Re: [pysnmp-users] pysnmp / pyasn1 decode problem with multi-line traps

[Ilya E. <il...@gl...>]

Oh, if you are using SNMPv1 you should check against the base class:

from pyasn1.type.univ import OctetString

if isinstance(oval, OctetString):
     ...

Perhaps this should be improved in pysnmp.

-ilya

On 03/12/2015 04:29 PM, Tom Kr. wrote:
> I made the following changes to the script.
>   
> ...
> from pysnmp.proto.rfc1902 import OctetString
>   
> def pySnmpCheck(oval):
>      if isinstance(oval, OctetString):
>          print("DEBUG: OctetString")
>          val = oval.asOctets()
>      else:
>          print("DEBUG: else")
>          val = oval
>      return val
>   
> ...
>              for oid, val in varBinds:
>                  val = pySnmpCheck(val)
>                  print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
> ...
>   
> Then I start grabbing the snmp messages again.
> Unfortunately every value of the message go through the else part.
> But how could this happen?
>   
> Is there a possibility to check which type of string the values have?
>   
> Tom
>
>
>
>> Am 11.03.2015 um 14:17 schrieb Ilya Etingof <il...@gl...>:
>>
>>
>> That's right, .asOctets() is only defined for OctetString type and its
>> subclasses. Therefore, to deal with octets of OctetString() you should
>> do additional check:
>>
>> from pysnmp.proto.rfc1902 import OctetString
>>
>> ...
>>
>> if isinstance(val, OctetString):
>>      val = val.asOctets()
>>
>> Keep in mind that octet string is not always the same as printable
>> string. The former is not immune to your terminal potentially eating
>> non-printable characters or garbling output in a funny way. Also, text
>> encoding is not defined by OctetString. To be on a safe side default
>> OctetString printout is done in hex whenever a non-printable is seen in
>> its contents.
>>
>> -ilya
>>
>>> On 03/11/2015 03:18 PM, Craig Small wrote:
>>>> On Wed, Mar 11, 2015 at 07:02:44AM +0100, Tom wrote:
>>>>     ;AttributeError: ObjectSyntax instance has no attribute 'asOctets'
>>> Are you sure each row is returning something asOctets makes sense for?
>>> An Integer doesn't make sense.
>>>
>>>>     Does it only works if a hex value is send by snmp?
>>> I believe it works for certain types of values, such as an OctetString
>>>
>>>>     How can I check if the value is hex or not?
>>> Not sure, but the types are found in pyasn1.type.univ so you could
>>> compare it to, say, univ.OctetString
>>>
>>> ObjectSyntax seems to be the superset of all types, from what I can tell
>>> it means pysnmp wasn't sure what the type should be.
>>>
>>> It's been an interesting and educational discussion anyhow.
>>>
>>>   - Craig
>>