Adding LeaseID checking in Txn needs a Cmp type method

[purpleidea]

I'd like to do Txn's like this:

If v3.Compare(v3.LeaseValue(keyPath), "=", someLeaseID) ...

Thanks to some lovely work @heyitsanthony pointed me to, you could write:

	LeaseValue := func(key string) v3.Cmp {
		return v3.Cmp{Key: []byte(key), Target: pb.Compare_LEASE}
	}

I'd propose adding this as a helper function alongside https://godoc.org/github.com/coreos/etcd/clientv3#Value but there are apparently some naming convention issues in "mapping directly to the mvccpb.KeyValue".

These are beyond my understanding of the internals, but this issue is to track this so interested users get a notification when this is fixed so we can update our code.

Thanks for the great feature!

[purpleidea]

I wrote a patch adding this if anyone would like it.
This is nice to avoid having the end user import pb and know that this trick is possible.

#8488

[davissp14]

https://github.com/coreos/etcd/blob/master/etcdserver/etcdserverpb/rpc.proto#L520

This feature doesn't seem to be working as expected. I am working on adding support for this here: https://github.com/davissp14/etcdv3-ruby/pull/95/files

The txn lease comparison seems to ALWAYS return successfully regardless of the comparison. Is this issue relevant here? If not, let me know and I can open up a new issue.

[xiang90]

@davissp14 what is the server version? the feature only works on master.

[davissp14]

@xiang90 That would explain it. The server version I am testing against is 3.2.6.

[heyitsanthony]

Fixed in master. Closing.

[danevandyck]

Have you considered adding comparison on lease ID to 3.2?

[gyuho]

@danevandyck This was fixed via #8324.
And will be included in our upcoming 3.3 release.