Golang read csv data row into struct

csv.go

package main

import (
	"bytes"
	"encoding/csv"
	"fmt"
	"io"
	"reflect"
)

type Reader struct {
	*csv.Reader
	Fields []string
}

func NewReader(r io.Reader) *Reader {
	rd := csv.NewReader(r)
	rd.FieldsPerRecord = -1
	fields, err := rd.Read()
	if err != nil {
		panic(err)
	}
	return &Reader{
		Reader: rd,
		Fields: fields,
	}
}

func (r *Reader) ReadInto(v interface{}) (err error) {
	rv := reflect.ValueOf(v)
	for rv.Kind() != reflect.Ptr || rv.IsNil() {
		return fmt.Errorf("Invalid type of output %s", reflect.TypeOf(v))
	}

	row, err := r.Read()
	if err != nil {
		return
	}

	mapping := make(map[string]string)
	lenrow := len(row)
	for idx, fieldname := range r.Fields {
		if idx < lenrow {
			mapping[fieldname] = row[idx]
		} else {
			mapping[fieldname] = ""
		}
	}

	typ := reflect.TypeOf(v).Elem()
	obj := rv.Elem()
	for i := 0; i < typ.NumField(); i++ {
		nf := typ.Field(i)
		name := nf.Tag.Get("csv")
		obj.FieldByName(nf.Name).SetString(mapping[name])
	}

	return nil
}

type Row struct {
	A string `csv:"a"`
	B string `csv:"b"`
}

func main() {
	src := bytes.NewReader([]byte(`a,b,c
1,2,3
2,3,4`))
	r := NewReader(src)
	for {
		var row Row
		err := r.ReadInto(&row)
		if err != nil {
			fmt.Println(err)
			return
		}
		fmt.Printf("%#v\n", row)
	}
}

https://play.golang.org/p/sakfw-IUyNm

main.Row{A:"1", B:"2"}
main.Row{A:"2", B:"3"}
EOF