Hi OSGi devs and experts, I've got a problem which I really want to solve in an elegant way but I think I haven't found the appropriate pieces yet.
The problem is the following: I want to create some abstraction for a little data management system which should be connected to different data backends at the same time (e.g. S3, Dropbox, local/network filesystem, ...). Now let's consider a simple example of the logic involving the following standard CRUD operations (because I want to publish that in a single ReST endpoint): * create (e.g. upload) * read (get metadata or list objects/files/buckets/... or just download) * update (e.g. re-upload or change metadata) * delete So, what I actually want is the following: 1.) For creating/uploading a new object, a specific data backend may be specified via HTTP header or determined automatically (e.g. based on expected size or some other metadata). 2.) For listing existing objects all service instances/data backends shall be queried at the same time (in parallel) and results combined into a single list. 3.) For retrieving object metadata, downloading a specific object, modifying, deleting it or executing some other operation with a specific object, the correct service instance/data backend is called. So, for case 1 I would need some way to evaluate the contextual information of the upcoming service call (in this case the HTTP header). If that is not available, I'll have to look at some service instance information that helps me figuring out where to put some object (DNS-SD or ZeroConf keep popping up conceptually here in my head). For case 2 I just need to actually execute the same call for each available service instance (like a network broadcast). For case 3 I need to know somehow (this could be done by a local object identity/location mapping) which service instance is responsible (or allowed to) manage a specific object. Now, I could code all this inside the ReST layer. However, what I really want is to make it abstract in a way that I can hook it into other places as well. So, the initial caller 'A' should just have code like this: private B b; //... myObjectId = b.create(newObject); //... List objects = b.list(filter, sort, paging); //... myObject = b.get(myObjectId); //... b.updateMetadata(myObjectMetadata); //... b.delete(myObjectId); So that the ReST layer does not even have to know that there is more than just one backend. The magic should be done outside in a generic way if possible, so that I could re-use it as it is for other types of services. Does that idea sound familiar to someone? Has that been solved already and I just missed something? I first started with the idea of using an aggregating proxy plus a FindHook and stuff, but this imposes the runtime issue that consumers need to be refreshed which I want to avoid if possible. The main problem I think here is to present a single service instance to the consumer for which there actually exists no real service registration as it is just some kind of invocation handler with a specialized purpose (routing/broadcasting service requests). I would be thankful for any ideas! Thanx, Ancoron _______________________________________________ OSGi Developer Mail List [email protected] https://mail.osgi.org/mailman/listinfo/osgi-dev
