Issue #4116: Make infile and outfile parameters of flrender script from python-abp optional

abp/filters/sources.py

 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-present eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
 
 """Helper classes that handle IO for filter list parsing and rendering."""
 
 import io
 from os import path
+import sys
 
 try:
     from urllib2 import urlopen, HTTPError
 except ImportError:  # The module was renamed in Python 3.
     from urllib.request import urlopen
     from urllib.error import HTTPError
 
 __all__ = ['NotFound', 'FSSource', 'TopSource', 'WebSource']
 
 
@@ skipping 69 matching lines @@
     """
 
     is_inheritable = False
 
     def __init__(self, encoding='utf-8'):
         super(TopSource, self).__init__('.', encoding)
 
     def _resolve_path(self, path_in_source):
         return path_in_source
 
+    def get(self, path_in_source):
+        """Read the data. Handles stdin, on top of file input.
+
+        Parameters
+        ----------
+        path_in_source : str
+            Path to the file inside of source or '-' for stdin.
+
+        Returns
+        -------
+        generator or str
+            Lines in the file/ from stdin.
+
+        """
+        if path_in_source == '-':
+            lines = sys.stdin.readlines()
+            for line in lines:
+                yield line.rstrip('\n')
+        else:
+            lines = super(TopSource, self).get(path_in_source)
+            for line in lines:
+                yield line
+
 
 class WebSource(object):
     """Handler for http or https.
 
     Parameters
     ----------
     protocol : str
         Protocol to use: "http" or "https".
     default_encoding : str
         Encoding to use when the server doesn't specify it (default: utf-8).
@@ skipping 29 matching lines @@
             get_param = (getattr(info, 'get_param', None) or
                          getattr(info, 'getparam', None))
             encoding = get_param('charset') or self.default_encoding
             for line in response:
                 yield line.decode(encoding).rstrip()
         except HTTPError as err:
             if err.code == 404:
                 raise NotFound("HTTP 404 Not found: '{}:{}'"
                                .format(self.protocol, path_in_source))
             raise err