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

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

Right, in 'val' you are getting the whole SNMP PDU value structure, not 
just a leaf scalar. That's the reason it does not match OctetString 
class instance check.

Use .getVarBinds() method instead of .getVarBindsList(). The former 
returns a list of tuples of terminal values, while the latter returns 
original var-bindings list from SNMP PDU which always holds a 
record-like structure for value.

-ilya

On 03/12/2015 05:29 PM, Tom Kr. wrote:
> Hmm, I'm confused.
> With this changes I also get hex values back and I still enter the else part for each value.
>   
> import sys,os
>   
> sys.path.append('/usr/share/pyshared/')
>   
> from pysnmp.carrier.asynsock.dispatch import AsynsockDispatcher
> from pysnmp.carrier.asynsock.dgram import udp, udp6
> from pyasn1.codec.ber import decoder
> from pysnmp.proto import api
> #from pysnmp.proto.rfc1902 import OctetString
> from pyasn1.type.univ import OctetString
>   
> def pySnmpCheck(oval):
>      if isinstance(oval, OctetString):
>          print("DEBUG: OctetString")
>          val = oval.asOctets()
>      else:
>          print("DEBUG: else")
>          val = oval
>      return val
>   
> If this information are useful, this is the header I've got.
>   
> # python snmp-transports.py
> Notification message from (1, 3, 6, 1, 6, 1, 1):('xxx.xxx.xxx.xxx', 52032):
> Enterprise: 1.3.6.1.4.1.18494.2
> Agent Address: xxx.xxx.xxx.xxx
> Generic Trap: 'enterpriseSpecific'
> Specific Trap: 1
> Uptime: 1
> Var-binds:
> DEBUG: else
> 1.3.6.1.4.1.18494.2.1.9 = ObjectSyntax:
> simple=SimpleSyntax:
> string=0x4f70657261746f722058585858585858585858203a20585858585858585858582c2058585858585858202c204c6f63616c6c792061757468656e74696361746564202d207375636365737366756c6c79207369676e6564206f6e20746f20746865207465726d696e616c20275858582e5858582e582e584058272061742031343a3238207573696e672027585858585858585820585858205858585858585858272e0a4f70657261746f722050726f66696c65733a2058585858585858585858585858
>   
> Tom
>   
>   
>
>
>
>> Am 12.03.2015 um 14:39 schrieb Ilya Etingof <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