mv internal lib

lib/osutil/atomic.go

@@ -0,0 +1,101 @@
+// 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 (
+	"errors"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+var (
+	ErrClosed  = errors.New("write to closed writer")
+	TempPrefix = ".syncthing.tmp."
+)
+
+// An AtomicWriter is an *os.File that writes to a temporary file in the same
+// directory as the final path. On successfull Close the file is renamed to
+// it's final path. Any error on Write or during Close is accumulated and
+// returned on Close, so a lazy user can ignore errors until Close.
+type AtomicWriter struct {
+	path string
+	next *os.File
+	err  error
+}
+
+// CreateAtomic is like os.Create with a FileMode, except a temporary file
+// name is used instead of the given name.
+func CreateAtomic(path string, mode os.FileMode) (*AtomicWriter, error) {
+	fd, err := ioutil.TempFile(filepath.Dir(path), TempPrefix)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := os.Chmod(fd.Name(), mode); err != nil {
+		fd.Close()
+		os.Remove(fd.Name())
+		return nil, err
+	}
+
+	w := &AtomicWriter{
+		path: path,
+		next: fd,
+	}
+
+	return w, nil
+}
+
+// Write is like io.Writer, but is a no-op on an already failed AtomicWriter.
+func (w *AtomicWriter) Write(bs []byte) (int, error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	n, err := w.next.Write(bs)
+	if err != nil {
+		w.err = err
+		w.next.Close()
+	}
+	return n, err
+}
+
+// Close closes the temporary file and renames it to the final path. It is
+// invalid to call Write() or Close() after Close().
+func (w *AtomicWriter) Close() error {
+	if w.err != nil {
+		return w.err
+	}
+
+	// Try to not leave temp file around, but ignore error.
+	defer os.Remove(w.next.Name())
+
+	if err := w.next.Close(); err != nil {
+		w.err = err
+		return err
+	}
+
+	// Remove the destination file, on Windows only. If it fails, and not due
+	// to the file not existing, we won't be able to complete the rename
+	// either. Return this error because it may be more informative. On non-
+	// Windows we want the atomic rename behavior so we don't attempt remove.
+	if runtime.GOOS == "windows" {
+		if err := os.Remove(w.path); err != nil && !os.IsNotExist(err) {
+			return err
+		}
+	}
+
+	if err := os.Rename(w.next.Name(), w.path); err != nil {
+		w.err = err
+		return err
+	}
+
+	// Set w.err to return appropriately for any future operations.
+	w.err = ErrClosed
+
+	return nil
+}

lib/osutil/atomic_test.go

@@ -0,0 +1,85 @@
+// 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"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestCreateAtomicCreate(t *testing.T) {
+	os.RemoveAll("testdata")
+	defer os.RemoveAll("testdata")
+
+	if err := os.Mkdir("testdata", 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	w, err := CreateAtomic("testdata/file", 0644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	n, err := w.Write([]byte("hello"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 5 {
+		t.Fatal("written bytes", n, "!= 5")
+	}
+
+	if _, err := ioutil.ReadFile("testdata/file"); err == nil {
+		t.Fatal("file should not exist")
+	}
+
+	if err := w.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	bs, err := ioutil.ReadFile("testdata/file")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(bs, []byte("hello")) {
+		t.Error("incorrect data")
+	}
+}
+
+func TestCreateAtomicReplace(t *testing.T) {
+	os.RemoveAll("testdata")
+	defer os.RemoveAll("testdata")
+
+	if err := os.Mkdir("testdata", 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ioutil.WriteFile("testdata/file", []byte("some old data"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	w, err := CreateAtomic("testdata/file", 0644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := w.Write([]byte("hello")); err != nil {
+		t.Fatal(err)
+	}
+	if err := w.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	bs, err := ioutil.ReadFile("testdata/file")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(bs, []byte("hello")) {
+		t.Error("incorrect data")
+	}
+}

lib/osutil/filenames_darwin.go

@@ -0,0 +1,17 @@
+// Copyright (C) 2014 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 "golang.org/x/text/unicode/norm"
+
+func NormalizedFilename(s string) string {
+	return norm.NFC.String(s)
+}
+
+func NativeFilename(s string) string {
+	return norm.NFD.String(s)
+}

lib/osutil/filenames_unix.go

@@ -0,0 +1,19 @@
+// Copyright (C) 2014 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/.
+
+// +build !windows,!darwin
+
+package osutil
+
+import "golang.org/x/text/unicode/norm"
+
+func NormalizedFilename(s string) string {
+	return norm.NFC.String(s)
+}
+
+func NativeFilename(s string) string {
+	return s
+}

lib/osutil/filenames_windows.go

@@ -0,0 +1,21 @@
+// Copyright (C) 2014 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 (
+	"path/filepath"
+
+	"golang.org/x/text/unicode/norm"
+)
+
+func NormalizedFilename(s string) string {
+	return norm.NFC.String(filepath.ToSlash(s))
+}
+
+func NativeFilename(s string) string {
+	return filepath.FromSlash(s)
+}

lib/osutil/glob_unix.go

@@ -0,0 +1,17 @@
+// 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/.
+
+// +build !windows
+
+package osutil
+
+import (
+	"path/filepath"
+)
+
+func Glob(pattern string) (matches []string, err error) {
+	return filepath.Glob(pattern)
+}

lib/osutil/glob_windows.go

@@ -0,0 +1,93 @@
+// 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/.
+
+// +build windows
+
+package osutil
+
+import (
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// Glob implements filepath.Glob, but works with Windows long path prefixes.
+// Deals with https://github.com/golang/go/issues/10577
+func Glob(pattern string) (matches []string, err error) {
+	if !hasMeta(pattern) {
+		if _, err = os.Lstat(pattern); err != nil {
+			return nil, nil
+		}
+		return []string{pattern}, nil
+	}
+
+	dir, file := filepath.Split(pattern)
+	switch dir {
+	case "":
+		dir = "."
+	case string(filepath.Separator):
+		// nothing
+	default:
+		dir = dir[0 : len(dir)-1] // chop off trailing separator
+	}
+
+	if !hasMeta(dir) {
+		return glob(dir, file, nil)
+	}
+
+	var m []string
+	m, err = Glob(dir)
+	if err != nil {
+		return
+	}
+	for _, d := range m {
+		matches, err = glob(d, file, matches)
+		if err != nil {
+			return
+		}
+	}
+	return
+}
+
+func hasMeta(path string) bool {
+	// Strip off Windows long path prefix if it exists.
+	if strings.HasPrefix(path, "\\\\?\\") {
+		path = path[4:]
+	}
+	// TODO(niemeyer): Should other magic characters be added here?
+	return strings.IndexAny(path, "*?[") >= 0
+}
+
+func glob(dir, pattern string, matches []string) (m []string, e error) {
+	m = matches
+	fi, err := os.Stat(dir)
+	if err != nil {
+		return
+	}
+	if !fi.IsDir() {
+		return
+	}
+	d, err := os.Open(dir)
+	if err != nil {
+		return
+	}
+	defer d.Close()
+
+	names, _ := d.Readdirnames(-1)
+	sort.Strings(names)
+
+	for _, n := range names {
+		matched, err := filepath.Match(pattern, n)
+		if err != nil {
+			return m, err
+		}
+		if matched {
+			m = append(m, filepath.Join(dir, n))
+		}
+	}
+	return
+}

lib/osutil/hidden_unix.go

@@ -0,0 +1,19 @@
+// Copyright (C) 2014 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/.
+
+// +build !windows
+
+package osutil
+
+func HideFile(path string) error {
+	return nil
+}
+
+func ShowFile(path string) error {
+	return nil
+}
+
+func HideConsole() {}

lib/osutil/hidden_windows.go

@@ -0,0 +1,52 @@
+// Copyright (C) 2014 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/.
+
+// +build windows
+
+package osutil
+
+import "syscall"
+
+func HideFile(path string) error {
+	p, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return err
+	}
+
+	attrs, err := syscall.GetFileAttributes(p)
+	if err != nil {
+		return err
+	}
+
+	attrs |= syscall.FILE_ATTRIBUTE_HIDDEN
+	return syscall.SetFileAttributes(p, attrs)
+}
+
+func ShowFile(path string) error {
+	p, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return err
+	}
+
+	attrs, err := syscall.GetFileAttributes(p)
+	if err != nil {
+		return err
+	}
+
+	attrs &^= syscall.FILE_ATTRIBUTE_HIDDEN
+	return syscall.SetFileAttributes(p, attrs)
+}
+
+func HideConsole() {
+	getConsoleWindow := syscall.NewLazyDLL("kernel32.dll").NewProc("GetConsoleWindow")
+	showWindow := syscall.NewLazyDLL("user32.dll").NewProc("ShowWindow")
+	if getConsoleWindow.Find() == nil && showWindow.Find() == nil {
+		hwnd, _, _ := getConsoleWindow.Call()
+		if hwnd != 0 {
+			showWindow.Call(hwnd, 0)
+		}
+	}
+}

lib/osutil/lan_unix.go

@@ -0,0 +1,30 @@
+// 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/.
+
+// +build !windows
+
+package osutil
+
+import (
+	"net"
+)
+
+func GetLans() ([]*net.IPNet, error) {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return nil, err
+	}
+
+	nets := make([]*net.IPNet, 0, len(addrs))
+
+	for _, addr := range addrs {
+		net, ok := addr.(*net.IPNet)
+		if ok {
+			nets = append(nets, net)
+		}
+	}
+	return nets, nil
+}

lib/osutil/lan_windows.go

@@ -0,0 +1,83 @@
+// 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/.
+
+// +build windows
+
+package osutil
+
+import (
+	"net"
+	"os"
+	"strings"
+	"syscall"
+	"unsafe"
+)
+
+// Modified version of:
+// http://stackoverflow.com/questions/23529663/how-to-get-all-addresses-and-masks-from-local-interfaces-in-go
+// v4 only!
+
+func getAdapterList() (*syscall.IpAdapterInfo, error) {
+	b := make([]byte, 10240)
+	l := uint32(len(b))
+	a := (*syscall.IpAdapterInfo)(unsafe.Pointer(&b[0]))
+	// TODO(mikio): GetAdaptersInfo returns IP_ADAPTER_INFO that
+	// contains IPv4 address list only. We should use another API
+	// for fetching IPv6 stuff from the kernel.
+	err := syscall.GetAdaptersInfo(a, &l)
+	if err == syscall.ERROR_BUFFER_OVERFLOW {
+		b = make([]byte, l)
+		a = (*syscall.IpAdapterInfo)(unsafe.Pointer(&b[0]))
+		err = syscall.GetAdaptersInfo(a, &l)
+	}
+	if err != nil {
+		return nil, os.NewSyscallError("GetAdaptersInfo", err)
+	}
+	return a, nil
+}
+
+func GetLans() ([]*net.IPNet, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	nets := make([]*net.IPNet, 0, len(ifaces))
+
+	aList, err := getAdapterList()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, ifi := range ifaces {
+		for ai := aList; ai != nil; ai = ai.Next {
+			index := ai.Index
+
+			if ifi.Index == int(index) {
+				ipl := &ai.IpAddressList
+				for ; ipl != nil; ipl = ipl.Next {
+					ipStr := strings.Trim(string(ipl.IpAddress.String[:]), "\x00")
+					maskStr := strings.Trim(string(ipl.IpMask.String[:]), "\x00")
+					ip := net.ParseIP(ipStr)
+					maskip := net.ParseIP(maskStr)
+					if ip.IsUnspecified() || maskip.IsUnspecified() {
+						continue
+					}
+					nets = append(nets, &net.IPNet{
+						IP: ip,
+						Mask: net.IPv4Mask(
+							maskip[net.IPv6len-net.IPv4len],
+							maskip[net.IPv6len-net.IPv4len+1],
+							maskip[net.IPv6len-net.IPv4len+2],
+							maskip[net.IPv6len-net.IPv4len+3],
+						),
+					})
+				}
+			}
+		}
+	}
+	return nets, err
+}

lib/osutil/lstat_broken.go

@@ -0,0 +1,29 @@
+// 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/.
+
+// +build linux android
+
+package osutil
+
+import (
+	"os"
+	"syscall"
+	"time"
+)
+
+// Lstat is like os.Lstat, except lobotomized for Android. See
+// https://forum.syncthing.net/t/2395
+func Lstat(name string) (fi os.FileInfo, err error) {
+	for i := 0; i < 10; i++ { // We have to draw the line somewhere
+		fi, err = os.Lstat(name)
+		if err, ok := err.(*os.PathError); ok && err.Err == syscall.EINTR {
+			time.Sleep(time.Duration(i+1) * time.Millisecond)
+			continue
+		}
+		return
+	}
+	return
+}

lib/osutil/lstat_ok.go

@@ -0,0 +1,15 @@
+// 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/.
+
+// +build !linux,!android
+
+package osutil
+
+import "os"
+
+func Lstat(name string) (fi os.FileInfo, err error) {
+	return os.Lstat(name)
+}

lib/osutil/mkdirall.go

@@ -0,0 +1,17 @@
+// 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/.
+
+// +build !windows
+
+package osutil
+
+import (
+	"os"
+)
+
+func MkdirAll(path string, perm os.FileMode) error {
+	return os.MkdirAll(path, perm)
+}

lib/osutil/mkdirall_windows.go

@@ -0,0 +1,65 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Modified by Zillode to fix https://github.com/syncthing/syncthing/issues/1822
+// Sync with https://github.com/golang/go/blob/master/src/os/path.go
+// See https://github.com/golang/go/issues/10900
+
+package osutil
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+// MkdirAll creates a directory named path, along with any necessary parents,
+// and returns nil, or else returns an error.
+// The permission bits perm are used for all directories that MkdirAll creates.
+// If path is already a directory, MkdirAll does nothing and returns nil.
+func MkdirAll(path string, perm os.FileMode) error {
+	// Fast path: if we can tell whether path is a directory or file, stop with success or error.
+	dir, err := os.Stat(path)
+	if err == nil {
+		if dir.IsDir() {
+			return nil
+		}
+		return &os.PathError{"mkdir", path, syscall.ENOTDIR}
+	}
+
+	// Slow path: make sure parent exists and then call Mkdir for path.
+	i := len(path)
+	for i > 0 && os.IsPathSeparator(path[i-1]) { // Skip trailing path separator.
+		i--
+	}
+
+	j := i
+	for j > 0 && !os.IsPathSeparator(path[j-1]) { // Scan backward over element.
+		j--
+	}
+
+	if j > 1 {
+		// Create parent
+		parent := path[0 : j-1]
+		if parent != filepath.VolumeName(parent) {
+			err = MkdirAll(parent, perm)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	// Parent now exists; invoke Mkdir and use its result.
+	err = os.Mkdir(path, perm)
+	if err != nil {
+		// Handle arguments like "foo/." by
+		// double-checking that directory doesn't exist.
+		dir, err1 := os.Lstat(path)
+		if err1 == nil && dir.IsDir() {
+			return nil
+		}
+		return err
+	}
+	return nil
+}

lib/osutil/osutil.go

@@ -0,0 +1,212 @@
+// Copyright (C) 2014 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 implements utilities for native OS support.
+package osutil
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	"github.com/syncthing/syncthing/lib/sync"
+)
+
+var ErrNoHome = errors.New("No home directory found - set $HOME (or the platform equivalent).")
+
+// Try to keep this entire operation atomic-like. We shouldn't be doing this
+// often enough that there is any contention on this lock.
+var renameLock = sync.NewMutex()
+
+// TryRename renames a file, leaving source file intact in case of failure.
+// Tries hard to succeed on various systems by temporarily tweaking directory
+// permissions and removing the destination file when necessary.
+func TryRename(from, to string) error {
+	renameLock.Lock()
+	defer renameLock.Unlock()
+
+	return withPreparedTarget(from, to, func() error {
+		return os.Rename(from, to)
+	})
+}
+
+// Rename moves a temporary file to it's final place.
+// Will make sure to delete the from file if the operation fails, so use only
+// for situations like committing a temp file to it's final location.
+// Tries hard to succeed on various systems by temporarily tweaking directory
+// permissions and removing the destination file when necessary.
+func Rename(from, to string) error {
+	// Don't leave a dangling temp file in case of rename error
+	if !(runtime.GOOS == "windows" && strings.EqualFold(from, to)) {
+		defer os.Remove(from)
+	}
+	return TryRename(from, to)
+}
+
+// Copy copies the file content from source to destination.
+// Tries hard to succeed on various systems by temporarily tweaking directory
+// permissions and removing the destination file when necessary.
+func Copy(from, to string) (err error) {
+	return withPreparedTarget(from, to, func() error {
+		return copyFileContents(from, to)
+	})
+}
+
+// InWritableDir calls fn(path), while making sure that the directory
+// containing `path` is writable for the duration of the call.
+func InWritableDir(fn func(string) error, path string) error {
+	dir := filepath.Dir(path)
+	info, err := os.Stat(dir)
+	if err != nil {
+		return err
+	}
+	if !info.IsDir() {
+		return errors.New("Not a directory: " + path)
+	}
+	if info.Mode()&0200 == 0 {
+		// A non-writeable directory (for this user; we assume that's the
+		// relevant part). Temporarily change the mode so we can delete the
+		// file or directory inside it.
+		err = os.Chmod(dir, 0755)
+		if err == nil {
+			defer func() {
+				err = os.Chmod(dir, info.Mode())
+				if err != nil {
+					// We managed to change the permission bits like a
+					// millisecond ago, so it'd be bizarre if we couldn't
+					// change it back.
+					panic(err)
+				}
+			}()
+		}
+	}
+
+	return fn(path)
+}
+
+// Remove removes the given path. On Windows, removes the read-only attribute
+// from the target prior to deletion.
+func Remove(path string) error {
+	if runtime.GOOS == "windows" {
+		info, err := os.Stat(path)
+		if err != nil {
+			return err
+		}
+		if info.Mode()&0200 == 0 {
+			os.Chmod(path, 0700)
+		}
+	}
+	return os.Remove(path)
+}
+
+func ExpandTilde(path string) (string, error) {
+	if path == "~" {
+		return getHomeDir()
+	}
+
+	path = filepath.FromSlash(path)
+	if !strings.HasPrefix(path, fmt.Sprintf("~%c", os.PathSeparator)) {
+		return path, nil
+	}
+
+	home, err := getHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, path[2:]), nil
+}
+
+func getHomeDir() (string, error) {
+	var home string
+
+	switch runtime.GOOS {
+	case "windows":
+		home = filepath.Join(os.Getenv("HomeDrive"), os.Getenv("HomePath"))
+		if home == "" {
+			home = os.Getenv("UserProfile")
+		}
+	default:
+		home = os.Getenv("HOME")
+	}
+
+	if home == "" {
+		return "", ErrNoHome
+	}
+
+	return home, nil
+}
+
+// Tries hard to succeed on various systems by temporarily tweaking directory
+// permissions and removing the destination file when necessary.
+func withPreparedTarget(from, to string, f func() error) error {
+	// Make sure the destination directory is writeable
+	toDir := filepath.Dir(to)
+	if info, err := os.Stat(toDir); err == nil && info.IsDir() && info.Mode()&0200 == 0 {
+		os.Chmod(toDir, 0755)
+		defer os.Chmod(toDir, info.Mode())
+	}
+
+	// On Windows, make sure the destination file is writeable (or we can't delete it)
+	if runtime.GOOS == "windows" {
+		os.Chmod(to, 0666)
+		if !strings.EqualFold(from, to) {
+			err := os.Remove(to)
+			if err != nil && !os.IsNotExist(err) {
+				return err
+			}
+		}
+	}
+	return f()
+}
+
+// copyFileContents copies the contents of the file named src to the file named
+// by dst. The file will be created if it does not already exist. If the
+// destination file exists, all it's contents will be replaced by the contents
+// of the source file.
+func copyFileContents(src, dst string) (err error) {
+	in, err := os.Open(src)
+	if err != nil {
+		return
+	}
+	defer in.Close()
+	out, err := os.Create(dst)
+	if err != nil {
+		return
+	}
+	defer func() {
+		cerr := out.Close()
+		if err == nil {
+			err = cerr
+		}
+	}()
+	if _, err = io.Copy(out, in); err != nil {
+		return
+	}
+	err = out.Sync()
+	return
+}
+
+var execExts map[string]bool
+
+func init() {
+	// PATHEXT contains a list of executable file extensions, on Windows
+	pathext := filepath.SplitList(os.Getenv("PATHEXT"))
+	// We want the extensions in execExts to be lower case
+	execExts = make(map[string]bool, len(pathext))
+	for _, ext := range pathext {
+		execExts[strings.ToLower(ext)] = true
+	}
+}
+
+// IsWindowsExecutable returns true if the given path has an extension that is
+// in the list of executable extensions.
+func IsWindowsExecutable(path string) bool {
+	return execExts[strings.ToLower(filepath.Ext(path))]
+}

lib/osutil/osutil_test.go

@@ -0,0 +1,166 @@
+// Copyright (C) 2014 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_test
+
+import (
+	"os"
+	"runtime"
+	"testing"
+
+	"github.com/syncthing/syncthing/lib/osutil"
+)
+
+func TestInWriteableDir(t *testing.T) {
+	err := os.RemoveAll("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll("testdata")
+
+	os.Mkdir("testdata", 0700)
+	os.Mkdir("testdata/rw", 0700)
+	os.Mkdir("testdata/ro", 0500)
+
+	create := func(name string) error {
+		fd, err := os.Create(name)
+		if err != nil {
+			return err
+		}
+		fd.Close()
+		return nil
+	}
+
+	// These should succeed
+
+	err = osutil.InWritableDir(create, "testdata/file")
+	if err != nil {
+		t.Error("testdata/file:", err)
+	}
+	err = osutil.InWritableDir(create, "testdata/rw/foo")
+	if err != nil {
+		t.Error("testdata/rw/foo:", err)
+	}
+	err = osutil.InWritableDir(os.Remove, "testdata/rw/foo")
+	if err != nil {
+		t.Error("testdata/rw/foo:", err)
+	}
+
+	err = osutil.InWritableDir(create, "testdata/ro/foo")
+	if err != nil {
+		t.Error("testdata/ro/foo:", err)
+	}
+	err = osutil.InWritableDir(os.Remove, "testdata/ro/foo")
+	if err != nil {
+		t.Error("testdata/ro/foo:", err)
+	}
+
+	// These should not
+
+	err = osutil.InWritableDir(create, "testdata/nonexistent/foo")
+	if err == nil {
+		t.Error("testdata/nonexistent/foo returned nil error")
+	}
+	err = osutil.InWritableDir(create, "testdata/file/foo")
+	if err == nil {
+		t.Error("testdata/file/foo returned nil error")
+	}
+}
+
+func TestInWritableDirWindowsRemove(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skipf("Tests not required")
+		return
+	}
+
+	err := os.RemoveAll("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll("testdata")
+
+	create := func(name string) error {
+		fd, err := os.Create(name)
+		if err != nil {
+			return err
+		}
+		fd.Close()
+		return nil
+	}
+
+	os.Mkdir("testdata", 0700)
+
+	os.Mkdir("testdata/windows", 0500)
+	os.Mkdir("testdata/windows/ro", 0500)
+	create("testdata/windows/ro/readonly")
+	os.Chmod("testdata/windows/ro/readonly", 0500)
+
+	for _, path := range []string{"testdata/windows/ro/readonly", "testdata/windows/ro", "testdata/windows"} {
+		err := os.Remove(path)
+		if err == nil {
+			t.Errorf("Expected error %s", path)
+		}
+	}
+
+	for _, path := range []string{"testdata/windows/ro/readonly", "testdata/windows/ro", "testdata/windows"} {
+		err := osutil.InWritableDir(osutil.Remove, path)
+		if err != nil {
+			t.Errorf("Unexpected error %s: %s", path, err)
+		}
+	}
+}
+
+func TestInWritableDirWindowsRename(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skipf("Tests not required")
+		return
+	}
+
+	err := os.RemoveAll("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll("testdata")
+
+	create := func(name string) error {
+		fd, err := os.Create(name)
+		if err != nil {
+			return err
+		}
+		fd.Close()
+		return nil
+	}
+
+	os.Mkdir("testdata", 0700)
+
+	os.Mkdir("testdata/windows", 0500)
+	os.Mkdir("testdata/windows/ro", 0500)
+	create("testdata/windows/ro/readonly")
+	os.Chmod("testdata/windows/ro/readonly", 0500)
+
+	for _, path := range []string{"testdata/windows/ro/readonly", "testdata/windows/ro", "testdata/windows"} {
+		err := os.Rename(path, path+"new")
+		if err == nil {
+			t.Skipf("seem like this test doesn't work here")
+			return
+		}
+	}
+
+	rename := func(path string) error {
+		return osutil.Rename(path, path+"new")
+	}
+
+	for _, path := range []string{"testdata/windows/ro/readonly", "testdata/windows/ro", "testdata/windows"} {
+		err := osutil.InWritableDir(rename, path)
+		if err != nil {
+			t.Errorf("Unexpected error %s: %s", path, err)
+		}
+		_, err = os.Stat(path + "new")
+		if err != nil {
+			t.Errorf("Unexpected error %s: %s", path, err)
+		}
+	}
+}

lib/osutil/replacingwriter.go

@@ -0,0 +1,48 @@
+// Copyright (C) 2014 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"
+	"io"
+)
+
+type ReplacingWriter struct {
+	Writer io.Writer
+	From   byte
+	To     []byte
+}
+
+func (w ReplacingWriter) Write(bs []byte) (int, error) {
+	var n, written int
+	var err error
+
+	newlineIdx := bytes.IndexByte(bs, w.From)
+	for newlineIdx >= 0 {
+		n, err = w.Writer.Write(bs[:newlineIdx])
+		written += n
+		if err != nil {
+			break
+		}
+		if len(w.To) > 0 {
+			n, err := w.Writer.Write(w.To)
+			if n == len(w.To) {
+				written++
+			}
+			if err != nil {
+				break
+			}
+		}
+		bs = bs[newlineIdx+1:]
+		newlineIdx = bytes.IndexByte(bs, w.From)
+	}
+
+	n, err = w.Writer.Write(bs)
+	written += n
+
+	return written, err
+}

lib/osutil/replacingwriter_test.go

@@ -0,0 +1,44 @@
+// Copyright (C) 2014 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"
+	"fmt"
+	"testing"
+)
+
+var testcases = []struct {
+	from byte
+	to   []byte
+	a, b string
+}{
+	{'\n', []byte{'\r', '\n'}, "", ""},
+	{'\n', []byte{'\r', '\n'}, "foo", "foo"},
+	{'\n', []byte{'\r', '\n'}, "foo\n", "foo\r\n"},
+	{'\n', []byte{'\r', '\n'}, "foo\nbar", "foo\r\nbar"},
+	{'\n', []byte{'\r', '\n'}, "foo\nbar\nbaz", "foo\r\nbar\r\nbaz"},
+	{'\n', []byte{'\r', '\n'}, "\nbar", "\r\nbar"},
+	{'o', []byte{'x', 'l', 'r'}, "\nfoo", "\nfxlrxlr"},
+	{'o', nil, "\nfoo", "\nf"},
+	{'f', []byte{}, "\nfoo", "\noo"},
+}
+
+func TestReplacingWriter(t *testing.T) {
+	for _, tc := range testcases {
+		var buf bytes.Buffer
+		w := ReplacingWriter{
+			Writer: &buf,
+			From:   tc.from,
+			To:     tc.to,
+		}
+		fmt.Fprint(w, tc.a)
+		if buf.String() != tc.b {
+			t.Errorf("%q != %q", buf.String(), tc.b)
+		}
+	}
+}