feat: sniff_override_fallback

docs/configuration/shared/listen.md

@@ -8,6 +8,7 @@
   "udp_fragment": false,
   "sniff": false,
   "sniff_override_destination": false,
+  "sniff_override_fallback": false,
   "sniff_timeout": "300ms",
   "domain_strategy": "prefer_ipv6",
   "udp_timeout": 300,
@@ -58,6 +59,12 @@ Override the connection destination address with the sniffed domain.
 
 If the domain name is invalid (like tor), this will not work.
 
+#### sniff_override_fallback
+
+If the sniffed domain fails to be resolved when `sniff_override_destination` is enabled, use the original destination address as fallback.
+
+Helpful when using customized domain.
+
 #### sniff_timeout
 
 Timeout for sniffing.

docs/configuration/shared/listen.zh.md

@@ -8,6 +8,7 @@
   "udp_fragment": false,
   "sniff": false,
   "sniff_override_destination": false,
+  "sniff_override_fallback": false,
   "sniff_timeout": "300ms",
   "domain_strategy": "prefer_ipv6",
   "udp_timeout": 300,
@@ -59,6 +60,12 @@
 
 如果域名无效（如 Tor），将不生效。
 
+#### sniff_override_fallback
+
+当 `sniff_override_destination` 开启且探测出的域名解析失败时，回退使用原连接目标地址。
+
+当使用自定义域名时有帮助。
+
 #### sniff_timeout
 
 探测超时时间。

option/inbound.go

@@ -112,6 +112,7 @@ func (h *Inbound) UnmarshalJSON(bytes []byte) error {
 type InboundOptions struct {
 	SniffEnabled             bool           `json:"sniff,omitempty"`
 	SniffOverrideDestination bool           `json:"sniff_override_destination,omitempty"`
+	SniffOverrideFallback    bool           `json:"sniff_override_fallback,omitempty"`
 	SniffTimeout             Duration       `json:"sniff_timeout,omitempty"`
 	DomainStrategy           DomainStrategy `json:"domain_strategy,omitempty"`
 }

route/router.go

@@ -645,6 +645,9 @@ func (r *Router) RouteConnection(ctx context.Context, conn net.Conn, metadata ad
 			metadata.Protocol = sniffMetadata.Protocol
 			metadata.Domain = sniffMetadata.Domain
 			if metadata.InboundOptions.SniffOverrideDestination && M.IsDomainName(metadata.Domain) {
+				if metadata.InboundOptions.SniffOverrideFallback && metadata.Destination.Addr.IsValid() {
+					metadata.DestinationAddresses = []netip.Addr{metadata.Destination.Addr}
+				}
 				metadata.Destination = M.Socksaddr{
 					Fqdn: metadata.Domain,
 					Port: metadata.Destination.Port,
@@ -676,10 +679,14 @@ func (r *Router) RouteConnection(ctx context.Context, conn net.Conn, metadata ad
 	if metadata.Destination.IsFqdn() && dns.DomainStrategy(metadata.InboundOptions.DomainStrategy) != dns.DomainStrategyAsIS {
 		addresses, err := r.Lookup(adapter.WithContext(ctx, &metadata), metadata.Destination.Fqdn, dns.DomainStrategy(metadata.InboundOptions.DomainStrategy))
 		if err != nil {
-			return err
+			if len(metadata.DestinationAddresses) == 0 {
+				return err
+			}
+			r.logger.WarnContext(ctx, "using original destination [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
+		} else {
+			metadata.DestinationAddresses = addresses
+			r.dnsLogger.DebugContext(ctx, "resolved [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
 		}
-		metadata.DestinationAddresses = addresses
-		r.dnsLogger.DebugContext(ctx, "resolved [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
 	}
 	ctx, matchedRule, detour, err := r.match(ctx, &metadata, r.defaultOutboundForConnection)
 	if err != nil {
@@ -784,10 +791,14 @@ func (r *Router) RoutePacketConnection(ctx context.Context, conn N.PacketConn, m
 	if metadata.Destination.IsFqdn() && dns.DomainStrategy(metadata.InboundOptions.DomainStrategy) != dns.DomainStrategyAsIS {
 		addresses, err := r.Lookup(adapter.WithContext(ctx, &metadata), metadata.Destination.Fqdn, dns.DomainStrategy(metadata.InboundOptions.DomainStrategy))
 		if err != nil {
-			return err
+			if len(metadata.DestinationAddresses) == 0 {
+				return err
+			}
+			r.logger.WarnContext(ctx, "using original destination [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
+		} else {
+			metadata.DestinationAddresses = addresses
+			r.dnsLogger.DebugContext(ctx, "resolved [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
 		}
-		metadata.DestinationAddresses = addresses
-		r.dnsLogger.DebugContext(ctx, "resolved [", strings.Join(F.MapToString(metadata.DestinationAddresses), " "), "]")
 	}
 	ctx, matchedRule, detour, err := r.match(ctx, &metadata, r.defaultOutboundForPacketConnection)
 	if err != nil {