cmd/tailscale, cmd/tailscaled, paths: add paths package for default paths

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

cmd/tailscale/tailscale.go

@@ -23,6 +23,7 @@ import (
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"tailscale.com/ipn"
 	"tailscale.com/logpolicy"
+	"tailscale.com/paths"
 	"tailscale.com/safesocket"
 )
 
@@ -56,7 +57,7 @@ func main() {
 	}
 
 	upf := flag.NewFlagSet("up", flag.ExitOnError)
-	upf.StringVar(&upArgs.socket, "socket", "/run/tailscale/tailscaled.sock", "path to tailscaled's unix socket")
+	upf.StringVar(&upArgs.socket, "socket", paths.DefaultTailscaledSocket(), "path to tailscaled's unix socket")
 	upf.StringVar(&upArgs.server, "login-server", "https://login.tailscale.com", "base URL of control server")
 	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", false, "accept routes advertised by other Tailscale nodes")
 	upf.BoolVar(&upArgs.noSingleRoutes, "no-single-routes", false, "don't install routes to single nodes")

cmd/tailscaled/tailscaled.go

@@ -19,6 +19,7 @@ import (
 	"github.com/pborman/getopt/v2"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/logpolicy"
+	"tailscale.com/paths"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/magicsock"
 )
@@ -37,8 +38,8 @@ func main() {
 	debug := getopt.StringLong("debug", 0, "", "Address of debug server")
 	tunname := getopt.StringLong("tun", 0, "tailscale0", "tunnel interface name")
 	listenport := getopt.Uint16Long("port", 'p', magicsock.DefaultPort, "WireGuard port (0=autoselect)")
-	statepath := getopt.StringLong("state", 0, "", "Path of state file")
-	socketpath := getopt.StringLong("socket", 's', "tailscaled.sock", "Path of the service unix socket")
+	statepath := getopt.StringLong("state", 0, paths.DefaultTailscaledStateFile(), "Path of state file")
+	socketpath := getopt.StringLong("socket", 's', paths.DefaultTailscaledSocket(), "Path of the service unix socket")
 
 	logf := wgengine.RusagePrefixLog(log.Printf)
 
@@ -80,7 +81,7 @@ func main() {
 		SocketPath:         *socketpath,
 		StatePath:          *statepath,
 		AutostartStateKey:  globalStateKey,
-		LegacyConfigPath:   "/var/lib/tailscale/relay.conf",
+		LegacyConfigPath:   paths.LegacyConfigPath,
 		SurviveDisconnects: true,
 	}
 	err = ipnserver.Run(context.Background(), logf, pol.PublicID.String(), opts, e)

paths/paths.go

@@ -0,0 +1,40 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package paths returns platform and user-specific default paths to
+// Tailscale files and directories.
+package paths
+
+import (
+	"os"
+	"runtime"
+)
+
+// LegacyConfigPath is the path used by the pre-tailscaled "relaynode"
+// daemon's config file.
+const LegacyConfigPath = "/var/lib/tailscale/relay.conf"
+
+// DefaultTailscaledSocket returns the path to the tailscaled Unix socket
+// or the empty string if there's no reasonable default.
+func DefaultTailscaledSocket() string {
+	if runtime.GOOS == "windows" {
+		return ""
+	}
+	if fi, err := os.Stat("/run"); err == nil && fi.IsDir() {
+		return "/run/tailscale/tailscaled.sock"
+	}
+	return "tailscaled.sock"
+}
+
+var stateFileFunc func() string
+
+// DefaultTailscaledStateFile returns the default path to the
+// tailscaled state file, or the empty string if there's no reasonable
+// default value.
+func DefaultTailscaledStateFile() string {
+	if f := stateFileFunc; f != nil {
+		return f()
+	}
+	return ""
+}

paths/paths_unix.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows
+
+package paths
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+)
+
+func init() {
+	stateFileFunc = stateFileUnix
+}
+
+func stateFileUnix() string {
+	// TODO: use other default paths on other GOOSes probably. This works for Linux.
+	const varLib = "/var/lib/tailscale/tailscaled.state"
+	try := varLib
+	for i := 0; i < 3; i++ { // check writability of the file, /var/lib/tailscale, and /var/lib
+		err := unix.Access(try, unix.O_RDWR)
+		println(fmt.Sprintf("Access(%q) = %v", try, err))
+		if err == nil {
+			return varLib
+		}
+		try = filepath.Dir(try)
+	}
+
+	// TODO: try some $HOME/.tailscale or XDG path? But will it
+	// even work usefully enough as non-root? Probably not. Maybe
+	// best to require it be explicit in that case.
+	return ""
+}