Windows datetime/strftime behavior workaround

fakenet/listeners/BannerFactory.py

@@ -1,3 +1,4 @@
+import re
 import random
 import socket
 import string
@@ -7,34 +8,85 @@ class Banner():
     """Act like a string, but actually get date/time components on the fly."""
 
     def __init__(self, banner, insertions):
-        self.banner = banner
+        # On Windows, datetime.datetime.now().strftime() will choke on %(...)s
+        # and similar insertion tokens. To pacify it, prepend an additional
+        # percent sign before each such token so that strftime() will quietly
+        # translate the double percent sign into a single percent sign for
+        # later consumption by the format operation in which insertion strings
+        # such as %(servername)s will be substituted.
+        banner_safe = re.sub(r'%\(([^\)]+)\)', r'%%(\1)', banner)
+
+        # Enable/disable test path to simulate length of 75 but actual string
+        # of length 76 to test what happens around pyftpdlib/handlers.py:1321
+        # when the return value of len() is <= the threshold of 75 characters
+        # but the string's actual length (which is generated in a subsequent
+        # call to __repr__()) exceeds that threshold value.
+        self.test_pyftpdlib_handler_banner_threshold75 = False
+
+        if self.test_pyftpdlib_handler_banner_threshold75:
+            self.len_75 = len(self.str_75)
+            self.str_76 = 'a' * 76
+
+        self.banner = banner_safe
         self.insertions = insertions
+
         # Indicate an error in the banner early-on as opposed to
         # when a login or other event occurs.
-        test = self.failEarly()
+        testbanner, testlen = self.failEarly()
 
     def failEarly(self):
         """Raise exceptions upon construction rather than later."""
-        return self.fmt()
+
+        # Test generating banner
+        banner_generated = str(self)
+
+        # Test generating and getting length of banner
+        banner_generated_len = len(self)
+
+        return banner_generated, banner_generated_len
 
     def __len__(self):
         """Needed for pyftpdlib.
         
         If the length changes between the time when the caller obtains the
-        length and the time when they reference the string, then... *shrug*?
+        length and the time when the caller obtains the latest generated
+        string, then there is not much that could reasonably be done. It would
+        be possible to cache the formatted banner with a short expiry so that
+        temporally clustered __len__ and __repr__ call sequences would view
+        consistent and coherent string contents, however this seems like
+        overkill since the use case is really just allowing pyftpdlib to
+        determine which way to send the response (directly versus push() if the
+        length exceeds a threshold of 75 characters). In this case, if the
+        banner string length and contents are inconsistent, it appears that the
+        only effect will be to erroneously send the message differently. Test
+        code has been left in place for easy repro in case this proves to be an
+        issue on some future/other platform.
         """
+        # Test path: simulate length of 75 but actual string of length 76 (part
+        # 1/2) to test pyftpdlib/handlers.py:1321
+        if self.test_pyftpdlib_handler_banner_threshold75:
+            return self.len_75
+
+        # Normal path: return the length of the banner generated by self.fmt()
         return len(self.fmt())
 
     def __repr__(self):
         return self.fmt()
 
     def fmt(self):
+        # Test path: simulate length of 75 but actual string of length 76 (part
+        # 2/2) to test pyftpdlib/handlers.py:1321
+        if self.test_pyftpdlib_handler_banner_threshold75:
+            return self.str_76
+
+        # Normal path: generate banner
         banner = self.banner
         banner = datetime.datetime.now().strftime(banner)
         banner = banner % self.insertions
         banner = banner.replace('\\n', '\n').replace('\\t', '\t')
         return banner
 
+
 class BannerFactory():
     def genBanner(self, config, bannerdict, defaultbannerkey='!generic'):
         """Select and format a banner.