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Re: [ecf-dev] A general question around REST
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I started playing with Bryan's bundles; it seems that the minimum
execution environment is set to 1.6; is that a requirement for this to
work? My environment needs to be 1.5 so that would be a show stopper for
me. I will try to modify that and run that to see if it fails anywhere...
Thanks,
Ali.
On 3/9/2011 4:47 PM, Scott Lewis wrote:
Hi Ali,
Hi Scott.
Many thanks, as usual, for your detailed and valuable response. Yes,
indeed the mixed scenario that you described would be the ideal
situation for me. You had mentioned you were looking into that; are
you planning to wait for the final changes on Bryan's side to happen
first?
I've just had casual emails with Bryan about some ideas for how the
Restlet+OSGi bridge could be enhanced to support the creation of OSGi
remote services (using ECF's impl). I've opened a new enhancement
request [1] specifically for this integration. I think that Bryan,
I, and any others that are interested...like Ali...but of course
anyone who's interested can (and hopefully will) participate and
contribute...should use this bug to discuss what
changes/generalizations are needed...and where...and discuss how to
get any desired/necessary changes in place in the relevant part of
things (i.e. Restlet, OSGi/Restlet integration, ECF REST API, remote
services, etc). I think we should also use this bug to get clarity on
use cases...and desired API...so if people have thoughts here please
join [1]. Hopefully Bryan will join the bug and we can have a
technical discussion there about the things we've discussed in private
(Bryan fwiw...feel free to post my emails to the bug comments if you
decide/prefer).
Looking forward to seeing the mixed scenario working,
Me too. It's going to take some cooperative effort in several areas
(e.g. Bryan, me/other ECF contributors/committers, perhaps
Restlet/Jerome), but actually I don't think it will actually take very
much...because most of the pieces here are in place, and working just
fine in their respective domains (e.g. REST/Restlet servers, OSGi
remote services, etc).
Thanks(inadvance) for your interest and participation. :)
Scott
[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=339442
Thanks again,
Ali.
On 3/9/2011 4:10 PM, Scott Lewis wrote:
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.
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