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Date: Tue, 31 May 2011 21:17:50 -0500
From: Tim Chase <python.list@tim.thechases.com>
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To: Python <python-list@python.org>
Subject: Sanitizing filename strings across platforms
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:6775

Scenario: a file-name from potentially untrusted sources may have 
odd filenames that need to be sanitized for the underlying OS. 
On *nix, this generally just means "don't use '/' or \x00 in your 
string", while on Win32, there are a host of verboten characters 
and file-names.  Then there's also checking the abspath/normpath 
of the resulting name to make sure it's still in the intended folder.


I've read through [1] and have started to glom together various 
bits from that thread.  My current course of action is something like

  SACRED_WIN32_FNAMES = set(
    ['CON', 'PRN', 'CLOCK$', 'AUX', 'NUL'] +
    ['LPT%i' % i for i in range(32)] +
    ['CON%i' % i for i in range(32)] +

  def sanitize_filename(fname):
    sane = set(string.letters + string.digits + '-_.[]{}()$')
    results = ''.join(c for c in fname if c in sane)
    # might have to check sans-extension
    if results.upper() in SACRED_WIN32_FNAMES:
      results = "_" + results
    return results

but if somebody already has war-hardened code they'd be willing 
to share, I'd appreciate any thoughts.

Thanks,

-tkc

[1]
http://stackoverflow.com/questions/295135/turn-a-string-into-a-valid-filename-in-python