[Zope] howto write download: Product.state --> client file

[hans]

the product should be able to download its own state to the client file
system.

code in DTML:
<b>Save to (client) file? (download)</b>
   <a href="<dtml-var "URL1">/manage_save_file"><b>download</b></a>

code in manage_save_file:
 def manage_save_file(self, REQUEST=None):
  """save state to client file"""

  tmpFile = StringIO()
  tmpFile.write(repr(self.tabstree)) # now repr, pickle l8er
  tmpFile.close()

  fname = self.id + '.' + self.fsuffix # to give download a filename

  REQUEST.RESPONSE.setHeader('content-disposition', 'attachment;
filename="%s" ' % (fname))
  REQUEST.RESPONSE.setHeader('content-type',         'text/plain')

  if REQUEST is not None:
   return tmpFile

what is wrong/missing & where could i retrieve the info (in lieu of
asking)