commit 941fba7a64a92c4259dc555121e84e076ed2d7f2
Author: Jesse Li <jessejesse123@gmail.com>
Date:   Sat Dec 21 23:14:33 2019 -0500

    Parse torrent and fetch peers

diff --git a/main.go b/main.go
new file mode 100644
index 0000000..350d0e6
--- /dev/null
+++ b/main.go
@@ -0,0 +1,22 @@
+package main
+
+import (
+	"log"
+	"os"
+
+	"github.com/veggiedefender/torrent-client/torrent"
+)
+
+func main() {
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	to, err := torrent.Open(file)
+	if err != nil {
+		log.Fatal(err)
+	}
+	to.Download()
+}
diff --git a/torrent/torrent.go b/torrent/torrent.go
new file mode 100644
index 0000000..3c4546a
--- /dev/null
+++ b/torrent/torrent.go
@@ -0,0 +1,65 @@
+package torrent
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/sha1"
+	"fmt"
+	"io"
+
+	"github.com/jackpal/bencode-go"
+)
+
+const port = 6881
+
+// Info info
+type Info struct {
+	Pieces      string `bencode:"pieces"`
+	PieceLength int    `bencode:"piece length"`
+	Length      int    `bencode:"length"`
+	Name        string `bencode:"name"`
+}
+
+// Torrent torrent
+type Torrent struct {
+	Announce string `bencode:"announce"`
+	Info     Info   `bencode:"info"`
+}
+
+// Download downloads a torrent
+func (to *Torrent) Download() error {
+	peerID := make([]byte, 20)
+	_, err := rand.Read(peerID)
+	if err != nil {
+		return err
+	}
+
+	tracker := Tracker{
+		PeerID:  peerID,
+		Torrent: to,
+		Port:    port,
+	}
+	peers, err := tracker.getPeers()
+	fmt.Println(peers)
+	return nil
+}
+
+// Open parses a torrent file
+func Open(r io.Reader) (*Torrent, error) {
+	to := Torrent{}
+	err := bencode.Unmarshal(r, &to)
+	if err != nil {
+		return nil, err
+	}
+	return &to, nil
+}
+
+func (i *Info) hash() ([]byte, error) {
+	var buf bytes.Buffer
+	err := bencode.Marshal(&buf, *i)
+	if err != nil {
+		return nil, err
+	}
+	h := sha1.Sum(buf.Bytes())
+	return h[:], nil
+}
diff --git a/torrent/tracker.go b/torrent/tracker.go
new file mode 100644
index 0000000..1159f19
--- /dev/null
+++ b/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
+}