From adf38a1dbd085c19c4c87ad242e0b340f1655fcb Mon Sep 17 00:00:00 2001
From: jet2tlf <jet2tlf@gmail.com>
Date: Mon, 3 Jun 2024 14:59:28 -0300
Subject: codecrafters submit [skip ci]

---
 cmd/mybittorrent/client.go | 54 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

(limited to 'cmd/mybittorrent/client.go')

diff --git a/cmd/mybittorrent/client.go b/cmd/mybittorrent/client.go
index f3988b6..ef3d860 100644
--- a/cmd/mybittorrent/client.go
+++ b/cmd/mybittorrent/client.go
@@ -1,9 +1,13 @@
 package main
 
 import (
+	"bytes"
 	"encoding/binary"
+	"encoding/hex"
 	"fmt"
+	"io"
 	"log/slog"
+	"net"
 	"net/http"
 	"net/url"
 	"os"
@@ -30,6 +34,8 @@ type PeerResponse struct {
 	Peers    []string
 }
 
+type HandshakeMessage []byte
+
 func NewClient(peerId string, port int) *Client {
 	return &Client{
 		PeerId:   peerId,
@@ -134,3 +140,51 @@ func (c *Client) GetPeers(filename string) (PeerResponse, error) {
 		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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