1 files changed, 238 insertions, 0 deletions
diff --git a/pkg/p2p/network.go b/pkg/p2p/network.go
new file mode 100644
index 0000000..3362b4a
--- /dev/null
+++ b/pkg/p2p/network.go
@@ -0,0 +1,238 @@
+package p2p
+
+import (
+	"bufio"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"sync"
+	"time"
+
+	"go.uber.org/zap"
+)
+
+// `Message` represents a structured message on this network.
+type Message struct {
+	Timestamp int64  `json:"timestamp"`
+	Source    string `json:"source"`
+	Payload   []byte `json:"payload"`
+}
+
+// A network ID is represented by a string
+type NetworkID string
+
+// This type represents the function that is called every time a new message
+// arrives to the server.
+type NetworkMessageReceiveFunc func(msg Message)
+
+// This type represent the callback function invokes every new handshake between
+// two peers
+type NetworkHandshakeFunc func() error
+
+func DefaultHandshake() error {
+	return nil
+}
+
+// Network options to define on new `TCPNetwork`
+type TCPNetworkOpts struct {
+	ListenAddr  string
+	RetryDelay  time.Duration
+	HandshakeFn NetworkHandshakeFunc
+	OnReceiveFn NetworkMessageReceiveFunc
+	Logger      *zap.Logger
+}
+
+// TCPNetwork represents a full-duplex TCP peer.
+type TCPNetwork struct {
+	sync.Mutex
+	TCPNetworkOpts
+
+	id          NetworkID
+	listener    net.Listener
+	connections map[NetworkID]net.Conn
+}
+
+// Initiliaze a new TCP network
+func NewTCPNetwork(localID NetworkID, opts TCPNetworkOpts) *TCPNetwork {
+	n := &TCPNetwork{
+		TCPNetworkOpts: opts,
+		id:             localID,
+		connections:    make(map[NetworkID]net.Conn),
+	}
+
+	go n.startServer()
+
+	return n
+}
+
+// Close listener' connection
+func (n *TCPNetwork) Close() error {
+	return n.listener.Close()
+}
+
+// Add a new peer connection to the local peer
+func (n *TCPNetwork) AddPeer(remoteID NetworkID, addr string) {
+	go n.retryConnect(remoteID, addr)
+}
+
+// Send methods is used to send a message to a specified remote peer
+func (n *TCPNetwork) Send(remoteID NetworkID, payload []byte) error {
+	n.Lock()
+	conn, exists := n.connections[remoteID]
+	n.Unlock()
+
+	if !exists {
+		return fmt.Errorf("not connected to peer %s", remoteID)
+	}
+
+	msg := Message{
+		Payload:   payload,
+		Source:    n.listener.Addr().String(),
+		Timestamp: time.Now().Unix(),
+	}
+
+	data, err := json.Marshal(msg)
+	if err != nil {
+		return fmt.Errorf("failed to marshal message: %v", err)
+	}
+
+	_, err = conn.Write(append(data, '\n'))
+	if err != nil {
+		n.Logger.Sugar().Errorf("failed to send message to %s: %v. Reconnecting...", remoteID, err)
+		n.Lock()
+		delete(n.connections, remoteID)
+		n.Unlock()
+
+		go n.retryConnect(remoteID, "")
+
+		return fmt.Errorf("failed to send message: %v", err)
+	}
+
+	return nil
+}
+
+// RegisterHandler registers a callback for a message type.
+func (n *TCPNetwork) RegisterHandler(callback NetworkMessageReceiveFunc) {
+	n.OnReceiveFn = callback
+}
+
+// startServer starts a TCP server to accept connections.
+func (n *TCPNetwork) startServer() error {
+	var err error
+
+	n.listener, err = net.Listen("tcp", n.ListenAddr)
+	if err != nil {
+		n.Logger.Sugar().Errorf("failed to start server: %v", err)
+		return err
+	}
+
+	go n.listenLoop()
+
+	n.Logger.Sugar().Infof("server started on %s\n", n.ListenAddr)
+
+	return nil
+
+}
+
+func (n *TCPNetwork) listenLoop() error {
+	for {
+		conn, err := n.listener.Accept()
+		if errors.Is(err, net.ErrClosed) {
+			n.Logger.Sugar().Errorf("connection is closed in such a way: %v\n", err)
+			return err
+		}
+
+		if err != nil {
+			n.Logger.Sugar().Errorf("failed to accept connection: %v\n", err)
+			continue
+		}
+
+		remoteAddr := conn.RemoteAddr().String()
+		n.Lock()
+		n.connections[NetworkID(remoteAddr)] = conn
+		if err := n.HandshakeFn(); err != nil {
+			n.Logger.Sugar().Errorf("error on handshaking: %v\n", err)
+			return err
+		}
+		n.Unlock()
+		n.RetryDelay = 2 * time.Second
+
+		n.Logger.Sugar().Infof("connected to remote peer %s\n", remoteAddr)
+
+		// Read loop
+		go n.listenForMessages(conn)
+	}
+}
+
+// listenForMessages listens for incoming messages.
+func (n *TCPNetwork) listenForMessages(conn net.Conn) {
+	reader := bufio.NewReader(conn)
+
+	for {
+		data, err := reader.ReadBytes('\n')
+		if err != nil {
+			n.Logger.Debug("connection lost. Reconnecting...")
+			n.Lock()
+
+			// FIXME: a better way to re-establish the connection between peer
+			for id, c := range n.connections {
+				if c == conn {
+					delete(n.connections, id)
+					go n.retryConnect(id, "")
+					break
+				}
+			}
+			n.Unlock()
+			return
+		}
+
+		var message Message
+		if err := json.Unmarshal(data, &message); err != nil {
+			n.Logger.Sugar().Errorf("failed to unmarshal message: %v\n", err)
+			continue
+		}
+
+		n.Logger.Sugar().Infof("Received message from '%s': %s", message.Source, string(message.Payload))
+
+		n.OnReceiveFn(message)
+	}
+}
+
+// retryConnect attempts to connect to a remote peer.
+func (n *TCPNetwork) retryConnect(remoteID NetworkID, addr string) {
+	for {
+		n.Lock()
+		_, exists := n.connections[remoteID]
+		n.Unlock()
+
+		if exists {
+			time.Sleep(5 * time.Second)
+			continue
+		}
+
+		conn, err := net.Dial("tcp", addr)
+
+		if err != nil {
+			n.Logger.Sugar().Errorf("failed to connect to %s: %v. Retrying in %v...", remoteID, err, n.RetryDelay)
+			time.Sleep(n.RetryDelay)
+			if n.RetryDelay < 30*time.Second {
+				n.RetryDelay *= 2
+			} else {
+				n.Lock()
+				delete(n.connections, remoteID)
+				n.Unlock()
+				n.Logger.Sugar().Infof("removed %s connection", remoteID)
+				return
+			}
+			continue
+		}
+
+		n.Lock()
+		n.connections[remoteID] = conn
+		n.Unlock()
+		n.Logger.Sugar().Infof("successfully connected to peer %s!", remoteID)
+
+		go n.listenForMessages(conn)
+	}
+}