From b3318a94b73809c228a3e06f3e14e7e5384e109b Mon Sep 17 00:00:00 2001
From: lifenjoiner <lifenjoiner@163.com>
Date: Thu, 6 Apr 2023 03:17:51 +0800
Subject: [PATCH] Try dnscrypt-proxy to resolve configured hosts when
 ignore_system_dns (#2204)

---
 dnscrypt-proxy/example-dnscrypt-proxy.toml | 10 +++++-
 dnscrypt-proxy/proxy.go                    |  2 ++
 dnscrypt-proxy/serversInfo.go              |  1 +
 dnscrypt-proxy/xtransport.go               | 39 ++++++++++++++++------
 4 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/dnscrypt-proxy/example-dnscrypt-proxy.toml b/dnscrypt-proxy/example-dnscrypt-proxy.toml
index e7214f561c..402462456e 100644
--- a/dnscrypt-proxy/example-dnscrypt-proxy.toml
+++ b/dnscrypt-proxy/example-dnscrypt-proxy.toml
@@ -258,7 +258,15 @@ cert_refresh_delay = 240
 bootstrap_resolvers = ['9.9.9.11:53', '8.8.8.8:53']
 
 
-## Always use the bootstrap resolver before the system DNS settings.
+## This is a switch for prior bootstrap resolvers.
+##
+## Most of the time, the system DNS leads to dnscrypt-proxy itself,
+## if you set up dnscrypt-proxy in the system DNS chain.
+##
+## If true, dnscrypt-proxy will directly try on its own service instead.
+## Together with bootstrap resolvers, upstream hosts will be resolved most
+## of the time.
+## The system DNS still will be a last resort, if it has been ignored.
 
 ignore_system_dns = true
 
diff --git a/dnscrypt-proxy/proxy.go b/dnscrypt-proxy/proxy.go
index d535af2583..b7edf32912 100644
--- a/dnscrypt-proxy/proxy.go
+++ b/dnscrypt-proxy/proxy.go
@@ -242,6 +242,8 @@ func (proxy *Proxy) StartProxy() {
 			dlog.Fatal(err)
 		}
 	}
+	proxy.xTransport.internalResolverReady = false
+	proxy.xTransport.internalResolvers = proxy.listenAddresses
 	liveServers, err := proxy.serversInfo.refresh(proxy)
 	if liveServers > 0 {
 		proxy.certIgnoreTimestamp = false
diff --git a/dnscrypt-proxy/serversInfo.go b/dnscrypt-proxy/serversInfo.go
index 14c1b86b70..11a02245ee 100644
--- a/dnscrypt-proxy/serversInfo.go
+++ b/dnscrypt-proxy/serversInfo.go
@@ -232,6 +232,7 @@ func (serversInfo *ServersInfo) refresh(proxy *Proxy) (int, error) {
 	for _, registeredServer := range registeredServers {
 		if err = serversInfo.refreshServer(proxy, registeredServer.name, registeredServer.stamp); err == nil {
 			liveServers++
+			proxy.xTransport.internalResolverReady = true
 		}
 	}
 	serversInfo.Lock()
diff --git a/dnscrypt-proxy/xtransport.go b/dnscrypt-proxy/xtransport.go
index 874c8d5a22..493fa0a10f 100644
--- a/dnscrypt-proxy/xtransport.go
+++ b/dnscrypt-proxy/xtransport.go
@@ -61,6 +61,8 @@ type XTransport struct {
 	timeout                  time.Duration
 	cachedIPs                CachedIPs
 	altSupport               AltSupport
+	internalResolvers        []string
+	internalResolverReady    bool
 	bootstrapResolvers       []string
 	mainProto                string
 	ignoreSystemDNS          bool
@@ -371,16 +373,17 @@ func (xTransport *XTransport) resolveUsingResolvers(
 	proto, host string,
 	resolvers []string,
 ) (ip net.IP, ttl time.Duration, err error) {
+	err = errors.New("Empty resolvers")
 	for i, resolver := range resolvers {
 		ip, ttl, err = xTransport.resolveUsingResolver(proto, host, resolver)
 		if err == nil {
 			if i > 0 {
-				dlog.Infof("Resolution succeeded with bootstrap resolver %s[%s]", proto, resolver)
+				dlog.Infof("Resolution succeeded with resolver %s[%s]", proto, resolver)
 				resolvers[0], resolvers[i] = resolvers[i], resolvers[0]
 			}
 			break
 		}
-		dlog.Infof("Unable to resolve [%s] using bootstrap resolver %s[%s]: %v", host, proto, resolver, err)
+		dlog.Infof("Unable to resolve [%s] using resolver %s[%s]: %v", host, proto, resolver, err)
 	}
 	return
 }
@@ -400,23 +403,37 @@ func (xTransport *XTransport) resolveAndUpdateCache(host string) error {
 	var foundIP net.IP
 	var ttl time.Duration
 	var err error
-	if !xTransport.ignoreSystemDNS {
+	protos := []string{"udp", "tcp"}
+	if xTransport.mainProto == "tcp" {
+		protos = []string{"tcp", "udp"}
+	}
+	if xTransport.ignoreSystemDNS {
+		if xTransport.internalResolverReady {
+			for _, proto := range protos {
+				foundIP, ttl, err = xTransport.resolveUsingResolvers(proto, host, xTransport.internalResolvers)
+				if err == nil {
+					break
+				}
+			}
+		} else {
+			err = errors.New("Service is not usable yet")
+			dlog.Noticef("%s", err)
+		}
+	} else {
 		foundIP, ttl, err = xTransport.resolveUsingSystem(host)
-	}
-	if xTransport.ignoreSystemDNS || err != nil {
-		protos := []string{"udp", "tcp"}
-		if xTransport.mainProto == "tcp" {
-			protos = []string{"tcp", "udp"}
+		if err != nil {
+			err = errors.New("System DNS is not usable yet")
+			dlog.Noticef("%s", err)
 		}
+	}
+	if err != nil {
 		for _, proto := range protos {
 			if err != nil {
 				dlog.Noticef(
-					"System DNS configuration not usable yet, exceptionally resolving [%s] using bootstrap resolvers over %s",
+					"Resolving server host [%s] using bootstrap resolvers over %s",
 					host,
 					proto,
 				)
-			} else {
-				dlog.Debugf("Resolving [%s] using bootstrap resolvers over %s", host, proto)
 			}
 			foundIP, ttl, err = xTransport.resolveUsingResolvers(proto, host, xTransport.bootstrapResolvers)
 			if err == nil {