bpo-38863: Improve is_cgi() in http.server

is_cgi() function of http.server library does not currently handle a
cgi script if one of the cgi_directories is located at the
sub-directory of given path. Since is_cgi() in CGIHTTPRequestHandler
class separates given path into (dir, rest) based on the first seen
'/', multi-level directories like /sub/dir/cgi-bin/hello.py is divided
into head=/sub, rest=dir/cgi-bin/hello.py then check whether '/sub'
exists in cgi_directories = [..., '/sub/dir/cgi-bin'].
This patch makes the is_cgi() keep expanding dir part to the next '/'
then checking if that expanded path exists in the cgi_directories.

Signed-off-by: Siwon Kang <[email protected]>

Author: kkangshawn

Lib/http/server.py

@@ -1014,8 +1014,10 @@ def is_cgi(self):
         """
         collapsed_path = _url_collapse_path(self.path)
         dir_sep = collapsed_path.find('/', 1)
-        head, tail = collapsed_path[:dir_sep], collapsed_path[dir_sep+1:]
-        if head in self.cgi_directories:
+        while dir_sep > 0 and not collapsed_path[:dir_sep] in self.cgi_directories:
+            dir_sep = collapsed_path.find('/', dir_sep+1)
+        if dir_sep > 0:
+            head, tail = collapsed_path[:dir_sep], collapsed_path[dir_sep+1:]
             self.cgi_info = head, tail
             return True
         return False