Wireshark · Wireshark-dev: [Wireshark-dev] no size information in fixed header-length for tcp_dissect_pdus()

[Robert Naumann <robert.naumann@xxxxxxxxxxxxxxxxxxxx>]

hello,

in the rfb-protocol i've to dissect i got some zlib-compressed 
FramebufferUpdates. The PDU-header doenst contain any information about 
the compressed data-bytes, so i decided to sniff in the compressed data, 
as there are  the lenght information of one compressed part is stored.  
So i can move on the datastream to the next size information until the 
end of the PDU. My GET_PDU_LEN()- function reports the correct size of 
the hole PDU. Now to the problems i got. 

The fixed-length-parameter is set to something, because i dont have any 
information about the length of the PDU in my PDU-header. As far as i 
understood i should set the fixed-lenght-parameter to the databytes 
which are containing the size information of my last compressed part. 
the number of compressed parts in the PDU is variable, so the best way 
is to calculate how much compressed parts my PDU contains. Do i have a 
chance to calculate the length before i'm using the function 
tcp_dissect_pdus()? If so, plz can anyone tell me how?

For testing purposes i tried with a fixed lenght for my first 
zlib-compressed FramebufferUpdate-PDU. My GET_PDU_LEN()- function still 
reports the correct size of the hole PDU, but wireshark doesn't seem to 
use this size. Instead the size of my fixed length parameter is used an 
i get a wrong dissection.

kindest regard

Robert