[oslc-core] Unrecognized content
Arthur Ryman
ryman at ca.ibm.com
Sun Sep 23 21:40:41 EDT 2012
Jim,
+1 except for stronger wording about errors:
A Service provider MUST return an error code if recognized content is
invalid.
Regards,
___________________________________________________________________________
Arthur Ryman
DE, Chief Architect, Reporting &
Portfolio Strategy and Management
IBM Software, Rational
Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
From:
James Conallen <jconallen at us.ibm.com>
To:
Steve K Speicher <sspeiche at us.ibm.com>
Cc:
Oslc-Core at open-services.net, oslc-core-bounces at open-services.net
Date:
09/18/2012 09:16 AM
Subject:
Re: [oslc-core] Unrecognized content
Sent by:
oslc-core-bounces at open-services.net
Ok, how about this update for the Unknown properties and content section:
For OSLC Defined Resources, clients SHOULD assume that an OSLC Service
will discard unknown property values. An OSLC Service MAY discard property
values that are not part of the resource definition or Resource Shape
known by the server. If a client needs verification that the requested
update was accepted it SHOULD note the ETag returned with the PUT, then
immediately GET the resource back and compare the ETag and contents with
its expectations. The Service SHOULD not return an error code for
unrecognized content. A Service provider MAY return an error code if
recognized content is invalid.
The rule is different for clients. When doing an update, OSLC clients MUST
preserve any unknown property-values and other content in OSLC Defined
Resources.
Thanks,
jim conallen
Rational Design Management (DM) Integration Architect, OSLC AM Lead
jconallen at us.ibm.com
Rational Software, IBM Software Group
Steve K Speicher---09/18/2012 08:51:25 AM---+1 We are saying it can
happen, we just need a proposal for how clients can learn this. We
require
From: Steve K Speicher/Raleigh/IBM at IBMUS
To: Oslc-Core at open-services.net,
Date: 09/18/2012 08:51 AM
Subject: Re: [oslc-core] Unrecognized content
Sent by: oslc-core-bounces at open-services.net
+1 We are saying it can happen, we just need a proposal for how clients
can learn this. We require a round trip now: PUT, GET, then check.
Steve Speicher
IBM Rational Software
OSLC - Lifecycle integration inspired by the web ->
http://open-services.net
> From: Arthur Ryman <ryman at ca.ibm.com>
> To: James Conallen/Philadelphia/IBM at IBMUS,
> Cc: Oslc-Core at open-services.net, Adam Neal <Adam_Neal at ca.ibm.com>, oslc-
> core-bounces at open-services.net
> Date: 09/14/2012 01:59 PM
> Subject: Re: [oslc-core] Unrecognized content
> Sent by: oslc-core-bounces at open-services.net
>
> Jim,
>
> I think we may be stretching the analogy here.
>
> I am OK with you proposal: "I am ok if we just state that this scenario
> can happen, and that the client is responsible for determining if the
> update was successful (from its view) by GETing the representation
> immediately after and checking the content and comparing the ETags."
>
> Pls draft some text and say where it should be included so we have a
> concrete proposal on the table.
>
> Regards,
>
___________________________________________________________________________
>
> Arthur Ryman
>
> DE, Chief Architect, Reporting &
> Portfolio Strategy and Management
> IBM Software, Rational
>
> Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
>
>
>
>
>
> From:
> James Conallen/Philadelphia/IBM at IBMUS
> To:
> Arthur Ryman/Toronto/IBM at IBMCA
> Cc:
> Adam Neal <Adam_Neal at ca.ibm.com>, Oslc-Core at open-services.net,
> oslc-core-bounces at open-services.net
> Date:
> 09/13/2012 04:44 PM
> Subject:
> Re: [oslc-core] Unrecognized content
>
>
> Arthur,
>
> While I am not advocating that we respond with a 4xx when the server
does
> not update a resource at a client's request. I point it out as an
example
> of how even RFC2616 requires some interpretation in context.
>
> What I do want to do is address this very real problem (that DM and RRC
> are experiencing) that clients have when attempting to update resources
> (in general).
>
> Using your own Java analogy, a program that essentially is
>
> x = -42;
> out.println( x );
>
> where the output is +42, because this particular type of variable only
> understands positive integers, and the programmer doesn't know this. Now
> he is forced to check every time he makes an assignment before
proceeding
> with the program
>
> x = -42;
> if( x != -42 ) throw exception
>
> I think because the OSLC explicitly says that the server can ignore
> unrecognized content, and there is no guaranteed way for a client to
know
> what content the server recognizes, the onus is on the client to be
> responsible for checking the results. I think we should provide some
> guidance and raise awareness of this scenario in our specs
> (non-normatively), so client developers can be prepared for this
> situation.
>
> I am ok if we just state that this scenario can happen, and that the
> client is responsible for determining if the update was successful (from
> its view) by GETing the representation immediately after and checking
the
> content and comparing the ETags.
>
>
> Thanks,
>
> jim conallen
> Rational Design Management (DM) Integration Architect, OSLC AM Lead
> jconallen at us.ibm.com
> Rational Software, IBM Software Group
>
>
>
>
>
>
> From: Arthur Ryman/Toronto/IBM at IBMCA
> To: James Conallen/Philadelphia/IBM at IBMUS,
> Cc: Adam Neal <Adam_Neal at ca.ibm.com>, Oslc-Core at open-services.net,
> oslc-core-bounces at open-services.net
> Date: 09/13/2012 04:03 PM
> Subject: Re: [oslc-core] Unrecognized content
>
>
> Jim,
>
> I disagree. The server ignored the content it didn't understand and did
> the update, but the before and after state was the same. According to
your
> proposal, if I did a GET and then immediately PUT the resource, that
> should also result in an error because nothing changed. That would not
be
> reasonable.
>
> Consider the following Java program:
>
> int x = 42;
> x = 42;
>
> That shouldn't result in a compiler error.
>
> In fact, the behavior of the server is somewhat undefined if a PUT would
> result in no change to the resource. The server could try to be clever
and
> only update the resource if some property changed. Or it could take the
> request literally and replace the resource with an identical copy, but
as
> a side affect, the modification date of the resource might change.
>
>
> Regards,
>
___________________________________________________________________________
>
> Arthur Ryman
>
> DE, Chief Architect, Reporting &
> Portfolio Strategy and Management
> IBM Software, Rational
>
> Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
>
>
>
>
>
>
> From:
> James Conallen/Philadelphia/IBM at IBMUS
> To:
> Arthur Ryman <ryman at ca.ibm.com>
> Cc:
> Adam Neal <Adam_Neal at ca.ibm.com>, Oslc-Core at open-services.net,
> oslc-core-bounces at open-services.net
> Date:
> 09/07/2012 11:16 AM
> Subject:
> Re: [oslc-core] Unrecognized content
>
>
> Hey Arthur,
>
> The spec for the PUT method says:
>
> If an existing resource is modified, either the 200 (OK) or 204 (No
> Content) response codes SHOULD be sent to indicate successful completion
> of the request. If the resource could not be created or modified with
the
> Request-URI, an appropriate error response SHOULD be given that reflects
> the nature of the problem.
>
> In this scenario the server did not modify the resource, because it
didn't
> recognize the content. So according to RFC 2616 we should be returning
an
> error response.
>
>
> Thanks,
>
> jim conallen
> Rational Design Management (DM) Integration Architect, OSLC AM Lead
> jconallen at us.ibm.com
> Rational Software, IBM Software Group
>
>
>
>
>
>
> From: Arthur Ryman <ryman at ca.ibm.com>
> To: James Conallen/Philadelphia/IBM at IBMUS,
> Cc: Adam Neal <Adam_Neal at ca.ibm.com>, Oslc-Core at open-services.net,
> oslc-core-bounces at open-services.net
> Date: 09/07/2012 10:15 AM
> Subject: Re: [oslc-core] Unrecognized content
>
>
>
> -1 for the 400 response code
>
> Jim, I don't understand what you are asking for. The spec already makes
it
>
> clear that the server will discard unrecognized content. The client
should
>
> expect that. What aspect of behavior is unclear?
>
> Regards,
>
___________________________________________________________________________
>
>
> Arthur Ryman
>
> DE, Chief Architect, Reporting &
> Portfolio Strategy and Management
> IBM Software, Rational
>
> Toronto Lab | +1-905-413-3077 (office) | +1-416-939-5063 (mobile)
>
>
>
>
>
> From:
> James Conallen <jconallen at us.ibm.com>
> To:
> Oslc-Core at open-services.net
> Cc:
> Adam Neal/Ottawa/IBM at IBMCA
> Date:
> 09/07/2012 09:03 AM
> Subject:
> [oslc-core] Unrecognized content
> Sent by:
> oslc-core-bounces at open-services.net
>
>
>
> In the current specification we have the statement:
> For OSLC Defined Resources, clients SHOULD assume that an OSLC Service
> will discard unknown property values. An OSLC Service MAY discard
property
>
> values that are not part of the resource definition or Resource Shape
> known by the server.
>
> We are running into a problem. When a client (in this case another
> application server) PUTs an update to a resource that includes a 'link'
to
>
> another OSLC resource, and the server, at the time does not recognize
the
> link type, the link is not accepted, but a 200 OK is returned. The
server
>
> returns a 200 OK, because it feels like it can ignore the unrecognized
> link. The client gets that 200 OK, and thinks that the link was
> successfully added.
>
> This doesn't feel right. The only way a client can be sure that the PUT
> worked as expected is to re-GET the resource and compare it to what it
> expected to see (with the new link included), and maybe do a little
> looking at ETags to make sure things haven't changed in between.
>
> I guess the server could instead return a 400 Bad Request, and include
in
> the response the reason for not accepting the PUT. But if the content
> that was submitted really should just be ignored (i.e. is part of a
future
>
> version of the resource), then we don't want to abort the update.
>
> The OSLC verbage does not provide any guidance as to what to do. It
would
>
> be helpful if we had more detailed explanation of this statement in the
> spec.
>
>
> Thanks,
>
> jim conallen
> Rational Design Management (DM) Integration Architect, OSLC AM Lead
> jconallen at us.ibm.com
> Rational Software, IBM Software Group
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