- fix multiple vulnerabilities in af_proxy_http

- fix vulnerability in rewrite_relative_url() which prevented some URLs from being properly absolutized
- fetch_file_contents: validate all URLs before requesting them
- validate URLs: explicitly whitelist http and https scheme, forbid everything else
- DiskCache/cached_url: only serve whitelisted content types (images, video)
- simplify filename/URL handling code, remove and consolidate some less-used functions

classes/diskcache.php

@@ -191,7 +191,7 @@ class DiskCache {
 	];
 
 	public function __construct($dir) {
-		$this->dir = CACHE_DIR . "/" . clean_filename($dir);
+		$this->dir = CACHE_DIR . "/" . basename(clean($dir));
 	}
 
 	public function getDir() {
@@ -227,9 +227,7 @@ class DiskCache {
 	}
 
 	public function getFullPath($filename) {
-		$filename = clean_filename($filename);
-
-		return $this->dir . "/" . $filename;
+		return $this->dir . "/" . basename(clean($filename));
 	}
 
 	public function put($filename, $data) {