#
# Command Responder
#
# Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with
# the following options:
#
# * SNMPv3
# * with USM username usr-md5-none
# * using alternative set of Managed Objects addressed by
#   contextEngineId: 8000000001020304, contextName: my-context
# * allow access to SNMPv2-MIB objects (1.3.6.1.2.1)
# * over IPv4/UDP, listening at 127.0.0.1:161
# 
# Either of the following Net-SNMP's commands will walk this Agent:
#
# $ snmpwalk -v3 -u usr-md5-none -l authNoPriv -A authkey1 -E 8000000001020304 -n my-context 127.0.0.1 .1.3.6
# $ snmpwalk -v3 -u usr-md5-none -l authNoPriv -A authkey1 -E 8000000001020304 127.0.0.1 .1.3.6
#
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413 import cmdrsp, context
from pysnmp.carrier.asynsock.dgram import udp
from pysnmp.smi import instrum, builder
from pysnmp.proto.api import v2c

# Create SNMP engine
snmpEngine = engine.SnmpEngine()

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('127.0.0.1', 161))
)

# SNMPv3/USM setup

# user: usr-md5-none, auth: MD5, priv NONE
config.addV3User(
    snmpEngine, 'usr-md5-none',
    config.usmHMACMD5AuthProtocol, 'authkey1'
)

# Allow full MIB access for each user at VACM
config.addVacmUser(snmpEngine, 3, 'usr-md5-none', 'authNoPriv', (1,3,6,1,2,1), (1,3,6,1,2,1)) 

# Create an SNMP context with ContextEngineId = 8000000001020304
snmpContext = context.SnmpContext(
    snmpEngine, contextEngineId=v2c.OctetString(hexValue='8000000001020304')
)

# Create an [empty] set of Managed Objects (MibBuilder), pass it to
# Management Instrumentation Controller and register at SNMP Context
# under ContextName 'my-context'
snmpContext.registerContextName(
    v2c.OctetString('my-context'),                      # Context Name
    instrum.MibInstrumController(builder.MibBuilder())  # Managed Objects
)

# Register SNMP Applications at the SNMP engine for particular SNMP context
cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
cmdrsp.SetCommandResponder(snmpEngine, snmpContext)
cmdrsp.NextCommandResponder(snmpEngine, snmpContext)
cmdrsp.BulkCommandResponder(snmpEngine, snmpContext)

# Register an imaginary never-ending job to keep I/O dispatcher running forever
snmpEngine.transportDispatcher.jobStarted(1)

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