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Improve time sync accuracy #15

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6c6db1f
Improve time sync accuracy
nuubik May 28, 2025
ad0abad
Run time sync periodically
nuubik May 28, 2025
a7674b6
Merge pull request #16 from CDPTechnologies/codex/update-time-sync-to…
cdptech May 28, 2025
44f4930
Share time offset across applications on same host (#17)
nuubik May 28, 2025
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4 changes: 4 additions & 0 deletions README.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -447,6 +447,10 @@ node.subscribeToValues(valueConsumer, fs, sampleRate)
Subscribe to value changes on this node. On each value change valueConsumer function is called
with value of the nodes value_type and UTC Unix timestamp in nanoseconds (nanoseconds from 01.01.1970).
Timestamp refers to the time of value change in connected application on target controller.
If the client detects a time synchronization offset larger than 3 seconds,
incoming timestamps are automatically adjusted by that offset. The offset is
determined by sending three consecutive time-sync requests and using the
smallest offset reported.

- Example

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68 changes: 65 additions & 3 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -322,6 +322,7 @@ studio.protocol.BINARY_TYPE = "arraybuffer";
*/
studio.internal = (function(proto) {
var obj = {};
var hostTimeOffsets = new Map();

obj.structure = {
REMOVE: 0,
Expand Down Expand Up @@ -715,6 +716,7 @@ studio.internal = (function(proto) {
var appName = "";
var appId = undefined;
var appUrl = composeUrl(url);
var host = new URL(appUrl).hostname;
var socket = new WebSocket(appUrl);
var handler = new proto.Handler(socket, notificationListener);
var requests = [];
Expand All @@ -725,6 +727,9 @@ studio.internal = (function(proto) {
var onError;
var onOpen;
var reauthRequestPending = false;
var timeOffsetNs = hostTimeOffsets.get(host) || 0;
var timeSyncTimer = null;
var timeSyncSamples = [];
socket.binaryType = proto.BINARY_TYPE;
nodeMap.set(systemNode.id(), systemNode);
handler.onContainer = handleIncomingContainer;
Expand All @@ -747,7 +752,13 @@ studio.internal = (function(proto) {

onMessage = function(evt) { handler.handle(evt.data); };
onError = function (ev) { console.log("Socket error: " + ev.data); };
onOpen = function() { appConnection.resubscribe(systemNode); };
onOpen = function() {
appConnection.resubscribe(systemNode);
startTimeSync();
if (!timeSyncTimer) {
timeSyncTimer = setInterval(startTimeSync, 30000);
}
};
onClosed = function (event) {
var reason;

Expand Down Expand Up @@ -781,6 +792,7 @@ studio.internal = (function(proto) {
reason = "Unknown reason";

console.log("Socket close: " + reason);
stopTimeSync();

if (autoConnect)
{
Expand Down Expand Up @@ -834,6 +846,55 @@ studio.internal = (function(proto) {
requests = [];
}

function makeCurrentTimeRequest() {
var msg = new proto.Container();
msg.message_type = proto.ContainerType.eCurrentTimeRequest;
send(msg);
}

function setTimeOffset(offset) {
timeOffsetNs = offset;
hostTimeOffsets.set(host, offset);
}

function beginTimeSync() {
if (timeSyncSamples.length === 0) {
makeCurrentTimeRequest();
}
}

function parseCurrentTimeResponse(serverTime) {
var localNs = Date.now() * 1000000;
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@Karmo7 Karmo7 Jun 19, 2025

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Here also 1E6

var offsetCandidate = serverTime - localNs;
timeSyncSamples.push(offsetCandidate);
if (timeSyncSamples.length < 3) {
makeCurrentTimeRequest();
return;
}
var minOffset = Math.min.apply(null, timeSyncSamples);
timeSyncSamples = [];
if (Math.abs(minOffset) > 3000000000) {
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@Karmo7 Karmo7 Jun 19, 2025

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I'd prefer the 3E9 syntax for large numbers. It is very annoying to count the zeros

setTimeOffset(minOffset);
}
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@Karmo7 Karmo7 Jun 19, 2025

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Shouldn't there be an else clause to reset the offset for the case previously due to some network issue offset was very high but now is under 3 seconds?

}

function startTimeSync() {
beginTimeSync();
}

function stopTimeSync() {
if (timeSyncTimer) {
clearInterval(timeSyncTimer);
timeSyncTimer = null;
}
}

function applyTimeOffset(ts) {
if (ts === undefined || ts === null)
return ts;
return ts + (hostTimeOffsets.get(host) || 0);
}

this.makeStructureRequest = function(id) {
var msg = new proto.Container();
msg.message_type = proto.ContainerType.eStructureRequest;
Expand Down Expand Up @@ -990,7 +1051,7 @@ studio.internal = (function(proto) {
var variantValue = protoResponse[i];
var node = nodeMap.get(variantValue.node_id);
if (node)
node.receiveValue(proto.valueFromVariant(variantValue, node.info().value_type), variantValue.timestamp);
node.receiveValue(proto.valueFromVariant(variantValue, node.info().value_type), applyTimeOffset(variantValue.timestamp));
}
}

Expand All @@ -1014,7 +1075,7 @@ studio.internal = (function(proto) {
sender: variantValue.sender,
code: variantValue.code,
status: variantValue.status,
timestamp: variantValue.timestamp,
timestamp: applyTimeOffset(variantValue.timestamp),
data: variantValue.data
};
node.receiveEvent(event);
Expand Down Expand Up @@ -1068,6 +1129,7 @@ studio.internal = (function(proto) {
parseEventResponse(protoContainer.event_response);
break;
case proto.ContainerType.eCurrentTimeResponse:
parseCurrentTimeResponse(protoContainer.current_time_response);
break;
case proto.ContainerType.eReauthResponse:
parseReauthResponse(protoContainer.re_auth_response, metadata);
Expand Down