[ovirt-devel] [ATN] Introduction of RESTAPI metamodel
Roman Mohr
rmohr at redhat.com
Tue Oct 27 11:55:49 UTC 2015
On Tue, Oct 27, 2015 at 12:16 PM, Juan Hernández <jhernand at redhat.com>
wrote:
> On 10/27/2015 11:28 AM, Roman Mohr wrote:
> >
> >
> > On Tue, Oct 27, 2015 at 10:47 AM, Juan Hernández <jhernand at redhat.com
> > <mailto:jhernand at redhat.com>> wrote:
> >
> > On 10/27/2015 10:16 AM, Roman Mohr wrote:
> > >
> > >
> > > On Mon, Oct 26, 2015 at 5:32 PM, Juan Hernández <
> jhernand at redhat.com <mailto:jhernand at redhat.com>
> > > <mailto:jhernand at redhat.com <mailto:jhernand at redhat.com>>> wrote:
> > >
> > > On 10/26/2015 04:56 PM, Roman Mohr wrote:
> > > > Hi Juan,
> > > >
> > > > The way to specify the contract look pretty clean and nice.
> > > > I would love to read a few words about the big picture. What
> > is the
> > > > final scenario?
> > > >
> > >
> > > The motivation for this change is that currently we don't have
> > a central
> > > place where the RESTAPI is specified, rather we have several
> > different
> > > places, using several different technologies:
> > >
> > > * XML schema for the data model.
> > > * JAX-RS for part of the operational model (without the
> > parameters).
> > > * rsdl_metadata.yaml for the parameters of the operational
> model.
> > >
> > > This makes it difficult to infer information about the model.
> For
> > > example, the generators of the SDKs have to download the XML
> > schema, and
> > > the RSDL (which is generated from the JAX-RS interfaces using
> > reflection
> > > and combining it with the information from the
> > rsdl_metadata.yaml file)
> > > and then they have to do their own computations to extract
> > what they
> > > need.
> > >
> > > Same happens with the CLI: it has to extract the information
> > it needs
> > > from the Python code generated for the Python SDK, yet another
> > level of
> > > indirection.
> > >
> > >
> > > You are right, that definitely needs to be cleaned up. I just want
> to
> > > discuss a few points below with you.
> > >
> > >
> > >
> > > We are also lacking a comprehensive reference documentation of
> the
> > > RESTAPI. What we currently have has been written by hand, and
> > gets out
> > > of sync very quickly, and we don't even notice.
> > >
> > >
> > > Did you also consider swagger? It is made for exactly that purpose.
> > > I created a demo in [1] which uses resteasy, weld,
> hibernate-validator
> > > and swagger to demonstrate how to do DRY with jaxrs.
> > > Would be great to hear you thoughts on that.
> > >
> > > And there is the great swagger-ui [8] to display the documentation
> > in a
> > > more human readable way.
> > >
> >
> > Yes, I considered Swagger, and rejected it because it is JSON
> centric,
> > and I think JSON isn't as good as Java to represent the contracts of
> our
> > RESTAPI.
> >
> >
> > You just write plain jax-rs, swagger just creates a description out of
> > it. So the source defining the contract is pure java (jax-rs with some
> > swagger annotations for description, etc.).
> > Or am I missing the point here?
> >
>
> If I understand correctly the Swagger core is a JSON (or YAML)
> specification of the API. From that you can generate JAX-RS annotated
> code, not the other way around. So the specification document that you
> write is a JSON document.
>
You are right, my terminology here was not clear. Swagger is just a
specification. Swagger-core and swagger-jaxrs are the ones which can create
the documnetation out of JAX-RS resources.
> Alternatively, you can use the Swagger annotations to decorate your
> implementation, both the entity classes and the JAX-RS resource
> implementations, and then extract the model from that. But this is
> putting the implementation before the specification. That is where we
> are today, and it causes multiple problems. I think it is better to have
> the specification and the implementation separate. Swagger does that
> well when using JSON directly, our metamodel also does it well, but
> using a better language.
>
Isn't our problem that we have everything scattered arount the place and
not that we are using JAX-RS? I don't think that this has anything to do
with specification before implementation or implementation before
specification.
> >
> >
> > In addition we need to do these changes in a smooth way, without
> causing
> > big changes in the middle. For example, in the first step we need to
> > preserve the JAX-RS interfaces as they are today, to avoid massive
> > changes to all the resource implementations. This could be done with
> >
> > Swagger, but would require custom code generators. With less effort
> we
> > can do our own.
> >
> >
> > This is of course generally a difficult task. But I do not know why it
> > would be more difficult to write a custom swagger reader (if we even
> > have to, it can read the interfaces as well) .
> > They are pretty streight forward. Just look at [9], this contains the
> > wole jax-rs specific code to generate the swagger documentation.
> >
> > But yes, I don't know every detail here of the engine and can't clearly
> > say that integrating that would just streight forward (my feeling tells
> > me that it would not be too hard). I am just under the impression that
> > we would benefit from that. Just reduces custom magic to a minimum.
> >
>
> Using something like Swagger would be certainly possible, and not that
> hard, but it requires an effort. For example, say that we decide to use
> the Swagger annotations. Then we will need to add these annotations to
> all our JAX-RS resource implementations. That is a non trivial effort.
> We would need to add the annotations to the entities as well. But wait,
> we don't have such entities, only XML schema. So we would need a reader
> that parses XML schema, and creating it requires effort.
You can just create the entities/daos once like we do now on every build
and annotate them once and drop the whole xml.
> Where do we put
> the documentation then? Part in the JAX-RS interfaces, part in the XML
> schema.
I don't understand that. There is only one documentation and implementation
source, that is the JAX-RS resource and the entity/dao accepted by the
endpoint.
The XML schema can just be removed. The documentation in swagger format for
other tools like swagger-codegen and swagger-ci can be made available
through swagger-maven-plugin or a servlet in the engine which generates the
swagger json on the fly (like I did in [1])
> We are already there, and we ended up with no documentation at
> all. In my view the sum of these efforts is higher than doing our own
> metamodel.
>
>
>
>
> >
> > Swagger UI is certainly great. I did test it and it is really good.
> We
> > may be able to copy some concepts.
> >
> > >
> > >
> > > To solve these issues I intend to have the specification of
> > the RESTAPI
> > > only in one place, and using only one technology. I decided to
> > use Java
> > > interfaces for that. Note however that they are just the
> > support for the
> > > information, like paper is the support for ink. I decided to
> > use Java
> > > because it is easy to create, modify and re-factor using tools
> > familiar
> > > to most of us.
> > >
> > > These source of these interfaces is analysed (using QDox,
> > currently) and
> > > a "model" of the RESTAPI is generated in memory. This model is
> > > independent of the supporting Java source, and easy to
> > consume. For
> > > example, imagine that you want to list all the types available
> > in the
> > > model and for each one display its documentation:
> > >
> > > Model model = ...;
> > > for (Type type : model.getTypes()) {
> > > Name name = type.getName();
> > > String doc = type.getDoc();
> > > System.out.println(name + ": " + doc);
> > > }
> > >
> > > Something like this, but more elaborate, will be part of a web
> > > application that provides comprehensive reference
> documentation,
> > > assuming that we dedicate the time to write documentation
> > comments in
> > > the specification.
> > >
> > > I intend to use this model also to do simplify the generators
> > of the
> > > SDKs and the CLI.
> > >
> > > In addition these are some of the things that I would like to
> > change in
> > > the near future (for 4.0):
> > >
> > > * Move the specification of the parameters of operations out
> > of the
> > > rsdl_metadata.yaml file and into the model. For example:
> > >
> > > @Service
> > > public VmService {
> > > /**
> > > * The operation to add a virtual machine.
> > > */
> > > interface Add {
> > > /**
> > > * The representation of the virtual machine is received
> > > * as parameter, and the representation of the created
> > > * virtual machine is returned as result.
> > > */
> > > @In @Out Vm vm();
> > >
> > > /**
> > > * In the future, we will be able to specify other
> > > * parameters here.
> > > */
> > > @In Boolean force();
> > >
> > > /**
> > > * Even with default values.
> > > */
> > > @In default Boolean force() { return true; }
> > >
> > > /**
> > > * And we will be able to specify constraints, which
> > > * will replace the rsdl_metadata.yaml file.
> > > */
> > > @Constraint
> > > default boolean vmNameMustNotBeNull() {
> > > return vm().name() != null;
> > > }
> > > }
> > > }
> > >
> > > * Enforce the constraints automatically. If the constraints
> > are in the
> > > model, then we can just check them and reject requests before
> > delivering
> > > them to the application. Currently we do this manually (and
> often
> > > forget) with calls to "validate(...)" methods.
> > >
> > >
> > >
> > > Did you consider just annotating the DTOs with JSR-303 annotations
> and
> > > integrate a validator with jax-rs?
> > > See [2] for an example.
> > >
> >
> > This is a great way to implement a system, but the goal here isn't to
> > implement it, rather to specify it. Using annotations in this way
> won't
> > help the generators of the SDKs, for example, to figure out what
> > parameters are required, mandatory, etc.
> >
> >
> > Swagger understands them. From my example project, swagger created that
> >
> > description:
> > type: "string"
> > minLength: 10
> > maxLength: 100
> >
> > out of
> >
> > @Size(min=10, max=100) # jsr-303
> > private String description;
> >
> > and so does swagger-codegen which can generate clients in java, python,
> ...
> >
>
> This is extracting the specification from the implementation, which
> isn't correct in my opinion, it should be the opposite. Not saying that
> this makes Swagger bad, it is nice that it has this capability, but I
> think we can do it better.
>
In my opition this is the main advantage of that. It is DRY while still
having full control of the implementation.
> > >
> > >
> > > * Generate the Java classes directly from the model. Instead
> of Model ->
> > > XML Schema -> Java, we can do Model -> Java. This will allow
> us to solve
> > > some of the XJC compiler limitations, like the horrible way we
> handle
> > > arrays today.
> > >
> > >
> > > Swagger [3] is a rest documentation specification. There is also a
> maven
> > > plugin [4] and you can create clients for example with [5].
> > >
> > >
> > >
> > > * Replace JAX-RS with a simpler infrastructure that supports
> better
> > > streaming and CDI injection.
> > >
> > >
> > >
> > > With resteasy-cdi you have pretty good injection support for
> resteasy.
> > > Run the demo in [1] to see it in action and look at the file at
> [6].
> > >
> >
> > Resteasy-CDI isn't standard, it only works with Resteasy. If we rely
> on
> > it then we re tied to Resteasy for ever.
> >
> >
> > Even jersey has support for that (I think it is called jeryse-gf-cdi),
> > but why would we want switch? I don't think that jboss will drop
> > resteasy and it also works fine outside of full blown containers. I
> > don't think that this is an argument.
> >
>
> Well, nobody thought that JBoss would drop Tomcat, and they did. Nobody
> thought that Resteasy would change the SPI from 2.x to 3.x, and they did.\
>
It will be there for the next year or another library which offers the same
thing. Having injections in Jax-rs resources is important for spring,
jboss, glassfish and others there will always be ways to do that. I don't
know why we should create our own 'custom standard' just because another
standard does not include dependency injection when we can just extend it
so easily.
> We want (well, I want) to get out of JAX-RS because it doesn't support
> well CDI and streaming.
>
Why should streaming resources be in the rest interface?
>
> >
> > >
> > >
> > > * Add support for multiple versions of the API, using the
> "Version"
> > > header, and generating different Java classes for entities and
> services.
> > > For example, if we have versions 4 and 5 of the model as
> separate
> > > artifacts, then we can generate "V4Vm" and "V5Vm" entity
> classes, and
> > > "V4VmService" and "V5VmService" service classes. These can be
> used
> > > simultaneously in the server, so we can have in the same engine
> > > implementations for multiple versions.
> > >
> > >
> > > There are also many ways to do that. Here [7] is a pretty clean
> way to
> > > do it with jax-rs and you will have everything related in one
> resource.
> > >
> >
> > Yes, there are many ways. In my opinion it is better to use the HTTP
> > "Version" header, and to forward requests to different resource
> > implementations without requiring different URLs or different
> > content types.
> >
> > Have no strong opinion there, just seemed to be a good choice regarding
> > to versioning limitations in jax-rs and our use of jax-rs subresources.
> >
> >
> > >
> > >
> > > The final picture isn't completely defined yet.
> > >
> > > Regards,
> > > Juan Hernandez
> > >
> > > > On Mon, Oct 26, 2015 at 4:03 PM, Juan Hernández <
> jhernand at redhat.com <mailto:jhernand at redhat.com>
> > <mailto:jhernand at redhat.com <mailto:jhernand at redhat.com>>
> > > > <mailto:jhernand at redhat.com <mailto:jhernand at redhat.com>
> > <mailto:jhernand at redhat.com <mailto:jhernand at redhat.com>>>> wrote:
> > > >
> > > > Hello,
> > > >
> > > > I will soon merge the following patches that introduce a
> new
> > > way to
> > > > specify the contracts of the RESTAPI:
> > > >
> > > > restapi: Introduce metamodel
> > > > https://gerrit.ovirt.org/45852
> > > >
> > > > restapi: Use metamodel
> > > > https://gerrit.ovirt.org/46478
> > > >
> > > > restapi: Generate JAX-RS interfaces from model
> > > > https://gerrit.ovirt.org/47337
> > > >
> > > >
> > >
> > > > Looks pretty much like we are replacing one way of
> > annotating things
> > > > with another way of specifying things.
> > > > Could you elaborate what the benefit of that way of
> > description is?
> > > >
> > > > How would I customize endpoints with e.g. @Gzip annotations?
> > Would
> > > I at
> > > > the end still have my JAX-RS annotates resource classes?
> > > >
> > > >
> > > > These patches introduce a new "metamodel" concept, and
> move
> > > the current
> > > > specification of the RESTAPI based on XML schema and
> JAX-RS
> > > interfaces
> > > > to a new "model" built on the new metamodel.
> > > >
> > > >
> > > > What does this mean for you in practical terms?
> > Currently when
> > > you want
> > > > to introduce or modify one of the data types used by the
> > > RESTAPI you
> > > > start by modifying the XML schema. Once the patches are
> > merged
> > > the XML
> > > > schema will never be touched, as it will be automatically
> > > generated from
> > > > the "model". For example, imagine that you need to add a
> new
> > > "color"
> > > > attribute to the "VM" entity. To do so with the new
> > model you
> > > will have
> > > > to modify the following file, which is the specification
> of
> > > the "Vm"
> > > > entity, written as a Java interface:
> > > >
> > > >
> > > >
> > >
> >
> https://gerrit.ovirt.org/#/c/46478/16/backend/manager/modules/restapi/model/src/main/java/types/Vm.java
> > > >
> > > > In that interface you will have to add a line like this:
> > > >
> > > > String color();
> > > >
> > > > Note that this Java interface is just the specification
> > of the
> > > entity,
> > > > it won't be used at all during runtime. Instead of that
> the
> > > XML schema
> > > > will be generated from it, and then Java will be
> generated
> > > from the XML
> > > > schema, as we do today (this will change in the future,
> but
> > > not yet).
> > > >
> > > > Same for the services. If you want to add a new "paint"
> > action
> > > to the
> > > > "Vm" resource then you won't modify the JAX-RS
> interfaces,
> > > instead of
> > > > that you will modify the following file, which is the
> > > specification of
> > > > the "Vm" service, written as a Java interface:
> > > >
> > > >
> > > >
> > >
> >
> https://gerrit.ovirt.org/#/c/47337/6/backend/manager/modules/restapi/model/src/main/java/services/VmService.java
> > > >
> > > > In that interface you will need to add a sub-interface
> > > representing the
> > > > action:
> > > >
> > > > interface Paint {
> > > > }
> > > >
> > > > The JAX-RS interface will be generated from that.
> > Currently these
> > > > sub-interfaces are empty. In the future they will
> > contain the
> > > > specifications of the parameters (currently in the
> > > rsdl_metadata.yml
> > > > file).
> > > >
> > > >
> > > >
> > > > These changes will currently affect only the
> > specification of the
> > > > RESTAPI, not the implementation, so in in the
> > > "Backend*Resource" classes
> > > > things won't change yet.
> > > >
> > > >
> > > > Currently I do not really understand where we are going
> > here. Are we
> > > > trying to get rid of rdsl?
> > > >
> > > > So basically two questions:
> > > >
> > > > 1) What is the final goal?
> > > > 2) What speaks agains using Hibernate validator on Daos in
> > combination
> > > > with JAX-RS annotated resources (and just removing all
> > interfaces, as
> > > > far as I can see we only have one implementation per
> > endpoint) and
> > > > creating all schemas and clients through SWAGGER tooling?
> > > >
> > > >
> > > > If you have doubts, please let me know.
> > > >
> > > > Regards,
> > > > Juan Hernandez
> > > >
> > > > --
> > > > Dirección Comercial: C/Jose Bardasano Baos, 9, Edif.
> > Gorbea 3,
> > > planta
> > > > 3ºD, 28016 Madrid, Spain
> > > > Inscrita en el Reg. Mercantil de Madrid – C.I.F.
> B82657941 -
> > > Red Hat
> > > > S.L.
> > > > _______________________________________________
> > > > Devel mailing list
> > > > Devel at ovirt.org <mailto:Devel at ovirt.org>
> > <mailto:Devel at ovirt.org <mailto:Devel at ovirt.org>>
> > > <mailto:Devel at ovirt.org <mailto:Devel at ovirt.org>
> > <mailto:Devel at ovirt.org <mailto:Devel at ovirt.org>>>
> > > > http://lists.ovirt.org/mailman/listinfo/devel
> > > >
> > > >
> > > > Thanks,
> > > >
> > > > Roman
> > >
> > >
> > > --
> > > Dirección Comercial: C/Jose Bardasano Baos, 9, Edif. Gorbea 3,
> > planta
> > > 3ºD, 28016 Madrid, Spain
> > > Inscrita en el Reg. Mercantil de Madrid – C.I.F. B82657941 -
> > Red Hat
> > > S.L.
> > >
> > >
> > >
> > > I don't know if it is the right thing to do to invent something new
> > > here. I personally would prefer to thread a path which is very
> > common on
> > > the java community.
> > > I would love follow the DRY principle regarding to the stack and
> the
> > > code and would just use the great community projects there.
> > >
> > > It would also completely eliminate any custom magic. The JAX-RS
> > and CDI
> > > magic is pretty standard and easy to understand.
> > > From my perspective, real JAX-RS resoures have the advantage of
> > >
> > > * being very easy to understand (there is magic, but the
> > connection to
> > > the real endpoint is pretty clear)
> > > * being easy to customize suff, like adding @GZip to an annotation
> > > * describing pretty clearly the connection between the generated
> rest
> > > interface and the internal services
> > >
> > > Finally writing hand crafted tests is also much easier.
> > >
> > > What are your thoughts about that?
> > >
> > > Best Regards,
> > > Roman
> > >
> > >
> > > [1] https://github.com/rmohr/jetty-maven-cdi-demo
> > > [2]
> > >
> >
> https://github.com/rmohr/jetty-maven-cdi-demo/blob/master/src/main/java/rmohr/examples/cdi/MyDto.java
> > > [3] http://swagger.io/
> > > [4] https://github.com/kongchen/swagger-maven-plugin
> > > [5] https://github.com/swagger-api/swagger-codegen
> > > [6]
> > >
> >
> https://github.com/rmohr/jetty-maven-cdi-demo/blob/master/src/main/java/rmohr/examples/cdi/RestSubResource.java
> > > [7]
> > >
> >
> http://maxenglander.com/2013/04/23/basic-restful-api-versioning-in-jersey.html
> > > [8] https://github.com/swagger-api/swagger-ui
> > >
> >
> > [9]
> >
> https://github.com/swagger-api/swagger-core/blob/master/modules/swagger-jaxrs/src/main/java/io/swagger/jaxrs/Reader.java
> >
>
> --
> Dirección Comercial: C/Jose Bardasano Baos, 9, Edif. Gorbea 3, planta
> 3ºD, 28016 Madrid, Spain
> Inscrita en el Reg. Mercantil de Madrid – C.I.F. B82657941 - Red Hat S.L.
>
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