From 66e2d3a40a661e3b03a93cfd681bcece33777c59 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong@windscribe.com>
Date: Tue, 12 Aug 2025 16:46:57 +0700
Subject: [PATCH] refactor: move network monitoring to separate goroutine

- Move network monitoring initialization out of serveDNS() function
- Start network monitoring in a separate goroutine during program startup
- Remove context parameter from monitorNetworkChanges() as it's not used
- Simplify serveDNS() function signature by removing unused context parameter
- Ensure network monitoring starts only once during initial run, not on reload

This change improves separation of concerns by isolating network monitoring
from DNS serving logic, and prevents potential issues with multiple
monitoring goroutines if starting multiple listeners.
---
 cmd/cli/dns_proxy.go | 10 ++--------
 cmd/cli/prog.go      |  8 +++++++-
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/cmd/cli/dns_proxy.go b/cmd/cli/dns_proxy.go
index 33012fa..6cc36c8 100644
--- a/cmd/cli/dns_proxy.go
+++ b/cmd/cli/dns_proxy.go
@@ -84,13 +84,7 @@ type upstreamForResult struct {
 	srcAddr        string
 }
 
-func (p *prog) serveDNS(mainCtx context.Context, listenerNum string) error {
-	// Start network monitoring
-	if err := p.monitorNetworkChanges(mainCtx); err != nil {
-		mainLog.Load().Error().Err(err).Msg("Failed to start network monitoring")
-		// Don't return here as we still want DNS service to run
-	}
-
+func (p *prog) serveDNS(listenerNum string) error {
 	listenerConfig := p.cfg.Listener[listenerNum]
 	// make sure ip is allocated
 	if allocErr := p.allocateIP(listenerConfig.IP); allocErr != nil {
@@ -1187,7 +1181,7 @@ func FlushDNSCache() error {
 }
 
 // monitorNetworkChanges starts monitoring for network interface changes
-func (p *prog) monitorNetworkChanges(ctx context.Context) error {
+func (p *prog) monitorNetworkChanges() error {
 	mon, err := netmon.New(func(format string, args ...any) {
 		// Always fetch the latest logger (and inject the prefix)
 		mainLog.Load().Printf("netmon: "+format, args...)
diff --git a/cmd/cli/prog.go b/cmd/cli/prog.go
index 90f403d..fd36620 100644
--- a/cmd/cli/prog.go
+++ b/cmd/cli/prog.go
@@ -533,6 +533,12 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 	for listenerNum := range p.cfg.Listener {
 		p.cfg.Listener[listenerNum].Init()
 		if !reload {
+			go func() {
+				// Start network monitoring
+				if err := p.monitorNetworkChanges(); err != nil {
+					mainLog.Load().Error().Err(err).Msg("Failed to start network monitoring")
+				}
+			}()
 			go func(listenerNum string) {
 				listenerConfig := p.cfg.Listener[listenerNum]
 				upstreamConfig := p.cfg.Upstream[listenerNum]
@@ -541,7 +547,7 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 				}
 				addr := net.JoinHostPort(listenerConfig.IP, strconv.Itoa(listenerConfig.Port))
 				mainLog.Load().Info().Msgf("starting DNS server on listener.%s: %s", listenerNum, addr)
-				if err := p.serveDNS(ctx, listenerNum); err != nil {
+				if err := p.serveDNS(listenerNum); err != nil {
 					mainLog.Load().Fatal().Err(err).Msgf("unable to start dns proxy on listener.%s", listenerNum)
 				}
 				mainLog.Load().Debug().Msgf("end of serveDNS listener.%s: %s", listenerNum, addr)