"""
Pull MIB subtree
++++++++++++++++

Send a series of SNMP GETNEXT requests
* with SNMPv3 with user 'usr-none-none', no auth and no privacy protocols
* over IPv4/UDP
* to an Agent at 195.218.195.228:161
* for an OID in string form
* stop whenever received OID goes out of initial prefix (it may be a table)

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

| $ snmpwalk -v3 -l noAuthNoPriv -u usr-none-none -ObentU 195.218.195.228:161  1.3.6.1.2.1.1 

"""#
from pysnmp.entity import engine, config
from pysnmp.carrier.asyncore.dgram import udp
from pysnmp.entity.rfc3413 import cmdgen
from pysnmp.proto import rfc1902

# Initial OID prefix
initialOID = rfc1902.ObjectName('1.3.6.1.2.1.1')

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

#
# SNMPv3/USM setup
#

# user: usr-none-none, auth: none, priv: none
config.addV3User(
    snmpEngine, 'usr-none-none',
)
config.addTargetParams(snmpEngine, 'my-creds', 'usr-none-none', 'noAuthNoPriv')

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

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

# Error/response receiver
def cbFun(snmpEngine, sendRequestHandle, errorIndication,
          errorStatus, errorIndex, varBindTable, cbCtx):
    if errorIndication:
        print(errorIndication)
        return
    if errorStatus:
        print('%s at %s' % (
            errorStatus.prettyPrint(),
            errorIndex and varBindTable[-1][int(errorIndex)-1][0] or '?'
            )
        )
        return  # stop on error
    for varBindRow in varBindTable:
        for oid, val in varBindRow:
            if initialOID.isPrefixOf(oid):
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
            else:
                return False # signal dispatcher to stop
    return True # signal dispatcher to continue

# Prepare initial request to be sent
cmdgen.NextCommandGenerator().sendVarBinds(
    snmpEngine,
    'my-router',
    None, '',  # contextEngineId, contextName
    [ (initialOID, None) ],
    cbFun
)

# Run I/O dispatcher which would send pending queries and process responses
snmpEngine.transportDispatcher.runDispatcher()
