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tar-split/archive/tar/writer.go

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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
}