// Copyright 2009 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 tar
// TODO(dsymonds):
// - pax extensions
import (
"bytes"
"errors"
"io"
"io/ioutil"
"os"
"strconv"
"strings"
"time"
)
var (
ErrHeader = errors.New("archive/tar: invalid tar header")
)
const maxNanoSecondIntSize = 9
// A Reader provides sequential access to the contents of a tar archive.
// A tar archive consists of a sequence of files.
// The Next method advances to the next file in the archive (including the first),
// and then it can be treated as an io.Reader to access the file's data.
type Reader struct {
r io.Reader
err error
pad int64 // amount of padding (ignored) after current file entry
curr numBytesReader // reader for current file entry
hdrBuff [blockSize]byte // buffer to use in readHeader
}
// A numBytesReader is an io.Reader with a numBytes method, returning the number
// of bytes remaining in the underlying encoded data.
type numBytesReader interface {
io.Reader
numBytes() int64
}
// A regFileReader is a numBytesReader for reading file data from a tar archive.
type regFileReader struct {
r io.Reader // underlying reader
nb int64 // number of unread bytes for current file entry
}
// A sparseFileReader is a numBytesReader for reading sparse file data from a tar archive.
type sparseFileReader struct {
rfr *regFileReader // reads the sparse-encoded file data
sp []sparseEntry // the sparse map for the file
pos int64 // keeps track of file position
tot int64 // total size of the file
}
// Keywords for GNU sparse files in a PAX extended header
const (
paxGNUSparseNumBlocks = "GNU.sparse.numblocks"
paxGNUSparseOffset = "GNU.sparse.offset"
paxGNUSparseNumBytes = "GNU.sparse.numbytes"
paxGNUSparseMap = "GNU.sparse.map"
paxGNUSparseName = "GNU.sparse.name"
paxGNUSparseMajor = "GNU.sparse.major"
paxGNUSparseMinor = "GNU.sparse.minor"
paxGNUSparseSize = "GNU.sparse.size"
paxGNUSparseRealSize = "GNU.sparse.realsize"
)
// Keywords for old GNU sparse headers
const (
oldGNUSparseMainHeaderOffset = 386
oldGNUSparseMainHeaderIsExtendedOffset = 482
oldGNUSparseMainHeaderNumEntries = 4
oldGNUSparseExtendedHeaderIsExtendedOffset = 504
oldGNUSparseExtendedHeaderNumEntries = 21
oldGNUSparseOffsetSize = 12
oldGNUSparseNumBytesSize = 12
)
// NewReader creates a new Reader reading from r.
func NewReader(r io.Reader) *Reader { return &Reader{r: r} }
// Next advances to the next entry in the tar archive.
//
// io.EOF is returned at the end of the input.
func (tr *Reader) Next() (*Header, error) {
var hdr *Header
if tr.err == nil {
tr.skipUnread()
}
if tr.err != nil {
return hdr, tr.err
}
hdr = tr.readHeader()
if hdr == nil {
return hdr, tr.err
}
// Check for PAX/GNU header.
switch hdr.Typeflag {
case TypeXHeader:
// PAX extended header
headers, err := parsePAX(tr)
if err != nil {
return nil, err
}
// We actually read the whole file,
// but this skips alignment padding
tr.skipUnread()
if tr.err != nil {
return nil, tr.err
}
hdr = tr.readHeader()
if hdr == nil {
return nil, tr.err
}
mergePAX(hdr, headers)
// Check for a PAX format sparse file
sp, err := tr.checkForGNUSparsePAXHeaders(hdr, headers)
if err != nil {
tr.err = err
return nil, err
}
if sp != nil {
// Current file is a PAX format GNU sparse file.
// Set the current file reader to a sparse file reader.
tr.curr = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
}
return hdr, nil
case TypeGNULongName:
// We have a GNU long name header. Its contents are the real file name.
realname, err := ioutil.ReadAll(tr)
if err != nil {
return nil, err
}
hdr, err := tr.Next()
hdr.Name = cString(realname)
return hdr, err
case TypeGNULongLink:
// We have a GNU long link header.
realname, err := ioutil.ReadAll(tr)
if err != nil {
return nil, err
}
hdr, err := tr.Next()
hdr.Linkname = cString(realname)
return hdr, err
}
return hdr, tr.err
}
// checkForGNUSparsePAXHeaders checks the PAX headers for GNU sparse headers. If they are found, then
// this function reads the sparse map and returns it. Unknown sparse formats are ignored, causing the file to
// be treated as a regular file.
func (tr *Reader) checkForGNUSparsePAXHeaders(hdr *Header, headers map[string]string) ([]sparseEntry, error) {
var sparseFormat string
// Check for sparse format indicators
major, majorOk := headers[paxGNUSparseMajor]
minor, minorOk := headers[paxGNUSparseMinor]
sparseName, sparseNameOk := headers[paxGNUSparseName]
_, sparseMapOk := headers[paxGNUSparseMap]
sparseSize, sparseSizeOk := headers[paxGNUSparseSize]
sparseRealSize, sparseRealSizeOk := headers[paxGNUSparseRealSize]
// Identify which, if any, sparse format applies from which PAX headers are set
if majorOk && minorOk {
sparseFormat = major + "." + minor
} else if sparseNameOk && sparseMapOk {
sparseFormat = "0.1"
} else if sparseSizeOk {
sparseFormat = "0.0"
} else {
// Not a PAX format GNU sparse file.
return nil, nil
}
// Check for unknown sparse format
if sparseFormat != "0.0" && sparseFormat != "0.1" && sparseFormat != "1.0" {
return nil, nil
}
// Update hdr from GNU sparse PAX headers
if sparseNameOk {
hdr.Name = sparseName
}
if sparseSizeOk {
realSize, err := strconv.ParseInt(sparseSize, 10, 0)
if err != nil {
return nil, ErrHeader
}
hdr.Size = realSize
} else if sparseRealSizeOk {
realSize, err := strconv.ParseInt(sparseRealSize, 10, 0)
if err != nil {
return nil, ErrHeader
}
hdr.Size = realSize
}
// Set up the sparse map, according to the particular sparse format in use
var sp []sparseEntry
var err error
switch sparseFormat {
case "0.0", "0.1":
sp, err = readGNUSparseMap0x1(headers)
case "1.0":
sp, err = readGNUSparseMap1x0(tr.curr)
}
return sp, err
}
// mergePAX merges well known headers according to PAX standard.
// In general headers with the same name as those found
// in the header struct overwrite those found in the header
// struct with higher precision or longer values. Esp. useful
// for name and linkname fields.
func mergePAX(hdr *Header, headers map[string]string) error {
for k, v := range headers {
switch k {
case paxPath:
hdr.Name = v
case paxLinkpath:
hdr.Linkname = v
case paxGname:
hdr.Gname = v
case paxUname:
hdr.Uname = v
case paxUid:
uid, err := strconv.ParseInt(v, 10, 0)
if err != nil {
return err
}
hdr.Uid = int(uid)
case paxGid:
gid, err := strconv.ParseInt(v, 10, 0)
if err != nil {
return err
}
hdr.Gid = int(gid)
case paxAtime:
t, err := parsePAXTime(v)
if err != nil {
return err
}
hdr.AccessTime = t
case paxMtime:
t, err := parsePAXTime(v)
if err != nil {
return err
}
hdr.ModTime = t
case paxCtime:
t, err := parsePAXTime(v)
if err != nil {
return err
}
hdr.ChangeTime = t
case paxSize:
size, err := strconv.ParseInt(v, 10, 0)
if err != nil {
return err
}
hdr.Size = int64(size)
default:
if strings.HasPrefix(k, paxXattr) {
if hdr.Xattrs == nil {
hdr.Xattrs = make(map[string]string)
}
hdr.Xattrs[k[len(paxXattr):]] = v
}
}
}
return nil
}
// parsePAXTime takes a string of the form %d.%d as described in
// the PAX specification.
func parsePAXTime(t string) (time.Time, error) {
buf := []byte(t)
pos := bytes.IndexByte(buf, '.')
var seconds, nanoseconds int64
var err error
if pos == -1 {
seconds, err = strconv.ParseInt(t, 10, 0)
if err != nil {
return time.Time{}, err
}
} else {
seconds, err = strconv.ParseInt(string(buf[:pos]), 10, 0)
if err != nil {
return time.Time{}, err
}
nano_buf := string(buf[pos+1:])
// Pad as needed before converting to a decimal.
// For example .030 -> .030000000 -> 30000000 nanoseconds
if len(nano_buf) < maxNanoSecondIntSize {
// Right pad
nano_buf += strings.Repeat("0", maxNanoSecondIntSize-len(nano_buf))
} else if len(nano_buf) > maxNanoSecondIntSize {
// Right truncate
nano_buf = nano_buf[:maxNanoSecondIntSize]
}
nanoseconds, err = strconv.ParseInt(string(nano_buf), 10, 0)
if err != nil {
return time.Time{}, err
}
}
ts := time.Unix(seconds, nanoseconds)
return ts, nil
}
// parsePAX parses PAX headers.
// If an extended header (type 'x') is invalid, ErrHeader is returned
func parsePAX(r io.Reader) (map[string]string, error) {
buf, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
}
// For GNU PAX sparse format 0.0 support.
// This function transforms the sparse format 0.0 headers into sparse format 0.1 headers.
var sparseMap bytes.Buffer
headers := make(map[string]string)
// Each record is constructed as
// "%d %s=%s\n", length, keyword, value
for len(buf) > 0 {
// or the header was empty to start with.
var sp int
// The size field ends at the first space.
sp = bytes.IndexByte(buf, ' ')
if sp == -1 {
return nil, ErrHeader
}
// Parse the first token as a decimal integer.
n, err := strconv.ParseInt(string(buf[:sp]), 10, 0)
if err != nil || n < 5 || int64(len(buf)) < n {
return nil, ErrHeader
}
// Extract everything between the decimal and the n -1 on the
// beginning to eat the ' ', -1 on the end to skip the newline.
var record []byte
record, buf = buf[sp+1:n-1], buf[n:]
// The first equals is guaranteed to mark the end of the key.
// Everything else is value.
eq := bytes.IndexByte(record, '=')
if eq == -1 {
return nil, ErrHeader
}
key, value := record[:eq], record[eq+1:]
keyStr := string(key)
if keyStr == paxGNUSparseOffset || keyStr == paxGNUSparseNumBytes {
// GNU sparse format 0.0 special key. Write to sparseMap instead of using the headers map.
sparseMap.Write(value)
sparseMap.Write([]byte{','})
} else {
// Normal key. Set the value in the headers map.
headers[keyStr] = string(value)
}
}
if sparseMap.Len() != 0 {
// Add sparse info to headers, chopping off the extra comma
sparseMap.Truncate(sparseMap.Len() - 1)
headers[paxGNUSparseMap] = sparseMap.String()
}
return headers, nil
}
// cString parses bytes as a NUL-terminated C-style string.
// If a NUL byte is not found then the whole slice is returned as a string.
func cString(b []byte) string {
n := 0
for n < len(b) && b[n] != 0 {
n++
}
return string(b[0:n])
}
func (tr *Reader) octal(b []byte) int64 {
// Check for binary format first.
if len(b) > 0 && b[0]&0x80 != 0 {
var x int64
for i, c := range b {
if i == 0 {
c &= 0x7f // ignore signal bit in first byte
}
x = x<<8 | int64(c)
}
return x
}
// Because unused fields are filled with NULs, we need
// to skip leading NULs. Fields may also be padded with
// spaces or NULs.
// So we remove leading and trailing NULs and spaces to
// be sure.
b = bytes.Trim(b, " \x00")
if len(b) == 0 {
return 0
}
x, err := strconv.ParseUint(cString(b), 8, 64)
if err != nil {
tr.err = err
}
return int64(x)
}
// skipUnread skips any unread bytes in the existing file entry, as well as any alignment padding.
func (tr *Reader) skipUnread() {
nr := tr.numBytes() + tr.pad // number of bytes to skip
tr.curr, tr.pad = nil, 0
if sr, ok := tr.r.(io.Seeker); ok {
if _, err := sr.Seek(nr, os.SEEK_CUR); err == nil {
return
}
}
_, tr.err = io.CopyN(ioutil.Discard, tr.r, nr)
}
func (tr *Reader) verifyChecksum(header []byte) bool {
if tr.err != nil {
return false
}
given := tr.octal(header[148:156])
unsigned, signed := checksum(header)
return given == unsigned || given == signed
}
func (tr *Reader) readHeader() *Header {
header := tr.hdrBuff[:]
copy(header, zeroBlock)
if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
return nil
}
// Two blocks of zero bytes marks the end of the archive.
if bytes.Equal(header, zeroBlock[0:blockSize]) {
if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
return nil
}
if bytes.Equal(header, zeroBlock[0:blockSize]) {
tr.err = io.EOF
} else {
tr.err = ErrHeader // zero block and then non-zero block
}
return nil
}
if !tr.verifyChecksum(header) {
tr.err = ErrHeader
return nil
}
// Unpack
hdr := new(Header)
s := slicer(header)
hdr.Name = cString(s.next(100))
hdr.Mode = tr.octal(s.next(8))
hdr.Uid = int(tr.octal(s.next(8)))
hdr.Gid = int(tr.octal(s.next(8)))
hdr.Size = tr.octal(s.next(12))
if hdr.Size < 0 {
tr.err = ErrHeader
return nil
}
hdr.ModTime = time.Unix(tr.octal(s.next(12)), 0)
s.next(8) // chksum
hdr.Typeflag = s.next(1)[0]
hdr.Linkname = cString(s.next(100))
// The remainder of the header depends on the value of magic.
// The original (v7) version of tar had no explicit magic field,
// so its magic bytes, like the rest of the block, are NULs.
magic := string(s.next(8)) // contains version field as well.
var format string
switch {
case magic[:6] == "ustar\x00": // POSIX tar (1003.1-1988)
if string(header[508:512]) == "tar\x00" {
format = "star"
} else {
format = "posix"
}
case magic == "ustar \x00": // old GNU tar
format = "gnu"
}
switch format {
case "posix", "gnu", "star":
hdr.Uname = cString(s.next(32))
hdr.Gname = cString(s.next(32))
devmajor := s.next(8)
devminor := s.next(8)
if hdr.Typeflag == TypeChar || hdr.Typeflag == TypeBlock {
hdr.Devmajor = tr.octal(devmajor)
hdr.Devminor = tr.octal(devminor)
}
var prefix string
switch format {
case "posix", "gnu":
prefix = cString(s.next(155))
case "star":
prefix = cString(s.next(131))
hdr.AccessTime = time.Unix(tr.octal(s.next(12)), 0)
hdr.ChangeTime = time.Unix(tr.octal(s.next(12)), 0)
}
if len(prefix) > 0 {
hdr.Name = prefix + "/" + hdr.Name
}
}
if tr.err != nil {
tr.err = ErrHeader
return nil
}
// Maximum value of hdr.Size is 64 GB (12 octal digits),
// so there's no risk of int64 overflowing.
nb := int64(hdr.Size)
tr.pad = -nb & (blockSize - 1) // blockSize is a power of two
// Set the current file reader.
tr.curr = ®FileReader{r: tr.r, nb: nb}
// Check for old GNU sparse format entry.
if hdr.Typeflag == TypeGNUSparse {
// Get the real size of the file.
hdr.Size = tr.octal(header[483:495])
// Read the sparse map.
sp := tr.readOldGNUSparseMap(header)
if tr.err != nil {
return nil
}
// Current file is a GNU sparse file. Update the current file reader.
tr.curr = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
}
return hdr
}
// A sparseEntry holds a single entry in a sparse file's sparse map.
// A sparse entry indicates the offset and size in a sparse file of a
// block of data.
type sparseEntry struct {
offset int64
numBytes int64
}
// readOldGNUSparseMap reads the sparse map as stored in the old GNU sparse format.
// The sparse map is stored in the tar header if it's small enough. If it's larger than four entries,
// then one or more extension headers are used to store the rest of the sparse map.
func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
isExtended := header[oldGNUSparseMainHeaderIsExtendedOffset] != 0
spCap := oldGNUSparseMainHeaderNumEntries
if isExtended {
spCap += oldGNUSparseExtendedHeaderNumEntries
}
sp := make([]sparseEntry, 0, spCap)
s := slicer(header[oldGNUSparseMainHeaderOffset:])
// Read the four entries from the main tar header
for i := 0; i < oldGNUSparseMainHeaderNumEntries; i++ {
offset := tr.octal(s.next(oldGNUSparseOffsetSize))
numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
if tr.err != nil {
tr.err = ErrHeader
return nil
}
if offset == 0 && numBytes == 0 {
break
}
sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
}
for isExtended {
// There are more entries. Read an extension header and parse its entries.
sparseHeader := make([]byte, blockSize)
if _, tr.err = io.ReadFull(tr.r, sparseHeader); tr.err != nil {
return nil
}
isExtended = sparseHeader[oldGNUSparseExtendedHeaderIsExtendedOffset] != 0
s = slicer(sparseHeader)
for i := 0; i < oldGNUSparseExtendedHeaderNumEntries; i++ {
offset := tr.octal(s.next(oldGNUSparseOffsetSize))
numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
if tr.err != nil {
tr.err = ErrHeader
return nil
}
if offset == 0 && numBytes == 0 {
break
}
sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
}
}
return sp
}
// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format version 1.0.
// The sparse map is stored just before the file data and padded out to the nearest block boundary.
func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
buf := make([]byte, 2*blockSize)
sparseHeader := buf[:blockSize]
// readDecimal is a helper function to read a decimal integer from the sparse map
// while making sure to read from the file in blocks of size blockSize
readDecimal := func() (int64, error) {
// Look for newline
nl := bytes.IndexByte(sparseHeader, '\n')
if nl == -1 {
if len(sparseHeader) >= blockSize {
// This is an error
return 0, ErrHeader
}
oldLen := len(sparseHeader)
newLen := oldLen + blockSize
if cap(sparseHeader) < newLen {
// There's more header, but we need to make room for the next block
copy(buf, sparseHeader)
sparseHeader = buf[:newLen]
} else {
// There's more header, and we can just reslice
sparseHeader = sparseHeader[:newLen]
}
// Now that sparseHeader is large enough, read next block
if _, err := io.ReadFull(r, sparseHeader[oldLen:newLen]); err != nil {
return 0, err
}
// Look for a newline in the new data
nl = bytes.IndexByte(sparseHeader[oldLen:newLen], '\n')
if nl == -1 {
// This is an error
return 0, ErrHeader
}
nl += oldLen // We want the position from the beginning
}
// Now that we've found a newline, read a number
n, err := strconv.ParseInt(string(sparseHeader[:nl]), 10, 0)
if err != nil {
return 0, ErrHeader
}
// Update sparseHeader to consume this number
sparseHeader = sparseHeader[nl+1:]
return n, nil
}
// Read the first block
if _, err := io.ReadFull(r, sparseHeader); err != nil {
return nil, err
}
// The first line contains the number of entries
numEntries, err := readDecimal()
if err != nil {
return nil, err
}
// Read all the entries
sp := make([]sparseEntry, 0, numEntries)
for i := int64(0); i < numEntries; i++ {
// Read the offset
offset, err := readDecimal()
if err != nil {
return nil, err
}
// Read numBytes
numBytes, err := readDecimal()
if err != nil {
return nil, err
}
sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
}
return sp, nil
}
// readGNUSparseMap0x1 reads the sparse map as stored in GNU's PAX sparse format version 0.1.
// The sparse map is stored in the PAX headers.
func readGNUSparseMap0x1(headers map[string]string) ([]sparseEntry, error) {
// Get number of entries
numEntriesStr, ok := headers[paxGNUSparseNumBlocks]
if !ok {
return nil, ErrHeader
}
numEntries, err := strconv.ParseInt(numEntriesStr, 10, 0)
if err != nil {
return nil, ErrHeader
}
sparseMap := strings.Split(headers[paxGNUSparseMap], ",")
// There should be two numbers in sparseMap for each entry
if int64(len(sparseMap)) != 2*numEntries {
return nil, ErrHeader
}
// Loop through the entries in the sparse map
sp := make([]sparseEntry, 0, numEntries)
for i := int64(0); i < numEntries; i++ {
offset, err := strconv.ParseInt(sparseMap[2*i], 10, 0)
if err != nil {
return nil, ErrHeader
}
numBytes, err := strconv.ParseInt(sparseMap[2*i+1], 10, 0)
if err != nil {
return nil, ErrHeader
}
sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
}
return sp, nil
}
// numBytes returns the number of bytes left to read in the current file's entry
// in the tar archive, or 0 if there is no current file.
func (tr *Reader) numBytes() int64 {
if tr.curr == nil {
// No current file, so no bytes
return 0
}
return tr.curr.numBytes()
}
// Read reads from the current entry in the tar archive.
// It returns 0, io.EOF when it reaches the end of that entry,
// until Next is called to advance to the next entry.
func (tr *Reader) Read(b []byte) (n int, err error) {
if tr.curr == nil {
return 0, io.EOF
}
n, err = tr.curr.Read(b)
if err != nil && err != io.EOF {
tr.err = err
}
return
}
func (rfr *regFileReader) Read(b []byte) (n int, err error) {
if rfr.nb == 0 {
// file consumed
return 0, io.EOF
}
if int64(len(b)) > rfr.nb {
b = b[0:rfr.nb]
}
n, err = rfr.r.Read(b)
rfr.nb -= int64(n)
if err == io.EOF && rfr.nb > 0 {
err = io.ErrUnexpectedEOF
}
return
}
// numBytes returns the number of bytes left to read in the file's data in the tar archive.
func (rfr *regFileReader) numBytes() int64 {
return rfr.nb
}
// readHole reads a sparse file hole ending at offset toOffset
func (sfr *sparseFileReader) readHole(b []byte, toOffset int64) int {
n64 := toOffset - sfr.pos
if n64 > int64(len(b)) {
n64 = int64(len(b))
}
n := int(n64)
for i := 0; i < n; i++ {
b[i] = 0
}
sfr.pos += n64
return n
}
// Read reads the sparse file data in expanded form.
func (sfr *sparseFileReader) Read(b []byte) (n int, err error) {
if len(sfr.sp) == 0 {
// No more data fragments to read from.
if sfr.pos < sfr.tot {
// We're in the last hole
n = sfr.readHole(b, sfr.tot)
return
}
// Otherwise, we're at the end of the file
return 0, io.EOF
}
if sfr.tot < sfr.sp[0].offset {
return 0, io.ErrUnexpectedEOF
}
if sfr.pos < sfr.sp[0].offset {
// We're in a hole
n = sfr.readHole(b, sfr.sp[0].offset)
return
}
// We're not in a hole, so we'll read from the next data fragment
posInFragment := sfr.pos - sfr.sp[0].offset
bytesLeft := sfr.sp[0].numBytes - posInFragment
if int64(len(b)) > bytesLeft {
b = b[0:bytesLeft]
}
n, err = sfr.rfr.Read(b)
sfr.pos += int64(n)
if int64(n) == bytesLeft {
// We're done with this fragment
sfr.sp = sfr.sp[1:]
}
if err == io.EOF && sfr.pos < sfr.tot {
// We reached the end of the last fragment's data, but there's a final hole
err = nil
}
return
}
// numBytes returns the number of bytes left to read in the sparse file's
// sparse-encoded data in the tar archive.
func (sfr *sparseFileReader) numBytes() int64 {
return sfr.rfr.nb
}