Wireshark · Wireshark-dev: Re: [Wireshark-dev] Help on ASN2Wrs

["Kukosa, Tomas" <tomas.kukosa@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Tulip,

 

all t_... are rules for lex.py and all p_... are rules for yacc.py.

See http://www.dabeaz.com/ply/ply.html

 

The t_error() is special rule for error handling.

 

If the lex.py finds during rules analysis the rule t_error() it saves it into self.lexerrorf. I.e. when error occures the self.lexerrorf(tok) calling invokes t_error(tok) calling.

 

Best regards,

  Tomas

 

PS: I am sorry that the asn2wrs.py is not very readable and would need code cleaning and probably few refactorings. But when I started to write it (based on Aaron S. Lav's PyZ3950 package) I was not able to imagine how much of ASN.1 complexicity we would need to have implemented.

 

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From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of tulip neo
Sent: Thursday, March 26, 2009 7:54 AM
To: wireshark-dev@xxxxxxxxxxxxx
Subject: [Wireshark-dev] Help on ASN2Wrs

Hi List,
Good morning.
I have some problem with  ASn2wrs.I m developing a parser which should be capable of generating target code(c/c++) from ASN description.In other words asn->python data structure->xml->c/c++.I went through the asn2wrs.py bit by bit and found it very intresting and help full.I need to store different elements and there type and child in some data structure so that i can be able to generate a message tree.
 
pls help me how should i proceed.One doubt with Lex.py and asn2wrs.py
 
snippets from lex.py
 
 # No match. Call t_error() if defined.

                if self.lexerrorf:
                    tok = LexToken()
                    tok.value = self.lexdata[lexpos:]
                    tok.lineno = self.lineno
                    tok.type = "error"
                    tok.lexer = self
                    tok.lexpos = lexpos
                    self.lexpos = lexpos
                    newtok = self.lexerrorf(tok)
                    if lexpos == self.lexpos:
 
How does above self.lexerrorf(tok) calls t_error() of asn2wrs.py.i dont also understand why it is t_.i understand atleast it defines rules.but how both are maped?same case with the definitions starting with def p_.do Prefix P_ and t_ have any significance?how they are maped from lex.py?
 
snippets from asn2wrs.py
def t_error(t):
  global input_file
  raise LexError(t, input_file)
 
Br
Tulip

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