Fix UDP conn stuck on sniff

This change only avoids permanent hangs. We need to implement read deadlines for UDP conns in 1.10 for server inbounds.

route/router.go

@@ -951,34 +951,57 @@ func (r *Router) RoutePacketConnection(ctx context.Context, conn N.PacketConn, m
 	}*/
 
 	if metadata.InboundOptions.SniffEnabled || metadata.Destination.Addr.IsUnspecified() {
-		buffer := buf.NewPacket()
-		destination, err := conn.ReadPacket(buffer)
+		var (
+			buffer      = buf.NewPacket()
+			destination M.Socksaddr
+			done        = make(chan struct{})
+			err         error
+		)
+		go func() {
+			sniffTimeout := C.ReadPayloadTimeout
+			if metadata.InboundOptions.SniffTimeout > 0 {
+				sniffTimeout = time.Duration(metadata.InboundOptions.SniffTimeout)
+			}
+			conn.SetReadDeadline(time.Now().Add(sniffTimeout))
+			destination, err = conn.ReadPacket(buffer)
+			conn.SetReadDeadline(time.Time{})
+			close(done)
+		}()
+		select {
+		case <-done:
+		case <-ctx.Done():
+			conn.Close()
+			return ctx.Err()
+		}
 		if err != nil {
 			buffer.Release()
-			return err
-		}
-		if metadata.Destination.Addr.IsUnspecified() {
-			metadata.Destination = destination
-		}
-		if metadata.InboundOptions.SniffEnabled {
-			sniffMetadata, _ := sniff.PeekPacket(ctx, buffer.Bytes(), sniff.DomainNameQuery, sniff.QUICClientHello, sniff.STUNMessage)
-			if sniffMetadata != nil {
-				metadata.Protocol = sniffMetadata.Protocol
-				metadata.Domain = sniffMetadata.Domain
-				if metadata.InboundOptions.SniffOverrideDestination && M.IsDomainName(metadata.Domain) {
-					metadata.Destination = M.Socksaddr{
-						Fqdn: metadata.Domain,
-						Port: metadata.Destination.Port,
+			if !errors.Is(err, os.ErrDeadlineExceeded) {
+				return err
+			}
+		} else {
+			if metadata.Destination.Addr.IsUnspecified() {
+				metadata.Destination = destination
+			}
+			if metadata.InboundOptions.SniffEnabled {
+				sniffMetadata, _ := sniff.PeekPacket(ctx, buffer.Bytes(), sniff.DomainNameQuery, sniff.QUICClientHello, sniff.STUNMessage)
+				if sniffMetadata != nil {
+					metadata.Protocol = sniffMetadata.Protocol
+					metadata.Domain = sniffMetadata.Domain
+					if metadata.InboundOptions.SniffOverrideDestination && M.IsDomainName(metadata.Domain) {
+						metadata.Destination = M.Socksaddr{
+							Fqdn: metadata.Domain,
+							Port: metadata.Destination.Port,
+						}
+					}
+					if metadata.Domain != "" {
+						r.logger.DebugContext(ctx, "sniffed packet protocol: ", metadata.Protocol, ", domain: ", metadata.Domain)
+					} else {
+						r.logger.DebugContext(ctx, "sniffed packet protocol: ", metadata.Protocol)
 					}
-				}
-				if metadata.Domain != "" {
-					r.logger.DebugContext(ctx, "sniffed packet protocol: ", metadata.Protocol, ", domain: ", metadata.Domain)
-				} else {
-					r.logger.DebugContext(ctx, "sniffed packet protocol: ", metadata.Protocol)
 				}
 			}
+			conn = bufio.NewCachedPacketConn(conn, buffer, destination)
 		}
-		conn = bufio.NewCachedPacketConn(conn, buffer, destination)
 	}
 	if r.dnsReverseMapping != nil && metadata.Domain == "" {
 		domain, loaded := r.dnsReverseMapping.Query(metadata.Destination.Addr)