Support v3 etcd api

[raoofm]

Support v3 etcd api https://github.com/coreos/etcd/blob/master/Documentation/dev-guide/api_reference_v3.md

[adohe-zz]

@raoofm Sorry about reply so late, I just get more time to do this. What do you think about this? Do you have any good idea? I want to first implement all key-value interfaces.

[raoofm]

I'll take a look at what you have. I'll be interested in this, if you need any help implementing.

I see a v3 branch will check that.

[adohe-zz]

@raoofm I just add some init commits in v3 branch, this is far from complete, I want to keep this step by step and I will focus on this this week. Really appreciate your help if you have time. Thanks very much :)

[adohe-zz]

@raoofm I am thinking about some implementation details, and I want to make this a good start. There are two proposals I have got:
Proposal 1:
Implement all services in one client:

public class EtcdClient {

    /*
     * KV service
     */

   public ListenableFuture<?> range(RangeRequest request) {

   }

    public ListenableFuture<?> put(PutRequest request) {

    }

    /*
     * Lease service
     */

    public ListenableFuture<?> leaseGrant(LeaseGrantRequest request) {

    }

    public ListenableFuture<?> leaseRevoke(LeaseRevokeRequest request) {

    }
}

Proposal2
Implement different service in different client, and write a wrapper client to aggregate clients:

public class EtcdClient {

    public KV kv() {

    }

    public Lease lease() {

    }
}

class KV {

    public ListenableFuture<?> range(RangeRequest request) {

    }

    public ListenableFuture<?> put(PutRequest request) {

    }
}

class Lease {

    public ListenableFuture<?> leaseGrant(LeaseGrantRequest request) {

    }

    public ListenableFuture<?> leaseRevoke(LeaseRevokeRequest request) {

    }
}

I think proposal1 is more straightforward, we are constructing a huge client, the code snippet could be very long. Proposal2 divides these services to different sub-client, and we can implement services step by step. so what do you think?

[raoofm]

As of now Proposal2 seems to be a good starting point... I was just thinking loudly that how big would it be to change from proposal 2 to proposal 1 later.

I think you earlier mentioned to wrap up the kv impl first, so proposal2 sounds good. What say?

[adohe-zz]

@raoofm as of now, etcd v3 has six kind of services: KV, Watch, Lease, Cluster, Maintenance, Auth, at the very beginning, we may just implement KV, Watch, Lease services, for proposal2, we separate different services to different sub-client, as we add more service implementation, we add more sub-clients, I am not even going to combine all these sub-clients to one huge client at last. We can keep this. wdyt?

[raoofm]

@adohe makes sense