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main.go
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main.go
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package main
import (
"encoding/binary"
"errors"
bin "github.com/saylorsolutions/binmap"
"io"
)
type version = byte
const (
v1 version = iota + 1
v2
)
type User struct {
username string
}
func (u *User) mapperV1() bin.Mapper {
return bin.NullTermString(&u.username)
}
func (u *User) mapperV2() bin.Mapper {
return bin.FixedString(&u.username, 32)
}
func (u *User) mapper() bin.Mapper {
return bin.Any(
func(r io.Reader, endian binary.ByteOrder) error {
var v version
if err := bin.Byte(&v).Read(r, endian); err != nil {
return err
}
switch v {
case v1:
return u.mapperV1().Read(r, endian)
case v2:
return u.mapperV2().Read(r, endian)
default:
return errors.New("unknown version")
}
},
func(w io.Writer, endian binary.ByteOrder) error {
var v = v2
return bin.MapSequence(
bin.Byte(&v),
u.mapperV2(),
).Write(w, endian)
},
)
}
func (u *User) Read(r io.Reader) error {
return u.mapper().Read(r, binary.BigEndian)
}
func (u *User) Write(w io.Writer) error {
return u.mapper().Write(w, binary.BigEndian)
}