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Re: Streaming and Well-Formedness

From: Marc Hadley <Marc.Hadley@Sun.COM>
Date: Tue, 01 Apr 2003 09:49:05 -0500
To: Noah Mendelsohn/Cambridge/IBM <noah_mendelsohn@us.ibm.com>
Cc: xml-dist-app@w3.org
Message-id: <15DFD84C-6451-11D7-8D6B-0003937568DC@sun.com>

I agree that there are cases where streaming is difficult, but there 
are some cases where streaming is useful. E.g. a receiver can send a 
mustUnderstand fault without waiting for the (potentially large) body 
of the incoming message to be completely received.


On Monday, Mar 31, 2003, at 20:50 US/Eastern, Noah 
Mendelsohn/Cambridge/IBM wrote:

> A recent internal discussion at IBM has led me to question the degree 
> to
> which SOAP is amendable to streaming.  On the one hand, we know that 
> our
> mustUnderstand rules tend to preclude streaming until at least the 
> start of
> the body, but I had more or less assumed that we would allow for 
> streaming
> past that, and indeed I believe that in the description of the
> Request/Response pattern [1] we specifically allow for this by saying:
> -----------------------
> Bindings that implement this MEP MAY provide for streaming of SOAP
> responses. That is, responding SOAP nodes MAY begin transmission of a 
> response while a SOAP request is still being received and processed. 
> When
> SOAP nodes implement bindings that support streaming, the following 
> rules
> apply:
> * All the rules in [SOAP Part 1] Binding Framework regarding streaming 
> of
> individual SOAP messages MUST be obeyed for both request and response 
> messages.
> * When using streaming SOAP bindings, requesting SOAP nodes MUST avoid
> deadlock by accepting and if necessary processing SOAP response 
> information
> while the SOAP request is being transmitted.
> --Note:
> --Depending on the implementation used and the size of the messages
> involved, this rule MAY require that SOAP applications stream
> application-level response processing in parallel with request 
> generation.
> * A requesting SOAP node MAY enter the "Fail" state, and thus abort
> transmission of the outbound SOAP request, based on information 
> contained
> in an incoming streamed SOAP response.
> -----------------------
> The referenced section in part 1 says [2]:
> -----------------------
> Bindings MAY provide for streaming when processing messages. That is, 
> nodes MAY begin processing a received SOAP message as soon as the 
> necessary
> information is available. SOAP processing is specified in terms of SOAP
> message infosets (see 5. SOAP Message Construct). Although streaming 
> receivers will acquire such XML infosets incrementally, SOAP processing
> MUST yield results identical to those that would have been achieved if 
> the
> entire SOAP envelope were available prior to the start of processing. 
> For
> example, as provided in 2.6 Processing SOAP Messages, identification of
> targeted SOAP header blocks, and checking of all mustUnderstand 
> attributes
> is to be done before successful processing can proceed. Depending on 
> the
> representation used for the XML infoset, and the order in which it is
> transmitted, this rule might limit the degree to which streaming can be
> achieved.
> -----------------------
> That all makes sense, except for one thing.  When using the obvious 
> XML 1.0
> serialization as in the HTTP binding, we do not even know that the XML 
> is
> well formed until the end.
> So my question:  other than the usual provision that allows for 
> rollback
> etc., do we in fact support any form of streaming when using the HTTP
> binding (or any other XML 1.0 serialization)?  Seems to me the rules 
> above
> preclude it.   Once we start to do useful application processing, we 
> can't
> send a fault, particularly if we have started to stream a response 
> while
> the request is still coming in as signaled in [1].   Is this old news? 
>  I
> guess I sort of knew it in the back of my mind all along, but this is 
> the
> first time I've really thought through the implications.  Am I missing
> something? Thanks.
> [1] http://www.w3.org/TR/2002/CR-soap12-part2-20021219/#bindformdesc
> [2] http://www.w3.org/TR/2002/CR-soap12-part1-20021219/#bindfw
> ------------------------------------------------------------------
> Noah Mendelsohn                              Voice: 1-617-693-4036
> IBM Corporation                                Fax: 1-617-693-8676
> One Rogers Street
> Cambridge, MA 02142
> ------------------------------------------------------------------
Marc Hadley <marc.hadley@sun.com>
Web Technologies and Standards, Sun Microsystems.
Received on Tuesday, 1 April 2003 09:51:41 UTC

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