archive/zip: zip64 support

R=golang-dev, r, adg
CC=golang-dev
https://golang.org/cl/6463050

src/pkg/archive/zip/reader.go

@@ -103,7 +103,7 @@ func (z *Reader) init(r io.ReaderAt, size int64) error {
 		}
 		z.File = append(z.File, f)
 	}
-	if uint16(len(z.File)) != end.directoryRecords {
+	if uint16(len(z.File)) != uint16(end.directoryRecords) { // only compare 16 bits here
 		// Return the readDirectoryHeader error if we read
 		// the wrong number of directory entries.
 		return err
@@ -123,7 +123,7 @@ func (f *File) Open() (rc io.ReadCloser, err error) {
 	if err != nil {
 		return
 	}
-	size := int64(f.CompressedSize)
+	size := int64(f.CompressedSize64)
 	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
 	switch f.Method {
 	case Store: // (no compression)
@@ -220,6 +220,8 @@ func readDirectoryHeader(f *File, r io.Reader) error {
 	f.CRC32 = b.uint32()
 	f.CompressedSize = b.uint32()
 	f.UncompressedSize = b.uint32()
+	f.CompressedSize64 = uint64(f.CompressedSize)
+	f.UncompressedSize64 = uint64(f.UncompressedSize)
 	filenameLen := int(b.uint16())
 	extraLen := int(b.uint16())
 	commentLen := int(b.uint16())
@@ -233,6 +235,28 @@ func readDirectoryHeader(f *File, r io.Reader) error {
 	f.Name = string(d[:filenameLen])
 	f.Extra = d[filenameLen : filenameLen+extraLen]
 	f.Comment = string(d[filenameLen+extraLen:])
+
+	if len(f.Extra) > 0 {
+		b := readBuf(f.Extra)
+		for len(b) > 0 {
+			tag := b.uint16()
+			size := b.uint16()
+			if tag == zip64ExtraId {
+				// update directory values from the zip64 extra block
+				eb := readBuf(b)
+				if len(eb) >= 8 {
+					f.UncompressedSize64 = eb.uint64()
+				}
+				if len(eb) >= 8 {
+					f.CompressedSize64 = eb.uint64()
+				}
+				if len(eb) >= 8 {
+					f.headerOffset = int64(eb.uint64())
+				}
+			}
+			b = b[size:]
+		}
+	}
 	return nil
 }
 
@@ -263,15 +287,23 @@ func readDataDescriptor(r io.Reader, f *File) error {
 		return err
 	}
 	b := readBuf(buf[:12])
-	f.CRC32 = b.uint32()
-	f.CompressedSize = b.uint32()
-	f.UncompressedSize = b.uint32()
+	if b.uint32() != f.CRC32 {
+		return ErrChecksum
+	}
+
+	// The two sizes that follow here can be either 32 bits or 64 bits
+	// but the spec is not very clear on this and different
+	// interpretations has been made causing incompatibilities. We
+	// already have the sizes from the central directory so we can
+	// just ignore these.
+
 	return nil
 }
 
 func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error) {
 	// look for directoryEndSignature in the last 1k, then in the last 65k
 	var buf []byte
+	var directoryEndOffset int64
 	for i, bLen := range []int64{1024, 65 * 1024} {
 		if bLen > size {
 			bLen = size
@@ -282,6 +314,7 @@ func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error)
 		}
 		if p := findSignatureInBlock(buf); p >= 0 {
 			buf = buf[p:]
+			directoryEndOffset = size - bLen + int64(p)
 			break
 		}
 		if i == 1 || bLen == size {
@@ -292,12 +325,12 @@ func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error)
 	// read header into struct
 	b := readBuf(buf[4:]) // skip signature
 	d := &directoryEnd{
-		diskNbr:            b.uint16(),
-		dirDiskNbr:         b.uint16(),
-		dirRecordsThisDisk: b.uint16(),
-		directoryRecords:   b.uint16(),
-		directorySize:      b.uint32(),
-		directoryOffset:    b.uint32(),
+		diskNbr:            uint32(b.uint16()),
+		dirDiskNbr:         uint32(b.uint16()),
+		dirRecordsThisDisk: uint64(b.uint16()),
+		directoryRecords:   uint64(b.uint16()),
+		directorySize:      uint64(b.uint32()),
+		directoryOffset:    uint64(b.uint32()),
 		commentLen:         b.uint16(),
 	}
 	l := int(d.commentLen)
@@ -305,9 +338,62 @@ func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error)
 		return nil, errors.New("zip: invalid comment length")
 	}
 	d.comment = string(b[:l])
+
+	p, err := findDirectory64End(r, directoryEndOffset)
+	if err == nil && p >= 0 {
+		err = readDirectory64End(r, p, d)
+	}
+	if err != nil {
+		return nil, err
+	}
 	return d, nil
 }
 
+// findDirectory64End tries to read the zip64 locator just before the
+// directory end and returns the offset of the zip64 directory end if
+// found.
+func findDirectory64End(r io.ReaderAt, directoryEndOffset int64) (int64, error) {
+	locOffset := directoryEndOffset - directory64LocLen
+	if locOffset < 0 {
+		return -1, nil // no need to look for a header outside the file
+	}
+	buf := make([]byte, directory64LocLen)
+	if _, err := r.ReadAt(buf, locOffset); err != nil {
+		return -1, err
+	}
+	b := readBuf(buf)
+	if sig := b.uint32(); sig != directory64LocSignature {
+		return -1, nil
+	}
+	b = b[4:]       // skip number of the disk with the start of the zip64 end of central directory
+	p := b.uint64() // relative offset of the zip64 end of central directory record
+	return int64(p), nil
+}
+
+// readDirectory64End reads the zip64 directory end and updates the
+// directory end with the zip64 directory end values.
+func readDirectory64End(r io.ReaderAt, offset int64, d *directoryEnd) (err error) {
+	buf := make([]byte, directory64EndLen)
+	if _, err := r.ReadAt(buf, offset); err != nil {
+		return err
+	}
+
+	b := readBuf(buf)
+	if sig := b.uint32(); sig != directory64EndSignature {
+		return ErrFormat
+	}
+
+	b = b[12:]                        // skip dir size, version and version needed (uint64 + 2x uint16)
+	d.diskNbr = b.uint32()            // number of this disk
+	d.dirDiskNbr = b.uint32()         // number of the disk with the start of the central directory
+	d.dirRecordsThisDisk = b.uint64() // total number of entries in the central directory on this disk
+	d.directoryRecords = b.uint64()   // total number of entries in the central directory
+	d.directorySize = b.uint64()      // size of the central directory
+	d.directoryOffset = b.uint64()    // offset of start of central directory with respect to the starting disk number
+
+	return nil
+}
+
 func findSignatureInBlock(b []byte) int {
 	for i := len(b) - directoryEndLen; i >= 0; i-- {
 		// defined from directoryEndSignature in struct.go
@@ -335,3 +421,9 @@ func (b *readBuf) uint32() uint32 {
 	*b = (*b)[4:]
 	return v
 }
+
+func (b *readBuf) uint64() uint64 {
+	v := binary.LittleEndian.Uint64(*b)
+	*b = (*b)[8:]
+	return v
+}

src/pkg/archive/zip/reader_test.go

@@ -206,6 +206,17 @@ var tests = []ZipTest{
 			},
 		},
 	},
+	{
+		Name: "zip64.zip",
+		File: []ZipTestFile{
+			{
+				Name:    "README",
+				Content: []byte("This small file is in ZIP64 format.\n"),
+				Mtime:   "08-10-12 14:33:32",
+				Mode:    0644,
+			},
+		},
+	},
 }
 
 var crossPlatform = []ZipTestFile{

src/pkg/archive/zip/struct.go

@@ -7,12 +7,19 @@ Package zip provides support for reading and writing ZIP archives.
 
 See: http://www.pkware.com/documents/casestudies/APPNOTE.TXT
 
-This package does not support ZIP64 or disk spanning.
+This package does not support disk spanning.
+
+A note about ZIP64:
+
+To be backwards compatible the FileHeader has both 32 and 64 bit Size
+fields. The 64 bit fields will always contain the correct value and
+for normal archives both fields will be the same. For files requiring
+the ZIP64 format the 32 bit fields will be 0xffffffff and the 64 bit
+fields must be used instead.
 */
 package zip
 
 import (
-	"errors"
 	"os"
 	"time"
 )
@@ -27,11 +34,16 @@ const (
 	fileHeaderSignature      = 0x04034b50
 	directoryHeaderSignature = 0x02014b50
 	directoryEndSignature    = 0x06054b50
+	directory64LocSignature  = 0x07064b50
+	directory64EndSignature  = 0x06064b50
 	dataDescriptorSignature  = 0x08074b50 // de-facto standard; required by OS X Finder
 	fileHeaderLen            = 30         // + filename + extra
 	directoryHeaderLen       = 46         // + filename + extra + comment
 	directoryEndLen          = 22         // + comment
 	dataDescriptorLen        = 16         // four uint32: descriptor signature, crc32, compressed size, size
+	dataDescriptor64Len      = 24         // descriptor with 8 byte sizes
+	directory64LocLen        = 20         //
+	directory64EndLen        = 56         // + extra
 
 	// Constants for the first byte in CreatorVersion
 	creatorFAT    = 0
@@ -39,22 +51,35 @@ const (
 	creatorNTFS   = 11
 	creatorVFAT   = 14
 	creatorMacOSX = 19
+
+	// version numbers
+	zipVersion20 = 20 // 2.0
+	zipVersion45 = 45 // 4.5 (reads and writes zip64 archives)
+
+	// limits for non zip64 files
+	uint16max = (1 << 16) - 1
+	uint32max = (1 << 32) - 1
+
+	// extra header id's
+	zip64ExtraId = 0x0001 // zip64 Extended Information Extra Field
 )
 
 type FileHeader struct {
-	Name             string
-	CreatorVersion   uint16
-	ReaderVersion    uint16
-	Flags            uint16
-	Method           uint16
-	ModifiedTime     uint16 // MS-DOS time
-	ModifiedDate     uint16 // MS-DOS date
-	CRC32            uint32
-	CompressedSize   uint32
-	UncompressedSize uint32
-	Extra            []byte
-	ExternalAttrs    uint32 // Meaning depends on CreatorVersion
-	Comment          string
+	Name               string
+	CreatorVersion     uint16
+	ReaderVersion      uint16
+	Flags              uint16
+	Method             uint16
+	ModifiedTime       uint16 // MS-DOS time
+	ModifiedDate       uint16 // MS-DOS date
+	CRC32              uint32
+	CompressedSize     uint32 // deprecated; use CompressedSize64
+	UncompressedSize   uint32 // deprecated; use UncompressedSize64
+	CompressedSize64   uint64
+	UncompressedSize64 uint64
+	Extra              []byte
+	ExternalAttrs      uint32 // Meaning depends on CreatorVersion
+	Comment            string
 }
 
 // FileInfo returns an os.FileInfo for the FileHeader.
@@ -67,8 +92,13 @@ type headerFileInfo struct {
 	fh *FileHeader
 }
 
-func (fi headerFileInfo) Name() string       { return fi.fh.Name }
-func (fi headerFileInfo) Size() int64        { return int64(fi.fh.UncompressedSize) }
+func (fi headerFileInfo) Name() string { return fi.fh.Name }
+func (fi headerFileInfo) Size() int64 {
+	if fi.fh.UncompressedSize64 > 0 {
+		return int64(fi.fh.UncompressedSize64)
+	}
+	return int64(fi.fh.UncompressedSize)
+}
 func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
 func (fi headerFileInfo) ModTime() time.Time { return fi.fh.ModTime() }
 func (fi headerFileInfo) Mode() os.FileMode  { return fi.fh.Mode() }
@@ -78,25 +108,27 @@ func (fi headerFileInfo) Sys() interface{}   { return fi.fh }
 // os.FileInfo.
 func FileInfoHeader(fi os.FileInfo) (*FileHeader, error) {
 	size := fi.Size()
-	if size > (1<<32 - 1) {
-		return nil, errors.New("zip: file over 4GB")
-	}
 	fh := &FileHeader{
-		Name:             fi.Name(),
-		UncompressedSize: uint32(size),
+		Name:               fi.Name(),
+		UncompressedSize64: uint64(size),
 	}
 	fh.SetModTime(fi.ModTime())
 	fh.SetMode(fi.Mode())
+	if fh.UncompressedSize64 > uint32max {
+		fh.UncompressedSize = uint32max
+	} else {
+		fh.UncompressedSize = uint32(fh.UncompressedSize64)
+	}
 	return fh, nil
 }
 
 type directoryEnd struct {
-	diskNbr            uint16 // unused
-	dirDiskNbr         uint16 // unused
-	dirRecordsThisDisk uint16 // unused
-	directoryRecords   uint16
-	directorySize      uint32
-	directoryOffset    uint32 // relative to file
+	diskNbr            uint32 // unused
+	dirDiskNbr         uint32 // unused
+	dirRecordsThisDisk uint64 // unused
+	directoryRecords   uint64
+	directorySize      uint64
+	directoryOffset    uint64 // relative to file
 	commentLen         uint16
 	comment            string
 }
@@ -190,6 +222,11 @@ func (h *FileHeader) SetMode(mode os.FileMode) {
 	}
 }
 
+// isZip64 returns true if the file size exceeds the 32 bit limit
+func (fh *FileHeader) isZip64() bool {
+	return fh.CompressedSize64 > uint32max || fh.UncompressedSize64 > uint32max
+}
+
 func msdosModeToFileMode(m uint32) (mode os.FileMode) {
 	if m&msdosDir != 0 {
 		mode = os.ModeDir | 0777

src/pkg/archive/zip/writer.go

@@ -27,7 +27,7 @@ type Writer struct {
 
 type header struct {
 	*FileHeader
-	offset uint32
+	offset uint64
 }
 
 // NewWriter returns a new Writer writing a zip file to w.
@@ -62,14 +62,36 @@ func (w *Writer) Close() error {
 		b.uint16(h.ModifiedTime)
 		b.uint16(h.ModifiedDate)
 		b.uint32(h.CRC32)
-		b.uint32(h.CompressedSize)
-		b.uint32(h.UncompressedSize)
+		if h.isZip64() || h.offset > uint32max {
+			// the file needs a zip64 header. store maxint in both
+			// 32 bit size fields (and offset later) to signal that the
+			// zip64 extra header should be used.
+			b.uint32(uint32max) // compressed size
+			b.uint32(uint32max) // uncompressed size
+
+			// append a zip64 extra block to Extra
+			var buf [28]byte // 2x uint16 + 3x uint64
+			eb := writeBuf(buf[:])
+			eb.uint16(zip64ExtraId)
+			eb.uint16(24) // size = 3x uint64
+			eb.uint64(h.UncompressedSize64)
+			eb.uint64(h.CompressedSize64)
+			eb.uint64(h.offset)
+			h.Extra = append(h.Extra, buf[:]...)
+		} else {
+			b.uint32(h.CompressedSize)
+			b.uint32(h.UncompressedSize)
+		}
 		b.uint16(uint16(len(h.Name)))
 		b.uint16(uint16(len(h.Extra)))
 		b.uint16(uint16(len(h.Comment)))
 		b = b[4:] // skip disk number start and internal file attr (2x uint16)
 		b.uint32(h.ExternalAttrs)
-		b.uint32(h.offset)
+		if h.offset > uint32max {
+			b.uint32(uint32max)
+		} else {
+			b.uint32(uint32(h.offset))
+		}
 		if _, err := w.cw.Write(buf[:]); err != nil {
 			return err
 		}
@@ -85,15 +107,52 @@ func (w *Writer) Close() error {
 	}
 	end := w.cw.count
 
+	records := uint64(len(w.dir))
+	size := uint64(end - start)
+	offset := uint64(start)
+
+	if records > uint16max || size > uint32max || offset > uint32max {
+		var buf [directory64EndLen + directory64LocLen]byte
+		b := writeBuf(buf[:])
+
+		// zip64 end of central directory record
+		b.uint32(directory64EndSignature)
+		b.uint64(directory64EndLen)
+		b.uint16(zipVersion45) // version made by
+		b.uint16(zipVersion45) // version needed to extract
+		b.uint32(0)            // number of this disk
+		b.uint32(0)            // number of the disk with the start of the central directory
+		b.uint64(records)      // total number of entries in the central directory on this disk
+		b.uint64(records)      // total number of entries in the central directory
+		b.uint64(size)         // size of the central directory
+		b.uint64(offset)       // offset of start of central directory with respect to the starting disk number
+
+		// zip64 end of central directory locator
+		b.uint32(directory64LocSignature)
+		b.uint32(0)           // number of the disk with the start of the zip64 end of central directory
+		b.uint64(uint64(end)) // relative offset of the zip64 end of central directory record
+		b.uint32(1)           // total number of disks
+
+		if _, err := w.cw.Write(buf[:]); err != nil {
+			return err
+		}
+
+		// store max values in the regular end record to signal that
+		// that the zip64 values should be used instead
+		records = uint16max
+		size = uint32max
+		offset = uint32max
+	}
+
 	// write end record
 	var buf [directoryEndLen]byte
 	b := writeBuf(buf[:])
 	b.uint32(uint32(directoryEndSignature))
-	b = b[4:]                     // skip over disk number and first disk number (2x uint16)
-	b.uint16(uint16(len(w.dir)))  // number of entries this disk
-	b.uint16(uint16(len(w.dir)))  // number of entries total
-	b.uint32(uint32(end - start)) // size of directory
-	b.uint32(uint32(start))       // start of directory
+	b = b[4:]                 // skip over disk number and first disk number (2x uint16)
+	b.uint16(uint16(records)) // number of entries this disk
+	b.uint16(uint16(records)) // number of entries total
+	b.uint32(uint32(size))    // size of directory
+	b.uint32(uint32(offset))  // start of directory
 	// skipped size of comment (always zero)
 	if _, err := w.cw.Write(buf[:]); err != nil {
 		return err
@@ -127,8 +186,9 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
 	}
 
 	fh.Flags |= 0x8 // we will write a data descriptor
-	fh.CreatorVersion = fh.CreatorVersion&0xff00 | 0x14
-	fh.ReaderVersion = 0x14
+
+	fh.CreatorVersion = fh.CreatorVersion&0xff00 | zipVersion20 // preserve compatibility byte
+	fh.ReaderVersion = zipVersion20
 
 	fw := &fileWriter{
 		zipw:      w.cw,
@@ -151,7 +211,7 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
 
 	h := &header{
 		FileHeader: fh,
-		offset:     uint32(w.cw.count),
+		offset:     uint64(w.cw.count),
 	}
 	w.dir = append(w.dir, h)
 	fw.header = h
@@ -173,9 +233,9 @@ func writeHeader(w io.Writer, h *FileHeader) error {
 	b.uint16(h.Method)
 	b.uint16(h.ModifiedTime)
 	b.uint16(h.ModifiedDate)
-	b.uint32(h.CRC32)
-	b.uint32(h.CompressedSize)
-	b.uint32(h.UncompressedSize)
+	b.uint32(0) // since we are writing a data descriptor crc32,
+	b.uint32(0) // compressed size,
+	b.uint32(0) // and uncompressed size should be zero
 	b.uint16(uint16(len(h.Name)))
 	b.uint16(uint16(len(h.Extra)))
 	if _, err := w.Write(buf[:]); err != nil {
@@ -218,17 +278,40 @@ func (w *fileWriter) close() error {
 	// update FileHeader
 	fh := w.header.FileHeader
 	fh.CRC32 = w.crc32.Sum32()
-	fh.CompressedSize = uint32(w.compCount.count)
-	fh.UncompressedSize = uint32(w.rawCount.count)
+	fh.CompressedSize64 = uint64(w.compCount.count)
+	fh.UncompressedSize64 = uint64(w.rawCount.count)
 
-	// write data descriptor
-	var buf [dataDescriptorLen]byte
-	b := writeBuf(buf[:])
+	if fh.isZip64() {
+		fh.CompressedSize = uint32max
+		fh.UncompressedSize = uint32max
+		fh.ReaderVersion = zipVersion45 // requires 4.5 - File uses ZIP64 format extensions
+	} else {
+		fh.CompressedSize = uint32(fh.CompressedSize64)
+		fh.UncompressedSize = uint32(fh.UncompressedSize64)
+	}
+
+	// Write data descriptor. This is more complicated than one would
+	// think, see e.g. comments in zipfile.c:putextended() and
+	// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7073588.
+	// The approach here is to write 8 byte sizes if needed without
+	// adding a zip64 extra in the local header (too late anyway).
+	var buf []byte
+	if fh.isZip64() {
+		buf = make([]byte, dataDescriptor64Len)
+	} else {
+		buf = make([]byte, dataDescriptorLen)
+	}
+	b := writeBuf(buf)
 	b.uint32(dataDescriptorSignature) // de-facto standard, required by OS X
 	b.uint32(fh.CRC32)
-	b.uint32(fh.CompressedSize)
-	b.uint32(fh.UncompressedSize)
-	_, err := w.zipw.Write(buf[:])
+	if fh.isZip64() {
+		b.uint64(fh.CompressedSize64)
+		b.uint64(fh.UncompressedSize64)
+	} else {
+		b.uint32(fh.CompressedSize)
+		b.uint32(fh.UncompressedSize)
+	}
+	_, err := w.zipw.Write(buf)
 	return err
 }
 
@@ -262,3 +345,8 @@ func (b *writeBuf) uint32(v uint32) {
 	binary.LittleEndian.PutUint32(*b, v)
 	*b = (*b)[4:]
 }
+
+func (b *writeBuf) uint64(v uint64) {
+	binary.LittleEndian.PutUint64(*b, v)
+	*b = (*b)[8:]
+}

src/pkg/archive/zip/zip_test.go

@@ -9,7 +9,8 @@ package zip
 import (
 	"bytes"
 	"fmt"
-	"reflect"
+	"io"
+	"io/ioutil"
 	"strings"
 	"testing"
 	"time"
@@ -58,6 +59,33 @@ func TestModTime(t *testing.T) {
 	}
 }
 
+func testHeaderRoundTrip(fh *FileHeader, wantUncompressedSize uint32, wantUncompressedSize64 uint64, t *testing.T) {
+	fi := fh.FileInfo()
+	fh2, err := FileInfoHeader(fi)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := fh2.Name, fh.Name; got != want {
+		t.Errorf("Name: got %s, want %s\n", got, want)
+	}
+	if got, want := fh2.UncompressedSize, wantUncompressedSize; got != want {
+		t.Errorf("UncompressedSize: got %d, want %d\n", got, want)
+	}
+	if got, want := fh2.UncompressedSize64, wantUncompressedSize64; got != want {
+		t.Errorf("UncompressedSize64: got %d, want %d\n", got, want)
+	}
+	if got, want := fh2.ModifiedTime, fh.ModifiedTime; got != want {
+		t.Errorf("ModifiedTime: got %d, want %d\n", got, want)
+	}
+	if got, want := fh2.ModifiedDate, fh.ModifiedDate; got != want {
+		t.Errorf("ModifiedDate: got %d, want %d\n", got, want)
+	}
+
+	if sysfh, ok := fi.Sys().(*FileHeader); !ok && sysfh != fh {
+		t.Errorf("Sys didn't return original *FileHeader")
+	}
+}
+
 func TestFileHeaderRoundTrip(t *testing.T) {
 	fh := &FileHeader{
 		Name:             "foo.txt",
@@ -65,17 +93,83 @@ func TestFileHeaderRoundTrip(t *testing.T) {
 		ModifiedTime:     1234,
 		ModifiedDate:     5678,
 	}
-	fi := fh.FileInfo()
-	fh2, err := FileInfoHeader(fi)
+	testHeaderRoundTrip(fh, fh.UncompressedSize, uint64(fh.UncompressedSize), t)
+}
 
-	// Ignore these fields:
-	fh2.CreatorVersion = 0
-	fh2.ExternalAttrs = 0
+func TestFileHeaderRoundTrip64(t *testing.T) {
+	fh := &FileHeader{
+		Name:               "foo.txt",
+		UncompressedSize64: 9876543210,
+		ModifiedTime:       1234,
+		ModifiedDate:       5678,
+	}
+	testHeaderRoundTrip(fh, uint32max, fh.UncompressedSize64, t)
+}
 
-	if !reflect.DeepEqual(fh, fh2) {
-		t.Errorf("mismatch\n input=%#v\noutput=%#v\nerr=%v", fh, fh2, err)
+func TestZip64(t *testing.T) {
+	if testing.Short() {
+		t.Logf("slow test; skipping")
+		return
 	}
-	if sysfh, ok := fi.Sys().(*FileHeader); !ok && sysfh != fh {
-		t.Errorf("Sys didn't return original *FileHeader")
+	// write 2^32 bytes plus "END\n" to a zip file
+	buf := new(bytes.Buffer)
+	w := NewWriter(buf)
+	f, err := w.Create("huge.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	chunk := make([]byte, 1024)
+	for i := range chunk {
+		chunk[i] = '.'
+	}
+	chunk[len(chunk)-1] = '\n'
+	end := []byte("END\n")
+	for i := 0; i < (1<<32)/1024; i++ {
+		_, err := f.Write(chunk)
+		if err != nil {
+			t.Fatal("write chunk:", err)
+		}
+	}
+	_, err = f.Write(end)
+	if err != nil {
+		t.Fatal("write end:", err)
+	}
+	if err := w.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	// read back zip file and check that we get to the end of it
+	r, err := NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))
+	if err != nil {
+		t.Fatal("reader:", err)
+	}
+	f0 := r.File[0]
+	rc, err := f0.Open()
+	if err != nil {
+		t.Fatal("opening:", err)
+	}
+	for i := 0; i < (1<<32)/1024; i++ {
+		_, err := io.ReadFull(rc, chunk)
+		if err != nil {
+			t.Fatal("read:", err)
+		}
+	}
+	gotEnd, err := ioutil.ReadAll(rc)
+	if err != nil {
+		t.Fatal("read end:", err)
+	}
+	if !bytes.Equal(gotEnd, end) {
+		t.Errorf("End of zip64 archive %q, want %q", gotEnd, end)
+	}
+	err = rc.Close()
+	if err != nil {
+		t.Fatal("closing:", err)
+	}
+	if got, want := f0.UncompressedSize, uint32(uint32max); got != want {
+		t.Errorf("UncompressedSize %d, want %d", got, want)
+	}
+
+	if got, want := f0.UncompressedSize64, (1<<32)+uint64(len(end)); got != want {
+		t.Errorf("UncompressedSize64 %d, want %d", got, want)
 	}
 }