Return the correct Content-Type for SVG favicons (#3032)

* Return the correct Content-Type for SVG favicons

* Use mime_content_type to check file type

* Use tab instead of spaces

* Remove extra blank lines

Co-authored-by: Frans de Jonge <fransdejonge@gmail.com>

* Update f.php

* Better obey HTTP/1.1 304 Not Modified rules about headers https://tools.ietf.org/html/rfc2616#section-10.3.5
* Do not fail if the optional `fileinfo` is not available
* Handle more cases such as PNG, GIF, BMP...

* Add Content-Type for default favicon

* Do not repeat HTTP headers in HTTP 304 response

According to https://tools.ietf.org/html/rfc2616#section-10.3.5 it is better not to repeat HTTP headers in a HTTP 304 Not Modified response

Co-authored-by: Frans de Jonge <fransdejonge@gmail.com>
Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>

p/f.php

@@ -5,10 +5,10 @@ require(LIB_PATH . '/favicons.php');
 require(LIB_PATH . '/http-conditional.php');
 
 function show_default_favicon($cacheSeconds = 3600) {
-	header('Content-Disposition: inline; filename="default_favicon.ico"');
-
 	$default_mtime = @filemtime(DEFAULT_FAVICON);
 	if (!httpConditional($default_mtime, $cacheSeconds, 2)) {
+		header('Content-Type: image/x-icon');
+		header('Content-Disposition: inline; filename="default_favicon.ico"');
 		readfile(DEFAULT_FAVICON);
 	}
 }
@@ -24,8 +24,6 @@ $ico = FAVICONS_DIR . $id . '.ico';
 $ico_mtime = @filemtime($ico);
 $txt_mtime = @filemtime($txt);
 
-header('Content-Type: image/x-icon');
-
 if ($ico_mtime == false || $ico_mtime < $txt_mtime || ($ico_mtime < time() - (mt_rand(15, 20) * 86400))) {
 	if ($txt_mtime == false) {
 		show_default_favicon(1800);
@@ -45,8 +43,17 @@ if ($ico_mtime == false || $ico_mtime < $txt_mtime || ($ico_mtime < time() - (mt
 	}
 }
 
-header('Content-Disposition: inline; filename="' . $id . '.ico"');
-
 if (!httpConditional($ico_mtime, mt_rand(14, 21) * 86400, 2)) {
+	$ico_content_type = 'image/x-icon';
+	if (function_exists('mime_content_type')) {
+		$ico_content_type = mime_content_type($ico);
+	}
+	switch ($ico_content_type) {
+		case 'image/svg':
+			$ico_content_type = 'image/svg+xml';
+			break;
+	}
+	header('Content-Type: ' . $ico_content_type);
+	header('Content-Disposition: inline; filename="' . $id . '.ico"');
 	readfile($ico);
 }