From 7801dcd8497d26aa5b83315550fc34ef3f220a57 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Thu, 27 Aug 2015 11:58:48 +0100
Subject: [PATCH] Factor out common loop receiving from netlink

---
 net/if.go    | 47 ++++++++++++++++++++++++++++-------------------
 net/route.go | 49 ++++++++++++++++++++++---------------------------
 2 files changed, 50 insertions(+), 46 deletions(-)

diff --git a/net/if.go b/net/if.go
index 8270bcec..b99993ec 100644
--- a/net/if.go
+++ b/net/if.go
@@ -26,7 +26,7 @@ func ensureInterface(s *nl.NetlinkSocket, ifaceName string) (*net.Interface, err
 	if iface, err := findInterface(ifaceName); err == nil {
 		return iface, nil
 	}
-	waitForIfUp(s, ifaceName)
+	netlinkReceiveUntil(s, matchIfName(ifaceName))
 	iface, err := findInterface(ifaceName)
 	return iface, err
 }
@@ -48,7 +48,7 @@ func EnsureInterfaceAndMcastRoute(ifaceName string) (*net.Interface, error) {
 	if CheckRouteExists(ifaceName, dest) {
 		return iface, err
 	}
-	waitForRoute(s, ifaceName, dest)
+	netlinkReceiveUntil(s, matchRoute(ifaceName, dest))
 	return iface, err
 }
 
@@ -62,30 +62,39 @@ func findInterface(ifaceName string) (iface *net.Interface, err error) {
 	return
 }
 
-func waitForIfUp(s *nl.NetlinkSocket, ifaceName string) error {
+func netlinkReceiveUntil(s *nl.NetlinkSocket, f func(syscall.NetlinkMessage) (bool, error)) error {
 	for {
 		msgs, err := s.Receive()
 		if err != nil {
 			return err
 		}
 		for _, m := range msgs {
-			switch m.Header.Type {
-			case syscall.RTM_NEWLINK: // receive this type for link 'up'
-				ifmsg := nl.DeserializeIfInfomsg(m.Data)
-				attrs, err := syscall.ParseNetlinkRouteAttr(&m)
-				if err != nil {
-					return err
-				}
-				name := ""
-				for _, attr := range attrs {
-					if attr.Attr.Type == syscall.IFA_LABEL {
-						name = string(attr.Value[:len(attr.Value)-1])
-					}
-				}
-				if ifaceName == name && ifmsg.Flags&syscall.IFF_UP != 0 {
-					return nil
-				}
+			if done, err := f(m); done {
+				return err
 			}
 		}
 	}
 }
+
+func matchIfName(ifaceName string) func(m syscall.NetlinkMessage) (bool, error) {
+	return func(m syscall.NetlinkMessage) (bool, error) {
+		switch m.Header.Type {
+		case syscall.RTM_NEWLINK: // receive this type for link 'up'
+			ifmsg := nl.DeserializeIfInfomsg(m.Data)
+			attrs, err := syscall.ParseNetlinkRouteAttr(&m)
+			if err != nil {
+				return true, err
+			}
+			name := ""
+			for _, attr := range attrs {
+				if attr.Attr.Type == syscall.IFA_LABEL {
+					name = string(attr.Value[:len(attr.Value)-1])
+				}
+			}
+			if ifaceName == name && ifmsg.Flags&syscall.IFF_UP != 0 {
+				return true, nil
+			}
+		}
+		return false, nil
+	}
+}
diff --git a/net/route.go b/net/route.go
index 990458b3..65dcfc89 100644
--- a/net/route.go
+++ b/net/route.go
@@ -66,35 +66,30 @@ func CheckRouteExists(ifaceName string, dest net.IP) bool {
 	return found
 }
 
-func waitForRoute(s *nl.NetlinkSocket, ifaceName string, dest net.IP) error {
-	native := nl.NativeEndian()
-	for {
-		msgs, err := s.Receive()
-		if err != nil {
-			return err
-		}
-		for _, m := range msgs {
-			switch m.Header.Type {
-			case syscall.RTM_NEWROUTE:
-				attrs, err := syscall.ParseNetlinkRouteAttr(&m)
-				if err != nil {
-					return err
-				}
-				var ip net.IP
-				var link netlink.Link
-				for _, attr := range attrs {
-					switch attr.Attr.Type {
-					case syscall.RTA_DST:
-						ip = attr.Value
-					case syscall.RTA_OIF:
-						index := int(native.Uint32(attr.Value[0:4]))
-						link, _ = netlink.LinkByIndex(index)
-					}
-				}
-				if link.Attrs().Name == ifaceName && ip.Equal(dest) {
-					return nil
+func matchRoute(ifaceName string, dest net.IP) func(m syscall.NetlinkMessage) (bool, error) {
+	return func(m syscall.NetlinkMessage) (bool, error) {
+		switch m.Header.Type {
+		case syscall.RTM_NEWROUTE:
+			attrs, err := syscall.ParseNetlinkRouteAttr(&m)
+			if err != nil {
+				return true, err
+			}
+			var ip net.IP
+			var link netlink.Link
+			for _, attr := range attrs {
+				switch attr.Attr.Type {
+				case syscall.RTA_DST:
+					ip = attr.Value
+				case syscall.RTA_OIF:
+					native := nl.NativeEndian()
+					index := int(native.Uint32(attr.Value[0:4]))
+					link, _ = netlink.LinkByIndex(index)
 				}
 			}
+			if link.Attrs().Name == ifaceName && ip.Equal(dest) {
+				return true, nil
+			}
 		}
+		return false, nil
 	}
 }