[#278] client: Support wrapped errors in error checkers

Client errors are quite often wrapped in context. When checking a
specific error, it is required not to lose the ability to determine it,
regardless of the attached context. In previous implementation `IsErr*`
functions didn't support wrapped errors.

Make `IsErr*` functions to preliminarily unwrap `error` argument before
type assertion. Use `errors.Unwrap` for this instead of `errors.As`
since the latter has the overhead of filling in an error.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

client/errors.go

@@ -1,11 +1,24 @@
 package client
 
-import apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
+import (
+	"errors"
+
+	apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
+)
+
+// unwraps err using errors.Unwrap and returns the result.
+func unwrapErr(err error) error {
+	for e := errors.Unwrap(err); e != nil; e = errors.Unwrap(err) {
+		err = e
+	}
+
+	return err
+}
 
 // IsErrContainerNotFound checks if err corresponds to NeoFS status
-// return corresponding to missing container.
+// return corresponding to missing container. Supports wrapped errors.
 func IsErrContainerNotFound(err error) bool {
-	switch err.(type) {
+	switch unwrapErr(err).(type) {
 	default:
 		return false
 	case
@@ -16,9 +29,9 @@ func IsErrContainerNotFound(err error) bool {
 }
 
 // IsErrObjectNotFound checks if err corresponds to NeoFS status
-// return corresponding to missing object.
+// return corresponding to missing object. Supports wrapped errors.
 func IsErrObjectNotFound(err error) bool {
-	switch err.(type) {
+	switch unwrapErr(err).(type) {
 	default:
 		return false
 	case
@@ -29,9 +42,9 @@ func IsErrObjectNotFound(err error) bool {
 }
 
 // IsErrObjectAlreadyRemoved checks if err corresponds to NeoFS status
-// return corresponding to already removed object.
+// return corresponding to already removed object. Supports wrapped errors.
 func IsErrObjectAlreadyRemoved(err error) bool {
-	switch err.(type) {
+	switch unwrapErr(err).(type) {
 	default:
 		return false
 	case

client/errors_test.go

@@ -1,6 +1,7 @@
 package client_test
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/nspcc-dev/neofs-sdk-go/client"
@@ -39,6 +40,7 @@ func TestErrors(t *testing.T) {
 
 		for i := range tc.errs {
 			require.True(t, tc.check(tc.errs[i]), tc.errs[i])
+			require.True(t, tc.check(fmt.Errorf("some context: %w", tc.errs[i])), tc.errs[i])
 		}
 	}
 }