net/tsaddr: add func ContainsExitRoutes

Change-Id: I772441a406083e2fe0f9374b2b23d89aac18928f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/prefs.go

@@ -18,6 +18,7 @@ import (
 
 	"inet.af/netaddr"
 	"tailscale.com/atomicfile"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/persist"
 	"tailscale.com/types/preftype"
@@ -442,18 +443,7 @@ func (p *Prefs) AdvertisesExitNode() bool {
 	if p == nil {
 		return false
 	}
-	var v4, v6 bool
+	return tsaddr.ContainsExitRoutes(p.AdvertiseRoutes)
-	for _, r := range p.AdvertiseRoutes {
-		if r.Bits() != 0 {
-			continue
-		}
-		if r.IP().Is4() {
-			v4 = true
-		} else if r.IP().Is6() {
-			v6 = true
-		}
-	}
-	return v4 && v6
 }
 
 // SetAdvertiseExitNode mutates p (if non-nil) to add or remove the two

net/tsaddr/tsaddr.go

@@ -213,3 +213,28 @@ func PrefixIs4(p netaddr.IPPrefix) bool { return p.IP().Is4() }
 
 // PrefixIs6 reports whether p is an IPv6 prefix.
 func PrefixIs6(p netaddr.IPPrefix) bool { return p.IP().Is6() }
+
+// ContainsExitRoutes reports whether rr contains both the IPv4 and
+// IPv6 /0 route.
+func ContainsExitRoutes(rr []netaddr.IPPrefix) bool {
+	var v4, v6 bool
+	for _, r := range rr {
+		if r == allIPv4 {
+			v4 = true
+		} else if r == allIPv6 {
+			v6 = true
+		}
+	}
+	return v4 && v6
+}
+
+var (
+	allIPv4 = netaddr.MustParseIPPrefix("0.0.0.0/0")
+	allIPv6 = netaddr.MustParseIPPrefix("::/0")
+)
+
+// AllIPv4 returns 0.0.0.0/0.
+func AllIPv4() netaddr.IPPrefix { return allIPv4 }
+
+// AllIPv6 returns ::/0.
+func AllIPv6() netaddr.IPPrefix { return allIPv6 }