Token remover: fix timestamp check

The timestamp calculation was incorrect. The bytes need to be
interpreted as big-endian and the result is just a timestamp rather than
a snowflake.

1 files changed, 16 insertions, 10 deletions

diff --git a/bot/cogs/token_remover.py b/bot/cogs/token_remover.py
index 244d52edb..957c8a690 100644
--- a/bot/cogs/token_remover.py
+++ b/bot/cogs/token_remover.py
@@ -2,13 +2,10 @@ import base64
 import binascii
 import logging
 import re
-import struct
 import typing as t
-from datetime import datetime
 
 from discord import Colour, Message
 from discord.ext.commands import Cog
-from discord.utils import snowflake_time
 
 from bot.bot import Bot
 from bot.cogs.moderation import ModLog
@@ -29,7 +26,7 @@ DELETION_MESSAGE_TEMPLATE = (
     "Feel free to re-post it with the token removed. "
     "If you believe this was a mistake, please let us know!"
 )
-DISCORD_EPOCH_TIMESTAMP = datetime(2017, 1, 1)
+DISCORD_EPOCH = 1_420_070_400_000
 TOKEN_EPOCH = 1_293_840_000
 TOKEN_RE = re.compile(
     r"[^\s\.()\"']+"  # Matches token part 1: The user ID string, encoded as base64
@@ -160,18 +157,27 @@ class TokenRemover(Cog):
     @staticmethod
     def is_valid_timestamp(b64_content: str) -> bool:
         """
-        Check potential token to see if it contains a valid timestamp.
+        Return True if `b64_content` decodes to a valid timestamp.
 
-        See: https://discordapp.com/developers/docs/reference#snowflakes
+        If the timestamp is greater than the Discord epoch, it's probably valid.
+        See: https://i.imgur.com/7WdehGn.png
         """
         b64_content += '=' * (-len(b64_content) % 4)
 
         try:
-            content = base64.urlsafe_b64decode(b64_content)
-            snowflake = struct.unpack('i', content)[0]
-        except (binascii.Error, struct.error, ValueError):
+            decoded_bytes = base64.urlsafe_b64decode(b64_content)
+            timestamp = int.from_bytes(decoded_bytes, byteorder="big")
+        except (binascii.Error, ValueError) as e:
+            log.debug(f"Failed to decode token timestamp '{b64_content}': {e}")
+            return False
+
+        # Seems like newer tokens don't need the epoch added, but add anyway since an upper bound
+        # is not checked.
+        if timestamp + TOKEN_EPOCH >= DISCORD_EPOCH:
+            return True
+        else:
+            log.debug(f"Invalid token timestamp '{b64_content}': smaller than Discord epoch")
             return False
-        return snowflake_time(snowflake + TOKEN_EPOCH) < DISCORD_EPOCH_TIMESTAMP
 
 
 def setup(bot: Bot) -> None: