[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

Some time ago I wrote a program that reads Microsoft IIS web log files and converts them into PCAP-NG format.  I then wrote a matching dissector to produce nice neat output.  I want to rewrite it because:

 

1. The field names and data types are defined in the first record of the PCAP-NG file – this is how the dissector knows the layout of the file
2. Each data record is encapsulated in a dummy Ethernet frame and I want to eliminate this
3. I’d like to make it more general so that it can also deal with CSV, TSV and, later, variable format log records

 

My plan is to:

 

1. Insert the field name and data type information into a new IDB option block
2. Write a plugin_if function to enable a dissector to get a pointer to the IDB information and hence get my hands on the field names and data types
3. Define a new link type for the IDB; working name is Text Data Format (TDF)
   1. I understand that I have to ask for this (a value for DLT_TDF) from the tcpdump-workers@xxxxxxxxxxxxxxxxx
   2. This means that the TDF records would be below (within) the Frame
4. Add a new WTAP_ENCAP_TDF definition in wtap.h
5. Add an appropriate entry to the pcap_to_wtap_map[] array in pcap-common.c
6. Write a dissector for the TDF records (dissect_tdf)
7. Use dissector_add_uint("wtap_encap", WTAP_ENCAP_TDF, tdf_handle) to hook the dissector into the correct point in the table

 

Does this look like a reasonable plan?

 

Have a missed an existing feature that I should be using?  I remember seeing Graham Bloises presentation on three ways to write dissectors; C, LUA and something else.  Wasn’t the something else about using a high-level description of the packets.  I’d look it up but I’m on a plane at the moment.

 

Thanks and regards…Paul

 

PS:  Bit of an update.  Just made the changes to eliminate the Ethernet headers (with dummy DLT_TDF value), modified my dissector and it works!  Wow - that was a lot simpler than I thought.

 

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