enhancement: base context + errgroup; propagate cancellation; graceful shutdown

- main: add base context via signal.NotifyContext; establish errgroup and use it to supervise background tasks; convert ticker to context-aware periodicBandwidthCheck; run HTTP server under errgroup and add graceful shutdown; treat context.Canceled as normal exit
- relay: thread parent context through UDPProxyServer; add cancel func; make packet reader, workers, and cleanup tickers exit on ctx.Done; Stop cancels, closes listener and downstream UDP connections, and closes packet channel to drain workers
- proxy: drop earlier parent context hook for SNI proxy per review; rely on existing Stop() for graceful shutdown

Benefits:
- unified lifecycle and deterministic shutdown across components
- prevents leaked goroutines/tickers and closes sockets cleanly
- consolidated error handling via g.Wait(), with context cancellation treated as non-error
- sets foundation for child errgroups and future structured concurrency

relay/relay.go

@@ -1,6 +1,7 @@
 package relay
 
 import (
+	"context"
 	"bytes"
 	"encoding/binary"
 	"encoding/json"
@@ -112,6 +113,8 @@ type UDPProxyServer struct {
 	connections   sync.Map // map[string]*DestinationConn where key is destination "ip:port"
 	privateKey    wgtypes.Key
 	packetChan    chan Packet
+	ctx           context.Context
+	cancel        context.CancelFunc
 
 	// Session tracking for WireGuard peers
 	// Key format: "senderIndex:receiverIndex"
@@ -123,14 +126,17 @@ type UDPProxyServer struct {
 	ReachableAt string
 }
 
-// NewUDPProxyServer initializes the server with a buffered packet channel.
-func NewUDPProxyServer(addr, serverURL string, privateKey wgtypes.Key, reachableAt string) *UDPProxyServer {
+// NewUDPProxyServer initializes the server with a buffered packet channel and derived context.
+func NewUDPProxyServer(parentCtx context.Context, addr, serverURL string, privateKey wgtypes.Key, reachableAt string) *UDPProxyServer {
+	ctx, cancel := context.WithCancel(parentCtx)
 	return &UDPProxyServer{
 		addr:        addr,
 		serverURL:   serverURL,
 		privateKey:  privateKey,
 		packetChan:  make(chan Packet, 1000),
 		ReachableAt: reachableAt,
+		ctx:         ctx,
+		cancel:      cancel,
 	}
 }
 
@@ -177,17 +183,51 @@ func (s *UDPProxyServer) Start() error {
 }
 
 func (s *UDPProxyServer) Stop() {
-	s.conn.Close()
+	// Signal all background goroutines to stop
+	if s.cancel != nil {
+		s.cancel()
+	}
+	// Close listener to unblock reads
+	if s.conn != nil {
+		_ = s.conn.Close()
+	}
+	// Close all downstream UDP connections
+	s.connections.Range(func(key, value interface{}) bool {
+		if dc, ok := value.(*DestinationConn); ok && dc.conn != nil {
+			_ = dc.conn.Close()
+		}
+		return true
+	})
+	// Close packet channel to stop workers
+	select {
+	case <-s.ctx.Done():
+	default:
+	}
+	close(s.packetChan)
 }
 
 // readPackets continuously reads from the UDP socket and pushes packets into the channel.
 func (s *UDPProxyServer) readPackets() {
 	for {
+		// Exit promptly if context is canceled
+		select {
+		case <-s.ctx.Done():
+			return
+		default:
+		}
 		buf := bufferPool.Get().([]byte)
 		n, remoteAddr, err := s.conn.ReadFromUDP(buf)
 		if err != nil {
-			logger.Error("Error reading UDP packet: %v", err)
-			continue
+			// If we're shutting down, exit
+			select {
+			case <-s.ctx.Done():
+				bufferPool.Put(buf[:1500])
+				return
+			default:
+				logger.Error("Error reading UDP packet: %v", err)
+				bufferPool.Put(buf[:1500])
+				continue
+			}
 		}
 		s.packetChan <- Packet{data: buf[:n], remoteAddr: remoteAddr, n: n}
 	}
@@ -588,49 +628,67 @@ func (s *UDPProxyServer) handleResponses(conn *net.UDPConn, destAddr *net.UDPAdd
 // Add a cleanup method to periodically remove idle connections
 func (s *UDPProxyServer) cleanupIdleConnections() {
 	ticker := time.NewTicker(5 * time.Minute)
-	for range ticker.C {
-		now := time.Now()
-		s.connections.Range(func(key, value interface{}) bool {
-			destConn := value.(*DestinationConn)
-			if now.Sub(destConn.lastUsed) > 10*time.Minute {
-				destConn.conn.Close()
-				s.connections.Delete(key)
-			}
-			return true
-		})
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			now := time.Now()
+			s.connections.Range(func(key, value interface{}) bool {
+				destConn := value.(*DestinationConn)
+				if now.Sub(destConn.lastUsed) > 10*time.Minute {
+					destConn.conn.Close()
+					s.connections.Delete(key)
+				}
+				return true
+			})
+		case <-s.ctx.Done():
+			return
+		}
 	}
 }
 
 // New method to periodically remove idle sessions
 func (s *UDPProxyServer) cleanupIdleSessions() {
 	ticker := time.NewTicker(5 * time.Minute)
-	for range ticker.C {
-		now := time.Now()
-		s.wgSessions.Range(func(key, value interface{}) bool {
-			session := value.(*WireGuardSession)
-			if now.Sub(session.LastSeen) > 15*time.Minute {
-				s.wgSessions.Delete(key)
-				logger.Debug("Removed idle session: %s", key)
-			}
-			return true
-		})
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			now := time.Now()
+			s.wgSessions.Range(func(key, value interface{}) bool {
+				session := value.(*WireGuardSession)
+				if now.Sub(session.LastSeen) > 15*time.Minute {
+					s.wgSessions.Delete(key)
+					logger.Debug("Removed idle session: %s", key)
+				}
+				return true
+			})
+		case <-s.ctx.Done():
+			return
+		}
 	}
 }
 
 // New method to periodically remove idle proxy mappings
 func (s *UDPProxyServer) cleanupIdleProxyMappings() {
 	ticker := time.NewTicker(10 * time.Minute)
-	for range ticker.C {
-		now := time.Now()
-		s.proxyMappings.Range(func(key, value interface{}) bool {
-			mapping := value.(ProxyMapping)
-			// Remove mappings that haven't been used in 30 minutes
-			if now.Sub(mapping.LastUsed) > 30*time.Minute {
-				s.proxyMappings.Delete(key)
-				logger.Debug("Removed idle proxy mapping: %s", key)
-			}
-			return true
-		})
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			now := time.Now()
+			s.proxyMappings.Range(func(key, value interface{}) bool {
+				mapping := value.(ProxyMapping)
+				// Remove mappings that haven't been used in 30 minutes
+				if now.Sub(mapping.LastUsed) > 30*time.Minute {
+					s.proxyMappings.Delete(key)
+					logger.Debug("Removed idle proxy mapping: %s", key)
+				}
+				return true
+			})
+		case <-s.ctx.Done():
+			return
+		}
 	}
 }
 
@@ -943,23 +1001,29 @@ func (s *UDPProxyServer) tryRebuildSession(pattern *CommunicationPattern) {
 // cleanupIdleCommunicationPatterns periodically removes idle communication patterns
 func (s *UDPProxyServer) cleanupIdleCommunicationPatterns() {
 	ticker := time.NewTicker(10 * time.Minute)
-	for range ticker.C {
-		now := time.Now()
-		s.commPatterns.Range(func(key, value interface{}) bool {
-			pattern := value.(*CommunicationPattern)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			now := time.Now()
+			s.commPatterns.Range(func(key, value interface{}) bool {
+				pattern := value.(*CommunicationPattern)
 
-			// Get the most recent activity
-			lastActivity := pattern.LastFromClient
-			if pattern.LastFromDest.After(lastActivity) {
-				lastActivity = pattern.LastFromDest
-			}
+				// Get the most recent activity
+				lastActivity := pattern.LastFromClient
+				if pattern.LastFromDest.After(lastActivity) {
+					lastActivity = pattern.LastFromDest
+				}
 
-			// Remove patterns that haven't had activity in 20 minutes
-			if now.Sub(lastActivity) > 20*time.Minute {
-				s.commPatterns.Delete(key)
-				logger.Debug("Removed idle communication pattern: %s", key)
-			}
-			return true
-		})
+				// Remove patterns that haven't had activity in 20 minutes
+				if now.Sub(lastActivity) > 20*time.Minute {
+					s.commPatterns.Delete(key)
+					logger.Debug("Removed idle communication pattern: %s", key)
+				}
+				return true
+			})
+		case <-s.ctx.Done():
+			return
+		}
 	}
 }