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Re: XHR LC comments

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Sun, 18 May 2008 22:07:52 -0500
Message-ID: <4830EF08.4070009@mit.edu>
To: Bjoern Hoehrmann <derhoermi@gmx.net>
CC: "Web API WG (public)" <public-webapi@w3.org>

Bjoern Hoehrmann wrote:
>> Which you can, with a non-NS-aware XML parser.
> 
> My point was that the XHR draft currently requires using a namespace-
> aware one

On the server side?  Can you point me to where it makes that requirement?

I'm not suggesting that the parser XHR uses for data it receives from the server 
be changed; I'm suggesting that the server should be able to use whatever XML 
parser it wishes.

>> The problem is that figuring out whether a DOM fragment can usefully
>> be serialized as a ns-wellformed string is a bit of a pain.
> 
> Could you elaborate on this point? You need to serialize the document
> before starting to send it

Agreed.

> and you can rather easily check for ns-wf during serialization if you implement
> the serialization yourself

Perhaps.  This is less clear to me.  In particular, it's not that clear to me 
that its trivial to decide whether a given DOM has a ns-wellformed 
serialization.  Certainly there have been a number of past bugs in the Gecko 
serializer dealing with this aspect of things, and I wouldn't bet my life on 
there not being any now.

> Even if you cannot do it during serialization, the algorithm to do it on the
> document object is relatively simple aswell.

The concept of "namespace well-formed" applies to strings, not document objects, 
last I checked.  Though Firefox does prevent creation of attribute nodes with 
the prefix "xmlns" in random namespaces, so maybe I'm wrong about that.

In any case, let me give an example, as requested.

   var doc = document.implementation.createDocument("", "", null);
   var el = doc.createElementNS("ns1", "x:y");
   el.setAttributeNS("ns2", "x:z", "val");
   doc.appendChild(el);
   var xhr = new XMLHttpRequest();
   xhr.open("POST", "echo.cgi", false);
   xhr.send(doc);
   alert(xhr.responseText);

Here echo.cgi is the following CGI:

   #!/usr/bin/perl 

   print "Content-Type: text/plain\n\n";
   while (<>) {
     print;
   }

Here are the results I see:

   Firefox 3rc1:

     <x:y xmlns:x="ns1" a0:z="val" xmlns:a0="ns2"/>

   Opera 9.25:

     <?xml version="1.0"?><x:y x:z="val" xmlns:x="ns1"/>

   Safari 3.1:

     <x:y x:z="val" />

Ignoring the Safari serialization, which is not in fact ns-wellformed no matter 
how you slice it, the other two are ns-wellformed XML.  Neither one roundtrips 
to quite the original document.  Which one is "correct" per the current spec? 
Or is it neither one?  Should an exception have been thrown in this case?  Why 
or why not?  If there shouldn't have been an exception in this case, how is a UA 
to determine that?

I'm not saying these are impossible things to define; just that they're far from 
obvious (as witness the three serializations above) and therefore perhaps need 
definition in this spec if we want interoperability.

-Boris
Received on Monday, 19 May 2008 03:08:42 GMT

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