"""
Custom ContextEngineId and ContextName
++++++++++++++++++++++++++++++++++++++

Send a SNMP GET request
* with SNMPv3 with user 'usr-md5-none', SHA auth and no privacy protocols
* for MIB instance identified by
* contextEngineId: 0x80004fb805636c6f75644dab22cc
* contextName: da761cfc8c94d3aceef4f60f049105ba
* using Twisted framework for network transport
* over IPv4/UDP
* to an Agent at 195.218.195.228:161
* for an OID in tuple form

This script performs similar to the following Net-SNMP command:

| $ snmpget -v3 -l authNoPriv -u usr-md5-none -A authkey1 -E 80004fb805636c6f75644dab22cc -n da761cfc8c94d3aceef4f60f049105ba -ObentU 195.218.195.228:161  1.3.6.1.2.1.1.1.0

"""#
from twisted.internet import reactor, defer
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413.twisted import cmdgen
from pysnmp.proto import rfc1902
from pysnmp.carrier.twisted.dgram import udp

# Create SNMP engine instance
snmpEngine = engine.SnmpEngine()

#
# SNMPv3/USM setup
#

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

#
# Setup transport endpoint and bind it with security settings yielding
# a target name
#

# UDP/IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTwistedTransport().openClientMode()
)
config.addTargetAddr(
    snmpEngine, 'my-router',
    udp.domainName, ('195.218.195.228', 161),
    'my-creds'
)

# Error/response receiver
def cbFun(response, *args):
    snmpEngine, errorIndication, errorStatus, errorIndex, varBinds = response
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print('%s at %s' % (
                errorStatus.prettyPrint(),
                errorIndex and varBinds[int(errorIndex)-1][0] or '?'
            )
        )
    else:
        for oid, val in varBinds:
            print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    reactor.stop()

# Prepare request to be sent yielding Twisted deferred object
df = cmdgen.GetCommandGenerator().sendVarBinds(
    snmpEngine,
    'my-router',
    rfc1902.OctetString(hexValue='80004fb805636c6f75644dab22cc'),
    rfc1902.OctetString('da761cfc8c94d3aceef4f60f049105ba'),
    [ ('1.3.6.1.2.1.1.1.0', None) ]
)

# Register error/response receiver function at deferred
df.addCallback(cbFun)

# Run Twisted main loop
reactor.run()