Sample python3 code for listening to SNMP trap events

snmptrap_listener.py

#!/usr/bin/env python3
"""
Heavily borrowed from https://stackoverflow.com/q/33752602

dependencies:

    sudo apt install python3-pysnmp4 python3-pyasn1

To run:

    sudo ./snmptrap_listener.py

To test:

    sudo snmptrap -v1 -c public 127.0.0.1 1.3.6.1.4.1.20408.4.1.1.2 127.0.0.1 1 1 123 1.3.6.1.2.1.1.1.0 s test

"""
from pysnmp.carrier.asynsock.dispatch import AsynsockDispatcher
from pysnmp.carrier.asynsock.dgram import udp, udp6
from pyasn1.codec.ber import decoder
from pysnmp.proto import api

def cbFun(transportDispatcher, transportDomain, transportAddress, wholeMsg):
    while wholeMsg:
        print('')
        msgVer = int(api.decodeMessageVersion(wholeMsg))
        
        if msgVer in api.protoModules:
            pMod = api.protoModules[msgVer]
        else:
            print('Unsupported SNMP version %s' % msgVer)
            return

        reqMsg, wholeMsg = decoder.decode(wholeMsg, asn1Spec=pMod.Message())
        print('Notification message from {}:{}: '.format(transportDomain, transportAddress))
        reqPDU = pMod.apiMessage.getPDU(reqMsg)
        
        if reqPDU.isSameTypeWith(pMod.TrapPDU()):
            if msgVer == api.protoVersion1:
                pdu = pMod.apiTrapPDU
                print('Enterprise: {}'.format(pdu.getEnterprise(reqPDU).prettyPrint()))
                print('Agent Address: {}'.format(pdu.getAgentAddr(reqPDU).prettyPrint()))
                print('Generic Trap: {}'.format(pdu.getGenericTrap(reqPDU).prettyPrint()))
                print('Specific Trap: {}'.format(pdu.getSpecificTrap(reqPDU).prettyPrint()))
                print('Uptime: {}'.format(pdu.getTimeStamp(reqPDU).prettyPrint()))
                varBinds = pdu.getVarBindList(reqPDU)
            else:
                varBinds = pMod.apiPDU.getVarBindList(reqPDU)

            print('Var-binds:')
            for varBind in varBinds:  # SNMP response contents
                for i in range(len(varBind)):
                    print(varBind[i].prettyPrint())
                    print('')

    return wholeMsg

if __name__ == "__main__":
    transportDispatcher = AsynsockDispatcher()

    transportDispatcher.registerRecvCbFun(cbFun)

    # UDP/IPv4
    transportDispatcher.registerTransport(
        #udp.domainName, udp.UdpSocketTransport().openServerMode(('localhost', 162))
        udp.domainName, udp.UdpSocketTransport().openServerMode(('', 162))
    )

    # UDP/IPv6
    transportDispatcher.registerTransport(
        udp6.domainName, udp6.Udp6SocketTransport().openServerMode(('::1', 162))
    )

    transportDispatcher.jobStarted(1)

    try:
        # Dispatcher will never finish as job#1 never reaches zero
        print('Waiting for SNMP trap events...')
        transportDispatcher.runDispatcher()

    except KeyboardInterrupt:
        transportDispatcher.closeDispatcher()

    except:
        transportDispatcher.closeDispatcher()
        raise