What am I missing? The field extractor always returns nil, so the seq value is always -1. The frame number is correct, however, so I know the code is being executed. In my listener code I used the same field extractor for the 802.15.4 seq number and it worked fine there.
-- I define my "protocol":
local post154_proto = Proto("post802154", "Extra analysis of 802.15.4 fields", "Post802514");
-- I define 2 fields:
local F_frmNum = ProtoField.framenum("post802154.frmNum", "Wireshark frame number", base.DEC)
local F_seqNum = ProtoField.int8("post802154.seqNum", "802.15.4 seq number", base.DEC)
-- I add the field to my protocol:
post154_proto.fields = { F_frmNum, F_seqNum }
-- I declare a field extractor:
local seq_no = Field.new("ieee802.15.4.seq_no")
-- I register my postdissector:
register_postdissector(post154_proto)
-- And I create a dissector function that uses the field extractor to add an item to the display tree:
function post154_proto.dissector(tvbuffer, pinfo, treeitem)
-- Get frame number from pinfo
local fnum = pinfo.number
-- Get value from field extractor (-1 if field is nil)
local seq = -1
if seq_no() then seq=seq_no().value end
-- Add our extra protocol subtree
local subtreeitem = treeitem:add(post154_proto, tvbuffer)
-- Display the field value
subtreeitem:add(F_frmNum, tvbuffer(0,0), fnum)
subtreeitem:add(F_seqNum, tvbuffer(0,0), seq)
end
