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Re: [ecf-dev] A general question around REST

Hello Ali,

A brief/summary explanation: ECF's REST support currently allows REST-based services to be easily exposed to OSGi clients as OSGi remote services.

A brief example: Twitter has a REST-based service, that...that uses json for serialization (of both parameters and return value). Using ECF's remote services (and the REST client support that extends this remote services API), it's possible to create a OSGi service (i.e. defined by a java interface), that exposes part (or all) of the twitter REST API as an OSGi remote service. There's a code example in the tests here [1] (this code example is not currently working because of a change in the Twitter authentication mechanism...that we have not been able to adjust for yet...my apologies about that).

The creation of OSGi remote services for REST-based services is quite easy and flexible...there are more excellent code examples of doing this here [2]. These examples are by Pavel Samolisov.

To summarize: ECF's REST support is currently focused on allowing people to easily create providers to expose REST-based services (of whatever kind/implementation) as OSGi remote services. It does *not* currently define a server-side API for exposing REST-based services (i.e. defining the server-side of a REST-based service).

This is where the Restlet work, and the Restlet+OSGi work (for REST-based services) described by Bryan...come in. Restlet and the work pointed to by Bryan allow one to easily define/expose a Restlet service (in OSGi or not). Such a service is a servlet, registered with the OSGi HttpService dynamically by Bryan's Restlet+OSGi integration code. Once a service is registered, it can be accessed by whatever client is desired...e.g. a web browser, some client written in javascript, a client written in java, or an OSGi client written in java.

Now...I've recently been looking into the feasibility of doing the following: Given Restlet, and Bryan's Restlet+OSGi work, and the ECF REST API, and ECF's impl of OSGi remote services it would be very easy to have a Restlet Application/Router...that was defined by the programmer for a given service, and used by Bryan's Restlet+OSGi work...be automatically exposed as *both* a 'normal' REST service (accessible from browser as well as clients), *and* an OSGi remote service (with a java interface defining the service contract, and a *system-created proxy* that implements the actual remote method invocation via the REST-based calls. For your use case (if I understand it correctly), this would be valuable, because it would allow all variety of clients...e.g. browser, clients in other languages...*and* with the ECF REST remote services it would allow/support all nice things about OSGi services...e.g. using ServiceTrackers, using declarative services...as well as all the nice things about ECF's impl of OSGi remote services and now remote services admin (e.g. the control/management of the remote service export and import process, load balancing use cases, enterprise topology managers, security, service interface versioning, etc., etc).

The stuff described in the above paragraph may seem like a lot...but with the pieces that already exist (Restlet, OSGi+Restlet integration, ECF REST API, ECF impl of OSGi remote services/RSA...it's really not very much...because it's just integrating the various APIs on the REST server as well as the REST client. I've been in recent communication with Bryan about doing exactly this...i.e. using the pieces listed together on an OSGi server (and OSGi clients as well) to expose (via Restlet+OSGi) a REST-based service to *both* 'normal' clients, as well as exposing the *same* service (really the same server/service code...in fact with one service registration) as an OSGi remote service proxy....using all the same proxy dynamic proxy creation code.

Now...Bryan's work is just getting hardened (is my understanding), and I think there may have to be some small additions to his work to allow for the ECF/OSGi remote service export (where...according to the RSA spec...the remote service host exports an EndpointDescription that has an 'endpoint id'...e.g. http://myhost.com/path/to/rest-based/service. But I don't believe that it will be anything very large/significant to get everything working together.

So given your use case involves exposing REST-based services as both 'normal' http requests/responses as well as OSGi services, I think that the tecnology mix described above seems like a good fit.

Does this make sense? If not, please let me know where it doesn't and I will attempt to be clearer.

Scott

P.S. One other comment: Because of the way that the ECF REST-based client support is written, it's also quite possible (I would say easy) to create clients for remote services that use SOAP+http for exposing a remote service. There are examples of doing this here [2] as well. Further, part of ECF 3.5 is the creation by Pavel of an XML-RPC provider as well XML-RPC-exposed services into OSGi service clients. The point being that the ECF REST-based client support is written in a way that allows the marshalling (i.e. serialization of parameters and return values) to be easily customized (to json, xml, soap, or whatever), and the http request/response protocol to easily be customized as well. I'm not saying this API is perfect yet...and it's possible it could use some generalization, but so far it's been able to do a number of things (at least as exemplified by [2]).

[1 ]http://git.eclipse.org/c/ecf/org.eclipse.ecf.git/tree/tests/bundles/org.eclipse.ecf.tests.remoteservice.rest/src/org/eclipse/ecf/tests/remoteservice/rest/twitter/TwitterRemoteServiceTest.java
[2] https://github.com/ECF/ECF-Examples



Hi Ali,

I've not looked into how the ECF REST support works, but I can offer you an interesting solution based on Restlet here:

http://code.google.com/a/eclipselabs.org/p/restlet-integration-with-equinox/

This solution allows you to have your REST services all coded in OSGi (even supports hot-plug) and any generic HTTP client.  I'm sure Scott will give you a good answer on the ECF end.

Bryan

On Mar 9, 2011, at 1:28 PM, Ali Naddaf wrote:

Hello everyone.

I understand that ECF has a REST provider support. My question is whether the following use case is covered by ECF, in general, or I need to look for a different solution: I have a an (Equinox based) OSGi environment and I would like to for my services (provided by bundles that I have in my environment) be also exposed externally as REST web services. So far, I was using something similar to what Peter had written (webrpc) that would expose public services with almost no extra work as some sort of rpc calls over http. Anyhow, for a general consumption of my OSGi services as REST web services by any external client (i.e. not just another OSGi environment), is the ECF still a correct solution?


Many thanks, Ali. _______________________________________________ ecf-dev mailing list ecf-dev@xxxxxxxxxxx https://dev.eclipse.org/mailman/listinfo/ecf-dev
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