[#278] client: Add session error checkers

Add `IsErrSessionExpired` and `IsErrSessionNotFound` functions which
assert corresponding session errors.

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

client/errors.go

@@ -53,3 +53,29 @@ func IsErrObjectAlreadyRemoved(err error) bool {
 		return true
 	}
 }
+
+// IsErrSessionExpired checks if err corresponds to NeoFS status return
+// corresponding to expired session. Supports wrapped errors.
+func IsErrSessionExpired(err error) bool {
+	switch unwrapErr(err).(type) {
+	default:
+		return false
+	case
+		apistatus.SessionTokenExpired,
+		*apistatus.SessionTokenExpired:
+		return true
+	}
+}
+
+// IsErrSessionNotFound checks if err corresponds to NeoFS status return
+// corresponding to missing session. Supports wrapped errors.
+func IsErrSessionNotFound(err error) bool {
+	switch unwrapErr(err).(type) {
+	default:
+		return false
+	case
+		apistatus.SessionTokenNotFound,
+		*apistatus.SessionTokenNotFound:
+		return true
+	}
+}

client/errors_test.go

@@ -35,6 +35,19 @@ func TestErrors(t *testing.T) {
 				new(apistatus.ObjectAlreadyRemoved),
 			},
 		},
+		{
+			check: client.IsErrSessionExpired,
+			errs: []error{
+				apistatus.SessionTokenExpired{},
+				new(apistatus.SessionTokenExpired),
+			},
+		}, {
+			check: client.IsErrSessionNotFound,
+			errs: []error{
+				apistatus.SessionTokenNotFound{},
+				new(apistatus.SessionTokenNotFound),
+			},
+		},
 	} {
 		require.NotEmpty(t, tc.errs)