How to measure precise packet times?

Quick maths leads me to this - MEASURED_MS / (1000 / FPS) = 1ms -> 17 / (1000 / 60) = 1.02ms.. but not sure

xyz wym? My server and client are separate nodes.

# client_node.gd
class_name ClientNode
extends Node

var udp := PacketPeerUDP.new()
var connected = false
var timer = Timer.new()
func _ready():
	var error = udp.connect_to_host("127.0.0.1", 4242)
	add_child(timer)
	timer.wait_time=1
	timer.timeout.connect(_on_timeout)
	
	if error != OK:
		print("ClientNode didnt connect")
	else:
		print("ClientNode connected")
		timer.start()
		print("Timer started!")
func _process(delta):

	if udp.get_available_packet_count() > 0:
		var ut = Time.get_unix_time_from_system()
		var ms = Time.get_ticks_msec()
		
		var packet_ms = udp.get_packet().get_string_from_utf8().to_int()
		
		var latency = ms - packet_ms
		print("tick: %s ms" % ms)
		print("latency: %s ms" % latency)
		connected = true
		
		
func _on_timeout():
		var ut = Time.get_unix_time_from_system()
		var ms = str(Time.get_ticks_msec()) #str(int(ut * 1000))
		
		udp.put_packet(ms.to_utf8_buffer())

# server_node.gd
class_name ServerNode
extends Node

var server := UDPServer.new()
var peers = []

func _ready():
	var error = server.listen(4242)
	if error != OK:
		print("ServerNode didnt listten")
	else:
		print("ServerNode listenning")
		

func _process(delta):
	server.poll() # Important!
	if server.is_connection_available():
		var peer: PacketPeerUDP = server.take_connection()
		var packet = peer.get_packet()
		#print("Accepted peer: %s:%s" % [peer.get_packet_ip(), peer.get_packet_port()])
		#print("Received data: %s" % [packet.get_string_from_utf8()])
		# Reply so it knows we received the message.
		peer.put_packet(packet)
		# Keep a reference so we can keep contacting the remote peer.
		peers.append(peer)

	for i in range(0, peers.size()):
		if peers[i].get_available_packet_count() > 0:
			var packet = peers[i].get_packet()
			peers[i].put_packet(packet)
		pass # Do something with the connected peers.

# main.gd
extends Control


# Called when the node enters the scene tree for the first time.
func _ready() -> void:
	pass # Replace with function body.


# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(delta: float) -> void:
	pass

xyz Im sorry im still not following.

Client node starts timer.
_on_timeout -> put packet.

Then on server node in the process i listen for available packets. If packet i put_packet back to the peer.

On client in the process i listen for available packets. If packet i get current time and return the difference.

Not sure how can i listen for packet outside the process function?

xyz how do i specify when the process is called, in other node? Do i add "client" node as child of the server node?

But this wont fix this problem when im doing it with multple machines. so on one machine i would have client process and on other machine i would have server process.. the resulting time wastage would be still incorrect..

Or maybe i dont understand something obvious?

xyz ok, got it

#main.gd
extends Control
@onready var udp_ping_server: ServerNode = $UdpPingServer
@onready var udp_ping_client: ClientNode = $UdpPingClient


# Called when the node enters the scene tree for the first time.
func _ready() -> void:
	pass # Replace with function body.


# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(delta: float) -> void:
	if udp_ping_client.udp.get_available_packet_count() > 0:
		var ut = Time.get_unix_time_from_system()
		var ms = Time.get_ticks_msec()
		
		var packet_ms = udp_ping_client.udp.get_packet().get_string_from_utf8().to_int()
		var fps = Engine.get_frames_per_second()
		
		var latency = ms - packet_ms
		var engine_time = 1000 / fps
		var real_latency = latency - engine_time
		#print("tick: %s ms" % ms)
		print("latency: %s ms" % latency)
		#print("latency: %s ms" % real_latency)
	
	udp_ping_server.server.poll() # Important!
	if udp_ping_server.server.is_connection_available():
		var peer: PacketPeerUDP = udp_ping_server.server.take_connection()
		var packet = peer.get_packet()

		peer.put_packet(packet)
		# Keep a reference so we can keep contacting the remote peer.
		udp_ping_server.peers.append(peer)
		
	for i in range(0, udp_ping_server.peers.size()):
		if udp_ping_server.peers[i].get_available_packet_count() > 0:
			var packet = udp_ping_server.peers[i].get_packet()
			udp_ping_server.peers[i].put_packet(packet)
		pass # Do something with the connected peers.

		
	pass

output:

Godot Engine v4.3.dev6.official.89850d553 - https://godotengine.org
Vulkan 1.3.277 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 3090

ClientNode connected
Timer started!
ServerNode listenning
latency: 6 ms
latency: 1 ms
latency: 1 ms
latency: 1 ms
latency: 1 ms
latency: 1 ms
--- Debugging process stopped ---

well actually idk.. maybe my pc is too fast for this.. i mean i tested this before on garbage can, compared to my gaming rig ..

The old method returns me:

Godot Engine v4.2.1.stable.official.b09f793f5 - https://godotengine.org
Vulkan API 1.3.277 - Forward+ - Using Vulkan Device #0: NVIDIA - NVIDIA GeForce RTX 3090
 
ServerNode listenning
ClientNode connected
Timer started!
latency: 5 ms
latency: 3 ms
latency: 3 ms
latency: 2 ms
latency: 3 ms
latency: 2 ms
latency: 2 ms
latency: 3 ms
--- Debugging process stopped ---

But the new one 1ms.. man.. gotta have to wait for tomorrow when i get back at work and test this on that garbage pc

ok so did a test on laptop.. yes it works like you said..
Old method

new method

xyz imma try to write separate app for server and client and then test over wifi on local network..

Do you mean if i write all in one node one script - sever and client, putting client code that sends packet at the top of the process function?

ok so wrote client app, just the client part, and im getting bad pings

Server is running on other machine..

Terminal ping gives me these numbers

Running server on laptop and client on my power pc,

Godot Engine v4.3.dev6.official.89850d553 - https://godotengine.org
Vulkan 1.3.277 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 3090

ClientNode connected
Timer started!
latency: 8 ms
latency: 5 ms
latency: 53 ms
latency: 86 ms
latency: 19 ms
latency: 36 ms
latency: 53 ms
latency: 67 ms
latency: 97 ms
latency: 8 ms
latency: 56 ms
latency: 70 ms
latency: 97 ms
--- Debugging process stopped ---
``` 
yikes :(