Raise LimitExceedError when the ratelimiting is throttling requests

synapse/api/errors.py

@@ -40,10 +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:
@@ -54,6 +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."""
@@ -92,13 +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))
 

synapse/handlers/_base.py

@@ -14,7 +14,7 @@
 # limitations under the License.
 
 from twisted.internet import defer
-from synapse.api.errors import cs_error, Codes
+from synapse.api.errors import LimitExceededError
 
 class BaseHandler(object):
 
@@ -38,9 +38,7 @@ class BaseHandler(object):
             burst_count=self.hs.config.rc_message_burst_count,
         )
         if not allowed:
-            raise cs_error(
-                "Limit exceeded",
-                Codes.LIMIT_EXCEEDED,
+            raise LimitExceededError(
                 retry_after_ms=1000*(time_allowed - time_now),
             )