go writer 源码
golang writer 代码
文件路径：/src/archive/tar/writer.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
import (
"fmt"
"io"
"path"
"sort"
"strings"
"time"
)
// Writer provides sequential writing of a tar archive.
// Write.WriteHeader begins a new file with the provided Header,
// and then Writer can be treated as an io.Writer to supply that file's data.
type Writer struct {
w io.Writer
pad int64 // Amount of padding to write after current file entry
curr fileWriter // Writer for current file entry
hdr Header // Shallow copy of Header that is safe for mutations
blk block // Buffer to use as temporary local storage
// err is a persistent error.
// It is only the responsibility of every exported method of Writer to
// ensure that this error is sticky.
err error
}
// NewWriter creates a new Writer writing to w.
func NewWriter(w io.Writer) *Writer {
return &Writer{w: w, curr: ®FileWriter{w, 0}}
}
type fileWriter interface {
io.Writer
fileState
ReadFrom(io.Reader) (int64, error)
}
// Flush finishes writing the current file's block padding.
// The current file must be fully written before Flush can be called.
//
// This is unnecessary as the next call to WriteHeader or Close
// will implicitly flush out the file's padding.
func (tw *Writer) Flush() error {
if tw.err != nil {
return tw.err
}
if nb := tw.curr.logicalRemaining(); nb > 0 {
return fmt.Errorf("archive/tar: missed writing %d bytes", nb)
}
if _, tw.err = tw.w.Write(zeroBlock[:tw.pad]); tw.err != nil {
return tw.err
}
tw.pad = 0
return nil
}
// WriteHeader writes hdr and prepares to accept the file's contents.
// The Header.Size determines how many bytes can be written for the next file.
// If the current file is not fully written, then this returns an error.
// This implicitly flushes any padding necessary before writing the header.
func (tw *Writer) WriteHeader(hdr *Header) error {
if err := tw.Flush(); err != nil {
return err
}
tw.hdr = *hdr // Shallow copy of Header
// Avoid usage of the legacy TypeRegA flag, and automatically promote
// it to use TypeReg or TypeDir.
if tw.hdr.Typeflag == TypeRegA {
if strings.HasSuffix(tw.hdr.Name, "/") {
tw.hdr.Typeflag = TypeDir
} else {
tw.hdr.Typeflag = TypeReg
}
}
// Round ModTime and ignore AccessTime and ChangeTime unless
// the format is explicitly chosen.
// This ensures nominal usage of WriteHeader (without specifying the format)
// does not always result in the PAX format being chosen, which
// causes a 1KiB increase to every header.
if tw.hdr.Format == FormatUnknown {
tw.hdr.ModTime = tw.hdr.ModTime.Round(time.Second)
tw.hdr.AccessTime = time.Time{}
tw.hdr.ChangeTime = time.Time{}
}
allowedFormats, paxHdrs, err := tw.hdr.allowedFormats()
switch {
case allowedFormats.has(FormatUSTAR):
tw.err = tw.writeUSTARHeader(&tw.hdr)
return tw.err
case allowedFormats.has(FormatPAX):
tw.err = tw.writePAXHeader(&tw.hdr, paxHdrs)
return tw.err
case allowedFormats.has(FormatGNU):
tw.err = tw.writeGNUHeader(&tw.hdr)
return tw.err
default:
return err // Non-fatal error
}
}
func (tw *Writer) writeUSTARHeader(hdr *Header) error {
// Check if we can use USTAR prefix/suffix splitting.
var namePrefix string
if prefix, suffix, ok := splitUSTARPath(hdr.Name); ok {
namePrefix, hdr.Name = prefix, suffix
}
// Pack the main header.
var f formatter
blk := tw.templateV7Plus(hdr, f.formatString, f.formatOctal)
f.formatString(blk.toUSTAR().prefix(), namePrefix)
blk.setFormat(FormatUSTAR)
if f.err != nil {
return f.err // Should never happen since header is validated
}
return tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag)
}
func (tw *Writer) writePAXHeader(hdr *Header, paxHdrs map[string]string) error {
realName, realSize := hdr.Name, hdr.Size
// TODO(dsnet): Re-enable this when adding sparse support.
// See https://golang.org/issue/22735
/*
// Handle sparse files.
var spd sparseDatas
var spb []byte
if len(hdr.SparseHoles) > 0 {
sph := append([]sparseEntry{}, hdr.SparseHoles...) // Copy sparse map
sph = alignSparseEntries(sph, hdr.Size)
spd = invertSparseEntries(sph, hdr.Size)
// Format the sparse map.
hdr.Size = 0 // Replace with encoded size
spb = append(strconv.AppendInt(spb, int64(len(spd)), 10), '\n')
for _, s := range spd {
hdr.Size += s.Length
spb = append(strconv.AppendInt(spb, s.Offset, 10), '\n')
spb = append(strconv.AppendInt(spb, s.Length, 10), '\n')
}
pad := blockPadding(int64(len(spb)))
spb = append(spb, zeroBlock[:pad]...)
hdr.Size += int64(len(spb)) // Accounts for encoded sparse map
// Add and modify appropriate PAX records.
dir, file := path.Split(realName)
hdr.Name = path.Join(dir, "GNUSparseFile.0", file)
paxHdrs[paxGNUSparseMajor] = "1"
paxHdrs[paxGNUSparseMinor] = "0"
paxHdrs[paxGNUSparseName] = realName
paxHdrs[paxGNUSparseRealSize] = strconv.FormatInt(realSize, 10)
paxHdrs[paxSize] = strconv.FormatInt(hdr.Size, 10)
delete(paxHdrs, paxPath) // Recorded by paxGNUSparseName
}
*/
_ = realSize
// Write PAX records to the output.
isGlobal := hdr.Typeflag == TypeXGlobalHeader
if len(paxHdrs) > 0 || isGlobal {
// Sort keys for deterministic ordering.
var keys []string
for k := range paxHdrs {
keys = append(keys, k)
}
sort.Strings(keys)
// Write each record to a buffer.
var buf strings.Builder
for _, k := range keys {
rec, err := formatPAXRecord(k, paxHdrs[k])
if err != nil {
return err
}
buf.WriteString(rec)
}
// Write the extended header file.
var name string
var flag byte
if isGlobal {
name = realName
if name == "" {
name = "GlobalHead.0.0"
}
flag = TypeXGlobalHeader
} else {
dir, file := path.Split(realName)
name = path.Join(dir, "PaxHeaders.0", file)
flag = TypeXHeader
}
data := buf.String()
if err := tw.writeRawFile(name, data, flag, FormatPAX); err != nil || isGlobal {
return err // Global headers return here
}
}
// Pack the main header.
var f formatter // Ignore errors since they are expected
fmtStr := func(b []byte, s string) { f.formatString(b, toASCII(s)) }
blk := tw.templateV7Plus(hdr, fmtStr, f.formatOctal)
blk.setFormat(FormatPAX)
if err := tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag); err != nil {
return err
}
// TODO(dsnet): Re-enable this when adding sparse support.
// See https://golang.org/issue/22735
/*
// Write the sparse map and setup the sparse writer if necessary.
if len(spd) > 0 {
// Use tw.curr since the sparse map is accounted for in hdr.Size.
if _, err := tw.curr.Write(spb); err != nil {
return err
}
tw.curr = &sparseFileWriter{tw.curr, spd, 0}
}
*/
return nil
}
func (tw *Writer) writeGNUHeader(hdr *Header) error {
// Use long-link files if Name or Linkname exceeds the field size.
const longName = "././@LongLink"
if len(hdr.Name) > nameSize {
data := hdr.Name + "\x00"
if err := tw.writeRawFile(longName, data, TypeGNULongName, FormatGNU); err != nil {
return err
}
}
if len(hdr.Linkname) > nameSize {
data := hdr.Linkname + "\x00"
if err := tw.writeRawFile(longName, data, TypeGNULongLink, FormatGNU); err != nil {
return err
}
}
// Pack the main header.
var f formatter // Ignore errors since they are expected
var spd sparseDatas
var spb []byte
blk := tw.templateV7Plus(hdr, f.formatString, f.formatNumeric)
if !hdr.AccessTime.IsZero() {
f.formatNumeric(blk.toGNU().accessTime(), hdr.AccessTime.Unix())
}
if !hdr.ChangeTime.IsZero() {
f.formatNumeric(blk.toGNU().changeTime(), hdr.ChangeTime.Unix())
}
// TODO(dsnet): Re-enable this when adding sparse support.
// See https://golang.org/issue/22735
/*
if hdr.Typeflag == TypeGNUSparse {
sph := append([]sparseEntry{}, hdr.SparseHoles...) // Copy sparse map
sph = alignSparseEntries(sph, hdr.Size)
spd = invertSparseEntries(sph, hdr.Size)
// Format the sparse map.
formatSPD := func(sp sparseDatas, sa sparseArray) sparseDatas {
for i := 0; len(sp) > 0 && i < sa.MaxEntries(); i++ {
f.formatNumeric(sa.Entry(i).Offset(), sp[0].Offset)
f.formatNumeric(sa.Entry(i).Length(), sp[0].Length)
sp = sp[1:]
}
if len(sp) > 0 {
sa.IsExtended()[0] = 1
}
return sp
}
sp2 := formatSPD(spd, blk.GNU().Sparse())
for len(sp2) > 0 {
var spHdr block
sp2 = formatSPD(sp2, spHdr.Sparse())
spb = append(spb, spHdr[:]...)
}
// Update size fields in the header block.
realSize := hdr.Size
hdr.Size = 0 // Encoded size; does not account for encoded sparse map
for _, s := range spd {
hdr.Size += s.Length
}
copy(blk.V7().Size(), zeroBlock[:]) // Reset field
f.formatNumeric(blk.V7().Size(), hdr.Size)
f.formatNumeric(blk.GNU().RealSize(), realSize)
}
*/
blk.setFormat(FormatGNU)
if err := tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag); err != nil {
return err
}
// Write the extended sparse map and setup the sparse writer if necessary.
if len(spd) > 0 {
// Use tw.w since the sparse map is not accounted for in hdr.Size.
if _, err := tw.w.Write(spb); err != nil {
return err
}
tw.curr = &sparseFileWriter{tw.curr, spd, 0}
}
return nil
}
type (
stringFormatter func([]byte, string)
numberFormatter func([]byte, int64)
)
// templateV7Plus fills out the V7 fields of a block using values from hdr.
// It also fills out fields (uname, gname, devmajor, devminor) that are
// shared in the USTAR, PAX, and GNU formats using the provided formatters.
//
// The block returned is only valid until the next call to
// templateV7Plus or writeRawFile.
func (tw *Writer) templateV7Plus(hdr *Header, fmtStr stringFormatter, fmtNum numberFormatter) *block {
tw.blk.reset()
modTime := hdr.ModTime
if modTime.IsZero() {
modTime = time.Unix(0, 0)
}
v7 := tw.blk.toV7()
v7.typeFlag()[0] = hdr.Typeflag
fmtStr(v7.name(), hdr.Name)
fmtStr(v7.linkName(), hdr.Linkname)
fmtNum(v7.mode(), hdr.Mode)
fmtNum(v7.uid(), int64(hdr.Uid))
fmtNum(v7.gid(), int64(hdr.Gid))
fmtNum(v7.size(), hdr.Size)
fmtNum(v7.modTime(), modTime.Unix())
ustar := tw.blk.toUSTAR()
fmtStr(ustar.userName(), hdr.Uname)
fmtStr(ustar.groupName(), hdr.Gname)
fmtNum(ustar.devMajor(), hdr.Devmajor)
fmtNum(ustar.devMinor(), hdr.Devminor)
return &tw.blk
}
// writeRawFile writes a minimal file with the given name and flag type.
// It uses format to encode the header format and will write data as the body.
// It uses default values for all of the other fields (as BSD and GNU tar does).
func (tw *Writer) writeRawFile(name, data string, flag byte, format Format) error {
tw.blk.reset()
// Best effort for the filename.
name = toASCII(name)
if len(name) > nameSize {
name = name[:nameSize]
}
name = strings.TrimRight(name, "/")
var f formatter
v7 := tw.blk.toV7()
v7.typeFlag()[0] = flag
f.formatString(v7.name(), name)
f.formatOctal(v7.mode(), 0)
f.formatOctal(v7.uid(), 0)
f.formatOctal(v7.gid(), 0)
f.formatOctal(v7.size(), int64(len(data))) // Must be < 8GiB
f.formatOctal(v7.modTime(), 0)
tw.blk.setFormat(format)
if f.err != nil {
return f.err // Only occurs if size condition is violated
}
// Write the header and data.
if err := tw.writeRawHeader(&tw.blk, int64(len(data)), flag); err != nil {
return err
}
_, err := io.WriteString(tw, data)
return err
}
// writeRawHeader writes the value of blk, regardless of its value.
// It sets up the Writer such that it can accept a file of the given size.
// If the flag is a special header-only flag, then the size is treated as zero.
func (tw *Writer) writeRawHeader(blk *block, size int64, flag byte) error {
if err := tw.Flush(); err != nil {
return err
}
if _, err := tw.w.Write(blk[:]); err != nil {
return err
}
if isHeaderOnlyType(flag) {
size = 0
}
tw.curr = ®FileWriter{tw.w, size}
tw.pad = blockPadding(size)
return nil
}
// 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
}
// Write writes to the current file in the tar archive.
// Write returns the error ErrWriteTooLong if more than
// Header.Size bytes are written after WriteHeader.
//
// Calling Write on special types like TypeLink, TypeSymlink, TypeChar,
// TypeBlock, TypeDir, and TypeFifo returns (0, ErrWriteTooLong) regardless
// of what the Header.Size claims.
func (tw *Writer) Write(b []byte) (int, error) {
if tw.err != nil {
return 0, tw.err
}
n, err := tw.curr.Write(b)
if err != nil && err != ErrWriteTooLong {
tw.err = err
}
return n, err
}
// readFrom populates the content of the current file by reading from r.
// The bytes read must match the number of remaining bytes in the current file.
//
// If the current file is sparse and r is an io.ReadSeeker,
// then readFrom uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are all NULs.
// This always reads the last byte to ensure r is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735
func (tw *Writer) readFrom(r io.Reader) (int64, error) {
if tw.err != nil {
return 0, tw.err
}
n, err := tw.curr.ReadFrom(r)
if err != nil && err != ErrWriteTooLong {
tw.err = err
}
return n, err
}
// Close closes the tar archive by flushing the padding, and writing the footer.
// If the current file (from a prior call to WriteHeader) is not fully written,
// then this returns an error.
func (tw *Writer) Close() error {
if tw.err == ErrWriteAfterClose {
return nil
}
if tw.err != nil {
return tw.err
}
// Trailer: two zero blocks.
err := tw.Flush()
for i := 0; i < 2 && err == nil; i++ {
_, err = tw.w.Write(zeroBlock[:])
}
// Ensure all future actions are invalid.
tw.err = ErrWriteAfterClose
return err // Report IO errors
}
// regFileWriter is a fileWriter for writing data to a regular file entry.
type regFileWriter struct {
w io.Writer // Underlying Writer
nb int64 // Number of remaining bytes to write
}
func (fw *regFileWriter) Write(b []byte) (n int, err error) {
overwrite := int64(len(b)) > fw.nb
if overwrite {
b = b[:fw.nb]
}
if len(b) > 0 {
n, err = fw.w.Write(b)
fw.nb -= int64(n)
}
switch {
case err != nil:
return n, err
case overwrite:
return n, ErrWriteTooLong
default:
return n, nil
}
}
func (fw *regFileWriter) ReadFrom(r io.Reader) (int64, error) {
return io.Copy(struct{ io.Writer }{fw}, r)
}
// logicalRemaining implements fileState.logicalRemaining.
func (fw regFileWriter) logicalRemaining() int64 {
return fw.nb
}
// logicalRemaining implements fileState.physicalRemaining.
func (fw regFileWriter) physicalRemaining() int64 {
return fw.nb
}
// sparseFileWriter is a fileWriter for writing data to a sparse file entry.
type sparseFileWriter struct {
fw fileWriter // Underlying fileWriter
sp sparseDatas // Normalized list of data fragments
pos int64 // Current position in sparse file
}
func (sw *sparseFileWriter) Write(b []byte) (n int, err error) {
overwrite := int64(len(b)) > sw.logicalRemaining()
if overwrite {
b = b[:sw.logicalRemaining()]
}
b0 := b
endPos := sw.pos + int64(len(b))
for endPos > sw.pos && err == nil {
var nf int // Bytes written in fragment
dataStart, dataEnd := sw.sp[0].Offset, sw.sp[0].endOffset()
if sw.pos < dataStart { // In a hole fragment
bf := b[:min(int64(len(b)), dataStart-sw.pos)]
nf, err = zeroWriter{}.Write(bf)
} else { // In a data fragment
bf := b[:min(int64(len(b)), dataEnd-sw.pos)]
nf, err = sw.fw.Write(bf)
}
b = b[nf:]
sw.pos += int64(nf)
if sw.pos >= dataEnd && len(sw.sp) > 1 {
sw.sp = sw.sp[1:] // Ensure last fragment always remains
}
}
n = len(b0) - len(b)
switch {
case err == ErrWriteTooLong:
return n, errMissData // Not possible; implies bug in validation logic
case err != nil:
return n, err
case sw.logicalRemaining() == 0 && sw.physicalRemaining() > 0:
return n, errUnrefData // Not possible; implies bug in validation logic
case overwrite:
return n, ErrWriteTooLong
default:
return n, nil
}
}
func (sw *sparseFileWriter) ReadFrom(r io.Reader) (n int64, err error) {
rs, ok := r.(io.ReadSeeker)
if ok {
if _, err := rs.Seek(0, io.SeekCurrent); err != nil {
ok = false // Not all io.Seeker can really seek
}
}
if !ok {
return io.Copy(struct{ io.Writer }{sw}, r)
}
var readLastByte bool
pos0 := sw.pos
for sw.logicalRemaining() > 0 && !readLastByte && err == nil {
var nf int64 // Size of fragment
dataStart, dataEnd := sw.sp[0].Offset, sw.sp[0].endOffset()
if sw.pos < dataStart { // In a hole fragment
nf = dataStart - sw.pos
if sw.physicalRemaining() == 0 {
readLastByte = true
nf--
}
_, err = rs.Seek(nf, io.SeekCurrent)
} else { // In a data fragment
nf = dataEnd - sw.pos
nf, err = io.CopyN(sw.fw, rs, nf)
}
sw.pos += nf
if sw.pos >= dataEnd && len(sw.sp) > 1 {
sw.sp = sw.sp[1:] // Ensure last fragment always remains
}
}
// If the last fragment is a hole, then seek to 1-byte before EOF, and
// read a single byte to ensure the file is the right size.
if readLastByte && err == nil {
_, err = mustReadFull(rs, []byte{0})
sw.pos++
}
n = sw.pos - pos0
switch {
case err == io.EOF:
return n, io.ErrUnexpectedEOF
case err == ErrWriteTooLong:
return n, errMissData // Not possible; implies bug in validation logic
case err != nil:
return n, err
case sw.logicalRemaining() == 0 && sw.physicalRemaining() > 0:
return n, errUnrefData // Not possible; implies bug in validation logic
default:
return n, ensureEOF(rs)
}
}
func (sw sparseFileWriter) logicalRemaining() int64 {
return sw.sp[len(sw.sp)-1].endOffset() - sw.pos
}
func (sw sparseFileWriter) physicalRemaining() int64 {
return sw.fw.physicalRemaining()
}
// zeroWriter may only be written with NULs, otherwise it returns errWriteHole.
type zeroWriter struct{}
func (zeroWriter) Write(b []byte) (int, error) {
for i, c := range b {
if c != 0 {
return i, errWriteHole
}
}
return len(b), nil
}
// ensureEOF checks whether r is at EOF, reporting ErrWriteTooLong if not so.
func ensureEOF(r io.Reader) error {
n, err := tryReadFull(r, []byte{0})
switch {
case n > 0:
return ErrWriteTooLong
case err == io.EOF:
return nil
default:
return err
}
}
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