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Re: draft-fielding-uri-rfc2396bis-02

From: Rob Cameron <cameron@cs.sfu.ca>
Date: Sat, 24 May 2003 12:00:25 -0700 (PDT)
Message-Id: <200305241900.h4OJ0P612980@orpheus.cs.sfu.ca>
To: fielding@apache.org, uri@w3.org


Here are some comments on my first experience with rfc2396bis-02
this morning as well as some comments on further work.

1.  abnf2re had no problems with the grammar; it took only a few
    minutes to update my parser to work with this grammar.

2.  Overall, the restructuring of the grammar seems much
    easier to follow, particularly with respect to empty
    components.

3.  I wonder whether net_path should be named something
    else, just so people don't get the idea that it is
    a path for the purpose of 5.2.

4.  I have been working on the  inverse of the algorithm
    of section 5.2 for resolving relative references.
    I thought an algorithm for that might appear in this draft.

Anyway, here's what I have in Python, close enough to the
pseudcode of section 5.2 to be understood, I think.

def compute_relative_URI(base, abs):
    Base_scheme, Base_authority, Base_path, Base_query, Base_fragment = parseURI(base)
    A_scheme, A_authority, A_path, A_query, A_fragment = parseURI(abs)
    if Base_scheme != A_scheme: return abs
    elif Base_authority != A_authority:
        return buildURI(None, A_authority, A_path, A_query, A_fragment)
    elif Base_path == A_path: return buildURI(None, None, '', A_query, A_fragment)
    else:
        Base_segments = string.split(Base_path, '/')
        A_segments = string.split(A_path, '/')
        common = common_prefix_length(Base_segments, A_segments)
        Base_extra = len(Base_segments) - common
        if Base_extra == 0:   # must include final common component
            rel_segments = A_segments[common-1:]
        else:
            rel_segments = (Base_extra - 1) * ['..'] + A_segments[common:]
        if re.search(':', rel_segments[0]) or rel_segments[0] == '':
            rel_segments = ['.'] + rel_segments
        return buildURI(None, None, string.join(rel_segments, '/'), A_query, A_fragment)

I have been comparing my algorithms with the uripath.py implementation
and do find some discrepancies.  Comments on the following examples
would be welcome.  (Also, there was a note about two interoperable
implementations for standardization - is what I'm doing helpful?)

a.  relative reference .//x

My resolve_relative_reference and join of uripath.py agree:

>>> join('http://a/b/c/', './/x')
'http://a/b/c//x'

>>> resolve_relative_URI('http://a/b/c/', './/x')
'http://a/b/c//x'

But refTo of uripath.py does not invert.

>>> refTo('http://a/b/c/', 'http://a/b/c//x')
'http://a/b/c//x'

>>> compute_relative_URI('http://a/b/c/', 'http://a/b/c//x')
'.//x'

b.  relative reference ./f:g

I think refTo of uripath.py is incorrect here.

>>> join('http://a/b/c/', './f:g')
'http://a/b/c/f:g'
>>> resolve_relative_URI('http://a/b/c/', './f:g')
'http://a/b/c/f:g'

>>> refTo('http://a/b/c/', 'http://a/b/c/f:g')
'f:g'
>>> compute_relative_URI('http://a/b/c/', 'http://a/b/c/f:g')
'./f:g'
join('http://a/b/c?y', '?z')

c.  relative reference ?y

>>> resolve_relative_URI('http://a/b/c/d;p?q', '?y')
'http://a/b/c/d;p?y'
>>> compute_relative_URI('http://a/b/c/d;p?q', 'http://a/b/c/d;p?y')
'?y'

uripath.py does not seem to agree with the spec:

>>> join('http://a/b/c/d;p?q', '?y')
'http://a/b/c/?y'
Received on Saturday, 24 May 2003 15:00:34 GMT

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