1 files changed, 8 insertions, 1 deletions
diff --git a/app/df.php b/app/df.php
index 80aec5a..c6e45fd 100644
--- a/app/df.php
+++ b/app/df.php
@@ -31,7 +31,8 @@ require_once "class/mesg.class.php";
 /*
  * Serve the resource at the given URI in response to the current
  * request.  When finished, this function will exit PHP and terminate
- * this script.
+ * this script.  The response instructs the client to cache the
+ * result for 24 hours.
  */
 function serveResource(string $uri, ?string $filename = NULL) : void
 {
@@ -40,8 +41,14 @@ function serveResource(string $uri, ?string $filename = NULL) : void
     if (!$f)
         exit;
 
+    $cachelen = 86400; // secs, 24-hours
+    $cachedate = gmdate("D, d M Y H:i:s", time() + $cachelen);
+
     header("Content-Type: " . mime_content_type($uri));
     header("Content-Length: " . filesize($uri));
+    header("Expires: " . $cachedate);
+    header("Cache-Control: max-age=" . $cachelen);
+    header("Pragma: cache");
 
     if ($filename)
         header("Content-Disposition: attachment; filename=\"" . $filename . "\"");