General
The asn2wrs compiler can be used to create a dissector from an ASN.1 specification of a protocol. It is work in progress but has been used to create a number of dissectors.
It supports:
ITU-T Recommendation X.680 (07/2002), Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation
ITU-T Recommendation X.681 (07/2002), Information technology - Abstract Syntax Notation One (ASN.1): Information object specification
ITU-T Recommendation X.682 (07/2002), Information technology - Abstract Syntax Notation One (ASN.1): Constraint specification
ITU-T Recommendation X.683 (07/2002), Information technology - Abstract Syntax Notation One (ASN.1): Parameterization of ASN.1 specifications
Limitations: Add text here
Inbuilt support for:
ITU-T Recommendation X.880 (07/1994), Information technology - Remote Operations: Concepts, model and notation
How to
The compiler needs 4 input files, an ASN.1 description of a protocol, a .cnf file, and two template files. An ASN.1 specification may have to be edited to work, however work is in progress to at least read all ASN1 specifications. Changing the ASN1 file is beeing depreciated as this creates problems when updating protocols. The H.248 Binary encoding dissector is a good example of a dissector with relatively small changes (work in progress) http://anonsvn.wireshark.org/viewvc/viewvc.cgi/trunk/asn1/h248/ ... add more here
A complete simple UDP-based dissector can be viewed at FooPage.
Understanding error messages
When running asn2wrs, you could get the following errors:
LexToken error An error like this:
__main__.ParseError: LexToken(DOT,'.',71)
means that something is not understood in the ASN1 file, line 71, around the dot (.) - can be the dot itself.
__main__.ParseError: LexToken(SEMICOLON,';',88)
- means that the ';' (SEMICOLON) is not understood. Maybe removing it will work?
Handmassaging the ASN file
This is beeing depreciated. Instead if something is unsupported then prefered way is to report it on the Wireshar dev-mailng list or in bugzilla so asn2wrs can be updated.
Commandline syntax
asn2wrs [-h|?] [-d dbg] [-b] [-p proto] [-c conform_file] [-e] input_file(s) ...
-h|? : usage
-b : BER (default is PER)
-u : unaligned (default is aligned)
-p proto : protocol name (implies -S)
default is module-name from input_file (renamed by #.MODULE if
present)
-F : create 'field functions'
-T : tagged type support (experimental)
-o name : output files name core (default is <proto>)
-O dir : output directory
-c conform_file : conformation file
-I path : path for conformance file includes
-e : create conformation file for exported types
-S : single output for multiple modules
-s template : single file output (template is input file without .c/.h exten
sion)
-k : keep intermediate files though single file output is used
-L : suppress #line directive from .cnf file
input_file(s) : input ASN.1 file(s)
-d dbg : debug output, dbg = [l][y][p][s][a][t][c][m][o]
l - lex
y - yacc
p - parsing
s - internal ASN.1 structure
a - list of assignments
t - tables
c - conformance values
m - list of compiled modules with dependency
o - list of output files
Generated files
Intermeddiate files created:
- packet-proto-ett.c
- packet-proto-ettarr.c
- packet-proto-fn.c
- packet-proto-hf.c
- packet-proto-hfarr.c
- packet-proto-val.h
- packet-proto-exp.h
- packet-proto-table.c
These files should be included in the template file as in the examples(some are optional).
Explanation for .cnf file and template file .cnf file keywords
Step by step instruction
- Create a directory for your protocol in the /asn1 directory and put your asn1 file there.
- Copy makefile.nmake and Makefile from another asn1 dissector and edit the protocol name asn1 filename and the parameters to asn2wrs.py to suite your needs.
- Create an .cnf file either by copying an existing one and edit it or use the empty example above.
- Create template files eiter by copying suitable existing ones and edit them or use the examples above puting your protocol name in the apropriate places.
- Test generate your dissector by running the makefile.
- Depending on the outcome you may have to edit your .cnf file asn1 file etc...
Discussion
sy: Separate the page into two