Re: [xml] relative uri

On Tue, Oct 20, 2009 at 04:51:58PM +0200, François Delyon wrote:
Hi all,

I have some remarks about the implementation of xmlBuildRelativeURI  in 
uri.c (libxml 2.7.3)

1-critical bug
line 2371
      if ((ref->path[pos] == '.') && (ref->path[pos+1] == '/'))
            pos += 2;
      if ((*bptr == '.') && (bptr[1] == '/'))
            bptr += 2;
      else if ((*bptr == '/') && (ref->path[pos] != '/'))
      while ((bptr[pos] == ref->path[pos]) && (bptr[pos] != 0))

      if (bptr[pos] == ref->path[pos]) {
          val = xmlStrdup(BAD_CAST "");
          goto done;          /* (I can't imagine why anyone would do this) */

the use of bptr[pos]  is irrelevant. I suspect that the first four lines 
have been added quickly to solve some bad case.

 Why ? Example, reason to your jugement ?

My opinion is that the four first lines are not very important (the same 
kind of problem may occur later in the path) and that  

 that's basically looks like URI normalization see
section 5.2.4, though that code was done with preceeding RFC 2396 in

xmlBuildRelativeURI should normalize the paths before processing in  
order to get human and efficient  relative uris.

  yes that could be improved that way, using xmlNormalizeURIPath()

2- bad answer.
if the basepath is "/a/b" and the path is "/a/c:d", xmlBuildRelativeURI 
return "c:d" which is not a relative uri. The relative uri is "./c:d"
This remark is perhaps not very useful for libxml2 since  
xmlBuildRelativeURI is called in very few places.

  Hum, right that's a special case if : is in the first segment of the
remaining path, but it sounds more like an escaping problem to me, the :
should be escaped to make sure it's not misinterpreted at parsing time
  "c%3Ad" rather than "./c:d"
one way is to extend the xmlURIEscapeStr at the end to also convert :

3- cosmetic problem
line 2392
      else if ((ref->path[ix] == 0) && (ix > 1) && (ref->path[ix - 1] ==  
          ix -= 2;
basepath "/a/b" path "/a/c" gives "../a/c" where I expect "c"
basepath "/a/b" path "/a/" gives "../a/" where I expect "."

  hum, more fixes and tests would be nice, yes

 xmlBuildRelativeURI  return things like xmlURIEscapeStr(uptr, BAD_CAST 
Must I understand that the path in a xmlURIPtr is not escaped?
I think that I missed something.

  the strings in xmlURI, i.e. after parsing are no more escaped.
but since we return a serialized URI then escaping need to be done


I am not familiar with the development of libxml, but I can suggest the 
following code to build a relative path.

  Can you please apply some of the above comments and provide a
contextual diff, (using diff -c or dff -u on the files before or after
the change, with git, a git diff on the command line will show you the
diff from the modified files) . Then provide the patch as an attachment
to make sure it won't me modified by mail transmission,



Daniel Veillard      | libxml Gnome XML XSLT toolkit
daniel veillard com  | Rpmfind RPM search engine | virtualization library

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