EngineId package structure - Encoding and Decoding

Hi,

For Sending Informs, I am using a snmpagent other than net-snmp.
But the manager is net-snmp.

While decoding the engineId that received in the discovery packet in the
agent side, it is null. But the size seems to valid length some +ve integer.

To debug the same I want to know in net-snmp where the engineId is encoded
and how.
I want to know the package structure.

Rgds,
Jc