Implement API features

[kragniz]

The following gRPC methods should have comparative functionality in the python-etcd3 API. This issue is to keep track of features that still require some implementation.

Auth

• [ ] AuthEnable
• [ ] AuthDisable
• [ ] Authenticate
• [ ] UserAdd
• [ ] UserGet
• [ ] UserList
• [ ] UserDelete
• [ ] UserChangePassword
• [ ] UserGrantRole
• [ ] UserRevokeRole
• [ ] RoleAdd
• [ ] RoleGet
• [ ] RoleList
• [ ] RoleDelete
• [ ] RoleGrantPermission
• [ ] RoleRevokePermission

Cluster

• [x] MemberAdd
• [x] MemberRemove
• [x] MemberUpdate
• [x] MemberList

KV

• [x] Range
• [x] Put
• [x] DeleteRange
• [x] Txn
• [x] Compact

Lease

• [x] LeaseGrant
• [x] LeaseRevoke
• [x] LeaseKeepAlive
• [x] LeaseTimeToLive

Maintenance

• [ ] Alarm
• [x] Status
• [x] Defragment
• [ ] Hash
• [ ] Snapshot

Watch

• [x] Watch

[CyberDem0n]

Unfortunately KV implementation is not feature-full yet. Response on Range request must return not only values (and keys) but all available meta-data (create_revision, mod_revision, version, lease) together with ResponseHeader, otherwise it is not possible to implement something more complex than a child-toy app listing keys and values... :(

Also I think KeyNotFoundError exception should be to raised only for get(key) methods, but not for get_prefix and get_all (it is kinda OK to have an empty ranges).

[kragniz]

Yeah, this list is mostly about which parts of the gRPC api have been implemented, not which parts have a finished publicly facing api.

About the KV stuff, I started #53. Feel free to write your thoughts there.

[akuchibotla]

New to this repository and contributing in general and hoping to get into it with smaller feature additions. Do you think that adding a contains feature would be useful to determine whether or not a key is contained within an etcd instance? I understand it's quite trivial to check but it would make for a more complete KV api.

[kragniz]

@akuchibotla exists(key) might be useful, although it's generally easier to check if get(key) returns None.

If you want something small to work on, you could implement Hash? (https://github.com/coreos/etcd/blob/master/Documentation/dev-guide/api_reference_v3.md#service-maintenance-etcdserveretcdserverpbrpcproto)