Net-SNMP v5.9.3 with python 3.6.3.
I'm not sure if this has only become an issue since the move of strings from
bytes to Unicode in Python 3 but I cannot set an OID value to an octet string
containing octets >=128.
I am trying to set a MAC address in an OID.
macAddress = '\x02\0\0\0\x80\xff'
varbind = netsnmp.Varbind(oidSvcMacNameAddr, iid, macAddress,
'OCTETSTR')
The python bindings convert everything to strings in the Varbind object.
class Varbind(object):
def __init__(self, tag=None, iid=None, val=None, type_arg=None):
self.tag = STR(tag)
self.iid = STR(iid)
self.val = STR(val)
self.type = STR(type_arg)
The result on the wire of the performing an SNMP set on using the values above
is:
variable-bindings: 2 items
TIMETRA-GLOBAL-MIB::tmnxSRObjs.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49
(1.3.6.1.4.1.6527.3.1.2.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49):
02000000c280c3bf
Object Name:
1.3.6.1.4.1.6527.3.1.2.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49
(TIMETRA-GLOBAL-MIB::tmnxSRObjs.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49)
Value (OctetString): 02000000c280c3bf
TIMETRA-GLOBAL-MIB::tmnxSRObjs.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49
(1.3.6.1.4.1.6527.3.1.2.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49):
020000007f55
Object Name:
1.3.6.1.4.1.6527.3.1.2.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49
(TIMETRA-GLOBAL-MIB::tmnxSRObjs.4.2.59.1.4.10.83.84.69.45.80.79.76.84.48.49)
Value (OctetString): 020000007f55
As a result an error is returned because the octet string is 8 bytes rather
than 6.
Note: Setting values <0x80 works without issue. The second variable binding is
using a macAddress = '\x02\0\0\0\x7f\x55' is correct and when used without the
1st binding sets the value.
Within the library bindings, the val attribute is read using the function
py_netsnmp_attr_string, which calls PyUnicode_AsUTF8AndSize function which
returns a UTF8 encoded char buffer. The value sent on the wire is the UTF-8
encoded string.
>>> macAddress = '\x02\0\0\0\x80\xff'
>>> macAddress
'\x02\x00\x00\x00\x80ΓΏ'
>>> macAddress.encode('utf8')
b'\x02\x00\x00\x00\xc2\x80\xc3\xbf'
UTF8 encoding is probably a poor choice for encoding octet strings. I believe
that if the string was encoded as latin-1 (which is the same as iso-8859-1)
within the bindings the problem wouldn't occur.
>>> macAddress.encode('latin-1')
b'\x02\x00\x00\x00\x80\xff'
Does anyone have any idea of how to cleverly work around this or failing that
patch the bindings?
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