2 files changed, 93 insertions, 7 deletions
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index 21ededc5ae..23ce0af277 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -28,6 +28,7 @@ class Codes(object):
     UNKNOWN = "M_UNKNOWN"
     NOT_FOUND = "M_NOT_FOUND"
     UNKNOWN_TOKEN = "M_UNKNOWN_TOKEN"
+    LIMIT_EXCEEDED = "M_LIMIT_EXCEEDED"
 
 
 class CodeMessageException(Exception):
@@ -39,10 +40,13 @@ class CodeMessageException(Exception):
         self.code = code
         self.msg = msg
 
+    def error_dict(self):
+        return cs_error(self.msg)
+
 
 class SynapseError(CodeMessageException):
     """A base error which can be caught for all synapse events."""
-    def __init__(self, code, msg, errcode=""):
+    def __init__(self, code, msg, errcode=Codes.UNKNOWN):
         """Constructs a synapse error.
 
         Args:
@@ -53,6 +57,11 @@ class SynapseError(CodeMessageException):
         super(SynapseError, self).__init__(code, msg)
         self.errcode = errcode
 
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+        )
 
 class RoomError(SynapseError):
     """An error raised when a room event fails."""
@@ -91,13 +100,25 @@ class StoreError(SynapseError):
     pass
 
 
-def cs_exception(exception):
-    if isinstance(exception, SynapseError):
+class LimitExceededError(SynapseError):
+    """A client has sent too many requests and is being throttled.
+    """
+    def __init__(self, code=429, msg="Too Many Requests", retry_after_ms=None,
+                 errcode=Codes.LIMIT_EXCEEDED):
+        super(LimitExceededError, self).__init__(code, msg, errcode)
+        self.retry_after_ms = retry_after_ms
+
+    def error_dict(self):
         return cs_error(
-            exception.msg,
-            Codes.UNKNOWN if not exception.errcode else exception.errcode)
-    elif isinstance(exception, CodeMessageException):
-        return cs_error(exception.msg)
+            self.msg,
+            self.errcode,
+            retry_after_ms=self.retry_after_ms,
+        )
+
+
+def cs_exception(exception):
+    if isinstance(exception, CodeMessageException):
+        return exception.error_dict()
     else:
         logging.error("Unknown exception type: %s", type(exception))
 
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]