18 func (i *Integer) Read(r io.Reader) error {
19 return binary.Read(r, binary.BigEndian, i)
23 Protocol = "\x13BitTorrent protocol"
27 Choke MessageType = iota
38 HandshakeExtendedID = 0
44 Index, Begin, Length Integer
48 ExtendedPayload []byte
51 func (msg Message) MarshalBinary() (data []byte, err error) {
52 buf := &bytes.Buffer{}
54 err = buf.WriteByte(byte(msg.Type))
59 case Choke, Unchoke, Interested, NotInterested:
61 err = binary.Write(buf, binary.BigEndian, msg.Index)
63 for _, i := range []Integer{msg.Index, msg.Begin, msg.Length} {
64 err = binary.Write(buf, binary.BigEndian, i)
70 _, err = buf.Write(marshalBitfield(msg.Bitfield))
72 for _, i := range []Integer{msg.Index, msg.Begin} {
73 err = binary.Write(buf, binary.BigEndian, i)
78 n, err := buf.Write(msg.Piece)
82 if n != len(msg.Piece) {
86 err = buf.WriteByte(msg.ExtendedID)
90 _, err = buf.Write(msg.ExtendedPayload)
92 err = fmt.Errorf("unknown message type: %v", msg.Type)
95 data = make([]byte, 4+buf.Len())
96 binary.BigEndian.PutUint32(data, uint32(buf.Len()))
97 if buf.Len() != copy(data[4:], buf.Bytes()) {
103 type Decoder struct {
105 MaxLength Integer // TODO: Should this include the length header or not?
108 func (d *Decoder) Decode(msg *Message) (err error) {
110 err = binary.Read(d.R, binary.BigEndian, &length)
114 if length > d.MaxLength {
115 return errors.New("message too long")
121 msg.Keepalive = false
122 b := make([]byte, length)
123 _, err = io.ReadFull(d.R, b)
125 err = io.ErrUnexpectedEOF
131 r := bytes.NewReader(b)
133 written, _ := io.Copy(ioutil.Discard, r)
134 if written != 0 && err == nil {
135 err = fmt.Errorf("short read on message type %d, left %d bytes", msg.Type, written)
136 } else if err == io.EOF {
137 err = io.ErrUnexpectedEOF
140 msg.Keepalive = false
141 c, err := r.ReadByte()
145 msg.Type = MessageType(c)
147 case Choke, Unchoke, Interested, NotInterested:
150 err = msg.Index.Read(r)
151 case Request, Cancel:
152 for _, data := range []*Integer{&msg.Index, &msg.Begin, &msg.Length} {
159 b := make([]byte, length-1)
160 _, err = io.ReadFull(r, b)
161 msg.Bitfield = unmarshalBitfield(b)
163 for _, pi := range []*Integer{&msg.Index, &msg.Begin} {
172 msg.Piece, err = ioutil.ReadAll(r)
174 msg.ExtendedID, err = r.ReadByte()
178 msg.ExtendedPayload, err = ioutil.ReadAll(r)
180 err = fmt.Errorf("unknown message type %#v", c)
187 func (b Bytes) MarshalBinary() ([]byte, error) {
191 func unmarshalBitfield(b []byte) (bf []bool) {
192 for _, c := range b {
193 for i := 7; i >= 0; i-- {
194 bf = append(bf, (c>>uint(i))&1 == 1)
200 func marshalBitfield(bf []bool) (b []byte) {
201 b = make([]byte, (len(bf)+7)/8)
202 for i, have := range bf {
207 c |= 1 << uint(7-i%8)