9.8. idl2wrs: Creating dissectors from CORBA IDL files
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## 9.8. idl2wrs: Creating dissectors from CORBA IDL files

Many of Wireshark’s dissectors are automatically generated. This section shows how to generate one from a CORBA IDL file.

### 9.8.1. What is it?

As you have probably guessed from the name, `idl2wrs` takes a user specified IDL file and attempts to build a dissector that can decode the IDL traffic over GIOP. The resulting file is “C” code, that should compile okay as a Wireshark dissector.

`idl2wrs` parses the data struct given to it by the `omniidl` compiler, and using the GIOP API available in packet-giop.[ch], generates get_CDR_xxx calls to decode the CORBA traffic on the wire.

It consists of 4 main files.

README.idl2wrs
  This document
wireshark_be.py
  The main compiler backend
wireshark_gen.py
  A helper class, that generates the C code.
idl2wrs
  A simple shell script wrapper that the end user should use to generate the dissector from the IDL file(s).

### 9.8.2. Why do this?

It is important to understand what CORBA traffic looks like over GIOP/IIOP, and to help build a tool that can assist in troubleshooting CORBA interworking. This was especially the case after seeing a lot of discussions about how particular IDL types are represented inside an octet stream.

I have also had comments/feedback that this tool would be good for say a CORBA class when teaching students what CORBA traffic looks like “on the wire”.

It is also COOL to work on a great Open Source project such as the case with “Wireshark” (https://www.wireshark.org/).

### 9.8.3. How to use idl2wrs

To use the idl2wrs to generate Wireshark dissectors, you need the following:

- Python must be installed. See https://python.org/
- `omniidl` from the omniORB package must be available. See http://omniorb.sourceforge.net/
- Of course you need Wireshark installed to compile the code and tweak it if required. idl2wrs is part of the standard Wireshark distribution

To use idl2wrs to generate an Wireshark dissector from an idl file use the following procedure:

- To write the C code to stdout.

      $ idl2wrs <your_file.idl>

  e.g.:

      $ idl2wrs echo.idl

- To write to a file, just redirect the output.

      $ idl2wrs echo.idl > packet-test-idl.c

  You may wish to comment out the register_giop_user_module() code and that will leave you with heuristic dissection.

  If you don’t want to use the shell script wrapper, then try steps 3 or 4 instead.

- To write the C code to stdout.

      $ omniidl  -p ./ -b wireshark_be <your file.idl>

  e.g.:

      $ omniidl  -p ./ -b wireshark_be echo.idl

- To write to a file, just redirect the output.

      $ omniidl  -p ./ -b wireshark_be echo.idl > packet-test-idl.c

  You may wish to comment out the register_giop_user_module() code and that will leave you with heuristic dissection.

- Copy the resulting C code to subdirectory epan/dissectors/ inside your Wireshark source directory.

      $ cp packet-test-idl.c /dir/where/wireshark/lives/epan/dissectors/

  The new dissector has to be added to CMakeLists.txt in the same directory. Look for the declaration DISSECTOR_SRC and add the new dissector there. For example,

      DISSECTOR_SRC = \
              ${CMAKE_CURRENT_SOURCE_DIR}/packet-2dparityfec.c
              ${CMAKE_CURRENT_SOURCE_DIR}/packet-3com-njack.c
              ...

  becomes

      DISSECTOR_SRC = \
              ${CMAKE_CURRENT_SOURCE_DIR}/packet-test-idl.c       \
              ${CMAKE_CURRENT_SOURCE_DIR}/packet-2dparityfec.c    \
              ${CMAKE_CURRENT_SOURCE_DIR}/packet-3com-njack.c     \
              ...

For the next steps, go up to the top of your Wireshark source directory.

- Create a build dir

      $ mkdir build && cd build

- Run cmake

      $ cmake ..

- Build the code

      $ make

- Good Luck !!

### 9.8.4. TODO

- Exception code not generated (yet), but can be added manually.
- Enums not converted to symbolic values (yet), but can be added manually.
- Add command line options etc
- More I am sure :-)

### 9.8.5. Limitations

See the TODO list inside packet-giop.c

### 9.8.6. Notes

The `-p ./` option passed to omniidl indicates that the wireshark_be.py and wireshark_gen.py are residing in the current directory. This may need tweaking if you place these files somewhere else.

If it complains about being unable to find some modules (e.g. tempfile.py), you may want to check if PYTHONPATH is set correctly.

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