Merge pull request #16 from Microsoft/fixing_wim

Fix various WIM bugs
2026-08-29 05:16:31 -04:00 · 2016-04-06 17:10:02 -07:00
parent 9e60d867bd a7636ef88a
commit 9f57cbbcbc
4 changed files with 320 additions and 93 deletions
@@ -0,0 +1 @@
+*.exe
@@ -21,7 +21,7 @@ const (
 	maxBlockSize = 32768
 	windowSize   = 32768

-	treePathLenCount = 17
+	maxTreePathLen = 16

 	e8filesize  = 12000000
 	maxe8offset = 0x3fffffff
@@ -97,8 +97,8 @@ func (f *decompressor) feed() bool {
 // getBits retrieves the next n bits from the byte stream. n
 // must be <= 16. It sets f.err on error.
 func (f *decompressor) getBits(n byte) uint16 {
-	if f.nbits < 16 {
-		if !f.feed() && n > f.nbits {
+	if f.nbits < n {
+		if !f.feed() {
 			f.err = io.ErrUnexpectedEOF
 		}
 	}
@@ -115,12 +115,12 @@ type huffman struct {
 }

 // buildTable builds a huffman decoding table from a slice of code lengths,
-// one per code, in order. Each code length must be less than treePathLenCount.
+// one per code, in order. Each code length must be <= maxTreePathLen.
 // See https://en.wikipedia.org/wiki/Canonical_Huffman_code.
 func buildTable(codelens []byte) *huffman {
 	// Determine the number of codes of each length, and the
 	// maximum length.
-	var count [treePathLenCount]uint
+	var count [maxTreePathLen + 1]uint
 	var max byte
 	for _, cl := range codelens {
 		count[cl]++
@@ -134,7 +134,7 @@ func buildTable(codelens []byte) *huffman {
 	}

 	// Determine the first code of each length.
-	var first [treePathLenCount]uint
+	var first [maxTreePathLen + 1]uint
 	code := uint(0)
 	for i := byte(1); i <= max; i++ {
 		code <<= 1
@@ -178,7 +178,7 @@ func (f *decompressor) getCode(h *huffman) uint16 {
 		f.err = errCorrupt
 		return 0
 	}
-	if f.nbits < 16 {
+	if f.nbits < maxTreePathLen {
 		f.feed()
 	}
 	// For codes with length < h.maxbits, it doesn't matter
@@ -309,14 +309,21 @@ func (f *decompressor) readBlockHeader() (byte, uint16, error) {
 	case verbatimBlock, alignedOffsetBlock:
 		// The caller will read the huffman trees.
 	case uncompressedBlock:
-		// Not sure if this can happen...
-		if f.nbits > 16 || f.nbits == 0 {
-			return 0, 0, errCorrupt
+		if f.nbits > 16 {
+			panic("impossible: more than one 16-bit word remains")
 		}

-		// Drop the remaining bits in the current 16-bit word.
-		f.nbits = 0
-		f.c = 0
+		// Drop the remaining bits in the current 16-bit word
+		// If there are no bits left, discard a full 16-bit word.
+		n := f.nbits
+		if n == 0 {
+			n = 16
+		}
+
+		f.getBits(n)
+		if f.err != nil {
+			return 0, 0, f.err
+		}

 		// Read the LRU values for the next block.
 		var lru [12]byte
@@ -0,0 +1,51 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/Microsoft/go-winio/wim"
+)
+
+func main() {
+	flag.Parse()
+	f, err := os.Open(flag.Arg(0))
+	if err != nil {
+		panic(err)
+	}
+
+	w, err := wim.NewReader(f)
+	if err != nil {
+		panic(err)
+
+	}
+
+	fmt.Printf("%#v\n%#v\n", w.Image[0], w.Image[0].Windows)
+
+	dir, err := w.Image[0].Open()
+	if err != nil {
+		panic(err)
+	}
+
+	err = recur(dir)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func recur(d *wim.File) error {
+	files, err := d.Readdir()
+	if err != nil {
+		return fmt.Errorf("%s: %s", d.Name, err)
+	}
+	for _, f := range files {
+		if f.IsDir() {
+			err = recur(f)
+			if err != nil {
+				return fmt.Errorf("%s: %s", f.Name, err)
+			}
+		}
+	}
+	return nil
+}
@@ -9,14 +9,55 @@ import (
 	"bytes"
 	"crypto/sha1"
 	"encoding/binary"
+	"encoding/xml"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
-	"syscall"
+	"strconv"
+	"time"
 	"unicode/utf16"
 )

+// File attribute constants from Windows.
+const (
+	FILE_ATTRIBUTE_READONLY            = 0x00000001
+	FILE_ATTRIBUTE_HIDDEN              = 0x00000002
+	FILE_ATTRIBUTE_SYSTEM              = 0x00000004
+	FILE_ATTRIBUTE_DIRECTORY           = 0x00000010
+	FILE_ATTRIBUTE_ARCHIVE             = 0x00000020
+	FILE_ATTRIBUTE_DEVICE              = 0x00000040
+	FILE_ATTRIBUTE_NORMAL              = 0x00000080
+	FILE_ATTRIBUTE_TEMPORARY           = 0x00000100
+	FILE_ATTRIBUTE_SPARSE_FILE         = 0x00000200
+	FILE_ATTRIBUTE_REPARSE_POINT       = 0x00000400
+	FILE_ATTRIBUTE_COMPRESSED          = 0x00000800
+	FILE_ATTRIBUTE_OFFLINE             = 0x00001000
+	FILE_ATTRIBUTE_NOT_CONTENT_INDEXED = 0x00002000
+	FILE_ATTRIBUTE_ENCRYPTED           = 0x00004000
+	FILE_ATTRIBUTE_INTEGRITY_STREAM    = 0x00008000
+	FILE_ATTRIBUTE_VIRTUAL             = 0x00010000
+	FILE_ATTRIBUTE_NO_SCRUB_DATA       = 0x00020000
+	FILE_ATTRIBUTE_EA                  = 0x00040000
+)
+
+// Windows processor architectures.
+const (
+	PROCESSOR_ARCHITECTURE_INTEL         = 0
+	PROCESSOR_ARCHITECTURE_MIPS          = 1
+	PROCESSOR_ARCHITECTURE_ALPHA         = 2
+	PROCESSOR_ARCHITECTURE_PPC           = 3
+	PROCESSOR_ARCHITECTURE_SHX           = 4
+	PROCESSOR_ARCHITECTURE_ARM           = 5
+	PROCESSOR_ARCHITECTURE_IA64          = 6
+	PROCESSOR_ARCHITECTURE_ALPHA64       = 7
+	PROCESSOR_ARCHITECTURE_MSIL          = 8
+	PROCESSOR_ARCHITECTURE_AMD64         = 9
+	PROCESSOR_ARCHITECTURE_IA32_ON_WIN64 = 10
+	PROCESSOR_ARCHITECTURE_NEUTRAL       = 11
+	PROCESSOR_ARCHITECTURE_ARM64         = 12
+)
+
 var wimImageTag = [...]byte{'M', 'S', 'W', 'I', 'M', 0, 0, 0}

 type guid struct {
@@ -128,9 +169,9 @@ type direntry struct {
 	SecurityID       uint32
 	SubdirOffset     int64
 	Unused1, Unused2 int64
-	CreationTime     syscall.Filetime
-	LastAccessTime   syscall.Filetime
-	LastWriteTime    syscall.Filetime
+	CreationTime     Filetime
+	LastAccessTime   Filetime
+	LastWriteTime    Filetime
 	Hash             SHA1Hash
 	Padding          uint32
 	ReparseHardLink  int64
@@ -150,14 +191,96 @@ type streamentry struct {

 const streamentrySize = 38

+// Filetime represents a Windows time.
+type Filetime struct {
+	LowDateTime  uint32
+	HighDateTime uint32
+}
+
+// Time returns the time as time.Time.
+func (ft *Filetime) Time() time.Time {
+	// 100-nanosecond intervals since January 1, 1601
+	nsec := int64(ft.HighDateTime)<<32 + int64(ft.LowDateTime)
+	// change starting time to the Epoch (00:00:00 UTC, January 1, 1970)
+	nsec -= 116444736000000000
+	// convert into nanoseconds
+	nsec *= 100
+	return time.Unix(0, nsec)
+}
+
+// UnmarshalXML unmarshals the time from a WIM XML blob.
+func (ft *Filetime) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	type time struct {
+		Low  string `xml:"LOWPART"`
+		High string `xml:"HIGHPART"`
+	}
+	var t time
+	err := d.DecodeElement(&t, &start)
+	if err != nil {
+		return err
+	}
+
+	low, err := strconv.ParseUint(t.Low, 0, 32)
+	if err != nil {
+		return err
+	}
+	high, err := strconv.ParseUint(t.High, 0, 32)
+	if err != nil {
+		return err
+	}
+
+	ft.LowDateTime = uint32(low)
+	ft.HighDateTime = uint32(high)
+	return nil
+}
+
+type info struct {
+	Image []ImageInfo `xml:"IMAGE"`
+}
+
+// ImageInfo contains information about the image.
+type ImageInfo struct {
+	Name         string       `xml:"NAME"`
+	Index        int          `xml:"INDEX,attr"`
+	CreationTime Filetime     `xml:"CREATIONTIME"`
+	ModTime      Filetime     `xml:"LASTMODIFICATIONTIME"`
+	Windows      *WindowsInfo `xml:"WINDOWS"`
+}
+
+// WindowsInfo contains information about the Windows installation in the image.
+type WindowsInfo struct {
+	Arch             byte     `xml:"ARCH"`
+	ProductName      string   `xml:"PRODUCTNAME"`
+	EditionID        string   `xml:"EDITIONID"`
+	InstallationType string   `xml:"INSTALLATIONTYPE"`
+	ProductType      string   `xml:"PRODUCTTYPE"`
+	Languages        []string `xml:"LANGUAGES>LANGUAGE"`
+	DefaultLanguage  string   `xml:"LANGUAGES>DEFAULT"`
+	Version          Version  `xml:"VERSION"`
+	SystemRoot       string   `xml:"SYSTEMROOT"`
+}
+
+// Version represents a Windows build version.
+type Version struct {
+	Major   int `xml:"MAJOR"`
+	Minor   int `xml:"MINOR"`
+	Build   int `xml:"BUILD"`
+	SPBuild int `xml:"SPBUILD"`
+	SPLevel int `xml:"SPLEVEL"`
+}
+
 // ParseError is returned when the WIM cannot be parsed.
 type ParseError struct {
 	Oper string
+	Path string
 	Err  error
 }

 func (e *ParseError) Error() string {
-	return "WIM parse error at " + e.Oper + ": " + e.Err.Error()
+	if e.Path == "" {
+		return "WIM parse error at " + e.Oper + ": " + e.Err.Error()
+	}
+	return fmt.Sprintf("WIM parse error: %s %s: %s", e.Oper, e.Path, e.Err.Error())
 }

 // Reader provides functions to read a WIM file.
@@ -166,7 +289,8 @@ type Reader struct {
 	r        io.ReaderAt
 	fileData map[SHA1Hash]resourceDescriptor

-	Image []*Image // The WIM's images.
+	XMLInfo string   // The XML information about the WIM.
+	Image   []*Image // The WIM's images.
 }

 // Image represents an image within a WIM file.
@@ -175,6 +299,8 @@ type Image struct {
 	offset     resourceDescriptor
 	sds        [][]byte
 	rootOffset int64
+
+	ImageInfo
 }

 // StreamHeader contains alternate data stream metadata.
@@ -197,15 +323,14 @@ type FileHeader struct {
 	ShortName          string
 	Attributes         uint32
 	SecurityDescriptor []byte
-	CreationTime       syscall.Filetime
-	LastAccessTime     syscall.Filetime
-	LastWriteTime      syscall.Filetime
+	CreationTime       Filetime
+	LastAccessTime     Filetime
+	LastWriteTime      Filetime
 	Hash               SHA1Hash
 	Size               int64
 	LinkID             int64
 	ReparseTag         uint32
 	ReparseReserved    uint32
-	ReparseStream      *Stream
 }

 // File represents a file or directory in a WIM image.
@@ -227,7 +352,7 @@ func NewReader(f io.ReaderAt) (*Reader, error) {
 	}

 	if r.hdr.ImageTag != wimImageTag {
-		return nil, &ParseError{"image tag", errors.New("not a WIM file")}
+		return nil, &ParseError{Oper: "image tag", Err: errors.New("not a WIM file")}
 	}

 	if r.hdr.Flags&^supportedHdrFlags != 0 {
@@ -246,8 +371,30 @@ func NewReader(f io.ReaderAt) (*Reader, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	xmlinfo, err := r.readXML()
+	if err != nil {
+		return nil, err
+	}
+
+	var info info
+	err = xml.Unmarshal([]byte(xmlinfo), &info)
+	if err != nil {
+		return nil, &ParseError{Oper: "XML info", Err: err}
+	}
+
+	for i, img := range images {
+		for _, imgInfo := range info.Image {
+			if imgInfo.Index == i+1 {
+				img.ImageInfo = imgInfo
+				break
+			}
+		}
+	}
+
 	r.fileData = fileData
 	r.Image = images
+	r.XMLInfo = xmlinfo
 	return r, nil
 }

@@ -281,8 +428,7 @@ func (r *Reader) readResource(hdr *resourceDescriptor) ([]byte, error) {
 	return ioutil.ReadAll(rsrc)
 }

-// ReadXML reads the XML metadata from a WIM.
-func (r *Reader) ReadXML() (string, error) {
+func (r *Reader) readXML() (string, error) {
 	if r.hdr.XMLData.CompressedSize() == 0 {
 		return "", nil
 	}
@@ -295,12 +441,12 @@ func (r *Reader) ReadXML() (string, error) {
 	XMLData := make([]uint16, r.hdr.XMLData.OriginalSize/2)
 	err = binary.Read(rsrc, binary.LittleEndian, XMLData)
 	if err != nil {
-		return "", &ParseError{"XML data", err}
+		return "", &ParseError{Oper: "XML data", Err: err}
 	}

 	// The BOM will always indicate little-endian UTF-16.
 	if XMLData[0] != 0xfeff {
-		return "", &ParseError{"XML data", errors.New("invalid BOM")}
+		return "", &ParseError{Oper: "XML data", Err: errors.New("invalid BOM")}
 	}
 	return string(utf16.Decode(XMLData[1:])), nil
 }
@@ -311,39 +457,39 @@ func (r *Reader) readOffsetTable(res *resourceDescriptor) (map[SHA1Hash]resource

 	offsetTable, err := r.readResource(res)
 	if err != nil {
-		return nil, nil, &ParseError{"offset table", err}
+		return nil, nil, &ParseError{Oper: "offset table", Err: err}
 	}

 	br := bytes.NewReader(offsetTable)
-	for {
+	for i := 0; ; i++ {
 		var res streamDescriptor
 		err := binary.Read(br, binary.LittleEndian, &res)
 		if err == io.EOF {
 			break
 		}
 		if err != nil {
-			return nil, nil, &ParseError{"offset table", err}
+			return nil, nil, &ParseError{Oper: "offset table", Err: err}
 		}
 		if res.Flags()&^supportedResFlags != 0 {
-			return nil, nil, &ParseError{"offset table", errors.New("unsupported resource flag")}
+			return nil, nil, &ParseError{Oper: "offset table", Err: errors.New("unsupported resource flag")}
 		}

 		// Validation for ad-hoc testing
 		if validate {
 			sec, err := r.resourceReader(&res.resourceDescriptor)
 			if err != nil {
-				return nil, nil, err
+				panic(fmt.Sprint(i, err))
 			}
 			hash := sha1.New()
 			_, err = io.Copy(hash, sec)
 			sec.Close()
 			if err != nil {
-				return nil, nil, err
+				panic(fmt.Sprint(i, err))
 			}
 			var cmphash SHA1Hash
 			copy(cmphash[:], hash.Sum(nil))
 			if cmphash != res.Hash {
-				return nil, nil, errors.New("hash mismatch")
+				panic(fmt.Sprint(i, "hash mismatch"))
 			}
 		}

@@ -359,7 +505,7 @@ func (r *Reader) readOffsetTable(res *resourceDescriptor) (map[SHA1Hash]resource
 	}

 	if len(images) != int(r.hdr.ImageCount) {
-		return nil, nil, &ParseError{"offset table", errors.New("mismatched image count")}
+		return nil, nil, &ParseError{Oper: "offset table", Err: errors.New("mismatched image count")}
 	}

 	return fileData, images, nil
@@ -369,7 +515,7 @@ func (r *Reader) readSecurityDescriptors(rsrc io.Reader) (sds [][]byte, n int64,
 	var secBlock securityblockDisk
 	err = binary.Read(rsrc, binary.LittleEndian, &secBlock)
 	if err != nil {
-		err = &ParseError{"security table", err}
+		err = &ParseError{Oper: "security table", Err: err}
 		return
 	}

@@ -378,7 +524,7 @@ func (r *Reader) readSecurityDescriptors(rsrc io.Reader) (sds [][]byte, n int64,
 	secSizes := make([]int64, secBlock.NumEntries)
 	err = binary.Read(rsrc, binary.LittleEndian, &secSizes)
 	if err != nil {
-		err = &ParseError{"security table sizes", err}
+		err = &ParseError{Oper: "security table sizes", Err: err}
 		return
 	}

@@ -389,7 +535,7 @@ func (r *Reader) readSecurityDescriptors(rsrc io.Reader) (sds [][]byte, n int64,
 		sd := make([]byte, size&0xffffffff)
 		_, err = io.ReadFull(rsrc, sd)
 		if err != nil {
-			err = &ParseError{"security descriptor", err}
+			err = &ParseError{Oper: "security descriptor", Err: err}
 			return
 		}
 		n += int64(len(sd))
@@ -398,7 +544,7 @@ func (r *Reader) readSecurityDescriptors(rsrc io.Reader) (sds [][]byte, n int64,

 	secsize := int64((secBlock.TotalLength + 7) &^ 7)
 	if n > secsize {
-		err = &ParseError{"security descriptor", errors.New("security descriptor table too small")}
+		err = &ParseError{Oper: "security descriptor", Err: errors.New("security descriptor table too small")}
 		return
 	}

@@ -432,7 +578,7 @@ func (img *Image) Open() (*File, error) {
 		return nil, err
 	}
 	if len(f) != 1 {
-		return nil, &ParseError{"root directory", errors.New("expected exactly 1 root directory entry")}
+		return nil, &ParseError{Oper: "root directory", Err: errors.New("expected exactly 1 root directory entry")}
 	}
 	return f[0], err
 }
@@ -457,7 +603,7 @@ func (img *Image) readdir(rsrc io.Reader) ([]*File, error) {
 func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 	lengthBuf, err := r.Peek(8)
 	if err != nil {
-		return nil, &ParseError{"directory length check", err}
+		return nil, &ParseError{Oper: "directory length check", Err: err}
 	}

 	left := int(binary.LittleEndian.Uint64(lengthBuf))
@@ -466,24 +612,46 @@ func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 	}

 	if left < direntrySize {
-		return nil, &ParseError{"directory entry", errors.New("size too short")}
+		return nil, &ParseError{Oper: "directory entry", Err: errors.New("size too short")}
 	}

 	var dentry direntry
 	err = binary.Read(r, binary.LittleEndian, &dentry)
 	if err != nil {
-		return nil, &ParseError{"directory entry", err}
+		return nil, &ParseError{Oper: "directory entry", Err: err}
 	}

 	left -= direntrySize

+	namesLen := int(dentry.FileNameLength + 2 + dentry.ShortNameLength)
+	if left < namesLen {
+		return nil, &ParseError{Oper: "directory entry", Err: errors.New("size too short for names")}
+	}
+
+	names := make([]uint16, namesLen/2)
+	err = binary.Read(r, binary.LittleEndian, names)
+	if err != nil {
+		return nil, &ParseError{Oper: "file name", Err: err}
+	}
+
+	left -= namesLen
+
+	var name, shortName string
+	if dentry.FileNameLength > 0 {
+		name = string(utf16.Decode(names[:dentry.FileNameLength/2]))
+	}
+
+	if dentry.ShortNameLength > 0 {
+		shortName = string(utf16.Decode(names[dentry.FileNameLength/2+1:]))
+	}
+
 	var offset resourceDescriptor
 	zerohash := SHA1Hash{}
 	if dentry.Hash != zerohash {
 		var ok bool
 		offset, ok = img.wim.fileData[dentry.Hash]
 		if !ok {
-			return nil, &ParseError{"directory entry", fmt.Errorf("could not find file data matching hash %v", dentry.Hash)}
+			return nil, &ParseError{Oper: "directory entry", Path: name, Err: fmt.Errorf("could not find file data matching hash %#v", dentry)}
 		}
 	}

@@ -495,6 +663,8 @@ func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 			LastWriteTime:  dentry.LastWriteTime,
 			Hash:           dentry.Hash,
 			Size:           offset.OriginalSize,
+			Name:           name,
+			ShortName:      shortName,
 		},

 		offset:       offset,
@@ -502,38 +672,28 @@ func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 		subdirOffset: dentry.SubdirOffset,
 	}

-	if dentry.Attributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT == 0 {
+	isDir := false
+
+	if dentry.Attributes&FILE_ATTRIBUTE_REPARSE_POINT == 0 {
 		f.LinkID = dentry.ReparseHardLink
+		if dentry.Attributes&FILE_ATTRIBUTE_DIRECTORY != 0 {
+			isDir = true
+		}
 	} else {
 		f.ReparseTag = uint32(dentry.ReparseHardLink)
 		f.ReparseReserved = uint32(dentry.ReparseHardLink >> 32)
 	}

+	if isDir && f.subdirOffset == 0 {
+		return nil, &ParseError{Oper: "directory entry", Path: name, Err: errors.New("no subdirectory data for directory")}
+	} else if !isDir && f.subdirOffset != 0 {
+		return nil, &ParseError{Oper: "directory entry", Path: name, Err: errors.New("unexpected subdirectory data for non-directory")}
+	}
+
 	if dentry.SecurityID != 0xffffffff {
 		f.SecurityDescriptor = img.sds[dentry.SecurityID]
 	}

-	namesLen := int(dentry.FileNameLength + 2 + dentry.ShortNameLength)
-	if left < namesLen {
-		return nil, &ParseError{"directory entry", errors.New("size too short for names")}
-	}
-
-	names := make([]uint16, namesLen/2)
-	err = binary.Read(r, binary.LittleEndian, names)
-	if err != nil {
-		return nil, &ParseError{"file name", err}
-	}
-
-	left -= namesLen
-
-	if dentry.FileNameLength > 0 {
-		f.Name = string(utf16.Decode(names[:dentry.FileNameLength/2]))
-	}
-
-	if dentry.ShortNameLength > 0 {
-		f.ShortName = string(utf16.Decode(names[dentry.FileNameLength/2+1:]))
-	}
-
 	_, err = r.Discard(left)
 	if err != nil {
 		return nil, err
@@ -546,19 +706,20 @@ func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 			if err != nil {
 				return nil, err
 			}
-			if !(s.Name == "" && s.Size == 0) {
-				if dentry.Attributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 && s.Name == "" {
-					f.ReparseStream = s
-				} else {
-					streams = append(streams, s)
-				}
+			// The first unnamed stream should be treated as the file stream.
+			if i == 0 && s.Name == "" {
+				f.Hash = s.Hash
+				f.Size = s.Size
+				f.offset = s.offset
+			} else if s.Name != "" {
+				streams = append(streams, s)
 			}
 		}
 		f.Streams = streams
 	}

-	if dentry.Attributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 && f.ReparseStream == nil {
-		return nil, &ParseError{"directory entry", errors.New("reparse point is missing reparse stream")}
+	if dentry.Attributes&FILE_ATTRIBUTE_REPARSE_POINT != 0 && f.Size == 0 {
+		return nil, &ParseError{Oper: "directory entry", Path: name, Err: errors.New("reparse point is missing reparse stream")}
 	}

 	return f, nil
@@ -567,28 +728,41 @@ func (img *Image) readNextEntry(r *bufio.Reader) (*File, error) {
 func (img *Image) readNextStream(r *bufio.Reader) (*Stream, error) {
 	lengthBuf, err := r.Peek(8)
 	if err != nil {
-		return nil, &ParseError{"stream length check", err}
+		return nil, &ParseError{Oper: "stream length check", Err: err}
 	}

 	left := int(binary.LittleEndian.Uint64(lengthBuf))
 	if left < streamentrySize {
-		return nil, &ParseError{"stream entry", errors.New("size too short")}
+		return nil, &ParseError{Oper: "stream entry", Err: errors.New("size too short")}
 	}

 	var sentry streamentry
 	err = binary.Read(r, binary.LittleEndian, &sentry)
 	if err != nil {
-		return nil, &ParseError{"stream entry", err}
+		return nil, &ParseError{Oper: "stream entry", Err: err}
 	}

 	left -= streamentrySize

+	if left < int(sentry.NameLength) {
+		return nil, &ParseError{Oper: "stream entry", Err: errors.New("size too short for name")}
+	}
+
+	names := make([]uint16, sentry.NameLength/2)
+	err = binary.Read(r, binary.LittleEndian, names)
+	if err != nil {
+		return nil, &ParseError{Oper: "file name", Err: err}
+	}
+
+	left -= int(sentry.NameLength)
+	name := string(utf16.Decode(names))
+
 	var offset resourceDescriptor
 	if sentry.Hash != (SHA1Hash{}) {
 		var ok bool
 		offset, ok = img.wim.fileData[sentry.Hash]
 		if !ok {
-			return nil, &ParseError{"stream entry", fmt.Errorf("could not find file data matching hash %v", sentry.Hash)}
+			return nil, &ParseError{Oper: "stream entry", Path: name, Err: fmt.Errorf("could not find file data matching hash %v", sentry.Hash)}
 		}
 	}

@@ -596,24 +770,12 @@ func (img *Image) readNextStream(r *bufio.Reader) (*Stream, error) {
 		StreamHeader: StreamHeader{
 			Hash: sentry.Hash,
 			Size: offset.OriginalSize,
+			Name: name,
 		},
 		wim:    img.wim,
 		offset: offset,
 	}

-	if left < int(sentry.NameLength) {
-		return nil, &ParseError{"stream entry", errors.New("size too short for name")}
-	}
-
-	names := make([]uint16, sentry.NameLength/2)
-	err = binary.Read(r, binary.LittleEndian, names)
-	if err != nil {
-		return nil, &ParseError{"file name", err}
-	}
-
-	left -= int(sentry.NameLength)
-	s.Name = string(utf16.Decode(names))
-
 	_, err = r.Discard(left)
 	if err != nil {
 		return nil, err
@@ -634,7 +796,7 @@ func (f *File) Open() (io.ReadCloser, error) {

 // Readdir reads the directory entries.
 func (f *File) Readdir() ([]*File, error) {
-	if f.Attributes&syscall.FILE_ATTRIBUTE_DIRECTORY == 0 {
+	if !f.IsDir() {
 		return nil, errors.New("not a directory")
 	}
 	rsrc, err := f.img.wim.resourceReaderWithOffset(&f.img.offset, f.subdirOffset)
@@ -644,3 +806,9 @@ func (f *File) Readdir() ([]*File, error) {
 	defer rsrc.Close()
 	return f.img.readdir(rsrc)
 }
+
+// IsDir returns whether the given file is a directory. It returns false when it
+// is a directory reparse point.
+func (f *FileHeader) IsDir() bool {
+	return f.Attributes&(FILE_ATTRIBUTE_DIRECTORY|FILE_ATTRIBUTE_REPARSE_POINT) == FILE_ATTRIBUTE_DIRECTORY
+}