Re: [xml-dev] hashing

I'm just concerned about being conceptually identical.
Instances might be rendered differently by different processors
but as long as they're conceptually the same that's the only
concern.  So running them through a canonicalization engine
works great for this. 

Anyway, thanks for the code, I gave it a try and it works great.

Eric

Rich Salz () wrote:
> If you're concerned about byte-for-byte identical, hashing each file
> is okay; if you're concerned about semantic identical (e.g., the order
> of attributes doesn't matter) than use standard XML canonicalization
> or something similar (but it won't be as good:)
> 
> Her's a portable python script that compares all files named on
> the command-line:
> 
> ; cat x.py
> import sys,sha
> from xml.dom.ext.reader import PyExpat
> from xml.dom.ext.c14n import Canonicalize
> 
> hashes = {}
> for f in sys.argv:
>     o = sha.sha()
>     if 1:
>         # simple hash of contents
>         o.update(open(f).read())
>     else:
>         # sha(c14n(doc))
>         r = PyExpat.Reader()
>         dom = r.fromStream(open(f))
>         o.update(Canonicalize(dom))
>     h = o.digest()
>     other = hashes.get(h, None)
>     if other:
>         print 'duplicate', f, other
>     else:
>         hashes[h] = f
> ;
> 
> --
> Rich Salz                  Chief Security Architect
> DataPower Technology       http://www.datapower.com
> XS40 XML Security Gateway  http://www.datapower.com/products/xs40.html
> XML Security Overview      http://www.datapower.com/xmldev/xmlsecurity.html
> 
> 
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