413 lines
9.8 KiB
Go
413 lines
9.8 KiB
Go
package tracker
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import (
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"context"
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"crypto/rand"
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"encoding/binary"
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"errors"
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"fmt"
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"net"
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"net/http"
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"net/url"
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"strconv"
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"strings"
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"time"
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"github.com/jackpal/bencode-go"
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"github.com/veggiedefender/torrent-client/internal/torrentfile"
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)
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type TrackerResponse struct {
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FailureReason string `bencode:"failure reason"`
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Interval int `bencode:"interval"`
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Peers string `bencode:"peers"`
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}
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type Peer struct {
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IP net.IP
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Port uint16
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}
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type AnnounceOptions struct {
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PeerID [20]byte
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Port uint16
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Uploaded int64
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Downloaded int64
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NumWant int
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Timeout time.Duration
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}
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type httpDoer interface {
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Do(req *http.Request) (*http.Response, error)
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}
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func GetPeers(ctx context.Context, tf *torrentfile.TorrentFile, opts AnnounceOptions) ([]Peer, error) {
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if tf == nil {
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return nil, errors.New("torrent metadata is nil")
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}
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return GetPeersFromURL(ctx, tf.Announce, tf, opts)
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}
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func GetPeersFromURL(ctx context.Context, announce string, tf *torrentfile.TorrentFile, opts AnnounceOptions) ([]Peer, error) {
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if tf == nil {
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return nil, errors.New("torrent metadata is nil")
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}
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opts = normalizeOptions(opts)
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announceURL, err := url.Parse(announce)
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if err != nil {
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return nil, fmt.Errorf("invalid tracker URL %q: %w", announce, err)
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}
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switch announceURL.Scheme {
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case "http", "https":
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client := &http.Client{Timeout: opts.Timeout}
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return getPeersWithClient(ctx, client, announceURL, tf, opts)
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case "udp":
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return getPeersUDP(ctx, announceURL, tf, opts)
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default:
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return nil, fmt.Errorf("unsupported tracker scheme %q (only http/https/udp are supported)", announceURL.Scheme)
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}
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}
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func getPeersWithClient(ctx context.Context, client httpDoer, announceURL *url.URL, tf *torrentfile.TorrentFile, opts AnnounceOptions) ([]Peer, error) {
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opts = normalizeOptions(opts)
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if client == nil {
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client = &http.Client{Timeout: opts.Timeout}
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}
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announceURLString, err := buildAnnounceURL(announceURL, tf, opts)
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if err != nil {
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return nil, err
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}
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req, err := http.NewRequestWithContext(ctx, http.MethodGet, announceURLString, nil)
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if err != nil {
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return nil, err
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}
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resp, err := client.Do(req)
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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return nil, fmt.Errorf("tracker returned HTTP %d", resp.StatusCode)
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}
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var tr TrackerResponse
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err = bencode.Unmarshal(resp.Body, &tr)
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if err != nil {
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return nil, err
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}
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if tr.FailureReason != "" {
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return nil, fmt.Errorf("tracker failure: %s", tr.FailureReason)
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}
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return parsePeers([]byte(tr.Peers))
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}
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func getPeersUDP(ctx context.Context, announceURL *url.URL, tf *torrentfile.TorrentFile, opts AnnounceOptions) ([]Peer, error) {
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if announceURL == nil {
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return nil, errors.New("tracker URL is nil")
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}
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if announceURL.Scheme != "udp" {
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return nil, fmt.Errorf("tracker URL scheme %q is not udp", announceURL.Scheme)
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}
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if announceURL.Host == "" {
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return nil, errors.New("tracker URL host is empty")
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}
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dialer := net.Dialer{Timeout: opts.Timeout}
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conn, err := dialer.DialContext(ctx, "udp", announceURL.Host)
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if err != nil {
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return nil, err
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}
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defer conn.Close()
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deadline := time.Now().Add(opts.Timeout)
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if ctxDeadline, ok := ctx.Deadline(); ok && ctxDeadline.Before(deadline) {
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deadline = ctxDeadline
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}
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if err := conn.SetDeadline(deadline); err != nil {
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return nil, err
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}
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connectTx, err := randomUint32()
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if err != nil {
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return nil, err
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}
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connectReq := buildUDPConnectRequest(connectTx)
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if _, err := conn.Write(connectReq[:]); err != nil {
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return nil, err
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}
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resp := make([]byte, 65535)
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n, err := conn.Read(resp)
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if err != nil {
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return nil, err
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}
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connectionID, err := parseUDPConnectResponse(resp[:n], connectTx)
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if err != nil {
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return nil, err
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}
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announceTx, err := randomUint32()
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if err != nil {
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return nil, err
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}
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key, err := randomUint32()
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if err != nil {
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return nil, err
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}
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announceReq, err := buildUDPAnnounceRequest(connectionID, announceTx, tf, opts, key)
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if err != nil {
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return nil, err
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}
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if _, err := conn.Write(announceReq); err != nil {
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return nil, err
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}
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n, err = conn.Read(resp)
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if err != nil {
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return nil, err
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}
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return parseUDPAnnounceResponse(resp[:n], announceTx)
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}
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func normalizeOptions(opts AnnounceOptions) AnnounceOptions {
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if opts.Port == 0 {
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opts.Port = 6881
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}
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if opts.NumWant <= 0 {
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opts.NumWant = 50
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}
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if opts.Timeout <= 0 {
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opts.Timeout = 10 * time.Second
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}
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return opts
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}
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func buildAnnounceURL(baseURL *url.URL, tf *torrentfile.TorrentFile, opts AnnounceOptions) (string, error) {
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if tf == nil {
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return "", errors.New("torrent metadata is nil")
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}
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if baseURL == nil {
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return "", errors.New("tracker URL is nil")
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}
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if baseURL.Scheme != "http" && baseURL.Scheme != "https" {
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return "", fmt.Errorf("unsupported tracker scheme %q (only http/https are supported)", baseURL.Scheme)
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}
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if baseURL.Host == "" {
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return "", errors.New("tracker URL host is empty")
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}
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uploaded := opts.Uploaded
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if uploaded < 0 {
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uploaded = 0
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}
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downloaded := opts.Downloaded
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if downloaded < 0 {
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downloaded = 0
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}
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left := int64(tf.Length) - downloaded
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if left < 0 {
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left = 0
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}
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parts := make([]string, 0, 10)
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if baseURL.RawQuery != "" {
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parts = append(parts, baseURL.RawQuery)
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}
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parts = append(parts,
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"info_hash="+escapeBinary(tf.InfoHash[:]),
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"peer_id="+escapeBinary(opts.PeerID[:]),
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"port="+strconv.Itoa(int(opts.Port)),
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"uploaded="+strconv.FormatInt(uploaded, 10),
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"downloaded="+strconv.FormatInt(downloaded, 10),
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"left="+strconv.FormatInt(left, 10),
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"compact=1",
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"numwant="+strconv.Itoa(opts.NumWant),
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)
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cloned := *baseURL
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cloned.RawQuery = strings.Join(parts, "&")
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return cloned.String(), nil
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}
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func buildUDPConnectRequest(transactionID uint32) [16]byte {
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var req [16]byte
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binary.BigEndian.PutUint64(req[0:8], 0x41727101980)
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binary.BigEndian.PutUint32(req[8:12], 0)
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binary.BigEndian.PutUint32(req[12:16], transactionID)
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return req
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}
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func parseUDPConnectResponse(payload []byte, expectedTransactionID uint32) (uint64, error) {
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if len(payload) < 8 {
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return 0, fmt.Errorf("udp tracker connect response too short: %d bytes", len(payload))
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}
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action := binary.BigEndian.Uint32(payload[0:4])
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transactionID := binary.BigEndian.Uint32(payload[4:8])
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if transactionID != expectedTransactionID {
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return 0, fmt.Errorf("udp tracker connect transaction mismatch: expected %d, got %d", expectedTransactionID, transactionID)
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}
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if action == 3 {
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return 0, parseUDPTrackerError(payload)
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}
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if action != 0 {
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return 0, fmt.Errorf("unexpected udp tracker connect action %d", action)
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}
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if len(payload) < 16 {
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return 0, fmt.Errorf("udp tracker connect response too short: %d bytes", len(payload))
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}
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return binary.BigEndian.Uint64(payload[8:16]), nil
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}
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func buildUDPAnnounceRequest(connectionID uint64, transactionID uint32, tf *torrentfile.TorrentFile, opts AnnounceOptions, key uint32) ([]byte, error) {
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if tf == nil {
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return nil, errors.New("torrent metadata is nil")
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}
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uploaded := opts.Uploaded
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if uploaded < 0 {
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uploaded = 0
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}
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downloaded := opts.Downloaded
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if downloaded < 0 {
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downloaded = 0
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}
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left := int64(tf.Length) - downloaded
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if left < 0 {
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left = 0
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}
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req := make([]byte, 98)
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binary.BigEndian.PutUint64(req[0:8], connectionID)
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binary.BigEndian.PutUint32(req[8:12], 1)
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binary.BigEndian.PutUint32(req[12:16], transactionID)
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copy(req[16:36], tf.InfoHash[:])
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copy(req[36:56], opts.PeerID[:])
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binary.BigEndian.PutUint64(req[56:64], uint64(downloaded))
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binary.BigEndian.PutUint64(req[64:72], uint64(left))
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binary.BigEndian.PutUint64(req[72:80], uint64(uploaded))
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binary.BigEndian.PutUint32(req[80:84], 0)
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binary.BigEndian.PutUint32(req[84:88], 0)
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binary.BigEndian.PutUint32(req[88:92], key)
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binary.BigEndian.PutUint32(req[92:96], uint32(int32(opts.NumWant)))
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binary.BigEndian.PutUint16(req[96:98], opts.Port)
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return req, nil
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}
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func parseUDPAnnounceResponse(payload []byte, expectedTransactionID uint32) ([]Peer, error) {
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if len(payload) < 8 {
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return nil, fmt.Errorf("udp tracker announce response too short: %d bytes", len(payload))
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}
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action := binary.BigEndian.Uint32(payload[0:4])
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transactionID := binary.BigEndian.Uint32(payload[4:8])
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if transactionID != expectedTransactionID {
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return nil, fmt.Errorf("udp tracker announce transaction mismatch: expected %d, got %d", expectedTransactionID, transactionID)
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}
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if action == 3 {
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return nil, parseUDPTrackerError(payload)
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}
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if action != 1 {
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return nil, fmt.Errorf("unexpected udp tracker announce action %d", action)
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}
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if len(payload) < 20 {
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return nil, fmt.Errorf("udp tracker announce response too short: %d bytes", len(payload))
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}
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return parsePeers(payload[20:])
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}
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func parseUDPTrackerError(payload []byte) error {
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if len(payload) > 8 {
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return fmt.Errorf("udp tracker failure: %s", strings.TrimSpace(string(payload[8:])))
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}
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return errors.New("udp tracker failure")
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}
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func escapeBinary(data []byte) string {
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const hex = "0123456789ABCDEF"
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var b strings.Builder
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for _, c := range data {
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if isURLUnreserved(c) {
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b.WriteByte(c)
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continue
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}
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b.WriteByte('%')
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b.WriteByte(hex[c>>4])
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b.WriteByte(hex[c&0x0F])
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}
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return b.String()
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}
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func isURLUnreserved(c byte) bool {
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switch {
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case c >= 'a' && c <= 'z':
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return true
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case c >= 'A' && c <= 'Z':
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return true
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case c >= '0' && c <= '9':
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return true
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case c == '-', c == '.', c == '_', c == '~':
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return true
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default:
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return false
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}
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}
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func parsePeers(data []byte) ([]Peer, error) {
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if len(data) == 0 {
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return []Peer{}, nil
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}
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if len(data)%6 != 0 {
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return nil, fmt.Errorf("invalid compact peers length %d", len(data))
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}
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var peers []Peer
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for i := 0; i < len(data); i += 6 {
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ip := net.IP(data[i : i+4])
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port := uint16(data[i+4])<<8 |
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uint16(data[i+5])
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peers = append(peers, Peer{
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IP: ip,
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Port: port,
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})
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}
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return peers, nil
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}
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func randomUint32() (uint32, error) {
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var b [4]byte
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if _, err := rand.Read(b[:]); err != nil {
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return 0, err
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}
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return binary.BigEndian.Uint32(b[:]), nil
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}
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