manet: reduce allocations in resolve unspecified address

net/ip.go

@@ -60,6 +60,9 @@
 // or /ip6zone/<any value>/ip6/<one of the preceding ip6 values>/*
 func IsIPLoopback(m ma.Multiaddr) bool {
 	m = zoneless(m)
+	if m == nil {
+		return false
+	}
 	c, _ := ma.SplitFirst(m)
 	if c == nil {
 		return false
@@ -76,6 +79,9 @@
 // routable.
 func IsIP6LinkLocal(m ma.Multiaddr) bool {
 	m = zoneless(m)
+	if m == nil {
+		return false
+	}
 	c, _ := ma.SplitFirst(m)
 	if c == nil || c.Protocol().Code != ma.P_IP6 {
 		return false

net/net_test.go

@@ -682,3 +682,12 @@ func TestNetListener(t *testing.T) {
 	}
 	nc.Close()
 }
+
+func BenchmarkResolveUnspecifiedAddress(b *testing.B) {
+	b.ReportAllocs()
+	a := ma.StringCast("/ip4/0.0.0.0/udp/42/quic-v1")
+	iaddrs, _ := interfaceAddresses()
+	for i := 0; i < b.N; i++ {
+		ResolveUnspecifiedAddress(a, iaddrs)
+	}
+}

net/resolve.go

@@ -11,22 +11,26 @@ import (
 // from the network stack. (this is so you can provide a cached value if resolving many addrs)
 func ResolveUnspecifiedAddress(resolve ma.Multiaddr, ifaceAddrs []ma.Multiaddr) ([]ma.Multiaddr, error) {
 	// split address into its components
-	split := ma.Split(resolve)
+	first, rest := ma.SplitFirst(resolve)
 
 	// if first component (ip) is not unspecified, use it as is.
-	if !IsIPUnspecified(split[0]) {
+	if !IsIPUnspecified(first) {
 		return []ma.Multiaddr{resolve}, nil
 	}
 
+	resolveProto := resolve.Protocols()[0].Code
 	out := make([]ma.Multiaddr, 0, len(ifaceAddrs))
 	for _, ia := range ifaceAddrs {
+		iafirst, _ := ma.SplitFirst(ia)
 		// must match the first protocol to be resolve.
-		if ia.Protocols()[0].Code != resolve.Protocols()[0].Code {
+		if iafirst.Protocol().Code != resolveProto {
 			continue
 		}
 
-		split[0] = ia
-		joined := ma.Join(split...)
+		joined := ia
+		if rest != nil {
+			joined = ma.Join(ia, rest)
+		}
 		out = append(out, joined)
 	}
 	if len(out) < 1 {

net/resolve_test.go

@@ -13,6 +13,7 @@ func TestResolvingAddrs(t *testing.T) {
 		newMultiaddr(t, "/ip4/1.2.3.4/tcp/1234"),
 		newMultiaddr(t, "/ip6/::/tcp/1234"),
 		newMultiaddr(t, "/ip6/::100/tcp/1234"),
+		newMultiaddr(t, "/ip4/0.0.0.0"),
 	}
 
 	iface := []ma.Multiaddr{
@@ -29,6 +30,8 @@ func TestResolvingAddrs(t *testing.T) {
 		newMultiaddr(t, "/ip6/::1/tcp/1234"),
 		newMultiaddr(t, "/ip6/::f/tcp/1234"),
 		newMultiaddr(t, "/ip6/::100/tcp/1234"),
+		newMultiaddr(t, "/ip4/127.0.0.1"),
+		newMultiaddr(t, "/ip4/10.20.30.40"),
 	}
 
 	actual, err := ResolveUnspecifiedAddresses(unspec, iface)

util.go

@@ -27,16 +27,14 @@ func Join(ms ...Multiaddr) Multiaddr {
 	}
 
 	length := 0
-	bs := make([][]byte, len(ms))
-	for i, m := range ms {
-		bs[i] = m.Bytes()
-		length += len(bs[i])
+	for _, m := range ms {
+		length += len(m.Bytes())
 	}
 
 	bidx := 0
 	b := make([]byte, length)
-	for _, mb := range bs {
-		bidx += copy(b[bidx:], mb)
+	for _, mb := range ms {
+		bidx += copy(b[bidx:], mb.Bytes())
 	}
 	return &multiaddr{bytes: b}
 }