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// 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"
"compress/flate"
"encoding/binary"
"errors"
"hash"
"hash/crc32"
"io"
"io/ioutil"
"os"
)
var (
ErrFormat = errors.New("zip: not a valid zip file")
ErrAlgorithm = errors.New("zip: unsupported compression algorithm")
ErrChecksum = errors.New("zip: checksum error")
)
type Reader struct {
r io.ReaderAt
File []*File
Comment string
}
type ReadCloser struct {
f *os.File
Reader
}
type File struct {
FileHeader
zipr io.ReaderAt
zipsize int64
headerOffset int64
}
func (f *File) hasDataDescriptor() bool {
return f.Flags&0x8 != 0
}
// OpenReader will open the Zip file specified by name and return a ReadCloser.
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 {
f.Close()
return nil, err
}
r.f = f
return r, nil
}
// NewReader returns a new Reader reading from r, which is assumed to
// have the given size in bytes.
func NewReader(r io.ReaderAt, size int64) (*Reader, error) {
zr := new(Reader)
if err := zr.init(r, size); err != nil {
return nil, err
}
return zr, nil
}
func (z *Reader) init(r io.ReaderAt, size int64) error {
end, err := readDirectoryEnd(r, size)
if err != nil {
return err
}
z.r = r
z.File = make([]*File, 0, end.directoryRecords)
z.Comment = end.comment
rs := io.NewSectionReader(r, 0, size)
if _, err = rs.Seek(int64(end.directoryOffset), os.SEEK_SET); 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 a ErrFormat or UnexpectedEOF if
// the file count modulo 65536 is incorrect.
for {
f := &File{zipr: r, zipsize: size}
err = readDirectoryHeader(f, buf)
if err == ErrFormat || err == io.ErrUnexpectedEOF {
break
}
if err != nil {
return err
}
z.File = append(z.File, f)
}
if uint16(len(z.File)) != end.directoryRecords {
// Return the readDirectoryHeader error if we read
// the wrong number of directory entries.
return err
}
return nil
}
// Close closes the Zip file, rendering it unusable for I/O.
func (rc *ReadCloser) Close() error {
return rc.f.Close()
}
// Open returns a ReadCloser that provides access to the File's contents.
// It is safe to Open and Read from files concurrently.
func (f *File) Open() (rc io.ReadCloser, err error) {
bodyOffset, err := f.findBodyOffset()
if err != nil {
return
}
size := int64(f.CompressedSize)
if size == 0 && f.hasDataDescriptor() {
// permit SectionReader to see the rest of the file
size = f.zipsize - (f.headerOffset + bodyOffset)
}
r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
switch f.Method {
case Store: // (no compression)
rc = ioutil.NopCloser(r)
case Deflate:
rc = flate.NewReader(r)
default:
err = ErrAlgorithm
}
if rc != nil {
rc = &checksumReader{rc, crc32.NewIEEE(), f, r}
}
return
}
type checksumReader struct {
rc io.ReadCloser
hash hash.Hash32
f *File
zipr io.Reader // for reading the data descriptor
}
func (r *checksumReader) Read(b []byte) (n int, err error) {
n, err = r.rc.Read(b)
r.hash.Write(b[:n])
if err != io.EOF {
return
}
if r.f.hasDataDescriptor() {
if err = readDataDescriptor(r.zipr, r.f); err != nil {
return
}
}
if r.hash.Sum32() != r.f.CRC32 {
err = ErrChecksum
}
return
}
func (r *checksumReader) Close() error { return r.rc.Close() }
func readFileHeader(f *File, r io.Reader) error {
var b [fileHeaderLen]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return err
}
c := binary.LittleEndian
if sig := c.Uint32(b[:4]); sig != fileHeaderSignature {
return ErrFormat
}
f.ReaderVersion = c.Uint16(b[4:6])
f.Flags = c.Uint16(b[6:8])
f.Method = c.Uint16(b[8:10])
f.ModifiedTime = c.Uint16(b[10:12])
f.ModifiedDate = c.Uint16(b[12:14])
f.CRC32 = c.Uint32(b[14:18])
f.CompressedSize = c.Uint32(b[18:22])
f.UncompressedSize = c.Uint32(b[22:26])
filenameLen := int(c.Uint16(b[26:28]))
extraLen := int(c.Uint16(b[28:30]))
d := make([]byte, filenameLen+extraLen)
if _, err := io.ReadFull(r, d); err != nil {
return err
}
f.Name = string(d[:filenameLen])
f.Extra = d[filenameLen:]
return nil
}
// findBodyOffset does the minimum work to verify the file has a header
// and returns the file body offset.
func (f *File) findBodyOffset() (int64, error) {
r := io.NewSectionReader(f.zipr, f.headerOffset, f.zipsize-f.headerOffset)
var b [fileHeaderLen]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return 0, err
}
c := binary.LittleEndian
if sig := c.Uint32(b[:4]); sig != fileHeaderSignature {
return 0, ErrFormat
}
filenameLen := int(c.Uint16(b[26:28]))
extraLen := int(c.Uint16(b[28:30]))
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 b [directoryHeaderLen]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return err
}
c := binary.LittleEndian
if sig := c.Uint32(b[:4]); sig != directoryHeaderSignature {
return ErrFormat
}
f.CreatorVersion = c.Uint16(b[4:6])
f.ReaderVersion = c.Uint16(b[6:8])
f.Flags = c.Uint16(b[8:10])
f.Method = c.Uint16(b[10:12])
f.ModifiedTime = c.Uint16(b[12:14])
f.ModifiedDate = c.Uint16(b[14:16])
f.CRC32 = c.Uint32(b[16:20])
f.CompressedSize = c.Uint32(b[20:24])
f.UncompressedSize = c.Uint32(b[24:28])
filenameLen := int(c.Uint16(b[28:30]))
extraLen := int(c.Uint16(b[30:32]))
commentLen := int(c.Uint16(b[32:34]))
// startDiskNumber := c.Uint16(b[34:36]) // Unused
// internalAttributes := c.Uint16(b[36:38]) // Unused
f.ExternalAttrs = c.Uint32(b[38:42])
f.headerOffset = int64(c.Uint32(b[42:46]))
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:])
return nil
}
func readDataDescriptor(r io.Reader, f *File) error {
var b [dataDescriptorLen]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return err
}
c := binary.LittleEndian
f.CRC32 = c.Uint32(b[:4])
f.CompressedSize = c.Uint32(b[4:8])
f.UncompressedSize = c.Uint32(b[8:12])
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 b []byte
for i, bLen := range []int64{1024, 65 * 1024} {
if bLen > size {
bLen = size
}
b = make([]byte, int(bLen))
if _, err := r.ReadAt(b, size-bLen); err != nil && err != io.EOF {
return nil, err
}
if p := findSignatureInBlock(b); p >= 0 {
b = b[p:]
break
}
if i == 1 || bLen == size {
return nil, ErrFormat
}
}
// read header into struct
c := binary.LittleEndian
d := new(directoryEnd)
d.diskNbr = c.Uint16(b[4:6])
d.dirDiskNbr = c.Uint16(b[6:8])
d.dirRecordsThisDisk = c.Uint16(b[8:10])
d.directoryRecords = c.Uint16(b[10:12])
d.directorySize = c.Uint32(b[12:16])
d.directoryOffset = c.Uint32(b[16:20])
d.commentLen = c.Uint16(b[20:22])
d.comment = string(b[22 : 22+int(d.commentLen)])
return d, 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
}
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