119 lines
2.5 KiB
Go
119 lines
2.5 KiB
Go
package peer_protocol
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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)
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// This is a lazy union representing all the possible fields for messages. Go doesn't have ADTs, and
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// I didn't choose to use type-assertions.
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type Message struct {
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Keepalive bool
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Type MessageType
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Index, Begin, Length Integer
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Piece []byte
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Bitfield []bool
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ExtendedID ExtensionNumber
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ExtendedPayload []byte
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Port uint16
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}
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func MakeCancelMessage(piece, offset, length Integer) Message {
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return Message{
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Type: Cancel,
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Index: piece,
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Begin: offset,
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Length: length,
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}
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}
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func (msg Message) RequestSpec() (ret RequestSpec) {
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return RequestSpec{
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msg.Index,
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msg.Begin,
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func() Integer {
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if msg.Type == Piece {
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return Integer(len(msg.Piece))
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} else {
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return msg.Length
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}
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}(),
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}
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}
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func (msg Message) MustMarshalBinary() []byte {
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b, err := msg.MarshalBinary()
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if err != nil {
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panic(err)
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}
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return b
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}
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func (msg Message) MarshalBinary() (data []byte, err error) {
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buf := &bytes.Buffer{}
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if !msg.Keepalive {
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err = buf.WriteByte(byte(msg.Type))
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if err != nil {
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return
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}
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switch msg.Type {
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case Choke, Unchoke, Interested, NotInterested, HaveAll, HaveNone:
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case Have:
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err = binary.Write(buf, binary.BigEndian, msg.Index)
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case Request, Cancel, Reject:
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for _, i := range []Integer{msg.Index, msg.Begin, msg.Length} {
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err = binary.Write(buf, binary.BigEndian, i)
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if err != nil {
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break
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}
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}
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case Bitfield:
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_, err = buf.Write(marshalBitfield(msg.Bitfield))
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case Piece:
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for _, i := range []Integer{msg.Index, msg.Begin} {
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err = binary.Write(buf, binary.BigEndian, i)
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if err != nil {
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return
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}
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}
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n, err := buf.Write(msg.Piece)
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if err != nil {
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break
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}
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if n != len(msg.Piece) {
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panic(n)
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}
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case Extended:
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err = buf.WriteByte(byte(msg.ExtendedID))
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if err != nil {
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return
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}
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_, err = buf.Write(msg.ExtendedPayload)
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case Port:
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err = binary.Write(buf, binary.BigEndian, msg.Port)
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default:
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err = fmt.Errorf("unknown message type: %v", msg.Type)
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}
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}
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data = make([]byte, 4+buf.Len())
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binary.BigEndian.PutUint32(data, uint32(buf.Len()))
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if buf.Len() != copy(data[4:], buf.Bytes()) {
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panic("bad copy")
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}
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return
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}
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func marshalBitfield(bf []bool) (b []byte) {
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b = make([]byte, (len(bf)+7)/8)
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for i, have := range bf {
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if !have {
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continue
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}
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c := b[i/8]
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c |= 1 << uint(7-i%8)
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b[i/8] = c
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}
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return
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}
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