non allocating AsSlice

src/net/netip/netip.go

@@ -701,18 +701,26 @@ func (ip Addr) As4() (a4 [4]byte) {
 
 // AsSlice returns an IPv4 or IPv6 address in its respective 4-byte or 16-byte representation.
 func (ip Addr) AsSlice() []byte {
+	var ret []byte
+	if ip.z == z4 {
+		ret = make([]byte, 4)
+	} else {
+		ret = make([]byte, 16)
+	}
+	return ip.asSlice(ret)
+}
+
+func (ip Addr) asSlice(ret []byte) []byte {
 	switch ip.z {
 	case z0:
 		return nil
 	case z4:
-		var ret [4]byte
 		bePutUint32(ret[:], uint32(ip.addr.lo))
-		return ret[:]
+		return ret
 	default:
-		var ret [16]byte
 		bePutUint64(ret[:8], ip.addr.hi)
 		bePutUint64(ret[8:], ip.addr.lo)
-		return ret[:]
+		return ret
 	}
 }
 

src/net/netip/netip_test.go

@@ -2008,6 +2008,36 @@ func TestAsSlice(t *testing.T) {
 	}
 }
 
+func BenchmarkAsSliceAddrv4(b *testing.B) {
+	addr := MustParseAddr("192.0.2.1")
+	for i := 0; i < b.N; i++ {
+		addr.AsSlice()
+	}
+}
+
+func BenchmarkAsSliceAddrv6(b *testing.B) {
+	addr := MustParseAddr("2001:db8::1")
+	for i := 0; i < b.N; i++ {
+		addr.AsSlice()
+	}
+}
+
+var asSliceOut []byte
+
+func BenchmarkAsSliceAddrv4Escapes(b *testing.B) {
+	addr := MustParseAddr("192.0.2.1")
+	for i := 0; i < b.N; i++ {
+		asSliceOut = addr.AsSlice()
+	}
+}
+
+func BenchmarkAsSliceAddrv6Escapes(b *testing.B) {
+	addr := MustParseAddr("2001:db8::1")
+	for i := 0; i < b.N; i++ {
+		asSliceOut = addr.AsSlice()
+	}
+}
+
 var sink16 [16]byte
 
 func BenchmarkAs16(b *testing.B) {