1 files changed, 65 insertions, 0 deletions
diff --git a/synapse/api/ratelimiting.py b/synapse/api/ratelimiting.py
new file mode 100644
index 0000000000..ab26c2376a
--- /dev/null
+++ b/synapse/api/ratelimiting.py
@@ -0,0 +1,65 @@
+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
+            messagecount = 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]