Re: [pysnmp-dev] Asyncio support in Python 3

[R. D. M. <rdm...@bi...>]

On Tue, 04 Nov 2014 23:30:29 +0300, Ilya Etingof <il...@gl...> wrote:
> Hi Matt,
> 
> I’ve applied your patch to pysnmp and slightly reworked it afterwards. Please, try to use pysnmp development code and let me know in case of any issues:
> 
> download latest CVS snapshot <http://pysnmp.cvs.sourceforge.net/viewvc/pysnmp/pysnmp/?view=tar>
> 
> Please be aware that I’ve slightly changed the API you introduced in your patch to make it more uniform with the rest of pysnmp. See examples for details.
> 
> I’m also interested in real-world use cases of the asyncio transport to better adapt pysnmp API.

On a somewhat different note...

This is not a real world example, but it does show how the asyncio API
(can) differ from that of pysnmp.  This is an example I got working of a
simple snmpv1 'get', based on the 'low level' get example.  (Instead of
printing errors, it should probably use set_exception.)

I'm working on incorporating a more advanced version of this technique
(that will handle multiple gets) into the application I'm writing.

I also created a pynsmp asyncio transport patch, but frankly I couldn't
figure out how to use the sort of intermediate-level API that is shown
in the examples for the Twisted transport in my own application, so I
gave up on that approach.  Fortunately I only need v1.

----------------------------------------------------------------------
from pyasn1.codec.ber import encoder, decoder
from pysnmp.proto import api
import asyncio

# Protocol version to use
pMod = api.protoModules[api.protoVersion1]

# Build PDU
reqPDU =  pMod.GetRequestPDU()
pMod.apiPDU.setDefaults(reqPDU)
pMod.apiPDU.setVarBinds(
    reqPDU, ( ('1.3.6.1.2.1.1.1.0', pMod.Null('')),
              ('1.3.6.1.2.1.1.3.0', pMod.Null('')) )
    )

# Build message
reqMsg = pMod.Message()
pMod.apiMessage.setDefaults(reqMsg)
pMod.apiMessage.setCommunity(reqMsg, 'public')
pMod.apiMessage.setPDU(reqMsg, reqPDU)

# Future for the result.
reqFut = asyncio.Future()

class SNMPProtocol(asyncio.DatagramProtocol):

    def datagram_received(self, data, transport_address):
        res = []
        while data:
            rspMsg, data = decoder.decode(data, asn1Spec=pMod.Message())
            rspPDU = pMod.apiMessage.getPDU(rspMsg)
            # Match response to request
            if pMod.apiPDU.getRequestID(reqPDU)==pMod.apiPDU.getRequestID(rspPDU):
                # Check for SNMP errors reported
                errorStatus = pMod.apiPDU.getErrorStatus(rspPDU)
                if errorStatus:
                    print(errorStatus.prettyPrint())
                else:
                    for oid, val in pMod.apiPDU.getVarBinds(rspPDU):
                        res.append((oid, val))
        reqFut.set_result(res)


@asyncio.coroutine
def get(reqMsg):
    snmp.sendto(encoder.encode(reqMsg))
    return reqFut

@asyncio.coroutine
def main():
    for oid, val in (yield from asyncio.wait_for(get(reqMsg), timeout=3)):
        print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

loop = asyncio.get_event_loop()
snmp, snmp_proto = loop.run_until_complete(
    loop.create_datagram_endpoint(SNMPProtocol,
                                  remote_addr=('demo.snmplabs.com', 161)))
loop.run_until_complete(main())