1 files changed, 181 insertions, 0 deletions
diff --git a/cmd/mybittorrent/peer.go b/cmd/mybittorrent/peer.go
new file mode 100644
index 0000000..3b40493
--- /dev/null
+++ b/cmd/mybittorrent/peer.go
@@ -0,0 +1,181 @@
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"os"
+)
+
+type HandshakeMessage []byte
+
+type Peer struct {
+	conn      net.Conn
+	handshake HandshakeMessage
+	ct        *ClientTorrent
+	msgCh     chan *IncomingMessage
+}
+
+func (p *Peer) PeerIdHexString() string {
+	return hex.EncodeToString(p.handshake[48:])
+}
+
+func (p *Peer) InfoHash() []byte {
+	return p.handshake[28:48]
+}
+
+func (p *Peer) Close() error {
+	err := p.conn.Close()
+	if err != nil {
+		return errors.Join(fmt.Errorf("failed to close peer connection: %s", p.conn.RemoteAddr()), err)
+	}
+
+	return nil
+}
+
+func (p *Peer) DownloadPiece(outFile string, index int) error {
+	if index >= p.ct.Meta.PieceCount() {
+		return nil
+	}
+
+	var data = new(bytes.Buffer)
+	blockLens := p.ct.Meta.BlockLens(index)
+	var blockIndex = 0
+
+	requestFn := func() error {
+		if blockIndex == len(blockLens) {
+			return nil
+		}
+
+		r := RequestPayload{
+			Index:  uint32(index),
+			Begin:  uint32(blockIndex * BlockSize),
+			Length: blockLens[blockIndex],
+		}
+
+		return p.WriteMessage(MessageTypeRequest, r.Bytes())
+	}
+
+	for {
+		if blockIndex == len(blockLens) {
+			break
+		}
+
+		msg, err := p.ReadMessage()
+		if err != nil {
+			return err
+		}
+
+		switch msg.MessageType {
+		case MessageTypeBitfield:
+			if err != nil {
+				return err
+			}
+
+			err = p.WriteMessage(MessageTypeInterested, nil)
+			if err != nil {
+				return err
+			}
+
+		case MessageTypeUnchoke:
+			if err = requestFn(); err != nil {
+				return err
+			}
+
+		case MessageTypePiece:
+			var block BlockPayload
+
+			_, err = block.Write(msg.Payload)
+			if err != nil {
+				return err
+			}
+
+			_, err = data.Write(block.Block)
+			if err != nil {
+				return err
+			}
+
+			blockIndex++
+
+			if err = requestFn(); err != nil {
+				return err
+			}
+
+		default:
+			return fmt.Errorf("unimplemented message type: %d", msg.MessageType)
+		}
+	}
+
+	if !p.ct.Meta.CheckHash(index, data.Bytes()) {
+		return fmt.Errorf("invalid hash value")
+	}
+
+	out, err := os.Create(outFile)
+	if err != nil {
+		return errors.Join(fmt.Errorf("failed to create file"), err)
+	}
+
+	_, err = out.Write(data.Bytes())
+	if err != nil {
+		return errors.Join(fmt.Errorf("failed to write file"), err)
+	}
+
+	err = out.Close()
+	if err != nil {
+		return errors.Join(fmt.Errorf("failed to close file"), err)
+	}
+
+	return nil
+}
+
+func (p *Peer) ReadMessage() (*IncomingMessage, error) {
+	lenBuf := make([]byte, 4)
+
+	_, err := p.conn.Read(lenBuf)
+	if err != nil {
+		return nil, errors.Join(fmt.Errorf("failed to read message length"), err)
+	}
+
+	msgLen := binary.BigEndian.Uint32(lenBuf) - 1
+	typeBuf := make([]byte, 1)
+
+	_, err = p.conn.Read(typeBuf)
+	if err != nil {
+		return nil, errors.Join(fmt.Errorf("failed to read message type"), err)
+	}
+
+	msgType := MessageType(typeBuf[0])
+	if msgLen == 0 {
+		return &IncomingMessage{
+			Len:         msgLen,
+			MessageType: msgType,
+		}, nil
+	}
+
+	payloadBuf := make([]byte, msgLen)
+
+	_, err = io.ReadFull(p.conn, payloadBuf)
+	if err != nil {
+		return nil, errors.Join(fmt.Errorf("failed to read message payload"), err)
+	}
+
+	return &IncomingMessage{
+		Len:         msgLen,
+		MessageType: msgType,
+		Payload:     payloadBuf,
+	}, nil
+}
+
+func (p *Peer) WriteMessage(t MessageType, payload []byte) error {
+	msg := &OutgoingMessage{
+		MessageType: t,
+		Writer:      p.conn,
+	}
+
+	_, err := msg.Write(payload)
+	return err
+}