Detect chat flooding by counting lines

Reject comments by line count. Ratelimit users by number of lines sent
in chat.

anonstream/__init__.py

@@ -66,8 +66,10 @@ def create_app(config_file):
         'CHAT_NAME_MIN_CONTRAST': config['chat']['min_name_contrast'],
         'CHAT_BACKGROUND_COLOUR': color_to_colour(config['chat']['background_color']),
         'CHAT_LEGACY_TRIPCODE_ALGORITHM': config['chat']['legacy_tripcode_algorithm'],
-        'FLOOD_DURATION': config['flood']['duration'],
-        'FLOOD_THRESHOLD': config['flood']['threshold'],
+        'FLOOD_MESSAGE_DURATION': config['flood']['messages']['duration'],
+        'FLOOD_MESSAGE_THRESHOLD': config['flood']['messages']['threshold'],
+        'FLOOD_LINE_DURATION': config['flood']['lines']['duration'],
+        'FLOOD_LINE_THRESHOLD': config['flood']['lines']['threshold'],
         'CAPTCHA_LIFETIME': config['captcha']['lifetime'],
         'CAPTCHA_FONTS': config['captcha']['fonts'],
         'CAPTCHA_ALPHABET': config['captcha']['alphabet'],

anonstream/chat.py

@@ -8,7 +8,7 @@ from quart import current_app, escape
 
 from anonstream.broadcast import broadcast, broadcast_users_update
 from anonstream.helpers.chat import generate_nonce_hash, get_scrollback
-from anonstream.utils.chat import get_message_for_websocket
+from anonstream.utils.chat import get_message_for_websocket, get_approx_linespan
 
 CONFIG = current_app.config
 MESSAGES_BY_ID = current_app.messages_by_id
@@ -33,6 +33,26 @@ def add_chat_message(user, nonce, comment, ignore_empty=False):
     if ignore_empty and len(comment) == 0:
         return False
 
+    timestamp_ms = time.time_ns() // 1_000_000
+    timestamp = timestamp_ms // 1000
+
+    # Check user
+    while user['linespan']:
+        linespan_timestamp, _ = user['linespan'][0]
+        if timestamp - linespan_timestamp >= CONFIG['FLOOD_LINE_DURATION']:
+            user['linespan'].popleft()
+        else:
+            break
+    total_recent_linespan = sum(map(
+        lambda linespan_tuple: linespan_tuple[1],
+        user['linespan'],
+    ))
+    if total_recent_linespan > CONFIG['FLOOD_LINE_THRESHOLD']:
+        raise Rejected(
+            f'Chat overuse in the last '
+            f'{CONFIG["FLOOD_LINE_DURATION"]:.0f} seconds'
+        )
+
     # Check message
     message_id = generate_nonce_hash(nonce)
     if message_id in MESSAGES_BY_ID:
@@ -41,10 +61,18 @@ def add_chat_message(user, nonce, comment, ignore_empty=False):
         raise Rejected('Message was empty')
     if len(comment) > 512:
         raise Rejected('Message exceeded 512 chars')
+    if comment.count('\n') + 1 > 12:
+        raise Rejected('Message exceeded 12 lines')
+
+    linespan = get_approx_linespan(comment)
+    if linespan > 12:
+        raise Rejected('Message would span too many lines')
+
+    # Record linespan
+    linespan_tuple = (timestamp, linespan)
+    user['linespan'].append(linespan_tuple)
 
     # Create and add message
-    timestamp_ms = time.time_ns() // 1_000_000
-    timestamp = timestamp_ms // 1000
     try:
         last_message = next(reversed(MESSAGES))
     except StopIteration:

anonstream/helpers/user.py

@@ -3,7 +3,7 @@
 
 import hashlib
 import base64
-from collections import OrderedDict
+from collections import deque, OrderedDict
 from math import inf
 
 from quart import current_app
@@ -45,6 +45,7 @@ def generate_user(timestamp, token, broadcaster, presence):
             'watching': -inf,
         },
         'presence': presence,
+        'linespan': deque(),
     }
 
 def get_default_name(user):

anonstream/user.py

@@ -152,12 +152,12 @@ def deverify(timestamp, user):
     n_user_messages = 0
     for message in reversed(MESSAGES):
         message_sent_ago = timestamp - message['timestamp']
-        if message_sent_ago >= CONFIG['FLOOD_DURATION']:
+        if message_sent_ago >= CONFIG['FLOOD_MESSAGE_DURATION']:
             break
         elif message['token'] == user['token']:
             n_user_messages += 1
 
-    if n_user_messages >= CONFIG['FLOOD_THRESHOLD']:
+    if n_user_messages >= CONFIG['FLOOD_MESSAGE_THRESHOLD']:
         user['verified'] = False
 
 def _update_presence(timestamp, user):

anonstream/utils/chat.py

@@ -3,6 +3,7 @@
 
 import base64
 import hashlib
+import math
 import secrets
 
 class NonceReuse(Exception):
@@ -18,3 +19,10 @@ def get_message_for_websocket(user, message):
         **{key: message[key] for key in message_keys},
         **{key: user[key] for key in user_keys},
     }
+
+def get_approx_linespan(text):
+    def height(line):
+        return math.ceil(len(line) / 48)
+    linespan = sum(map(height, text.splitlines()))
+    linespan = linespan if linespan > 0 else 1
+    return linespan

config.toml

@@ -49,10 +49,14 @@ min_name_contrast = 3.0
 background_color = "#232327"
 legacy_tripcode_algorithm = false
 
-[flood]
+[flood.messages]
 duration = 20.0
 threshold = 4
 
+[flood.lines]
+duration = 20.0
+threshold = 20
+
 [thresholds]
 user_notwatching = 8.0
 user_tentative = 20.0