Use existing PAX headers for time

This removes the MSWINDOWS.* time fields and uses PAX times directly. I
didn't previously realize that PAX times could be negative, which
eliminates the need to store Windows times in a different format.

This also uses the LIBARCHIVE.creationtime field for creation times to
match OS X behavior.

backuptar/tar.go

@@ -30,10 +30,6 @@ const (
 
 const (
 	hdrFileAttributes     = "fileattr"
-	hdrAccessTime         = "accesstime"
-	hdrChangeTime         = "changetime"
-	hdrCreateTime         = "createtime"
-	hdrWriteTime          = "writetime"
 	hdrSecurityDescriptor = "sd"
 	hdrMountPoint         = "mountpoint"
 )
@@ -82,21 +78,7 @@ func copySparse(t *tar.Writer, br *winio.BackupStreamReader) error {
 	return nil
 }
 
-func win32TimeFromTar(key string, hdrs map[string]string, unixTime time.Time) syscall.Filetime {
-	if s, ok := hdrs[key]; ok {
-		n, err := strconv.ParseUint(s, 10, 64)
-		if err == nil {
-			return syscall.Filetime{uint32(n & 0xffffffff), uint32(n >> 32)}
-		}
-	}
-	return syscall.NsecToFiletime(unixTime.UnixNano())
-}
-
-func win32TimeToTar(ft syscall.Filetime) (string, time.Time) {
-	return fmt.Sprintf("%d", uint64(ft.LowDateTime)+(uint64(ft.HighDateTime)<<32)), time.Unix(0, ft.Nanoseconds())
-}
-
-// Writes a file to a tar writer using data from a Win32 backup stream.
+// WriteTarFileFromBackupStream writes a file to a tar writer using data from a Win32 backup stream.
 //
 // This encodes Win32 metadata as tar pax vendor extensions starting with MSWINDOWS.
 //
@@ -104,30 +86,22 @@ func win32TimeToTar(ft syscall.Filetime) (string, time.Time) {
 //
 // MSWINDOWS.fileattr: The Win32 file attributes, as a decimal value
 //
-// MSWINDOWS.accesstime: The last access time, as a Filetime expressed as a 64-bit decimal value.
-//
-// MSWINDOWS.createtime: The creation time, as a Filetime expressed as a 64-bit decimal value.
-//
-// MSWINDOWS.changetime: The creation time, as a Filetime expressed as a 64-bit decimal value.
-//
-// MSWINDOWS.writetime: The creation time, as a Filetime expressed as a 64-bit decimal value.
-//
 // MSWINDOWS.sd: The Win32 security descriptor, in SDDL (string) format
 //
 // MSWINDOWS.mountpoint: If present, this is a mount point and not a symlink, even though the type is '2' (symlink)
 func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size int64, fileInfo *winio.FileBasicInfo) error {
 	name = filepath.ToSlash(name)
 	hdr := &tar.Header{
-		Name:       name,
-		Size:       size,
-		Typeflag:   tar.TypeReg,
-		Winheaders: make(map[string]string),
+		Name:         name,
+		Size:         size,
+		Typeflag:     tar.TypeReg,
+		ModTime:      time.Unix(0, fileInfo.LastWriteTime.Nanoseconds()),
+		ChangeTime:   time.Unix(0, fileInfo.ChangeTime.Nanoseconds()),
+		AccessTime:   time.Unix(0, fileInfo.LastAccessTime.Nanoseconds()),
+		CreationTime: time.Unix(0, fileInfo.CreationTime.Nanoseconds()),
+		Winheaders:   make(map[string]string),
 	}
 	hdr.Winheaders[hdrFileAttributes] = fmt.Sprintf("%d", fileInfo.FileAttributes)
-	hdr.Winheaders[hdrAccessTime], hdr.AccessTime = win32TimeToTar(fileInfo.LastAccessTime)
-	hdr.Winheaders[hdrChangeTime], hdr.ChangeTime = win32TimeToTar(fileInfo.ChangeTime)
-	hdr.Winheaders[hdrCreateTime], _ = win32TimeToTar(fileInfo.CreationTime)
-	hdr.Winheaders[hdrWriteTime], hdr.ModTime = win32TimeToTar(fileInfo.LastWriteTime)
 
 	if (fileInfo.FileAttributes & syscall.FILE_ATTRIBUTE_DIRECTORY) != 0 {
 		hdr.Mode |= c_ISDIR
@@ -252,7 +226,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size
 	return nil
 }
 
-// Retrieves basic Win32 file information from a tar header, using the additional metadata written by
+// FileInfoFromHeader retrieves basic Win32 file information from a tar header, using the additional metadata written by
 // WriteTarFileFromBackupStream.
 func FileInfoFromHeader(hdr *tar.Header) (name string, size int64, fileInfo *winio.FileBasicInfo, err error) {
 	name = hdr.Name
@@ -260,10 +234,10 @@ func FileInfoFromHeader(hdr *tar.Header) (name string, size int64, fileInfo *win
 		size = hdr.Size
 	}
 	fileInfo = &winio.FileBasicInfo{
-		LastAccessTime: win32TimeFromTar(hdrAccessTime, hdr.Winheaders, hdr.AccessTime),
-		LastWriteTime:  win32TimeFromTar(hdrWriteTime, hdr.Winheaders, hdr.ModTime),
-		ChangeTime:     win32TimeFromTar(hdrChangeTime, hdr.Winheaders, hdr.ChangeTime),
-		CreationTime:   win32TimeFromTar(hdrCreateTime, hdr.Winheaders, hdr.ModTime),
+		LastAccessTime: syscall.NsecToFiletime(hdr.AccessTime.UnixNano()),
+		LastWriteTime:  syscall.NsecToFiletime(hdr.ModTime.UnixNano()),
+		ChangeTime:     syscall.NsecToFiletime(hdr.ChangeTime.UnixNano()),
+		CreationTime:   syscall.NsecToFiletime(hdr.CreationTime.UnixNano()),
 	}
 	if attrStr, ok := hdr.Winheaders[hdrFileAttributes]; ok {
 		attr, err := strconv.ParseUint(attrStr, 10, 32)
@@ -279,7 +253,7 @@ func FileInfoFromHeader(hdr *tar.Header) (name string, size int64, fileInfo *win
 	return
 }
 
-// Writes a Win32 backup stream from the current tar file. Since this function may process multiple
+// WriteBackupStreamFromTarFile writes a Win32 backup stream from the current tar file. Since this function may process multiple
 // tar file entries in order to collect all the alternate data streams for the file, it returns the next
 // tar file that was not processed, or io.EOF is there are no more.
 func WriteBackupStreamFromTarFile(w io.Writer, t *tar.Reader, hdr *tar.Header) (*tar.Header, error) {

backuptar/tar_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"io/ioutil"
 	"os"
+	"path/filepath"
+	"reflect"
 	"testing"
 
 	"github.com/Microsoft/go-winio"
@@ -61,5 +63,22 @@ func TestRoundTrip(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	ensurePresent(t, hdr.Winheaders, "fileattr", "sd", "accesstime", "changetime", "createtime", "writetime")
+	name, size, bi2, err := FileInfoFromHeader(hdr)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if name != filepath.ToSlash(f.Name()) {
+		t.Errorf("got name %s, expected %s", name, filepath.ToSlash(f.Name()))
+	}
+
+	if size != fi.Size() {
+		t.Errorf("got size %d, expected %d", size, fi.Size())
+	}
+
+	if !reflect.DeepEqual(*bi, *bi2) {
+		t.Errorf("got %#v, expected %#v", *bi, *bi2)
+	}
+
+	ensurePresent(t, hdr.Winheaders, "fileattr", "sd")
 }