Notice of Ignored Error Message

[aykutalparslan]

In certain cases, a server may notify a client that its incoming message was ignored for whatever reason. Note that such a notification cannot be generated unless a message is correctly decoded by the server.

bad_msg_notification#a7eff811 bad_msg_id:long bad_msg_seqno:int error_code:int = BadMsgNotification;
bad_server_salt#edab447b bad_msg_id:long bad_msg_seqno:int error_code:int new_server_salt:long = BadMsgNotification;

Here, error_code can also take on the following values:

• 16: msg_id too low (most likely, client time is wrong; it would be worthwhile to synchronize it using msg_id notifications and re-send the original message with the “correct” msg_id or wrap it in a container with a new msg_id if the original message had waited too long on the client to be transmitted)
• 17: msg_id too high (similar to the previous case, the client time has to be synchronized, and the message re-sent with the correct msg_id)
• 18: incorrect two lower order msg_id bits (the server expects client message msg_id to be divisible by 4)
• 19: container msg_id is the same as msg_id of a previously received message (this must never happen)
• 20: message too old, and it cannot be verified whether the server has received a message with this msg_id or not
• 32: msg_seqno too low (the server has already received a message with a lower msg_id but with either a higher or an equal and odd seqno)
• 33: msg_seqno too high (similarly, there is a message with a higher msg_id but with either a lower or an equal and odd seqno)
• 34: an even msg_seqno expected (irrelevant message), but odd received
• 35: odd msg_seqno expected (relevant message), but even received
• 48: incorrect server salt (in this case, the bad_server_salt response is received with the correct salt, and the message is to be re-sent with it)
• 64: invalid container.

The intention is that error_code values are grouped (error_code >> 4): for example, the codes 0x40 - 0x4f correspond to errors in container decomposition.

Notifications of an ignored message do not require acknowledgment (i.e., are irrelevant).

Important: if server_salt has changed on the server or if client time is incorrect, any query will result in a notification in the above format. The client must check that it has, in fact, recently sent a message with the specified msg_id, and if that is the case, update its time correction value (the difference between the client’s and the server’s clocks) and the server salt based on msg_id and the server_salt notification, so as to use these to (re)send future messages. In the meantime, the original message (the one that caused the error message to be returned) must also be re-sent with a better msg_id and/or server_salt.

In addition, the client can update the server_salt value used to send messages to the server, based on the values of RPC responses or containers carrying an RPC response, provided that this RPC response is actually a match for the query sent recently. (If there is doubt, it is best not to update since there is risk of a replay attack).