all: Convert folders to use filesystem abstraction

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4228

lib/osutil/net.go

@@ -0,0 +1,56 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package osutil
+
+import (
+	"bytes"
+	"net"
+)
+
+// ResolveInterfaceAddresses returns available addresses of the given network
+// type for a given interface.
+func ResolveInterfaceAddresses(network, nameOrMac string) []string {
+	intf, err := net.InterfaceByName(nameOrMac)
+	if err == nil {
+		return interfaceAddresses(network, intf)
+	}
+
+	mac, err := net.ParseMAC(nameOrMac)
+	if err != nil {
+		return []string{nameOrMac}
+	}
+
+	intfs, err := net.Interfaces()
+	if err != nil {
+		return []string{nameOrMac}
+	}
+
+	for _, intf := range intfs {
+		if bytes.Equal(intf.HardwareAddr, mac) {
+			return interfaceAddresses(network, &intf)
+		}
+	}
+
+	return []string{nameOrMac}
+}
+
+func interfaceAddresses(network string, intf *net.Interface) []string {
+	var out []string
+	addrs, err := intf.Addrs()
+	if err != nil {
+		return out
+	}
+
+	for _, addr := range addrs {
+		ipnet, ok := addr.(*net.IPNet)
+		if ok && (network == "tcp" || (network == "tcp4" && len(ipnet.IP) == net.IPv4len) || (network == "tcp6" && len(ipnet.IP) == net.IPv6len)) {
+			out = append(out, ipnet.IP.String())
+		}
+	}
+
+	return out
+}