fix GHSA-f54q-j679-p9hh: reflected-XSS in cookie-setters;

it was possible to set cookie values which contained newlines,
thus terminating the http header and bleeding into the body.

We now disallow control-characters in queries,
but still allow them in paths, as copyparty supports
filenames containing newlines and other mojibake.

The changes in `set_k304` are not necessary in fixing the vulnerability,
but makes the behavior more correct.

copyparty/httpsrv.py

@@ -4,6 +4,7 @@ from __future__ import print_function, unicode_literals
 import base64
 import math
 import os
+import re
 import socket
 import sys
 import threading
@@ -138,6 +139,8 @@ class HttpSrv(object):
         zs = os.path.join(self.E.mod, "web", "deps", "prism.js.gz")
         self.prism = os.path.exists(zs)
 
+        self.ptn_cc = re.compile(r"[\x00-\x1f]")
+
         self.mallow = "GET HEAD POST PUT DELETE OPTIONS".split()
         if not self.args.no_dav:
             zs = "PROPFIND PROPPATCH LOCK UNLOCK MKCOL COPY MOVE"