Caching for static files (lastModified)

[vatsake]

Not sure why, but my last modified is at year 1970.

pricesHandler = &server.serveStatic("/electricity-prices.json", LittleFS, "/electricity-prices.json");
pricesHandler->setLastModified(getElectricityPricesUpdatedAt());

time_t getElectricityPricesUpdatedAt() {
  time_t now = getTime();
  time_t currTime;

  if (hour(now) >= 17) {
    // today at 17:00
    currTime = tmConvert_t(
      year(now),
      month(now),
      day(now),
      17, 0, 0);
  } else {
    // yesterday at 17:00
    time_t yesterday = now - 86400;
    currTime = tmConvert_t(
      year(yesterday),
      month(yesterday),
      day(yesterday),
      17, 0, 0);
  }

  Serial.println(currTime); // Prints 1762189200
  return currTime;
}

NB! Time is set when calling setLastModified()

[mathieucarbou]

Hi @vatsake : please try to point to main branch that will be released soon: there has been some fixes recently.

lib_deps = https://github.com/ESP32Async/ESPAsyncWebServer

Let us know, thanks!

update: also to have time on esp32 you need NTP.
I see nowhere in your code where you ensure that NTP is sync before calling that ?

Do you have an MRE (little ino file - isolated example) that allows to reproduce that ?

For now it is hard to tell if there is really a bug or this is more an issue in your code.

[vatsake]

Hi
I've tried reproducing... But I can't... 😁

In my original project I even tried setting the last modified in loop which should update it every time. It still set it to 1970..
No idea what's going on :D

[mathieucarbou]

well, if one day you see it again, you can try isolate your code to reproduce it with only the asyncws library to determine if this is a bug linked to us. THis is easy to do by copy pasting one of the project example and adapting it.

[vortigont]

this pricesHandler->setLastModified(getElectricityPricesUpdatedAt()); works only once! on setup when time is not set yet, it does not triggers on each request. In general you do not need to set it at all, if you are using LittleFS the webserver will pick file's date from FS, which is usually the same as you use when creating FS image.

[mathieucarbou]

Ref:

ESPAsyncWebServer/examples/Templates/Templates.ino

Lines 92 to 105 in 652f70e

	// By explicitly calling setLastModified() on the handler object, we enable
	// sending the caching headers, even when a template is in use.
	// This pattern should never be used with template data that can change.
	// Example below: USER never changes.
	//
	// curl -v http://192.168.4.1/index.html
	server.serveStatic("/index.html", LittleFS, "/template.html")
	.setTemplateProcessor([](const String &var) -> String {
	if (var == "USER") {
	return "Bob";
	}
	return emptyString;
	})
	.setLastModified("Sun, 28 Sep 2025 01:02:03 GMT");