split systemops for operating systems and add linux

client/internal/routemanager/systemops_linux.go

@@ -61,6 +61,45 @@ func removeFromRouteTable(prefix netip.Prefix) error {
 	return nil
 }
 
+func existsInRouteTable(prefix netip.Prefix) (bool, error) {
+	tab, err := syscall.NetlinkRIB(syscall.RTM_GETROUTE, syscall.AF_UNSPEC)
+	if err != nil {
+		return nil, err
+	}
+	msgs, err := syscall.ParseNetlinkMessage(tab)
+	if err != nil {
+		return nil, err
+	}
+loop:
+	for _, m := range msgs {
+		switch m.Header.Type {
+		case syscall.NLMSG_DONE:
+			break loop
+		case syscall.RTM_NEWROUTE:
+			rt := (*routeInfoInMemory)(unsafe.Pointer(&m.Data[0]))
+			attrs, err := syscall.ParseNetlinkRouteAttr(&m)
+			if err != nil {
+				return nil, err
+			}
+			if rt.Family != syscall.AF_INET {
+				continue loop
+			}
+
+			for _, attr := range attrs {
+				if attr.Attr.Type == syscall.RTA_DST {
+					ip := net.IP(attr.Value)
+					mask := net.CIDRMask(int(rt.DstLen), len(attr.Value)*8)
+					cidr, _ := mask.Size()
+					if ip.String() == prefix.Addr().String() && cidr == prefix.Bits() {
+						return true, nil
+					}
+				}
+			}
+		}
+	}
+	return false, nil
+}
+
 func enableIPForwarding() error {
 	bytes, err := os.ReadFile(ipv4ForwardingPath)
 	if err != nil {