Asynchronous: Twisted¶
Twisted is quite old and widly used
I/O framework. With Twisted, your code will mostly live in isolated
functions, but unlike as it is with callback-based design, with Twisted
work-in-progress is represented by a
Deferred
class instance effectively
carrying state and context of running operation. Your callback functions
will be attached to these Deferred objects and invoked as Deferred
is done.
Based on Twisted infrastructure, individual asynchronous functions could be chained to run sequentially or in parallel.
In most examples approximate analogues of well known Net-SNMP snmp* tools command line options are shown. That may help those readers who, by chance are familiar with Net-SNMP tools, better understanding what example code doe
Here’s a quick example on a simple SNMP GET by high-level API:
with SNMPv1, community ‘public’
over IPv4/UDP
to an Agent at demo.snmplabs.com:161
for two instances of SNMPv2-MIB::sysDescr.0 MIB object,
based on Twisted I/O framework
from twisted.internet.task import react
from pysnmp.hlapi.twisted import *
def success(args, hostname):
(errorStatus, errorIndex, varBinds) = args
if errorStatus:
print('%s: %s at %s' % (hostname,
errorStatus.prettyPrint(),
errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
else:
for varBind in varBinds:
print(' = '.join([x.prettyPrint() for x in varBind]))
def failure(errorIndication, hostname):
print('%s failure: %s' % (hostname, errorIndication))
# noinspection PyUnusedLocal
def getSysDescr(reactor, hostname):
d = getCmd(SnmpEngine(),
CommunityData('public', mpModel=0),
UdpTransportTarget((hostname, 161)),
ContextData(),
ObjectType(ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0)))
d.addCallback(success, hostname).addErrback(failure, hostname)
return d
react(getSysDescr, ['demo.snmplabs.com'])
To make use of SNMPv3 and USM, the following code performs a series of SNMP GETNEXT operations effectively fetching a table of SNMP variables from SNMP Agent:
with SNMPv3, user ‘usr-none-none’, no authentication, no privacy
over IPv4/UDP
to an Agent at demo.snmplabs.com:161
for all OIDs past SNMPv2-MIB::system
run till end-of-mib condition is reported by Agent
based on Twisted I/O framework
from twisted.internet.task import react
from pysnmp.hlapi.twisted import *
def success(args, reactor, snmpEngine):
(errorStatus, errorIndex, varBindTable) = args
if errorStatus:
print('%s: %s at %s' % (hostname,
errorStatus.prettyPrint(),
errorIndex and varBindTable[0][int(errorIndex) - 1][0] or '?'))
else:
for varBindRow in varBindTable:
for varBind in varBindRow:
print(' = '.join([x.prettyPrint() for x in varBind]))
if not isEndOfMib(varBindTable[-1]):
return getbulk(reactor, snmpEngine, *varBindTable[-1])
def failure(errorIndication):
print(errorIndication)
def getbulk(reactor, snmpEngine, varBinds):
d = bulkCmd(snmpEngine,
UsmUserData('usr-none-none'),
UdpTransportTarget(('demo.snmplabs.com', 161)),
ContextData(),
0, 50,
varBinds)
d.addCallback(success, reactor, snmpEngine).addErrback(failure)
return d
react(getbulk, [SnmpEngine(), ObjectType(ObjectIdentity('SNMPv2-MIB', 'system'))])
More examples on Command Generator API usage follow.
Sending SNMP TRAP’s and INFORM’s is as easy with PySNMP library. The following code sends SNMP TRAP:
SNMPv1
with community name ‘public’
over IPv4/UDP
send TRAP notification
with Generic Trap #1 (warmStart) and Specific Trap 0
with default Uptime
with default Agent Address
with Enterprise OID 1.3.6.1.4.1.20408.4.1.1.2
include managed object information ‘1.3.6.1.2.1.1.1.0’ = ‘my system’
from twisted.internet.task import react
from pysnmp.hlapi.twisted import *
def success(args, hostname):
(errorStatus, errorIndex, varBinds) = args
if errorStatus:
print('%s: %s at %s' % (
hostname,
errorStatus.prettyPrint(),
errorIndex and varBinds[int(errorIndex) - 1][0] or '?'
)
)
else:
for varBind in varBinds:
print(' = '.join([x.prettyPrint() for x in varBind]))
def failure(errorIndication, hostname):
print('%s failure: %s' % (hostname, errorIndication))
# noinspection PyUnusedLocal
def run(reactor, hostname):
d = sendNotification(
SnmpEngine(),
CommunityData('public', mpModel=0),
UdpTransportTarget((hostname, 162)),
ContextData(),
'trap',
NotificationType(
ObjectIdentity('1.3.6.1.6.3.1.1.5.2')
).addVarBinds(
('1.3.6.1.6.3.1.1.4.3.0', '1.3.6.1.4.1.20408.4.1.1.2'),
('1.3.6.1.2.1.1.1.0', OctetString('my system'))
)
)
d.addCallback(success, hostname).addErrback(failure, hostname)
return d
react(run, ['demo.snmplabs.com'])
More examples on Notification Originator API usage follow.
More sophisticated or less popular SNMP operations can still be performed with PySNMP through its Native API to Standard SNMP Applications.