this type to a client when the client makes MonitorConnections Request.
+	// Event with this type contains all connections that Monitor Connection Server
+	// currently has.
 	ConnectionEventType_INITIAL_STATE_TRANSFER ConnectionEventType = 0
-	ConnectionEventType_UPDATE                 ConnectionEventType = 1
-	ConnectionEventType_DELETE                 ConnectionEventType = 2
+	// UPDATE - Monitor Connection Server sends event with this type when the
+	// connection changes. For exapmle, when the state of the connection has been changed.
+	ConnectionEventType_UPDATE ConnectionEventType = 1
+	// DELETE - Monitor Connection Server sends event with this type when the connection
+	// has been closed.
+	ConnectionEventType_DELETE ConnectionEventType = 2
 )
 
 // Enum value maps for ConnectionEventType.
@@ -512,7 +529,8 @@ type MonitorScopeSelector struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	PathSegments []*PathSegment `protobuf:"bytes,1,rep,name=path_segments,json=pathSegments,proto3" json:"path_segments,omitempty"`
+	PathSegments   []*PathSegment `protobuf:"bytes,1,rep,name=path_segments,json=pathSegments,proto3" json:"path_segments,omitempty"`
+	NetworkService []string       `protobuf:"bytes,2,rep,name=network_service,json=networkService,proto3" json:"network_service,omitempty"`
 }
 
 func (x *MonitorScopeSelector) Reset() {
@@ -554,6 +572,13 @@ func (x *MonitorScopeSelector) GetPathSegments() []*PathSegment {
 	return nil
 }
 
+func (x *MonitorScopeSelector) GetNetworkService() []string {
+	if x != nil {
+		return x.NetworkService
+	}
+	return nil
+}
+
 var File_connection_proto protoreflect.FileDescriptor
 
 var file_connection_proto_rawDesc = []byte{
@@ -640,33 +665,35 @@ var file_connection_proto_rawDesc = []byte{
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 }
 
 var (
diff --git a/pkg/api/networkservice/connection.proto b/pkg/api/networkservice/connection.proto
index 9fbe87e..e8eceee 100644
--- a/pkg/api/networkservice/connection.proto
+++ b/pkg/api/networkservice/connection.proto
@@ -91,6 +91,7 @@ message ConnectionEvent {
 
 message MonitorScopeSelector {
   repeated PathSegment path_segments = 1;
+  repeated string network_service = 2;
 }
 
 service MonitorConnection {
diff --git a/pkg/api/networkservice/connection_helpers.go b/pkg/api/networkservice/connection_helpers.go
index c37ef85..7aa1149 100644
--- a/pkg/api/networkservice/connection_helpers.go
+++ b/pkg/api/networkservice/connection_helpers.go
@@ -37,12 +37,38 @@ func (x *Connection) Clone() *Connection {
 	return proto.Clone(x).(*Connection)
 }
 
+// Iterate through the selector.NetworkService array looking for a network service
+// that matches the Connection.NetworkService, treating an empty selector.NetworkService
+// array as a wildcard
+func (x *Connection) matchesNetworkService(networkService []string) bool {
+	if len(networkService) == 0 {
+		return true
+	}
+
+	for _, v := range networkService {
+		if v == x.GetNetworkService() {
+			// matched network service
+			return true
+		}
+	}
+
+	return false
+}
+
 // MatchesMonitorScopeSelector - Returns true of the connection matches the selector
 func (x *Connection) MatchesMonitorScopeSelector(selector *MonitorScopeSelector) bool {
 	if x == nil {
 		return false
 	}
 	// Note: Empty selector always matches a non-nil Connection
+	if len(selector.GetPathSegments()) == 0 && len(selector.GetNetworkService()) == 0 {
+		return true
+	}
+	// Compare network service names
+	if !x.matchesNetworkService(selector.GetNetworkService()) {
+		return false
+	}
+	// Empty PathSegments in selector, treat as wildcard
 	if len(selector.GetPathSegments()) == 0 {
 		return true
 	}

[denis-tingaikin]

OK, let's consider how it can be done with the current API.

Problem

Monitor events for a specific network service that implements N endpoints.

Solution (without API modifications)

1. Start watch registry for a specific network service // requires one stream 
2. Start watching the registry for endpoints that implement a specific network service // requires one stream.
3. Create a monitor service for each endpoint and use MonitorSelector with `MonitorSelector.PathSegment.name = endpoint.name'. // requires N streams

Solution with API modification

1. Start watching for events with MonitorSelector.NetworkService=networkService // requires one stream.

[denis-tingaikin]

So, if I don't miss anything, then proposed solution looks good to me.

@edwarnicke Could you also have a look?