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- // 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):
- // - catch more errors (no first header, etc.)
- import (
- "bytes"
- "errors"
- "fmt"
- "io"
- "path"
- "sort"
- "strconv"
- "strings"
- "time"
- )
- var (
- ErrWriteTooLong = errors.New("archive/tar: write too long")
- ErrFieldTooLong = errors.New("archive/tar: header field too long")
- ErrWriteAfterClose = errors.New("archive/tar: write after close")
- errInvalidHeader = errors.New("archive/tar: header field too long or contains invalid values")
- )
- // A Writer provides sequential writing of a tar archive in POSIX.1 format.
- // A tar archive consists of a sequence of files.
- // Call WriteHeader to begin a new file, and then call Write to supply that file's data,
- // writing at most hdr.Size bytes in total.
- type Writer struct {
- w io.Writer
- err error
- nb int64 // number of unwritten bytes for current file entry
- pad int64 // amount of padding to write after current file entry
- closed bool
- usedBinary bool // whether the binary numeric field extension was used
- preferPax bool // use pax header instead of binary numeric header
- hdrBuff [blockSize]byte // buffer to use in writeHeader when writing a regular header
- paxHdrBuff [blockSize]byte // buffer to use in writeHeader when writing a pax header
- }
- type formatter struct {
- err error // Last error seen
- }
- // NewWriter creates a new Writer writing to w.
- func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
- // Flush finishes writing the current file (optional).
- func (tw *Writer) Flush() error {
- if tw.nb > 0 {
- tw.err = fmt.Errorf("archive/tar: missed writing %d bytes", tw.nb)
- return tw.err
- }
- n := tw.nb + tw.pad
- for n > 0 && tw.err == nil {
- nr := n
- if nr > blockSize {
- nr = blockSize
- }
- var nw int
- nw, tw.err = tw.w.Write(zeroBlock[0:nr])
- n -= int64(nw)
- }
- tw.nb = 0
- tw.pad = 0
- return tw.err
- }
- // Write s into b, terminating it with a NUL if there is room.
- func (f *formatter) formatString(b []byte, s string) {
- if len(s) > len(b) {
- f.err = ErrFieldTooLong
- return
- }
- ascii := toASCII(s)
- copy(b, ascii)
- if len(ascii) < len(b) {
- b[len(ascii)] = 0
- }
- }
- // Encode x as an octal ASCII string and write it into b with leading zeros.
- func (f *formatter) formatOctal(b []byte, x int64) {
- s := strconv.FormatInt(x, 8)
- // leading zeros, but leave room for a NUL.
- for len(s)+1 < len(b) {
- s = "0" + s
- }
- f.formatString(b, s)
- }
- // fitsInBase256 reports whether x can be encoded into n bytes using base-256
- // encoding. Unlike octal encoding, base-256 encoding does not require that the
- // string ends with a NUL character. Thus, all n bytes are available for output.
- //
- // If operating in binary mode, this assumes strict GNU binary mode; which means
- // that the first byte can only be either 0x80 or 0xff. Thus, the first byte is
- // equivalent to the sign bit in two's complement form.
- func fitsInBase256(n int, x int64) bool {
- var binBits = uint(n-1) * 8
- return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
- }
- // Write x into b, as binary (GNUtar/star extension).
- func (f *formatter) formatNumeric(b []byte, x int64) {
- if fitsInBase256(len(b), x) {
- for i := len(b) - 1; i >= 0; i-- {
- b[i] = byte(x)
- x >>= 8
- }
- b[0] |= 0x80 // Highest bit indicates binary format
- return
- }
- f.formatOctal(b, 0) // Last resort, just write zero
- f.err = ErrFieldTooLong
- }
- var (
- minTime = time.Unix(0, 0)
- // There is room for 11 octal digits (33 bits) of mtime.
- maxTime = minTime.Add((1<<33 - 1) * time.Second)
- )
- // WriteHeader writes hdr and prepares to accept the file's contents.
- // WriteHeader calls Flush if it is not the first header.
- // Calling after a Close will return ErrWriteAfterClose.
- func (tw *Writer) WriteHeader(hdr *Header) error {
- return tw.writeHeader(hdr, true)
- }
- // WriteHeader writes hdr and prepares to accept the file's contents.
- // WriteHeader calls Flush if it is not the first header.
- // Calling after a Close will return ErrWriteAfterClose.
- // As this method is called internally by writePax header to allow it to
- // suppress writing the pax header.
- func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
- if tw.closed {
- return ErrWriteAfterClose
- }
- if tw.err == nil {
- tw.Flush()
- }
- if tw.err != nil {
- return tw.err
- }
- // a map to hold pax header records, if any are needed
- paxHeaders := make(map[string]string)
- // TODO(shanemhansen): we might want to use PAX headers for
- // subsecond time resolution, but for now let's just capture
- // too long fields or non ascii characters
- var f formatter
- var header []byte
- // We need to select which scratch buffer to use carefully,
- // since this method is called recursively to write PAX headers.
- // If allowPax is true, this is the non-recursive call, and we will use hdrBuff.
- // If allowPax is false, we are being called by writePAXHeader, and hdrBuff is
- // already being used by the non-recursive call, so we must use paxHdrBuff.
- header = tw.hdrBuff[:]
- if !allowPax {
- header = tw.paxHdrBuff[:]
- }
- copy(header, zeroBlock)
- s := slicer(header)
- // Wrappers around formatter that automatically sets paxHeaders if the
- // argument extends beyond the capacity of the input byte slice.
- var formatString = func(b []byte, s string, paxKeyword string) {
- needsPaxHeader := paxKeyword != paxNone && len(s) > len(b) || !isASCII(s)
- if needsPaxHeader {
- paxHeaders[paxKeyword] = s
- return
- }
- f.formatString(b, s)
- }
- var formatNumeric = func(b []byte, x int64, paxKeyword string) {
- // Try octal first.
- s := strconv.FormatInt(x, 8)
- if len(s) < len(b) {
- f.formatOctal(b, x)
- return
- }
- // If it is too long for octal, and PAX is preferred, use a PAX header.
- if paxKeyword != paxNone && tw.preferPax {
- f.formatOctal(b, 0)
- s := strconv.FormatInt(x, 10)
- paxHeaders[paxKeyword] = s
- return
- }
- tw.usedBinary = true
- f.formatNumeric(b, x)
- }
- // keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
- pathHeaderBytes := s.next(fileNameSize)
- formatString(pathHeaderBytes, hdr.Name, paxPath)
- // Handle out of range ModTime carefully.
- var modTime int64
- if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
- modTime = hdr.ModTime.Unix()
- }
- f.formatOctal(s.next(8), hdr.Mode) // 100:108
- formatNumeric(s.next(8), int64(hdr.Uid), paxUid) // 108:116
- formatNumeric(s.next(8), int64(hdr.Gid), paxGid) // 116:124
- formatNumeric(s.next(12), hdr.Size, paxSize) // 124:136
- formatNumeric(s.next(12), modTime, paxNone) // 136:148 --- consider using pax for finer granularity
- s.next(8) // chksum (148:156)
- s.next(1)[0] = hdr.Typeflag // 156:157
- formatString(s.next(100), hdr.Linkname, paxLinkpath)
- copy(s.next(8), []byte("ustar\x0000")) // 257:265
- formatString(s.next(32), hdr.Uname, paxUname) // 265:297
- formatString(s.next(32), hdr.Gname, paxGname) // 297:329
- formatNumeric(s.next(8), hdr.Devmajor, paxNone) // 329:337
- formatNumeric(s.next(8), hdr.Devminor, paxNone) // 337:345
- // keep a reference to the prefix to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
- prefixHeaderBytes := s.next(155)
- formatString(prefixHeaderBytes, "", paxNone) // 345:500 prefix
- // Use the GNU magic instead of POSIX magic if we used any GNU extensions.
- if tw.usedBinary {
- copy(header[257:265], []byte("ustar \x00"))
- }
- _, paxPathUsed := paxHeaders[paxPath]
- // try to use a ustar header when only the name is too long
- if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
- prefix, suffix, ok := splitUSTARPath(hdr.Name)
- if ok {
- // Since we can encode in USTAR format, disable PAX header.
- delete(paxHeaders, paxPath)
- // Update the path fields
- formatString(pathHeaderBytes, suffix, paxNone)
- formatString(prefixHeaderBytes, prefix, paxNone)
- }
- }
- // The chksum field is terminated by a NUL and a space.
- // This is different from the other octal fields.
- chksum, _ := checksum(header)
- f.formatOctal(header[148:155], chksum) // Never fails
- header[155] = ' '
- // Check if there were any formatting errors.
- if f.err != nil {
- tw.err = f.err
- return tw.err
- }
- if allowPax {
- for k, v := range hdr.Xattrs {
- paxHeaders[paxXattr+k] = v
- }
- }
- if len(paxHeaders) > 0 {
- if !allowPax {
- return errInvalidHeader
- }
- if err := tw.writePAXHeader(hdr, paxHeaders); err != nil {
- return err
- }
- }
- tw.nb = int64(hdr.Size)
- tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize
- _, tw.err = tw.w.Write(header)
- return tw.err
- }
- // splitUSTARPath splits a path according to USTAR prefix and suffix rules.
- // If the path is not splittable, then it will return ("", "", false).
- func splitUSTARPath(name string) (prefix, suffix string, ok bool) {
- length := len(name)
- if length <= fileNameSize || !isASCII(name) {
- return "", "", false
- } else if length > fileNamePrefixSize+1 {
- length = fileNamePrefixSize + 1
- } else if name[length-1] == '/' {
- length--
- }
- i := strings.LastIndex(name[:length], "/")
- nlen := len(name) - i - 1 // nlen is length of suffix
- plen := i // plen is length of prefix
- if i <= 0 || nlen > fileNameSize || nlen == 0 || plen > fileNamePrefixSize {
- return "", "", false
- }
- return name[:i], name[i+1:], true
- }
- // writePaxHeader writes an extended pax header to the
- // archive.
- func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) error {
- // Prepare extended header
- ext := new(Header)
- ext.Typeflag = TypeXHeader
- // Setting ModTime is required for reader parsing to
- // succeed, and seems harmless enough.
- ext.ModTime = hdr.ModTime
- // The spec asks that we namespace our pseudo files
- // with the current pid. However, this results in differing outputs
- // for identical inputs. As such, the constant 0 is now used instead.
- // golang.org/issue/12358
- dir, file := path.Split(hdr.Name)
- fullName := path.Join(dir, "PaxHeaders.0", file)
- ascii := toASCII(fullName)
- if len(ascii) > 100 {
- ascii = ascii[:100]
- }
- ext.Name = ascii
- // Construct the body
- var buf bytes.Buffer
- // Keys are sorted before writing to body to allow deterministic output.
- var keys []string
- for k := range paxHeaders {
- keys = append(keys, k)
- }
- sort.Strings(keys)
- for _, k := range keys {
- fmt.Fprint(&buf, formatPAXRecord(k, paxHeaders[k]))
- }
- ext.Size = int64(len(buf.Bytes()))
- if err := tw.writeHeader(ext, false); err != nil {
- return err
- }
- if _, err := tw.Write(buf.Bytes()); err != nil {
- return err
- }
- if err := tw.Flush(); err != nil {
- return err
- }
- return nil
- }
- // formatPAXRecord formats a single PAX record, prefixing it with the
- // appropriate length.
- func formatPAXRecord(k, v string) string {
- const padding = 3 // Extra padding for ' ', '=', and '\n'
- size := len(k) + len(v) + padding
- size += len(strconv.Itoa(size))
- record := fmt.Sprintf("%d %s=%s\n", size, k, v)
- // Final adjustment if adding size field increased the record size.
- if len(record) != size {
- size = len(record)
- record = fmt.Sprintf("%d %s=%s\n", size, k, v)
- }
- return record
- }
- // Write writes to the current entry in the tar archive.
- // Write returns the error ErrWriteTooLong if more than
- // hdr.Size bytes are written after WriteHeader.
- func (tw *Writer) Write(b []byte) (n int, err error) {
- if tw.closed {
- err = ErrWriteAfterClose
- return
- }
- overwrite := false
- if int64(len(b)) > tw.nb {
- b = b[0:tw.nb]
- overwrite = true
- }
- n, err = tw.w.Write(b)
- tw.nb -= int64(n)
- if err == nil && overwrite {
- err = ErrWriteTooLong
- return
- }
- tw.err = err
- return
- }
- // Close closes the tar archive, flushing any unwritten
- // data to the underlying writer.
- func (tw *Writer) Close() error {
- if tw.err != nil || tw.closed {
- return tw.err
- }
- tw.Flush()
- tw.closed = true
- if tw.err != nil {
- return tw.err
- }
- // trailer: two zero blocks
- for i := 0; i < 2; i++ {
- _, tw.err = tw.w.Write(zeroBlock)
- if tw.err != nil {
- break
- }
- }
- return tw.err
- }
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