package peer_protocol import ( "bufio" "encoding/binary" "fmt" "io" "sync" "github.com/pkg/errors" ) type Decoder struct { R *bufio.Reader Pool *sync.Pool 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 = length.Read(d.R) if err != nil { return fmt.Errorf("reading message length: %w", err) } if length > d.MaxLength { return errors.New("message too long") } if length == 0 { msg.Keepalive = true return } r := d.R readByte := func() (byte, error) { length-- return d.R.ReadByte() } c, err := readByte() if err != nil { return } msg.Type = MessageType(c) switch msg.Type { case Choke, Unchoke, Interested, NotInterested, HaveAll, HaveNone: case Have, AllowedFast, Suggest: length -= 4 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 } } length -= 12 case Bitfield: b := make([]byte, length) _, err = io.ReadFull(r, b) length = 0 msg.Bitfield = unmarshalBitfield(b) case Piece: for _, pi := range []*Integer{&msg.Index, &msg.Begin} { err := pi.Read(r) if err != nil { return err } } length -= 8 dataLen := int64(length) msg.Piece = (*d.Pool.Get().(*[]byte)) if int64(cap(msg.Piece)) < dataLen { return errors.New("piece data longer than expected") } msg.Piece = msg.Piece[:dataLen] _, err := io.ReadFull(r, msg.Piece) if err != nil { return fmt.Errorf("reading piece data: %w", err) } length = 0 case Extended: var b byte b, err = readByte() if err != nil { break } msg.ExtendedID = ExtensionNumber(b) msg.ExtendedPayload = make([]byte, length) _, err = io.ReadFull(r, msg.ExtendedPayload) if err == io.EOF { err = io.ErrUnexpectedEOF } length = 0 case Port: err = binary.Read(r, binary.BigEndian, &msg.Port) length -= 2 default: err = fmt.Errorf("unknown message type %#v", c) } if err == nil && length != 0 { err = fmt.Errorf("%v unused bytes in message type %v", length, msg.Type) } return } func readByte(r io.Reader) (b byte, err error) { var arr [1]byte n, err := r.Read(arr[:]) b = arr[0] if n == 1 { err = nil return } if err == nil { panic(err) } return } 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 }