Add custom unmarshaling support

internal/decoding/decoding.go

@@ -39,8 +39,25 @@ func Decode(data []byte, v interface{}, asArray bool) error {
 	return err
 }
 
+type Unmarshaler interface {
+	UnmarshalMsgpack(any) (any, error)
+}
+
 func (d *decoder) decode(rv reflect.Value, offset int) (int, error) {
 	k := rv.Kind()
+	if uv, ok := rv.Interface().(Unmarshaler); ok {
+		v, o, err := d.asInterface(offset, k)
+		if err != nil {
+			return 0, err
+		}
+		v, err = uv.UnmarshalMsgpack(v)
+		if err != nil {
+			return 0, err
+		}
+		rv.Set(reflect.ValueOf(v))
+		offset = o
+		return offset, nil
+	}
 	switch k {
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		v, o, err := d.asInt(offset, k)

internal/decoding/decoding_test.go

@@ -1,7 +1,9 @@
 package decoding
 
 import (
+	"net"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/shamaton/msgpack/v2/def"
@@ -744,4 +746,81 @@ func Test_decodeWithCode(t *testing.T) {
 		var vv any = int8(3)
 		tu.Equal(t, v.V, vv)
 	})
+
+	t.Run("StructWithCustomDecodeMethod", func(t *testing.T) {
+		testcases := AsXXXTestCases[bool]{
+			{
+				Name:     "error",
+				Data:     []byte{def.Int8},
+				Error:    def.ErrTooShortBytes,
+				MethodAs: method,
+			},
+			{
+				Name:     "ok",
+				Data:     []byte{def.Int8, 3},
+				Expected: true,
+				MethodAs: method,
+			},
+		}
+		v := new(StructWithCustomDecodeMethod)
+		target = v
+		testcases.Run(t)
+		tu.Equal(t, v.A, 9)
+		tu.Equal(t, v.B, "Happy birthday!")
+	})
+
+	t.Run("CustomDecodeNetAddrWhitelist", func(t *testing.T) {
+		testcases := AsXXXTestCases[bool]{
+			{
+				Name:     "error",
+				Data:     []byte{def.Int8, 0},
+				Error:    def.ErrCanNotDecode,
+				MethodAs: method,
+			},
+			{
+				Name:     "ok",
+				Data:     []byte{def.Str8, 24, '1', '9', '2', '.', '1', '6', '8', '.', '1', '.', '0', '/', '2', '4', ',', '0', '.', '0', '.', '0', '.', '0', '/', '0'},
+				Expected: true,
+				MethodAs: method,
+			},
+		}
+		v := new(NetAddrWhitelist)
+		target = v
+		testcases.Run(t)
+		tu.Equal(t, len(*v), 2)
+		tu.Equal(t, (*v)[0].String(), "192.168.1.0/24")
+		tu.Equal(t, (*v)[1].String(), "0.0.0.0/0")
+	})
+
+}
+
+type StructWithCustomDecodeMethod struct {
+	A int
+	B string
+}
+
+func (s StructWithCustomDecodeMethod) UnmarshalMsgpack(value any) (any, error) {
+	if v, ok := value.(int8); ok {
+		s.A = int(v) * 3
+		s.B = "Happy birthday!"
+		return s, nil
+	}
+	return nil, def.ErrCanNotDecode
+}
+
+type NetAddrWhitelist []net.IPNet
+
+func (a NetAddrWhitelist) UnmarshalMsgpack(value any) (any, error) {
+	if v, ok := value.(string); ok {
+		nets := strings.Split(v, ",")
+		for _, netw := range nets {
+			_, ipnet, err := net.ParseCIDR(netw)
+			if err != nil {
+				return nil, err
+			}
+			a = append(a, *ipnet)
+		}
+		return a, nil
+	}
+	return nil, def.ErrCanNotDecode
 }