Re: [apps-discuss] apps-team review of draft-merrick-jms-uri-10

Tim Bray <tbray@textuality.com> Mon, 31 January 2011 23:23 UTC

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Date: Mon, 31 Jan 2011 15:27:03 -0800
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From: Tim Bray <tbray@textuality.com>
To: Eric Johnson <eric@tibco.com>
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Cc: derek.rokicki@softwareag.com, SM <sm+ietf@elandsys.com>, Apps Discuss <discuss@apps.ietf.org>, The IESG <iesg-secretary@ietf.org>, m8philli@uk.ibm.com, peaston@progress.com
Subject: Re: [apps-discuss] apps-team review of draft-merrick-jms-uri-10
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Just to be clear, I'm not terribly upset; it does appear that my input
was useful, and if the IESG wants to register a URI scheme that I
personally think is a little wonky, they're totally within their
rights and in fact I'm open to the arguments about collision avoidance
and so on.   I was just baffled as a consequence of having missed the
subsequent discussion.

Thanks for taking the time to pull that together!  -Tim



On Mon, Jan 31, 2011 at 3:03 PM, Eric Johnson <eric@tibco.com> wrote:
> Hi Tim,
>
> Alexey Melnikov asked that I recreate the full email response that I managed
> to delete/fail to send the first time around.
>
> In any case, just as an overview, this is the URL that manages to capture
> the changes mostly specific to your feedback:
> http://tools.ietf.org/rfcdiff?difftype=--hwdiff&url2=draft-merrick-jms-uri-11.txt
>
>
> On 12/16/10 4:01 PM, Tim Bray wrote:
>
> I have been selected as the Applications Area Review Team reviewer for
> this draft (for background on apps-review, please see
> http://www.apps.ietf.org/content/applications-area-review-team).
> Please resolve these comments along with any other Last Call comments
> you may receive. Please wait for direction from your document shepherd
> or AD before posting a new version of the draft.
>
> Document: draft-merrick-jms-uri-10
> Title: URI Scheme for Java(tm) Message Service 1.0
> Reviewer: Tim Bray
> Review Date: Dec 16, 2010
> Summary: The draft has some mechanical issues which are not
> show-stoppers. I have questions whether this ought to be an RFC since
> there seems very modest expectation of interoperability between
> implementations; why, then, an IETF RFC, which suggests that the
> resulting URIs should be useful for identification of resources on an
> internetworked scale.
> Major Issues:
>
> 1. the draft suggests that given a “jms:” URI, there is little
> expectation that, without checking on the value of the “variant” and
> for the presence of vendor-specific parameters, it can be used
> interoperably in more than one implementation. In which case, I have
> to wonder about the appropriateness of using a *Uniform* resource
> identifier for whatever purposes are contemplated for these things;
>
> If nothing else, we're trying to bring uniformity to syntax and semantics
> for "jms" schemes that exist in the wild, and register *something*.
>
> no
> motivations or use-cases are provided.
>
> Perhaps you missed the references in section 6? The draft itself cites two
> other standards efforts using the JMS URI - SOAP/JMS - where the "jms" URI
> scheme will be used in the same place an HTTP URI might appear, and the
> OASIS SCA Bindings TC, where the URI indicates the destination of an SCA
> reference using a JMS binding.
>
> The last paragraph of section 1 is troubling. For convenience, I quote:
> <<<<<
> As a consequence of building upon an API, rather than a protocol, the
> utility of a "jms" URI depends on the context in which it is used.
> That context includes agreement on the same JMS provider or underlying
> protocol, agreement on how to look up endpoints (JNDI), and when using
> serialized Java object messages, sufficiently similar Java Class
> environments that serialized objects can be appropriately read and
> written. Users of this scheme need to establish the necessary shared
> context parts as just enumerated - a context which can span the globe,
> or merely a small local network. With that shared context, this URI
> scheme enables endpoint identification in a uniform way, and the means
> to connect to those endpoints.
>
> Given this, what are the advantages of having a *Uniform* resource
> identifier, if there is not much expectation of uniformity in
> implementations?
>
> Some answers:
>
> One can deploy a "bridge" between two JMS providers, thus providing
> interoperability between two JMS implementation, such that one client is
> unaware that the other client is not using the same JMS provider.
> Via the JCP, JMS cements an API.  We're looking to establish
> interoperability at the level above that API, not at the level of the
> implementation of that API. That the implementations are not the same
> underneath that API ought not prevent standards efforts on top of the API
> that has been cemented by the JCP.
>
> We're stuck, in that our use-cases demand a URL (for example, in the place
> of HTTP scheme URIs in WSDL), but we're building upon an API rather than an
> actual protocol. In the end, we think it a better idea to register the
> scheme than not.
>
> 2. Section 3.3 says “ If users plan switching between JMS vendors,
> they might also need to plan on regenerating resources that contain
> URIs in this vendor specific form”; this sharpens my concerns about
> the lack of interoperability...
>
> I’m getting the impression, reading this, that “jms:jndi” is probably
> quite interoperable, but the variants are maybe a back-door for vendor
> abuse.
>
> Originally, we wrote the spec to only accommodate the JNDI approach.  We
> eventually exposed three broad reasons for the variants:
>
> The JMS API itself.  The original 1.0 spec of JMS had two ways of
> establishing Destination objects, neither of which used JNDI (our "topic"
> and "queue" variants). The 1.1 version of the spec introduced the JNDI
> approach, and that's the obviously preferred method.
> Broadest possible compatibility with existing uses of "JMS" URI schemes. In
> the early days of JMS, vendors defined their own ways to establish JMS
> Destinations, and we want to make sure that the proposed URI encompasses
> those possibilities, so that clients of the JMS scheme can look at the
> variant and know unambiguously that theh *don't* understand, rather than
> attempting to work with a "jms" URI, not working, and not knowing why.
> Future proofing. Some JMS messaging products are based on documented
> protocols. Should they establish a better way of identifying JMS
> Destinations, and write up a new variant for doing so, this enables
> accessing said destinations, without revisiting the JMS URI scheme.
>
> None of the authors working on the scheme anticipate registering any new
> variants.
>
> Originally, we did not want an IANA registry to allow for additional
> variants, but previous feedback pushed us in that direction.
>
> Minor Issues:
>
> 1. Section 1. Need references for terms like javax.jms.Destination for
> people who aren’t familiar with Java pathname voodoo.
>
> I added [REF-JMS] here.
>
> 2. Section 4 para beginning “Each variant can have query
> parameters...” - did you consider separating the variant prefix from
> the rest of the parameter name with “.” or some other syntax marker? I
> note that you use “jndi-” for another class of parameter names below.
>
> We considered a lot of options here. Realistically, I can probably come up
> with any sort of post-hoc rationalization. Using the "jndi" prefix for the
> "jndi" variant, without any such separator worked out naturally based on the
> initial proposals we started from, followed by introducing the variants.
>
> 3. Same paragraph. Should the variant be used as a prefix even if it’s
> a vendor-supplied one starting with “vnd.”? An example of this would
> be nice.
>
> Excellent point.  I added an example of "vnd.example.exParameter."
>
> 4. 4.1.1 and so on, should the draft impose any constraints on the
> syntax of these parameter values? Perhaps they are inherited from the
> referenced sections in the JMS 1.1 spec? If so, please say so. Ah, I
> see that 4.1.3 does specify some syntax, albeit loosely; there are a
> lot of different syntaxes which may be used to specify “ number
> between 0 and 9, inclusive”. Are you OK with 0x3 or, for timeToLive,
> “1,500”?
>
> 4.1.1 - says "PERSISTENT" or "NON_PERSISTENT".
>
> 4.1.2 & 4.13 - now indicate an expectation of decimal syntax.
>
> 5. 4.2.1 Perhaps a note prior to launching into all the parameters on
> syntax constraints, with, I’m assuming, normative references into the
> JMS spec?
>
> In section 4.2.1.1, I added a reference to the Java Language Specification.
> Excellent catch.  Thank you.
>
> 6. 4.2.2 includes great gobs of Java code illustrating how to use such
> an endpoint. Does this not contradict with the assertion at the top of
> section 4 which says “ Operations available on JMS destinations are
> fully and normatively defined by the JMS specification and as such,
> are out of scope for this URI specification”?
>
> I changed the title of the section to read "Example of," clarified that this
> was an example specifically using Java, and that one "might start" with the
> approach that follows.
>
> In any case, 4.2.2 needs a bit of preparatory language explaining what
> it is. Is it normative behavior for implementations? Is it there for
> illustrative purposes? Is it required to use Java, or could I code
> something equivalent in C# or Ruby? A few paragraphs in there’s a
> passing reference to “the following (non-normative) code...”
>
> I think I addressed that with the additions I noted just above.
>
> 7. 4.3.1, see comments on 4.2.2 above. Is this description of
> programming practice normative, illustrative, or what?
>
> I added the phrase "or its equivalent" to highlight that the Java methods
> were not the only way - especially since some vendors provide non-Java APIs.
>
> 8. Section 6, 3rd para: I haven’t ever seen anything like the note
> about what an OASIS TC might be doing in an RFC before, but possibly
> I’ve just missed the examples.
>
> Since this section discusses the actual use cases, I can't really do much
> but note where those use cases stem from.
>
> 9. Section 7, last para: “As described in Section 4, others can define
> additional variants”... there is no description in Section 4 of how to
> define additional variants. Also, while the language in the opening of
> the draft suggests that the set of variants is open-ended, this is the
> first explicit mention of this possibility that I encountered. Is
> there a registry?
>
> Oh, there it is in section 9.2. OK, I think that the beginning of the
> doc needs to say that the set of variants is open-ended and
> vendor-extensible. It also smells like a big huge honking
> interoperability hole.
>
> I added a sentence in the introduction: "Vendors defining additional
> variants are strongly encouraged to register them with IANA as documented in
> Section 9.2.1."
>
> As for the interoperability hole, I believe I addressed that above.
>
> Nits:
>
> 1. Section 4 para 3, superfluous comma after “Both the variant”.
>
> Replaced much of this text based on other feedback.
>
> 2. Section 4 para beginning “Each variant can have query
> parameters...” - did you consider separating the variant prefix from
> the rest of the parameter name with “.” or some other syntax marker? I
> note that you use “jndi-” for another class of parameter names below.
>
> See my comment to item #2 of yours above.
>
> 3. Section 4.1 I assume “shared” means “available in all variants”? If
> so, why not say so?
>
> Added clarifying text.
>
> 4. Section 4.1 first para, the word “property” suddenly appears for
> the first time. Is this a synonym of “parameter”?
>
> Added clarifying text, which I think clears up the distinction between the
> parameters (in the URI), and the JMS Message properties.
>
> 5. Section 4.1.1 Lots of references here need to be turned into RFC
> style with square brackets
>
> We already reference the JMS specification, and tried to avoid repeating
> references when they were referenced by acronyms already defined (JMS).
>
> 5. Same section, missing full stop after “following shared parameters”.
>
> Fixed with new text.
>
> 6. 4.1.1 Probably more idiomatic of normative text to say, instead of
> “This MUST be”, “The value of this parameter MUST be...”
>
> Fixed.
>
> 7. 4.1.1 Missing full-stop at end.
>
> Fixed.
>
> 8. 6, 2nd para: What’s an “SPI”?
>
> Added a parenthetical indicating the abbreviation.
>
> As I've said before, thank you very much for the wonderfully thorough
> review.
>
>
> -Eric.
>