#
# Notification Receiver
#
# Receive SNMP TRAP/INFORM messages with the following options:
#
# * SNMPv1/SNMPv2c
# * with any SNMP community matching regexp '.*love.*'
# * over IPv4/UDP, listening at 127.0.0.1:162
# * print received data on stdout
# 
# Either of the following Net-SNMP's commands will send notifications to this
# receiver:
#
# $ snmptrap -v1 -c rollover 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
# $ snmpinform -v2c -c glove 127.0.0.1 123 1.3.6.1.6.3.1.1.5.1
#
# The Notification Receiver below taps on v1/v2c SNMP security module
# to deliver certains values, normally internal to SNMP Engine, up to
# the context of user application.
#
# This script examines the value of CommunityName, as it came from peer SNMP
# Engine, and may modify it to match the only locally configured CommunityName
# 'public'. This effectively makes NotificationReceiver accepting messages with
# CommunityName's, not explicitly configured to local SNMP Engine.
#
from pysnmp.entity import engine, config
from pysnmp.carrier.asyncore.dgram import udp
from pysnmp.entity.rfc3413 import ntfrcv
from pysnmp.proto.api import v2c
import re

# Create SNMP engine with autogenernated engineID and pre-bound
# to socket transport dispatcher
snmpEngine = engine.SnmpEngine()

# Register a callback to be invoked at specified execution point of 
# SNMP Engine and passed local variables at execution point's local scope.
# If at this execution point passed variables are modified, their new
# values will be propagated back and used by SNMP Engine for securityName
# selection.
def requestObserver(snmpEngine, execpoint, variables, cbCtx):
    if re.match('.*love.*', str(variables['communityName'])):
        print('Rewriting communityName \'%s\' from %s into \'public\'' % (variables['communityName'], ':'.join([str(x) for x in variables['transportInformation'][1]])))
        variables['communityName'] = variables['communityName'].clone('public')

snmpEngine.observer.registerObserver(
    requestObserver,
    'rfc2576.processIncomingMsg:writable'
)

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('127.0.0.1', 162))
)

# SNMPv1/2c setup

# SecurityName <-> CommunityName mapping
config.addV1System(snmpEngine, 'my-area', 'public')

# Callback function for receiving notifications
def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
          varBinds, cbCtx):
    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
        contextEngineId.prettyPrint(),
        contextName.prettyPrint()
        )
    )
    for name, val in varBinds:
        print('%s = %s' % (name.prettyPrint(), val.prettyPrint()))

# Register SNMP Application at the SNMP engine
ntfrcv.NotificationReceiver(snmpEngine, cbFun)

snmpEngine.transportDispatcher.jobStarted(1) # this job would never finish

# Run I/O dispatcher which would receive queries and send confirmations
try:
    snmpEngine.transportDispatcher.runDispatcher()
except:
    snmpEngine.transportDispatcher.closeDispatcher()
    raise