305 lines
6.8 KiB
Go
305 lines
6.8 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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/*
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The zip package provides support for reading ZIP archives.
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See: http://www.pkware.com/documents/casestudies/APPNOTE.TXT
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This package does not support ZIP64 or disk spanning.
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*/
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package zip
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import (
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"bufio"
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"bytes"
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"compress/flate"
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"hash"
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"hash/crc32"
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"encoding/binary"
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"io"
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"io/ioutil"
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"os"
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)
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var (
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FormatError = os.NewError("not a valid zip file")
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UnsupportedMethod = os.NewError("unsupported compression algorithm")
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ChecksumError = os.NewError("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 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 uint32
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bodyOffset 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 Reader.
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func OpenReader(name string) (*Reader, os.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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return nil, err
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}
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return NewReader(f, fi.Size)
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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, os.Error) {
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end, err := readDirectoryEnd(r, size)
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if err != nil {
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return nil, err
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}
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z := &Reader{
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r: r,
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File: make([]*File, end.directoryRecords),
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Comment: end.comment,
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}
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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 nil, err
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}
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buf := bufio.NewReader(rs)
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for i := range z.File {
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z.File[i] = &File{zipr: r, zipsize: size}
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if err := readDirectoryHeader(z.File[i], buf); err != nil {
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return nil, err
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}
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}
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return z, 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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func (f *File) Open() (rc io.ReadCloser, err os.Error) {
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off := int64(f.headerOffset)
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if f.bodyOffset == 0 {
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r := io.NewSectionReader(f.zipr, off, f.zipsize-off)
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if err = readFileHeader(f, r); err != nil {
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return
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}
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if f.bodyOffset, err = r.Seek(0, os.SEEK_CUR); err != nil {
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return
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}
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}
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size := int64(f.CompressedSize)
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if f.hasDataDescriptor() {
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if size == 0 {
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// permit SectionReader to see the rest of the file
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size = f.zipsize - (off + f.bodyOffset)
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} else {
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size += dataDescriptorLen
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}
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}
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r := io.NewSectionReader(f.zipr, off+f.bodyOffset, size)
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switch f.Method {
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case 0: // store (no compression)
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rc = ioutil.NopCloser(r)
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case 8: // DEFLATE
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rc = flate.NewReader(r)
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default:
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err = UnsupportedMethod
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}
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if rc != nil {
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rc = &checksumReader{rc, crc32.NewIEEE(), f, r}
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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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f *File
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zipr io.Reader // for reading the data descriptor
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}
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func (r *checksumReader) Read(b []byte) (n int, err os.Error) {
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n, err = r.rc.Read(b)
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r.hash.Write(b[:n])
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if err != os.EOF {
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return
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}
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if r.f.hasDataDescriptor() {
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if err = readDataDescriptor(r.zipr, r.f); err != nil {
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return
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}
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}
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if r.hash.Sum32() != r.f.CRC32 {
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err = ChecksumError
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}
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return
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}
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func (r *checksumReader) Close() os.Error { return r.rc.Close() }
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func readFileHeader(f *File, r io.Reader) (err os.Error) {
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defer func() {
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if rerr, ok := recover().(os.Error); ok {
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err = rerr
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}
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}()
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var (
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signature uint32
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filenameLength uint16
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extraLength uint16
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)
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read(r, &signature)
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if signature != fileHeaderSignature {
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return FormatError
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}
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read(r, &f.ReaderVersion)
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read(r, &f.Flags)
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read(r, &f.Method)
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read(r, &f.ModifiedTime)
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read(r, &f.ModifiedDate)
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read(r, &f.CRC32)
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read(r, &f.CompressedSize)
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read(r, &f.UncompressedSize)
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read(r, &filenameLength)
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read(r, &extraLength)
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f.Name = string(readByteSlice(r, filenameLength))
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f.Extra = readByteSlice(r, extraLength)
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return
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}
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func readDirectoryHeader(f *File, r io.Reader) (err os.Error) {
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defer func() {
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if rerr, ok := recover().(os.Error); ok {
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err = rerr
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}
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}()
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var (
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signature uint32
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filenameLength uint16
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extraLength uint16
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commentLength uint16
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startDiskNumber uint16 // unused
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internalAttributes uint16 // unused
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externalAttributes uint32 // unused
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)
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read(r, &signature)
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if signature != directoryHeaderSignature {
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return FormatError
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}
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read(r, &f.CreatorVersion)
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read(r, &f.ReaderVersion)
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read(r, &f.Flags)
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read(r, &f.Method)
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read(r, &f.ModifiedTime)
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read(r, &f.ModifiedDate)
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read(r, &f.CRC32)
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read(r, &f.CompressedSize)
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read(r, &f.UncompressedSize)
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read(r, &filenameLength)
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read(r, &extraLength)
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read(r, &commentLength)
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read(r, &startDiskNumber)
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read(r, &internalAttributes)
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read(r, &externalAttributes)
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read(r, &f.headerOffset)
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f.Name = string(readByteSlice(r, filenameLength))
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f.Extra = readByteSlice(r, extraLength)
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f.Comment = string(readByteSlice(r, commentLength))
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return
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}
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func readDataDescriptor(r io.Reader, f *File) (err os.Error) {
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defer func() {
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if rerr, ok := recover().(os.Error); ok {
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err = rerr
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}
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}()
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read(r, &f.CRC32)
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read(r, &f.CompressedSize)
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read(r, &f.UncompressedSize)
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return
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}
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func readDirectoryEnd(r io.ReaderAt, size int64) (d *directoryEnd, err os.Error) {
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// look for directoryEndSignature in the last 1k, then in the last 65k
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var b []byte
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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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b = make([]byte, int(bLen))
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if _, err := r.ReadAt(b, size-bLen); err != nil && err != os.EOF {
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return nil, err
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}
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if p := findSignatureInBlock(b); p >= 0 {
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b = b[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, FormatError
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}
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}
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// read header into struct
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defer func() {
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if rerr, ok := recover().(os.Error); ok {
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err = rerr
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d = nil
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}
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}()
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br := bytes.NewBuffer(b[4:]) // skip over signature
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d = new(directoryEnd)
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read(br, &d.diskNbr)
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read(br, &d.dirDiskNbr)
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read(br, &d.dirRecordsThisDisk)
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read(br, &d.directoryRecords)
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read(br, &d.directorySize)
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read(br, &d.directoryOffset)
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read(br, &d.commentLen)
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d.comment = string(readByteSlice(br, d.commentLen))
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return d, nil
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}
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func findSignatureInBlock(b []byte) int {
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const minSize = 4 + 2 + 2 + 2 + 2 + 4 + 4 + 2 // fixed part of header
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for i := len(b) - minSize; 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+minSize-2]) | int(b[i+minSize-1])<<8
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if n+minSize+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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func read(r io.Reader, data interface{}) {
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if err := binary.Read(r, binary.LittleEndian, data); err != nil {
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panic(err)
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}
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}
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func readByteSlice(r io.Reader, l uint16) []byte {
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b := make([]byte, l)
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if l == 0 {
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return b
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}
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if _, err := io.ReadFull(r, b); err != nil {
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panic(err)
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}
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return b
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}
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