syncthing/discover/encoding.go
2013-12-22 21:35:05 -05:00

161 lines
3.0 KiB
Go

package discover
import (
"encoding/binary"
"errors"
"fmt"
)
type Packet struct {
Magic uint32 // AnnouncementMagic or QueryMagic
Port uint16 // unset if magic == QueryMagic
ID string
IP []byte // zero length in local announcements
}
var (
errBadMagic = errors.New("bad magic")
errFormat = errors.New("incorrect packet format")
)
func EncodePacket(pkt Packet) []byte {
if l := len(pkt.IP); l != 0 && l != 4 && l != 16 {
// bad ip format
return nil
}
var idbs = []byte(pkt.ID)
var l = 4 + 4 + len(idbs) + pad(len(idbs))
if pkt.Magic == AnnouncementMagic {
l += 4 + 4 + len(pkt.IP)
}
var buf = make([]byte, l)
var offset = 0
binary.BigEndian.PutUint32(buf[offset:], pkt.Magic)
offset += 4
if pkt.Magic == AnnouncementMagic {
binary.BigEndian.PutUint16(buf[offset:], uint16(pkt.Port))
offset += 4
}
binary.BigEndian.PutUint32(buf[offset:], uint32(len(idbs)))
offset += 4
copy(buf[offset:], idbs)
offset += len(idbs) + pad(len(idbs))
if pkt.Magic == AnnouncementMagic {
binary.BigEndian.PutUint32(buf[offset:], uint32(len(pkt.IP)))
offset += 4
copy(buf[offset:], pkt.IP)
offset += len(pkt.IP)
}
return buf
}
func DecodePacket(buf []byte) (*Packet, error) {
var p Packet
var offset int
if len(buf) < 4 {
// short packet
return nil, errFormat
}
p.Magic = binary.BigEndian.Uint32(buf[offset:])
offset += 4
if p.Magic != AnnouncementMagic && p.Magic != QueryMagic {
return nil, errBadMagic
}
if p.Magic == AnnouncementMagic {
// Port Number
if len(buf) < offset+4 {
// short packet
return nil, errFormat
}
p.Port = binary.BigEndian.Uint16(buf[offset:])
offset += 2
reserved := binary.BigEndian.Uint16(buf[offset:])
if reserved != 0 {
return nil, errFormat
}
offset += 2
}
// Node ID
if len(buf) < offset+4 {
// short packet
return nil, errFormat
}
l := binary.BigEndian.Uint32(buf[offset:])
offset += 4
if len(buf) < offset+int(l)+pad(int(l)) {
// short packet
return nil, errFormat
}
idbs := buf[offset : offset+int(l)]
p.ID = string(idbs)
offset += int(l) + pad(int(l))
if p.Magic == AnnouncementMagic {
// IP
if len(buf) < offset+4 {
// short packet
return nil, errFormat
}
l = binary.BigEndian.Uint32(buf[offset:])
offset += 4
if l != 0 && l != 4 && l != 16 {
// weird ip length
return nil, errFormat
}
if len(buf) < offset+int(l) {
// short packet
return nil, errFormat
}
if l > 0 {
p.IP = buf[offset : offset+int(l)]
offset += int(l)
}
}
if len(buf[offset:]) > 0 {
// extra data
return nil, errFormat
}
return &p, nil
}
func pad(l int) int {
d := l % 4
if d == 0 {
return 0
}
return 4 - d
}
func ipStr(ip []byte) string {
switch len(ip) {
case 4:
return fmt.Sprintf("%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3])
case 16:
return fmt.Sprintf("%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x",
ip[0], ip[1], ip[2], ip[3],
ip[4], ip[5], ip[6], ip[7],
ip[8], ip[9], ip[10], ip[11],
ip[12], ip[13], ip[14], ip[15])
default:
return ""
}
}