Auto-merge from mysql-5.1-bugteam for bug#42503.

1 files changed, 11 insertions, 1 deletions

diff --git a/sql/net_serv.cc b/sql/net_serv.cc
index 6f0b7a817ca..488e27296b6 100644
--- a/sql/net_serv.cc
+++ b/sql/net_serv.cc
@@ -164,7 +164,17 @@ my_bool net_realloc(NET *net, size_t length)
   DBUG_ENTER("net_realloc");
   DBUG_PRINT("enter",("length: %lu", (ulong) length));
 
-  if (length >= net->max_packet_size)
+  /*
+    When compression is off, net->where_b is always 0.
+    With compression turned on, net->where_b may indicate
+    that we still have a piece of the previous logical
+    packet in the buffer, unprocessed. Take it into account
+    when checking that max_allowed_packet is not exceeded.
+    This ensures that the client treats max_allowed_packet
+    limit identically, regardless of compression being on
+    or off.
+  */
+  if (length >= (net->max_packet_size + net->where_b))
   {
     DBUG_PRINT("error", ("Packet too large. Max size: %lu",
                          net->max_packet_size));