net/{dnscache,interfaces}: use netaddr.IP.IsPrivate, delete copied code

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

net/dnscache/dnscache.go

@@ -249,7 +249,7 @@ func (r *Resolver) lookupIP(host string) (ip, ip6 net.IP, allIPs []net.IPAddr, e
 }
 
 func (r *Resolver) addIPCache(host string, ip, ip6 net.IP, allIPs []net.IPAddr, d time.Duration) {
-	if isPrivateIP(ip) {
+	if naIP, _ := netaddr.FromStdIP(ip); naIP.IsPrivate() {
 		// Don't cache obviously wrong entries from captive portals.
 		// TODO: use DoH or DoT for the forwarding resolver?
 		if debug {
@@ -275,24 +275,6 @@ func (r *Resolver) addIPCache(host string, ip, ip6 net.IP, allIPs []net.IPAddr,
 	}
 }
 
-func mustCIDR(s string) *net.IPNet {
-	_, ipNet, err := net.ParseCIDR(s)
-	if err != nil {
-		panic(err)
-	}
-	return ipNet
-}
-
-func isPrivateIP(ip net.IP) bool {
-	return private1.Contains(ip) || private2.Contains(ip) || private3.Contains(ip)
-}
-
-var (
-	private1 = mustCIDR("10.0.0.0/8")
-	private2 = mustCIDR("172.16.0.0/12")
-	private3 = mustCIDR("192.168.0.0/16")
-)
-
 type DialContextFunc func(ctx context.Context, network, address string) (net.Conn, error)
 
 // Dialer returns a wrapped DialContext func that uses the provided dnsCache.

net/dnscache/dnscache_test.go

@@ -14,24 +14,6 @@ import (
 
 var dialTest = flag.String("dial-test", "", "if non-empty, addr:port to test dial")
 
-func TestIsPrivateIP(t *testing.T) {
-	tests := []struct {
-		ip   string
-		want bool
-	}{
-		{"10.1.2.3", true},
-		{"172.16.1.100", true},
-		{"192.168.1.1", true},
-		{"1.2.3.4", false},
-	}
-
-	for _, test := range tests {
-		if got := isPrivateIP(net.ParseIP(test.ip)); got != test.want {
-			t.Errorf("isPrivateIP(%q)=%v, want %v", test.ip, got, test.want)
-		}
-	}
-}
-
 func TestDialer(t *testing.T) {
 	if *dialTest == "" {
 		t.Skip("skipping; --dial-test is blank")

net/interfaces/interfaces.go

@@ -479,7 +479,7 @@ func HTTPOfListener(ln net.Listener) string {
 	var privateIP string
 	ForeachInterfaceAddress(func(i Interface, pfx netaddr.IPPrefix) {
 		ip := pfx.IP()
-		if isPrivateIP(ip) {
+		if ip.IsPrivate() {
 			if privateIP == "" {
 				privateIP = ip.String()
 			}
@@ -519,21 +519,15 @@ func LikelyHomeRouterIP() (gateway, myIP netaddr.IP, ok bool) {
 		if !i.IsUp() || ip.IsZero() || !myIP.IsZero() {
 			return
 		}
-		for _, prefix := range privatev4s {
-			if prefix.Contains(gateway) && prefix.Contains(ip) {
-				myIP = ip
-				ok = true
-				return
-			}
+		if gateway.IsPrivate() && ip.IsPrivate() {
+			myIP = ip
+			ok = true
+			return
 		}
 	})
 	return gateway, myIP, !myIP.IsZero()
 }
 
-func isPrivateIP(ip netaddr.IP) bool {
-	return private1.Contains(ip) || private2.Contains(ip) || private3.Contains(ip)
-}
-
 // isUsableV4 reports whether ip is a usable IPv4 address which could
 // conceivably be used to get Internet connectivity. Globally routable and
 // private IPv4 addresses are always Usable, and link local 169.254.x.x
@@ -557,20 +551,8 @@ func isUsableV6(ip netaddr.IP) bool {
 		(tsaddr.IsULA(ip) && !tsaddr.TailscaleULARange().Contains(ip))
 }
 
-func mustCIDR(s string) netaddr.IPPrefix {
-	prefix, err := netaddr.ParseIPPrefix(s)
-	if err != nil {
-		panic(err)
-	}
-	return prefix
-}
-
 var (
-	private1   = mustCIDR("10.0.0.0/8")
-	private2   = mustCIDR("172.16.0.0/12")
-	private3   = mustCIDR("192.168.0.0/16")
-	privatev4s = []netaddr.IPPrefix{private1, private2, private3}
-	v6Global1  = mustCIDR("2000::/3")
+	v6Global1 = netaddr.MustParseIPPrefix("2000::/3")
 )
 
 // anyInterestingIP reports whether pfxs contains any IP that matches

net/interfaces/interfaces_darwin_test.go

@@ -73,7 +73,7 @@ func likelyHomeRouterIPDarwinExec() (ret netaddr.IP, ok bool) {
 			return nil
 		}
 		ip, err := netaddr.ParseIP(string(mem.Append(nil, ipm)))
-		if err == nil && isPrivateIP(ip) {
+		if err == nil && ip.IsPrivate() {
 			ret = ip
 			// We've found what we're looking for.
 			return errStopReadingNetstatTable

net/interfaces/interfaces_linux.go

@@ -72,7 +72,7 @@ func likelyHomeRouterIPLinux() (ret netaddr.IP, ok bool) {
 			return nil // ignore error, skip line and keep going
 		}
 		ip := netaddr.IPv4(byte(ipu32), byte(ipu32>>8), byte(ipu32>>16), byte(ipu32>>24))
-		if isPrivateIP(ip) {
+		if ip.IsPrivate() {
 			ret = ip
 		}
 		return nil

net/interfaces/interfaces_windows.go

@@ -93,7 +93,7 @@ func likelyHomeRouterIPWindows() (ret netaddr.IP, ok bool) {
 		}
 	}
 
-	if !ret.IsZero() && !isPrivateIP(ret) {
+	if !ret.IsZero() && !ret.IsPrivate() {
 		// Default route has a non-private gateway
 		return netaddr.IP{}, false
 	}