asyncio code in pysnmp is not responding as expected

Question

I am new to pysnmp library. I tried the sample code provide in the documentation in snmplabs with certain modification as shown below.

import asyncio
from pysnmp.hlapi.asyncio import *
@asyncio.coroutine
def run(host,oid):
    errorIndication, errorStatus, errorIndex, varBinds = yield from getCmd(
        SnmpEngine(),
        CommunityData('public'),
        UdpTransportTarget((host, 161)),
        ContextData(),
        ObjectType(ObjectIdentity(oid))
    )
    print(errorIndication, errorStatus, errorIndex, varBinds)


asyncio.get_event_loop().run_until_complete(run('demo.snmplabs.com','1.3.6.1.2.1.1.1.0'))
print("asynch_1")
asyncio.get_event_loop().run_until_complete(run('198.155.104.8','1.3.6.1.2.1.1.1.0'))
print("asynch_2")
asyncio.get_event_loop().run_until_complete(run('snmp.live.gambitcommunications.com','1.3.6.1.2.1.1.1.0'))
print("asynch_3")

In the above i tried to query get-command for different agents. In which "198.155.104.8" is a dummy agent ip which doesnt exists. I expect the out as

None 0 0 [ObjectType(ObjectIdentity( payload [1.3.6.1.2.1.1.1.0]>),  subtypeSpec , , > encoding iso-8859-1 payload [Linux zeus 4.8.6...11 CDT 2016 i686]>)]
asynch_1

None 0 0 [ObjectType(ObjectIdentity( payload [1.3.6.1.2.1.1.1.0]>),  subtypeSpec , , > encoding iso-8859-1 payload [Cisco Internetwo...5:14 by kellythw]>)]
asynch_3

No SNMP response received before timeout 0 0 []
asynch_2

Since there is no agent referring to "198.155.104.8" the code should not wait in the second request it should print the third request.

But i am getting the output as shown below


None 0 0 [ObjectType(ObjectIdentity( payload [1.3.6.1.2.1.1.1.0]>),  subtypeSpec , , > encoding iso-8859-1 payload [Linux zeus 4.8.6...11 CDT 2016 i686]>)]
asynch_1
No SNMP response received before timeout 0 0 []
asynch_2
None 0 0 [ObjectType(ObjectIdentity( payload [1.3.6.1.2.1.1.1.0]>),  subtypeSpec , , > encoding iso-8859-1 payload [Cisco Internetwo...5:14 by kellythw]>)]
asynch_3

Since i am new to snmp. I am not able to get through the solution for using asyncio code for querying multiple agent at a time.

Please help in understanding the problem. As well as rectify my code if a writing it in a wrong way.

Any help will be appreciable.

Thanks in advance

Ilya Gruntal · Accepted Answer

This answer will clarify why run_until_complete() blocks your code execution.

In short you have to create a list of tasks (couroutines) for the loop and then run it asynchronously gathered altogether.

With modern async / await syntax (Python 3.5+) your refactored code would look something like this:

import asyncio
from pysnmp.hlapi.asyncio import *

async def run(host,oid):
    errorIndication, errorStatus, errorIndex, varBinds = await getCmd(
        SnmpEngine(),
        CommunityData('public'),
        UdpTransportTarget((host, 161)),
        ContextData(),
        ObjectType(ObjectIdentity(oid))
    )
    print(errorIndication, errorStatus, errorIndex, varBinds)

async def main():
    tasks = []
    tasks.append(run('demo.snmplabs.com','1.3.6.1.2.1.1.1.0'))
    tasks.append(run('198.155.104.8','1.3.6.1.2.1.1.1.0'))
    tasks.append(run('snmp.live.gambitcommunications.com','1.3.6.1.2.1.1.1.0'))
    results = await asyncio.gather(*tasks)

if __name__ == '__main__':
    asyncio.run(main())

Please take a look at this example by Ilya Etingof @ github

As a side note: it's better to keep a single, reusable SnmpEngine object within your script/thread. This object is expensive to initialized, it holds various caches so re-creating it slows down pysnmp a great deal. (с) etingof

that advice boosts the performance big time (~3 times faster). Below is another version of the code with additional errors handling and returning a readable result.

import asyncio
import pysnmp.hlapi.asyncio as snmp

async def get(host,oid):
    result = []
    try:
        snmp_engine = snmp.SnmpEngine()
        response = await snmp.getCmd(snmp_engine,
                                     snmp.CommunityData('public'),
                                     snmp.UdpTransportTarget((host, 161)),
                                     snmp.ContextData(),
                                     snmp.ObjectType(snmp.ObjectIdentity(oid)))

        errorIndication, errorStatus, errorIndex, varBinds = response

        if errorIndication:                
            print(f'{host}: errorIndication: {errorIndication}')
        elif errorStatus:
            print('{}: {} at {}'.format(host, errorStatus.prettyPrint(), errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
        else:
            for varBind in varBinds:
                result.append([x.prettyPrint() for x in varBind])

        snmp_engine.transportDispatcher.closeDispatcher()

    except Exception as err:
        print (f'Error at SNMP get() due to {err}')

    finally:
        print(f'Get {host}, {oid}: {result}')
        return result

async def main():
    tasks = []
    tasks.append(get('demo.snmplabs.com','1.3.6.1.2.1.1.1.0'))
    tasks.append(get('198.155.104.8','1.3.6.1.2.1.1.1.0'))
    tasks.append(get('snmp.live.gambitcommunications.com','1.3.6.1.2.1.1.1.0'))
    results = await asyncio.gather(*tasks)
    print(f'main() results: {results}')

if __name__ == '__main__':
    asyncio.run(main())

For more understanding on asyncio please see tutorials below:

Best wishes.

asyncio code in pysnmp is not responding as expected

Answers (1)

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