1 files changed, 79 insertions, 0 deletions
diff --git a/synapse/api/ratelimiting.py b/synapse/api/ratelimiting.py
new file mode 100644
index 0000000000..b25358090f
--- /dev/null
+++ b/synapse/api/ratelimiting.py
@@ -0,0 +1,79 @@
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import collections
+
+
+class Ratelimiter(object):
+    """
+    Ratelimit message sending by user.
+    """
+
+    def __init__(self):
+        self.message_counts = collections.OrderedDict()
+
+    def send_message(self, user_id, time_now_s, msg_rate_hz, burst_count):
+        """Can the user send a message?
+        Args:
+            user_id: The user sending a message.
+            time_now_s: The time now.
+            msg_rate_hz: The long term number of messages a user can send in a
+                second.
+            burst_count: How many messages the user can send before being
+                limited.
+        Returns:
+            A pair of a bool indicating if they can send a message now and a
+                time in seconds of when they can next send a message.
+        """
+        self.prune_message_counts(time_now_s)
+        message_count, time_start, _ignored = self.message_counts.pop(
+            user_id, (0., time_now_s, None),
+        )
+        time_delta = time_now_s - time_start
+        sent_count = message_count - time_delta * msg_rate_hz
+        if sent_count < 0:
+            allowed = True
+            time_start = time_now_s
+            message_count = 1.
+        elif sent_count > burst_count - 1.:
+            allowed = False
+        else:
+            allowed = True
+            message_count += 1
+
+        self.message_counts[user_id] = (
+            message_count, time_start, msg_rate_hz
+        )
+
+        if msg_rate_hz > 0:
+            time_allowed = (
+                time_start + (message_count - burst_count + 1) / msg_rate_hz
+            )
+            if time_allowed < time_now_s:
+                time_allowed = time_now_s
+        else:
+            time_allowed = -1
+
+        return allowed, time_allowed
+
+    def prune_message_counts(self, time_now_s):
+        for user_id in self.message_counts.keys():
+            message_count, time_start, msg_rate_hz = (
+                self.message_counts[user_id]
+            )
+            time_delta = time_now_s - time_start
+            if message_count - time_delta * msg_rate_hz > 0:
+                break
+            else:
+                del self.message_counts[user_id]