Cannot unmarshal struct when key is not English

[artemklevtsov]

Seems realted with #234.

package main

import (
	"fmt"

	"encoding/json"

	gjson "github.com/goccy/go-json"
)

type MyType struct {
	Msg string `json:"Сообщение"`
}

func main() {
	b := []byte(`{"Сообщение":"Текст"}`)

	var expected MyType
	json.Unmarshal(b, &expected)
	fmt.Printf("got json object: %+v\n", expected)

	var actual MyType
	gjson.Unmarshal(b, &actual)
	fmt.Printf("got gjson object: %+v\n", actual)
}

Exptected

got json object: {Msg:Текст}
got gjson object: {Msg:Текст}

Actual

got json object: {Msg:Текст}
got gjson object: {Msg:}

go version go1.19.3 linux/amd64
github.com/goccy/go-json v0.10.0

[orisano]

The root cause of this issue is that the tag name is strings.ToLower for case insensitive lookup of field names in the structure, but the decoding process only looks up from the largeToSmallTable and does not consider the locale.

https://go.dev/play/p/xRsK6qvU3XJ

Code:

var (
	largeToSmallTable [256]byte
)

func init() {
	for i := 0; i < 256; i++ {
		c := i
		if 'A' <= c && c <= 'Z' {
			c += 'a' - 'A'
		}
		largeToSmallTable[i] = byte(c)
	}
}

func toLower(s string) string {
	var b []byte
	for _, c := range []byte(s) {
		b = append(b, largeToSmallTable[c])
	}
	return string(b)
}

func main() {
	s := "Сообщение"
	fmt.Println(toLower(s))
	fmt.Println(strings.ToLower(s))
}

Output:

Сообщение
сообщение

@goccy How do we correct the problem?