1 files changed, 17 insertions, 0 deletions
diff --git a/app/df.php b/app/df.php
index 80aec5a..348daa2 100644
--- a/app/df.php
+++ b/app/df.php
@@ -37,11 +37,28 @@ function serveResource(string $uri, ?string $filename = NULL) : void
 {
     $f = fopen($uri, "rb");
 
+    /* no file */
     if (!$f)
         exit;
 
+    /* enable client caching */
+    header("Cache-Control: max-age=0");
+    header("Pragma: cache");
+
+    $hash = hash_file("sha256", $uri);
+
+    /* validate client cache */
+    if (isset($_SERVER['HTTP_IF_NONE_MATCH']) &&
+            $_SERVER['HTTP_IF_NONE_MATCH'] == $hash)
+    {
+        header("HTTP/1.1 304 Not Modified");
+        exit;
+    }
+
+    /* resource metadata */
     header("Content-Type: " . mime_content_type($uri));
     header("Content-Length: " . filesize($uri));
+    header("ETag: " . $hash);
 
     if ($filename)
         header("Content-Disposition: attachment; filename=\"" . $filename . "\"");