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package main
import (
"bytes"
"encoding/binary"
"encoding/hex"
"fmt"
"io"
"log/slog"
"net"
"net/http"
"net/url"
"os"
"strconv"
bencode "github.com/jackpal/bencode-go"
)
type Client struct {
PeerId string
Port int
Torrents map[string]ClientTorrent
}
type ClientTorrent struct {
Meta Meta
Uploaded int
Downloaded int
Left int
}
type PeerResponse struct {
Interval int
Peers []string
}
type HandshakeMessage []byte
func NewClient(peerId string, port int) *Client {
return &Client{
PeerId: peerId,
Port: port,
Torrents: make(map[string]ClientTorrent),
}
}
func (c *Client) AddTorrentFile(filename string) (ClientTorrent, error) {
f, err := os.Open(filename)
defer func(f *os.File) {
err := f.Close()
if err != nil {
slog.Error("Failed to close file", "filename", filename)
}
}(f)
if err != nil {
fmt.Println("Failed to open file: ", os.Args[2])
}
var meta Meta
if err = bencode.Unmarshal(f, &meta); err != nil {
return ClientTorrent{}, err
}
t := ClientTorrent{
Meta: meta,
Uploaded: 0,
Downloaded: 0,
Left: meta.Info.Length,
}
c.Torrents[filename] = t
return t, nil
}
func (ct ClientTorrent) getUrl(c Client) (string, error) {
u, err := url.Parse(ct.Meta.Announce)
if err != nil {
return "", err
}
q := u.Query()
infoHash, err := ct.Meta.InfoHash()
if err != nil {
return "", err
}
q.Set("info_hash", string(infoHash))
q.Set("peer_id", c.PeerId)
q.Set("port", strconv.Itoa(c.Port))
q.Set("uploaded", strconv.Itoa(ct.Uploaded))
q.Set("downloaded", strconv.Itoa(ct.Downloaded))
q.Set("left", strconv.Itoa(ct.Left))
q.Set("compact", "1")
u.RawQuery = q.Encode()
return u.String(), nil
}
func DecodePeers(b []byte) []string {
val := make([]string, 0, len(b)/6)
for i := 0; i < len(b); i += 6 {
val = append(val, fmt.Sprintf("%d.%d.%d.%d:%d", b[i], b[i+1], b[i+2], b[i+3], binary.BigEndian.Uint16(b[i+4:i+6])))
}
return val
}
func (c *Client) GetPeers(filename string) (PeerResponse, error) {
ct, ok := c.Torrents[filename]
if !ok {
return PeerResponse{}, fmt.Errorf("missing file from client: %s", filename)
}
u, err := ct.getUrl(*c)
if err != nil {
return PeerResponse{}, err
}
getResp, err := http.Get(u)
if err != nil {
return PeerResponse{}, err
}
var resp struct {
Interval int
Peers string
}
err = bencode.Unmarshal(getResp.Body, &resp)
if err != nil {
return PeerResponse{}, err
}
return PeerResponse{
Interval: resp.Interval,
Peers: DecodePeers([]byte(resp.Peers)),
}, err
}
func (m HandshakeMessage) PeerIdHex() string {
return hex.EncodeToString(m[48:])
}
func (c *Client) Handshake(filename, peerAddr string) (HandshakeMessage, error) {
ct, ok := c.Torrents[filename]
if !ok {
return nil, fmt.Errorf("missing torrent file: %s", filename)
}
buf := new(bytes.Buffer)
buf.WriteByte(19)
buf.WriteString("BitTorrent protocol")
buf.Write([]byte{0, 0, 0, 0, 0, 0, 0, 0})
hash, err := ct.Meta.InfoHash()
if err != nil {
return nil, err
}
buf.Write(hash)
buf.WriteString(c.PeerId)
conn, err := net.Dial("tcp", peerAddr)
defer func(conn net.Conn) {
err := conn.Close()
if err != nil {
slog.Error("failed to close connection", "peerAddr", peerAddr)
}
}(conn)
if err != nil {
return nil, err
}
_, err = buf.WriteTo(conn)
if err != nil {
return nil, err
}
respBuf := make([]byte, 68)
_, err = io.LimitReader(conn, 68).Read(respBuf)
return respBuf, nil
}
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