From e3a792d50d77f6b31d145ca9cc8f9013d2488e0f Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong@windscribe.com>
Date: Wed, 3 May 2023 18:12:40 +0700
Subject: [PATCH] cmd/ctrld: start listener with no default upstream

We can have more listeners than upstreams.
---
 cmd/ctrld/dns_proxy.go | 3 +++
 cmd/ctrld/prog.go      | 3 +--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/cmd/ctrld/dns_proxy.go b/cmd/ctrld/dns_proxy.go
index f473634..af49bbf 100644
--- a/cmd/ctrld/dns_proxy.go
+++ b/cmd/ctrld/dns_proxy.go
@@ -257,6 +257,9 @@ func (p *prog) proxy(ctx context.Context, upstreams []string, failoverRcodes []i
 		return answer
 	}
 	for n, upstreamConfig := range upstreamConfigs {
+		if upstreamConfig == nil {
+			continue
+		}
 		answer := resolve(n, upstreamConfig, msg)
 		if answer == nil {
 			if serveStaleCache && staleAnswer != nil {
diff --git a/cmd/ctrld/prog.go b/cmd/ctrld/prog.go
index a170b36..f19aeda 100644
--- a/cmd/ctrld/prog.go
+++ b/cmd/ctrld/prog.go
@@ -91,8 +91,7 @@ func (p *prog) run() {
 			listenerConfig := p.cfg.Listener[listenerNum]
 			upstreamConfig := p.cfg.Upstream[listenerNum]
 			if upstreamConfig == nil {
-				mainLog.Error().Msgf("missing upstream config for: [listener.%s]", listenerNum)
-				return
+				mainLog.Warn().Msgf("no default upstream for: [listener.%s]", listenerNum)
 			}
 			addr := net.JoinHostPort(listenerConfig.IP, strconv.Itoa(listenerConfig.Port))
 			mainLog.Info().Msgf("Starting DNS server on listener.%s: %s", listenerNum, addr)