Function to check if a network overlaps with existing routes

net/route.go

@@ -0,0 +1,28 @@
+package net
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/vishvananda/netlink"
+)
+
+// A network is considered free if it does not overlap any existing
+// routes on this host. This is the same approach taken by Docker.
+func CheckNetworkFree(subnet *net.IPNet) error {
+	routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
+	if err != nil {
+		return err
+	}
+	for _, route := range routes {
+		if route.Dst != nil && overlaps(route.Dst, subnet) {
+			return fmt.Errorf("network %s would overlap with route %s", subnet, route.Dst)
+		}
+	}
+	return nil
+}
+
+// Two networks overlap if the start-point of one is inside the other.
+func overlaps(n1, n2 *net.IPNet) bool {
+	return n1.Contains(n2.IP) || n2.Contains(n1.IP)
+}

net/route_test.go

@@ -0,0 +1,25 @@
+package net
+
+import (
+	"net"
+	"testing"
+
+	wt "github.com/weaveworks/weave/testing"
+)
+
+func TestOverlap(t *testing.T) {
+	_, subnet1, _ := net.ParseCIDR("10.0.3.0/24")
+	_, subnet2, _ := net.ParseCIDR("10.0.4.0/24")
+	_, subnet3, _ := net.ParseCIDR("10.0.3.128/25")
+	_, subnet4, _ := net.ParseCIDR("10.0.3.192/25")
+	_, universe, _ := net.ParseCIDR("10.0.0.0/8")
+	wt.AssertEquals(t, overlaps(subnet1, subnet2), false)
+	wt.AssertEquals(t, overlaps(subnet2, subnet1), false)
+	wt.AssertEquals(t, overlaps(subnet1, subnet1), true)
+	wt.AssertEquals(t, overlaps(subnet1, subnet3), true)
+	wt.AssertEquals(t, overlaps(subnet1, subnet4), true)
+	wt.AssertEquals(t, overlaps(subnet2, subnet4), false)
+	wt.AssertEquals(t, overlaps(subnet4, subnet2), false)
+	wt.AssertEquals(t, overlaps(universe, subnet1), true)
+	wt.AssertEquals(t, overlaps(subnet1, universe), true)
+}