Member Avatar for Shanti C

Tel me any good explanation about "if-modified-since http header" . and how to use it in our web sites?????

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@ifModifiedSince is a conditional request header used to avoid retransmitting unchanged resources. A client sends an HTTP-date in If-Modified-Since; the server compares that date with the resource’s last modification time and typically returns 304 Not Modified (no body) when nothing changed, or 200 OK with the full body and an updated Last-Modified header when it has. See the spec for conditional requests (RFC 7232) and a practical reference on the header (MDN If-Modified-Since).

How to verify support and diagnose the problem that mentioned about missing logs:

  • Inspect response headers in browser DevTools (Network tab) for Last-Modified or ETag.

  • Run a quick client test with curl to see whether the server honors the header:

    curl -I https://example.com/page
curl -I -H "If-Modified-Since: Wed, 21 Oct 2015 07:28:00 GMT" https://example.com/page

    A 304 on the second request means the server honored the conditional header. If the server always returns 200, it likely isn’t setting Last-Modified (or an ETag) and thus can’t evaluate the condition.

Notes on enabling/support:

  • Static files: most web servers set Last-Modified automatically and handle If-Modified-Since.

  • Dynamic pages: the application must send a correct Last-Modified header (use GMT/HTTP-date format). Example (PHP):

    <?php
header('Last-Modified: ' . gmdate('D, d M Y H:i:s', $timestamp) . ' GMT');
?>

Cautions and practical points:

  • If both If-None-Match (ETag) and If-Modified-Since are present, the server must ignore If-Modified-Since per the spec (see RFC 7232).
  • Hosting access logs are often not exposed via FTP on shared hosts; check the control panel (cPanel/hosting dashboard) or ask the provider. Look in logs for 304 responses to confirm conditional requests are working.
  • For SEO and bandwidth: correct Last-Modified/ETag reduces unnecessary downloads, but avoid serving stale content by ensuring the timestamp or ETag truly reflects content changes.
Member Avatar for Shanti C

i have found some good information here.

But i can't find whether my webserver supports or not....
i can't find log file in my ftp....

shanti
INDIA

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