Encoding and decoding fails for template with first ie element being varlen

[shravan86]

Hello,

PROBLEM:

If we define a template with the first ie element being a varlen, then the decoding does not seem to work.
Please see the below to reproduce the issue -

import ipfix.template
import ipfix.ie
import hexdump
from datetime import datetime
from ipaddress import ip_address

msg = ipfix.message.MessageBuffer()

msg.begin_export(8304)

ipfix.ie.use_iana_default()

tmpl = ipfix.template.from_ielist(256,
ipfix.ie.spec_list(("applicationName",
"flowStartMilliseconds",
"sourceIPv4Address",
"destinationIPv4Address",
"packetDeltaCount")))

msg.add_template(tmpl)

msg.export_ensure_set(256)

rec = { "applicationName" : "testing123",
"flowStartMilliseconds" : datetime.strptime("2013-06-21 14:00:00",
"%Y-%m-%d %H:%M:%S"),
"sourceIPv4Address" : ip_address("10.1.2.3"),
"destinationIPv4Address" : ip_address("10.5.6.7"),
"packetDeltaCount" : 27}

msg.export_namedict(rec)

print(msg)
print(hexdump.dump(msg.to_bytes()))

###################################################

READER

###################################################

msg1 = ipfix.message.MessageBuffer()
msg1.from_bytes(msg.to_bytes())

for rec in msg1.namedict_iterator():
print(sorted(rec.items()))

FIX:

The root cause of the issue is in template.py - encode_to() and decode_from() methods.

diff --git a/ipfix/template.py b/ipfix/template.py
index 1203e55..87a7f5b 100644
--- a/ipfix/template.py
+++ b/ipfix/template.py
@@ -187,7 +187,7 @@ class Template(object):
offset += packplan.st.size

     # short circuit on no varlen

•    if not self.varlenslice:
  

•    if self.varlenslice == None:
         return (vals, offset)
  
     # direct iteration over remaining IEs
  

@@ -239,7 +239,7 @@ class Template(object):
offset += packplan.st.size

     # shortcircuit no varlen

•    if not self.varlenslice:
  

•    if self.varlenslice == None:
         return offset
  
     # direct iteration over remaining IEs
  

If you are ok with this fix. Please let me know how to commit this change to master.
I have also attached the diff file.

Thanks
Shravan

diff.txt