[#83] client: Implement status library

Define base `Status` interface. Provide the functionality to distinguish
success and failure returns. Provide functionality to transport statuses
over NeoFS API V2 protocol. Support success `OK` and failure `INTERNAL`
returns.

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

client/status/v2_test.go

@@ -0,0 +1,145 @@
+package apistatus_test
+
+import (
+	"errors"
+	"testing"
+
+	apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
+	"github.com/stretchr/testify/require"
+)
+
+func TestToStatusV2(t *testing.T) {
+	type statusConstructor func() apistatus.Status
+
+	for _, testItem := range [...]struct {
+		status interface{} // Status or statusConstructor
+		codeV2 uint64
+	}{
+		{
+			status: errors.New("some error"),
+			codeV2: 1024,
+		},
+		{
+			status: 1,
+			codeV2: 0,
+		},
+		{
+			status: "text",
+			codeV2: 0,
+		},
+		{
+			status: true,
+			codeV2: 0,
+		},
+		{
+			status: true,
+			codeV2: 0,
+		},
+		{
+			status: nil,
+			codeV2: 0,
+		},
+		{
+			status: (statusConstructor)(func() apistatus.Status {
+				var st apistatus.ServerInternal
+
+				st.SetMessage("internal error message")
+
+				return st
+			}),
+			codeV2: 1024,
+		},
+	} {
+		var st apistatus.Status
+
+		if cons, ok := testItem.status.(statusConstructor); ok {
+			st = cons()
+		} else {
+			st = testItem.status
+		}
+
+		stv2 := apistatus.ToStatusV2(st)
+
+		// must generate the same status.Status message
+		require.EqualValues(t, testItem.codeV2, stv2.Code())
+
+		_, ok := st.(apistatus.StatusV2)
+		if ok {
+			// restore and convert again
+			restored := apistatus.FromStatusV2(stv2)
+
+			res := apistatus.ToStatusV2(restored)
+
+			// must generate the same status.Status message
+			require.Equal(t, stv2, res)
+		}
+	}
+}
+
+func TestFromStatusV2(t *testing.T) {
+	type statusConstructor func() apistatus.Status
+
+	for _, testItem := range [...]struct {
+		status interface{} // Status or statusConstructor
+		codeV2 uint64
+	}{
+		{
+			status: errors.New("some error"),
+			codeV2: 1024,
+		},
+		{
+			status: 1,
+			codeV2: 0,
+		},
+		{
+			status: "text",
+			codeV2: 0,
+		},
+		{
+			status: true,
+			codeV2: 0,
+		},
+		{
+			status: true,
+			codeV2: 0,
+		},
+		{
+			status: nil,
+			codeV2: 0,
+		},
+		{
+			status: (statusConstructor)(func() apistatus.Status {
+				var st apistatus.ServerInternal
+
+				st.SetMessage("internal error message")
+
+				return st
+			}),
+			codeV2: 1024,
+		},
+	} {
+		var st apistatus.Status
+
+		if cons, ok := testItem.status.(statusConstructor); ok {
+			st = cons()
+		} else {
+			st = testItem.status
+		}
+
+		stv2 := apistatus.ToStatusV2(st)
+
+		// must generate the same status.Status message
+		require.EqualValues(t, testItem.codeV2, stv2.Code())
+
+		_, ok := st.(apistatus.StatusV2)
+		if ok {
+			// restore and convert again
+			restored := apistatus.FromStatusV2(stv2)
+
+			res := apistatus.ToStatusV2(restored)
+
+			// must generate the same status.Status message
+			require.Equal(t, stv2, res)
+		}
+	}
+}