go reader 源码
golang reader 代码
文件路径：/src/archive/tar/reader.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 (
"bytes"
"io"
"strconv"
"strings"
"time"
)
// Reader provides sequential access to the contents of a tar archive.
// Reader.Next advances to the next file in the archive (including the first),
// and then Reader can be treated as an io.Reader to access the file's data.
type Reader struct {
r io.Reader
pad int64 // Amount of padding (ignored) after current file entry
curr fileReader // Reader for current file entry
blk block // Buffer to use as temporary local storage
// err is a persistent error.
// It is only the responsibility of every exported method of Reader to
// ensure that this error is sticky.
err error
}
type fileReader interface {
io.Reader
fileState
WriteTo(io.Writer) (int64, error)
}
// NewReader creates a new Reader reading from r.
func NewReader(r io.Reader) *Reader {
return &Reader{r: r, curr: ®FileReader{r, 0}}
}
// Next advances to the next entry in the tar archive.
// The Header.Size determines how many bytes can be read for the next file.
// Any remaining data in the current file is automatically discarded.
//
// io.EOF is returned at the end of the input.
func (tr *Reader) Next() (*Header, error) {
if tr.err != nil {
return nil, tr.err
}
hdr, err := tr.next()
tr.err = err
return hdr, err
}
func (tr *Reader) next() (*Header, error) {
var paxHdrs map[string]string
var gnuLongName, gnuLongLink string
// Externally, Next iterates through the tar archive as if it is a series of
// files. Internally, the tar format often uses fake "files" to add meta
// data that describes the next file. These meta data "files" should not
// normally be visible to the outside. As such, this loop iterates through
// one or more "header files" until it finds a "normal file".
format := FormatUSTAR | FormatPAX | FormatGNU
for {
// Discard the remainder of the file and any padding.
if err := discard(tr.r, tr.curr.physicalRemaining()); err != nil {
return nil, err
}
if _, err := tryReadFull(tr.r, tr.blk[:tr.pad]); err != nil {
return nil, err
}
tr.pad = 0
hdr, rawHdr, err := tr.readHeader()
if err != nil {
return nil, err
}
if err := tr.handleRegularFile(hdr); err != nil {
return nil, err
}
format.mayOnlyBe(hdr.Format)
// Check for PAX/GNU special headers and files.
switch hdr.Typeflag {
case TypeXHeader, TypeXGlobalHeader:
format.mayOnlyBe(FormatPAX)
paxHdrs, err = parsePAX(tr)
if err != nil {
return nil, err
}
if hdr.Typeflag == TypeXGlobalHeader {
mergePAX(hdr, paxHdrs)
return &Header{
Name: hdr.Name,
Typeflag: hdr.Typeflag,
Xattrs: hdr.Xattrs,
PAXRecords: hdr.PAXRecords,
Format: format,
}, nil
}
continue // This is a meta header affecting the next header
case TypeGNULongName, TypeGNULongLink:
format.mayOnlyBe(FormatGNU)
realname, err := io.ReadAll(tr)
if err != nil {
return nil, err
}
var p parser
switch hdr.Typeflag {
case TypeGNULongName:
gnuLongName = p.parseString(realname)
case TypeGNULongLink:
gnuLongLink = p.parseString(realname)
}
continue // This is a meta header affecting the next header
default:
// The old GNU sparse format is handled here since it is technically
// just a regular file with additional attributes.
if err := mergePAX(hdr, paxHdrs); err != nil {
return nil, err
}
if gnuLongName != "" {
hdr.Name = gnuLongName
}
if gnuLongLink != "" {
hdr.Linkname = gnuLongLink
}
if hdr.Typeflag == TypeRegA {
if strings.HasSuffix(hdr.Name, "/") {
hdr.Typeflag = TypeDir // Legacy archives use trailing slash for directories
} else {
hdr.Typeflag = TypeReg
}
}
// The extended headers may have updated the size.
// Thus, setup the regFileReader again after merging PAX headers.
if err := tr.handleRegularFile(hdr); err != nil {
return nil, err
}
// Sparse formats rely on being able to read from the logical data
// section; there must be a preceding call to handleRegularFile.
if err := tr.handleSparseFile(hdr, rawHdr); err != nil {
return nil, err
}
// Set the final guess at the format.
if format.has(FormatUSTAR) && format.has(FormatPAX) {
format.mayOnlyBe(FormatUSTAR)
}
hdr.Format = format
return hdr, nil // This is a file, so stop
}
}
}
// handleRegularFile sets up the current file reader and padding such that it
// can only read the following logical data section. It will properly handle
// special headers that contain no data section.
func (tr *Reader) handleRegularFile(hdr *Header) error {
nb := hdr.Size
if isHeaderOnlyType(hdr.Typeflag) {
nb = 0
}
if nb < 0 {
return ErrHeader
}
tr.pad = blockPadding(nb)
tr.curr = ®FileReader{r: tr.r, nb: nb}
return nil
}
// handleSparseFile checks if the current file is a sparse format of any type
// and sets the curr reader appropriately.
func (tr *Reader) handleSparseFile(hdr *Header, rawHdr *block) error {
var spd sparseDatas
var err error
if hdr.Typeflag == TypeGNUSparse {
spd, err = tr.readOldGNUSparseMap(hdr, rawHdr)
} else {
spd, err = tr.readGNUSparsePAXHeaders(hdr)
}
// If sp is non-nil, then this is a sparse file.
// Note that it is possible for len(sp) == 0.
if err == nil && spd != nil {
if isHeaderOnlyType(hdr.Typeflag) || !validateSparseEntries(spd, hdr.Size) {
return ErrHeader
}
sph := invertSparseEntries(spd, hdr.Size)
tr.curr = &sparseFileReader{tr.curr, sph, 0}
}
return err
}
// readGNUSparsePAXHeaders checks the PAX headers for GNU sparse headers.
// If they are found, then this function reads the sparse map and returns it.
// This assumes that 0.0 headers have already been converted to 0.1 headers
// by the PAX header parsing logic.
func (tr *Reader) readGNUSparsePAXHeaders(hdr *Header) (sparseDatas, error) {
// Identify the version of GNU headers.
var is1x0 bool
major, minor := hdr.PAXRecords[paxGNUSparseMajor], hdr.PAXRecords[paxGNUSparseMinor]
switch {
case major == "0" && (minor == "0" || minor == "1"):
is1x0 = false
case major == "1" && minor == "0":
is1x0 = true
case major != "" || minor != "":
return nil, nil // Unknown GNU sparse PAX version
case hdr.PAXRecords[paxGNUSparseMap] != "":
is1x0 = false // 0.0 and 0.1 did not have explicit version records, so guess
default:
return nil, nil // Not a PAX format GNU sparse file.
}
hdr.Format.mayOnlyBe(FormatPAX)
// Update hdr from GNU sparse PAX headers.
if name := hdr.PAXRecords[paxGNUSparseName]; name != "" {
hdr.Name = name
}
size := hdr.PAXRecords[paxGNUSparseSize]
if size == "" {
size = hdr.PAXRecords[paxGNUSparseRealSize]
}
if size != "" {
n, err := strconv.ParseInt(size, 10, 64)
if err != nil {
return nil, ErrHeader
}
hdr.Size = n
}
// Read the sparse map according to the appropriate format.
if is1x0 {
return readGNUSparseMap1x0(tr.curr)
}
return readGNUSparseMap0x1(hdr.PAXRecords)
}
// mergePAX merges paxHdrs into hdr for all relevant fields of Header.
func mergePAX(hdr *Header, paxHdrs map[string]string) (err error) {
for k, v := range paxHdrs {
if v == "" {
continue // Keep the original USTAR value
}
var id64 int64
switch k {
case paxPath:
hdr.Name = v
case paxLinkpath:
hdr.Linkname = v
case paxUname:
hdr.Uname = v
case paxGname:
hdr.Gname = v
case paxUid:
id64, err = strconv.ParseInt(v, 10, 64)
hdr.Uid = int(id64) // Integer overflow possible
case paxGid:
id64, err = strconv.ParseInt(v, 10, 64)
hdr.Gid = int(id64) // Integer overflow possible
case paxAtime:
hdr.AccessTime, err = parsePAXTime(v)
case paxMtime:
hdr.ModTime, err = parsePAXTime(v)
case paxCtime:
hdr.ChangeTime, err = parsePAXTime(v)
case paxSize:
hdr.Size, err = strconv.ParseInt(v, 10, 64)
default:
if strings.HasPrefix(k, paxSchilyXattr) {
if hdr.Xattrs == nil {
hdr.Xattrs = make(map[string]string)
}
hdr.Xattrs[k[len(paxSchilyXattr):]] = v
}
}
if err != nil {
return ErrHeader
}
}
hdr.PAXRecords = paxHdrs
return 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 := io.ReadAll(r)
if err != nil {
return nil, err
}
sbuf := string(buf)
// For GNU PAX sparse format 0.0 support.
// This function transforms the sparse format 0.0 headers into format 0.1
// headers since 0.0 headers were not PAX compliant.
var sparseMap []string
paxHdrs := make(map[string]string)
for len(sbuf) > 0 {
key, value, residual, err := parsePAXRecord(sbuf)
if err != nil {
return nil, ErrHeader
}
sbuf = residual
switch key {
case paxGNUSparseOffset, paxGNUSparseNumBytes:
// Validate sparse header order and value.
if (len(sparseMap)%2 == 0 && key != paxGNUSparseOffset) ||
(len(sparseMap)%2 == 1 && key != paxGNUSparseNumBytes) ||
strings.Contains(value, ",") {
return nil, ErrHeader
}
sparseMap = append(sparseMap, value)
default:
paxHdrs[key] = value
}
}
if len(sparseMap) > 0 {
paxHdrs[paxGNUSparseMap] = strings.Join(sparseMap, ",")
}
return paxHdrs, nil
}
// readHeader reads the next block header and assumes that the underlying reader
// is already aligned to a block boundary. It returns the raw block of the
// header in case further processing is required.
//
// The err will be set to io.EOF only when one of the following occurs:
// - Exactly 0 bytes are read and EOF is hit.
// - Exactly 1 block of zeros is read and EOF is hit.
// - At least 2 blocks of zeros are read.
func (tr *Reader) readHeader() (*Header, *block, error) {
// Two blocks of zero bytes marks the end of the archive.
if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
return nil, nil, err // EOF is okay here; exactly 0 bytes read
}
if bytes.Equal(tr.blk[:], zeroBlock[:]) {
if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
return nil, nil, err // EOF is okay here; exactly 1 block of zeros read
}
if bytes.Equal(tr.blk[:], zeroBlock[:]) {
return nil, nil, io.EOF // normal EOF; exactly 2 block of zeros read
}
return nil, nil, ErrHeader // Zero block and then non-zero block
}
// Verify the header matches a known format.
format := tr.blk.getFormat()
if format == FormatUnknown {
return nil, nil, ErrHeader
}
var p parser
hdr := new(Header)
// Unpack the V7 header.
v7 := tr.blk.toV7()
hdr.Typeflag = v7.typeFlag()[0]
hdr.Name = p.parseString(v7.name())
hdr.Linkname = p.parseString(v7.linkName())
hdr.Size = p.parseNumeric(v7.size())
hdr.Mode = p.parseNumeric(v7.mode())
hdr.Uid = int(p.parseNumeric(v7.uid()))
hdr.Gid = int(p.parseNumeric(v7.gid()))
hdr.ModTime = time.Unix(p.parseNumeric(v7.modTime()), 0)
// Unpack format specific fields.
if format > formatV7 {
ustar := tr.blk.toUSTAR()
hdr.Uname = p.parseString(ustar.userName())
hdr.Gname = p.parseString(ustar.groupName())
hdr.Devmajor = p.parseNumeric(ustar.devMajor())
hdr.Devminor = p.parseNumeric(ustar.devMinor())
var prefix string
switch {
case format.has(FormatUSTAR | FormatPAX):
hdr.Format = format
ustar := tr.blk.toUSTAR()
prefix = p.parseString(ustar.prefix())
// For Format detection, check if block is properly formatted since
// the parser is more liberal than what USTAR actually permits.
notASCII := func(r rune) bool { return r >= 0x80 }
if bytes.IndexFunc(tr.blk[:], notASCII) >= 0 {
hdr.Format = FormatUnknown // Non-ASCII characters in block.
}
nul := func(b []byte) bool { return int(b[len(b)-1]) == 0 }
if !(nul(v7.size()) && nul(v7.mode()) && nul(v7.uid()) && nul(v7.gid()) &&
nul(v7.modTime()) && nul(ustar.devMajor()) && nul(ustar.devMinor())) {
hdr.Format = FormatUnknown // Numeric fields must end in NUL
}
case format.has(formatSTAR):
star := tr.blk.toSTAR()
prefix = p.parseString(star.prefix())
hdr.AccessTime = time.Unix(p.parseNumeric(star.accessTime()), 0)
hdr.ChangeTime = time.Unix(p.parseNumeric(star.changeTime()), 0)
case format.has(FormatGNU):
hdr.Format = format
var p2 parser
gnu := tr.blk.toGNU()
if b := gnu.accessTime(); b[0] != 0 {
hdr.AccessTime = time.Unix(p2.parseNumeric(b), 0)
}
if b := gnu.changeTime(); b[0] != 0 {
hdr.ChangeTime = time.Unix(p2.parseNumeric(b), 0)
}
// Prior to Go1.8, the Writer had a bug where it would output
// an invalid tar file in certain rare situations because the logic
// incorrectly believed that the old GNU format had a prefix field.
// This is wrong and leads to an output file that mangles the
// atime and ctime fields, which are often left unused.
//
// In order to continue reading tar files created by former, buggy
// versions of Go, we skeptically parse the atime and ctime fields.
// If we are unable to parse them and the prefix field looks like
// an ASCII string, then we fallback on the pre-Go1.8 behavior
// of treating these fields as the USTAR prefix field.
//
// Note that this will not use the fallback logic for all possible
// files generated by a pre-Go1.8 toolchain. If the generated file
// happened to have a prefix field that parses as valid
// atime and ctime fields (e.g., when they are valid octal strings),
// then it is impossible to distinguish between a valid GNU file
// and an invalid pre-Go1.8 file.
//
// See https://golang.org/issues/12594
// See https://golang.org/issues/21005
if p2.err != nil {
hdr.AccessTime, hdr.ChangeTime = time.Time{}, time.Time{}
ustar := tr.blk.toUSTAR()
if s := p.parseString(ustar.prefix()); isASCII(s) {
prefix = s
}
hdr.Format = FormatUnknown // Buggy file is not GNU
}
}
if len(prefix) > 0 {
hdr.Name = prefix + "/" + hdr.Name
}
}
return hdr, &tr.blk, p.err
}
// readOldGNUSparseMap reads the sparse map from 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.
//
// The Header.Size does not reflect the size of any extended headers used.
// Thus, this function will read from the raw io.Reader to fetch extra headers.
// This method mutates blk in the process.
func (tr *Reader) readOldGNUSparseMap(hdr *Header, blk *block) (sparseDatas, error) {
// Make sure that the input format is GNU.
// Unfortunately, the STAR format also has a sparse header format that uses
// the same type flag but has a completely different layout.
if blk.getFormat() != FormatGNU {
return nil, ErrHeader
}
hdr.Format.mayOnlyBe(FormatGNU)
var p parser
hdr.Size = p.parseNumeric(blk.toGNU().realSize())
if p.err != nil {
return nil, p.err
}
s := blk.toGNU().sparse()
spd := make(sparseDatas, 0, s.maxEntries())
for {
for i := 0; i < s.maxEntries(); i++ {
// This termination condition is identical to GNU and BSD tar.
if s.entry(i).offset()[0] == 0x00 {
break // Don't return, need to process extended headers (even if empty)
}
offset := p.parseNumeric(s.entry(i).offset())
length := p.parseNumeric(s.entry(i).length())
if p.err != nil {
return nil, p.err
}
spd = append(spd, sparseEntry{Offset: offset, Length: length})
}
if s.isExtended()[0] > 0 {
// There are more entries. Read an extension header and parse its entries.
if _, err := mustReadFull(tr.r, blk[:]); err != nil {
return nil, err
}
s = blk.toSparse()
continue
}
return spd, nil // Done
}
}
// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format
// version 1.0. The format of the sparse map consists of a series of
// newline-terminated numeric fields. The first field is the number of entries
// and is always present. Following this are the entries, consisting of two
// fields (offset, length). This function must stop reading at the end
// boundary of the block containing the last newline.
//
// Note that the GNU manual says that numeric values should be encoded in octal
// format. However, the GNU tar utility itself outputs these values in decimal.
// As such, this library treats values as being encoded in decimal.
func readGNUSparseMap1x0(r io.Reader) (sparseDatas, error) {
var (
cntNewline int64
buf bytes.Buffer
blk block
)
// feedTokens copies data in blocks from r into buf until there are
// at least cnt newlines in buf. It will not read more blocks than needed.
feedTokens := func(n int64) error {
for cntNewline < n {
if _, err := mustReadFull(r, blk[:]); err != nil {
return err
}
buf.Write(blk[:])
for _, c := range blk {
if c == '\n' {
cntNewline++
}
}
}
return nil
}
// nextToken gets the next token delimited by a newline. This assumes that
// at least one newline exists in the buffer.
nextToken := func() string {
cntNewline--
tok, _ := buf.ReadString('\n')
return strings.TrimRight(tok, "\n")
}
// Parse for the number of entries.
// Use integer overflow resistant math to check this.
if err := feedTokens(1); err != nil {
return nil, err
}
numEntries, err := strconv.ParseInt(nextToken(), 10, 0) // Intentionally parse as native int
if err != nil || numEntries < 0 || int(2*numEntries) < int(numEntries) {
return nil, ErrHeader
}
// Parse for all member entries.
// numEntries is trusted after this since a potential attacker must have
// committed resources proportional to what this library used.
if err := feedTokens(2 * numEntries); err != nil {
return nil, err
}
spd := make(sparseDatas, 0, numEntries)
for i := int64(0); i < numEntries; i++ {
offset, err1 := strconv.ParseInt(nextToken(), 10, 64)
length, err2 := strconv.ParseInt(nextToken(), 10, 64)
if err1 != nil || err2 != nil {
return nil, ErrHeader
}
spd = append(spd, sparseEntry{Offset: offset, Length: length})
}
return spd, 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(paxHdrs map[string]string) (sparseDatas, error) {
// Get number of entries.
// Use integer overflow resistant math to check this.
numEntriesStr := paxHdrs[paxGNUSparseNumBlocks]
numEntries, err := strconv.ParseInt(numEntriesStr, 10, 0) // Intentionally parse as native int
if err != nil || numEntries < 0 || int(2*numEntries) < int(numEntries) {
return nil, ErrHeader
}
// There should be two numbers in sparseMap for each entry.
sparseMap := strings.Split(paxHdrs[paxGNUSparseMap], ",")
if len(sparseMap) == 1 && sparseMap[0] == "" {
sparseMap = sparseMap[:0]
}
if int64(len(sparseMap)) != 2*numEntries {
return nil, ErrHeader
}
// Loop through the entries in the sparse map.
// numEntries is trusted now.
spd := make(sparseDatas, 0, numEntries)
for len(sparseMap) >= 2 {
offset, err1 := strconv.ParseInt(sparseMap[0], 10, 64)
length, err2 := strconv.ParseInt(sparseMap[1], 10, 64)
if err1 != nil || err2 != nil {
return nil, ErrHeader
}
spd = append(spd, sparseEntry{Offset: offset, Length: length})
sparseMap = sparseMap[2:]
}
return spd, nil
}
// Read reads from the current file in the tar archive.
// It returns (0, io.EOF) when it reaches the end of that file,
// until Next is called to advance to the next file.
//
// If the current file is sparse, then the regions marked as a hole
// are read back as NUL-bytes.
//
// Calling Read on special types like TypeLink, TypeSymlink, TypeChar,
// TypeBlock, TypeDir, and TypeFifo returns (0, io.EOF) regardless of what
// the Header.Size claims.
func (tr *Reader) Read(b []byte) (int, error) {
if tr.err != nil {
return 0, tr.err
}
n, err := tr.curr.Read(b)
if err != nil && err != io.EOF {
tr.err = err
}
return n, err
}
// writeTo writes the content of the current file to w.
// The bytes written matches the number of remaining bytes in the current file.
//
// If the current file is sparse and w is an io.WriteSeeker,
// then writeTo uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are filled with NULs.
// This always writes the last byte to ensure w is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735
func (tr *Reader) writeTo(w io.Writer) (int64, error) {
if tr.err != nil {
return 0, tr.err
}
n, err := tr.curr.WriteTo(w)
if err != nil {
tr.err = err
}
return n, err
}
// regFileReader is a fileReader for reading data from a regular file entry.
type regFileReader struct {
r io.Reader // Underlying Reader
nb int64 // Number of remaining bytes to read
}
func (fr *regFileReader) Read(b []byte) (n int, err error) {
if int64(len(b)) > fr.nb {
b = b[:fr.nb]
}
if len(b) > 0 {
n, err = fr.r.Read(b)
fr.nb -= int64(n)
}
switch {
case err == io.EOF && fr.nb > 0:
return n, io.ErrUnexpectedEOF
case err == nil && fr.nb == 0:
return n, io.EOF
default:
return n, err
}
}
func (fr *regFileReader) WriteTo(w io.Writer) (int64, error) {
return io.Copy(w, struct{ io.Reader }{fr})
}
// logicalRemaining implements fileState.logicalRemaining.
func (fr regFileReader) logicalRemaining() int64 {
return fr.nb
}
// logicalRemaining implements fileState.physicalRemaining.
func (fr regFileReader) physicalRemaining() int64 {
return fr.nb
}
// sparseFileReader is a fileReader for reading data from a sparse file entry.
type sparseFileReader struct {
fr fileReader // Underlying fileReader
sp sparseHoles // Normalized list of sparse holes
pos int64 // Current position in sparse file
}
func (sr *sparseFileReader) Read(b []byte) (n int, err error) {
finished := int64(len(b)) >= sr.logicalRemaining()
if finished {
b = b[:sr.logicalRemaining()]
}
b0 := b
endPos := sr.pos + int64(len(b))
for endPos > sr.pos && err == nil {
var nf int // Bytes read in fragment
holeStart, holeEnd := sr.sp[0].Offset, sr.sp[0].endOffset()
if sr.pos < holeStart { // In a data fragment
bf := b[:min(int64(len(b)), holeStart-sr.pos)]
nf, err = tryReadFull(sr.fr, bf)
} else { // In a hole fragment
bf := b[:min(int64(len(b)), holeEnd-sr.pos)]
nf, err = tryReadFull(zeroReader{}, bf)
}
b = b[nf:]
sr.pos += int64(nf)
if sr.pos >= holeEnd && len(sr.sp) > 1 {
sr.sp = sr.sp[1:] // Ensure last fragment always remains
}
}
n = len(b0) - len(b)
switch {
case err == io.EOF:
return n, errMissData // Less data in dense file than sparse file
case err != nil:
return n, err
case sr.logicalRemaining() == 0 && sr.physicalRemaining() > 0:
return n, errUnrefData // More data in dense file than sparse file
case finished:
return n, io.EOF
default:
return n, nil
}
}
func (sr *sparseFileReader) WriteTo(w io.Writer) (n int64, err error) {
ws, ok := w.(io.WriteSeeker)
if ok {
if _, err := ws.Seek(0, io.SeekCurrent); err != nil {
ok = false // Not all io.Seeker can really seek
}
}
if !ok {
return io.Copy(w, struct{ io.Reader }{sr})
}
var writeLastByte bool
pos0 := sr.pos
for sr.logicalRemaining() > 0 && !writeLastByte && err == nil {
var nf int64 // Size of fragment
holeStart, holeEnd := sr.sp[0].Offset, sr.sp[0].endOffset()
if sr.pos < holeStart { // In a data fragment
nf = holeStart - sr.pos
nf, err = io.CopyN(ws, sr.fr, nf)
} else { // In a hole fragment
nf = holeEnd - sr.pos
if sr.physicalRemaining() == 0 {
writeLastByte = true
nf--
}
_, err = ws.Seek(nf, io.SeekCurrent)
}
sr.pos += nf
if sr.pos >= holeEnd && len(sr.sp) > 1 {
sr.sp = sr.sp[1:] // Ensure last fragment always remains
}
}
// If the last fragment is a hole, then seek to 1-byte before EOF, and
// write a single byte to ensure the file is the right size.
if writeLastByte && err == nil {
_, err = ws.Write([]byte{0})
sr.pos++
}
n = sr.pos - pos0
switch {
case err == io.EOF:
return n, errMissData // Less data in dense file than sparse file
case err != nil:
return n, err
case sr.logicalRemaining() == 0 && sr.physicalRemaining() > 0:
return n, errUnrefData // More data in dense file than sparse file
default:
return n, nil
}
}
func (sr sparseFileReader) logicalRemaining() int64 {
return sr.sp[len(sr.sp)-1].endOffset() - sr.pos
}
func (sr sparseFileReader) physicalRemaining() int64 {
return sr.fr.physicalRemaining()
}
type zeroReader struct{}
func (zeroReader) Read(b []byte) (int, error) {
for i := range b {
b[i] = 0
}
return len(b), nil
}
// mustReadFull is like io.ReadFull except it returns
// io.ErrUnexpectedEOF when io.EOF is hit before len(b) bytes are read.
func mustReadFull(r io.Reader, b []byte) (int, error) {
n, err := tryReadFull(r, b)
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return n, err
}
// tryReadFull is like io.ReadFull except it returns
// io.EOF when it is hit before len(b) bytes are read.
func tryReadFull(r io.Reader, b []byte) (n int, err error) {
for len(b) > n && err == nil {
var nn int
nn, err = r.Read(b[n:])
n += nn
}
if len(b) == n && err == io.EOF {
err = nil
}
return n, err
}
// discard skips n bytes in r, reporting an error if unable to do so.
func discard(r io.Reader, n int64) error {
// If possible, Seek to the last byte before the end of the data section.
// Do this because Seek is often lazy about reporting errors; this will mask
// the fact that the stream may be truncated. We can rely on the
// io.CopyN done shortly afterwards to trigger any IO errors.
var seekSkipped int64 // Number of bytes skipped via Seek
if sr, ok := r.(io.Seeker); ok && n > 1 {
// Not all io.Seeker can actually Seek. For example, os.Stdin implements
// io.Seeker, but calling Seek always returns an error and performs
// no action. Thus, we try an innocent seek to the current position
// to see if Seek is really supported.
pos1, err := sr.Seek(0, io.SeekCurrent)
if pos1 >= 0 && err == nil {
// Seek seems supported, so perform the real Seek.
pos2, err := sr.Seek(n-1, io.SeekCurrent)
if pos2 < 0 || err != nil {
return err
}
seekSkipped = pos2 - pos1
}
}
copySkipped, err := io.CopyN(io.Discard, r, n-seekSkipped)
if err == io.EOF && seekSkipped+copySkipped < n {
err = io.ErrUnexpectedEOF
}
return err
}
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