serve 88x31 buttons from cache URLs instead of base64, preload the art font

inc/buttons.php

@@ -20,10 +20,10 @@ const BUTTONS_88x31 = [
 const BUTTON_CACHE_TTL = 7 * 86400; // re-fetch each button at most once a week
 
 /**
- * Fetch a remote image, cache it locally, and return it as a base64 data: URI.
- * Returns null on failure so the caller can fall back to hotlinking.
+ * Fetch a remote image into the local cache (at most once a week) and return
+ * the cache file's path, or null if it couldn't be fetched.
  */
-function button_data_uri(string $url): ?string
+function button_cache(string $url): ?string
 {
     $dir = DATA_DIR . '/buttons';
     @mkdir($dir, 0775, true);
@@ -47,19 +47,19 @@ function button_data_uri(string $url): ?string
         }
     }
 
-    if (!is_file($file)) {
-        return null;
-    }
+    return is_file($file) ? $file : null;
+}
 
-    $raw = (string) file_get_contents($file);
-    $nl  = strpos($raw, "\n");
-    if ($nl === false) {
-        return null;
-    }
-
-    $type = substr($raw, 0, $nl);
-    $data = substr($raw, $nl + 1);
-    return 'data:' . $type . ';base64,' . base64_encode($data);
+/**
+ * Where the page should load a button from: our own copy (button.php serves
+ * it, versioned by the cache file's mtime so browsers can keep it), or the
+ * original if fetching failed. Was inlined as base64 before, which made every
+ * page ~260 KB heavier.
+ */
+function button_src(string $url): string
+{
+    $file = button_cache($url);
+    return $file ? '/button.php?h=' . basename($file) . '&v=' . filemtime($file) : $url;
 }
 
 /** Render the whole 88x31 button row as HTML. */
@@ -67,7 +67,7 @@ function render_buttons_88x31(): string
 {
     $html = '';
     foreach (BUTTONS_88x31 as $b) {
-        $uri = button_data_uri($b['src']) ?? $b['src']; // fall back to hotlink if fetch failed
+        $uri = button_src($b['src']);
         $img = '<img src="' . htmlspecialchars($uri) . '" alt="' . htmlspecialchars($b['alt']) . '" width="88" height="31">';
         $href = $b['href'] ?? '';
         if ($href !== '') {