For this protocol it is sufficient to know the source port only. Hence it is sufficient to have two different calls to tcp_dissect_pdus with different input functions to the get_pdu_len() function pointer based on the source port in the pinfo structure at hand there. Thank you for pointing this out.
/ Regards, Peter ronnie sahlberg wrote: > Is it sufficient to know which tcp port the packet came from in order > to decide which protocol it is? > > If so, you can get this info from the pinfo structure which is > available in the tcp_dissect_pdus() fucntion but not passed to the > get_pdu_len() helper. > > > Two possibilities: > either you can add a pinfo structure as argument to the get_pdu_len() > fucntion > but that would change the signature and need a big patch to change all > its callers (maybe this is the correct solution) > > optionally you can look at packet-ldap.c which has a similar problem. > packet-ldap.c first detects whether SASL wrapping is present or not > and then calls either of two different tcp_dissect_pdus() with > different get_len/dissect_payload functions depending on whether the > payload is normal ldap or ldap wrapped inside sasl > > > you could solve this by > 1, have one unique get_len/dissect_payload pair for each protocol that > is transported. > 2, in the main dissector function, check pinfo for the ports that were > used in the tcp layer and then > call the appropriate tcp_dissect_pdus() function. > > this is probably the easiest solution. > > > mvh > ronnie s > > > > > > On 9/12/06, Peter Johansson <[EMAIL PROTECTED]> wrote: >> Hi! >> >> I have come a across a really old protocol on top of TCP that I want to >> be able to decode using wireshark. Unfortunately the protocol's header >> is "polymorphic" and mean different things depending on from which >> source port the message is being sent. Hence the length of the PDU >> cannot be computed looking at the protocol header alone. >> To make it easier to implement desegmentation of this protocol on top of >> TCP I would like to use the tcp_dissect_pdus(...) function in >> packet-tcp, however the with the information supplied in the callback to >> packet-my_own_decoder_with_some_obscude_header I cannot determine the >> PDU length. To do this properly I would require the packet_info >> structure also being passed along in the call from packet-tcp's >> tcp_dissect_pdus. >> Would you approve of changing the interface to the function pointer >> "guint (*get_pdu_len)(tvbuff_t *, int)" into "guint >> (*get_pdu_len)(tvbuff_t *, int, packet_info*)" instead? >> >> Please let me know and I will get on with the changes, supplying a list >> of patches asap. Taking the current set of dissectors into account, I >> would have to make changes to 66 dissectors in the current version. >> >> / Regards, Peter >> _______________________________________________ >> Wireshark-dev mailing list >> [email protected] >> http://www.wireshark.org/mailman/listinfo/wireshark-dev >> > -- ____________________________________________________________ Peter Johansson Phone : +46 (0)8 752 81 00 Contactor Data AB Mobile: +46 (0)70 608 3063 Finlandsgatan 14 MailTo:[EMAIL PROTECTED] 164 74 Kista SMS :[EMAIL PROTECTED] SWEDEN Contactor ingår i ContactorArete Gruppen, www.cagruppen.se _______________________________________________ Wireshark-dev mailing list [email protected] http://www.wireshark.org/mailman/listinfo/wireshark-dev
