Replace `core/container.ErrNotFound` error returned by `Source.Get`
interface method with `apistatus.ContainerNotFound` status error. This
error is returned by storage node's server as NeoFS API statuses.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
We don't use custom names and the only place where custom method option
is used it provides the default name and can be omitted.
Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
`Get` method of `Container` contract returns binary session token, key and
signature along with container.
Provide `Signature`, `PublicKey` and `SessionToken` getters from `GetValues`
structure. Parse and set all values in `Client.Get` methods.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
