Adding upstream version 1.21.8.upstream/1.21.8

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 979 insertions, 0 deletions

diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
new file mode 100644
index 0000000..1fde1de
--- /dev/null
+++ b/src/archive/zip/reader.go
@@ -0,0 +1,979 @@
+// Copyright 2010 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.
+
+package zip
+
+import (
+	"bufio"
+	"encoding/binary"
+	"errors"
+	"hash"
+	"hash/crc32"
+	"internal/godebug"
+	"io"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+)
+
+var zipinsecurepath = godebug.New("zipinsecurepath")
+
+var (
+	ErrFormat       = errors.New("zip: not a valid zip file")
+	ErrAlgorithm    = errors.New("zip: unsupported compression algorithm")
+	ErrChecksum     = errors.New("zip: checksum error")
+	ErrInsecurePath = errors.New("zip: insecure file path")
+)
+
+// A Reader serves content from a ZIP archive.
+type Reader struct {
+	r             io.ReaderAt
+	File          []*File
+	Comment       string
+	decompressors map[uint16]Decompressor
+
+	// Some JAR files are zip files with a prefix that is a bash script.
+	// The baseOffset field is the start of the zip file proper.
+	baseOffset int64
+
+	// fileList is a list of files sorted by ename,
+	// for use by the Open method.
+	fileListOnce sync.Once
+	fileList     []fileListEntry
+}
+
+// A ReadCloser is a Reader that must be closed when no longer needed.
+type ReadCloser struct {
+	f *os.File
+	Reader
+}
+
+// A File is a single file in a ZIP archive.
+// The file information is in the embedded FileHeader.
+// The file content can be accessed by calling Open.
+type File struct {
+	FileHeader
+	zip          *Reader
+	zipr         io.ReaderAt
+	headerOffset int64 // includes overall ZIP archive baseOffset
+	zip64        bool  // zip64 extended information extra field presence
+}
+
+// OpenReader will open the Zip file specified by name and return a ReadCloser.
+//
+// If any file inside the archive uses a non-local name
+// (as defined by [filepath.IsLocal]) or a name containing backslashes
+// and the GODEBUG environment variable contains `zipinsecurepath=0`,
+// OpenReader returns the reader with an ErrInsecurePath error.
+// A future version of Go may introduce this behavior by default.
+// Programs that want to accept non-local names can ignore
+// the ErrInsecurePath error and use the returned reader.
+func OpenReader(name string) (*ReadCloser, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	fi, err := f.Stat()
+	if err != nil {
+		f.Close()
+		return nil, err
+	}
+	r := new(ReadCloser)
+	if err = r.init(f, fi.Size()); err != nil && err != ErrInsecurePath {
+		f.Close()
+		return nil, err
+	}
+	r.f = f
+	return r, err
+}
+
+// NewReader returns a new Reader reading from r, which is assumed to
+// have the given size in bytes.
+//
+// If any file inside the archive uses a non-local name
+// (as defined by [filepath.IsLocal]) or a name containing backslashes
+// and the GODEBUG environment variable contains `zipinsecurepath=0`,
+// NewReader returns the reader with an ErrInsecurePath error.
+// A future version of Go may introduce this behavior by default.
+// Programs that want to accept non-local names can ignore
+// the ErrInsecurePath error and use the returned reader.
+func NewReader(r io.ReaderAt, size int64) (*Reader, error) {
+	if size < 0 {
+		return nil, errors.New("zip: size cannot be negative")
+	}
+	zr := new(Reader)
+	var err error
+	if err = zr.init(r, size); err != nil && err != ErrInsecurePath {
+		return nil, err
+	}
+	return zr, err
+}
+
+func (r *Reader) init(rdr io.ReaderAt, size int64) error {
+	end, baseOffset, err := readDirectoryEnd(rdr, size)
+	if err != nil {
+		return err
+	}
+	r.r = rdr
+	r.baseOffset = baseOffset
+	// Since the number of directory records is not validated, it is not
+	// safe to preallocate r.File without first checking that the specified
+	// number of files is reasonable, since a malformed archive may
+	// indicate it contains up to 1 << 128 - 1 files. Since each file has a
+	// header which will be _at least_ 30 bytes we can safely preallocate
+	// if (data size / 30) >= end.directoryRecords.
+	if end.directorySize < uint64(size) && (uint64(size)-end.directorySize)/30 >= end.directoryRecords {
+		r.File = make([]*File, 0, end.directoryRecords)
+	}
+	r.Comment = end.comment
+	rs := io.NewSectionReader(rdr, 0, size)
+	if _, err = rs.Seek(r.baseOffset+int64(end.directoryOffset), io.SeekStart); err != nil {
+		return err
+	}
+	buf := bufio.NewReader(rs)
+
+	// The count of files inside a zip is truncated to fit in a uint16.
+	// Gloss over this by reading headers until we encounter
+	// a bad one, and then only report an ErrFormat or UnexpectedEOF if
+	// the file count modulo 65536 is incorrect.
+	for {
+		f := &File{zip: r, zipr: rdr}
+		err = readDirectoryHeader(f, buf)
+		if err == ErrFormat || err == io.ErrUnexpectedEOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		f.headerOffset += r.baseOffset
+		r.File = append(r.File, f)
+	}
+	if uint16(len(r.File)) != uint16(end.directoryRecords) { // only compare 16 bits here
+		// Return the readDirectoryHeader error if we read
+		// the wrong number of directory entries.
+		return err
+	}
+	if zipinsecurepath.Value() == "0" {
+		for _, f := range r.File {
+			if f.Name == "" {
+				// Zip permits an empty file name field.
+				continue
+			}
+			// The zip specification states that names must use forward slashes,
+			// so consider any backslashes in the name insecure.
+			if !filepath.IsLocal(f.Name) || strings.Contains(f.Name, `\`) {
+				zipinsecurepath.IncNonDefault()
+				return ErrInsecurePath
+			}
+		}
+	}
+	return nil
+}
+
+// RegisterDecompressor registers or overrides a custom decompressor for a
+// specific method ID. If a decompressor for a given method is not found,
+// Reader will default to looking up the decompressor at the package level.
+func (r *Reader) RegisterDecompressor(method uint16, dcomp Decompressor) {
+	if r.decompressors == nil {
+		r.decompressors = make(map[uint16]Decompressor)
+	}
+	r.decompressors[method] = dcomp
+}
+
+func (r *Reader) decompressor(method uint16) Decompressor {
+	dcomp := r.decompressors[method]
+	if dcomp == nil {
+		dcomp = decompressor(method)
+	}
+	return dcomp
+}
+
+// Close closes the Zip file, rendering it unusable for I/O.
+func (rc *ReadCloser) Close() error {
+	return rc.f.Close()
+}
+
+// DataOffset returns the offset of the file's possibly-compressed
+// data, relative to the beginning of the zip file.
+//
+// Most callers should instead use Open, which transparently
+// decompresses data and verifies checksums.
+func (f *File) DataOffset() (offset int64, err error) {
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return
+	}
+	return f.headerOffset + bodyOffset, nil
+}
+
+// Open returns a ReadCloser that provides access to the File's contents.
+// Multiple files may be read concurrently.
+func (f *File) Open() (io.ReadCloser, error) {
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return nil, err
+	}
+	if strings.HasSuffix(f.Name, "/") {
+		// The ZIP specification (APPNOTE.TXT) specifies that directories, which
+		// are technically zero-byte files, must not have any associated file
+		// data. We previously tried failing here if f.CompressedSize64 != 0,
+		// but it turns out that a number of implementations (namely, the Java
+		// jar tool) don't properly set the storage method on directories
+		// resulting in a file with compressed size > 0 but uncompressed size ==
+		// 0. We still want to fail when a directory has associated uncompressed
+		// data, but we are tolerant of cases where the uncompressed size is
+		// zero but compressed size is not.
+		if f.UncompressedSize64 != 0 {
+			return &dirReader{ErrFormat}, nil
+		} else {
+			return &dirReader{io.EOF}, nil
+		}
+	}
+	size := int64(f.CompressedSize64)
+	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
+	dcomp := f.zip.decompressor(f.Method)
+	if dcomp == nil {
+		return nil, ErrAlgorithm
+	}
+	var rc io.ReadCloser = dcomp(r)
+	var desr io.Reader
+	if f.hasDataDescriptor() {
+		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
+	}
+	rc = &checksumReader{
+		rc:   rc,
+		hash: crc32.NewIEEE(),
+		f:    f,
+		desr: desr,
+	}
+	return rc, nil
+}
+
+// OpenRaw returns a Reader that provides access to the File's contents without
+// decompression.
+func (f *File) OpenRaw() (io.Reader, error) {
+	bodyOffset, err := f.findBodyOffset()
+	if err != nil {
+		return nil, err
+	}
+	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, int64(f.CompressedSize64))
+	return r, nil
+}
+
+type dirReader struct {
+	err error
+}
+
+func (r *dirReader) Read([]byte) (int, error) {
+	return 0, r.err
+}
+
+func (r *dirReader) Close() error {
+	return nil
+}
+
+type checksumReader struct {
+	rc    io.ReadCloser
+	hash  hash.Hash32
+	nread uint64 // number of bytes read so far
+	f     *File
+	desr  io.Reader // if non-nil, where to read the data descriptor
+	err   error     // sticky error
+}
+
+func (r *checksumReader) Stat() (fs.FileInfo, error) {
+	return headerFileInfo{&r.f.FileHeader}, nil
+}
+
+func (r *checksumReader) Read(b []byte) (n int, err error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+	n, err = r.rc.Read(b)
+	r.hash.Write(b[:n])
+	r.nread += uint64(n)
+	if r.nread > r.f.UncompressedSize64 {
+		return 0, ErrFormat
+	}
+	if err == nil {
+		return
+	}
+	if err == io.EOF {
+		if r.nread != r.f.UncompressedSize64 {
+			return 0, io.ErrUnexpectedEOF
+		}
+		if r.desr != nil {
+			if err1 := readDataDescriptor(r.desr, r.f); err1 != nil {
+				if err1 == io.EOF {
+					err = io.ErrUnexpectedEOF
+				} else {
+					err = err1
+				}
+			} else if r.hash.Sum32() != r.f.CRC32 {
+				err = ErrChecksum
+			}
+		} else {
+			// If there's not a data descriptor, we still compare
+			// the CRC32 of what we've read against the file header
+			// or TOC's CRC32, if it seems like it was set.
+			if r.f.CRC32 != 0 && r.hash.Sum32() != r.f.CRC32 {
+				err = ErrChecksum
+			}
+		}
+	}
+	r.err = err
+	return
+}
+
+func (r *checksumReader) Close() error { return r.rc.Close() }
+
+// findBodyOffset does the minimum work to verify the file has a header
+// and returns the file body offset.
+func (f *File) findBodyOffset() (int64, error) {
+	var buf [fileHeaderLen]byte
+	if _, err := f.zipr.ReadAt(buf[:], f.headerOffset); err != nil {
+		return 0, err
+	}
+	b := readBuf(buf[:])
+	if sig := b.uint32(); sig != fileHeaderSignature {
+		return 0, ErrFormat
+	}
+	b = b[22:] // skip over most of the header
+	filenameLen := int(b.uint16())
+	extraLen := int(b.uint16())
+	return int64(fileHeaderLen + filenameLen + extraLen), nil
+}
+
+// readDirectoryHeader attempts to read a directory header from r.
+// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
+// and ErrFormat if it doesn't find a valid header signature.
+func readDirectoryHeader(f *File, r io.Reader) error {
+	var buf [directoryHeaderLen]byte
+	if _, err := io.ReadFull(r, buf[:]); err != nil {
+		return err
+	}
+	b := readBuf(buf[:])
+	if sig := b.uint32(); sig != directoryHeaderSignature {
+		return ErrFormat
+	}
+	f.CreatorVersion = b.uint16()
+	f.ReaderVersion = b.uint16()
+	f.Flags = b.uint16()
+	f.Method = b.uint16()
+	f.ModifiedTime = b.uint16()
+	f.ModifiedDate = b.uint16()
+	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())
+	b = b[4:] // skipped start disk number and internal attributes (2x uint16)
+	f.ExternalAttrs = b.uint32()
+	f.headerOffset = int64(b.uint32())
+	d := make([]byte, filenameLen+extraLen+commentLen)
+	if _, err := io.ReadFull(r, d); err != nil {
+		return err
+	}
+	f.Name = string(d[:filenameLen])
+	f.Extra = d[filenameLen : filenameLen+extraLen]
+	f.Comment = string(d[filenameLen+extraLen:])
+
+	// Determine the character encoding.
+	utf8Valid1, utf8Require1 := detectUTF8(f.Name)
+	utf8Valid2, utf8Require2 := detectUTF8(f.Comment)
+	switch {
+	case !utf8Valid1 || !utf8Valid2:
+		// Name and Comment definitely not UTF-8.
+		f.NonUTF8 = true
+	case !utf8Require1 && !utf8Require2:
+		// Name and Comment use only single-byte runes that overlap with UTF-8.
+		f.NonUTF8 = false
+	default:
+		// Might be UTF-8, might be some other encoding; preserve existing flag.
+		// Some ZIP writers use UTF-8 encoding without setting the UTF-8 flag.
+		// Since it is impossible to always distinguish valid UTF-8 from some
+		// other encoding (e.g., GBK or Shift-JIS), we trust the flag.
+		f.NonUTF8 = f.Flags&0x800 == 0
+	}
+
+	needUSize := f.UncompressedSize == ^uint32(0)
+	needCSize := f.CompressedSize == ^uint32(0)
+	needHeaderOffset := f.headerOffset == int64(^uint32(0))
+
+	// Best effort to find what we need.
+	// Other zip authors might not even follow the basic format,
+	// and we'll just ignore the Extra content in that case.
+	var modified time.Time
+parseExtras:
+	for extra := readBuf(f.Extra); len(extra) >= 4; { // need at least tag and size
+		fieldTag := extra.uint16()
+		fieldSize := int(extra.uint16())
+		if len(extra) < fieldSize {
+			break
+		}
+		fieldBuf := extra.sub(fieldSize)
+
+		switch fieldTag {
+		case zip64ExtraID:
+			f.zip64 = true
+
+			// update directory values from the zip64 extra block.
+			// They should only be consulted if the sizes read earlier
+			// are maxed out.
+			// See golang.org/issue/13367.
+			if needUSize {
+				needUSize = false
+				if len(fieldBuf) < 8 {
+					return ErrFormat
+				}
+				f.UncompressedSize64 = fieldBuf.uint64()
+			}
+			if needCSize {
+				needCSize = false
+				if len(fieldBuf) < 8 {
+					return ErrFormat
+				}
+				f.CompressedSize64 = fieldBuf.uint64()
+			}
+			if needHeaderOffset {
+				needHeaderOffset = false
+				if len(fieldBuf) < 8 {
+					return ErrFormat
+				}
+				f.headerOffset = int64(fieldBuf.uint64())
+			}
+		case ntfsExtraID:
+			if len(fieldBuf) < 4 {
+				continue parseExtras
+			}
+			fieldBuf.uint32()        // reserved (ignored)
+			for len(fieldBuf) >= 4 { // need at least tag and size
+				attrTag := fieldBuf.uint16()
+				attrSize := int(fieldBuf.uint16())
+				if len(fieldBuf) < attrSize {
+					continue parseExtras
+				}
+				attrBuf := fieldBuf.sub(attrSize)
+				if attrTag != 1 || attrSize != 24 {
+					continue // Ignore irrelevant attributes
+				}
+
+				const ticksPerSecond = 1e7    // Windows timestamp resolution
+				ts := int64(attrBuf.uint64()) // ModTime since Windows epoch
+				secs := int64(ts / ticksPerSecond)
+				nsecs := (1e9 / ticksPerSecond) * int64(ts%ticksPerSecond)
+				epoch := time.Date(1601, time.January, 1, 0, 0, 0, 0, time.UTC)
+				modified = time.Unix(epoch.Unix()+secs, nsecs)
+			}
+		case unixExtraID, infoZipUnixExtraID:
+			if len(fieldBuf) < 8 {
+				continue parseExtras
+			}
+			fieldBuf.uint32()              // AcTime (ignored)
+			ts := int64(fieldBuf.uint32()) // ModTime since Unix epoch
+			modified = time.Unix(ts, 0)
+		case extTimeExtraID:
+			if len(fieldBuf) < 5 || fieldBuf.uint8()&1 == 0 {
+				continue parseExtras
+			}
+			ts := int64(fieldBuf.uint32()) // ModTime since Unix epoch
+			modified = time.Unix(ts, 0)
+		}
+	}
+
+	msdosModified := msDosTimeToTime(f.ModifiedDate, f.ModifiedTime)
+	f.Modified = msdosModified
+	if !modified.IsZero() {
+		f.Modified = modified.UTC()
+
+		// If legacy MS-DOS timestamps are set, we can use the delta between
+		// the legacy and extended versions to estimate timezone offset.
+		//
+		// A non-UTC timezone is always used (even if offset is zero).
+		// Thus, FileHeader.Modified.Location() == time.UTC is useful for
+		// determining whether extended timestamps are present.
+		// This is necessary for users that need to do additional time
+		// calculations when dealing with legacy ZIP formats.
+		if f.ModifiedTime != 0 || f.ModifiedDate != 0 {
+			f.Modified = modified.In(timeZone(msdosModified.Sub(modified)))
+		}
+	}
+
+	// Assume that uncompressed size 2³²-1 could plausibly happen in
+	// an old zip32 file that was sharding inputs into the largest chunks
+	// possible (or is just malicious; search the web for 42.zip).
+	// If needUSize is true still, it means we didn't see a zip64 extension.
+	// As long as the compressed size is not also 2³²-1 (implausible)
+	// and the header is not also 2³²-1 (equally implausible),
+	// accept the uncompressed size 2³²-1 as valid.
+	// If nothing else, this keeps archive/zip working with 42.zip.
+	_ = needUSize
+
+	if needCSize || needHeaderOffset {
+		return ErrFormat
+	}
+
+	return nil
+}
+
+func readDataDescriptor(r io.Reader, f *File) error {
+	var buf [dataDescriptorLen]byte
+	// The spec says: "Although not originally assigned a
+	// signature, the value 0x08074b50 has commonly been adopted
+	// as a signature value for the data descriptor record.
+	// Implementers should be aware that ZIP files may be
+	// encountered with or without this signature marking data
+	// descriptors and should account for either case when reading
+	// ZIP files to ensure compatibility."
+	//
+	// dataDescriptorLen includes the size of the signature but
+	// first read just those 4 bytes to see if it exists.
+	if _, err := io.ReadFull(r, buf[:4]); err != nil {
+		return err
+	}
+	off := 0
+	maybeSig := readBuf(buf[:4])
+	if maybeSig.uint32() != dataDescriptorSignature {
+		// No data descriptor signature. Keep these four
+		// bytes.
+		off += 4
+	}
+	if _, err := io.ReadFull(r, buf[off:12]); err != nil {
+		return err
+	}
+	b := readBuf(buf[:12])
+	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, baseOffset int64, 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
+		}
+		buf = make([]byte, int(bLen))
+		if _, err := r.ReadAt(buf, size-bLen); err != nil && err != io.EOF {
+			return nil, 0, err
+		}
+		if p := findSignatureInBlock(buf); p >= 0 {
+			buf = buf[p:]
+			directoryEndOffset = size - bLen + int64(p)
+			break
+		}
+		if i == 1 || bLen == size {
+			return nil, 0, ErrFormat
+		}
+	}
+
+	// read header into struct
+	b := readBuf(buf[4:]) // skip signature
+	d := &directoryEnd{
+		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)
+	if l > len(b) {
+		return nil, 0, errors.New("zip: invalid comment length")
+	}
+	d.comment = string(b[:l])
+
+	// These values mean that the file can be a zip64 file
+	if d.directoryRecords == 0xffff || d.directorySize == 0xffff || d.directoryOffset == 0xffffffff {
+		p, err := findDirectory64End(r, directoryEndOffset)
+		if err == nil && p >= 0 {
+			directoryEndOffset = p
+			err = readDirectory64End(r, p, d)
+		}
+		if err != nil {
+			return nil, 0, err
+		}
+	}
+
+	maxInt64 := uint64(1<<63 - 1)
+	if d.directorySize > maxInt64 || d.directoryOffset > maxInt64 {
+		return nil, 0, ErrFormat
+	}
+
+	baseOffset = directoryEndOffset - int64(d.directorySize) - int64(d.directoryOffset)
+
+	// Make sure directoryOffset points to somewhere in our file.
+	if o := baseOffset + int64(d.directoryOffset); o < 0 || o >= size {
+		return nil, 0, ErrFormat
+	}
+
+	// If the directory end data tells us to use a non-zero baseOffset,
+	// but we would find a valid directory entry if we assume that the
+	// baseOffset is 0, then just use a baseOffset of 0.
+	// We've seen files in which the directory end data gives us
+	// an incorrect baseOffset.
+	if baseOffset > 0 {
+		off := int64(d.directoryOffset)
+		rs := io.NewSectionReader(r, off, size-off)
+		if readDirectoryHeader(&File{}, rs) == nil {
+			baseOffset = 0
+		}
+	}
+
+	return d, baseOffset, 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
+	}
+	if b.uint32() != 0 { // number of the disk with the start of the zip64 end of central directory
+		return -1, nil // the file is not a valid zip64-file
+	}
+	p := b.uint64()      // relative offset of the zip64 end of central directory record
+	if b.uint32() != 1 { // total number of disks
+		return -1, nil // the file is not a valid zip64-file
+	}
+	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
+		if b[i] == 'P' && b[i+1] == 'K' && b[i+2] == 0x05 && b[i+3] == 0x06 {
+			// n is length of comment
+			n := int(b[i+directoryEndLen-2]) | int(b[i+directoryEndLen-1])<<8
+			if n+directoryEndLen+i <= len(b) {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+type readBuf []byte
+
+func (b *readBuf) uint8() uint8 {
+	v := (*b)[0]
+	*b = (*b)[1:]
+	return v
+}
+
+func (b *readBuf) uint16() uint16 {
+	v := binary.LittleEndian.Uint16(*b)
+	*b = (*b)[2:]
+	return v
+}
+
+func (b *readBuf) uint32() uint32 {
+	v := binary.LittleEndian.Uint32(*b)
+	*b = (*b)[4:]
+	return v
+}
+
+func (b *readBuf) uint64() uint64 {
+	v := binary.LittleEndian.Uint64(*b)
+	*b = (*b)[8:]
+	return v
+}
+
+func (b *readBuf) sub(n int) readBuf {
+	b2 := (*b)[:n]
+	*b = (*b)[n:]
+	return b2
+}
+
+// A fileListEntry is a File and its ename.
+// If file == nil, the fileListEntry describes a directory without metadata.
+type fileListEntry struct {
+	name  string
+	file  *File
+	isDir bool
+	isDup bool
+}
+
+type fileInfoDirEntry interface {
+	fs.FileInfo
+	fs.DirEntry
+}
+
+func (f *fileListEntry) stat() (fileInfoDirEntry, error) {
+	if f.isDup {
+		return nil, errors.New(f.name + ": duplicate entries in zip file")
+	}
+	if !f.isDir {
+		return headerFileInfo{&f.file.FileHeader}, nil
+	}
+	return f, nil
+}
+
+// Only used for directories.
+func (f *fileListEntry) Name() string      { _, elem, _ := split(f.name); return elem }
+func (f *fileListEntry) Size() int64       { return 0 }
+func (f *fileListEntry) Mode() fs.FileMode { return fs.ModeDir | 0555 }
+func (f *fileListEntry) Type() fs.FileMode { return fs.ModeDir }
+func (f *fileListEntry) IsDir() bool       { return true }
+func (f *fileListEntry) Sys() any          { return nil }
+
+func (f *fileListEntry) ModTime() time.Time {
+	if f.file == nil {
+		return time.Time{}
+	}
+	return f.file.FileHeader.Modified.UTC()
+}
+
+func (f *fileListEntry) Info() (fs.FileInfo, error) { return f, nil }
+
+func (f *fileListEntry) String() string {
+	return fs.FormatDirEntry(f)
+}
+
+// toValidName coerces name to be a valid name for fs.FS.Open.
+func toValidName(name string) string {
+	name = strings.ReplaceAll(name, `\`, `/`)
+	p := path.Clean(name)
+
+	p = strings.TrimPrefix(p, "/")
+
+	for strings.HasPrefix(p, "../") {
+		p = p[len("../"):]
+	}
+
+	return p
+}
+
+func (r *Reader) initFileList() {
+	r.fileListOnce.Do(func() {
+		// files and knownDirs map from a file/directory name
+		// to an index into the r.fileList entry that we are
+		// building. They are used to mark duplicate entries.
+		files := make(map[string]int)
+		knownDirs := make(map[string]int)
+
+		// dirs[name] is true if name is known to be a directory,
+		// because it appears as a prefix in a path.
+		dirs := make(map[string]bool)
+
+		for _, file := range r.File {
+			isDir := len(file.Name) > 0 && file.Name[len(file.Name)-1] == '/'
+			name := toValidName(file.Name)
+			if name == "" {
+				continue
+			}
+
+			if idx, ok := files[name]; ok {
+				r.fileList[idx].isDup = true
+				continue
+			}
+			if idx, ok := knownDirs[name]; ok {
+				r.fileList[idx].isDup = true
+				continue
+			}
+
+			for dir := path.Dir(name); dir != "."; dir = path.Dir(dir) {
+				dirs[dir] = true
+			}
+
+			idx := len(r.fileList)
+			entry := fileListEntry{
+				name:  name,
+				file:  file,
+				isDir: isDir,
+			}
+			r.fileList = append(r.fileList, entry)
+			if isDir {
+				knownDirs[name] = idx
+			} else {
+				files[name] = idx
+			}
+		}
+		for dir := range dirs {
+			if _, ok := knownDirs[dir]; !ok {
+				if idx, ok := files[dir]; ok {
+					r.fileList[idx].isDup = true
+				} else {
+					entry := fileListEntry{
+						name:  dir,
+						file:  nil,
+						isDir: true,
+					}
+					r.fileList = append(r.fileList, entry)
+				}
+			}
+		}
+
+		sort.Slice(r.fileList, func(i, j int) bool { return fileEntryLess(r.fileList[i].name, r.fileList[j].name) })
+	})
+}
+
+func fileEntryLess(x, y string) bool {
+	xdir, xelem, _ := split(x)
+	ydir, yelem, _ := split(y)
+	return xdir < ydir || xdir == ydir && xelem < yelem
+}
+
+// Open opens the named file in the ZIP archive,
+// using the semantics of fs.FS.Open:
+// paths are always slash separated, with no
+// leading / or ../ elements.
+func (r *Reader) Open(name string) (fs.File, error) {
+	r.initFileList()
+
+	if !fs.ValidPath(name) {
+		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
+	}
+	e := r.openLookup(name)
+	if e == nil {
+		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
+	}
+	if e.isDir {
+		return &openDir{e, r.openReadDir(name), 0}, nil
+	}
+	rc, err := e.file.Open()
+	if err != nil {
+		return nil, err
+	}
+	return rc.(fs.File), nil
+}
+
+func split(name string) (dir, elem string, isDir bool) {
+	if len(name) > 0 && name[len(name)-1] == '/' {
+		isDir = true
+		name = name[:len(name)-1]
+	}
+	i := len(name) - 1
+	for i >= 0 && name[i] != '/' {
+		i--
+	}
+	if i < 0 {
+		return ".", name, isDir
+	}
+	return name[:i], name[i+1:], isDir
+}
+
+var dotFile = &fileListEntry{name: "./", isDir: true}
+
+func (r *Reader) openLookup(name string) *fileListEntry {
+	if name == "." {
+		return dotFile
+	}
+
+	dir, elem, _ := split(name)
+	files := r.fileList
+	i := sort.Search(len(files), func(i int) bool {
+		idir, ielem, _ := split(files[i].name)
+		return idir > dir || idir == dir && ielem >= elem
+	})
+	if i < len(files) {
+		fname := files[i].name
+		if fname == name || len(fname) == len(name)+1 && fname[len(name)] == '/' && fname[:len(name)] == name {
+			return &files[i]
+		}
+	}
+	return nil
+}
+
+func (r *Reader) openReadDir(dir string) []fileListEntry {
+	files := r.fileList
+	i := sort.Search(len(files), func(i int) bool {
+		idir, _, _ := split(files[i].name)
+		return idir >= dir
+	})
+	j := sort.Search(len(files), func(j int) bool {
+		jdir, _, _ := split(files[j].name)
+		return jdir > dir
+	})
+	return files[i:j]
+}
+
+type openDir struct {
+	e      *fileListEntry
+	files  []fileListEntry
+	offset int
+}
+
+func (d *openDir) Close() error               { return nil }
+func (d *openDir) Stat() (fs.FileInfo, error) { return d.e.stat() }
+
+func (d *openDir) Read([]byte) (int, error) {
+	return 0, &fs.PathError{Op: "read", Path: d.e.name, Err: errors.New("is a directory")}
+}
+
+func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
+	n := len(d.files) - d.offset
+	if count > 0 && n > count {
+		n = count
+	}
+	if n == 0 {
+		if count <= 0 {
+			return nil, nil
+		}
+		return nil, io.EOF
+	}
+	list := make([]fs.DirEntry, n)
+	for i := range list {
+		s, err := d.files[d.offset+i].stat()
+		if err != nil {
+			return nil, err
+		}
+		list[i] = s
+	}
+	d.offset += n
+	return list, nil
+}