commit 15a92f508d8570f23bc6dc7d1837e26bc7b1e3fe
Author: Maciej Krzyżanowski <krzmaciek@gmail.com>
Date:   Thu Mar 21 22:36:25 2024 +0100

    Initial commit

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..46178f4
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module krzyzanowski.dev/p2pchat
+
+go 1.21.7
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..cb5bf00
--- /dev/null
+++ b/main.go
@@ -0,0 +1,291 @@
+package main
+
+import (
+	"bufio"
+	"encoding/json"
+	"io"
+	"log"
+	"net"
+	"os"
+	"sync"
+	"time"
+)
+
+type Peer struct {
+	id   int
+	conn net.Conn
+}
+
+type PeerInfo struct {
+	ID   int    `json:"id"`
+	Addr string `json:"addr"`
+}
+
+type EchoRequest struct {
+	EchoByte byte `json:"echoByte"`
+}
+
+type EchoResponse struct {
+	EchoByte byte `json:"echoByte"`
+}
+
+type ListPeersRequest struct {
+}
+
+type ListPeersResponse struct {
+	PeersInfo []PeerInfo `json:"peers"`
+}
+
+const (
+	echoRID      = 1
+	listPeersRID = 2
+)
+
+var peersList []Peer
+var peersListLock sync.RWMutex
+var idCounter int = 0
+var idCounterLock sync.Mutex
+
+func genNewID() int {
+	var newid int
+	idCounterLock.Lock()
+	idCounter++
+	newid = idCounter
+	idCounterLock.Unlock()
+	return newid
+}
+
+func peerSliceIndexOf(s []Peer, id int) int {
+	i := 0
+	var p Peer
+	for i, p = range s {
+		if p.id == id {
+			break
+		}
+	}
+	return i
+}
+
+func peerSliceRemove(s *[]Peer, i int) {
+	(*s)[i] = (*s)[len(*s)-1]
+	*s = (*s)[:len(*s)-1]
+}
+
+func handleDisconnection(id int) {
+	peersListLock.Lock()
+	p := peersList[peerSliceIndexOf(peersList, id)]
+	log.Printf("[Server] %s disconnected\n", p.conn.RemoteAddr())
+	peerSliceRemove(&peersList, peerSliceIndexOf(peersList, id))
+	peersListLock.Unlock()
+}
+
+func handlePeer(p Peer) {
+	br := bufio.NewReader(p.conn)
+	bw := bufio.NewWriter(p.conn)
+
+	for {
+		reqBytes, err := br.ReadBytes('\n')
+
+		if err == io.EOF {
+			handleDisconnection(p.id)
+			break
+		} else if err != nil {
+			log.Println(err)
+			break
+		}
+
+		if len(reqBytes) <= 1 {
+			log.Println("got request without id")
+			break
+		}
+
+		reqBytes = reqBytes[:len(reqBytes)-1]
+		operationCode := reqBytes[0]
+		reqJsonBytes := reqBytes[1:]
+		var resBytes []byte
+
+		if operationCode == echoRID {
+			resBytes, err = handleEcho(reqJsonBytes)
+		} else if operationCode == listPeersRID {
+			resBytes, err = handleListPeers(reqJsonBytes)
+		}
+
+		if err != nil {
+			log.Println(err)
+			continue
+		}
+
+		resBytes = append(resBytes, '\n')
+		_, err = bw.Write(resBytes)
+
+		if err != nil {
+			log.Println(err)
+			continue
+		}
+
+		err = bw.Flush()
+
+		if err != nil {
+			log.Println(err)
+		}
+	}
+}
+
+func handleEcho(reqBytes []byte) (resBytes []byte, err error) {
+	var echoReq EchoRequest
+	err = json.Unmarshal(reqBytes, &echoReq)
+
+	if err != nil {
+		return nil, err
+	}
+
+	echoRes := EchoResponse(echoReq)
+	resBytes, err = json.Marshal(echoRes)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return resBytes, nil
+}
+
+func handleListPeers(reqBytes []byte) (resBytes []byte, err error) {
+	// For the sake of conciseness -> currently unmarshalling empty slice to empty struct
+	var listPeersReq ListPeersRequest
+	err = json.Unmarshal(reqBytes, &listPeersReq)
+
+	if err != nil {
+		return nil, err
+	}
+
+	peersListLock.RLock()
+	peersFreeze := make([]Peer, len(peersList))
+	copy(peersFreeze, peersList)
+	peersListLock.RUnlock()
+	listPeersRes := ListPeersResponse{make([]PeerInfo, 0)}
+
+	for _, peer := range peersFreeze {
+		listPeersRes.PeersInfo = append(
+			listPeersRes.PeersInfo,
+			PeerInfo{peer.id, peer.conn.RemoteAddr().String()},
+		)
+	}
+
+	resBytes, err = json.Marshal(listPeersRes)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return resBytes, nil
+}
+
+func printConnectedPeers() {
+	peersListLock.RLock()
+	log.Println("[Server] Displaying all connections:")
+
+	for _, p := range peersList {
+		log.Printf("[Server] ID#%d: %s\n", p.id, p.conn.RemoteAddr())
+	}
+
+	peersListLock.RUnlock()
+}
+
+func runServer() {
+	ln, err := net.Listen("tcp", ":8080")
+
+	if err != nil {
+		log.Println(err)
+	}
+
+	peersList = make([]Peer, 0)
+
+	go func() {
+		for {
+			printConnectedPeers()
+			time.Sleep(time.Second * 5)
+		}
+	}()
+
+	for {
+		c, err := ln.Accept()
+
+		if err != nil {
+			log.Println(err)
+			break
+		}
+
+		log.Printf("[Server] client connected %s\n", c.RemoteAddr())
+		peersListLock.Lock()
+		np := Peer{genNewID(), c}
+		peersList = append(peersList, np)
+		peersListLock.Unlock()
+		go handlePeer(np)
+	}
+}
+
+func runClient() {
+	conn, err := net.Dial("tcp", ":8080")
+
+	if err != nil {
+		log.Println("[Client] err connecting")
+		return
+	}
+
+	defer func() {
+		_ = conn.Close()
+	}()
+
+	br := bufio.NewReader(conn)
+	bw := bufio.NewWriter(conn)
+
+	log.Println("[Client] connected to server")
+	time.Sleep(time.Second * 1)
+
+	echoReq := EchoRequest{5}
+	reqBytes, _ := json.Marshal(echoReq)
+	bw.WriteByte(echoRID)
+	bw.Write(reqBytes)
+	bw.WriteByte('\n')
+	bw.Flush()
+	resBytes, _ := br.ReadBytes('\n')
+	var echoRes EchoResponse
+	json.Unmarshal(resBytes, &echoRes)
+	log.Printf("[Client] echo sent (5), got %d\n", echoRes.EchoByte)
+
+	listReq := ListPeersRequest{}
+	reqBytes, _ = json.Marshal(listReq)
+	bw.WriteByte(listPeersRID)
+	bw.Write(reqBytes)
+	bw.WriteByte('\n')
+	bw.Flush()
+	resBytes, _ = br.ReadBytes('\n')
+	var listRes ListPeersResponse
+	json.Unmarshal(resBytes, &listRes)
+	log.Println("[Client] printing all peers:")
+
+	for _, peer := range listRes.PeersInfo {
+		log.Printf("[Client] Peer#%d from %s", peer.ID, peer.Addr)
+	}
+
+	time.Sleep(time.Second * 5)
+}
+
+func main() {
+	args := os.Args[1:]
+
+	if len(args) != 1 {
+		log.Fatalln("You must provide only one argument which is type of " +
+			"application: 'server' or 'client'")
+	}
+
+	runType := args[0]
+
+	if runType == "client" {
+		runClient()
+	} else if runType == "server" {
+		runServer()
+	} else {
+		log.Fatalf("Unknown run type %s\n", runType)
+	}
+}