Parse torrent and fetch peers

torrent/tracker.go

@@ -0,0 +1,95 @@
+package torrent
+
+import (
+	"encoding/binary"
+	"errors"
+	"net"
+	"net/http"
+	"net/url"
+	"strconv"
+
+	"github.com/jackpal/bencode-go"
+)
+
+// Tracker tracker
+type Tracker struct {
+	PeerID  []byte
+	Torrent *Torrent
+	Port    uint16
+}
+
+// TrackerResponse t
+type TrackerResponse struct {
+	Interval int    `bencode:"interval"`
+	Peers    string `bencode:"port"`
+}
+
+// Peer p
+type Peer struct {
+	IP   net.IP
+	Port uint16
+}
+
+func parsePeers(peersBin string) ([]Peer, error) {
+	peerSize := 6 // 4 for IP, 2 for port
+	numPeers := len(peersBin) / peerSize
+	if len(peersBin)%peerSize != 0 {
+		err := errors.New("Received malformed peers")
+		return nil, err
+	}
+	peers := make([]Peer, numPeers)
+	for i := 0; i < numPeers; i++ {
+		offset := i * peerSize
+		peers[i].IP = net.IP(peersBin[offset : offset+4])
+		peers[i].Port = binary.BigEndian.Uint16([]byte(peersBin[offset+4 : offset+6]))
+	}
+	return peers, nil
+}
+
+func (tr *Tracker) buildTrackerURL() (string, error) {
+	base, err := url.Parse(tr.Torrent.Announce)
+	if err != nil {
+		return "", err
+	}
+	infoHash, err := tr.Torrent.Info.hash()
+	if err != nil {
+		return "", err
+	}
+	params := url.Values{
+		"info_hash":  []string{string(infoHash)},
+		"peer_id":    []string{string(tr.PeerID)},
+		"port":       []string{strconv.Itoa(int(tr.Port))},
+		"uploaded":   []string{"0"},
+		"downloaded": []string{"0"},
+		"compact":    []string{"1"},
+		"left":       []string{strconv.Itoa(tr.Torrent.Info.Length)},
+	}
+	base.RawQuery = params.Encode()
+	return base.String(), nil
+}
+
+func (tr *Tracker) getPeers() ([]Peer, error) {
+	url, err := tr.buildTrackerURL()
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	trackerResp := TrackerResponse{}
+	err = bencode.Unmarshal(resp.Body, &trackerResp)
+	if err != nil {
+		return nil, err
+	}
+
+	peers, err := parsePeers(trackerResp.Peers)
+	if err != nil {
+		return nil, err
+	}
+
+	return peers, nil
+}