Add Windows node support.

The syscall.Stat_t doesn't exist on Windows, so it is replaced by an interface,
which Windows can fill out, and field access is replaced by function calls.

Common Unix functionality is put into "node_unix.go", so there is less boilerplate.

Symlinks are skipped on Windows, since they require admin privileges.

node.go

@@ -15,6 +15,7 @@ import (
 	"github.com/restic/restic/debug"
 	"github.com/restic/restic/pack"
 	"github.com/restic/restic/repository"
+	"runtime"
 )
 
 // Node is a file, directory or other item in a backup.
@@ -148,7 +149,7 @@ func (node *Node) CreateAt(path string, repo *repository.Repository) error {
 func (node Node) restoreMetadata(path string) error {
 	var err error
 
-	err = os.Lchown(path, int(node.UID), int(node.GID))
+	err = lchown(path, int(node.UID), int(node.GID))
 	if err != nil {
 		return errors.Annotate(err, "Lchown")
 	}
@@ -236,6 +237,10 @@ func (node Node) createFileAt(path string, repo *repository.Repository) error {
 }
 
 func (node Node) createSymlinkAt(path string) error {
+	// Windows does not allow non-admins to create soft links.
+	if runtime.GOOS == "windows" {
+		return nil
+	}
 	err := os.Symlink(node.LinkTarget, path)
 	if err != nil {
 		return errors.Annotate(err, "Symlink")
@@ -245,15 +250,15 @@ func (node Node) createSymlinkAt(path string) error {
 }
 
 func (node *Node) createDevAt(path string) error {
-	return syscall.Mknod(path, syscall.S_IFBLK|0600, int(node.Device))
+	return mknod(path, syscall.S_IFBLK|0600, int(node.Device))
 }
 
 func (node *Node) createCharDevAt(path string) error {
-	return syscall.Mknod(path, syscall.S_IFCHR|0600, int(node.Device))
+	return mknod(path, syscall.S_IFCHR|0600, int(node.Device))
 }
 
 func (node *Node) createFifoAt(path string) error {
-	return syscall.Mkfifo(path, 0600)
+	return mkfifo(path, 0600)
 }
 
 func (node Node) MarshalJSON() ([]byte, error) {
@@ -381,9 +386,19 @@ func (node *Node) isNewer(path string, fi os.FileInfo) bool {
 		return true
 	}
 
-	extendedStat := fi.Sys().(*syscall.Stat_t)
-	inode := extendedStat.Ino
-	size := uint64(extendedStat.Size)
+	size := uint64(fi.Size())
+
+	extendedStat, ok := toStatT(fi.Sys())
+	if !ok {
+		if node.ModTime != fi.ModTime() ||
+			node.Size != size {
+			debug.Log("node.isNewer", "node %v is newer: timestamp, size or inode changed", path)
+			return true
+		}
+		return false
+	}
+
+	inode := extendedStat.ino()
 
 	if node.ModTime != fi.ModTime() ||
 		node.ChangeTime != changeTime(extendedStat) ||
@@ -397,11 +412,11 @@ func (node *Node) isNewer(path string, fi os.FileInfo) bool {
 	return false
 }
 
-func (node *Node) fillUser(stat *syscall.Stat_t) error {
-	node.UID = stat.Uid
-	node.GID = stat.Gid
+func (node *Node) fillUser(stat statT) error {
+	node.UID = stat.uid()
+	node.GID = stat.gid()
 
-	username, err := lookupUsername(strconv.Itoa(int(stat.Uid)))
+	username, err := lookupUsername(strconv.Itoa(int(stat.uid())))
 	if err != nil {
 		return errors.Annotate(err, "fillUser")
 	}
@@ -439,12 +454,12 @@ func lookupUsername(uid string) (string, error) {
 }
 
 func (node *Node) fillExtra(path string, fi os.FileInfo) error {
-	stat, ok := fi.Sys().(*syscall.Stat_t)
+	stat, ok := toStatT(fi.Sys())
 	if !ok {
 		return nil
 	}
 
-	node.Inode = uint64(stat.Ino)
+	node.Inode = uint64(stat.ino())
 
 	node.fillTimes(stat)
 
@@ -456,15 +471,15 @@ func (node *Node) fillExtra(path string, fi os.FileInfo) error {
 
 	switch node.Type {
 	case "file":
-		node.Size = uint64(stat.Size)
-		node.Links = uint64(stat.Nlink)
+		node.Size = uint64(stat.size())
+		node.Links = uint64(stat.nlink())
 	case "dir":
 	case "symlink":
 		node.LinkTarget, err = os.Readlink(path)
 	case "dev":
-		node.Device = uint64(stat.Rdev)
+		node.Device = uint64(stat.rdev())
 	case "chardev":
-		node.Device = uint64(stat.Rdev)
+		node.Device = uint64(stat.rdev())
 	case "fifo":
 	case "socket":
 	default:
@@ -473,3 +488,32 @@ func (node *Node) fillExtra(path string, fi os.FileInfo) error {
 
 	return err
 }
+
+type statT interface {
+	dev() uint64
+	ino() uint64
+	nlink() uint64
+	uid() uint32
+	gid() uint32
+	rdev() uint64
+	size() int64
+	atim() syscall.Timespec
+	mtim() syscall.Timespec
+	ctim() syscall.Timespec
+}
+
+func mkfifo(path string, mode uint32) (err error) {
+	return mknod(path, mode|syscall.S_IFIFO, 0)
+}
+
+func (node *Node) fillTimes(stat statT) {
+	ctim := stat.ctim()
+	atim := stat.atim()
+	node.ChangeTime = time.Unix(ctim.Unix())
+	node.AccessTime = time.Unix(atim.Unix())
+}
+
+func changeTime(stat statT) time.Time {
+	ctim := stat.ctim()
+	return time.Unix(ctim.Unix())
+}