BUG#12659 error handling in federated needs improvement. Sanja pointed out...

BUG#12659 error handling in federated needs improvement. Sanja pointed out that we were copying an entire buffer, most of which was probably garbage, and possibly hidden by null termination in the middle of the buffer. Now we are only copying the error message.

sql/ha_federated.cc

@@ -2615,8 +2615,11 @@ int ha_federated::stash_remote_error()
 {
   DBUG_ENTER("ha_federated::stash_remote_error()");
   remote_error_number= mysql_errno(mysql);
-  my_snprintf(remote_error_buf, FEDERATED_QUERY_BUFFER_SIZE, 
-              mysql_error(mysql));
+  const char *remote_error= mysql_error(mysql);
+  remote_error_len= strlen(remote_error);
+  if(remote_error_len > (sizeof(remote_error_buf) - 1))
+    remote_error_len= (sizeof(remote_error_buf) - 1);
+  my_snprintf(remote_error_buf, remote_error_len + 1, remote_error);
   DBUG_RETURN(HA_FEDERATED_ERROR_WITH_REMOTE_SYSTEM);
 }
 
@@ -2630,10 +2633,11 @@ bool ha_federated::get_error_message(int error, String* buf)
     buf->append("Error on remote system: ");
     buf->qs_append(remote_error_number);
     buf->append(": ");
-    buf->append(remote_error_buf, FEDERATED_QUERY_BUFFER_SIZE);
+    buf->append(remote_error_buf, remote_error_len);
 
     remote_error_number= 0;
     remote_error_buf[0]= '\0';
+    remote_error_len= 0;
   }
   DBUG_PRINT("exit", ("message: %s", buf->ptr()));
   DBUG_RETURN(FALSE);

sql/ha_federated.h

@@ -159,6 +159,7 @@ class ha_federated: public handler
   MYSQL_ROW_OFFSET current_position;  // Current position used by ::position()
   int remote_error_number;
   char remote_error_buf[FEDERATED_QUERY_BUFFER_SIZE];
+  uint remote_error_len;
 
 private:
   /*