From c6abb18b2eb974ebee17fae191511f5d3601935f Mon Sep 17 00:00:00 2001
From: aherlihy <anna.herlihy@10gen.com>
Date: Fri, 5 Jun 2015 14:13:39 -0400
Subject: [PATCH] PYTHON-940 - Unhelpful and pretty wrong error message.

---
 pymongo/mongo_client.py             | 14 +++++++++++---
 pymongo/mongo_replica_set_client.py | 14 +++++++++++---
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/pymongo/mongo_client.py b/pymongo/mongo_client.py
index 8f47d4c94..84de75e67 100644
--- a/pymongo/mongo_client.py
+++ b/pymongo/mongo_client.py
@@ -1197,12 +1197,20 @@ class MongoClient(common.BaseObject):
         """
         header = self.__receive_data_on_socket(16, sock_info)
         length = struct.unpack("<i", header[:4])[0]
+
+        actual_op = struct.unpack("<i", header[12:])[0]
+        assert actual_op == operation, (
+            "wire protocol error: unknown opcode %r" % (actual_op,))
+
         # No rqst_id for exhaust cursor "getMore".
         if rqst_id is not None:
             resp_id = struct.unpack("<i", header[8:12])[0]
-            assert rqst_id == resp_id, "ids don't match %r %r" % (rqst_id,
-                                                                  resp_id)
-        assert operation == struct.unpack("<i", header[12:])[0]
+            assert rqst_id == resp_id, (
+                "wire protocol error: got response id %r but expected %r"
+                % (resp_id, rqst_id))
+
+        assert length > 16, ("wire protocol error: message length is shorter"
+                             " than standard message header: %r" % (length,))
 
         return self.__receive_data_on_socket(length - 16, sock_info)
 
diff --git a/pymongo/mongo_replica_set_client.py b/pymongo/mongo_replica_set_client.py
index 5ba7ef497..31a6a6a00 100644
--- a/pymongo/mongo_replica_set_client.py
+++ b/pymongo/mongo_replica_set_client.py
@@ -1482,12 +1482,20 @@ class MongoReplicaSetClient(common.BaseObject):
         """
         header = self.__recv_data(16, sock)
         length = struct.unpack("<i", header[:4])[0]
+
+        actual_op = struct.unpack("<i", header[12:])[0]
+        assert actual_op == operation, (
+            "wire protocol error: unknown opcode %r" % (actual_op,))
+
         # No rqst_id for exhaust cursor "getMore".
         if rqst_id is not None:
             resp_id = struct.unpack("<i", header[8:12])[0]
-            assert rqst_id == resp_id, "ids don't match %r %r" % (rqst_id,
-                                                                  resp_id)
-        assert operation == struct.unpack("<i", header[12:])[0]
+            assert rqst_id == resp_id, (
+                "wire protocol error: got response id %r but expected %r"
+                % (resp_id, rqst_id))
+
+        assert length > 16, ("wire protocol error: message length is shorter"
+                             " than standard message header: %r" % (length,))
 
         return self.__recv_data(length - 16, sock)