4 files changed, 200 insertions, 27 deletions
diff --git a/cmd/mybittorrent/client.go b/cmd/mybittorrent/client.go
new file mode 100644
index 0000000..f3988b6
--- /dev/null
+++ b/cmd/mybittorrent/client.go
@@ -0,0 +1,136 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"log/slog"
+	"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
+}
+
+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
+}
diff --git a/cmd/mybittorrent/file.go b/cmd/mybittorrent/file.go
deleted file mode 100644
index 498ea3f..0000000
--- a/cmd/mybittorrent/file.go
+++ /dev/null
@@ -1,13 +0,0 @@
-package main
-
-type Meta struct {
-	Announce string   `bencode:"announce"`
-	Info     FileInfo `bencode:"info"`
-}
-
-type FileInfo struct {
-	Length      int    `bencode:"length"`
-	Name        string `bencode:"name"`
-	PieceLength int    `bencode:"piece length"`
-	Pieces      string `bencode:"pieces"`
-}
diff --git a/cmd/mybittorrent/main.go b/cmd/mybittorrent/main.go
index 5eecb20..c460c35 100644
--- a/cmd/mybittorrent/main.go
+++ b/cmd/mybittorrent/main.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"crypto/sha1"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -26,31 +25,45 @@ func main() {
 		fmt.Println(string(jsonOutput))
 
 	case "info":
-		f, err := os.Open(os.Args[2])
+		c := NewClient("00112233445566778899", 6881)
+		tf, err := c.AddTorrentFile(os.Args[2])
 		if err != nil {
-			fmt.Println("Failed to open file: ", os.Args[2])
+			panic(err)
 		}
 
-		var meta Meta
-		if err = bencode.Unmarshal(f, &meta); err != nil {
+		fmt.Printf("Tracker URL: %s\n", tf.Meta.Announce)
+		fmt.Printf("Length: %d\n", tf.Meta.Info.Length)
+
+		infoHash, err := tf.Meta.InfoHash()
+		if err != nil {
 			panic(err)
 		}
 
-		fmt.Printf("Tracker URL: %s\n", meta.Announce)
-		fmt.Printf("Length: %d\n", meta.Info.Length)
+		fmt.Printf("Info Hash: %x", infoHash)
+
+		fmt.Printf("Piece Length: %d\n", tf.Meta.Info.PieceLength)
+		fmt.Println("Piece Hashes:")
+
+		for _, h := range tf.Meta.PieceHashes() {
+			fmt.Printf("%x\n", h)
+		}
 
-		sha := sha1.New()
-		if err = bencode.Marshal(sha, meta.Info); err != nil {
+	case "peers":
+		c := NewClient("00112233445566778899", 6881)
+
+		_, err := c.AddTorrentFile(os.Args[2])
+		if err != nil {
 			panic(err)
 		}
 
-		fmt.Printf("Info Hash: %x", sha.Sum(nil))
+		pr, err := c.GetPeers(os.Args[2])
 
-		fmt.Printf("Piece Length: %d\n", meta.Info.PieceLength)
-		fmt.Println("Piece Hashes:")
+		if err != nil {
+			panic(err)
+		}
 
-		for i := 0; i < len(meta.Info.Pieces); i += 20 {
-			fmt.Printf("%x\n", meta.Info.Pieces[i:i+20])
+		for _, peer := range pr.Peers {
+			fmt.Println(peer)
 		}
 
 	default:
diff --git a/cmd/mybittorrent/meta.go b/cmd/mybittorrent/meta.go
new file mode 100644
index 0000000..34369c4
--- /dev/null
+++ b/cmd/mybittorrent/meta.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"crypto/sha1"
+
+	bencode "github.com/jackpal/bencode-go"
+)
+
+type Meta struct {
+	Announce string   `bencode:"announce"`
+	Info     FileInfo `bencode:"info"`
+}
+
+type FileInfo struct {
+	Length      int    `bencode:"length"`
+	Name        string `bencode:"name"`
+	PieceLength int    `bencode:"piece length"`
+	Pieces      string `bencode:"pieces"`
+}
+
+func (m Meta) InfoHash() ([]byte, error) {
+	sha := sha1.New()
+	if err := bencode.Marshal(sha, m.Info); err != nil {
+		return nil, err
+	}
+
+	return sha.Sum(nil), nil
+}
+
+func (m Meta) PieceHashes() []string {
+	hashes := make([]string, 0, len(m.Info.Pieces)/20)
+	for i := 0; i < len(m.Info.Pieces); i += 20 {
+		hashes = append(hashes, m.Info.Pieces[i:i+20])
+	}
+
+	return hashes
+}