From ec0fa4781f9747adf8e3c167b642062de2530d41 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Sun, 23 Jul 2023 14:40:59 +0800
Subject: [PATCH] Improve fake-ip dual stack behavior

---
 route/router.go     |  2 ++
 route/router_dns.go | 20 ++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/route/router.go b/route/router.go
index c23c8a458e..125993c8e6 100644
--- a/route/router.go
+++ b/route/router.go
@@ -69,6 +69,7 @@ type Router struct {
 	transportDomainStrategy            map[dns.Transport]dns.DomainStrategy
 	dnsReverseMapping                  *DNSReverseMapping
 	fakeIPStore                        adapter.FakeIPStore
+	fakeIPDualStack                    bool
 	interfaceFinder                    myInterfaceFinder
 	autoDetectInterface                bool
 	defaultInterface                   string
@@ -253,6 +254,7 @@ func NewRouter(
 			inet6Range = fakeIPOptions.Inet6Range.Build()
 		}
 		router.fakeIPStore = fakeip.NewStore(router, router.logger, inet4Range, inet6Range)
+		router.fakeIPDualStack = inet4Range.IsValid() && inet6Range.IsValid()
 	}
 
 	usePlatformDefaultInterfaceMonitor := platformInterface != nil && platformInterface.UsePlatformDefaultInterfaceMonitor()
diff --git a/route/router_dns.go b/route/router_dns.go
index 0fe3735287..5d5682310a 100644
--- a/route/router_dns.go
+++ b/route/router_dns.go
@@ -63,14 +63,14 @@ func (r *Router) matchDNS(ctx context.Context) (context.Context, dns.Transport,
 			if domainStrategy, dsLoaded := r.transportDomainStrategy[transport]; dsLoaded {
 				return ctx, transport, domainStrategy
 			} else {
-				return ctx, transport, r.defaultDomainStrategy
+				return ctx, transport, dns.DomainStrategyAsIS
 			}
 		}
 	}
 	if domainStrategy, dsLoaded := r.transportDomainStrategy[r.defaultTransport]; dsLoaded {
 		return ctx, r.defaultTransport, domainStrategy
 	} else {
-		return ctx, r.defaultTransport, r.defaultDomainStrategy
+		return ctx, r.defaultTransport, dns.DomainStrategyAsIS
 	}
 }
 
@@ -128,6 +128,22 @@ func (r *Router) Lookup(ctx context.Context, domain string, strategy dns.DomainS
 	if strategy == dns.DomainStrategyAsIS {
 		strategy = transportStrategy
 	}
+	if strategy == dns.DomainStrategyAsIS {
+		switch r.defaultDomainStrategy {
+		case dns.DomainStrategyUseIPv4, dns.DomainStrategyUseIPv6:
+			strategy = r.defaultDomainStrategy
+		}
+	}
+	if strategy == dns.DomainStrategyAsIS && metadata.FakeIP && r.fakeIPDualStack {
+		if metadata.IPVersion == 4 {
+			strategy = dns.DomainStrategyUseIPv4
+		} else if metadata.IPVersion == 6 {
+			strategy = dns.DomainStrategyPreferIPv6
+		}
+	}
+	if strategy == dns.DomainStrategyAsIS {
+		strategy = r.defaultDomainStrategy
+	}
 	ctx, cancel := context.WithTimeout(ctx, C.DNSTimeout)
 	defer cancel()
 	addrs, err := r.dnsClient.Lookup(ctx, transport, domain, strategy)