[wildfly-dev] Management Parser Versioning

Tue Apr 28 11:04:01 EDT 2015

The following commit covers the WildFly side: -

https://github.com/darranl/wildfly/commit/8fc073eb11b71904d6235381ad2d3903ce3241aa

One problem with the current split is that as soon as you add a new 
management schema to core the integration with wildfly is broken 
immediately as some tests verify we write as version 3 when now we write 
as version 4.

I would suggest that as soon as we start development on WildFly 10 we 
create a very fast tag or core with just a few changes, probably just: -
  - Bump to Java 8
  - This schema version bump in this thread.
  - Any other build tweaks needed for Java 8.

WildFly can then use the new tag and have the same treatment.

Regards,
Darran Lofthouse.

On 27/04/15 17:14, Darran Lofthouse wrote:
> The following commits are now the end result of the re-factoring to
> allow a fork on new major versions and also to add version 4.0 of the
> schema: -
>
> https://github.com/wildfly/wildfly-core/compare/f4a07f4e9b41dc59823fea1813f947c67965525a...58faefb1fa830d0193f862da9958b2541aea7dad
>
> The changes look extensive but TBH the bulk is just moving of existing
> code and some duplicate for the fork for 4.
>
> I have distinct commits to show the steps taken but the key points are: -
>
> # Split out the model specific parsing from CommonXml into smaller
> implementations, this was to allow CommonXml to remain the common base
> without still containing version specific parsing.
>
> # Rework of ManagementXml to be version based and rework the delegate,
> the big problem we had was we were looping back on ourselves with static
> calls which did not cleanly map to versioned implementations.
>
> # Moved existing StandalonXml, HostXml, DomainXml, ManagementXml into
> 'Legacy' parsers and used existing class to load these on-demand.
>
> # Forked the legacy parsers to create the version 4 parsers, removed all
> version handling so a clean start for 4.
>
> At this point there is still plenty of parsing code not forked for 4 but
> TBH those are all relatively stable and rarely change, StandaloneXml,
> HostXml, DomainXml, and ManagementXml on the other hand have changed for
> every major version so far.
>
> Regards,
> Darran Lofthouse.
>
> On 23/04/15 16:37, Darran Lofthouse wrote:
>> On 23/04/15 16:32, Brian Stansberry wrote:
>>> I don't think I've ever rejected or even questioned a PR because it made
>>> a parser tolerant in the way you describe, so I'm fine with being tolerant.
>>
>> +1 I think the first two rules are what we need to advertise we support,
>> after all that is why we have schemas.  The third point is more about
>> the requirements being placed on the maintainer of the parser so if your
>> XML does not match the schema the best we say is "It may work, it may
>> not work and that can change without warning".
>>
>>> My only caveat is in no way do we have any commitment to be tolerant. If
>>> a change is implemented in such a way that the legacy schema parsing is
>>> tolerant, then it's tolerant for that change. Some other change may not
>>> be implemented that way and the parsing won't be tolerant. So we'll be
>>> inconsistent.
>>>
>>> I'm sure we're already inconsistent in this regard, so that doesn't
>>> worry me. The schema defines the rules. If you follow them, you know
>>> what you'll get. If you break them, maybe it will work anyway, maybe
>>> not. Our only guarantee if you break the rules is you'll either end up
>>> with a valid running configuration or we'll fail.
>>>
>>> On 4/23/15 10:17 AM, Darran Lofthouse wrote:
>>>> Thinking about future XML changes, once the parser is forked I think we
>>>> can also relax how we add new optional attributes and elements to the
>>>> schema.
>>>>
>>>> As I see it our main commitment is: -
>>>>
>>>> * XML that is valid according to the schema should parse without error. *
>>>>
>>>> I say 'should' as I believe in some cases documentation is relied upon
>>>> to describe valid combinations.
>>>>
>>>> * The XML we write must be valid according to the schema. *
>>>>
>>>> Don't see any justification for not following that one.
>>>>
>>>> * Parsers can be tolerant to XML that is technically invalid. *
>>>>
>>>> e.g. we are not big on enforcing sequence ordering.
>>>>
>>>> So lets say we have a release that contains a 4.0 version of the schema
>>>> I think if in version 4.1 of the schema we add an optional attribute or
>>>> element we can just add support for that attribute or element to the
>>>> existing parse method.
>>>>
>>>> Of course if the new attribute or element is required then we will need
>>>> to switch to something version specific to avoid rejecting previously
>>>> valid configuration.
>>>>
>>>> I know this is a long way off but I only raise this now as I realise
>>>> this has already happened where a new optional element has been added to
>>>> the schema.  Technically if we were strict about it the code is wrong
>>>> but the scenarios where it is going to break for someone are quite
>>>> contrived and I think this fits with tolerant parsing and we will
>>>> automatically fix on the next write.
>>>>
>>>> Regards,
>>>> Darran Lofthouse.
>>>>
>>>>
>>>> On 22/04/15 13:30, Brian Stansberry wrote:
>>>>> That's fine with me.
>>>>>
>>>>> On 4/22/15 6:20 AM, Darran Lofthouse wrote:
>>>>>> Working with the parsers for the core config has become increasingly
>>>>>> cryptic, we are now at the point where we have three different major
>>>>>> versions which diverge and converge as we work on them.  Most recent
>>>>>> changes have resulted in large sections of the config converging for 1.x
>>>>>> and 3.x leaving 2.x independent.
>>>>>>
>>>>>> So that I can add references to Elytron I am starting to add support for
>>>>>> version 4.
>>>>>>
>>>>>> One think that I have learned is that each major version tends to belong
>>>>>> to one branch of the codebase, all changes to that version happen on
>>>>>> that branch first: -
>>>>>>
>>>>>>         1.x - Maintained only for EAP
>>>>>>         2.x - WildFly 8.x branch
>>>>>>         3.x - WildFly Core master branch
>>>>>>
>>>>>> I would expect if further changes are made to core for WildFly 9
>>>>>> releases we will end up with 1.x branch of core and and 4.x version of
>>>>>> the schema will be owned by the master branch.
>>>>>>
>>>>>> To make things less cryptic I am proposing that until we find a better
>>>>>> solution for all subsequent major schema versions we just fork the
>>>>>> parser and all related classes.
>>>>>>
>>>>>> This will simplify the code being modified for the upstream development.
>>>>>>
>>>>>> Forward porting parsing changes will also become a simple copy and paste.
>>>>>>
>>>>>> For the current cryptic approach I think almost every engineer (and I am
>>>>>> finding it really hard to think of exceptions) that has worked in-depth
>>>>>> in this area has introduced at least one bug and I don't think the test
>>>>>> coverage is high enough to protect against this.
>>>>>>
>>>>>> Regards,
>>>>>> Darran Lofthouse.
>>>>>>
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>>>>>
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>>>
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