/
protocol.go
241 lines (223 loc) · 4.93 KB
/
protocol.go
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package peer_protocol
import (
"bufio"
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"io/ioutil"
)
type (
MessageType byte
Integer uint32
)
func (i *Integer) Read(r io.Reader) error {
return binary.Read(r, binary.BigEndian, i)
}
// It's perfectly fine to cast these to an int.
func (i Integer) Int() int {
return int(i)
}
const (
Protocol = "\x13BitTorrent protocol"
)
const (
Choke MessageType = iota
Unchoke // 1
Interested // 2
NotInterested // 3
Have // 4
Bitfield // 5
Request // 6
Piece // 7
Cancel // 8
Port // 9
// BEP 6
Suggest = 0xd // 13
HaveAll = 0xe // 14
HaveNone = 0xf // 15
Reject = 0x10 // 16
AllowedFast = 0x11 // 17
Extended = 20
HandshakeExtendedID = 0
RequestMetadataExtensionMsgType = 0
DataMetadataExtensionMsgType = 1
RejectMetadataExtensionMsgType = 2
)
type Message struct {
Keepalive bool
Type MessageType
Index, Begin, Length Integer
Piece []byte
Bitfield []bool
ExtendedID byte
ExtendedPayload []byte
Port uint16
}
func (msg Message) MarshalBinary() (data []byte, err error) {
buf := &bytes.Buffer{}
if !msg.Keepalive {
err = buf.WriteByte(byte(msg.Type))
if err != nil {
return
}
switch msg.Type {
case Choke, Unchoke, Interested, NotInterested, HaveAll, HaveNone:
case Have:
err = binary.Write(buf, binary.BigEndian, msg.Index)
case Request, Cancel, Reject:
for _, i := range []Integer{msg.Index, msg.Begin, msg.Length} {
err = binary.Write(buf, binary.BigEndian, i)
if err != nil {
break
}
}
case Bitfield:
_, err = buf.Write(marshalBitfield(msg.Bitfield))
case Piece:
for _, i := range []Integer{msg.Index, msg.Begin} {
err = binary.Write(buf, binary.BigEndian, i)
if err != nil {
return
}
}
n, err := buf.Write(msg.Piece)
if err != nil {
break
}
if n != len(msg.Piece) {
panic(n)
}
case Extended:
err = buf.WriteByte(msg.ExtendedID)
if err != nil {
return
}
_, err = buf.Write(msg.ExtendedPayload)
case Port:
err = binary.Write(buf, binary.BigEndian, msg.Port)
default:
err = fmt.Errorf("unknown message type: %v", msg.Type)
}
}
data = make([]byte, 4+buf.Len())
binary.BigEndian.PutUint32(data, uint32(buf.Len()))
if buf.Len() != copy(data[4:], buf.Bytes()) {
panic("bad copy")
}
return
}
type Decoder struct {
R *bufio.Reader
MaxLength Integer // TODO: Should this include the length header or not?
}
// io.EOF is returned if the source terminates cleanly on a message boundary.
func (d *Decoder) Decode(msg *Message) (err error) {
var length Integer
err = binary.Read(d.R, binary.BigEndian, &length)
if err != nil {
if err != io.EOF {
err = fmt.Errorf("error reading message length: %s", err)
}
return
}
if length > d.MaxLength {
return errors.New("message too long")
}
if length == 0 {
msg.Keepalive = true
return
}
msg.Keepalive = false
b := make([]byte, length)
_, err = io.ReadFull(d.R, b)
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
if err != io.ErrUnexpectedEOF {
err = fmt.Errorf("error reading message: %s", err)
}
return
}
r := bytes.NewReader(b)
// Check that all of r was utilized.
defer func() {
if err != nil {
return
}
if r.Len() != 0 {
err = fmt.Errorf("%d bytes unused in message type %d", r.Len(), msg.Type)
}
}()
msg.Keepalive = false
c, err := r.ReadByte()
if err != nil {
return
}
msg.Type = MessageType(c)
switch msg.Type {
case Choke, Unchoke, Interested, NotInterested, HaveAll, HaveNone:
return
case Have:
err = msg.Index.Read(r)
case Request, Cancel, Reject:
for _, data := range []*Integer{&msg.Index, &msg.Begin, &msg.Length} {
err = data.Read(r)
if err != nil {
break
}
}
case Bitfield:
b := make([]byte, length-1)
_, err = io.ReadFull(r, b)
msg.Bitfield = unmarshalBitfield(b)
case Piece:
for _, pi := range []*Integer{&msg.Index, &msg.Begin} {
err = pi.Read(r)
if err != nil {
break
}
}
if err != nil {
break
}
msg.Piece, err = ioutil.ReadAll(r)
case Extended:
msg.ExtendedID, err = r.ReadByte()
if err != nil {
break
}
msg.ExtendedPayload, err = ioutil.ReadAll(r)
case Port:
err = binary.Read(r, binary.BigEndian, &msg.Port)
default:
err = fmt.Errorf("unknown message type %#v", c)
}
return
}
type Bytes []byte
func (b Bytes) MarshalBinary() ([]byte, error) {
return b, nil
}
func unmarshalBitfield(b []byte) (bf []bool) {
for _, c := range b {
for i := 7; i >= 0; i-- {
bf = append(bf, (c>>uint(i))&1 == 1)
}
}
return
}
func marshalBitfield(bf []bool) (b []byte) {
b = make([]byte, (len(bf)+7)/8)
for i, have := range bf {
if !have {
continue
}
c := b[i/8]
c |= 1 << uint(7-i%8)
b[i/8] = c
}
return
}