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Re: Semantic Bug

From: Rob Cameron <cameron@cs.sfu.ca>
Date: Tue, 17 Jun 2003 10:45:28 -0700
To: "Roy T. Fielding" <fielding@apache.org>, "Mark Thomson" <marktt@excite.com>
Cc: uri@w3.org
Message-Id: <200306171045.28348.cameron@cs.sfu.ca>

Below I suggest modifications to section 5.3 that ensure correct URI 
construction for all (scheme, authority, path, query, fragment) 5-tuples.

Motivation:

Suppose that an infostructure is to be moved from h://a/b/c/d to f:/d with all 
links made relative.

It is not inconceivable that the document at h://a/b/c/d contains URIs like 
h://a/b/c//e and http://a/b/c/this:that

In the first case, the following relative_URI calculation may be performed.

(URIbis3.py) 
>>> compute_relative_URI('h://a/b/c/d', 'h://a/b/c//e') 
'.//e'

This relative URI is fine when resolved with respect to the original base, 
applying the algorithm of 5.2.

>>> resolve_relative_URI('h://a/b/c/d', './/e')
'h://a/b/c//e'

But when interpreted relative to f:/d, we have a problem. 
>>> resolve_relative_URI('f:/d', './/e')
'f://e'

Here e has been erroneously interpreted as an authority. 
build_URI('f', None, '//e', None, None) should ensure that "/." 
is prepended to path.

In the second case, the computation of a relative URI might attempt the 
following construction: build_URI(None, None, 'this:that', None, None) 
yielding "this:that" rather than "./this:that" as mentioned at the end of 
section 4.2

For example, uripath.py exhibits this behaviour. 
>>> refTo('h://a/b/c/d', 'h://a/b/c/this:that')
'this:that'

With only slight modifications to 5.3, these ambiguities of URI 
construction can be avoided.

   if defined(scheme) then
      append scheme to result;
      append ":" to result;
   endif;

   if defined(authority) then
      append "//" to result;
      append authority to result;
   endif;

   if defined(path) then
      if defined(authority) then
         if path is neither empty nor begins with "/" then 
             error('an absolute or empty path is required')
         endif
      elsif path begins "//" then append "/." to result
      elsif not defined(scheme) and 
              the first path segment contains ":" then
        append "./" to result
      endif;
      append path to result
   else
      error('undefined path')
   endif;

   if defined(query) then
      append "?" to result;
      append query to result;
   endif;

   if defined(fragment) then
      append "#" to result;
      append fragment to result;
   endif;

   return result;
Received on Tuesday, 17 June 2003 13:45:34 GMT

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