Hello everybody,
I don't know if it is the right place to ask the question, let me know
if not.
I am currently writting a simple dissector using lua for a proprietary
protocol.
This protocol is quite basic ,i.e : frame start character+ data + frame
stop character .
But the problem is that the data field can contain frame start or stop
characters that must be escaped with an escape character.
In order to pass the data field to another dissector I have to remove
the escape characters from the tvb before. But there are no function to
remove data from a tvb nor a tvbrange nor byte array.
I then wrote the following code:
function netx_proto.dissector(buffer,pinfo,tree)
pinfo.cols.protocol = "NetX"
packetnum = pinfo.number
local subtree_packet = tree:add(netx_proto,buffer(),"NetX Protocol
("..buffer:len()..")")
local msgbufferarray = buffer(1,buffer:len()-2):bytes()--Here I get
a byte array containing the data section from the frame
local temparray=ByteArray.new()--allocation for a buffering byte array
local offset=0
for i=0,msgbufferarray:len()-2 do -- I go through the array
if (msgbufferarray:get_index(i+1)==0x5C
or msgbufferarray:get_index(i+1)==0x10
or msgbufferarray:get_index(i+1)==0x13)
and msgbufferarray:get_index(i)==0x5C then--here I m looking
for escape sequences
temparray.append(msgbufferarray:subset(offset,i+1))--if
found I get a subset for the array that I append to the buffering array
offset=offset+i+1
end
end
msgbuffer = Tvb.new_real(temparray)--Here I try to create a new tvb
without escape sequence from the temporary bytearray
I then have an runtime error telling me "attempt to call field
'new_real'(a nil value)". I'm quite puzzled as I can't find an example
of Tvb creation in the documentation and in forums.
If someone could give me a clue about how to solve my problem.
Thanks
Cyril
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