Merge pull request #38 from multiformats/feat/fast-loopback-check

Make the IP loopback check faster

Author: Stebalien

ip.go

@@ -24,6 +24,14 @@ var (
 	IP6Unspecified = ma.StringCast("/ip6/::")
 )
 
+// Loopback multiaddr prefixes. Any multiaddr beginning with one of the
+// following byte sequences is considered a loopback multiaddr.
+var loopbackPrefixes = [][]byte{
+	{ma.P_IP4, 127}, // 127.*
+	IP6LinkLocalLoopback.Bytes(),
+	IP6Loopback.Bytes(),
+}
+
 // IsThinWaist returns whether a Multiaddr starts with "Thin Waist" Protocols.
 // This means: /{IP4, IP6}[/{TCP, UDP}]
 func IsThinWaist(m ma.Multiaddr) bool {
@@ -52,21 +60,14 @@ func IsThinWaist(m ma.Multiaddr) bool {
 }
 
 // IsIPLoopback returns whether a Multiaddr is a "Loopback" IP address
-// This means either /ip4/127.0.0.1 or /ip6/::1
-// TODO: differentiate IsIPLoopback and OverIPLoopback
+// This means either /ip4/127.*.*.*, /ip6/::1, or /ip6/fe80::1
 func IsIPLoopback(m ma.Multiaddr) bool {
 	b := m.Bytes()
-
-	// /ip4/127 prefix (_entire_ /8 is loopback...)
-	if bytes.HasPrefix(b, []byte{ma.P_IP4, 127}) {
-		return true
+	for _, prefix := range loopbackPrefixes {
+		if bytes.HasPrefix(b, prefix) {
+			return true
+		}
 	}
-
-	// /ip6/::1
-	if !m.Decapsulate(IP6Loopback).Equal(m) || !m.Decapsulate(IP6LinkLocalLoopback).Equal(m) {
-		return true
-	}
-
 	return false
 }
 

net_test.go

@@ -314,6 +314,18 @@ func TestIPLoopback(t *testing.T) {
 		t.Error("IsIPLoopback failed (IP4Loopback)")
 	}
 
+	if !IsIPLoopback(newMultiaddr(t, "/ip4/127.1.80.9")) {
+		t.Error("IsIPLoopback failed (/ip4/127.1.80.9)")
+	}
+
+	if IsIPLoopback(newMultiaddr(t, "/ip4/112.123.11.1")) {
+		t.Error("IsIPLoopback false positive (/ip4/112.123.11.1)")
+	}
+
+	if IsIPLoopback(newMultiaddr(t, "/ip4/192.168.0.1/ip6/::1")) {
+		t.Error("IsIPLoopback false positive (/ip4/192.168.0.1/ip6/::1)")
+	}
+
 	if !IsIPLoopback(IP6Loopback) {
 		t.Error("IsIPLoopback failed (IP6Loopback)")
 	}