Merge branch 'master' into feature/writer

README.md

@@ -278,6 +278,7 @@ type test struct {
 	OffsetStart byte `bin:"offsetStart:42"` // move to 42 bytes from start position and read byte
 	OffsetEnd   byte `bin:"offsetEnd:-42"`  // move to -42 bytes from end position and read byte
 	OffsetStart byte `bin:"offsetStart:42, offset:10"` // also worked and equally `offsetStart:52`
+	OffsetWithRestore byte `bin:"offset:42, offsetRestore"` // move to 42 bytes from current position and read byte, then restore position to the previous one (before offset)
 
 	// Calculations supported +,-,/,* and are performed from left to right that is 2+2*2=8 not 6!!!
 	CalcTagValue []byte `bin:"len:10+5+2+3"` // equally len:20

binstruct_test.go

@@ -917,3 +917,19 @@ func Test_InnerSubField(t *testing.T) {
 	require.Equal(t, int8(5), v.Child.Len)
 	require.Equal(t, []byte{0x01, 0x02, 0x03, 0x04, 0x05}, v.S)
 }
+
+func Test_OffsetRestore(t *testing.T) {
+	var v struct {
+		Offset uint8
+		Size   uint8
+		Data   []byte `bin:"offsetStart:Offset,len:Size,offsetRestore"`
+		Other  []byte `bin:"len:3"`
+	}
+
+	err := UnmarshalBE([]byte{0x05, 0x02, 0x01, 0x02, 0x03, 0x04, 0x05}, &v)
+	require.NoError(t, err)
+	require.Equal(t, uint8(5), v.Offset)
+	require.Equal(t, uint8(2), v.Size)
+	require.Equal(t, []byte{0x04, 0x05}, v.Data)
+	require.Equal(t, []byte{0x01, 0x02, 0x03}, v.Other)
+}

tag.go

@@ -26,6 +26,7 @@ const (
 	tagTypeOffsetFromCurrent = "offset"
 	tagTypeOffsetFromStart   = "offsetStart"
 	tagTypeOffsetFromEnd     = "offsetEnd"
+	tagTypeOffsetRestore     = "offsetRestore"
 )
 
 type tag struct {
@@ -59,6 +60,9 @@ func parseTag(t string) ([]tag, error) {
 		case v == tagTypeIgnore:
 			tags = append(tags, tag{Type: tagTypeIgnore})
 
+		case v == tagTypeOffsetRestore:
+			tags = append(tags, tag{Type: tagTypeOffsetRestore})
+
 		case strings.HasPrefix(v, "["):
 			v = v + "," + t
 			var arrBalance int
@@ -130,11 +134,12 @@ type fieldOffset struct {
 }
 
 type fieldReadData struct {
-	Ignore   bool
-	Length   *int64
-	Offsets  []fieldOffset
-	FuncName string
-	Order    binary.ByteOrder
+	Ignore        bool
+	Length        *int64
+	Offsets       []fieldOffset
+	OffsetRestore bool
+	FuncName      string
+	Order         binary.ByteOrder
 
 	ElemFieldData *fieldReadData // if type Element
 }
@@ -258,6 +263,9 @@ func parseReadDataFromTags(structValue reflect.Value, tags []tag) (*fieldReadDat
 				Whence: io.SeekEnd,
 			})
 
+		case tagTypeOffsetRestore:
+			data.OffsetRestore = true
+
 		case tagTypeFunc:
 			data.FuncName = t.Value
 

tag_test.go

@@ -66,12 +66,13 @@ func Test_parseTag(t *testing.T) {
 		},
 		{
 			name: "multi tag",
-			tag:  "len:1, offset:2, offsetStart:3, offsetEnd:4",
+			tag:  "len:1, offset:2, offsetStart:3, offsetEnd:4, offsetRestore",
 			want: []tag{
 				{Type: "len", Value: "1"},
 				{Type: "offset", Value: "2"},
 				{Type: "offsetStart", Value: "3"},
 				{Type: "offsetEnd", Value: "4"},
+				{Type: "offsetRestore"},
 			},
 		},
 		{

unmarshal.go

@@ -3,6 +3,7 @@ package binstruct
 import (
 	"errors"
 	"fmt"
+	"io"
 	"reflect"
 	"strings"
 )
@@ -80,6 +81,14 @@ func (u *unmarshal) setValueToField(
 		r = r.WithOrder(fieldData.Order)
 	}
 
+	if fieldData.OffsetRestore {
+		currentOffset, err := r.Seek(0, io.SeekCurrent)
+		if err != nil {
+			return fmt.Errorf("get current offset: %w", err)
+		}
+		defer r.Seek(currentOffset, io.SeekStart)
+	}
+
 	err := setOffset(r, fieldData)
 	if err != nil {
 		return fmt.Errorf("set offset: %w", err)