In previous implementation `SignService` converted all `error` values to
`INTERNAL` server failure status. That was done for simplification only.
There is a need to transmit status errors as corresponding status
messages.
Make `SignService` to unwrap errors and convert them to status message
during writing to the response. Non-status errors are converted to
`INTERNAL` server failures. Status errors can also be wrapped in the
depths of the executable code, so `SignService` tries to unwrap them.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Upgrade NeoFS API Go library to version with status returns. Make all API
clients to pull out and return errors from failed statuses. Make signature
service to respond with status if client version supports it.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Replace UnaryHandler from structure to method arguments in order to reuse
single instance for different service methods.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
