On Tue, Oct 27, 2015 at 10:47 AM, Juan Hernández <[email protected]> wrote:
> On 10/27/2015 10:16 AM, Roman Mohr wrote: > > > > > > On Mon, Oct 26, 2015 at 5:32 PM, Juan Hernández <[email protected] > > <mailto:[email protected]>> 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? > > 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. > > 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, ... > > > > > * 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. > > > > > > * 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 < > [email protected] <mailto:[email protected]> > > > <mailto:[email protected] <mailto:[email protected]>>> 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 > > > [email protected] <mailto:[email protected]> > > <mailto:[email protected] <mailto:[email protected]>> > > > 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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