503 lines
13 KiB
Go
503 lines
13 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package zip
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import (
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"bufio"
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"encoding/binary"
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"errors"
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"fmt"
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"hash"
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"hash/crc32"
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"io"
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"os"
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)
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var (
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ErrFormat = errors.New("zip: not a valid zip file")
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ErrAlgorithm = errors.New("zip: unsupported compression algorithm")
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ErrChecksum = errors.New("zip: checksum error")
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)
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type Reader struct {
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r io.ReaderAt
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File []*File
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Comment string
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}
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type ReadCloser struct {
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f *os.File
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Reader
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}
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type File struct {
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FileHeader
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zipr io.ReaderAt
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zipsize int64
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headerOffset int64
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}
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func (f *File) hasDataDescriptor() bool {
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return f.Flags&0x8 != 0
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}
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// OpenReader will open the Zip file specified by name and return a ReadCloser.
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func OpenReader(name string) (*ReadCloser, error) {
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f, err := os.Open(name)
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if err != nil {
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return nil, err
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}
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fi, err := f.Stat()
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if err != nil {
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f.Close()
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return nil, err
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}
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r := new(ReadCloser)
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if err := r.init(f, fi.Size()); err != nil {
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f.Close()
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return nil, err
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}
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r.f = f
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return r, nil
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}
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// NewReader returns a new Reader reading from r, which is assumed to
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// have the given size in bytes.
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func NewReader(r io.ReaderAt, size int64) (*Reader, error) {
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zr := new(Reader)
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if err := zr.init(r, size); err != nil {
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return nil, err
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}
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return zr, nil
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}
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func (z *Reader) init(r io.ReaderAt, size int64) error {
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end, err := readDirectoryEnd(r, size)
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if err != nil {
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return err
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}
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if end.directoryRecords > uint64(size)/fileHeaderLen {
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return fmt.Errorf("archive/zip: TOC declares impossible %d files in %d byte zip", end.directoryRecords, size)
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}
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z.r = r
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z.File = make([]*File, 0, end.directoryRecords)
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z.Comment = end.comment
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rs := io.NewSectionReader(r, 0, size)
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if _, err = rs.Seek(int64(end.directoryOffset), os.SEEK_SET); err != nil {
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return err
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}
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buf := bufio.NewReader(rs)
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// The count of files inside a zip is truncated to fit in a uint16.
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// Gloss over this by reading headers until we encounter
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// a bad one, and then only report a ErrFormat or UnexpectedEOF if
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// the file count modulo 65536 is incorrect.
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for {
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f := &File{zipr: r, zipsize: size}
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err = readDirectoryHeader(f, buf)
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if err == ErrFormat || err == io.ErrUnexpectedEOF {
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break
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}
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if err != nil {
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return err
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}
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z.File = append(z.File, f)
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}
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if uint16(len(z.File)) != uint16(end.directoryRecords) { // only compare 16 bits here
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// Return the readDirectoryHeader error if we read
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// the wrong number of directory entries.
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return err
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}
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return nil
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}
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// Close closes the Zip file, rendering it unusable for I/O.
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func (rc *ReadCloser) Close() error {
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return rc.f.Close()
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}
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// DataOffset returns the offset of the file's possibly-compressed
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// data, relative to the beginning of the zip file.
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//
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// Most callers should instead use Open, which transparently
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// decompresses data and verifies checksums.
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func (f *File) DataOffset() (offset int64, err error) {
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bodyOffset, err := f.findBodyOffset()
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if err != nil {
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return
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}
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return f.headerOffset + bodyOffset, nil
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}
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// Open returns a ReadCloser that provides access to the File's contents.
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// Multiple files may be read concurrently.
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func (f *File) Open() (rc io.ReadCloser, err error) {
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bodyOffset, err := f.findBodyOffset()
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if err != nil {
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return
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}
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// If f is encrypted, CompressedSize64 includes salt, pwvv, encrypted data,
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// and auth code lengths
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size := int64(f.CompressedSize64)
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var r io.Reader
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rr := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
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// check for encryption
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if f.IsEncrypted() {
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if r, err = newDecryptionReader(rr, f); err != nil {
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return
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}
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} else {
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r = rr
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}
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dcomp := decompressor(f.Method)
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if dcomp == nil {
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err = ErrAlgorithm
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return
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}
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rc = dcomp(r)
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// If AE-2, skip CRC and possible dataDescriptor
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if f.isAE2() {
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return
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}
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var desr io.Reader
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if f.hasDataDescriptor() {
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desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
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}
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rc = &checksumReader{
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rc: rc,
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hash: crc32.NewIEEE(),
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f: f,
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desr: desr,
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}
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return
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}
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type checksumReader struct {
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rc io.ReadCloser
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hash hash.Hash32
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nread uint64 // number of bytes read so far
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f *File
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desr io.Reader // if non-nil, where to read the data descriptor
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err error // sticky error
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}
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func (r *checksumReader) Read(b []byte) (n int, err error) {
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if r.err != nil {
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return 0, r.err
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}
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n, err = r.rc.Read(b)
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r.hash.Write(b[:n])
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r.nread += uint64(n)
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if err == nil {
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return
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}
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if err == io.EOF {
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if r.nread != r.f.UncompressedSize64 {
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return 0, io.ErrUnexpectedEOF
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}
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if r.desr != nil {
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if err1 := readDataDescriptor(r.desr, r.f); err1 != nil {
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if err1 == io.EOF {
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err = io.ErrUnexpectedEOF
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} else {
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err = err1
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}
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} else if r.hash.Sum32() != r.f.CRC32 {
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err = ErrChecksum
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}
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} else {
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// If there's not a data descriptor, we still compare
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// the CRC32 of what we've read against the file header
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// or TOC's CRC32, if it seems like it was set.
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if r.f.CRC32 != 0 && r.hash.Sum32() != r.f.CRC32 {
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err = ErrChecksum
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}
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}
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}
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r.err = err
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return
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}
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func (r *checksumReader) Close() error { return r.rc.Close() }
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// findBodyOffset does the minimum work to verify the file has a header
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// and returns the file body offset.
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func (f *File) findBodyOffset() (int64, error) {
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var buf [fileHeaderLen]byte
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if _, err := f.zipr.ReadAt(buf[:], f.headerOffset); err != nil {
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return 0, err
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}
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b := readBuf(buf[:])
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if sig := b.uint32(); sig != fileHeaderSignature {
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return 0, ErrFormat
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}
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b = b[22:] // skip over most of the header
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filenameLen := int(b.uint16())
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extraLen := int(b.uint16())
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return int64(fileHeaderLen + filenameLen + extraLen), nil
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}
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// readDirectoryHeader attempts to read a directory header from r.
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// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
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// and ErrFormat if it doesn't find a valid header signature.
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func readDirectoryHeader(f *File, r io.Reader) error {
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var buf [directoryHeaderLen]byte
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if _, err := io.ReadFull(r, buf[:]); err != nil {
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return err
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}
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b := readBuf(buf[:])
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if sig := b.uint32(); sig != directoryHeaderSignature {
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return ErrFormat
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}
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f.CreatorVersion = b.uint16()
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f.ReaderVersion = b.uint16()
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f.Flags = b.uint16()
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f.Method = b.uint16()
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f.ModifiedTime = b.uint16()
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f.ModifiedDate = b.uint16()
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f.CRC32 = b.uint32()
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f.CompressedSize = b.uint32()
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f.UncompressedSize = b.uint32()
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f.CompressedSize64 = uint64(f.CompressedSize)
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f.UncompressedSize64 = uint64(f.UncompressedSize)
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filenameLen := int(b.uint16())
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extraLen := int(b.uint16())
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commentLen := int(b.uint16())
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b = b[4:] // skipped start disk number and internal attributes (2x uint16)
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f.ExternalAttrs = b.uint32()
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f.headerOffset = int64(b.uint32())
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d := make([]byte, filenameLen+extraLen+commentLen)
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if _, err := io.ReadFull(r, d); err != nil {
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return err
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}
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f.Name = string(d[:filenameLen])
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f.Extra = d[filenameLen : filenameLen+extraLen]
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f.Comment = string(d[filenameLen+extraLen:])
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if len(f.Extra) > 0 {
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b := readBuf(f.Extra)
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for len(b) >= 4 { // need at least tag and size
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tag := b.uint16()
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size := b.uint16()
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if int(size) > len(b) {
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return ErrFormat
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}
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eb := readBuf(b[:size])
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switch tag {
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case zip64ExtraId:
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// update directory values from the zip64 extra block
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if len(eb) >= 8 {
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f.UncompressedSize64 = eb.uint64()
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}
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if len(eb) >= 8 {
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f.CompressedSize64 = eb.uint64()
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}
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if len(eb) >= 8 {
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f.headerOffset = int64(eb.uint64())
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}
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case winzipAesExtraId:
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// grab the AE version
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f.ae = eb.uint16()
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// skip vendor ID
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_ = eb.uint16()
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// AES strength
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f.aesStrength = eb.uint8()
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// set the actual compression method.
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f.Method = eb.uint16()
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}
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b = b[size:]
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}
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// Should have consumed the whole header.
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// But popular zip & JAR creation tools are broken and
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// may pad extra zeros at the end, so accept those
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// too. See golang.org/issue/8186.
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for _, v := range b {
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if v != 0 {
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return ErrFormat
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}
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}
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}
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return nil
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}
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func readDataDescriptor(r io.Reader, f *File) error {
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var buf [dataDescriptorLen]byte
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// The spec says: "Although not originally assigned a
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// signature, the value 0x08074b50 has commonly been adopted
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// as a signature value for the data descriptor record.
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// Implementers should be aware that ZIP files may be
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// encountered with or without this signature marking data
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// descriptors and should account for either case when reading
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// ZIP files to ensure compatibility."
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//
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// dataDescriptorLen includes the size of the signature but
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// first read just those 4 bytes to see if it exists.
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if _, err := io.ReadFull(r, buf[:4]); err != nil {
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return err
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}
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off := 0
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maybeSig := readBuf(buf[:4])
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if maybeSig.uint32() != dataDescriptorSignature {
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// No data descriptor signature. Keep these four
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// bytes.
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off += 4
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}
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if _, err := io.ReadFull(r, buf[off:12]); err != nil {
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return err
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}
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b := readBuf(buf[:12])
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if b.uint32() != f.CRC32 {
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return ErrChecksum
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}
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// The two sizes that follow here can be either 32 bits or 64 bits
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// but the spec is not very clear on this and different
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// interpretations has been made causing incompatibilities. We
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// already have the sizes from the central directory so we can
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// just ignore these.
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return nil
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}
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func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, err error) {
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// look for directoryEndSignature in the last 1k, then in the last 65k
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var buf []byte
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var directoryEndOffset int64
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for i, bLen := range []int64{1024, 65 * 1024} {
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if bLen > size {
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bLen = size
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}
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buf = make([]byte, int(bLen))
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if _, err := r.ReadAt(buf, size-bLen); err != nil && err != io.EOF {
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return nil, err
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}
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if p := findSignatureInBlock(buf); p >= 0 {
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buf = buf[p:]
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directoryEndOffset = size - bLen + int64(p)
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break
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}
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if i == 1 || bLen == size {
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return nil, ErrFormat
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}
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}
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// read header into struct
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b := readBuf(buf[4:]) // skip signature
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d := &directoryEnd{
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diskNbr: uint32(b.uint16()),
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dirDiskNbr: uint32(b.uint16()),
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dirRecordsThisDisk: uint64(b.uint16()),
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directoryRecords: uint64(b.uint16()),
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directorySize: uint64(b.uint32()),
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directoryOffset: uint64(b.uint32()),
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commentLen: b.uint16(),
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}
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l := int(d.commentLen)
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if l > len(b) {
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return nil, errors.New("zip: invalid comment length")
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}
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d.comment = string(b[:l])
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p, err := findDirectory64End(r, directoryEndOffset)
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if err == nil && p >= 0 {
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err = readDirectory64End(r, p, d)
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}
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if err != nil {
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return nil, err
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}
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// Make sure directoryOffset points to somewhere in our file.
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if o := int64(d.directoryOffset); o < 0 || o >= size {
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return nil, ErrFormat
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}
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return d, nil
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}
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// findDirectory64End tries to read the zip64 locator just before the
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// directory end and returns the offset of the zip64 directory end if
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// found.
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func findDirectory64End(r io.ReaderAt, directoryEndOffset int64) (int64, error) {
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locOffset := directoryEndOffset - directory64LocLen
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if locOffset < 0 {
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return -1, nil // no need to look for a header outside the file
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}
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buf := make([]byte, directory64LocLen)
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if _, err := r.ReadAt(buf, locOffset); err != nil {
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return -1, err
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}
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b := readBuf(buf)
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if sig := b.uint32(); sig != directory64LocSignature {
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return -1, nil
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}
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b = b[4:] // skip number of the disk with the start of the zip64 end of central directory
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p := b.uint64() // relative offset of the zip64 end of central directory record
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return int64(p), nil
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}
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// readDirectory64End reads the zip64 directory end and updates the
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// directory end with the zip64 directory end values.
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func readDirectory64End(r io.ReaderAt, offset int64, d *directoryEnd) (err error) {
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buf := make([]byte, directory64EndLen)
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if _, err := r.ReadAt(buf, offset); err != nil {
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return err
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}
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b := readBuf(buf)
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if sig := b.uint32(); sig != directory64EndSignature {
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return ErrFormat
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}
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b = b[12:] // skip dir size, version and version needed (uint64 + 2x uint16)
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d.diskNbr = b.uint32() // number of this disk
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d.dirDiskNbr = b.uint32() // number of the disk with the start of the central directory
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d.dirRecordsThisDisk = b.uint64() // total number of entries in the central directory on this disk
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d.directoryRecords = b.uint64() // total number of entries in the central directory
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d.directorySize = b.uint64() // size of the central directory
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d.directoryOffset = b.uint64() // offset of start of central directory with respect to the starting disk number
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return nil
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}
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func findSignatureInBlock(b []byte) int {
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for i := len(b) - directoryEndLen; i >= 0; i-- {
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// defined from directoryEndSignature in struct.go
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if b[i] == 'P' && b[i+1] == 'K' && b[i+2] == 0x05 && b[i+3] == 0x06 {
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// n is length of comment
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n := int(b[i+directoryEndLen-2]) | int(b[i+directoryEndLen-1])<<8
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if n+directoryEndLen+i <= len(b) {
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return i
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}
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}
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}
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return -1
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}
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type readBuf []byte
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func (b *readBuf) uint8() byte {
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v := (*b)[0]
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*b = (*b)[1:]
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return v
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}
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func (b *readBuf) uint16() uint16 {
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v := binary.LittleEndian.Uint16(*b)
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*b = (*b)[2:]
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return v
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}
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func (b *readBuf) uint32() uint32 {
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v := binary.LittleEndian.Uint32(*b)
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*b = (*b)[4:]
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return v
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}
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func (b *readBuf) uint64() uint64 {
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v := binary.LittleEndian.Uint64(*b)
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*b = (*b)[8:]
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return v
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}
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