From 41307a5e00d7fc7a71240e8efce9aff299b2b494 Mon Sep 17 00:00:00 2001
From: Pavel Karpy <carpawell@nspcc.ru>
Date: Tue, 8 Jun 2021 21:28:36 +0300
Subject: [PATCH] [#302] pkg/xheader: Convert nil `XHeader` to nil message

Document that `XHeader.ToV2` method return `nil`
when called on `nil`. Document that `NewXHeaderFromV2`
function return `nil` when called on `nil`. Write
corresponding unit tests.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
---
 pkg/xheader.go      |  4 ++++
 pkg/xheader_test.go | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/pkg/xheader.go b/pkg/xheader.go
index 84d645c..7878677 100644
--- a/pkg/xheader.go
+++ b/pkg/xheader.go
@@ -8,6 +8,8 @@ import (
 type XHeader session.XHeader
 
 // NewXHeaderFromV2 wraps v2 XHeader message to XHeader.
+//
+// Nil session.XHeader converts to nil.
 func NewXHeaderFromV2(v *session.XHeader) *XHeader {
 	return (*XHeader)(v)
 }
@@ -18,6 +20,8 @@ func NewXHeader() *XHeader {
 }
 
 // ToV2 converts XHeader to v2 XHeader message.
+//
+// Nil XHeader converts to nil.
 func (x *XHeader) ToV2() *session.XHeader {
 	return (*session.XHeader)(x)
 }
diff --git a/pkg/xheader_test.go b/pkg/xheader_test.go
index 8f65227..66535be 100644
--- a/pkg/xheader_test.go
+++ b/pkg/xheader_test.go
@@ -3,6 +3,7 @@ package pkg
 import (
 	"testing"
 
+	"github.com/nspcc-dev/neofs-api-go/v2/session"
 	"github.com/stretchr/testify/require"
 )
 
@@ -23,3 +24,19 @@ func TestXHeader(t *testing.T) {
 	require.Equal(t, key, xV2.GetKey())
 	require.Equal(t, val, xV2.GetValue())
 }
+
+func TestNewXHeaderFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *session.XHeader
+
+		require.Nil(t, NewXHeaderFromV2(x))
+	})
+}
+
+func TestXHeader_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *XHeader
+
+		require.Nil(t, x.ToV2())
+	})
+}