[pysnmp-users] pysnmp: oneliners

[Ashirvaad R. <ax...@gm...>]

Hello

I am new to python and SNMP.
I am experiencing a little difficulty with pysnmp, and trawling through the
documentation, source code, and mailing lists has not been able to help me.
I hope someone can point me in the right direction with the information
below:

I am trying to use pysnmp to asynchronously poll a number of devices.

It seemed easiest to do this using pysnmp.entity.rfc3413.oneliner:
            handle = cmdgen.AsynCommandGenerator().asyncGetCmd(
                authData,
                transportTarget,
                varNames,
                (handle_asyn_snmp_response, (self, context_id)))
authData, transportTarget, varNames are correctly initialised before the
call to asyncGetCmd().
handle_asyn_snmp_response is the name of the callback function.
as the context data, i'm passing a reference to the calling object, and a
custom specified id (a string which is used to identify the request sender).
after the call to asyncGetCmd(), I store some data in a dictionary, using
"handle" as the key, based on the assumption that every request/response is
generated with a unique handle number.

That is not exactly how it turns out.

I send an SNMP NEXT request to each device:
            handle = cmdgen.AsynCommandGenerator().asyncNextCmd(
                authData,
                transportTarget,
                varNames,
                (handle_asyn_snmp_response, (self, context_id)))
When a response is received (if it is not timed out and no error has
occurred), I then send the same device an SNMP GET request, using an almost
identical call:
            handle = cmdgen.AsynCommandGenerator().asyncGetCmd(
                authData,
                transportTarget,
                varNames,
                (handle_asyn_snmp_response, (self, context_id)))

The problem is that this method always returns a handle ID of 1.
Looking at the source has revealed that a new instance of the command
generator is created for each call, and this is why the handle number is
never incremented.

One obvious way I managed to solve this problem was to extend the
cmdgen.AsynCommandGenerator class and change things a little in there, that
is by creating and reusing a single command generator object. That worked
for the case where I send out only SNMP NEXT or only SNMP GET requests.

But I am, within the same session, sending out both GET and NEXT requests,
and the handles generated are not unique.

Looking at the class hierarchy, I see that GetCommandGenerator,
SetCommandGenerator, NextCommandGenerator, and BulkCommandGenerator all
inherit from CommandGeneratorBase.
This means I have no way of getting them to obtain handles from a shared
source.

Any suggestions? I don't want to have to hack this whole project by
rewriting most of Ilya's code.
And I don't want to use a global counter that all instances of the command
generators read.
And the oneliner module so closely almost does exactly what I need it to do!
Is there something I can do to take advantage of its elegance, eloquence,
and simplicity?

Thanks for your time and patience!

Ashir

-- 
all is chaos. seek harmony, not control.
axdk