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moby--moby/vendor/archive/tar/writer.go
Tonis Tiigi 72df48d1ad vendor: add archive/tar
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
2017-07-13 19:08:19 -07:00

364 lines
11 KiB
Go

// 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 block // buffer to use in writeHeader when writing a regular header
paxHdrBuff block // buffer to use in writeHeader when writing a PAX header
}
// 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
}
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(dsnet): 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
// 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[:])
// Wrappers around formatter that automatically sets paxHeaders if the
// argument extends beyond the capacity of the input byte slice.
var f formatter
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)
}
// Handle out of range ModTime carefully.
var modTime int64
if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
modTime = hdr.ModTime.Unix()
}
v7 := header.V7()
formatString(v7.Name(), hdr.Name, paxPath)
// TODO(dsnet): The GNU format permits the mode field to be encoded in
// base-256 format. Thus, we can use formatNumeric instead of formatOctal.
f.formatOctal(v7.Mode(), hdr.Mode)
formatNumeric(v7.UID(), int64(hdr.Uid), paxUid)
formatNumeric(v7.GID(), int64(hdr.Gid), paxGid)
formatNumeric(v7.Size(), hdr.Size, paxSize)
// TODO(dsnet): Consider using PAX for finer time granularity.
formatNumeric(v7.ModTime(), modTime, paxNone)
v7.TypeFlag()[0] = hdr.Typeflag
formatString(v7.LinkName(), hdr.Linkname, paxLinkpath)
ustar := header.USTAR()
formatString(ustar.UserName(), hdr.Uname, paxUname)
formatString(ustar.GroupName(), hdr.Gname, paxGname)
formatNumeric(ustar.DevMajor(), hdr.Devmajor, paxNone)
formatNumeric(ustar.DevMinor(), hdr.Devminor, paxNone)
// TODO(dsnet): The logic surrounding the prefix field is broken when trying
// to encode the header as GNU format. The challenge with the current logic
// is that we are unsure what format we are using at any given moment until
// we have processed *all* of the fields. The problem is that by the time
// all fields have been processed, some work has already been done to handle
// each field under the assumption that it is for one given format or
// another. In some situations, this causes the Writer to be confused and
// encode a prefix field when the format being used is GNU. Thus, producing
// an invalid tar file.
//
// As a short-term fix, we disable the logic to use the prefix field, which
// will force the badly generated GNU files to become encoded as being
// the PAX format.
//
// As an alternative fix, we could hard-code preferPax to be true. However,
// this is problematic for the following reasons:
// * The preferPax functionality is not tested at all.
// * This can result in headers that try to use both the GNU and PAX
// features at the same time, which is also wrong.
//
// The proper fix for this is to use a two-pass method:
// * The first pass simply determines what set of formats can possibly
// encode the given header.
// * The second pass actually encodes the header as that given format
// without worrying about violating the format.
//
// See the following:
// https://golang.org/issue/12594
// https://golang.org/issue/17630
// https://golang.org/issue/9683
const usePrefix = false
// try to use a ustar header when only the name is too long
_, paxPathUsed := paxHeaders[paxPath]
if usePrefix && !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(v7.Name(), suffix, paxNone)
formatString(ustar.Prefix(), prefix, paxNone)
}
}
if tw.usedBinary {
header.SetFormat(formatGNU)
} else {
header.SetFormat(formatUSTAR)
}
// 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 = 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 <= nameSize || !isASCII(name) {
return "", "", false
} else if length > prefixSize+1 {
length = prefixSize + 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 > nameSize || nlen == 0 || plen > prefixSize {
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) > nameSize {
ascii = ascii[:nameSize]
}
ext.Name = ascii
// Construct the body
var buf bytes.Buffer
// Keys are sorted before writing to body to allow deterministic output.
keys := make([]string, 0, len(paxHeaders))
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
}
// 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
}