From 75a7ed132aa2b9afdeae45065ca607bf1cc89c19 Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Fri, 28 Nov 2025 08:08:43 -0500
Subject: [PATCH] Fix stale UI after firmware updates (#5120)

Add WEB_BUILD_TIME to html_ui.h and use it for ETag generation

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: DedeHai <6280424+DedeHai@users.noreply.github.com>
Co-authored-by: Aircoookie <21045690+Aircoookie@users.noreply.github.com>
---
 tools/cdata.js         | 8 ++++++++
 wled00/wled_server.cpp | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/cdata.js b/tools/cdata.js
index c569a6f2..759d24c2 100644
--- a/tools/cdata.js
+++ b/tools/cdata.js
@@ -38,6 +38,11 @@ const wledBanner = `
 \t\t\x1b[36m build script for web UI
 \x1b[0m`;
 
+// Generate build timestamp as UNIX timestamp (seconds since epoch)
+function generateBuildTime() {
+  return Math.floor(Date.now() / 1000);
+}
+
 const singleHeader = `/*
  * Binary array for the Web UI.
  * gzip is used for smaller size and improved speeds.
@@ -45,6 +50,9 @@ const singleHeader = `/*
  * Please see https://kno.wled.ge/advanced/custom-features/#changing-web-ui
  * to find out how to easily modify the web UI source!
  */
+
+// Automatically generated build time for cache busting (UNIX timestamp)
+#define WEB_BUILD_TIME ${generateBuildTime()}
  
 `;
 
diff --git a/wled00/wled_server.cpp b/wled00/wled_server.cpp
index d899d311..09aeaccf 100644
--- a/wled00/wled_server.cpp
+++ b/wled00/wled_server.cpp
@@ -67,7 +67,7 @@ static bool inLocalSubnet(const IPAddress &client) {
  */
 
 static void generateEtag(char *etag, uint16_t eTagSuffix) {
-  sprintf_P(etag, PSTR("%7d-%02x-%04x"), VERSION, cacheInvalidate, eTagSuffix);
+  sprintf_P(etag, PSTR("%u-%02x-%04x"), WEB_BUILD_TIME, cacheInvalidate, eTagSuffix);
 }
 
 static void setStaticContentCacheHeaders(AsyncWebServerResponse *response, int code, uint16_t eTagSuffix = 0) {