Implementing a table in a PySNMP agent

Question

I'm implementing a table using PySNMP as an SNMP agent.

I've followed the (PySNMP source) architecture of using an auto-generated TRS-MIB.py file, and a manually written __TRS-MIB.py file which contains the implementation.

I have made a working (2 row) table, but the code is really ugly, so there must be a better way of doing it. (Also, both rows will always have the same values, which is a bug.)

__TRS-MIB.py:

# Imported just in case new ASN.1 types would be created
from pyasn1.type import constraint, namedval
import time

# Imports

( Integer,
  ObjectIdentifier,
  OctetString, ) = mibBuilder.importSymbols(
  "ASN1",
  "Integer",
  "ObjectIdentifier",
  "OctetString"
  )
( Bits,
  Integer32,
  ModuleIdentity,
  MibIdentifier,
  MibScalar,
  MibScalarInstance,
  TimeTicks, ) = mibBuilder.importSymbols(
  "SNMPv2-SMI",
  "Bits",
  "Integer32",
  "ModuleIdentity",
  "MibIdentifier",
  "MibScalar",
  "MibScalarInstance",
  "TimeTicks"
  )

class TrsDeliveryTime(Integer32):
  def clone(self, **kwargs):
    if 'value' not in kwargs:
      kwargs['value'] = int(time.time())
    return Integer32.clone(self, **kwargs)

class TrsMessagesPerHour(Integer32):
  def clone(self, **kwargs):
    if 'value' not in kwargs:
      kwargs['value'] = -int(time.time())
    return Integer32.clone(self, **kwargs)

class TrsGatewayIndex(Integer32):
  def clone(self, **kwargs):
    if 'value' not in kwargs:
      kwargs['value'] = 0
    return Integer32.clone(self, **kwargs)

class TrsGatewayName(OctetString):
  def clone(self, **kwargs):
    if 'value' not in kwargs:
      kwargs['value'] = 'SMG0'
    return OctetString.clone(self, **kwargs)

class TrsGatewayState(OctetString):
  def clone(self, **kwargs):
    if 'value' not in kwargs:
      kwargs['value'] = 'UP' + str(int(time.time()))
    return OctetString.clone(self, **kwargs)

# Objects
( trsDeliveryTime,
  trsMessagesPerHour,
  trsGatewayTable,
  trsGatewayEntry,
  trsGatewayIndex,
  trsGatewayName,
  trsGatewayState, ) = mibBuilder.importSymbols(
  'TRS-MIB',
  'trsDeliveryTime',
  'trsMessagesPerHour',
  'trsGatewayTable',
  'trsGatewayEntry',
  'trsGatewayIndex',
  'trsGatewayName',
  'trsGatewayState', 
  )
__trsDeliveryTime = MibScalarInstance(trsDeliveryTime.name, (0,), TrsDeliveryTime(0))
__trsMessagesPerHour = MibScalarInstance(trsMessagesPerHour.name, (0,), TrsMessagesPerHour(0))
__trsGatewayIndex0 = MibScalarInstance(trsGatewayIndex.name, (0,), TrsGatewayIndex(0))
__trsGatewayName0 = MibScalarInstance(trsGatewayName.name, (0,), TrsGatewayName(0))
__trsGatewayState0 = MibScalarInstance(trsGatewayState.name, (0,), TrsGatewayState(0))
__trsGatewayIndex1 = MibScalarInstance(trsGatewayIndex.name, (1,), TrsGatewayIndex(0))
__trsGatewayName1 = MibScalarInstance(trsGatewayName.name, (1,), TrsGatewayName(0))
__trsGatewayState1 = MibScalarInstance(trsGatewayState.name, (1,), TrsGatewayState(0))


# Augmentions

# Exports

# Objects
mibBuilder.exportSymbols("__TRS-MIB",
                         trsDeliveryTime=__trsDeliveryTime,
                         trsMessagesPerHour=__trsMessagesPerHour,
                         trsGatewayTable=trsGatewayTable,
                         trsGatewayIndex0=__trsGatewayIndex0,
                         trsGatewayName0=__trsGatewayName0,
                         trsGatewayState0=__trsGatewayState0,
                         trsGatewayIndex1=__trsGatewayIndex1,
                         trsGatewayName1=__trsGatewayName1,
                         trsGatewayState1=__trsGatewayState1,
                         )

Answer 1

Not pretending this is a beautiful code, here's some optimization to your initial version. It's not tested as I do not have your TRS-MIB file at hand.

The idea is to specialize MibScalarInstance class (to make it serving different columns) by overriding its readGet() method which returns a var-bind pair to be reported back to SNMP Manager.

You should be able to run this MIB with the stock CommandResponder, just make sure to load up your MIB on startup.

import time

# Import managed objects
( trsDeliveryTime,
  trsMessagesPerHour,
  trsGatewayIndex,
  trsGatewayName,
  trsGatewayState, ) = mibBuilder.importSymbols(
  'TRS-MIB',
  'trsDeliveryTime',
  'trsMessagesPerHour',
  'trsGatewayIndex',
  'trsGatewayName',
  'trsGatewayState', 
  )

# Columnar managed objects instances implementation

class TrsDeliveryTimeInstance(MibScalarInstance):
  def readGet(self, name, val, *args):
    if name[-1] == 0:  # Row #0
      return self.name, self.syntax(int(time.time()))
    elif name[-1] == 1: # Row #1
      return self.name, self.syntax(time.time()//2)
    else:
      MibScalarInstance.readGet(self, name, val, *args)

class TrsMessagesPerHourInstance(MibScalarInstance):
  def readGet(self, name, val, *args):
    if name[-1] == 0: # Row #0
      return self.name, self.syntax(-int(time.time()))
    elif name[-1] == 1: # Row #1
      return self.name, self.syntax(-time.time()//2)
    else:
      MibScalarInstance.readGet(self, name, val, *args)

class TrsGatewayIndexInstance(MibScalarInstance):
  def readGet(self, name, val, *args):
    if name[-1] == 0: # Row #0
      return self.name, self.syntax(0)
    elif name[-1] == 1: # Row #1
      return self.name, self.syntax(1)
    else:
      MibScalarInstance.readGet(self, name, val, *args)

class TrsGatewayNameInstance(MibScalarInstance):
  def readGet(self, name, val, *args):
    if name[-1] == 0: # Row #0
      return self.name, self.syntax('SMG0')
    elif name[-1] == 1: # Row #1
      return self.name, self.syntax('SMG1')
    else:
      MibScalarInstance.readGet(self, name, val, *args)

class TrsGatewayStateInstance(MibScalarInstance):
  def readGet(self, name, val, *args):
    if name[-1] == 0: # Row #0
      return self.name, self.syntax('UP' + str(time.time()))
    elif name[-1] == 1: # Row #1
      return self.name, self.syntax('DOWN' + str(time.time()))
    else:
      MibScalarInstance.readGet(self, name, val, *args)

# Instantiate and export managed objects instances
mibBuilder.exportSymbols(
  "__TRS-MIB",
  # Row #0
  TrsDeliveryTimeInstance(trsDeliveryTime.getName(), 0, trsDeliveryTime.getSyntax()),
  TrsMessagesPerHourInstance(trsMessagesPerHour.getName(), 0, trsMessagesPerHour.getSyntax()),
  TrsGatewayIndexInstance(trsGatewayIndex.getName(), 0, trsGatewayIndex.getSyntax()),
  TrsGatewayNameInstance(trsGatewayName.getName(), 0, trsGatewayName.getSyntax()),
  TrsGatewayStateInstance(trsGatewayState.getName(), 0, trsGatewayState.getSyntax()),
  # Row #1
  TrsDeliveryTimeInstance(trsDeliveryTime.getName(), 1, trsDeliveryTime.getSyntax()),
  TrsMessagesPerHourInstance(trsMessagesPerHour.getName(), 1, trsMessagesPerHour.getSyntax()),
  TrsGatewayIndexInstance(trsGatewayIndex.getName(), 1, trsGatewayIndex.getSyntax()),
  TrsGatewayNameInstance(trsGatewayName.getName(), 1, trsGatewayName.getSyntax()),
  TrsGatewayStateInstance(trsGatewayState.getName(), 1, trsGatewayState.getSyntax())
)