Get golang struct tags, returning name of field, value of tag and the index in struct

get_tags_struct.go

package main

import (
    "errors"
    "fmt"
    "reflect"
)

type User struct {
    Id    int    `json:"Id" queryStr:"Id"`
    Name  string `json:"FieldName" queryStr:"FieldName"`
    Email string `json:"Email" queryStr:"Email"`
}

func main() {
    user := &User{
        Id:    1,
        Name:  "John Doe",
        Email: "john@example",
    }
    tags, err := GetTagIndex(user, "queryStr")
    if err != nil {
        panic(err)
    }
    fmt.Println(tags)
    return
}

type Tags struct {
    FieldName string
    ValueTag  string
    Index int64
}

func GetTagIndex(obj interface{}, tag string) (tags []Tags, err error){
    tp := reflect.ValueOf(obj)
    if reflect.ValueOf(obj).Kind() == reflect.Ptr {
        tp = reflect.ValueOf(obj).Elem()
    }
    typeOfS := tp.Type()
    for i := 0; i < tp.NumField(); i++ {
        f, _ := typeOfS.FieldByName(typeOfS.Field(i).Name)
        valueTag, ok := f.Tag.Lookup(tag)
        if !ok {
            continue
        }
        tags = append(tags, Tags{
            ValueTag: valueTag,
            FieldName: typeOfS.Field(i).Name,
            Index: int64(i),
        })
    }
    if len(tags) == 0 {
        err = errors.New("tag not founded")
    }
    return
}