[oslc-core] Unrecognized content

Steve K Speicher sspeiche at us.ibm.com
Tue Sep 18 08:50:48 EDT 2012


+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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> 
> 
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> 
> 
> 
> 
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