Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

57 files changed, 7311 insertions, 0 deletions

diff --git a/src/archive/tar/common.go b/src/archive/tar/common.go
new file mode 100644
index 0000000..c667cfc
--- /dev/null
+++ b/src/archive/tar/common.go
@@ -0,0 +1,723 @@
+// 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 implements access to tar archives.
+//
+// Tape archives (tar) are a file format for storing a sequence of files that
+// can be read and written in a streaming manner.
+// This package aims to cover most variations of the format,
+// including those produced by GNU and BSD tar tools.
+package tar
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"math"
+	"path"
+	"reflect"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// BUG: Use of the Uid and Gid fields in Header could overflow on 32-bit
+// architectures. If a large value is encountered when decoding, the result
+// stored in Header will be the truncated version.
+
+var (
+	ErrHeader          = errors.New("archive/tar: invalid tar header")
+	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")
+	errMissData        = errors.New("archive/tar: sparse file references non-existent data")
+	errUnrefData       = errors.New("archive/tar: sparse file contains unreferenced data")
+	errWriteHole       = errors.New("archive/tar: write non-NUL byte in sparse hole")
+)
+
+type headerError []string
+
+func (he headerError) Error() string {
+	const prefix = "archive/tar: cannot encode header"
+	var ss []string
+	for _, s := range he {
+		if s != "" {
+			ss = append(ss, s)
+		}
+	}
+	if len(ss) == 0 {
+		return prefix
+	}
+	return fmt.Sprintf("%s: %v", prefix, strings.Join(ss, "; and "))
+}
+
+// Type flags for Header.Typeflag.
+const (
+	// Type '0' indicates a regular file.
+	TypeReg  = '0'
+	TypeRegA = '\x00' // Deprecated: Use TypeReg instead.
+
+	// Type '1' to '6' are header-only flags and may not have a data body.
+	TypeLink    = '1' // Hard link
+	TypeSymlink = '2' // Symbolic link
+	TypeChar    = '3' // Character device node
+	TypeBlock   = '4' // Block device node
+	TypeDir     = '5' // Directory
+	TypeFifo    = '6' // FIFO node
+
+	// Type '7' is reserved.
+	TypeCont = '7'
+
+	// Type 'x' is used by the PAX format to store key-value records that
+	// are only relevant to the next file.
+	// This package transparently handles these types.
+	TypeXHeader = 'x'
+
+	// Type 'g' is used by the PAX format to store key-value records that
+	// are relevant to all subsequent files.
+	// This package only supports parsing and composing such headers,
+	// but does not currently support persisting the global state across files.
+	TypeXGlobalHeader = 'g'
+
+	// Type 'S' indicates a sparse file in the GNU format.
+	TypeGNUSparse = 'S'
+
+	// Types 'L' and 'K' are used by the GNU format for a meta file
+	// used to store the path or link name for the next file.
+	// This package transparently handles these types.
+	TypeGNULongName = 'L'
+	TypeGNULongLink = 'K'
+)
+
+// Keywords for PAX extended header records.
+const (
+	paxNone     = "" // Indicates that no PAX key is suitable
+	paxPath     = "path"
+	paxLinkpath = "linkpath"
+	paxSize     = "size"
+	paxUid      = "uid"
+	paxGid      = "gid"
+	paxUname    = "uname"
+	paxGname    = "gname"
+	paxMtime    = "mtime"
+	paxAtime    = "atime"
+	paxCtime    = "ctime"   // Removed from later revision of PAX spec, but was valid
+	paxCharset  = "charset" // Currently unused
+	paxComment  = "comment" // Currently unused
+
+	paxSchilyXattr = "SCHILY.xattr."
+
+	// Keywords for GNU sparse files in a PAX extended header.
+	paxGNUSparse          = "GNU.sparse."
+	paxGNUSparseNumBlocks = "GNU.sparse.numblocks"
+	paxGNUSparseOffset    = "GNU.sparse.offset"
+	paxGNUSparseNumBytes  = "GNU.sparse.numbytes"
+	paxGNUSparseMap       = "GNU.sparse.map"
+	paxGNUSparseName      = "GNU.sparse.name"
+	paxGNUSparseMajor     = "GNU.sparse.major"
+	paxGNUSparseMinor     = "GNU.sparse.minor"
+	paxGNUSparseSize      = "GNU.sparse.size"
+	paxGNUSparseRealSize  = "GNU.sparse.realsize"
+)
+
+// basicKeys is a set of the PAX keys for which we have built-in support.
+// This does not contain "charset" or "comment", which are both PAX-specific,
+// so adding them as first-class features of Header is unlikely.
+// Users can use the PAXRecords field to set it themselves.
+var basicKeys = map[string]bool{
+	paxPath: true, paxLinkpath: true, paxSize: true, paxUid: true, paxGid: true,
+	paxUname: true, paxGname: true, paxMtime: true, paxAtime: true, paxCtime: true,
+}
+
+// A Header represents a single header in a tar archive.
+// Some fields may not be populated.
+//
+// For forward compatibility, users that retrieve a Header from Reader.Next,
+// mutate it in some ways, and then pass it back to Writer.WriteHeader
+// should do so by creating a new Header and copying the fields
+// that they are interested in preserving.
+type Header struct {
+	// Typeflag is the type of header entry.
+	// The zero value is automatically promoted to either TypeReg or TypeDir
+	// depending on the presence of a trailing slash in Name.
+	Typeflag byte
+
+	Name     string // Name of file entry
+	Linkname string // Target name of link (valid for TypeLink or TypeSymlink)
+
+	Size  int64  // Logical file size in bytes
+	Mode  int64  // Permission and mode bits
+	Uid   int    // User ID of owner
+	Gid   int    // Group ID of owner
+	Uname string // User name of owner
+	Gname string // Group name of owner
+
+	// If the Format is unspecified, then Writer.WriteHeader rounds ModTime
+	// to the nearest second and ignores the AccessTime and ChangeTime fields.
+	//
+	// To use AccessTime or ChangeTime, specify the Format as PAX or GNU.
+	// To use sub-second resolution, specify the Format as PAX.
+	ModTime    time.Time // Modification time
+	AccessTime time.Time // Access time (requires either PAX or GNU support)
+	ChangeTime time.Time // Change time (requires either PAX or GNU support)
+
+	Devmajor int64 // Major device number (valid for TypeChar or TypeBlock)
+	Devminor int64 // Minor device number (valid for TypeChar or TypeBlock)
+
+	// Xattrs stores extended attributes as PAX records under the
+	// "SCHILY.xattr." namespace.
+	//
+	// The following are semantically equivalent:
+	//  h.Xattrs[key] = value
+	//  h.PAXRecords["SCHILY.xattr."+key] = value
+	//
+	// When Writer.WriteHeader is called, the contents of Xattrs will take
+	// precedence over those in PAXRecords.
+	//
+	// Deprecated: Use PAXRecords instead.
+	Xattrs map[string]string
+
+	// PAXRecords is a map of PAX extended header records.
+	//
+	// User-defined records should have keys of the following form:
+	//	VENDOR.keyword
+	// Where VENDOR is some namespace in all uppercase, and keyword may
+	// not contain the '=' character (e.g., "GOLANG.pkg.version").
+	// The key and value should be non-empty UTF-8 strings.
+	//
+	// When Writer.WriteHeader is called, PAX records derived from the
+	// other fields in Header take precedence over PAXRecords.
+	PAXRecords map[string]string
+
+	// Format specifies the format of the tar header.
+	//
+	// This is set by Reader.Next as a best-effort guess at the format.
+	// Since the Reader liberally reads some non-compliant files,
+	// it is possible for this to be FormatUnknown.
+	//
+	// If the format is unspecified when Writer.WriteHeader is called,
+	// then it uses the first format (in the order of USTAR, PAX, GNU)
+	// capable of encoding this Header (see Format).
+	Format Format
+}
+
+// sparseEntry represents a Length-sized fragment at Offset in the file.
+type sparseEntry struct{ Offset, Length int64 }
+
+func (s sparseEntry) endOffset() int64 { return s.Offset + s.Length }
+
+// A sparse file can be represented as either a sparseDatas or a sparseHoles.
+// As long as the total size is known, they are equivalent and one can be
+// converted to the other form and back. The various tar formats with sparse
+// file support represent sparse files in the sparseDatas form. That is, they
+// specify the fragments in the file that has data, and treat everything else as
+// having zero bytes. As such, the encoding and decoding logic in this package
+// deals with sparseDatas.
+//
+// However, the external API uses sparseHoles instead of sparseDatas because the
+// zero value of sparseHoles logically represents a normal file (i.e., there are
+// no holes in it). On the other hand, the zero value of sparseDatas implies
+// that the file has no data in it, which is rather odd.
+//
+// As an example, if the underlying raw file contains the 10-byte data:
+//	var compactFile = "abcdefgh"
+//
+// And the sparse map has the following entries:
+//	var spd sparseDatas = []sparseEntry{
+//		{Offset: 2,  Length: 5},  // Data fragment for 2..6
+//		{Offset: 18, Length: 3},  // Data fragment for 18..20
+//	}
+//	var sph sparseHoles = []sparseEntry{
+//		{Offset: 0,  Length: 2},  // Hole fragment for 0..1
+//		{Offset: 7,  Length: 11}, // Hole fragment for 7..17
+//		{Offset: 21, Length: 4},  // Hole fragment for 21..24
+//	}
+//
+// Then the content of the resulting sparse file with a Header.Size of 25 is:
+//	var sparseFile = "\x00"*2 + "abcde" + "\x00"*11 + "fgh" + "\x00"*4
+type (
+	sparseDatas []sparseEntry
+	sparseHoles []sparseEntry
+)
+
+// validateSparseEntries reports whether sp is a valid sparse map.
+// It does not matter whether sp represents data fragments or hole fragments.
+func validateSparseEntries(sp []sparseEntry, size int64) bool {
+	// Validate all sparse entries. These are the same checks as performed by
+	// the BSD tar utility.
+	if size < 0 {
+		return false
+	}
+	var pre sparseEntry
+	for _, cur := range sp {
+		switch {
+		case cur.Offset < 0 || cur.Length < 0:
+			return false // Negative values are never okay
+		case cur.Offset > math.MaxInt64-cur.Length:
+			return false // Integer overflow with large length
+		case cur.endOffset() > size:
+			return false // Region extends beyond the actual size
+		case pre.endOffset() > cur.Offset:
+			return false // Regions cannot overlap and must be in order
+		}
+		pre = cur
+	}
+	return true
+}
+
+// alignSparseEntries mutates src and returns dst where each fragment's
+// starting offset is aligned up to the nearest block edge, and each
+// ending offset is aligned down to the nearest block edge.
+//
+// Even though the Go tar Reader and the BSD tar utility can handle entries
+// with arbitrary offsets and lengths, the GNU tar utility can only handle
+// offsets and lengths that are multiples of blockSize.
+func alignSparseEntries(src []sparseEntry, size int64) []sparseEntry {
+	dst := src[:0]
+	for _, s := range src {
+		pos, end := s.Offset, s.endOffset()
+		pos += blockPadding(+pos) // Round-up to nearest blockSize
+		if end != size {
+			end -= blockPadding(-end) // Round-down to nearest blockSize
+		}
+		if pos < end {
+			dst = append(dst, sparseEntry{Offset: pos, Length: end - pos})
+		}
+	}
+	return dst
+}
+
+// invertSparseEntries converts a sparse map from one form to the other.
+// If the input is sparseHoles, then it will output sparseDatas and vice-versa.
+// The input must have been already validated.
+//
+// This function mutates src and returns a normalized map where:
+//	* adjacent fragments are coalesced together
+//	* only the last fragment may be empty
+//	* the endOffset of the last fragment is the total size
+func invertSparseEntries(src []sparseEntry, size int64) []sparseEntry {
+	dst := src[:0]
+	var pre sparseEntry
+	for _, cur := range src {
+		if cur.Length == 0 {
+			continue // Skip empty fragments
+		}
+		pre.Length = cur.Offset - pre.Offset
+		if pre.Length > 0 {
+			dst = append(dst, pre) // Only add non-empty fragments
+		}
+		pre.Offset = cur.endOffset()
+	}
+	pre.Length = size - pre.Offset // Possibly the only empty fragment
+	return append(dst, pre)
+}
+
+// fileState tracks the number of logical (includes sparse holes) and physical
+// (actual in tar archive) bytes remaining for the current file.
+//
+// Invariant: LogicalRemaining >= PhysicalRemaining
+type fileState interface {
+	LogicalRemaining() int64
+	PhysicalRemaining() int64
+}
+
+// allowedFormats determines which formats can be used.
+// The value returned is the logical OR of multiple possible formats.
+// If the value is FormatUnknown, then the input Header cannot be encoded
+// and an error is returned explaining why.
+//
+// As a by-product of checking the fields, this function returns paxHdrs, which
+// contain all fields that could not be directly encoded.
+// A value receiver ensures that this method does not mutate the source Header.
+func (h Header) allowedFormats() (format Format, paxHdrs map[string]string, err error) {
+	format = FormatUSTAR | FormatPAX | FormatGNU
+	paxHdrs = make(map[string]string)
+
+	var whyNoUSTAR, whyNoPAX, whyNoGNU string
+	var preferPAX bool // Prefer PAX over USTAR
+	verifyString := func(s string, size int, name, paxKey string) {
+		// NUL-terminator is optional for path and linkpath.
+		// Technically, it is required for uname and gname,
+		// but neither GNU nor BSD tar checks for it.
+		tooLong := len(s) > size
+		allowLongGNU := paxKey == paxPath || paxKey == paxLinkpath
+		if hasNUL(s) || (tooLong && !allowLongGNU) {
+			whyNoGNU = fmt.Sprintf("GNU cannot encode %s=%q", name, s)
+			format.mustNotBe(FormatGNU)
+		}
+		if !isASCII(s) || tooLong {
+			canSplitUSTAR := paxKey == paxPath
+			if _, _, ok := splitUSTARPath(s); !canSplitUSTAR || !ok {
+				whyNoUSTAR = fmt.Sprintf("USTAR cannot encode %s=%q", name, s)
+				format.mustNotBe(FormatUSTAR)
+			}
+			if paxKey == paxNone {
+				whyNoPAX = fmt.Sprintf("PAX cannot encode %s=%q", name, s)
+				format.mustNotBe(FormatPAX)
+			} else {
+				paxHdrs[paxKey] = s
+			}
+		}
+		if v, ok := h.PAXRecords[paxKey]; ok && v == s {
+			paxHdrs[paxKey] = v
+		}
+	}
+	verifyNumeric := func(n int64, size int, name, paxKey string) {
+		if !fitsInBase256(size, n) {
+			whyNoGNU = fmt.Sprintf("GNU cannot encode %s=%d", name, n)
+			format.mustNotBe(FormatGNU)
+		}
+		if !fitsInOctal(size, n) {
+			whyNoUSTAR = fmt.Sprintf("USTAR cannot encode %s=%d", name, n)
+			format.mustNotBe(FormatUSTAR)
+			if paxKey == paxNone {
+				whyNoPAX = fmt.Sprintf("PAX cannot encode %s=%d", name, n)
+				format.mustNotBe(FormatPAX)
+			} else {
+				paxHdrs[paxKey] = strconv.FormatInt(n, 10)
+			}
+		}
+		if v, ok := h.PAXRecords[paxKey]; ok && v == strconv.FormatInt(n, 10) {
+			paxHdrs[paxKey] = v
+		}
+	}
+	verifyTime := func(ts time.Time, size int, name, paxKey string) {
+		if ts.IsZero() {
+			return // Always okay
+		}
+		if !fitsInBase256(size, ts.Unix()) {
+			whyNoGNU = fmt.Sprintf("GNU cannot encode %s=%v", name, ts)
+			format.mustNotBe(FormatGNU)
+		}
+		isMtime := paxKey == paxMtime
+		fitsOctal := fitsInOctal(size, ts.Unix())
+		if (isMtime && !fitsOctal) || !isMtime {
+			whyNoUSTAR = fmt.Sprintf("USTAR cannot encode %s=%v", name, ts)
+			format.mustNotBe(FormatUSTAR)
+		}
+		needsNano := ts.Nanosecond() != 0
+		if !isMtime || !fitsOctal || needsNano {
+			preferPAX = true // USTAR may truncate sub-second measurements
+			if paxKey == paxNone {
+				whyNoPAX = fmt.Sprintf("PAX cannot encode %s=%v", name, ts)
+				format.mustNotBe(FormatPAX)
+			} else {
+				paxHdrs[paxKey] = formatPAXTime(ts)
+			}
+		}
+		if v, ok := h.PAXRecords[paxKey]; ok && v == formatPAXTime(ts) {
+			paxHdrs[paxKey] = v
+		}
+	}
+
+	// Check basic fields.
+	var blk block
+	v7 := blk.V7()
+	ustar := blk.USTAR()
+	gnu := blk.GNU()
+	verifyString(h.Name, len(v7.Name()), "Name", paxPath)
+	verifyString(h.Linkname, len(v7.LinkName()), "Linkname", paxLinkpath)
+	verifyString(h.Uname, len(ustar.UserName()), "Uname", paxUname)
+	verifyString(h.Gname, len(ustar.GroupName()), "Gname", paxGname)
+	verifyNumeric(h.Mode, len(v7.Mode()), "Mode", paxNone)
+	verifyNumeric(int64(h.Uid), len(v7.UID()), "Uid", paxUid)
+	verifyNumeric(int64(h.Gid), len(v7.GID()), "Gid", paxGid)
+	verifyNumeric(h.Size, len(v7.Size()), "Size", paxSize)
+	verifyNumeric(h.Devmajor, len(ustar.DevMajor()), "Devmajor", paxNone)
+	verifyNumeric(h.Devminor, len(ustar.DevMinor()), "Devminor", paxNone)
+	verifyTime(h.ModTime, len(v7.ModTime()), "ModTime", paxMtime)
+	verifyTime(h.AccessTime, len(gnu.AccessTime()), "AccessTime", paxAtime)
+	verifyTime(h.ChangeTime, len(gnu.ChangeTime()), "ChangeTime", paxCtime)
+
+	// Check for header-only types.
+	var whyOnlyPAX, whyOnlyGNU string
+	switch h.Typeflag {
+	case TypeReg, TypeChar, TypeBlock, TypeFifo, TypeGNUSparse:
+		// Exclude TypeLink and TypeSymlink, since they may reference directories.
+		if strings.HasSuffix(h.Name, "/") {
+			return FormatUnknown, nil, headerError{"filename may not have trailing slash"}
+		}
+	case TypeXHeader, TypeGNULongName, TypeGNULongLink:
+		return FormatUnknown, nil, headerError{"cannot manually encode TypeXHeader, TypeGNULongName, or TypeGNULongLink headers"}
+	case TypeXGlobalHeader:
+		h2 := Header{Name: h.Name, Typeflag: h.Typeflag, Xattrs: h.Xattrs, PAXRecords: h.PAXRecords, Format: h.Format}
+		if !reflect.DeepEqual(h, h2) {
+			return FormatUnknown, nil, headerError{"only PAXRecords should be set for TypeXGlobalHeader"}
+		}
+		whyOnlyPAX = "only PAX supports TypeXGlobalHeader"
+		format.mayOnlyBe(FormatPAX)
+	}
+	if !isHeaderOnlyType(h.Typeflag) && h.Size < 0 {
+		return FormatUnknown, nil, headerError{"negative size on header-only type"}
+	}
+
+	// Check PAX records.
+	if len(h.Xattrs) > 0 {
+		for k, v := range h.Xattrs {
+			paxHdrs[paxSchilyXattr+k] = v
+		}
+		whyOnlyPAX = "only PAX supports Xattrs"
+		format.mayOnlyBe(FormatPAX)
+	}
+	if len(h.PAXRecords) > 0 {
+		for k, v := range h.PAXRecords {
+			switch _, exists := paxHdrs[k]; {
+			case exists:
+				continue // Do not overwrite existing records
+			case h.Typeflag == TypeXGlobalHeader:
+				paxHdrs[k] = v // Copy all records
+			case !basicKeys[k] && !strings.HasPrefix(k, paxGNUSparse):
+				paxHdrs[k] = v // Ignore local records that may conflict
+			}
+		}
+		whyOnlyPAX = "only PAX supports PAXRecords"
+		format.mayOnlyBe(FormatPAX)
+	}
+	for k, v := range paxHdrs {
+		if !validPAXRecord(k, v) {
+			return FormatUnknown, nil, headerError{fmt.Sprintf("invalid PAX record: %q", k+" = "+v)}
+		}
+	}
+
+	// TODO(dsnet): Re-enable this when adding sparse support.
+	// See https://golang.org/issue/22735
+	/*
+		// Check sparse files.
+		if len(h.SparseHoles) > 0 || h.Typeflag == TypeGNUSparse {
+			if isHeaderOnlyType(h.Typeflag) {
+				return FormatUnknown, nil, headerError{"header-only type cannot be sparse"}
+			}
+			if !validateSparseEntries(h.SparseHoles, h.Size) {
+				return FormatUnknown, nil, headerError{"invalid sparse holes"}
+			}
+			if h.Typeflag == TypeGNUSparse {
+				whyOnlyGNU = "only GNU supports TypeGNUSparse"
+				format.mayOnlyBe(FormatGNU)
+			} else {
+				whyNoGNU = "GNU supports sparse files only with TypeGNUSparse"
+				format.mustNotBe(FormatGNU)
+			}
+			whyNoUSTAR = "USTAR does not support sparse files"
+			format.mustNotBe(FormatUSTAR)
+		}
+	*/
+
+	// Check desired format.
+	if wantFormat := h.Format; wantFormat != FormatUnknown {
+		if wantFormat.has(FormatPAX) && !preferPAX {
+			wantFormat.mayBe(FormatUSTAR) // PAX implies USTAR allowed too
+		}
+		format.mayOnlyBe(wantFormat) // Set union of formats allowed and format wanted
+	}
+	if format == FormatUnknown {
+		switch h.Format {
+		case FormatUSTAR:
+			err = headerError{"Format specifies USTAR", whyNoUSTAR, whyOnlyPAX, whyOnlyGNU}
+		case FormatPAX:
+			err = headerError{"Format specifies PAX", whyNoPAX, whyOnlyGNU}
+		case FormatGNU:
+			err = headerError{"Format specifies GNU", whyNoGNU, whyOnlyPAX}
+		default:
+			err = headerError{whyNoUSTAR, whyNoPAX, whyNoGNU, whyOnlyPAX, whyOnlyGNU}
+		}
+	}
+	return format, paxHdrs, err
+}
+
+// FileInfo returns an fs.FileInfo for the Header.
+func (h *Header) FileInfo() fs.FileInfo {
+	return headerFileInfo{h}
+}
+
+// headerFileInfo implements fs.FileInfo.
+type headerFileInfo struct {
+	h *Header
+}
+
+func (fi headerFileInfo) Size() int64        { return fi.h.Size }
+func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
+func (fi headerFileInfo) ModTime() time.Time { return fi.h.ModTime }
+func (fi headerFileInfo) Sys() interface{}   { return fi.h }
+
+// Name returns the base name of the file.
+func (fi headerFileInfo) Name() string {
+	if fi.IsDir() {
+		return path.Base(path.Clean(fi.h.Name))
+	}
+	return path.Base(fi.h.Name)
+}
+
+// Mode returns the permission and mode bits for the headerFileInfo.
+func (fi headerFileInfo) Mode() (mode fs.FileMode) {
+	// Set file permission bits.
+	mode = fs.FileMode(fi.h.Mode).Perm()
+
+	// Set setuid, setgid and sticky bits.
+	if fi.h.Mode&c_ISUID != 0 {
+		mode |= fs.ModeSetuid
+	}
+	if fi.h.Mode&c_ISGID != 0 {
+		mode |= fs.ModeSetgid
+	}
+	if fi.h.Mode&c_ISVTX != 0 {
+		mode |= fs.ModeSticky
+	}
+
+	// Set file mode bits; clear perm, setuid, setgid, and sticky bits.
+	switch m := fs.FileMode(fi.h.Mode) &^ 07777; m {
+	case c_ISDIR:
+		mode |= fs.ModeDir
+	case c_ISFIFO:
+		mode |= fs.ModeNamedPipe
+	case c_ISLNK:
+		mode |= fs.ModeSymlink
+	case c_ISBLK:
+		mode |= fs.ModeDevice
+	case c_ISCHR:
+		mode |= fs.ModeDevice
+		mode |= fs.ModeCharDevice
+	case c_ISSOCK:
+		mode |= fs.ModeSocket
+	}
+
+	switch fi.h.Typeflag {
+	case TypeSymlink:
+		mode |= fs.ModeSymlink
+	case TypeChar:
+		mode |= fs.ModeDevice
+		mode |= fs.ModeCharDevice
+	case TypeBlock:
+		mode |= fs.ModeDevice
+	case TypeDir:
+		mode |= fs.ModeDir
+	case TypeFifo:
+		mode |= fs.ModeNamedPipe
+	}
+
+	return mode
+}
+
+// sysStat, if non-nil, populates h from system-dependent fields of fi.
+var sysStat func(fi fs.FileInfo, h *Header) error
+
+const (
+	// Mode constants from the USTAR spec:
+	// See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06
+	c_ISUID = 04000 // Set uid
+	c_ISGID = 02000 // Set gid
+	c_ISVTX = 01000 // Save text (sticky bit)
+
+	// Common Unix mode constants; these are not defined in any common tar standard.
+	// Header.FileInfo understands these, but FileInfoHeader will never produce these.
+	c_ISDIR  = 040000  // Directory
+	c_ISFIFO = 010000  // FIFO
+	c_ISREG  = 0100000 // Regular file
+	c_ISLNK  = 0120000 // Symbolic link
+	c_ISBLK  = 060000  // Block special file
+	c_ISCHR  = 020000  // Character special file
+	c_ISSOCK = 0140000 // Socket
+)
+
+// FileInfoHeader creates a partially-populated Header from fi.
+// If fi describes a symlink, FileInfoHeader records link as the link target.
+// If fi describes a directory, a slash is appended to the name.
+//
+// Since fs.FileInfo's Name method only returns the base name of
+// the file it describes, it may be necessary to modify Header.Name
+// to provide the full path name of the file.
+func FileInfoHeader(fi fs.FileInfo, link string) (*Header, error) {
+	if fi == nil {
+		return nil, errors.New("archive/tar: FileInfo is nil")
+	}
+	fm := fi.Mode()
+	h := &Header{
+		Name:    fi.Name(),
+		ModTime: fi.ModTime(),
+		Mode:    int64(fm.Perm()), // or'd with c_IS* constants later
+	}
+	switch {
+	case fm.IsRegular():
+		h.Typeflag = TypeReg
+		h.Size = fi.Size()
+	case fi.IsDir():
+		h.Typeflag = TypeDir
+		h.Name += "/"
+	case fm&fs.ModeSymlink != 0:
+		h.Typeflag = TypeSymlink
+		h.Linkname = link
+	case fm&fs.ModeDevice != 0:
+		if fm&fs.ModeCharDevice != 0 {
+			h.Typeflag = TypeChar
+		} else {
+			h.Typeflag = TypeBlock
+		}
+	case fm&fs.ModeNamedPipe != 0:
+		h.Typeflag = TypeFifo
+	case fm&fs.ModeSocket != 0:
+		return nil, fmt.Errorf("archive/tar: sockets not supported")
+	default:
+		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
+	}
+	if fm&fs.ModeSetuid != 0 {
+		h.Mode |= c_ISUID
+	}
+	if fm&fs.ModeSetgid != 0 {
+		h.Mode |= c_ISGID
+	}
+	if fm&fs.ModeSticky != 0 {
+		h.Mode |= c_ISVTX
+	}
+	// If possible, populate additional fields from OS-specific
+	// FileInfo fields.
+	if sys, ok := fi.Sys().(*Header); ok {
+		// This FileInfo came from a Header (not the OS). Use the
+		// original Header to populate all remaining fields.
+		h.Uid = sys.Uid
+		h.Gid = sys.Gid
+		h.Uname = sys.Uname
+		h.Gname = sys.Gname
+		h.AccessTime = sys.AccessTime
+		h.ChangeTime = sys.ChangeTime
+		if sys.Xattrs != nil {
+			h.Xattrs = make(map[string]string)
+			for k, v := range sys.Xattrs {
+				h.Xattrs[k] = v
+			}
+		}
+		if sys.Typeflag == TypeLink {
+			// hard link
+			h.Typeflag = TypeLink
+			h.Size = 0
+			h.Linkname = sys.Linkname
+		}
+		if sys.PAXRecords != nil {
+			h.PAXRecords = make(map[string]string)
+			for k, v := range sys.PAXRecords {
+				h.PAXRecords[k] = v
+			}
+		}
+	}
+	if sysStat != nil {
+		return h, sysStat(fi, h)
+	}
+	return h, nil
+}
+
+// isHeaderOnlyType checks if the given type flag is of the type that has no
+// data section even if a size is specified.
+func isHeaderOnlyType(flag byte) bool {
+	switch flag {
+	case TypeLink, TypeSymlink, TypeChar, TypeBlock, TypeDir, TypeFifo:
+		return true
+	default:
+		return false
+	}
+}
+
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
diff --git a/src/archive/tar/example_test.go b/src/archive/tar/example_test.go
new file mode 100644
index 0000000..a2474b9
--- /dev/null
+++ b/src/archive/tar/example_test.go
@@ -0,0 +1,71 @@
+// Copyright 2013 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_test
+
+import (
+	"archive/tar"
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"os"
+)
+
+func Example_minimal() {
+	// Create and add some files to the archive.
+	var buf bytes.Buffer
+	tw := tar.NewWriter(&buf)
+	var files = []struct {
+		Name, Body string
+	}{
+		{"readme.txt", "This archive contains some text files."},
+		{"gopher.txt", "Gopher names:\nGeorge\nGeoffrey\nGonzo"},
+		{"todo.txt", "Get animal handling license."},
+	}
+	for _, file := range files {
+		hdr := &tar.Header{
+			Name: file.Name,
+			Mode: 0600,
+			Size: int64(len(file.Body)),
+		}
+		if err := tw.WriteHeader(hdr); err != nil {
+			log.Fatal(err)
+		}
+		if _, err := tw.Write([]byte(file.Body)); err != nil {
+			log.Fatal(err)
+		}
+	}
+	if err := tw.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Open and iterate through the files in the archive.
+	tr := tar.NewReader(&buf)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break // End of archive
+		}
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Printf("Contents of %s:\n", hdr.Name)
+		if _, err := io.Copy(os.Stdout, tr); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println()
+	}
+
+	// Output:
+	// Contents of readme.txt:
+	// This archive contains some text files.
+	// Contents of gopher.txt:
+	// Gopher names:
+	// George
+	// Geoffrey
+	// Gonzo
+	// Contents of todo.txt:
+	// Get animal handling license.
+}
diff --git a/src/archive/tar/format.go b/src/archive/tar/format.go
new file mode 100644
index 0000000..cfe24a5
--- /dev/null
+++ b/src/archive/tar/format.go
@@ -0,0 +1,303 @@
+// Copyright 2016 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 "strings"
+
+// Format represents the tar archive format.
+//
+// The original tar format was introduced in Unix V7.
+// Since then, there have been multiple competing formats attempting to
+// standardize or extend the V7 format to overcome its limitations.
+// The most common formats are the USTAR, PAX, and GNU formats,
+// each with their own advantages and limitations.
+//
+// The following table captures the capabilities of each format:
+//
+//	                  |  USTAR |       PAX |       GNU
+//	------------------+--------+-----------+----------
+//	Name              |   256B | unlimited | unlimited
+//	Linkname          |   100B | unlimited | unlimited
+//	Size              | uint33 | unlimited |    uint89
+//	Mode              | uint21 |    uint21 |    uint57
+//	Uid/Gid           | uint21 | unlimited |    uint57
+//	Uname/Gname       |    32B | unlimited |       32B
+//	ModTime           | uint33 | unlimited |     int89
+//	AccessTime        |    n/a | unlimited |     int89
+//	ChangeTime        |    n/a | unlimited |     int89
+//	Devmajor/Devminor | uint21 |    uint21 |    uint57
+//	------------------+--------+-----------+----------
+//	string encoding   |  ASCII |     UTF-8 |    binary
+//	sub-second times  |     no |       yes |        no
+//	sparse files      |     no |       yes |       yes
+//
+// The table's upper portion shows the Header fields, where each format reports
+// the maximum number of bytes allowed for each string field and
+// the integer type used to store each numeric field
+// (where timestamps are stored as the number of seconds since the Unix epoch).
+//
+// The table's lower portion shows specialized features of each format,
+// such as supported string encodings, support for sub-second timestamps,
+// or support for sparse files.
+//
+// The Writer currently provides no support for sparse files.
+type Format int
+
+// Constants to identify various tar formats.
+const (
+	// Deliberately hide the meaning of constants from public API.
+	_ Format = (1 << iota) / 4 // Sequence of 0, 0, 1, 2, 4, 8, etc...
+
+	// FormatUnknown indicates that the format is unknown.
+	FormatUnknown
+
+	// The format of the original Unix V7 tar tool prior to standardization.
+	formatV7
+
+	// FormatUSTAR represents the USTAR header format defined in POSIX.1-1988.
+	//
+	// While this format is compatible with most tar readers,
+	// the format has several limitations making it unsuitable for some usages.
+	// Most notably, it cannot support sparse files, files larger than 8GiB,
+	// filenames larger than 256 characters, and non-ASCII filenames.
+	//
+	// Reference:
+	//	http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06
+	FormatUSTAR
+
+	// FormatPAX represents the PAX header format defined in POSIX.1-2001.
+	//
+	// PAX extends USTAR by writing a special file with Typeflag TypeXHeader
+	// preceding the original header. This file contains a set of key-value
+	// records, which are used to overcome USTAR's shortcomings, in addition to
+	// providing the ability to have sub-second resolution for timestamps.
+	//
+	// Some newer formats add their own extensions to PAX by defining their
+	// own keys and assigning certain semantic meaning to the associated values.
+	// For example, sparse file support in PAX is implemented using keys
+	// defined by the GNU manual (e.g., "GNU.sparse.map").
+	//
+	// Reference:
+	//	http://pubs.opengroup.org/onlinepubs/009695399/utilities/pax.html
+	FormatPAX
+
+	// FormatGNU represents the GNU header format.
+	//
+	// The GNU header format is older than the USTAR and PAX standards and
+	// is not compatible with them. The GNU format supports
+	// arbitrary file sizes, filenames of arbitrary encoding and length,
+	// sparse files, and other features.
+	//
+	// It is recommended that PAX be chosen over GNU unless the target
+	// application can only parse GNU formatted archives.
+	//
+	// Reference:
+	//	https://www.gnu.org/software/tar/manual/html_node/Standard.html
+	FormatGNU
+
+	// Schily's tar format, which is incompatible with USTAR.
+	// This does not cover STAR extensions to the PAX format; these fall under
+	// the PAX format.
+	formatSTAR
+
+	formatMax
+)
+
+func (f Format) has(f2 Format) bool   { return f&f2 != 0 }
+func (f *Format) mayBe(f2 Format)     { *f |= f2 }
+func (f *Format) mayOnlyBe(f2 Format) { *f &= f2 }
+func (f *Format) mustNotBe(f2 Format) { *f &^= f2 }
+
+var formatNames = map[Format]string{
+	formatV7: "V7", FormatUSTAR: "USTAR", FormatPAX: "PAX", FormatGNU: "GNU", formatSTAR: "STAR",
+}
+
+func (f Format) String() string {
+	var ss []string
+	for f2 := Format(1); f2 < formatMax; f2 <<= 1 {
+		if f.has(f2) {
+			ss = append(ss, formatNames[f2])
+		}
+	}
+	switch len(ss) {
+	case 0:
+		return "<unknown>"
+	case 1:
+		return ss[0]
+	default:
+		return "(" + strings.Join(ss, " | ") + ")"
+	}
+}
+
+// Magics used to identify various formats.
+const (
+	magicGNU, versionGNU     = "ustar ", " \x00"
+	magicUSTAR, versionUSTAR = "ustar\x00", "00"
+	trailerSTAR              = "tar\x00"
+)
+
+// Size constants from various tar specifications.
+const (
+	blockSize  = 512 // Size of each block in a tar stream
+	nameSize   = 100 // Max length of the name field in USTAR format
+	prefixSize = 155 // Max length of the prefix field in USTAR format
+)
+
+// blockPadding computes the number of bytes needed to pad offset up to the
+// nearest block edge where 0 <= n < blockSize.
+func blockPadding(offset int64) (n int64) {
+	return -offset & (blockSize - 1)
+}
+
+var zeroBlock block
+
+type block [blockSize]byte
+
+// Convert block to any number of formats.
+func (b *block) V7() *headerV7       { return (*headerV7)(b) }
+func (b *block) GNU() *headerGNU     { return (*headerGNU)(b) }
+func (b *block) STAR() *headerSTAR   { return (*headerSTAR)(b) }
+func (b *block) USTAR() *headerUSTAR { return (*headerUSTAR)(b) }
+func (b *block) Sparse() sparseArray { return sparseArray(b[:]) }
+
+// GetFormat checks that the block is a valid tar header based on the checksum.
+// It then attempts to guess the specific format based on magic values.
+// If the checksum fails, then FormatUnknown is returned.
+func (b *block) GetFormat() Format {
+	// Verify checksum.
+	var p parser
+	value := p.parseOctal(b.V7().Chksum())
+	chksum1, chksum2 := b.ComputeChecksum()
+	if p.err != nil || (value != chksum1 && value != chksum2) {
+		return FormatUnknown
+	}
+
+	// Guess the magic values.
+	magic := string(b.USTAR().Magic())
+	version := string(b.USTAR().Version())
+	trailer := string(b.STAR().Trailer())
+	switch {
+	case magic == magicUSTAR && trailer == trailerSTAR:
+		return formatSTAR
+	case magic == magicUSTAR:
+		return FormatUSTAR | FormatPAX
+	case magic == magicGNU && version == versionGNU:
+		return FormatGNU
+	default:
+		return formatV7
+	}
+}
+
+// SetFormat writes the magic values necessary for specified format
+// and then updates the checksum accordingly.
+func (b *block) SetFormat(format Format) {
+	// Set the magic values.
+	switch {
+	case format.has(formatV7):
+		// Do nothing.
+	case format.has(FormatGNU):
+		copy(b.GNU().Magic(), magicGNU)
+		copy(b.GNU().Version(), versionGNU)
+	case format.has(formatSTAR):
+		copy(b.STAR().Magic(), magicUSTAR)
+		copy(b.STAR().Version(), versionUSTAR)
+		copy(b.STAR().Trailer(), trailerSTAR)
+	case format.has(FormatUSTAR | FormatPAX):
+		copy(b.USTAR().Magic(), magicUSTAR)
+		copy(b.USTAR().Version(), versionUSTAR)
+	default:
+		panic("invalid format")
+	}
+
+	// Update checksum.
+	// This field is special in that it is terminated by a NULL then space.
+	var f formatter
+	field := b.V7().Chksum()
+	chksum, _ := b.ComputeChecksum() // Possible values are 256..128776
+	f.formatOctal(field[:7], chksum) // Never fails since 128776 < 262143
+	field[7] = ' '
+}
+
+// ComputeChecksum computes the checksum for the header block.
+// POSIX specifies a sum of the unsigned byte values, but the Sun tar used
+// signed byte values.
+// We compute and return both.
+func (b *block) ComputeChecksum() (unsigned, signed int64) {
+	for i, c := range b {
+		if 148 <= i && i < 156 {
+			c = ' ' // Treat the checksum field itself as all spaces.
+		}
+		unsigned += int64(c)
+		signed += int64(int8(c))
+	}
+	return unsigned, signed
+}
+
+// Reset clears the block with all zeros.
+func (b *block) Reset() {
+	*b = block{}
+}
+
+type headerV7 [blockSize]byte
+
+func (h *headerV7) Name() []byte     { return h[000:][:100] }
+func (h *headerV7) Mode() []byte     { return h[100:][:8] }
+func (h *headerV7) UID() []byte      { return h[108:][:8] }
+func (h *headerV7) GID() []byte      { return h[116:][:8] }
+func (h *headerV7) Size() []byte     { return h[124:][:12] }
+func (h *headerV7) ModTime() []byte  { return h[136:][:12] }
+func (h *headerV7) Chksum() []byte   { return h[148:][:8] }
+func (h *headerV7) TypeFlag() []byte { return h[156:][:1] }
+func (h *headerV7) LinkName() []byte { return h[157:][:100] }
+
+type headerGNU [blockSize]byte
+
+func (h *headerGNU) V7() *headerV7       { return (*headerV7)(h) }
+func (h *headerGNU) Magic() []byte       { return h[257:][:6] }
+func (h *headerGNU) Version() []byte     { return h[263:][:2] }
+func (h *headerGNU) UserName() []byte    { return h[265:][:32] }
+func (h *headerGNU) GroupName() []byte   { return h[297:][:32] }
+func (h *headerGNU) DevMajor() []byte    { return h[329:][:8] }
+func (h *headerGNU) DevMinor() []byte    { return h[337:][:8] }
+func (h *headerGNU) AccessTime() []byte  { return h[345:][:12] }
+func (h *headerGNU) ChangeTime() []byte  { return h[357:][:12] }
+func (h *headerGNU) Sparse() sparseArray { return sparseArray(h[386:][:24*4+1]) }
+func (h *headerGNU) RealSize() []byte    { return h[483:][:12] }
+
+type headerSTAR [blockSize]byte
+
+func (h *headerSTAR) V7() *headerV7      { return (*headerV7)(h) }
+func (h *headerSTAR) Magic() []byte      { return h[257:][:6] }
+func (h *headerSTAR) Version() []byte    { return h[263:][:2] }
+func (h *headerSTAR) UserName() []byte   { return h[265:][:32] }
+func (h *headerSTAR) GroupName() []byte  { return h[297:][:32] }
+func (h *headerSTAR) DevMajor() []byte   { return h[329:][:8] }
+func (h *headerSTAR) DevMinor() []byte   { return h[337:][:8] }
+func (h *headerSTAR) Prefix() []byte     { return h[345:][:131] }
+func (h *headerSTAR) AccessTime() []byte { return h[476:][:12] }
+func (h *headerSTAR) ChangeTime() []byte { return h[488:][:12] }
+func (h *headerSTAR) Trailer() []byte    { return h[508:][:4] }
+
+type headerUSTAR [blockSize]byte
+
+func (h *headerUSTAR) V7() *headerV7     { return (*headerV7)(h) }
+func (h *headerUSTAR) Magic() []byte     { return h[257:][:6] }
+func (h *headerUSTAR) Version() []byte   { return h[263:][:2] }
+func (h *headerUSTAR) UserName() []byte  { return h[265:][:32] }
+func (h *headerUSTAR) GroupName() []byte { return h[297:][:32] }
+func (h *headerUSTAR) DevMajor() []byte  { return h[329:][:8] }
+func (h *headerUSTAR) DevMinor() []byte  { return h[337:][:8] }
+func (h *headerUSTAR) Prefix() []byte    { return h[345:][:155] }
+
+type sparseArray []byte
+
+func (s sparseArray) Entry(i int) sparseElem { return sparseElem(s[i*24:]) }
+func (s sparseArray) IsExtended() []byte     { return s[24*s.MaxEntries():][:1] }
+func (s sparseArray) MaxEntries() int        { return len(s) / 24 }
+
+type sparseElem []byte
+
+func (s sparseElem) Offset() []byte { return s[00:][:12] }
+func (s sparseElem) Length() []byte { return s[12:][:12] }
diff --git a/src/archive/tar/reader.go b/src/archive/tar/reader.go
new file mode 100644
index 0000000..1b1d5b4
--- /dev/null
+++ b/src/archive/tar/reader.go
@@ -0,0 +1,857 @@
+// 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: &regFileReader{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 = &regFileReader{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.V7()
+	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.USTAR()
+		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.USTAR()
+			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.STAR()
+			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.GNU()
+			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.USTAR()
+				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.GNU().RealSize())
+	if p.err != nil {
+		return nil, p.err
+	}
+	s := blk.GNU().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.Sparse()
+			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})
+}
+
+func (fr regFileReader) LogicalRemaining() int64 {
+	return fr.nb
+}
+
+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
+}
diff --git a/src/archive/tar/reader_test.go b/src/archive/tar/reader_test.go
new file mode 100644
index 0000000..789ddc1
--- /dev/null
+++ b/src/archive/tar/reader_test.go
@@ -0,0 +1,1610 @@
+// 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"
+	"crypto/md5"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"os"
+	"path"
+	"reflect"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestReader(t *testing.T) {
+	vectors := []struct {
+		file    string    // Test input file
+		headers []*Header // Expected output headers
+		chksums []string  // MD5 checksum of files, leave as nil if not checked
+		err     error     // Expected error to occur
+	}{{
+		file: "testdata/gnu.tar",
+		headers: []*Header{{
+			Name:     "small.txt",
+			Mode:     0640,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     5,
+			ModTime:  time.Unix(1244428340, 0),
+			Typeflag: '0',
+			Uname:    "dsymonds",
+			Gname:    "eng",
+			Format:   FormatGNU,
+		}, {
+			Name:     "small2.txt",
+			Mode:     0640,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     11,
+			ModTime:  time.Unix(1244436044, 0),
+			Typeflag: '0',
+			Uname:    "dsymonds",
+			Gname:    "eng",
+			Format:   FormatGNU,
+		}},
+		chksums: []string{
+			"e38b27eaccb4391bdec553a7f3ae6b2f",
+			"c65bd2e50a56a2138bf1716f2fd56fe9",
+		},
+	}, {
+		file: "testdata/sparse-formats.tar",
+		headers: []*Header{{
+			Name:     "sparse-gnu",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392395740, 0),
+			Typeflag: 0x53,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+			Format:   FormatGNU,
+		}, {
+			Name:     "sparse-posix-0.0",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392342187, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+			PAXRecords: map[string]string{
+				"GNU.sparse.size":      "200",
+				"GNU.sparse.numblocks": "95",
+				"GNU.sparse.map":       "1,1,3,1,5,1,7,1,9,1,11,1,13,1,15,1,17,1,19,1,21,1,23,1,25,1,27,1,29,1,31,1,33,1,35,1,37,1,39,1,41,1,43,1,45,1,47,1,49,1,51,1,53,1,55,1,57,1,59,1,61,1,63,1,65,1,67,1,69,1,71,1,73,1,75,1,77,1,79,1,81,1,83,1,85,1,87,1,89,1,91,1,93,1,95,1,97,1,99,1,101,1,103,1,105,1,107,1,109,1,111,1,113,1,115,1,117,1,119,1,121,1,123,1,125,1,127,1,129,1,131,1,133,1,135,1,137,1,139,1,141,1,143,1,145,1,147,1,149,1,151,1,153,1,155,1,157,1,159,1,161,1,163,1,165,1,167,1,169,1,171,1,173,1,175,1,177,1,179,1,181,1,183,1,185,1,187,1,189,1",
+			},
+			Format: FormatPAX,
+		}, {
+			Name:     "sparse-posix-0.1",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392340456, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+			PAXRecords: map[string]string{
+				"GNU.sparse.size":      "200",
+				"GNU.sparse.numblocks": "95",
+				"GNU.sparse.map":       "1,1,3,1,5,1,7,1,9,1,11,1,13,1,15,1,17,1,19,1,21,1,23,1,25,1,27,1,29,1,31,1,33,1,35,1,37,1,39,1,41,1,43,1,45,1,47,1,49,1,51,1,53,1,55,1,57,1,59,1,61,1,63,1,65,1,67,1,69,1,71,1,73,1,75,1,77,1,79,1,81,1,83,1,85,1,87,1,89,1,91,1,93,1,95,1,97,1,99,1,101,1,103,1,105,1,107,1,109,1,111,1,113,1,115,1,117,1,119,1,121,1,123,1,125,1,127,1,129,1,131,1,133,1,135,1,137,1,139,1,141,1,143,1,145,1,147,1,149,1,151,1,153,1,155,1,157,1,159,1,161,1,163,1,165,1,167,1,169,1,171,1,173,1,175,1,177,1,179,1,181,1,183,1,185,1,187,1,189,1",
+				"GNU.sparse.name":      "sparse-posix-0.1",
+			},
+			Format: FormatPAX,
+		}, {
+			Name:     "sparse-posix-1.0",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     200,
+			ModTime:  time.Unix(1392337404, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+			PAXRecords: map[string]string{
+				"GNU.sparse.major":    "1",
+				"GNU.sparse.minor":    "0",
+				"GNU.sparse.realsize": "200",
+				"GNU.sparse.name":     "sparse-posix-1.0",
+			},
+			Format: FormatPAX,
+		}, {
+			Name:     "end",
+			Mode:     420,
+			Uid:      1000,
+			Gid:      1000,
+			Size:     4,
+			ModTime:  time.Unix(1392398319, 0),
+			Typeflag: 0x30,
+			Linkname: "",
+			Uname:    "david",
+			Gname:    "david",
+			Devmajor: 0,
+			Devminor: 0,
+			Format:   FormatGNU,
+		}},
+		chksums: []string{
+			"6f53234398c2449fe67c1812d993012f",
+			"6f53234398c2449fe67c1812d993012f",
+			"6f53234398c2449fe67c1812d993012f",
+			"6f53234398c2449fe67c1812d993012f",
+			"b0061974914468de549a2af8ced10316",
+		},
+	}, {
+		file: "testdata/star.tar",
+		headers: []*Header{{
+			Name:       "small.txt",
+			Mode:       0640,
+			Uid:        73025,
+			Gid:        5000,
+			Size:       5,
+			ModTime:    time.Unix(1244592783, 0),
+			Typeflag:   '0',
+			Uname:      "dsymonds",
+			Gname:      "eng",
+			AccessTime: time.Unix(1244592783, 0),
+			ChangeTime: time.Unix(1244592783, 0),
+		}, {
+			Name:       "small2.txt",
+			Mode:       0640,
+			Uid:        73025,
+			Gid:        5000,
+			Size:       11,
+			ModTime:    time.Unix(1244592783, 0),
+			Typeflag:   '0',
+			Uname:      "dsymonds",
+			Gname:      "eng",
+			AccessTime: time.Unix(1244592783, 0),
+			ChangeTime: time.Unix(1244592783, 0),
+		}},
+	}, {
+		file: "testdata/v7.tar",
+		headers: []*Header{{
+			Name:     "small.txt",
+			Mode:     0444,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     5,
+			ModTime:  time.Unix(1244593104, 0),
+			Typeflag: '0',
+		}, {
+			Name:     "small2.txt",
+			Mode:     0444,
+			Uid:      73025,
+			Gid:      5000,
+			Size:     11,
+			ModTime:  time.Unix(1244593104, 0),
+			Typeflag: '0',
+		}},
+	}, {
+		file: "testdata/pax.tar",
+		headers: []*Header{{
+			Name:       "a/123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+			Mode:       0664,
+			Uid:        1000,
+			Gid:        1000,
+			Uname:      "shane",
+			Gname:      "shane",
+			Size:       7,
+			ModTime:    time.Unix(1350244992, 23960108),
+			ChangeTime: time.Unix(1350244992, 23960108),
+			AccessTime: time.Unix(1350244992, 23960108),
+			Typeflag:   TypeReg,
+			PAXRecords: map[string]string{
+				"path":  "a/123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+				"mtime": "1350244992.023960108",
+				"atime": "1350244992.023960108",
+				"ctime": "1350244992.023960108",
+			},
+			Format: FormatPAX,
+		}, {
+			Name:       "a/b",
+			Mode:       0777,
+			Uid:        1000,
+			Gid:        1000,
+			Uname:      "shane",
+			Gname:      "shane",
+			Size:       0,
+			ModTime:    time.Unix(1350266320, 910238425),
+			ChangeTime: time.Unix(1350266320, 910238425),
+			AccessTime: time.Unix(1350266320, 910238425),
+			Typeflag:   TypeSymlink,
+			Linkname:   "123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+			PAXRecords: map[string]string{
+				"linkpath": "123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100",
+				"mtime":    "1350266320.910238425",
+				"atime":    "1350266320.910238425",
+				"ctime":    "1350266320.910238425",
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		file: "testdata/pax-bad-hdr-file.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/pax-bad-mtime-file.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/pax-pos-size-file.tar",
+		headers: []*Header{{
+			Name:     "foo",
+			Mode:     0640,
+			Uid:      319973,
+			Gid:      5000,
+			Size:     999,
+			ModTime:  time.Unix(1442282516, 0),
+			Typeflag: '0',
+			Uname:    "joetsai",
+			Gname:    "eng",
+			PAXRecords: map[string]string{
+				"size": "000000000000000000000999",
+			},
+			Format: FormatPAX,
+		}},
+		chksums: []string{
+			"0afb597b283fe61b5d4879669a350556",
+		},
+	}, {
+		file: "testdata/pax-records.tar",
+		headers: []*Header{{
+			Typeflag: TypeReg,
+			Name:     "file",
+			Uname:    strings.Repeat("long", 10),
+			ModTime:  time.Unix(0, 0),
+			PAXRecords: map[string]string{
+				"GOLANG.pkg": "tar",
+				"comment":    "Hello, 世界",
+				"uname":      strings.Repeat("long", 10),
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		file: "testdata/pax-global-records.tar",
+		headers: []*Header{{
+			Typeflag:   TypeXGlobalHeader,
+			Name:       "global1",
+			PAXRecords: map[string]string{"path": "global1", "mtime": "1500000000.0"},
+			Format:     FormatPAX,
+		}, {
+			Typeflag: TypeReg,
+			Name:     "file1",
+			ModTime:  time.Unix(0, 0),
+			Format:   FormatUSTAR,
+		}, {
+			Typeflag:   TypeReg,
+			Name:       "file2",
+			PAXRecords: map[string]string{"path": "file2"},
+			ModTime:    time.Unix(0, 0),
+			Format:     FormatPAX,
+		}, {
+			Typeflag:   TypeXGlobalHeader,
+			Name:       "GlobalHead.0.0",
+			PAXRecords: map[string]string{"path": ""},
+			Format:     FormatPAX,
+		}, {
+			Typeflag: TypeReg,
+			Name:     "file3",
+			ModTime:  time.Unix(0, 0),
+			Format:   FormatUSTAR,
+		}, {
+			Typeflag:   TypeReg,
+			Name:       "file4",
+			ModTime:    time.Unix(1400000000, 0),
+			PAXRecords: map[string]string{"mtime": "1400000000"},
+			Format:     FormatPAX,
+		}},
+	}, {
+		file: "testdata/nil-uid.tar", // golang.org/issue/5290
+		headers: []*Header{{
+			Name:     "P1050238.JPG.log",
+			Mode:     0664,
+			Uid:      0,
+			Gid:      0,
+			Size:     14,
+			ModTime:  time.Unix(1365454838, 0),
+			Typeflag: TypeReg,
+			Linkname: "",
+			Uname:    "eyefi",
+			Gname:    "eyefi",
+			Devmajor: 0,
+			Devminor: 0,
+			Format:   FormatGNU,
+		}},
+	}, {
+		file: "testdata/xattrs.tar",
+		headers: []*Header{{
+			Name:       "small.txt",
+			Mode:       0644,
+			Uid:        1000,
+			Gid:        10,
+			Size:       5,
+			ModTime:    time.Unix(1386065770, 448252320),
+			Typeflag:   '0',
+			Uname:      "alex",
+			Gname:      "wheel",
+			AccessTime: time.Unix(1389782991, 419875220),
+			ChangeTime: time.Unix(1389782956, 794414986),
+			Xattrs: map[string]string{
+				"user.key":  "value",
+				"user.key2": "value2",
+				// Interestingly, selinux encodes the terminating null inside the xattr
+				"security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+			},
+			PAXRecords: map[string]string{
+				"mtime":                         "1386065770.44825232",
+				"atime":                         "1389782991.41987522",
+				"ctime":                         "1389782956.794414986",
+				"SCHILY.xattr.user.key":         "value",
+				"SCHILY.xattr.user.key2":        "value2",
+				"SCHILY.xattr.security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+			},
+			Format: FormatPAX,
+		}, {
+			Name:       "small2.txt",
+			Mode:       0644,
+			Uid:        1000,
+			Gid:        10,
+			Size:       11,
+			ModTime:    time.Unix(1386065770, 449252304),
+			Typeflag:   '0',
+			Uname:      "alex",
+			Gname:      "wheel",
+			AccessTime: time.Unix(1389782991, 419875220),
+			ChangeTime: time.Unix(1386065770, 449252304),
+			Xattrs: map[string]string{
+				"security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+			},
+			PAXRecords: map[string]string{
+				"mtime":                         "1386065770.449252304",
+				"atime":                         "1389782991.41987522",
+				"ctime":                         "1386065770.449252304",
+				"SCHILY.xattr.security.selinux": "unconfined_u:object_r:default_t:s0\x00",
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		// Matches the behavior of GNU, BSD, and STAR tar utilities.
+		file: "testdata/gnu-multi-hdrs.tar",
+		headers: []*Header{{
+			Name:     "GNU2/GNU2/long-path-name",
+			Linkname: "GNU4/GNU4/long-linkpath-name",
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '2',
+			Format:   FormatGNU,
+		}},
+	}, {
+		// GNU tar file with atime and ctime fields set.
+		// Created with the GNU tar v1.27.1.
+		//	tar --incremental -S -cvf gnu-incremental.tar test2
+		file: "testdata/gnu-incremental.tar",
+		headers: []*Header{{
+			Name:       "test2/",
+			Mode:       16877,
+			Uid:        1000,
+			Gid:        1000,
+			Size:       14,
+			ModTime:    time.Unix(1441973427, 0),
+			Typeflag:   'D',
+			Uname:      "rawr",
+			Gname:      "dsnet",
+			AccessTime: time.Unix(1441974501, 0),
+			ChangeTime: time.Unix(1441973436, 0),
+			Format:     FormatGNU,
+		}, {
+			Name:       "test2/foo",
+			Mode:       33188,
+			Uid:        1000,
+			Gid:        1000,
+			Size:       64,
+			ModTime:    time.Unix(1441973363, 0),
+			Typeflag:   '0',
+			Uname:      "rawr",
+			Gname:      "dsnet",
+			AccessTime: time.Unix(1441974501, 0),
+			ChangeTime: time.Unix(1441973436, 0),
+			Format:     FormatGNU,
+		}, {
+			Name:       "test2/sparse",
+			Mode:       33188,
+			Uid:        1000,
+			Gid:        1000,
+			Size:       536870912,
+			ModTime:    time.Unix(1441973427, 0),
+			Typeflag:   'S',
+			Uname:      "rawr",
+			Gname:      "dsnet",
+			AccessTime: time.Unix(1441991948, 0),
+			ChangeTime: time.Unix(1441973436, 0),
+			Format:     FormatGNU,
+		}},
+	}, {
+		// Matches the behavior of GNU and BSD tar utilities.
+		file: "testdata/pax-multi-hdrs.tar",
+		headers: []*Header{{
+			Name:     "bar",
+			Linkname: "PAX4/PAX4/long-linkpath-name",
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '2',
+			PAXRecords: map[string]string{
+				"linkpath": "PAX4/PAX4/long-linkpath-name",
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		// Both BSD and GNU tar truncate long names at first NUL even
+		// if there is data following that NUL character.
+		// This is reasonable as GNU long names are C-strings.
+		file: "testdata/gnu-long-nul.tar",
+		headers: []*Header{{
+			Name:     "0123456789",
+			Mode:     0644,
+			Uid:      1000,
+			Gid:      1000,
+			ModTime:  time.Unix(1486082191, 0),
+			Typeflag: '0',
+			Uname:    "rawr",
+			Gname:    "dsnet",
+			Format:   FormatGNU,
+		}},
+	}, {
+		// This archive was generated by Writer but is readable by both
+		// GNU and BSD tar utilities.
+		// The archive generated by GNU is nearly byte-for-byte identical
+		// to the Go version except the Go version sets a negative Devminor
+		// just to force the GNU format.
+		file: "testdata/gnu-utf8.tar",
+		headers: []*Header{{
+			Name: "☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹",
+			Mode: 0644,
+			Uid:  1000, Gid: 1000,
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '0',
+			Uname:    "☺",
+			Gname:    "⚹",
+			Format:   FormatGNU,
+		}},
+	}, {
+		// This archive was generated by Writer but is readable by both
+		// GNU and BSD tar utilities.
+		// The archive generated by GNU is nearly byte-for-byte identical
+		// to the Go version except the Go version sets a negative Devminor
+		// just to force the GNU format.
+		file: "testdata/gnu-not-utf8.tar",
+		headers: []*Header{{
+			Name:     "hi\x80\x81\x82\x83bye",
+			Mode:     0644,
+			Uid:      1000,
+			Gid:      1000,
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '0',
+			Uname:    "rawr",
+			Gname:    "dsnet",
+			Format:   FormatGNU,
+		}},
+	}, {
+		// BSD tar v3.1.2 and GNU tar v1.27.1 both rejects PAX records
+		// with NULs in the key.
+		file: "testdata/pax-nul-xattrs.tar",
+		err:  ErrHeader,
+	}, {
+		// BSD tar v3.1.2 rejects a PAX path with NUL in the value, while
+		// GNU tar v1.27.1 simply truncates at first NUL.
+		// We emulate the behavior of BSD since it is strange doing NUL
+		// truncations since PAX records are length-prefix strings instead
+		// of NUL-terminated C-strings.
+		file: "testdata/pax-nul-path.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/neg-size.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/issue10968.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/issue11169.tar",
+		err:  ErrHeader,
+	}, {
+		file: "testdata/issue12435.tar",
+		err:  ErrHeader,
+	}, {
+		// Ensure that we can read back the original Header as written with
+		// a buggy pre-Go1.8 tar.Writer.
+		file: "testdata/invalid-go17.tar",
+		headers: []*Header{{
+			Name:     "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/foo",
+			Uid:      010000000,
+			ModTime:  time.Unix(0, 0),
+			Typeflag: '0',
+		}},
+	}, {
+		// USTAR archive with a regular entry with non-zero device numbers.
+		file: "testdata/ustar-file-devs.tar",
+		headers: []*Header{{
+			Name:     "file",
+			Mode:     0644,
+			Typeflag: '0',
+			ModTime:  time.Unix(0, 0),
+			Devmajor: 1,
+			Devminor: 1,
+			Format:   FormatUSTAR,
+		}},
+	}, {
+		// Generated by Go, works on BSD tar v3.1.2 and GNU tar v.1.27.1.
+		file: "testdata/gnu-nil-sparse-data.tar",
+		headers: []*Header{{
+			Name:     "sparse.db",
+			Typeflag: TypeGNUSparse,
+			Size:     1000,
+			ModTime:  time.Unix(0, 0),
+			Format:   FormatGNU,
+		}},
+	}, {
+		// Generated by Go, works on BSD tar v3.1.2 and GNU tar v.1.27.1.
+		file: "testdata/gnu-nil-sparse-hole.tar",
+		headers: []*Header{{
+			Name:     "sparse.db",
+			Typeflag: TypeGNUSparse,
+			Size:     1000,
+			ModTime:  time.Unix(0, 0),
+			Format:   FormatGNU,
+		}},
+	}, {
+		// Generated by Go, works on BSD tar v3.1.2 and GNU tar v.1.27.1.
+		file: "testdata/pax-nil-sparse-data.tar",
+		headers: []*Header{{
+			Name:     "sparse.db",
+			Typeflag: TypeReg,
+			Size:     1000,
+			ModTime:  time.Unix(0, 0),
+			PAXRecords: map[string]string{
+				"size":                "1512",
+				"GNU.sparse.major":    "1",
+				"GNU.sparse.minor":    "0",
+				"GNU.sparse.realsize": "1000",
+				"GNU.sparse.name":     "sparse.db",
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		// Generated by Go, works on BSD tar v3.1.2 and GNU tar v.1.27.1.
+		file: "testdata/pax-nil-sparse-hole.tar",
+		headers: []*Header{{
+			Name:     "sparse.db",
+			Typeflag: TypeReg,
+			Size:     1000,
+			ModTime:  time.Unix(0, 0),
+			PAXRecords: map[string]string{
+				"size":                "512",
+				"GNU.sparse.major":    "1",
+				"GNU.sparse.minor":    "0",
+				"GNU.sparse.realsize": "1000",
+				"GNU.sparse.name":     "sparse.db",
+			},
+			Format: FormatPAX,
+		}},
+	}, {
+		file: "testdata/trailing-slash.tar",
+		headers: []*Header{{
+			Typeflag: TypeDir,
+			Name:     strings.Repeat("123456789/", 30),
+			ModTime:  time.Unix(0, 0),
+			PAXRecords: map[string]string{
+				"path": strings.Repeat("123456789/", 30),
+			},
+			Format: FormatPAX,
+		}},
+	}}
+
+	for _, v := range vectors {
+		t.Run(path.Base(v.file), func(t *testing.T) {
+			f, err := os.Open(v.file)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			defer f.Close()
+
+			// Capture all headers and checksums.
+			var (
+				tr      = NewReader(f)
+				hdrs    []*Header
+				chksums []string
+				rdbuf   = make([]byte, 8)
+			)
+			for {
+				var hdr *Header
+				hdr, err = tr.Next()
+				if err != nil {
+					if err == io.EOF {
+						err = nil // Expected error
+					}
+					break
+				}
+				hdrs = append(hdrs, hdr)
+
+				if v.chksums == nil {
+					continue
+				}
+				h := md5.New()
+				_, err = io.CopyBuffer(h, tr, rdbuf) // Effectively an incremental read
+				if err != nil {
+					break
+				}
+				chksums = append(chksums, fmt.Sprintf("%x", h.Sum(nil)))
+			}
+
+			for i, hdr := range hdrs {
+				if i >= len(v.headers) {
+					t.Fatalf("entry %d: unexpected header:\ngot %+v", i, *hdr)
+					continue
+				}
+				if !reflect.DeepEqual(*hdr, *v.headers[i]) {
+					t.Fatalf("entry %d: incorrect header:\ngot  %+v\nwant %+v", i, *hdr, *v.headers[i])
+				}
+			}
+			if len(hdrs) != len(v.headers) {
+				t.Fatalf("got %d headers, want %d headers", len(hdrs), len(v.headers))
+			}
+
+			for i, sum := range chksums {
+				if i >= len(v.chksums) {
+					t.Fatalf("entry %d: unexpected sum: got %s", i, sum)
+					continue
+				}
+				if sum != v.chksums[i] {
+					t.Fatalf("entry %d: incorrect checksum: got %s, want %s", i, sum, v.chksums[i])
+				}
+			}
+
+			if err != v.err {
+				t.Fatalf("unexpected error: got %v, want %v", err, v.err)
+			}
+			f.Close()
+		})
+	}
+}
+
+func TestPartialRead(t *testing.T) {
+	type testCase struct {
+		cnt    int    // Number of bytes to read
+		output string // Expected value of string read
+	}
+	vectors := []struct {
+		file  string
+		cases []testCase
+	}{{
+		file: "testdata/gnu.tar",
+		cases: []testCase{
+			{4, "Kilt"},
+			{6, "Google"},
+		},
+	}, {
+		file: "testdata/sparse-formats.tar",
+		cases: []testCase{
+			{2, "\x00G"},
+			{4, "\x00G\x00o"},
+			{6, "\x00G\x00o\x00G"},
+			{8, "\x00G\x00o\x00G\x00o"},
+			{4, "end\n"},
+		},
+	}}
+
+	for _, v := range vectors {
+		t.Run(path.Base(v.file), func(t *testing.T) {
+			f, err := os.Open(v.file)
+			if err != nil {
+				t.Fatalf("Open() error: %v", err)
+			}
+			defer f.Close()
+
+			tr := NewReader(f)
+			for i, tc := range v.cases {
+				hdr, err := tr.Next()
+				if err != nil || hdr == nil {
+					t.Fatalf("entry %d, Next(): got %v, want %v", i, err, nil)
+				}
+				buf := make([]byte, tc.cnt)
+				if _, err := io.ReadFull(tr, buf); err != nil {
+					t.Fatalf("entry %d, ReadFull(): got %v, want %v", i, err, nil)
+				}
+				if string(buf) != tc.output {
+					t.Fatalf("entry %d, ReadFull(): got %q, want %q", i, string(buf), tc.output)
+				}
+			}
+
+			if _, err := tr.Next(); err != io.EOF {
+				t.Fatalf("Next(): got %v, want EOF", err)
+			}
+		})
+	}
+}
+
+func TestUninitializedRead(t *testing.T) {
+	f, err := os.Open("testdata/gnu.tar")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	tr := NewReader(f)
+	_, err = tr.Read([]byte{})
+	if err == nil || err != io.EOF {
+		t.Errorf("Unexpected error: %v, wanted %v", err, io.EOF)
+	}
+
+}
+
+type reader struct{ io.Reader }
+type readSeeker struct{ io.ReadSeeker }
+type readBadSeeker struct{ io.ReadSeeker }
+
+func (rbs *readBadSeeker) Seek(int64, int) (int64, error) { return 0, fmt.Errorf("illegal seek") }
+
+// TestReadTruncation test the ending condition on various truncated files and
+// that truncated files are still detected even if the underlying io.Reader
+// satisfies io.Seeker.
+func TestReadTruncation(t *testing.T) {
+	var ss []string
+	for _, p := range []string{
+		"testdata/gnu.tar",
+		"testdata/ustar-file-reg.tar",
+		"testdata/pax-path-hdr.tar",
+		"testdata/sparse-formats.tar",
+	} {
+		buf, err := os.ReadFile(p)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		ss = append(ss, string(buf))
+	}
+
+	data1, data2, pax, sparse := ss[0], ss[1], ss[2], ss[3]
+	data2 += strings.Repeat("\x00", 10*512)
+	trash := strings.Repeat("garbage ", 64) // Exactly 512 bytes
+
+	vectors := []struct {
+		input string // Input stream
+		cnt   int    // Expected number of headers read
+		err   error  // Expected error outcome
+	}{
+		{"", 0, io.EOF}, // Empty file is a "valid" tar file
+		{data1[:511], 0, io.ErrUnexpectedEOF},
+		{data1[:512], 1, io.ErrUnexpectedEOF},
+		{data1[:1024], 1, io.EOF},
+		{data1[:1536], 2, io.ErrUnexpectedEOF},
+		{data1[:2048], 2, io.EOF},
+		{data1, 2, io.EOF},
+		{data1[:2048] + data2[:1536], 3, io.EOF},
+		{data2[:511], 0, io.ErrUnexpectedEOF},
+		{data2[:512], 1, io.ErrUnexpectedEOF},
+		{data2[:1195], 1, io.ErrUnexpectedEOF},
+		{data2[:1196], 1, io.EOF}, // Exact end of data and start of padding
+		{data2[:1200], 1, io.EOF},
+		{data2[:1535], 1, io.EOF},
+		{data2[:1536], 1, io.EOF}, // Exact end of padding
+		{data2[:1536] + trash[:1], 1, io.ErrUnexpectedEOF},
+		{data2[:1536] + trash[:511], 1, io.ErrUnexpectedEOF},
+		{data2[:1536] + trash, 1, ErrHeader},
+		{data2[:2048], 1, io.EOF}, // Exactly 1 empty block
+		{data2[:2048] + trash[:1], 1, io.ErrUnexpectedEOF},
+		{data2[:2048] + trash[:511], 1, io.ErrUnexpectedEOF},
+		{data2[:2048] + trash, 1, ErrHeader},
+		{data2[:2560], 1, io.EOF}, // Exactly 2 empty blocks (normal end-of-stream)
+		{data2[:2560] + trash[:1], 1, io.EOF},
+		{data2[:2560] + trash[:511], 1, io.EOF},
+		{data2[:2560] + trash, 1, io.EOF},
+		{data2[:3072], 1, io.EOF},
+		{pax, 0, io.EOF}, // PAX header without data is a "valid" tar file
+		{pax + trash[:1], 0, io.ErrUnexpectedEOF},
+		{pax + trash[:511], 0, io.ErrUnexpectedEOF},
+		{sparse[:511], 0, io.ErrUnexpectedEOF},
+		{sparse[:512], 0, io.ErrUnexpectedEOF},
+		{sparse[:3584], 1, io.EOF},
+		{sparse[:9200], 1, io.EOF}, // Terminate in padding of sparse header
+		{sparse[:9216], 1, io.EOF},
+		{sparse[:9728], 2, io.ErrUnexpectedEOF},
+		{sparse[:10240], 2, io.EOF},
+		{sparse[:11264], 2, io.ErrUnexpectedEOF},
+		{sparse, 5, io.EOF},
+		{sparse + trash, 5, io.EOF},
+	}
+
+	for i, v := range vectors {
+		for j := 0; j < 6; j++ {
+			var tr *Reader
+			var s1, s2 string
+
+			switch j {
+			case 0:
+				tr = NewReader(&reader{strings.NewReader(v.input)})
+				s1, s2 = "io.Reader", "auto"
+			case 1:
+				tr = NewReader(&reader{strings.NewReader(v.input)})
+				s1, s2 = "io.Reader", "manual"
+			case 2:
+				tr = NewReader(&readSeeker{strings.NewReader(v.input)})
+				s1, s2 = "io.ReadSeeker", "auto"
+			case 3:
+				tr = NewReader(&readSeeker{strings.NewReader(v.input)})
+				s1, s2 = "io.ReadSeeker", "manual"
+			case 4:
+				tr = NewReader(&readBadSeeker{strings.NewReader(v.input)})
+				s1, s2 = "ReadBadSeeker", "auto"
+			case 5:
+				tr = NewReader(&readBadSeeker{strings.NewReader(v.input)})
+				s1, s2 = "ReadBadSeeker", "manual"
+			}
+
+			var cnt int
+			var err error
+			for {
+				if _, err = tr.Next(); err != nil {
+					break
+				}
+				cnt++
+				if s2 == "manual" {
+					if _, err = tr.writeTo(io.Discard); err != nil {
+						break
+					}
+				}
+			}
+			if err != v.err {
+				t.Errorf("test %d, NewReader(%s) with %s discard: got %v, want %v",
+					i, s1, s2, err, v.err)
+			}
+			if cnt != v.cnt {
+				t.Errorf("test %d, NewReader(%s) with %s discard: got %d headers, want %d headers",
+					i, s1, s2, cnt, v.cnt)
+			}
+		}
+	}
+}
+
+// TestReadHeaderOnly tests that Reader does not attempt to read special
+// header-only files.
+func TestReadHeaderOnly(t *testing.T) {
+	f, err := os.Open("testdata/hdr-only.tar")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer f.Close()
+
+	var hdrs []*Header
+	tr := NewReader(f)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Errorf("Next(): got %v, want %v", err, nil)
+			continue
+		}
+		hdrs = append(hdrs, hdr)
+
+		// If a special flag, we should read nothing.
+		cnt, _ := io.ReadFull(tr, []byte{0})
+		if cnt > 0 && hdr.Typeflag != TypeReg {
+			t.Errorf("ReadFull(...): got %d bytes, want 0 bytes", cnt)
+		}
+	}
+
+	// File is crafted with 16 entries. The later 8 are identical to the first
+	// 8 except that the size is set.
+	if len(hdrs) != 16 {
+		t.Fatalf("len(hdrs): got %d, want %d", len(hdrs), 16)
+	}
+	for i := 0; i < 8; i++ {
+		hdr1, hdr2 := hdrs[i+0], hdrs[i+8]
+		hdr1.Size, hdr2.Size = 0, 0
+		if !reflect.DeepEqual(*hdr1, *hdr2) {
+			t.Errorf("incorrect header:\ngot  %+v\nwant %+v", *hdr1, *hdr2)
+		}
+	}
+}
+
+func TestMergePAX(t *testing.T) {
+	vectors := []struct {
+		in   map[string]string
+		want *Header
+		ok   bool
+	}{{
+		in: map[string]string{
+			"path":  "a/b/c",
+			"uid":   "1000",
+			"mtime": "1350244992.023960108",
+		},
+		want: &Header{
+			Name:    "a/b/c",
+			Uid:     1000,
+			ModTime: time.Unix(1350244992, 23960108),
+			PAXRecords: map[string]string{
+				"path":  "a/b/c",
+				"uid":   "1000",
+				"mtime": "1350244992.023960108",
+			},
+		},
+		ok: true,
+	}, {
+		in: map[string]string{
+			"gid": "gtgergergersagersgers",
+		},
+		ok: false,
+	}, {
+		in: map[string]string{
+			"missing":          "missing",
+			"SCHILY.xattr.key": "value",
+		},
+		want: &Header{
+			Xattrs: map[string]string{"key": "value"},
+			PAXRecords: map[string]string{
+				"missing":          "missing",
+				"SCHILY.xattr.key": "value",
+			},
+		},
+		ok: true,
+	}}
+
+	for i, v := range vectors {
+		got := new(Header)
+		err := mergePAX(got, v.in)
+		if v.ok && !reflect.DeepEqual(*got, *v.want) {
+			t.Errorf("test %d, mergePAX(...):\ngot  %+v\nwant %+v", i, *got, *v.want)
+		}
+		if ok := err == nil; ok != v.ok {
+			t.Errorf("test %d, mergePAX(...): got %v, want %v", i, ok, v.ok)
+		}
+	}
+}
+
+func TestParsePAX(t *testing.T) {
+	vectors := []struct {
+		in   string
+		want map[string]string
+		ok   bool
+	}{
+		{"", nil, true},
+		{"6 k=1\n", map[string]string{"k": "1"}, true},
+		{"10 a=name\n", map[string]string{"a": "name"}, true},
+		{"9 a=name\n", map[string]string{"a": "name"}, true},
+		{"30 mtime=1350244992.023960108\n", map[string]string{"mtime": "1350244992.023960108"}, true},
+		{"3 somelongkey=\n", nil, false},
+		{"50 tooshort=\n", nil, false},
+		{"13 key1=haha\n13 key2=nana\n13 key3=kaka\n",
+			map[string]string{"key1": "haha", "key2": "nana", "key3": "kaka"}, true},
+		{"13 key1=val1\n13 key2=val2\n8 key1=\n",
+			map[string]string{"key1": "", "key2": "val2"}, true},
+		{"22 GNU.sparse.size=10\n26 GNU.sparse.numblocks=2\n" +
+			"23 GNU.sparse.offset=1\n25 GNU.sparse.numbytes=2\n" +
+			"23 GNU.sparse.offset=3\n25 GNU.sparse.numbytes=4\n",
+			map[string]string{paxGNUSparseSize: "10", paxGNUSparseNumBlocks: "2", paxGNUSparseMap: "1,2,3,4"}, true},
+		{"22 GNU.sparse.size=10\n26 GNU.sparse.numblocks=1\n" +
+			"25 GNU.sparse.numbytes=2\n23 GNU.sparse.offset=1\n",
+			nil, false},
+		{"22 GNU.sparse.size=10\n26 GNU.sparse.numblocks=1\n" +
+			"25 GNU.sparse.offset=1,2\n25 GNU.sparse.numbytes=2\n",
+			nil, false},
+	}
+
+	for i, v := range vectors {
+		r := strings.NewReader(v.in)
+		got, err := parsePAX(r)
+		if !reflect.DeepEqual(got, v.want) && !(len(got) == 0 && len(v.want) == 0) {
+			t.Errorf("test %d, parsePAX():\ngot  %v\nwant %v", i, got, v.want)
+		}
+		if ok := err == nil; ok != v.ok {
+			t.Errorf("test %d, parsePAX(): got %v, want %v", i, ok, v.ok)
+		}
+	}
+}
+
+func TestReadOldGNUSparseMap(t *testing.T) {
+	populateSparseMap := func(sa sparseArray, sps []string) []string {
+		for i := 0; len(sps) > 0 && i < sa.MaxEntries(); i++ {
+			copy(sa.Entry(i), sps[0])
+			sps = sps[1:]
+		}
+		if len(sps) > 0 {
+			copy(sa.IsExtended(), "\x80")
+		}
+		return sps
+	}
+
+	makeInput := func(format Format, size string, sps ...string) (out []byte) {
+		// Write the initial GNU header.
+		var blk block
+		gnu := blk.GNU()
+		sparse := gnu.Sparse()
+		copy(gnu.RealSize(), size)
+		sps = populateSparseMap(sparse, sps)
+		if format != FormatUnknown {
+			blk.SetFormat(format)
+		}
+		out = append(out, blk[:]...)
+
+		// Write extended sparse blocks.
+		for len(sps) > 0 {
+			var blk block
+			sps = populateSparseMap(blk.Sparse(), sps)
+			out = append(out, blk[:]...)
+		}
+		return out
+	}
+
+	makeSparseStrings := func(sp []sparseEntry) (out []string) {
+		var f formatter
+		for _, s := range sp {
+			var b [24]byte
+			f.formatNumeric(b[:12], s.Offset)
+			f.formatNumeric(b[12:], s.Length)
+			out = append(out, string(b[:]))
+		}
+		return out
+	}
+
+	vectors := []struct {
+		input    []byte
+		wantMap  sparseDatas
+		wantSize int64
+		wantErr  error
+	}{{
+		input:   makeInput(FormatUnknown, ""),
+		wantErr: ErrHeader,
+	}, {
+		input:    makeInput(FormatGNU, "1234", "fewa"),
+		wantSize: 01234,
+		wantErr:  ErrHeader,
+	}, {
+		input:    makeInput(FormatGNU, "0031"),
+		wantSize: 031,
+	}, {
+		input:   makeInput(FormatGNU, "80"),
+		wantErr: ErrHeader,
+	}, {
+		input: makeInput(FormatGNU, "1234",
+			makeSparseStrings(sparseDatas{{0, 0}, {1, 1}})...),
+		wantMap:  sparseDatas{{0, 0}, {1, 1}},
+		wantSize: 01234,
+	}, {
+		input: makeInput(FormatGNU, "1234",
+			append(makeSparseStrings(sparseDatas{{0, 0}, {1, 1}}), []string{"", "blah"}...)...),
+		wantMap:  sparseDatas{{0, 0}, {1, 1}},
+		wantSize: 01234,
+	}, {
+		input: makeInput(FormatGNU, "3333",
+			makeSparseStrings(sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}})...),
+		wantMap:  sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}},
+		wantSize: 03333,
+	}, {
+		input: makeInput(FormatGNU, "",
+			append(append(
+				makeSparseStrings(sparseDatas{{0, 1}, {2, 1}}),
+				[]string{"", ""}...),
+				makeSparseStrings(sparseDatas{{4, 1}, {6, 1}})...)...),
+		wantMap: sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}},
+	}, {
+		input: makeInput(FormatGNU, "",
+			makeSparseStrings(sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}, {8, 1}, {10, 1}})...)[:blockSize],
+		wantErr: io.ErrUnexpectedEOF,
+	}, {
+		input: makeInput(FormatGNU, "",
+			makeSparseStrings(sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}, {8, 1}, {10, 1}})...)[:3*blockSize/2],
+		wantErr: io.ErrUnexpectedEOF,
+	}, {
+		input: makeInput(FormatGNU, "",
+			makeSparseStrings(sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}, {8, 1}, {10, 1}})...),
+		wantMap: sparseDatas{{0, 1}, {2, 1}, {4, 1}, {6, 1}, {8, 1}, {10, 1}},
+	}, {
+		input: makeInput(FormatGNU, "",
+			makeSparseStrings(sparseDatas{{10 << 30, 512}, {20 << 30, 512}})...),
+		wantMap: sparseDatas{{10 << 30, 512}, {20 << 30, 512}},
+	}}
+
+	for i, v := range vectors {
+		var blk block
+		var hdr Header
+		v.input = v.input[copy(blk[:], v.input):]
+		tr := Reader{r: bytes.NewReader(v.input)}
+		got, err := tr.readOldGNUSparseMap(&hdr, &blk)
+		if !equalSparseEntries(got, v.wantMap) {
+			t.Errorf("test %d, readOldGNUSparseMap(): got %v, want %v", i, got, v.wantMap)
+		}
+		if err != v.wantErr {
+			t.Errorf("test %d, readOldGNUSparseMap() = %v, want %v", i, err, v.wantErr)
+		}
+		if hdr.Size != v.wantSize {
+			t.Errorf("test %d, Header.Size = %d, want %d", i, hdr.Size, v.wantSize)
+		}
+	}
+}
+
+func TestReadGNUSparsePAXHeaders(t *testing.T) {
+	padInput := func(s string) string {
+		return s + string(zeroBlock[:blockPadding(int64(len(s)))])
+	}
+
+	vectors := []struct {
+		inputData string
+		inputHdrs map[string]string
+		wantMap   sparseDatas
+		wantSize  int64
+		wantName  string
+		wantErr   error
+	}{{
+		inputHdrs: nil,
+		wantErr:   nil,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: strconv.FormatInt(math.MaxInt64, 10),
+			paxGNUSparseMap:       "0,1,2,3",
+		},
+		wantErr: ErrHeader,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "4\x00",
+			paxGNUSparseMap:       "0,1,2,3",
+		},
+		wantErr: ErrHeader,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "4",
+			paxGNUSparseMap:       "0,1,2,3",
+		},
+		wantErr: ErrHeader,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "2",
+			paxGNUSparseMap:       "0,1,2,3",
+		},
+		wantMap: sparseDatas{{0, 1}, {2, 3}},
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "2",
+			paxGNUSparseMap:       "0, 1,2,3",
+		},
+		wantErr: ErrHeader,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "2",
+			paxGNUSparseMap:       "0,1,02,3",
+			paxGNUSparseRealSize:  "4321",
+		},
+		wantMap:  sparseDatas{{0, 1}, {2, 3}},
+		wantSize: 4321,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseNumBlocks: "2",
+			paxGNUSparseMap:       "0,one1,2,3",
+		},
+		wantErr: ErrHeader,
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseMajor:     "0",
+			paxGNUSparseMinor:     "0",
+			paxGNUSparseNumBlocks: "2",
+			paxGNUSparseMap:       "0,1,2,3",
+			paxGNUSparseSize:      "1234",
+			paxGNUSparseRealSize:  "4321",
+			paxGNUSparseName:      "realname",
+		},
+		wantMap:  sparseDatas{{0, 1}, {2, 3}},
+		wantSize: 1234,
+		wantName: "realname",
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseMajor:     "0",
+			paxGNUSparseMinor:     "0",
+			paxGNUSparseNumBlocks: "1",
+			paxGNUSparseMap:       "10737418240,512",
+			paxGNUSparseSize:      "10737418240",
+			paxGNUSparseName:      "realname",
+		},
+		wantMap:  sparseDatas{{10737418240, 512}},
+		wantSize: 10737418240,
+		wantName: "realname",
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseMajor:     "0",
+			paxGNUSparseMinor:     "0",
+			paxGNUSparseNumBlocks: "0",
+			paxGNUSparseMap:       "",
+		},
+		wantMap: sparseDatas{},
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseMajor:     "0",
+			paxGNUSparseMinor:     "1",
+			paxGNUSparseNumBlocks: "4",
+			paxGNUSparseMap:       "0,5,10,5,20,5,30,5",
+		},
+		wantMap: sparseDatas{{0, 5}, {10, 5}, {20, 5}, {30, 5}},
+	}, {
+		inputHdrs: map[string]string{
+			paxGNUSparseMajor:     "1",
+			paxGNUSparseMinor:     "0",
+			paxGNUSparseNumBlocks: "4",
+			paxGNUSparseMap:       "0,5,10,5,20,5,30,5",
+		},
+		wantErr: io.ErrUnexpectedEOF,
+	}, {
+		inputData: padInput("0\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{},
+	}, {
+		inputData: padInput("0\n")[:blockSize-1] + "#",
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{},
+	}, {
+		inputData: padInput("0"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   io.ErrUnexpectedEOF,
+	}, {
+		inputData: padInput("ab\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   ErrHeader,
+	}, {
+		inputData: padInput("1\n2\n3\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{{2, 3}},
+	}, {
+		inputData: padInput("1\n2\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   io.ErrUnexpectedEOF,
+	}, {
+		inputData: padInput("1\n2\n\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   ErrHeader,
+	}, {
+		inputData: string(zeroBlock[:]) + padInput("0\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   ErrHeader,
+	}, {
+		inputData: strings.Repeat("0", blockSize) + padInput("1\n5\n1\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{{5, 1}},
+	}, {
+		inputData: padInput(fmt.Sprintf("%d\n", int64(math.MaxInt64))),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantErr:   ErrHeader,
+	}, {
+		inputData: padInput(strings.Repeat("0", 300) + "1\n" + strings.Repeat("0", 1000) + "5\n" + strings.Repeat("0", 800) + "2\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{{5, 2}},
+	}, {
+		inputData: padInput("2\n10737418240\n512\n21474836480\n512\n"),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap:   sparseDatas{{10737418240, 512}, {21474836480, 512}},
+	}, {
+		inputData: padInput("100\n" + func() string {
+			var ss []string
+			for i := 0; i < 100; i++ {
+				ss = append(ss, fmt.Sprintf("%d\n%d\n", int64(i)<<30, 512))
+			}
+			return strings.Join(ss, "")
+		}()),
+		inputHdrs: map[string]string{paxGNUSparseMajor: "1", paxGNUSparseMinor: "0"},
+		wantMap: func() (spd sparseDatas) {
+			for i := 0; i < 100; i++ {
+				spd = append(spd, sparseEntry{int64(i) << 30, 512})
+			}
+			return spd
+		}(),
+	}}
+
+	for i, v := range vectors {
+		var hdr Header
+		hdr.PAXRecords = v.inputHdrs
+		r := strings.NewReader(v.inputData + "#") // Add canary byte
+		tr := Reader{curr: &regFileReader{r, int64(r.Len())}}
+		got, err := tr.readGNUSparsePAXHeaders(&hdr)
+		if !equalSparseEntries(got, v.wantMap) {
+			t.Errorf("test %d, readGNUSparsePAXHeaders(): got %v, want %v", i, got, v.wantMap)
+		}
+		if err != v.wantErr {
+			t.Errorf("test %d, readGNUSparsePAXHeaders() = %v, want %v", i, err, v.wantErr)
+		}
+		if hdr.Size != v.wantSize {
+			t.Errorf("test %d, Header.Size = %d, want %d", i, hdr.Size, v.wantSize)
+		}
+		if hdr.Name != v.wantName {
+			t.Errorf("test %d, Header.Name = %s, want %s", i, hdr.Name, v.wantName)
+		}
+		if v.wantErr == nil && r.Len() == 0 {
+			t.Errorf("test %d, canary byte unexpectedly consumed", i)
+		}
+	}
+}
+
+// testNonEmptyReader wraps an io.Reader and ensures that
+// Read is never called with an empty buffer.
+type testNonEmptyReader struct{ io.Reader }
+
+func (r testNonEmptyReader) Read(b []byte) (int, error) {
+	if len(b) == 0 {
+		return 0, errors.New("unexpected empty Read call")
+	}
+	return r.Reader.Read(b)
+}
+
+func TestFileReader(t *testing.T) {
+	type (
+		testRead struct { // Read(cnt) == (wantStr, wantErr)
+			cnt     int
+			wantStr string
+			wantErr error
+		}
+		testWriteTo struct { // WriteTo(testFile{ops}) == (wantCnt, wantErr)
+			ops     fileOps
+			wantCnt int64
+			wantErr error
+		}
+		testRemaining struct { // LogicalRemaining() == wantLCnt, PhysicalRemaining() == wantPCnt
+			wantLCnt int64
+			wantPCnt int64
+		}
+		testFnc interface{} // testRead | testWriteTo | testRemaining
+	)
+
+	type (
+		makeReg struct {
+			str  string
+			size int64
+		}
+		makeSparse struct {
+			makeReg makeReg
+			spd     sparseDatas
+			size    int64
+		}
+		fileMaker interface{} // makeReg | makeSparse
+	)
+
+	vectors := []struct {
+		maker fileMaker
+		tests []testFnc
+	}{{
+		maker: makeReg{"", 0},
+		tests: []testFnc{
+			testRemaining{0, 0},
+			testRead{0, "", io.EOF},
+			testRead{1, "", io.EOF},
+			testWriteTo{nil, 0, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{"", 1},
+		tests: []testFnc{
+			testRemaining{1, 1},
+			testRead{5, "", io.ErrUnexpectedEOF},
+			testWriteTo{nil, 0, io.ErrUnexpectedEOF},
+			testRemaining{1, 1},
+		},
+	}, {
+		maker: makeReg{"hello", 5},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testRead{5, "hello", io.EOF},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{"hello, world", 50},
+		tests: []testFnc{
+			testRemaining{50, 50},
+			testRead{7, "hello, ", nil},
+			testRemaining{43, 43},
+			testRead{5, "world", nil},
+			testRemaining{38, 38},
+			testWriteTo{nil, 0, io.ErrUnexpectedEOF},
+			testRead{1, "", io.ErrUnexpectedEOF},
+			testRemaining{38, 38},
+		},
+	}, {
+		maker: makeReg{"hello, world", 5},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testRead{0, "", nil},
+			testRead{4, "hell", nil},
+			testRemaining{1, 1},
+			testWriteTo{fileOps{"o"}, 1, nil},
+			testRemaining{0, 0},
+			testWriteTo{nil, 0, nil},
+			testRead{0, "", io.EOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{0, 2}, {5, 3}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testRead{3, "ab\x00", nil},
+			testRead{10, "\x00\x00cde", io.EOF},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{0, 2}, {5, 3}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testWriteTo{fileOps{"ab", int64(3), "cde"}, 8, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{0, 2}, {5, 3}}, 10},
+		tests: []testFnc{
+			testRemaining{10, 5},
+			testRead{100, "ab\x00\x00\x00cde\x00\x00", io.EOF},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abc", 5}, sparseDatas{{0, 2}, {5, 3}}, 10},
+		tests: []testFnc{
+			testRemaining{10, 5},
+			testRead{100, "ab\x00\x00\x00c", io.ErrUnexpectedEOF},
+			testRemaining{4, 2},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 2}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testRead{8, "\x00abc\x00\x00de", io.EOF},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 0}, {6, 0}, {6, 2}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testRead{8, "\x00abc\x00\x00de", io.EOF},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 0}, {6, 0}, {6, 2}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testWriteTo{fileOps{int64(1), "abc", int64(2), "de"}, 8, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 2}}, 10},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00de\x00\x00", io.EOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 2}}, 10},
+		tests: []testFnc{
+			testWriteTo{fileOps{int64(1), "abc", int64(2), "de", int64(1), "\x00"}, 10, nil},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 2}, {8, 0}, {8, 0}, {8, 0}, {8, 0}}, 10},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00de\x00\x00", io.EOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"", 0}, sparseDatas{}, 2},
+		tests: []testFnc{
+			testRead{100, "\x00\x00", io.EOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"", 8}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00", io.ErrUnexpectedEOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"ab", 2}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00ab", errMissData},
+		},
+	}, {
+		maker: makeSparse{makeReg{"ab", 8}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00ab", io.ErrUnexpectedEOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abc", 3}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00", errMissData},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abc", 8}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00", io.ErrUnexpectedEOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00de", errMissData},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 5}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testWriteTo{fileOps{int64(1), "abc", int64(2), "de"}, 8, errMissData},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcde", 8}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRead{100, "\x00abc\x00\x00de", io.ErrUnexpectedEOF},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcdefghEXTRA", 13}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRemaining{15, 13},
+			testRead{100, "\x00abc\x00\x00defgh\x00\x00\x00\x00", errUnrefData},
+			testWriteTo{nil, 0, errUnrefData},
+			testRemaining{0, 5},
+		},
+	}, {
+		maker: makeSparse{makeReg{"abcdefghEXTRA", 13}, sparseDatas{{1, 3}, {6, 5}}, 15},
+		tests: []testFnc{
+			testRemaining{15, 13},
+			testWriteTo{fileOps{int64(1), "abc", int64(2), "defgh", int64(4)}, 15, errUnrefData},
+			testRead{100, "", errUnrefData},
+			testRemaining{0, 5},
+		},
+	}}
+
+	for i, v := range vectors {
+		var fr fileReader
+		switch maker := v.maker.(type) {
+		case makeReg:
+			r := testNonEmptyReader{strings.NewReader(maker.str)}
+			fr = &regFileReader{r, maker.size}
+		case makeSparse:
+			if !validateSparseEntries(maker.spd, maker.size) {
+				t.Fatalf("invalid sparse map: %v", maker.spd)
+			}
+			sph := invertSparseEntries(maker.spd, maker.size)
+			r := testNonEmptyReader{strings.NewReader(maker.makeReg.str)}
+			fr = &regFileReader{r, maker.makeReg.size}
+			fr = &sparseFileReader{fr, sph, 0}
+		default:
+			t.Fatalf("test %d, unknown make operation: %T", i, maker)
+		}
+
+		for j, tf := range v.tests {
+			switch tf := tf.(type) {
+			case testRead:
+				b := make([]byte, tf.cnt)
+				n, err := fr.Read(b)
+				if got := string(b[:n]); got != tf.wantStr || err != tf.wantErr {
+					t.Errorf("test %d.%d, Read(%d):\ngot  (%q, %v)\nwant (%q, %v)", i, j, tf.cnt, got, err, tf.wantStr, tf.wantErr)
+				}
+			case testWriteTo:
+				f := &testFile{ops: tf.ops}
+				got, err := fr.WriteTo(f)
+				if _, ok := err.(testError); ok {
+					t.Errorf("test %d.%d, WriteTo(): %v", i, j, err)
+				} else if got != tf.wantCnt || err != tf.wantErr {
+					t.Errorf("test %d.%d, WriteTo() = (%d, %v), want (%d, %v)", i, j, got, err, tf.wantCnt, tf.wantErr)
+				}
+				if len(f.ops) > 0 {
+					t.Errorf("test %d.%d, expected %d more operations", i, j, len(f.ops))
+				}
+			case testRemaining:
+				if got := fr.LogicalRemaining(); got != tf.wantLCnt {
+					t.Errorf("test %d.%d, LogicalRemaining() = %d, want %d", i, j, got, tf.wantLCnt)
+				}
+				if got := fr.PhysicalRemaining(); got != tf.wantPCnt {
+					t.Errorf("test %d.%d, PhysicalRemaining() = %d, want %d", i, j, got, tf.wantPCnt)
+				}
+			default:
+				t.Fatalf("test %d.%d, unknown test operation: %T", i, j, tf)
+			}
+		}
+	}
+}
diff --git a/src/archive/tar/stat_actime1.go b/src/archive/tar/stat_actime1.go
new file mode 100644
index 0000000..1bdd1c9
--- /dev/null
+++ b/src/archive/tar/stat_actime1.go
@@ -0,0 +1,20 @@
+// Copyright 2012 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.
+
+// +build aix linux dragonfly openbsd solaris
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atim.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctim.Unix())
+}
diff --git a/src/archive/tar/stat_actime2.go b/src/archive/tar/stat_actime2.go
new file mode 100644
index 0000000..6f17dbe
--- /dev/null
+++ b/src/archive/tar/stat_actime2.go
@@ -0,0 +1,20 @@
+// Copyright 2012 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.
+
+// +build darwin freebsd netbsd
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atimespec.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctimespec.Unix())
+}
diff --git a/src/archive/tar/stat_unix.go b/src/archive/tar/stat_unix.go
new file mode 100644
index 0000000..581d87d
--- /dev/null
+++ b/src/archive/tar/stat_unix.go
@@ -0,0 +1,101 @@
+// Copyright 2012 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.
+
+// +build aix linux darwin dragonfly freebsd openbsd netbsd solaris
+
+package tar
+
+import (
+	"io/fs"
+	"os/user"
+	"runtime"
+	"strconv"
+	"sync"
+	"syscall"
+)
+
+func init() {
+	sysStat = statUnix
+}
+
+// userMap and groupMap caches UID and GID lookups for performance reasons.
+// The downside is that renaming uname or gname by the OS never takes effect.
+var userMap, groupMap sync.Map // map[int]string
+
+func statUnix(fi fs.FileInfo, h *Header) error {
+	sys, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return nil
+	}
+	h.Uid = int(sys.Uid)
+	h.Gid = int(sys.Gid)
+
+	// Best effort at populating Uname and Gname.
+	// The os/user functions may fail for any number of reasons
+	// (not implemented on that platform, cgo not enabled, etc).
+	if u, ok := userMap.Load(h.Uid); ok {
+		h.Uname = u.(string)
+	} else if u, err := user.LookupId(strconv.Itoa(h.Uid)); err == nil {
+		h.Uname = u.Username
+		userMap.Store(h.Uid, h.Uname)
+	}
+	if g, ok := groupMap.Load(h.Gid); ok {
+		h.Gname = g.(string)
+	} else if g, err := user.LookupGroupId(strconv.Itoa(h.Gid)); err == nil {
+		h.Gname = g.Name
+		groupMap.Store(h.Gid, h.Gname)
+	}
+
+	h.AccessTime = statAtime(sys)
+	h.ChangeTime = statCtime(sys)
+
+	// Best effort at populating Devmajor and Devminor.
+	if h.Typeflag == TypeChar || h.Typeflag == TypeBlock {
+		dev := uint64(sys.Rdev) // May be int32 or uint32
+		switch runtime.GOOS {
+		case "aix":
+			var major, minor uint32
+			major = uint32((dev & 0x3fffffff00000000) >> 32)
+			minor = uint32((dev & 0x00000000ffffffff) >> 0)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "linux":
+			// Copied from golang.org/x/sys/unix/dev_linux.go.
+			major := uint32((dev & 0x00000000000fff00) >> 8)
+			major |= uint32((dev & 0xfffff00000000000) >> 32)
+			minor := uint32((dev & 0x00000000000000ff) >> 0)
+			minor |= uint32((dev & 0x00000ffffff00000) >> 12)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "darwin", "ios":
+			// Copied from golang.org/x/sys/unix/dev_darwin.go.
+			major := uint32((dev >> 24) & 0xff)
+			minor := uint32(dev & 0xffffff)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "dragonfly":
+			// Copied from golang.org/x/sys/unix/dev_dragonfly.go.
+			major := uint32((dev >> 8) & 0xff)
+			minor := uint32(dev & 0xffff00ff)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "freebsd":
+			// Copied from golang.org/x/sys/unix/dev_freebsd.go.
+			major := uint32((dev >> 8) & 0xff)
+			minor := uint32(dev & 0xffff00ff)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "netbsd":
+			// Copied from golang.org/x/sys/unix/dev_netbsd.go.
+			major := uint32((dev & 0x000fff00) >> 8)
+			minor := uint32((dev & 0x000000ff) >> 0)
+			minor |= uint32((dev & 0xfff00000) >> 12)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		case "openbsd":
+			// Copied from golang.org/x/sys/unix/dev_openbsd.go.
+			major := uint32((dev & 0x0000ff00) >> 8)
+			minor := uint32((dev & 0x000000ff) >> 0)
+			minor |= uint32((dev & 0xffff0000) >> 8)
+			h.Devmajor, h.Devminor = int64(major), int64(minor)
+		default:
+			// TODO: Implement solaris (see https://golang.org/issue/8106)
+		}
+	}
+	return nil
+}
diff --git a/src/archive/tar/strconv.go b/src/archive/tar/strconv.go
new file mode 100644
index 0000000..f0b61e6
--- /dev/null
+++ b/src/archive/tar/strconv.go
@@ -0,0 +1,345 @@
+// Copyright 2016 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"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// hasNUL reports whether the NUL character exists within s.
+func hasNUL(s string) bool {
+	return strings.IndexByte(s, 0) >= 0
+}
+
+// isASCII reports whether the input is an ASCII C-style string.
+func isASCII(s string) bool {
+	for _, c := range s {
+		if c >= 0x80 || c == 0x00 {
+			return false
+		}
+	}
+	return true
+}
+
+// toASCII converts the input to an ASCII C-style string.
+// This is a best effort conversion, so invalid characters are dropped.
+func toASCII(s string) string {
+	if isASCII(s) {
+		return s
+	}
+	b := make([]byte, 0, len(s))
+	for _, c := range s {
+		if c < 0x80 && c != 0x00 {
+			b = append(b, byte(c))
+		}
+	}
+	return string(b)
+}
+
+type parser struct {
+	err error // Last error seen
+}
+
+type formatter struct {
+	err error // Last error seen
+}
+
+// parseString parses bytes as a NUL-terminated C-style string.
+// If a NUL byte is not found then the whole slice is returned as a string.
+func (*parser) parseString(b []byte) string {
+	if i := bytes.IndexByte(b, 0); i >= 0 {
+		return string(b[:i])
+	}
+	return string(b)
+}
+
+// formatString copies s into b, NUL-terminating if possible.
+func (f *formatter) formatString(b []byte, s string) {
+	if len(s) > len(b) {
+		f.err = ErrFieldTooLong
+	}
+	copy(b, s)
+	if len(s) < len(b) {
+		b[len(s)] = 0
+	}
+
+	// Some buggy readers treat regular files with a trailing slash
+	// in the V7 path field as a directory even though the full path
+	// recorded elsewhere (e.g., via PAX record) contains no trailing slash.
+	if len(s) > len(b) && b[len(b)-1] == '/' {
+		n := len(strings.TrimRight(s[:len(b)], "/"))
+		b[n] = 0 // Replace trailing slash with NUL terminator
+	}
+}
+
+// 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 {
+	binBits := uint(n-1) * 8
+	return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
+}
+
+// parseNumeric parses the input as being encoded in either base-256 or octal.
+// This function may return negative numbers.
+// If parsing fails or an integer overflow occurs, err will be set.
+func (p *parser) parseNumeric(b []byte) int64 {
+	// Check for base-256 (binary) format first.
+	// If the first bit is set, then all following bits constitute a two's
+	// complement encoded number in big-endian byte order.
+	if len(b) > 0 && b[0]&0x80 != 0 {
+		// Handling negative numbers relies on the following identity:
+		//	-a-1 == ^a
+		//
+		// If the number is negative, we use an inversion mask to invert the
+		// data bytes and treat the value as an unsigned number.
+		var inv byte // 0x00 if positive or zero, 0xff if negative
+		if b[0]&0x40 != 0 {
+			inv = 0xff
+		}
+
+		var x uint64
+		for i, c := range b {
+			c ^= inv // Inverts c only if inv is 0xff, otherwise does nothing
+			if i == 0 {
+				c &= 0x7f // Ignore signal bit in first byte
+			}
+			if (x >> 56) > 0 {
+				p.err = ErrHeader // Integer overflow
+				return 0
+			}
+			x = x<<8 | uint64(c)
+		}
+		if (x >> 63) > 0 {
+			p.err = ErrHeader // Integer overflow
+			return 0
+		}
+		if inv == 0xff {
+			return ^int64(x)
+		}
+		return int64(x)
+	}
+
+	// Normal case is base-8 (octal) format.
+	return p.parseOctal(b)
+}
+
+// formatNumeric encodes x into b using base-8 (octal) encoding if possible.
+// Otherwise it will attempt to use base-256 (binary) encoding.
+func (f *formatter) formatNumeric(b []byte, x int64) {
+	if fitsInOctal(len(b), x) {
+		f.formatOctal(b, x)
+		return
+	}
+
+	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
+}
+
+func (p *parser) parseOctal(b []byte) int64 {
+	// Because unused fields are filled with NULs, we need
+	// to skip leading NULs. Fields may also be padded with
+	// spaces or NULs.
+	// So we remove leading and trailing NULs and spaces to
+	// be sure.
+	b = bytes.Trim(b, " \x00")
+
+	if len(b) == 0 {
+		return 0
+	}
+	x, perr := strconv.ParseUint(p.parseString(b), 8, 64)
+	if perr != nil {
+		p.err = ErrHeader
+	}
+	return int64(x)
+}
+
+func (f *formatter) formatOctal(b []byte, x int64) {
+	if !fitsInOctal(len(b), x) {
+		x = 0 // Last resort, just write zero
+		f.err = ErrFieldTooLong
+	}
+
+	s := strconv.FormatInt(x, 8)
+	// Add leading zeros, but leave room for a NUL.
+	if n := len(b) - len(s) - 1; n > 0 {
+		s = strings.Repeat("0", n) + s
+	}
+	f.formatString(b, s)
+}
+
+// fitsInOctal reports whether the integer x fits in a field n-bytes long
+// using octal encoding with the appropriate NUL terminator.
+func fitsInOctal(n int, x int64) bool {
+	octBits := uint(n-1) * 3
+	return x >= 0 && (n >= 22 || x < 1<<octBits)
+}
+
+// parsePAXTime takes a string of the form %d.%d as described in the PAX
+// specification. Note that this implementation allows for negative timestamps,
+// which is allowed for by the PAX specification, but not always portable.
+func parsePAXTime(s string) (time.Time, error) {
+	const maxNanoSecondDigits = 9
+
+	// Split string into seconds and sub-seconds parts.
+	ss, sn := s, ""
+	if pos := strings.IndexByte(s, '.'); pos >= 0 {
+		ss, sn = s[:pos], s[pos+1:]
+	}
+
+	// Parse the seconds.
+	secs, err := strconv.ParseInt(ss, 10, 64)
+	if err != nil {
+		return time.Time{}, ErrHeader
+	}
+	if len(sn) == 0 {
+		return time.Unix(secs, 0), nil // No sub-second values
+	}
+
+	// Parse the nanoseconds.
+	if strings.Trim(sn, "0123456789") != "" {
+		return time.Time{}, ErrHeader
+	}
+	if len(sn) < maxNanoSecondDigits {
+		sn += strings.Repeat("0", maxNanoSecondDigits-len(sn)) // Right pad
+	} else {
+		sn = sn[:maxNanoSecondDigits] // Right truncate
+	}
+	nsecs, _ := strconv.ParseInt(sn, 10, 64) // Must succeed
+	if len(ss) > 0 && ss[0] == '-' {
+		return time.Unix(secs, -1*nsecs), nil // Negative correction
+	}
+	return time.Unix(secs, nsecs), nil
+}
+
+// formatPAXTime converts ts into a time of the form %d.%d as described in the
+// PAX specification. This function is capable of negative timestamps.
+func formatPAXTime(ts time.Time) (s string) {
+	secs, nsecs := ts.Unix(), ts.Nanosecond()
+	if nsecs == 0 {
+		return strconv.FormatInt(secs, 10)
+	}
+
+	// If seconds is negative, then perform correction.
+	sign := ""
+	if secs < 0 {
+		sign = "-"             // Remember sign
+		secs = -(secs + 1)     // Add a second to secs
+		nsecs = -(nsecs - 1e9) // Take that second away from nsecs
+	}
+	return strings.TrimRight(fmt.Sprintf("%s%d.%09d", sign, secs, nsecs), "0")
+}
+
+// parsePAXRecord parses the input PAX record string into a key-value pair.
+// If parsing is successful, it will slice off the currently read record and
+// return the remainder as r.
+func parsePAXRecord(s string) (k, v, r string, err error) {
+	// The size field ends at the first space.
+	sp := strings.IndexByte(s, ' ')
+	if sp == -1 {
+		return "", "", s, ErrHeader
+	}
+
+	// Parse the first token as a decimal integer.
+	n, perr := strconv.ParseInt(s[:sp], 10, 0) // Intentionally parse as native int
+	if perr != nil || n < 5 || int64(len(s)) < n {
+		return "", "", s, ErrHeader
+	}
+
+	afterSpace := int64(sp + 1)
+	beforeLastNewLine := n - 1
+	// In some cases, "length" was perhaps padded/malformed, and
+	// trying to index past where the space supposedly is goes past
+	// the end of the actual record.
+	// For example:
+	//    "0000000000000000000000000000000030 mtime=1432668921.098285006\n30 ctime=2147483649.15163319"
+	//                                  ^     ^
+	//                                  |     |
+	//                                  |  afterSpace=35
+	//                                  |
+	//                          beforeLastNewLine=29
+	// yet indexOf(firstSpace) MUST BE before endOfRecord.
+	//
+	// See https://golang.org/issues/40196.
+	if afterSpace >= beforeLastNewLine {
+		return "", "", s, ErrHeader
+	}
+
+	// Extract everything between the space and the final newline.
+	rec, nl, rem := s[afterSpace:beforeLastNewLine], s[beforeLastNewLine:n], s[n:]
+	if nl != "\n" {
+		return "", "", s, ErrHeader
+	}
+
+	// The first equals separates the key from the value.
+	eq := strings.IndexByte(rec, '=')
+	if eq == -1 {
+		return "", "", s, ErrHeader
+	}
+	k, v = rec[:eq], rec[eq+1:]
+
+	if !validPAXRecord(k, v) {
+		return "", "", s, ErrHeader
+	}
+	return k, v, rem, nil
+}
+
+// formatPAXRecord formats a single PAX record, prefixing it with the
+// appropriate length.
+func formatPAXRecord(k, v string) (string, error) {
+	if !validPAXRecord(k, v) {
+		return "", ErrHeader
+	}
+
+	const padding = 3 // Extra padding for ' ', '=', and '\n'
+	size := len(k) + len(v) + padding
+	size += len(strconv.Itoa(size))
+	record := strconv.Itoa(size) + " " + k + "=" + v + "\n"
+
+	// Final adjustment if adding size field increased the record size.
+	if len(record) != size {
+		size = len(record)
+		record = strconv.Itoa(size) + " " + k + "=" + v + "\n"
+	}
+	return record, nil
+}
+
+// validPAXRecord reports whether the key-value pair is valid where each
+// record is formatted as:
+//	"%d %s=%s\n" % (size, key, value)
+//
+// Keys and values should be UTF-8, but the number of bad writers out there
+// forces us to be a more liberal.
+// Thus, we only reject all keys with NUL, and only reject NULs in values
+// for the PAX version of the USTAR string fields.
+// The key must not contain an '=' character.
+func validPAXRecord(k, v string) bool {
+	if k == "" || strings.IndexByte(k, '=') >= 0 {
+		return false
+	}
+	switch k {
+	case paxPath, paxLinkpath, paxUname, paxGname:
+		return !hasNUL(v)
+	default:
+		return !hasNUL(k)
+	}
+}
diff --git a/src/archive/tar/strconv_test.go b/src/archive/tar/strconv_test.go
new file mode 100644
index 0000000..add65e2
--- /dev/null
+++ b/src/archive/tar/strconv_test.go
@@ -0,0 +1,441 @@
+// Copyright 2016 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 (
+	"math"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestFitsInBase256(t *testing.T) {
+	vectors := []struct {
+		in    int64
+		width int
+		ok    bool
+	}{
+		{+1, 8, true},
+		{0, 8, true},
+		{-1, 8, true},
+		{1 << 56, 8, false},
+		{(1 << 56) - 1, 8, true},
+		{-1 << 56, 8, true},
+		{(-1 << 56) - 1, 8, false},
+		{121654, 8, true},
+		{-9849849, 8, true},
+		{math.MaxInt64, 9, true},
+		{0, 9, true},
+		{math.MinInt64, 9, true},
+		{math.MaxInt64, 12, true},
+		{0, 12, true},
+		{math.MinInt64, 12, true},
+	}
+
+	for _, v := range vectors {
+		ok := fitsInBase256(v.width, v.in)
+		if ok != v.ok {
+			t.Errorf("fitsInBase256(%d, %d): got %v, want %v", v.in, v.width, ok, v.ok)
+		}
+	}
+}
+
+func TestParseNumeric(t *testing.T) {
+	vectors := []struct {
+		in   string
+		want int64
+		ok   bool
+	}{
+		// Test base-256 (binary) encoded values.
+		{"", 0, true},
+		{"\x80", 0, true},
+		{"\x80\x00", 0, true},
+		{"\x80\x00\x00", 0, true},
+		{"\xbf", (1 << 6) - 1, true},
+		{"\xbf\xff", (1 << 14) - 1, true},
+		{"\xbf\xff\xff", (1 << 22) - 1, true},
+		{"\xff", -1, true},
+		{"\xff\xff", -1, true},
+		{"\xff\xff\xff", -1, true},
+		{"\xc0", -1 * (1 << 6), true},
+		{"\xc0\x00", -1 * (1 << 14), true},
+		{"\xc0\x00\x00", -1 * (1 << 22), true},
+		{"\x87\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
+		{"\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
+		{"\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
+		{"\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
+		{"\x80\x7f\xff\xff\xff\xff\xff\xff\xff", math.MaxInt64, true},
+		{"\x80\x80\x00\x00\x00\x00\x00\x00\x00", 0, false},
+		{"\xff\x80\x00\x00\x00\x00\x00\x00\x00", math.MinInt64, true},
+		{"\xff\x7f\xff\xff\xff\xff\xff\xff\xff", 0, false},
+		{"\xf5\xec\xd1\xc7\x7e\x5f\x26\x48\x81\x9f\x8f\x9b", 0, false},
+
+		// Test base-8 (octal) encoded values.
+		{"0000000\x00", 0, true},
+		{" \x0000000\x00", 0, true},
+		{" \x0000003\x00", 3, true},
+		{"00000000227\x00", 0227, true},
+		{"032033\x00 ", 032033, true},
+		{"320330\x00 ", 0320330, true},
+		{"0000660\x00 ", 0660, true},
+		{"\x00 0000660\x00 ", 0660, true},
+		{"0123456789abcdef", 0, false},
+		{"0123456789\x00abcdef", 0, false},
+		{"01234567\x0089abcdef", 342391, true},
+		{"0123\x7e\x5f\x264123", 0, false},
+	}
+
+	for _, v := range vectors {
+		var p parser
+		got := p.parseNumeric([]byte(v.in))
+		ok := (p.err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("parseNumeric(%q): got parsing failure, want success", v.in)
+			} else {
+				t.Errorf("parseNumeric(%q): got parsing success, want failure", v.in)
+			}
+		}
+		if ok && got != v.want {
+			t.Errorf("parseNumeric(%q): got %d, want %d", v.in, got, v.want)
+		}
+	}
+}
+
+func TestFormatNumeric(t *testing.T) {
+	vectors := []struct {
+		in   int64
+		want string
+		ok   bool
+	}{
+		// Test base-8 (octal) encoded values.
+		{0, "0\x00", true},
+		{7, "7\x00", true},
+		{8, "\x80\x08", true},
+		{077, "77\x00", true},
+		{0100, "\x80\x00\x40", true},
+		{0, "0000000\x00", true},
+		{0123, "0000123\x00", true},
+		{07654321, "7654321\x00", true},
+		{07777777, "7777777\x00", true},
+		{010000000, "\x80\x00\x00\x00\x00\x20\x00\x00", true},
+		{0, "00000000000\x00", true},
+		{000001234567, "00001234567\x00", true},
+		{076543210321, "76543210321\x00", true},
+		{012345670123, "12345670123\x00", true},
+		{077777777777, "77777777777\x00", true},
+		{0100000000000, "\x80\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00", true},
+		{math.MaxInt64, "777777777777777777777\x00", true},
+
+		// Test base-256 (binary) encoded values.
+		{-1, "\xff", true},
+		{-1, "\xff\xff", true},
+		{-1, "\xff\xff\xff", true},
+		{(1 << 0), "0", false},
+		{(1 << 8) - 1, "\x80\xff", true},
+		{(1 << 8), "0\x00", false},
+		{(1 << 16) - 1, "\x80\xff\xff", true},
+		{(1 << 16), "00\x00", false},
+		{-1 * (1 << 0), "\xff", true},
+		{-1*(1<<0) - 1, "0", false},
+		{-1 * (1 << 8), "\xff\x00", true},
+		{-1*(1<<8) - 1, "0\x00", false},
+		{-1 * (1 << 16), "\xff\x00\x00", true},
+		{-1*(1<<16) - 1, "00\x00", false},
+		{537795476381659745, "0000000\x00", false},
+		{537795476381659745, "\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", true},
+		{-615126028225187231, "0000000\x00", false},
+		{-615126028225187231, "\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", true},
+		{math.MaxInt64, "0000000\x00", false},
+		{math.MaxInt64, "\x80\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff", true},
+		{math.MinInt64, "0000000\x00", false},
+		{math.MinInt64, "\xff\xff\xff\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
+		{math.MaxInt64, "\x80\x7f\xff\xff\xff\xff\xff\xff\xff", true},
+		{math.MinInt64, "\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
+	}
+
+	for _, v := range vectors {
+		var f formatter
+		got := make([]byte, len(v.want))
+		f.formatNumeric(got, v.in)
+		ok := (f.err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("formatNumeric(%d): got formatting failure, want success", v.in)
+			} else {
+				t.Errorf("formatNumeric(%d): got formatting success, want failure", v.in)
+			}
+		}
+		if string(got) != v.want {
+			t.Errorf("formatNumeric(%d): got %q, want %q", v.in, got, v.want)
+		}
+	}
+}
+
+func TestFitsInOctal(t *testing.T) {
+	vectors := []struct {
+		input int64
+		width int
+		ok    bool
+	}{
+		{-1, 1, false},
+		{-1, 2, false},
+		{-1, 3, false},
+		{0, 1, true},
+		{0 + 1, 1, false},
+		{0, 2, true},
+		{07, 2, true},
+		{07 + 1, 2, false},
+		{0, 4, true},
+		{0777, 4, true},
+		{0777 + 1, 4, false},
+		{0, 8, true},
+		{07777777, 8, true},
+		{07777777 + 1, 8, false},
+		{0, 12, true},
+		{077777777777, 12, true},
+		{077777777777 + 1, 12, false},
+		{math.MaxInt64, 22, true},
+		{012345670123, 12, true},
+		{01564164, 12, true},
+		{-012345670123, 12, false},
+		{-01564164, 12, false},
+		{-1564164, 30, false},
+	}
+
+	for _, v := range vectors {
+		ok := fitsInOctal(v.width, v.input)
+		if ok != v.ok {
+			t.Errorf("checkOctal(%d, %d): got %v, want %v", v.input, v.width, ok, v.ok)
+		}
+	}
+}
+
+func TestParsePAXTime(t *testing.T) {
+	vectors := []struct {
+		in   string
+		want time.Time
+		ok   bool
+	}{
+		{"1350244992.023960108", time.Unix(1350244992, 23960108), true},
+		{"1350244992.02396010", time.Unix(1350244992, 23960100), true},
+		{"1350244992.0239601089", time.Unix(1350244992, 23960108), true},
+		{"1350244992.3", time.Unix(1350244992, 300000000), true},
+		{"1350244992", time.Unix(1350244992, 0), true},
+		{"-1.000000001", time.Unix(-1, -1e0+0e0), true},
+		{"-1.000001", time.Unix(-1, -1e3+0e0), true},
+		{"-1.001000", time.Unix(-1, -1e6+0e0), true},
+		{"-1", time.Unix(-1, -0e0+0e0), true},
+		{"-1.999000", time.Unix(-1, -1e9+1e6), true},
+		{"-1.999999", time.Unix(-1, -1e9+1e3), true},
+		{"-1.999999999", time.Unix(-1, -1e9+1e0), true},
+		{"0.000000001", time.Unix(0, 1e0+0e0), true},
+		{"0.000001", time.Unix(0, 1e3+0e0), true},
+		{"0.001000", time.Unix(0, 1e6+0e0), true},
+		{"0", time.Unix(0, 0e0), true},
+		{"0.999000", time.Unix(0, 1e9-1e6), true},
+		{"0.999999", time.Unix(0, 1e9-1e3), true},
+		{"0.999999999", time.Unix(0, 1e9-1e0), true},
+		{"1.000000001", time.Unix(+1, +1e0-0e0), true},
+		{"1.000001", time.Unix(+1, +1e3-0e0), true},
+		{"1.001000", time.Unix(+1, +1e6-0e0), true},
+		{"1", time.Unix(+1, +0e0-0e0), true},
+		{"1.999000", time.Unix(+1, +1e9-1e6), true},
+		{"1.999999", time.Unix(+1, +1e9-1e3), true},
+		{"1.999999999", time.Unix(+1, +1e9-1e0), true},
+		{"-1350244992.023960108", time.Unix(-1350244992, -23960108), true},
+		{"-1350244992.02396010", time.Unix(-1350244992, -23960100), true},
+		{"-1350244992.0239601089", time.Unix(-1350244992, -23960108), true},
+		{"-1350244992.3", time.Unix(-1350244992, -300000000), true},
+		{"-1350244992", time.Unix(-1350244992, 0), true},
+		{"", time.Time{}, false},
+		{"0", time.Unix(0, 0), true},
+		{"1.", time.Unix(1, 0), true},
+		{"0.0", time.Unix(0, 0), true},
+		{".5", time.Time{}, false},
+		{"-1.3", time.Unix(-1, -3e8), true},
+		{"-1.0", time.Unix(-1, -0e0), true},
+		{"-0.0", time.Unix(-0, -0e0), true},
+		{"-0.1", time.Unix(-0, -1e8), true},
+		{"-0.01", time.Unix(-0, -1e7), true},
+		{"-0.99", time.Unix(-0, -99e7), true},
+		{"-0.98", time.Unix(-0, -98e7), true},
+		{"-1.1", time.Unix(-1, -1e8), true},
+		{"-1.01", time.Unix(-1, -1e7), true},
+		{"-2.99", time.Unix(-2, -99e7), true},
+		{"-5.98", time.Unix(-5, -98e7), true},
+		{"-", time.Time{}, false},
+		{"+", time.Time{}, false},
+		{"-1.-1", time.Time{}, false},
+		{"99999999999999999999999999999999999999999999999", time.Time{}, false},
+		{"0.123456789abcdef", time.Time{}, false},
+		{"foo", time.Time{}, false},
+		{"\x00", time.Time{}, false},
+		{"𝟵𝟴𝟳𝟲𝟱.𝟰𝟯𝟮𝟭𝟬", time.Time{}, false}, // Unicode numbers (U+1D7EC to U+1D7F5)
+		{"98765﹒43210", time.Time{}, false}, // Unicode period (U+FE52)
+	}
+
+	for _, v := range vectors {
+		ts, err := parsePAXTime(v.in)
+		ok := (err == nil)
+		if v.ok != ok {
+			if v.ok {
+				t.Errorf("parsePAXTime(%q): got parsing failure, want success", v.in)
+			} else {
+				t.Errorf("parsePAXTime(%q): got parsing success, want failure", v.in)
+			}
+		}
+		if ok && !ts.Equal(v.want) {
+			t.Errorf("parsePAXTime(%q): got (%ds %dns), want (%ds %dns)",
+				v.in, ts.Unix(), ts.Nanosecond(), v.want.Unix(), v.want.Nanosecond())
+		}
+	}
+}
+
+func TestFormatPAXTime(t *testing.T) {
+	vectors := []struct {
+		sec, nsec int64
+		want      string
+	}{
+		{1350244992, 0, "1350244992"},
+		{1350244992, 300000000, "1350244992.3"},
+		{1350244992, 23960100, "1350244992.0239601"},
+		{1350244992, 23960108, "1350244992.023960108"},
+		{+1, +1e9 - 1e0, "1.999999999"},
+		{+1, +1e9 - 1e3, "1.999999"},
+		{+1, +1e9 - 1e6, "1.999"},
+		{+1, +0e0 - 0e0, "1"},
+		{+1, +1e6 - 0e0, "1.001"},
+		{+1, +1e3 - 0e0, "1.000001"},
+		{+1, +1e0 - 0e0, "1.000000001"},
+		{0, 1e9 - 1e0, "0.999999999"},
+		{0, 1e9 - 1e3, "0.999999"},
+		{0, 1e9 - 1e6, "0.999"},
+		{0, 0e0, "0"},
+		{0, 1e6 + 0e0, "0.001"},
+		{0, 1e3 + 0e0, "0.000001"},
+		{0, 1e0 + 0e0, "0.000000001"},
+		{-1, -1e9 + 1e0, "-1.999999999"},
+		{-1, -1e9 + 1e3, "-1.999999"},
+		{-1, -1e9 + 1e6, "-1.999"},
+		{-1, -0e0 + 0e0, "-1"},
+		{-1, -1e6 + 0e0, "-1.001"},
+		{-1, -1e3 + 0e0, "-1.000001"},
+		{-1, -1e0 + 0e0, "-1.000000001"},
+		{-1350244992, 0, "-1350244992"},
+		{-1350244992, -300000000, "-1350244992.3"},
+		{-1350244992, -23960100, "-1350244992.0239601"},
+		{-1350244992, -23960108, "-1350244992.023960108"},
+	}
+
+	for _, v := range vectors {
+		got := formatPAXTime(time.Unix(v.sec, v.nsec))
+		if got != v.want {
+			t.Errorf("formatPAXTime(%ds, %dns): got %q, want %q",
+				v.sec, v.nsec, got, v.want)
+		}
+	}
+}
+
+func TestParsePAXRecord(t *testing.T) {
+	medName := strings.Repeat("CD", 50)
+	longName := strings.Repeat("AB", 100)
+
+	vectors := []struct {
+		in      string
+		wantRes string
+		wantKey string
+		wantVal string
+		ok      bool
+	}{
+		{"6 k=v\n\n", "\n", "k", "v", true},
+		{"19 path=/etc/hosts\n", "", "path", "/etc/hosts", true},
+		{"210 path=" + longName + "\nabc", "abc", "path", longName, true},
+		{"110 path=" + medName + "\n", "", "path", medName, true},
+		{"9 foo=ba\n", "", "foo", "ba", true},
+		{"11 foo=bar\n\x00", "\x00", "foo", "bar", true},
+		{"18 foo=b=\nar=\n==\x00\n", "", "foo", "b=\nar=\n==\x00", true},
+		{"27 foo=hello9 foo=ba\nworld\n", "", "foo", "hello9 foo=ba\nworld", true},
+		{"27 ☺☻☹=日a本b語ç\nmeow mix", "meow mix", "☺☻☹", "日a本b語ç", true},
+		{"17 \x00hello=\x00world\n", "17 \x00hello=\x00world\n", "", "", false},
+		{"1 k=1\n", "1 k=1\n", "", "", false},
+		{"6 k~1\n", "6 k~1\n", "", "", false},
+		{"6_k=1\n", "6_k=1\n", "", "", false},
+		{"6 k=1 ", "6 k=1 ", "", "", false},
+		{"632 k=1\n", "632 k=1\n", "", "", false},
+		{"16 longkeyname=hahaha\n", "16 longkeyname=hahaha\n", "", "", false},
+		{"3 somelongkey=\n", "3 somelongkey=\n", "", "", false},
+		{"50 tooshort=\n", "50 tooshort=\n", "", "", false},
+		{"0000000000000000000000000000000030 mtime=1432668921.098285006\n30 ctime=2147483649.15163319", "0000000000000000000000000000000030 mtime=1432668921.098285006\n30 ctime=2147483649.15163319", "mtime", "1432668921.098285006", false},
+		{"06 k=v\n", "06 k=v\n", "", "", false},
+		{"00006 k=v\n", "00006 k=v\n", "", "", false},
+		{"000006 k=v\n", "000006 k=v\n", "", "", false},
+		{"000000 k=v\n", "000000 k=v\n", "", "", false},
+		{"0 k=v\n", "0 k=v\n", "", "", false},
+		{"+0000005 x=\n", "+0000005 x=\n", "", "", false},
+	}
+
+	for _, v := range vectors {
+		key, val, res, err := parsePAXRecord(v.in)
+		ok := (err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("parsePAXRecord(%q): got parsing failure, want success", v.in)
+			} else {
+				t.Errorf("parsePAXRecord(%q): got parsing success, want failure", v.in)
+			}
+		}
+		if v.ok && (key != v.wantKey || val != v.wantVal) {
+			t.Errorf("parsePAXRecord(%q): got (%q: %q), want (%q: %q)",
+				v.in, key, val, v.wantKey, v.wantVal)
+		}
+		if res != v.wantRes {
+			t.Errorf("parsePAXRecord(%q): got residual %q, want residual %q",
+				v.in, res, v.wantRes)
+		}
+	}
+}
+
+func TestFormatPAXRecord(t *testing.T) {
+	medName := strings.Repeat("CD", 50)
+	longName := strings.Repeat("AB", 100)
+
+	vectors := []struct {
+		inKey string
+		inVal string
+		want  string
+		ok    bool
+	}{
+		{"k", "v", "6 k=v\n", true},
+		{"path", "/etc/hosts", "19 path=/etc/hosts\n", true},
+		{"path", longName, "210 path=" + longName + "\n", true},
+		{"path", medName, "110 path=" + medName + "\n", true},
+		{"foo", "ba", "9 foo=ba\n", true},
+		{"foo", "bar", "11 foo=bar\n", true},
+		{"foo", "b=\nar=\n==\x00", "18 foo=b=\nar=\n==\x00\n", true},
+		{"foo", "hello9 foo=ba\nworld", "27 foo=hello9 foo=ba\nworld\n", true},
+		{"☺☻☹", "日a本b語ç", "27 ☺☻☹=日a本b語ç\n", true},
+		{"xhello", "\x00world", "17 xhello=\x00world\n", true},
+		{"path", "null\x00", "", false},
+		{"null\x00", "value", "", false},
+		{paxSchilyXattr + "key", "null\x00", "26 SCHILY.xattr.key=null\x00\n", true},
+	}
+
+	for _, v := range vectors {
+		got, err := formatPAXRecord(v.inKey, v.inVal)
+		ok := (err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("formatPAXRecord(%q, %q): got format failure, want success", v.inKey, v.inVal)
+			} else {
+				t.Errorf("formatPAXRecord(%q, %q): got format success, want failure", v.inKey, v.inVal)
+			}
+		}
+		if got != v.want {
+			t.Errorf("formatPAXRecord(%q, %q): got %q, want %q",
+				v.inKey, v.inVal, got, v.want)
+		}
+	}
+}
diff --git a/src/archive/tar/tar_test.go b/src/archive/tar/tar_test.go
new file mode 100644
index 0000000..91b3840
--- /dev/null
+++ b/src/archive/tar/tar_test.go
@@ -0,0 +1,855 @@
+// Copyright 2012 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"
+	"errors"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"io/fs"
+	"math"
+	"os"
+	"path"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+type testError struct{ error }
+
+type fileOps []interface{} // []T where T is (string | int64)
+
+// testFile is an io.ReadWriteSeeker where the IO operations performed
+// on it must match the list of operations in ops.
+type testFile struct {
+	ops fileOps
+	pos int64
+}
+
+func (f *testFile) Read(b []byte) (int, error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if len(f.ops) == 0 {
+		return 0, io.EOF
+	}
+	s, ok := f.ops[0].(string)
+	if !ok {
+		return 0, errors.New("unexpected Read operation")
+	}
+
+	n := copy(b, s)
+	if len(s) > n {
+		f.ops[0] = s[n:]
+	} else {
+		f.ops = f.ops[1:]
+	}
+	f.pos += int64(len(b))
+	return n, nil
+}
+
+func (f *testFile) Write(b []byte) (int, error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if len(f.ops) == 0 {
+		return 0, errors.New("unexpected Write operation")
+	}
+	s, ok := f.ops[0].(string)
+	if !ok {
+		return 0, errors.New("unexpected Write operation")
+	}
+
+	if !strings.HasPrefix(s, string(b)) {
+		return 0, testError{fmt.Errorf("got Write(%q), want Write(%q)", b, s)}
+	}
+	if len(s) > len(b) {
+		f.ops[0] = s[len(b):]
+	} else {
+		f.ops = f.ops[1:]
+	}
+	f.pos += int64(len(b))
+	return len(b), nil
+}
+
+func (f *testFile) Seek(pos int64, whence int) (int64, error) {
+	if pos == 0 && whence == io.SeekCurrent {
+		return f.pos, nil
+	}
+	if len(f.ops) == 0 {
+		return 0, errors.New("unexpected Seek operation")
+	}
+	s, ok := f.ops[0].(int64)
+	if !ok {
+		return 0, errors.New("unexpected Seek operation")
+	}
+
+	if s != pos || whence != io.SeekCurrent {
+		return 0, testError{fmt.Errorf("got Seek(%d, %d), want Seek(%d, %d)", pos, whence, s, io.SeekCurrent)}
+	}
+	f.pos += s
+	f.ops = f.ops[1:]
+	return f.pos, nil
+}
+
+func equalSparseEntries(x, y []sparseEntry) bool {
+	return (len(x) == 0 && len(y) == 0) || reflect.DeepEqual(x, y)
+}
+
+func TestSparseEntries(t *testing.T) {
+	vectors := []struct {
+		in   []sparseEntry
+		size int64
+
+		wantValid    bool          // Result of validateSparseEntries
+		wantAligned  []sparseEntry // Result of alignSparseEntries
+		wantInverted []sparseEntry // Result of invertSparseEntries
+	}{{
+		in: []sparseEntry{}, size: 0,
+		wantValid:    true,
+		wantInverted: []sparseEntry{{0, 0}},
+	}, {
+		in: []sparseEntry{}, size: 5000,
+		wantValid:    true,
+		wantInverted: []sparseEntry{{0, 5000}},
+	}, {
+		in: []sparseEntry{{0, 5000}}, size: 5000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{0, 5000}},
+		wantInverted: []sparseEntry{{5000, 0}},
+	}, {
+		in: []sparseEntry{{1000, 4000}}, size: 5000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{1024, 3976}},
+		wantInverted: []sparseEntry{{0, 1000}, {5000, 0}},
+	}, {
+		in: []sparseEntry{{0, 3000}}, size: 5000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{0, 2560}},
+		wantInverted: []sparseEntry{{3000, 2000}},
+	}, {
+		in: []sparseEntry{{3000, 2000}}, size: 5000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{3072, 1928}},
+		wantInverted: []sparseEntry{{0, 3000}, {5000, 0}},
+	}, {
+		in: []sparseEntry{{2000, 2000}}, size: 5000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{2048, 1536}},
+		wantInverted: []sparseEntry{{0, 2000}, {4000, 1000}},
+	}, {
+		in: []sparseEntry{{0, 2000}, {8000, 2000}}, size: 10000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{0, 1536}, {8192, 1808}},
+		wantInverted: []sparseEntry{{2000, 6000}, {10000, 0}},
+	}, {
+		in: []sparseEntry{{0, 2000}, {2000, 2000}, {4000, 0}, {4000, 3000}, {7000, 1000}, {8000, 0}, {8000, 2000}}, size: 10000,
+		wantValid:    true,
+		wantAligned:  []sparseEntry{{0, 1536}, {2048, 1536}, {4096, 2560}, {7168, 512}, {8192, 1808}},
+		wantInverted: []sparseEntry{{10000, 0}},
+	}, {
+		in: []sparseEntry{{0, 0}, {1000, 0}, {2000, 0}, {3000, 0}, {4000, 0}, {5000, 0}}, size: 5000,
+		wantValid:    true,
+		wantInverted: []sparseEntry{{0, 5000}},
+	}, {
+		in: []sparseEntry{{1, 0}}, size: 0,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{-1, 0}}, size: 100,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{0, -1}}, size: 100,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{0, 0}}, size: -100,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{math.MaxInt64, 3}, {6, -5}}, size: 35,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{1, 3}, {6, -5}}, size: 35,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{math.MaxInt64, math.MaxInt64}}, size: math.MaxInt64,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{3, 3}}, size: 5,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{2, 0}, {1, 0}, {0, 0}}, size: 3,
+		wantValid: false,
+	}, {
+		in: []sparseEntry{{1, 3}, {2, 2}}, size: 10,
+		wantValid: false,
+	}}
+
+	for i, v := range vectors {
+		gotValid := validateSparseEntries(v.in, v.size)
+		if gotValid != v.wantValid {
+			t.Errorf("test %d, validateSparseEntries() = %v, want %v", i, gotValid, v.wantValid)
+		}
+		if !v.wantValid {
+			continue
+		}
+		gotAligned := alignSparseEntries(append([]sparseEntry{}, v.in...), v.size)
+		if !equalSparseEntries(gotAligned, v.wantAligned) {
+			t.Errorf("test %d, alignSparseEntries():\ngot  %v\nwant %v", i, gotAligned, v.wantAligned)
+		}
+		gotInverted := invertSparseEntries(append([]sparseEntry{}, v.in...), v.size)
+		if !equalSparseEntries(gotInverted, v.wantInverted) {
+			t.Errorf("test %d, inverseSparseEntries():\ngot  %v\nwant %v", i, gotInverted, v.wantInverted)
+		}
+	}
+}
+
+func TestFileInfoHeader(t *testing.T) {
+	fi, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("FileInfoHeader: %v", err)
+	}
+	if g, e := h.Name, "small.txt"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Mode, int64(fi.Mode().Perm()); g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(5); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+	// FileInfoHeader should error when passing nil FileInfo
+	if _, err := FileInfoHeader(nil, ""); err == nil {
+		t.Fatalf("Expected error when passing nil to FileInfoHeader")
+	}
+}
+
+func TestFileInfoHeaderDir(t *testing.T) {
+	fi, err := os.Stat("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("FileInfoHeader: %v", err)
+	}
+	if g, e := h.Name, "testdata/"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	// Ignoring c_ISGID for golang.org/issue/4867
+	if g, e := h.Mode&^c_ISGID, int64(fi.Mode().Perm()); g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(0); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+}
+
+func TestFileInfoHeaderSymlink(t *testing.T) {
+	testenv.MustHaveSymlink(t)
+
+	tmpdir, err := os.MkdirTemp("", "TestFileInfoHeaderSymlink")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+
+	link := filepath.Join(tmpdir, "link")
+	target := tmpdir
+	err = os.Symlink(target, link)
+	if err != nil {
+		t.Fatal(err)
+	}
+	fi, err := os.Lstat(link)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	h, err := FileInfoHeader(fi, target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := h.Name, fi.Name(); g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Linkname, target; g != e {
+		t.Errorf("Linkname = %q; want %q", g, e)
+	}
+	if g, e := h.Typeflag, byte(TypeSymlink); g != e {
+		t.Errorf("Typeflag = %v; want %v", g, e)
+	}
+}
+
+func TestRoundTrip(t *testing.T) {
+	data := []byte("some file contents")
+
+	var b bytes.Buffer
+	tw := NewWriter(&b)
+	hdr := &Header{
+		Name:       "file.txt",
+		Uid:        1 << 21, // Too big for 8 octal digits
+		Size:       int64(len(data)),
+		ModTime:    time.Now().Round(time.Second),
+		PAXRecords: map[string]string{"uid": "2097152"},
+		Format:     FormatPAX,
+		Typeflag:   TypeReg,
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("tw.WriteHeader: %v", err)
+	}
+	if _, err := tw.Write(data); err != nil {
+		t.Fatalf("tw.Write: %v", err)
+	}
+	if err := tw.Close(); err != nil {
+		t.Fatalf("tw.Close: %v", err)
+	}
+
+	// Read it back.
+	tr := NewReader(&b)
+	rHdr, err := tr.Next()
+	if err != nil {
+		t.Fatalf("tr.Next: %v", err)
+	}
+	if !reflect.DeepEqual(rHdr, hdr) {
+		t.Errorf("Header mismatch.\n got %+v\nwant %+v", rHdr, hdr)
+	}
+	rData, err := io.ReadAll(tr)
+	if err != nil {
+		t.Fatalf("Read: %v", err)
+	}
+	if !bytes.Equal(rData, data) {
+		t.Errorf("Data mismatch.\n got %q\nwant %q", rData, data)
+	}
+}
+
+type headerRoundTripTest struct {
+	h  *Header
+	fm fs.FileMode
+}
+
+func TestHeaderRoundTrip(t *testing.T) {
+	vectors := []headerRoundTripTest{{
+		// regular file.
+		h: &Header{
+			Name:     "test.txt",
+			Mode:     0644,
+			Size:     12,
+			ModTime:  time.Unix(1360600916, 0),
+			Typeflag: TypeReg,
+		},
+		fm: 0644,
+	}, {
+		// symbolic link.
+		h: &Header{
+			Name:     "link.txt",
+			Mode:     0777,
+			Size:     0,
+			ModTime:  time.Unix(1360600852, 0),
+			Typeflag: TypeSymlink,
+		},
+		fm: 0777 | fs.ModeSymlink,
+	}, {
+		// character device node.
+		h: &Header{
+			Name:     "dev/null",
+			Mode:     0666,
+			Size:     0,
+			ModTime:  time.Unix(1360578951, 0),
+			Typeflag: TypeChar,
+		},
+		fm: 0666 | fs.ModeDevice | fs.ModeCharDevice,
+	}, {
+		// block device node.
+		h: &Header{
+			Name:     "dev/sda",
+			Mode:     0660,
+			Size:     0,
+			ModTime:  time.Unix(1360578954, 0),
+			Typeflag: TypeBlock,
+		},
+		fm: 0660 | fs.ModeDevice,
+	}, {
+		// directory.
+		h: &Header{
+			Name:     "dir/",
+			Mode:     0755,
+			Size:     0,
+			ModTime:  time.Unix(1360601116, 0),
+			Typeflag: TypeDir,
+		},
+		fm: 0755 | fs.ModeDir,
+	}, {
+		// fifo node.
+		h: &Header{
+			Name:     "dev/initctl",
+			Mode:     0600,
+			Size:     0,
+			ModTime:  time.Unix(1360578949, 0),
+			Typeflag: TypeFifo,
+		},
+		fm: 0600 | fs.ModeNamedPipe,
+	}, {
+		// setuid.
+		h: &Header{
+			Name:     "bin/su",
+			Mode:     0755 | c_ISUID,
+			Size:     23232,
+			ModTime:  time.Unix(1355405093, 0),
+			Typeflag: TypeReg,
+		},
+		fm: 0755 | fs.ModeSetuid,
+	}, {
+		// setguid.
+		h: &Header{
+			Name:     "group.txt",
+			Mode:     0750 | c_ISGID,
+			Size:     0,
+			ModTime:  time.Unix(1360602346, 0),
+			Typeflag: TypeReg,
+		},
+		fm: 0750 | fs.ModeSetgid,
+	}, {
+		// sticky.
+		h: &Header{
+			Name:     "sticky.txt",
+			Mode:     0600 | c_ISVTX,
+			Size:     7,
+			ModTime:  time.Unix(1360602540, 0),
+			Typeflag: TypeReg,
+		},
+		fm: 0600 | fs.ModeSticky,
+	}, {
+		// hard link.
+		h: &Header{
+			Name:     "hard.txt",
+			Mode:     0644,
+			Size:     0,
+			Linkname: "file.txt",
+			ModTime:  time.Unix(1360600916, 0),
+			Typeflag: TypeLink,
+		},
+		fm: 0644,
+	}, {
+		// More information.
+		h: &Header{
+			Name:     "info.txt",
+			Mode:     0600,
+			Size:     0,
+			Uid:      1000,
+			Gid:      1000,
+			ModTime:  time.Unix(1360602540, 0),
+			Uname:    "slartibartfast",
+			Gname:    "users",
+			Typeflag: TypeReg,
+		},
+		fm: 0600,
+	}}
+
+	for i, v := range vectors {
+		fi := v.h.FileInfo()
+		h2, err := FileInfoHeader(fi, "")
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if strings.Contains(fi.Name(), "/") {
+			t.Errorf("FileInfo of %q contains slash: %q", v.h.Name, fi.Name())
+		}
+		name := path.Base(v.h.Name)
+		if fi.IsDir() {
+			name += "/"
+		}
+		if got, want := h2.Name, name; got != want {
+			t.Errorf("i=%d: Name: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Size, v.h.Size; got != want {
+			t.Errorf("i=%d: Size: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Uid, v.h.Uid; got != want {
+			t.Errorf("i=%d: Uid: got %d, want %d", i, got, want)
+		}
+		if got, want := h2.Gid, v.h.Gid; got != want {
+			t.Errorf("i=%d: Gid: got %d, want %d", i, got, want)
+		}
+		if got, want := h2.Uname, v.h.Uname; got != want {
+			t.Errorf("i=%d: Uname: got %q, want %q", i, got, want)
+		}
+		if got, want := h2.Gname, v.h.Gname; got != want {
+			t.Errorf("i=%d: Gname: got %q, want %q", i, got, want)
+		}
+		if got, want := h2.Linkname, v.h.Linkname; got != want {
+			t.Errorf("i=%d: Linkname: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Typeflag, v.h.Typeflag; got != want {
+			t.Logf("%#v %#v", v.h, fi.Sys())
+			t.Errorf("i=%d: Typeflag: got %q, want %q", i, got, want)
+		}
+		if got, want := h2.Mode, v.h.Mode; got != want {
+			t.Errorf("i=%d: Mode: got %o, want %o", i, got, want)
+		}
+		if got, want := fi.Mode(), v.fm; got != want {
+			t.Errorf("i=%d: fi.Mode: got %o, want %o", i, got, want)
+		}
+		if got, want := h2.AccessTime, v.h.AccessTime; got != want {
+			t.Errorf("i=%d: AccessTime: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.ChangeTime, v.h.ChangeTime; got != want {
+			t.Errorf("i=%d: ChangeTime: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.ModTime, v.h.ModTime; got != want {
+			t.Errorf("i=%d: ModTime: got %v, want %v", i, got, want)
+		}
+		if sysh, ok := fi.Sys().(*Header); !ok || sysh != v.h {
+			t.Errorf("i=%d: Sys didn't return original *Header", i)
+		}
+	}
+}
+
+func TestHeaderAllowedFormats(t *testing.T) {
+	vectors := []struct {
+		header  *Header           // Input header
+		paxHdrs map[string]string // Expected PAX headers that may be needed
+		formats Format            // Expected formats that can encode the header
+	}{{
+		header:  &Header{},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Size: 077777777777},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Size: 077777777777, Format: FormatUSTAR},
+		formats: FormatUSTAR,
+	}, {
+		header:  &Header{Size: 077777777777, Format: FormatPAX},
+		formats: FormatUSTAR | FormatPAX,
+	}, {
+		header:  &Header{Size: 077777777777, Format: FormatGNU},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Size: 077777777777 + 1},
+		paxHdrs: map[string]string{paxSize: "8589934592"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Size: 077777777777 + 1, Format: FormatPAX},
+		paxHdrs: map[string]string{paxSize: "8589934592"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{Size: 077777777777 + 1, Format: FormatGNU},
+		paxHdrs: map[string]string{paxSize: "8589934592"},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Mode: 07777777},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Mode: 07777777 + 1},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Devmajor: -123},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Devmajor: 1<<56 - 1},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Devmajor: 1 << 56},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Devmajor: -1 << 56},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Devmajor: -1<<56 - 1},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Name: "用戶名", Devmajor: -1 << 56},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{Size: math.MaxInt64},
+		paxHdrs: map[string]string{paxSize: "9223372036854775807"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Size: math.MinInt64},
+		paxHdrs: map[string]string{paxSize: "-9223372036854775808"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Uname: "0123456789abcdef0123456789abcdef"},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Uname: "0123456789abcdef0123456789abcdefx"},
+		paxHdrs: map[string]string{paxUname: "0123456789abcdef0123456789abcdefx"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{Name: "foobar"},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Name: strings.Repeat("a", nameSize)},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Name: strings.Repeat("a", nameSize+1)},
+		paxHdrs: map[string]string{paxPath: strings.Repeat("a", nameSize+1)},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Linkname: "用戶名"},
+		paxHdrs: map[string]string{paxLinkpath: "用戶名"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Linkname: strings.Repeat("用戶名\x00", nameSize)},
+		paxHdrs: map[string]string{paxLinkpath: strings.Repeat("用戶名\x00", nameSize)},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Linkname: "\x00hello"},
+		paxHdrs: map[string]string{paxLinkpath: "\x00hello"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Uid: 07777777},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Uid: 07777777 + 1},
+		paxHdrs: map[string]string{paxUid: "2097152"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Xattrs: nil},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Xattrs: map[string]string{"foo": "bar"}},
+		paxHdrs: map[string]string{paxSchilyXattr + "foo": "bar"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{Xattrs: map[string]string{"foo": "bar"}, Format: FormatGNU},
+		paxHdrs: map[string]string{paxSchilyXattr + "foo": "bar"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Xattrs: map[string]string{"用戶名": "\x00hello"}},
+		paxHdrs: map[string]string{paxSchilyXattr + "用戶名": "\x00hello"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{Xattrs: map[string]string{"foo=bar": "baz"}},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Xattrs: map[string]string{"foo": ""}},
+		paxHdrs: map[string]string{paxSchilyXattr + "foo": ""},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{ModTime: time.Unix(0, 0)},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(077777777777, 0)},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(077777777777+1, 0)},
+		paxHdrs: map[string]string{paxMtime: "8589934592"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(math.MaxInt64, 0)},
+		paxHdrs: map[string]string{paxMtime: "9223372036854775807"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(math.MaxInt64, 0), Format: FormatUSTAR},
+		paxHdrs: map[string]string{paxMtime: "9223372036854775807"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{ModTime: time.Unix(-1, 0)},
+		paxHdrs: map[string]string{paxMtime: "-1"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 500)},
+		paxHdrs: map[string]string{paxMtime: "1.0000005"},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 0)},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 0), Format: FormatPAX},
+		formats: FormatUSTAR | FormatPAX,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 500), Format: FormatUSTAR},
+		paxHdrs: map[string]string{paxMtime: "1.0000005"},
+		formats: FormatUSTAR,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 500), Format: FormatPAX},
+		paxHdrs: map[string]string{paxMtime: "1.0000005"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{ModTime: time.Unix(1, 500), Format: FormatGNU},
+		paxHdrs: map[string]string{paxMtime: "1.0000005"},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(-1, 500)},
+		paxHdrs: map[string]string{paxMtime: "-0.9999995"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ModTime: time.Unix(-1, 500), Format: FormatGNU},
+		paxHdrs: map[string]string{paxMtime: "-0.9999995"},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{AccessTime: time.Unix(0, 0)},
+		paxHdrs: map[string]string{paxAtime: "0"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{AccessTime: time.Unix(0, 0), Format: FormatUSTAR},
+		paxHdrs: map[string]string{paxAtime: "0"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{AccessTime: time.Unix(0, 0), Format: FormatPAX},
+		paxHdrs: map[string]string{paxAtime: "0"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{AccessTime: time.Unix(0, 0), Format: FormatGNU},
+		paxHdrs: map[string]string{paxAtime: "0"},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{AccessTime: time.Unix(-123, 0)},
+		paxHdrs: map[string]string{paxAtime: "-123"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{AccessTime: time.Unix(-123, 0), Format: FormatPAX},
+		paxHdrs: map[string]string{paxAtime: "-123"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{ChangeTime: time.Unix(123, 456)},
+		paxHdrs: map[string]string{paxCtime: "123.000000456"},
+		formats: FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{ChangeTime: time.Unix(123, 456), Format: FormatUSTAR},
+		paxHdrs: map[string]string{paxCtime: "123.000000456"},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{ChangeTime: time.Unix(123, 456), Format: FormatGNU},
+		paxHdrs: map[string]string{paxCtime: "123.000000456"},
+		formats: FormatGNU,
+	}, {
+		header:  &Header{ChangeTime: time.Unix(123, 456), Format: FormatPAX},
+		paxHdrs: map[string]string{paxCtime: "123.000000456"},
+		formats: FormatPAX,
+	}, {
+		header:  &Header{Name: "foo/", Typeflag: TypeDir},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}, {
+		header:  &Header{Name: "foo/", Typeflag: TypeReg},
+		formats: FormatUnknown,
+	}, {
+		header:  &Header{Name: "foo/", Typeflag: TypeSymlink},
+		formats: FormatUSTAR | FormatPAX | FormatGNU,
+	}}
+
+	for i, v := range vectors {
+		formats, paxHdrs, err := v.header.allowedFormats()
+		if formats != v.formats {
+			t.Errorf("test %d, allowedFormats(): got %v, want %v", i, formats, v.formats)
+		}
+		if formats&FormatPAX > 0 && !reflect.DeepEqual(paxHdrs, v.paxHdrs) && !(len(paxHdrs) == 0 && len(v.paxHdrs) == 0) {
+			t.Errorf("test %d, allowedFormats():\ngot  %v\nwant %s", i, paxHdrs, v.paxHdrs)
+		}
+		if (formats != FormatUnknown) && (err != nil) {
+			t.Errorf("test %d, unexpected error: %v", i, err)
+		}
+		if (formats == FormatUnknown) && (err == nil) {
+			t.Errorf("test %d, got nil-error, want non-nil error", i)
+		}
+	}
+}
+
+func Benchmark(b *testing.B) {
+	type file struct {
+		hdr  *Header
+		body []byte
+	}
+
+	vectors := []struct {
+		label string
+		files []file
+	}{{
+		"USTAR",
+		[]file{{
+			&Header{Name: "bar", Mode: 0640, Size: int64(3)},
+			[]byte("foo"),
+		}, {
+			&Header{Name: "world", Mode: 0640, Size: int64(5)},
+			[]byte("hello"),
+		}},
+	}, {
+		"GNU",
+		[]file{{
+			&Header{Name: "bar", Mode: 0640, Size: int64(3), Devmajor: -1},
+			[]byte("foo"),
+		}, {
+			&Header{Name: "world", Mode: 0640, Size: int64(5), Devmajor: -1},
+			[]byte("hello"),
+		}},
+	}, {
+		"PAX",
+		[]file{{
+			&Header{Name: "bar", Mode: 0640, Size: int64(3), Xattrs: map[string]string{"foo": "bar"}},
+			[]byte("foo"),
+		}, {
+			&Header{Name: "world", Mode: 0640, Size: int64(5), Xattrs: map[string]string{"foo": "bar"}},
+			[]byte("hello"),
+		}},
+	}}
+
+	b.Run("Writer", func(b *testing.B) {
+		for _, v := range vectors {
+			b.Run(v.label, func(b *testing.B) {
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					// Writing to io.Discard because we want to
+					// test purely the writer code and not bring in disk performance into this.
+					tw := NewWriter(io.Discard)
+					for _, file := range v.files {
+						if err := tw.WriteHeader(file.hdr); err != nil {
+							b.Errorf("unexpected WriteHeader error: %v", err)
+						}
+						if _, err := tw.Write(file.body); err != nil {
+							b.Errorf("unexpected Write error: %v", err)
+						}
+					}
+					if err := tw.Close(); err != nil {
+						b.Errorf("unexpected Close error: %v", err)
+					}
+				}
+			})
+		}
+	})
+
+	b.Run("Reader", func(b *testing.B) {
+		for _, v := range vectors {
+			var buf bytes.Buffer
+			var r bytes.Reader
+
+			// Write the archive to a byte buffer.
+			tw := NewWriter(&buf)
+			for _, file := range v.files {
+				tw.WriteHeader(file.hdr)
+				tw.Write(file.body)
+			}
+			tw.Close()
+			b.Run(v.label, func(b *testing.B) {
+				b.ReportAllocs()
+				// Read from the byte buffer.
+				for i := 0; i < b.N; i++ {
+					r.Reset(buf.Bytes())
+					tr := NewReader(&r)
+					if _, err := tr.Next(); err != nil {
+						b.Errorf("unexpected Next error: %v", err)
+					}
+					if _, err := io.Copy(io.Discard, tr); err != nil {
+						b.Errorf("unexpected Copy error : %v", err)
+					}
+				}
+			})
+		}
+	})
+
+}
diff --git a/src/archive/tar/testdata/file-and-dir.tar b/src/archive/tar/testdata/file-and-dir.tar
new file mode 100644
index 0000000..c18d428
--- /dev/null
+++ b/src/archive/tar/testdata/file-and-dir.tar
diff --git a/src/archive/tar/testdata/gnu-incremental.tar b/src/archive/tar/testdata/gnu-incremental.tar
new file mode 100644
index 0000000..4c442e5
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-incremental.tar
diff --git a/src/archive/tar/testdata/gnu-long-nul.tar b/src/archive/tar/testdata/gnu-long-nul.tar
new file mode 100644
index 0000000..28bc812
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-long-nul.tar
diff --git a/src/archive/tar/testdata/gnu-multi-hdrs.tar b/src/archive/tar/testdata/gnu-multi-hdrs.tar
new file mode 100644
index 0000000..8bcad55
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-multi-hdrs.tar
diff --git a/src/archive/tar/testdata/gnu-nil-sparse-data.tar b/src/archive/tar/testdata/gnu-nil-sparse-data.tar
new file mode 100644
index 0000000..df1aa83
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-nil-sparse-data.tar
diff --git a/src/archive/tar/testdata/gnu-nil-sparse-hole.tar b/src/archive/tar/testdata/gnu-nil-sparse-hole.tar
new file mode 100644
index 0000000..496abfe
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-nil-sparse-hole.tar
diff --git a/src/archive/tar/testdata/gnu-not-utf8.tar b/src/archive/tar/testdata/gnu-not-utf8.tar
new file mode 100644
index 0000000..81cec67
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-not-utf8.tar
diff --git a/src/archive/tar/testdata/gnu-sparse-big.tar b/src/archive/tar/testdata/gnu-sparse-big.tar
new file mode 100644
index 0000000..1a5cfc9
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-sparse-big.tar
diff --git a/src/archive/tar/testdata/gnu-utf8.tar b/src/archive/tar/testdata/gnu-utf8.tar
new file mode 100644
index 0000000..2c9c807
--- /dev/null
+++ b/src/archive/tar/testdata/gnu-utf8.tar
diff --git a/src/archive/tar/testdata/gnu.tar b/src/archive/tar/testdata/gnu.tar
new file mode 100644
index 0000000..fc899dc
--- /dev/null
+++ b/src/archive/tar/testdata/gnu.tar
diff --git a/src/archive/tar/testdata/hardlink.tar b/src/archive/tar/testdata/hardlink.tar
new file mode 100644
index 0000000..9cd1a26
--- /dev/null
+++ b/src/archive/tar/testdata/hardlink.tar
diff --git a/src/archive/tar/testdata/hdr-only.tar b/src/archive/tar/testdata/hdr-only.tar
new file mode 100644
index 0000000..f250340
--- /dev/null
+++ b/src/archive/tar/testdata/hdr-only.tar
diff --git a/src/archive/tar/testdata/invalid-go17.tar b/src/archive/tar/testdata/invalid-go17.tar
new file mode 100644
index 0000000..58f2488
--- /dev/null
+++ b/src/archive/tar/testdata/invalid-go17.tar
diff --git a/src/archive/tar/testdata/issue10968.tar b/src/archive/tar/testdata/issue10968.tar
new file mode 100644
index 0000000..1cc837b
--- /dev/null
+++ b/src/archive/tar/testdata/issue10968.tar
diff --git a/src/archive/tar/testdata/issue11169.tar b/src/archive/tar/testdata/issue11169.tar
new file mode 100644
index 0000000..4d71fa1
--- /dev/null
+++ b/src/archive/tar/testdata/issue11169.tar
diff --git a/src/archive/tar/testdata/issue12435.tar b/src/archive/tar/testdata/issue12435.tar
new file mode 100644
index 0000000..3542dd8
--- /dev/null
+++ b/src/archive/tar/testdata/issue12435.tar
diff --git a/src/archive/tar/testdata/neg-size.tar b/src/archive/tar/testdata/neg-size.tar
new file mode 100644
index 0000000..21edf38
--- /dev/null
+++ b/src/archive/tar/testdata/neg-size.tar
diff --git a/src/archive/tar/testdata/nil-uid.tar b/src/archive/tar/testdata/nil-uid.tar
new file mode 100644
index 0000000..cc9cfaa
--- /dev/null
+++ b/src/archive/tar/testdata/nil-uid.tar
diff --git a/src/archive/tar/testdata/pax-bad-hdr-file.tar b/src/archive/tar/testdata/pax-bad-hdr-file.tar
new file mode 100644
index 0000000..b97cc98
--- /dev/null
+++ b/src/archive/tar/testdata/pax-bad-hdr-file.tar
diff --git a/src/archive/tar/testdata/pax-bad-mtime-file.tar b/src/archive/tar/testdata/pax-bad-mtime-file.tar
new file mode 100644
index 0000000..9b22f7e
--- /dev/null
+++ b/src/archive/tar/testdata/pax-bad-mtime-file.tar
diff --git a/src/archive/tar/testdata/pax-global-records.tar b/src/archive/tar/testdata/pax-global-records.tar
new file mode 100644
index 0000000..3d3d241
--- /dev/null
+++ b/src/archive/tar/testdata/pax-global-records.tar
diff --git a/src/archive/tar/testdata/pax-multi-hdrs.tar b/src/archive/tar/testdata/pax-multi-hdrs.tar
new file mode 100644
index 0000000..14bc759
--- /dev/null
+++ b/src/archive/tar/testdata/pax-multi-hdrs.tar
diff --git a/src/archive/tar/testdata/pax-nil-sparse-data.tar b/src/archive/tar/testdata/pax-nil-sparse-data.tar
new file mode 100644
index 0000000..e59bd94
--- /dev/null
+++ b/src/archive/tar/testdata/pax-nil-sparse-data.tar
diff --git a/src/archive/tar/testdata/pax-nil-sparse-hole.tar b/src/archive/tar/testdata/pax-nil-sparse-hole.tar
new file mode 100644
index 0000000..b44327b
--- /dev/null
+++ b/src/archive/tar/testdata/pax-nil-sparse-hole.tar
diff --git a/src/archive/tar/testdata/pax-nul-path.tar b/src/archive/tar/testdata/pax-nul-path.tar
new file mode 100644
index 0000000..c78f82b
--- /dev/null
+++ b/src/archive/tar/testdata/pax-nul-path.tar
diff --git a/src/archive/tar/testdata/pax-nul-xattrs.tar b/src/archive/tar/testdata/pax-nul-xattrs.tar
new file mode 100644
index 0000000..881f517
--- /dev/null
+++ b/src/archive/tar/testdata/pax-nul-xattrs.tar
diff --git a/src/archive/tar/testdata/pax-path-hdr.tar b/src/archive/tar/testdata/pax-path-hdr.tar
new file mode 100644
index 0000000..ab8fc32
--- /dev/null
+++ b/src/archive/tar/testdata/pax-path-hdr.tar
diff --git a/src/archive/tar/testdata/pax-pos-size-file.tar b/src/archive/tar/testdata/pax-pos-size-file.tar
new file mode 100644
index 0000000..ea5ccf9
--- /dev/null
+++ b/src/archive/tar/testdata/pax-pos-size-file.tar
diff --git a/src/archive/tar/testdata/pax-records.tar b/src/archive/tar/testdata/pax-records.tar
new file mode 100644
index 0000000..276c211
--- /dev/null
+++ b/src/archive/tar/testdata/pax-records.tar
diff --git a/src/archive/tar/testdata/pax-sparse-big.tar b/src/archive/tar/testdata/pax-sparse-big.tar
new file mode 100644
index 0000000..65d1f8e
--- /dev/null
+++ b/src/archive/tar/testdata/pax-sparse-big.tar
diff --git a/src/archive/tar/testdata/pax.tar b/src/archive/tar/testdata/pax.tar
new file mode 100644
index 0000000..9bc24b6
--- /dev/null
+++ b/src/archive/tar/testdata/pax.tar
diff --git a/src/archive/tar/testdata/small.txt b/src/archive/tar/testdata/small.txt
new file mode 100644
index 0000000..b249bfc
--- /dev/null
+++ b/src/archive/tar/testdata/small.txt
@@ -0,0 +1 @@
+Kilts
\ No newline at end of file
diff --git a/src/archive/tar/testdata/small2.txt b/src/archive/tar/testdata/small2.txt
new file mode 100644
index 0000000..394ee3e
--- /dev/null
+++ b/src/archive/tar/testdata/small2.txt
@@ -0,0 +1 @@
+Google.com
diff --git a/src/archive/tar/testdata/sparse-formats.tar b/src/archive/tar/testdata/sparse-formats.tar
new file mode 100644
index 0000000..8bd4e74
--- /dev/null
+++ b/src/archive/tar/testdata/sparse-formats.tar
diff --git a/src/archive/tar/testdata/star.tar b/src/archive/tar/testdata/star.tar
new file mode 100644
index 0000000..59e2d4e
--- /dev/null
+++ b/src/archive/tar/testdata/star.tar
diff --git a/src/archive/tar/testdata/trailing-slash.tar b/src/archive/tar/testdata/trailing-slash.tar
new file mode 100644
index 0000000..93718b3
--- /dev/null
+++ b/src/archive/tar/testdata/trailing-slash.tar
diff --git a/src/archive/tar/testdata/ustar-file-devs.tar b/src/archive/tar/testdata/ustar-file-devs.tar
new file mode 100644
index 0000000..146e25b
--- /dev/null
+++ b/src/archive/tar/testdata/ustar-file-devs.tar
diff --git a/src/archive/tar/testdata/ustar-file-reg.tar b/src/archive/tar/testdata/ustar-file-reg.tar
new file mode 100644
index 0000000..c84fa27
--- /dev/null
+++ b/src/archive/tar/testdata/ustar-file-reg.tar
diff --git a/src/archive/tar/testdata/ustar.tar b/src/archive/tar/testdata/ustar.tar
new file mode 100644
index 0000000..29679d9
--- /dev/null
+++ b/src/archive/tar/testdata/ustar.tar
diff --git a/src/archive/tar/testdata/v7.tar b/src/archive/tar/testdata/v7.tar
new file mode 100644
index 0000000..eb65fc9
--- /dev/null
+++ b/src/archive/tar/testdata/v7.tar
diff --git a/src/archive/tar/testdata/writer-big-long.tar b/src/archive/tar/testdata/writer-big-long.tar
new file mode 100644
index 0000000..09fc5dd
--- /dev/null
+++ b/src/archive/tar/testdata/writer-big-long.tar
diff --git a/src/archive/tar/testdata/writer-big.tar b/src/archive/tar/testdata/writer-big.tar
new file mode 100644
index 0000000..435dcbc
--- /dev/null
+++ b/src/archive/tar/testdata/writer-big.tar
diff --git a/src/archive/tar/testdata/writer.tar b/src/archive/tar/testdata/writer.tar
new file mode 100644
index 0000000..e6d816a
--- /dev/null
+++ b/src/archive/tar/testdata/writer.tar
diff --git a/src/archive/tar/testdata/xattrs.tar b/src/archive/tar/testdata/xattrs.tar
new file mode 100644
index 0000000..9701950
--- /dev/null
+++ b/src/archive/tar/testdata/xattrs.tar
diff --git a/src/archive/tar/writer.go b/src/archive/tar/writer.go
new file mode 100644
index 0000000..e80498d
--- /dev/null
+++ b/src/archive/tar/writer.go
@@ -0,0 +1,653 @@
+// 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: &regFileWriter{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.USTAR().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.GNU().AccessTime(), hdr.AccessTime.Unix())
+	}
+	if !hdr.ChangeTime.IsZero() {
+		f.formatNumeric(blk.GNU().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.V7()
+	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.USTAR()
+	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.V7()
+	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 = &regFileWriter{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)
+}
+
+func (fw regFileWriter) LogicalRemaining() int64 {
+	return fw.nb
+}
+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
+	}
+}
diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
new file mode 100644
index 0000000..a00f02d
--- /dev/null
+++ b/src/archive/tar/writer_test.go
@@ -0,0 +1,1310 @@
+// 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"
+	"encoding/hex"
+	"errors"
+	"io"
+	"os"
+	"path"
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+	"testing/iotest"
+	"time"
+)
+
+func bytediff(a, b []byte) string {
+	const (
+		uniqueA  = "-  "
+		uniqueB  = "+  "
+		identity = "   "
+	)
+	var ss []string
+	sa := strings.Split(strings.TrimSpace(hex.Dump(a)), "\n")
+	sb := strings.Split(strings.TrimSpace(hex.Dump(b)), "\n")
+	for len(sa) > 0 && len(sb) > 0 {
+		if sa[0] == sb[0] {
+			ss = append(ss, identity+sa[0])
+		} else {
+			ss = append(ss, uniqueA+sa[0])
+			ss = append(ss, uniqueB+sb[0])
+		}
+		sa, sb = sa[1:], sb[1:]
+	}
+	for len(sa) > 0 {
+		ss = append(ss, uniqueA+sa[0])
+		sa = sa[1:]
+	}
+	for len(sb) > 0 {
+		ss = append(ss, uniqueB+sb[0])
+		sb = sb[1:]
+	}
+	return strings.Join(ss, "\n")
+}
+
+func TestWriter(t *testing.T) {
+	type (
+		testHeader struct { // WriteHeader(hdr) == wantErr
+			hdr     Header
+			wantErr error
+		}
+		testWrite struct { // Write(str) == (wantCnt, wantErr)
+			str     string
+			wantCnt int
+			wantErr error
+		}
+		testReadFrom struct { // ReadFrom(testFile{ops}) == (wantCnt, wantErr)
+			ops     fileOps
+			wantCnt int64
+			wantErr error
+		}
+		testClose struct { // Close() == wantErr
+			wantErr error
+		}
+		testFnc interface{} // testHeader | testWrite | testReadFrom | testClose
+	)
+
+	vectors := []struct {
+		file  string // Optional filename of expected output
+		tests []testFnc
+	}{{
+		// The writer test file was produced with this command:
+		// tar (GNU tar) 1.26
+		//   ln -s small.txt link.txt
+		//   tar -b 1 --format=ustar -c -f writer.tar small.txt small2.txt link.txt
+		file: "testdata/writer.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "small.txt",
+				Size:     5,
+				Mode:     0640,
+				Uid:      73025,
+				Gid:      5000,
+				Uname:    "dsymonds",
+				Gname:    "eng",
+				ModTime:  time.Unix(1246508266, 0),
+			}, nil},
+			testWrite{"Kilts", 5, nil},
+
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "small2.txt",
+				Size:     11,
+				Mode:     0640,
+				Uid:      73025,
+				Uname:    "dsymonds",
+				Gname:    "eng",
+				Gid:      5000,
+				ModTime:  time.Unix(1245217492, 0),
+			}, nil},
+			testWrite{"Google.com\n", 11, nil},
+
+			testHeader{Header{
+				Typeflag: TypeSymlink,
+				Name:     "link.txt",
+				Linkname: "small.txt",
+				Mode:     0777,
+				Uid:      1000,
+				Gid:      1000,
+				Uname:    "strings",
+				Gname:    "strings",
+				ModTime:  time.Unix(1314603082, 0),
+			}, nil},
+			testWrite{"", 0, nil},
+
+			testClose{nil},
+		},
+	}, {
+		// The truncated test file was produced using these commands:
+		//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+		//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+		file: "testdata/writer-big.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "tmp/16gig.txt",
+				Size:     16 << 30,
+				Mode:     0640,
+				Uid:      73025,
+				Gid:      5000,
+				Uname:    "dsymonds",
+				Gname:    "eng",
+				ModTime:  time.Unix(1254699560, 0),
+				Format:   FormatGNU,
+			}, nil},
+		},
+	}, {
+		// This truncated file was produced using this library.
+		// It was verified to work with GNU tar 1.27.1 and BSD tar 3.1.2.
+		//  dd if=/dev/zero bs=1G count=16 >> writer-big-long.tar
+		//  gnutar -xvf writer-big-long.tar
+		//  bsdtar -xvf writer-big-long.tar
+		//
+		// This file is in PAX format.
+		file: "testdata/writer-big-long.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     strings.Repeat("longname/", 15) + "16gig.txt",
+				Size:     16 << 30,
+				Mode:     0644,
+				Uid:      1000,
+				Gid:      1000,
+				Uname:    "guillaume",
+				Gname:    "guillaume",
+				ModTime:  time.Unix(1399583047, 0),
+			}, nil},
+		},
+	}, {
+		// This file was produced using GNU tar v1.17.
+		//	gnutar -b 4 --format=ustar (longname/)*15 + file.txt
+		file: "testdata/ustar.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     strings.Repeat("longname/", 15) + "file.txt",
+				Size:     6,
+				Mode:     0644,
+				Uid:      501,
+				Gid:      20,
+				Uname:    "shane",
+				Gname:    "staff",
+				ModTime:  time.Unix(1360135598, 0),
+			}, nil},
+			testWrite{"hello\n", 6, nil},
+			testClose{nil},
+		},
+	}, {
+		// This file was produced using GNU tar v1.26:
+		//	echo "Slartibartfast" > file.txt
+		//	ln file.txt hard.txt
+		//	tar -b 1 --format=ustar -c -f hardlink.tar file.txt hard.txt
+		file: "testdata/hardlink.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "file.txt",
+				Size:     15,
+				Mode:     0644,
+				Uid:      1000,
+				Gid:      100,
+				Uname:    "vbatts",
+				Gname:    "users",
+				ModTime:  time.Unix(1425484303, 0),
+			}, nil},
+			testWrite{"Slartibartfast\n", 15, nil},
+
+			testHeader{Header{
+				Typeflag: TypeLink,
+				Name:     "hard.txt",
+				Linkname: "file.txt",
+				Mode:     0644,
+				Uid:      1000,
+				Gid:      100,
+				Uname:    "vbatts",
+				Gname:    "users",
+				ModTime:  time.Unix(1425484303, 0),
+			}, nil},
+			testWrite{"", 0, nil},
+
+			testClose{nil},
+		},
+	}, {
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "bad-null.txt",
+				Xattrs:   map[string]string{"null\x00null\x00": "fizzbuzz"},
+			}, headerError{}},
+		},
+	}, {
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "null\x00.txt",
+			}, headerError{}},
+		},
+	}, {
+		file: "testdata/pax-records.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "file",
+				Uname:    strings.Repeat("long", 10),
+				PAXRecords: map[string]string{
+					"path":           "FILE", // Should be ignored
+					"GNU.sparse.map": "0,0",  // Should be ignored
+					"comment":        "Hello, 世界",
+					"GOLANG.pkg":     "tar",
+				},
+			}, nil},
+			testClose{nil},
+		},
+	}, {
+		// Craft a theoretically valid PAX archive with global headers.
+		// The GNU and BSD tar tools do not parse these the same way.
+		//
+		// BSD tar v3.1.2 parses and ignores all global headers;
+		// the behavior is verified by researching the source code.
+		//
+		//	$ bsdtar -tvf pax-global-records.tar
+		//	----------  0 0      0           0 Dec 31  1969 file1
+		//	----------  0 0      0           0 Dec 31  1969 file2
+		//	----------  0 0      0           0 Dec 31  1969 file3
+		//	----------  0 0      0           0 May 13  2014 file4
+		//
+		// GNU tar v1.27.1 applies global headers to subsequent records,
+		// but does not do the following properly:
+		//	* It does not treat an empty record as deletion.
+		//	* It does not use subsequent global headers to update previous ones.
+		//
+		//	$ gnutar -tvf pax-global-records.tar
+		//	---------- 0/0               0 2017-07-13 19:40 global1
+		//	---------- 0/0               0 2017-07-13 19:40 file2
+		//	gnutar: Substituting `.' for empty member name
+		//	---------- 0/0               0 1969-12-31 16:00
+		//	gnutar: Substituting `.' for empty member name
+		//	---------- 0/0               0 2014-05-13 09:53
+		//
+		// According to the PAX specification, this should have been the result:
+		//	---------- 0/0               0 2017-07-13 19:40 global1
+		//	---------- 0/0               0 2017-07-13 19:40 file2
+		//	---------- 0/0               0 2017-07-13 19:40 file3
+		//	---------- 0/0               0 2014-05-13 09:53 file4
+		file: "testdata/pax-global-records.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag:   TypeXGlobalHeader,
+				PAXRecords: map[string]string{"path": "global1", "mtime": "1500000000.0"},
+			}, nil},
+			testHeader{Header{
+				Typeflag: TypeReg, Name: "file1",
+			}, nil},
+			testHeader{Header{
+				Typeflag:   TypeReg,
+				Name:       "file2",
+				PAXRecords: map[string]string{"path": "file2"},
+			}, nil},
+			testHeader{Header{
+				Typeflag:   TypeXGlobalHeader,
+				PAXRecords: map[string]string{"path": ""}, // Should delete "path", but keep "mtime"
+			}, nil},
+			testHeader{Header{
+				Typeflag: TypeReg, Name: "file3",
+			}, nil},
+			testHeader{Header{
+				Typeflag:   TypeReg,
+				Name:       "file4",
+				ModTime:    time.Unix(1400000000, 0),
+				PAXRecords: map[string]string{"mtime": "1400000000"},
+			}, nil},
+			testClose{nil},
+		},
+	}, {
+		file: "testdata/gnu-utf8.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹☺☻☹",
+				Mode:     0644,
+				Uid:      1000, Gid: 1000,
+				Uname:   "☺",
+				Gname:   "⚹",
+				ModTime: time.Unix(0, 0),
+				Format:  FormatGNU,
+			}, nil},
+			testClose{nil},
+		},
+	}, {
+		file: "testdata/gnu-not-utf8.tar",
+		tests: []testFnc{
+			testHeader{Header{
+				Typeflag: TypeReg,
+				Name:     "hi\x80\x81\x82\x83bye",
+				Mode:     0644,
+				Uid:      1000,
+				Gid:      1000,
+				Uname:    "rawr",
+				Gname:    "dsnet",
+				ModTime:  time.Unix(0, 0),
+				Format:   FormatGNU,
+			}, nil},
+			testClose{nil},
+		},
+		// TODO(dsnet): Re-enable this test when adding sparse support.
+		// See https://golang.org/issue/22735
+		/*
+			}, {
+				file: "testdata/gnu-nil-sparse-data.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag:    TypeGNUSparse,
+						Name:        "sparse.db",
+						Size:        1000,
+						SparseHoles: []sparseEntry{{Offset: 1000, Length: 0}},
+					}, nil},
+					testWrite{strings.Repeat("0123456789", 100), 1000, nil},
+					testClose{},
+				},
+			}, {
+				file: "testdata/gnu-nil-sparse-hole.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag:    TypeGNUSparse,
+						Name:        "sparse.db",
+						Size:        1000,
+						SparseHoles: []sparseEntry{{Offset: 0, Length: 1000}},
+					}, nil},
+					testWrite{strings.Repeat("\x00", 1000), 1000, nil},
+					testClose{},
+				},
+			}, {
+				file: "testdata/pax-nil-sparse-data.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag:    TypeReg,
+						Name:        "sparse.db",
+						Size:        1000,
+						SparseHoles: []sparseEntry{{Offset: 1000, Length: 0}},
+					}, nil},
+					testWrite{strings.Repeat("0123456789", 100), 1000, nil},
+					testClose{},
+				},
+			}, {
+				file: "testdata/pax-nil-sparse-hole.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag:    TypeReg,
+						Name:        "sparse.db",
+						Size:        1000,
+						SparseHoles: []sparseEntry{{Offset: 0, Length: 1000}},
+					}, nil},
+					testWrite{strings.Repeat("\x00", 1000), 1000, nil},
+					testClose{},
+				},
+			}, {
+				file: "testdata/gnu-sparse-big.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag: TypeGNUSparse,
+						Name:     "gnu-sparse",
+						Size:     6e10,
+						SparseHoles: []sparseEntry{
+							{Offset: 0e10, Length: 1e10 - 100},
+							{Offset: 1e10, Length: 1e10 - 100},
+							{Offset: 2e10, Length: 1e10 - 100},
+							{Offset: 3e10, Length: 1e10 - 100},
+							{Offset: 4e10, Length: 1e10 - 100},
+							{Offset: 5e10, Length: 1e10 - 100},
+						},
+					}, nil},
+					testReadFrom{fileOps{
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+					}, 6e10, nil},
+					testClose{nil},
+				},
+			}, {
+				file: "testdata/pax-sparse-big.tar",
+				tests: []testFnc{
+					testHeader{Header{
+						Typeflag: TypeReg,
+						Name:     "pax-sparse",
+						Size:     6e10,
+						SparseHoles: []sparseEntry{
+							{Offset: 0e10, Length: 1e10 - 100},
+							{Offset: 1e10, Length: 1e10 - 100},
+							{Offset: 2e10, Length: 1e10 - 100},
+							{Offset: 3e10, Length: 1e10 - 100},
+							{Offset: 4e10, Length: 1e10 - 100},
+							{Offset: 5e10, Length: 1e10 - 100},
+						},
+					}, nil},
+					testReadFrom{fileOps{
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+						int64(1e10 - blockSize),
+						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),
+					}, 6e10, nil},
+					testClose{nil},
+				},
+		*/
+	}, {
+		file: "testdata/trailing-slash.tar",
+		tests: []testFnc{
+			testHeader{Header{Name: strings.Repeat("123456789/", 30)}, nil},
+			testClose{nil},
+		},
+	}, {
+		// Automatically promote zero value of Typeflag depending on the name.
+		file: "testdata/file-and-dir.tar",
+		tests: []testFnc{
+			testHeader{Header{Name: "small.txt", Size: 5}, nil},
+			testWrite{"Kilts", 5, nil},
+			testHeader{Header{Name: "dir/"}, nil},
+			testClose{nil},
+		},
+	}}
+
+	equalError := func(x, y error) bool {
+		_, ok1 := x.(headerError)
+		_, ok2 := y.(headerError)
+		if ok1 || ok2 {
+			return ok1 && ok2
+		}
+		return x == y
+	}
+	for _, v := range vectors {
+		t.Run(path.Base(v.file), func(t *testing.T) {
+			const maxSize = 10 << 10 // 10KiB
+			buf := new(bytes.Buffer)
+			tw := NewWriter(iotest.TruncateWriter(buf, maxSize))
+
+			for i, tf := range v.tests {
+				switch tf := tf.(type) {
+				case testHeader:
+					err := tw.WriteHeader(&tf.hdr)
+					if !equalError(err, tf.wantErr) {
+						t.Fatalf("test %d, WriteHeader() = %v, want %v", i, err, tf.wantErr)
+					}
+				case testWrite:
+					got, err := tw.Write([]byte(tf.str))
+					if got != tf.wantCnt || !equalError(err, tf.wantErr) {
+						t.Fatalf("test %d, Write() = (%d, %v), want (%d, %v)", i, got, err, tf.wantCnt, tf.wantErr)
+					}
+				case testReadFrom:
+					f := &testFile{ops: tf.ops}
+					got, err := tw.readFrom(f)
+					if _, ok := err.(testError); ok {
+						t.Errorf("test %d, ReadFrom(): %v", i, err)
+					} else if got != tf.wantCnt || !equalError(err, tf.wantErr) {
+						t.Errorf("test %d, ReadFrom() = (%d, %v), want (%d, %v)", i, got, err, tf.wantCnt, tf.wantErr)
+					}
+					if len(f.ops) > 0 {
+						t.Errorf("test %d, expected %d more operations", i, len(f.ops))
+					}
+				case testClose:
+					err := tw.Close()
+					if !equalError(err, tf.wantErr) {
+						t.Fatalf("test %d, Close() = %v, want %v", i, err, tf.wantErr)
+					}
+				default:
+					t.Fatalf("test %d, unknown test operation: %T", i, tf)
+				}
+			}
+
+			if v.file != "" {
+				want, err := os.ReadFile(v.file)
+				if err != nil {
+					t.Fatalf("ReadFile() = %v, want nil", err)
+				}
+				got := buf.Bytes()
+				if !bytes.Equal(want, got) {
+					t.Fatalf("incorrect result: (-got +want)\n%v", bytediff(got, want))
+				}
+			}
+		})
+	}
+}
+
+func TestPax(t *testing.T) {
+	// Create an archive with a large name
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat: %v", err)
+	}
+	// Force a PAX long name to be written
+	longName := strings.Repeat("ab", 100)
+	contents := strings.Repeat(" ", int(hdr.Size))
+	hdr.Name = longName
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != longName {
+		t.Fatal("Couldn't recover long file name")
+	}
+}
+
+func TestPaxSymlink(t *testing.T) {
+	// Create an archive with a large linkname
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	hdr.Typeflag = TypeSymlink
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+	// Force a PAX long linkname to be written
+	longLinkname := strings.Repeat("1234567890/1234567890", 10)
+	hdr.Linkname = longLinkname
+
+	hdr.Size = 0
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Linkname != longLinkname {
+		t.Fatal("Couldn't recover long link name")
+	}
+}
+
+func TestPaxNonAscii(t *testing.T) {
+	// Create an archive with non ascii. These should trigger a pax header
+	// because pax headers have a defined utf-8 encoding.
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+
+	// some sample data
+	chineseFilename := "文件名"
+	chineseGroupname := "組"
+	chineseUsername := "用戶名"
+
+	hdr.Name = chineseFilename
+	hdr.Gname = chineseGroupname
+	hdr.Uname = chineseUsername
+
+	contents := strings.Repeat(" ", int(hdr.Size))
+
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != chineseFilename {
+		t.Fatal("Couldn't recover unicode name")
+	}
+	if hdr.Gname != chineseGroupname {
+		t.Fatal("Couldn't recover unicode group")
+	}
+	if hdr.Uname != chineseUsername {
+		t.Fatal("Couldn't recover unicode user")
+	}
+}
+
+func TestPaxXattrs(t *testing.T) {
+	xattrs := map[string]string{
+		"user.key": "value",
+	}
+
+	// Create an archive with an xattr
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat: %v", err)
+	}
+	contents := "Kilts"
+	hdr.Xattrs = xattrs
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Test that we can get the xattrs back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(hdr.Xattrs, xattrs) {
+		t.Fatalf("xattrs did not survive round trip: got %+v, want %+v",
+			hdr.Xattrs, xattrs)
+	}
+}
+
+func TestPaxHeadersSorted(t *testing.T) {
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	if err != nil {
+		t.Fatalf("os.Stat: %v", err)
+	}
+	contents := strings.Repeat(" ", int(hdr.Size))
+
+	hdr.Xattrs = map[string]string{
+		"foo": "foo",
+		"bar": "bar",
+		"baz": "baz",
+		"qux": "qux",
+	}
+
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if _, err = writer.Write([]byte(contents)); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Simple test to make sure PAX extensions are in effect
+	if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
+		t.Fatal("Expected at least one PAX header to be written.")
+	}
+
+	// xattr bar should always appear before others
+	indices := []int{
+		bytes.Index(buf.Bytes(), []byte("bar=bar")),
+		bytes.Index(buf.Bytes(), []byte("baz=baz")),
+		bytes.Index(buf.Bytes(), []byte("foo=foo")),
+		bytes.Index(buf.Bytes(), []byte("qux=qux")),
+	}
+	if !sort.IntsAreSorted(indices) {
+		t.Fatal("PAX headers are not sorted")
+	}
+}
+
+func TestUSTARLongName(t *testing.T) {
+	// Create an archive with a path that failed to split with USTAR extension in previous versions.
+	fileinfo, err := os.Stat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	hdr, err := FileInfoHeader(fileinfo, "")
+	hdr.Typeflag = TypeDir
+	if err != nil {
+		t.Fatalf("os.Stat:1 %v", err)
+	}
+	// Force a PAX long name to be written. The name was taken from a practical example
+	// that fails and replaced ever char through numbers to anonymize the sample.
+	longName := "/0000_0000000/00000-000000000/0000_0000000/00000-0000000000000/0000_0000000/00000-0000000-00000000/0000_0000000/00000000/0000_0000000/000/0000_0000000/00000000v00/0000_0000000/000000/0000_0000000/0000000/0000_0000000/00000y-00/0000/0000/00000000/0x000000/"
+	hdr.Name = longName
+
+	hdr.Size = 0
+	var buf bytes.Buffer
+	writer := NewWriter(&buf)
+	if err := writer.WriteHeader(hdr); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Test that we can get a long name back out of the archive.
+	reader := NewReader(&buf)
+	hdr, err = reader.Next()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hdr.Name != longName {
+		t.Fatal("Couldn't recover long name")
+	}
+}
+
+func TestValidTypeflagWithPAXHeader(t *testing.T) {
+	var buffer bytes.Buffer
+	tw := NewWriter(&buffer)
+
+	fileName := strings.Repeat("ab", 100)
+
+	hdr := &Header{
+		Name:     fileName,
+		Size:     4,
+		Typeflag: 0,
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		t.Fatalf("Failed to write header: %s", err)
+	}
+	if _, err := tw.Write([]byte("fooo")); err != nil {
+		t.Fatalf("Failed to write the file's data: %s", err)
+	}
+	tw.Close()
+
+	tr := NewReader(&buffer)
+
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("Failed to read header: %s", err)
+		}
+		if header.Typeflag != TypeReg {
+			t.Fatalf("Typeflag should've been %d, found %d", TypeReg, header.Typeflag)
+		}
+	}
+}
+
+// failOnceWriter fails exactly once and then always reports success.
+type failOnceWriter bool
+
+func (w *failOnceWriter) Write(b []byte) (int, error) {
+	if !*w {
+		return 0, io.ErrShortWrite
+	}
+	*w = true
+	return len(b), nil
+}
+
+func TestWriterErrors(t *testing.T) {
+	t.Run("HeaderOnly", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		hdr := &Header{Name: "dir/", Typeflag: TypeDir}
+		if err := tw.WriteHeader(hdr); err != nil {
+			t.Fatalf("WriteHeader() = %v, want nil", err)
+		}
+		if _, err := tw.Write([]byte{0x00}); err != ErrWriteTooLong {
+			t.Fatalf("Write() = %v, want %v", err, ErrWriteTooLong)
+		}
+	})
+
+	t.Run("NegativeSize", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		hdr := &Header{Name: "small.txt", Size: -1}
+		if err := tw.WriteHeader(hdr); err == nil {
+			t.Fatalf("WriteHeader() = nil, want non-nil error")
+		}
+	})
+
+	t.Run("BeforeHeader", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		if _, err := tw.Write([]byte("Kilts")); err != ErrWriteTooLong {
+			t.Fatalf("Write() = %v, want %v", err, ErrWriteTooLong)
+		}
+	})
+
+	t.Run("AfterClose", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		hdr := &Header{Name: "small.txt"}
+		if err := tw.WriteHeader(hdr); err != nil {
+			t.Fatalf("WriteHeader() = %v, want nil", err)
+		}
+		if err := tw.Close(); err != nil {
+			t.Fatalf("Close() = %v, want nil", err)
+		}
+		if _, err := tw.Write([]byte("Kilts")); err != ErrWriteAfterClose {
+			t.Fatalf("Write() = %v, want %v", err, ErrWriteAfterClose)
+		}
+		if err := tw.Flush(); err != ErrWriteAfterClose {
+			t.Fatalf("Flush() = %v, want %v", err, ErrWriteAfterClose)
+		}
+		if err := tw.Close(); err != nil {
+			t.Fatalf("Close() = %v, want nil", err)
+		}
+	})
+
+	t.Run("PrematureFlush", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		hdr := &Header{Name: "small.txt", Size: 5}
+		if err := tw.WriteHeader(hdr); err != nil {
+			t.Fatalf("WriteHeader() = %v, want nil", err)
+		}
+		if err := tw.Flush(); err == nil {
+			t.Fatalf("Flush() = %v, want non-nil error", err)
+		}
+	})
+
+	t.Run("PrematureClose", func(t *testing.T) {
+		tw := NewWriter(new(bytes.Buffer))
+		hdr := &Header{Name: "small.txt", Size: 5}
+		if err := tw.WriteHeader(hdr); err != nil {
+			t.Fatalf("WriteHeader() = %v, want nil", err)
+		}
+		if err := tw.Close(); err == nil {
+			t.Fatalf("Close() = %v, want non-nil error", err)
+		}
+	})
+
+	t.Run("Persistence", func(t *testing.T) {
+		tw := NewWriter(new(failOnceWriter))
+		if err := tw.WriteHeader(&Header{}); err != io.ErrShortWrite {
+			t.Fatalf("WriteHeader() = %v, want %v", err, io.ErrShortWrite)
+		}
+		if err := tw.WriteHeader(&Header{Name: "small.txt"}); err == nil {
+			t.Errorf("WriteHeader() = got %v, want non-nil error", err)
+		}
+		if _, err := tw.Write(nil); err == nil {
+			t.Errorf("Write() = %v, want non-nil error", err)
+		}
+		if err := tw.Flush(); err == nil {
+			t.Errorf("Flush() = %v, want non-nil error", err)
+		}
+		if err := tw.Close(); err == nil {
+			t.Errorf("Close() = %v, want non-nil error", err)
+		}
+	})
+}
+
+func TestSplitUSTARPath(t *testing.T) {
+	sr := strings.Repeat
+
+	vectors := []struct {
+		input  string // Input path
+		prefix string // Expected output prefix
+		suffix string // Expected output suffix
+		ok     bool   // Split success?
+	}{
+		{"", "", "", false},
+		{"abc", "", "", false},
+		{"用戶名", "", "", false},
+		{sr("a", nameSize), "", "", false},
+		{sr("a", nameSize) + "/", "", "", false},
+		{sr("a", nameSize) + "/a", sr("a", nameSize), "a", true},
+		{sr("a", prefixSize) + "/", "", "", false},
+		{sr("a", prefixSize) + "/a", sr("a", prefixSize), "a", true},
+		{sr("a", nameSize+1), "", "", false},
+		{sr("/", nameSize+1), sr("/", nameSize-1), "/", true},
+		{sr("a", prefixSize) + "/" + sr("b", nameSize),
+			sr("a", prefixSize), sr("b", nameSize), true},
+		{sr("a", prefixSize) + "//" + sr("b", nameSize), "", "", false},
+		{sr("a/", nameSize), sr("a/", 77) + "a", sr("a/", 22), true},
+	}
+
+	for _, v := range vectors {
+		prefix, suffix, ok := splitUSTARPath(v.input)
+		if prefix != v.prefix || suffix != v.suffix || ok != v.ok {
+			t.Errorf("splitUSTARPath(%q):\ngot  (%q, %q, %v)\nwant (%q, %q, %v)",
+				v.input, prefix, suffix, ok, v.prefix, v.suffix, v.ok)
+		}
+	}
+}
+
+// TestIssue12594 tests that the Writer does not attempt to populate the prefix
+// field when encoding a header in the GNU format. The prefix field is valid
+// in USTAR and PAX, but not GNU.
+func TestIssue12594(t *testing.T) {
+	names := []string{
+		"0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/file.txt",
+		"0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32/33/file.txt",
+		"0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32/333/file.txt",
+		"0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32/33/34/35/36/37/38/39/40/file.txt",
+		"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000/file.txt",
+		"/home/support/.openoffice.org/3/user/uno_packages/cache/registry/com.sun.star.comp.deployment.executable.PackageRegistryBackend",
+	}
+
+	for i, name := range names {
+		var b bytes.Buffer
+
+		tw := NewWriter(&b)
+		if err := tw.WriteHeader(&Header{
+			Name: name,
+			Uid:  1 << 25, // Prevent USTAR format
+		}); err != nil {
+			t.Errorf("test %d, unexpected WriteHeader error: %v", i, err)
+		}
+		if err := tw.Close(); err != nil {
+			t.Errorf("test %d, unexpected Close error: %v", i, err)
+		}
+
+		// The prefix field should never appear in the GNU format.
+		var blk block
+		copy(blk[:], b.Bytes())
+		prefix := string(blk.USTAR().Prefix())
+		if i := strings.IndexByte(prefix, 0); i >= 0 {
+			prefix = prefix[:i] // Truncate at the NUL terminator
+		}
+		if blk.GetFormat() == FormatGNU && len(prefix) > 0 && strings.HasPrefix(name, prefix) {
+			t.Errorf("test %d, found prefix in GNU format: %s", i, prefix)
+		}
+
+		tr := NewReader(&b)
+		hdr, err := tr.Next()
+		if err != nil {
+			t.Errorf("test %d, unexpected Next error: %v", i, err)
+		}
+		if hdr.Name != name {
+			t.Errorf("test %d, hdr.Name = %s, want %s", i, hdr.Name, name)
+		}
+	}
+}
+
+// testNonEmptyWriter wraps an io.Writer and ensures that
+// Write is never called with an empty buffer.
+type testNonEmptyWriter struct{ io.Writer }
+
+func (w testNonEmptyWriter) Write(b []byte) (int, error) {
+	if len(b) == 0 {
+		return 0, errors.New("unexpected empty Write call")
+	}
+	return w.Writer.Write(b)
+}
+
+func TestFileWriter(t *testing.T) {
+	type (
+		testWrite struct { // Write(str) == (wantCnt, wantErr)
+			str     string
+			wantCnt int
+			wantErr error
+		}
+		testReadFrom struct { // ReadFrom(testFile{ops}) == (wantCnt, wantErr)
+			ops     fileOps
+			wantCnt int64
+			wantErr error
+		}
+		testRemaining struct { // LogicalRemaining() == wantLCnt, PhysicalRemaining() == wantPCnt
+			wantLCnt int64
+			wantPCnt int64
+		}
+		testFnc interface{} // testWrite | testReadFrom | testRemaining
+	)
+
+	type (
+		makeReg struct {
+			size    int64
+			wantStr string
+		}
+		makeSparse struct {
+			makeReg makeReg
+			sph     sparseHoles
+			size    int64
+		}
+		fileMaker interface{} // makeReg | makeSparse
+	)
+
+	vectors := []struct {
+		maker fileMaker
+		tests []testFnc
+	}{{
+		maker: makeReg{0, ""},
+		tests: []testFnc{
+			testRemaining{0, 0},
+			testWrite{"", 0, nil},
+			testWrite{"a", 0, ErrWriteTooLong},
+			testReadFrom{fileOps{""}, 0, nil},
+			testReadFrom{fileOps{"a"}, 0, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{1, "a"},
+		tests: []testFnc{
+			testRemaining{1, 1},
+			testWrite{"", 0, nil},
+			testWrite{"a", 1, nil},
+			testWrite{"bcde", 0, ErrWriteTooLong},
+			testWrite{"", 0, nil},
+			testReadFrom{fileOps{""}, 0, nil},
+			testReadFrom{fileOps{"a"}, 0, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{5, "hello"},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testWrite{"hello", 5, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{5, "\x00\x00\x00\x00\x00"},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testReadFrom{fileOps{"\x00\x00\x00\x00\x00"}, 5, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{5, "\x00\x00\x00\x00\x00"},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testReadFrom{fileOps{"\x00\x00\x00\x00\x00extra"}, 5, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{5, "abc\x00\x00"},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testWrite{"abc", 3, nil},
+			testRemaining{2, 2},
+			testReadFrom{fileOps{"\x00\x00"}, 2, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeReg{5, "\x00\x00abc"},
+		tests: []testFnc{
+			testRemaining{5, 5},
+			testWrite{"\x00\x00", 2, nil},
+			testRemaining{3, 3},
+			testWrite{"abc", 3, nil},
+			testReadFrom{fileOps{"z"}, 0, ErrWriteTooLong},
+			testWrite{"z", 0, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testRemaining{8, 5},
+			testWrite{"ab\x00\x00\x00cde", 8, nil},
+			testWrite{"a", 0, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testWrite{"ab\x00\x00\x00cdez", 8, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testWrite{"ab\x00", 3, nil},
+			testRemaining{5, 3},
+			testWrite{"\x00\x00cde", 5, nil},
+			testWrite{"a", 0, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testWrite{"ab", 2, nil},
+			testRemaining{6, 3},
+			testReadFrom{fileOps{int64(3), "cde"}, 6, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testReadFrom{fileOps{"ab", int64(3), "cde"}, 8, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{5, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testReadFrom{fileOps{"ab", int64(3), "cdeX"}, 8, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{4, "abcd"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testReadFrom{fileOps{"ab", int64(3), "cd"}, 7, io.ErrUnexpectedEOF},
+			testRemaining{1, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{4, "abcd"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testReadFrom{fileOps{"ab", int64(3), "cde"}, 7, errMissData},
+			testRemaining{1, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{6, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testReadFrom{fileOps{"ab", int64(3), "cde"}, 8, errUnrefData},
+			testRemaining{0, 1},
+		},
+	}, {
+		maker: makeSparse{makeReg{4, "abcd"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testWrite{"ab", 2, nil},
+			testRemaining{6, 2},
+			testWrite{"\x00\x00\x00", 3, nil},
+			testRemaining{3, 2},
+			testWrite{"cde", 2, errMissData},
+			testRemaining{1, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{6, "abcde"}, sparseHoles{{2, 3}}, 8},
+		tests: []testFnc{
+			testWrite{"ab", 2, nil},
+			testRemaining{6, 4},
+			testWrite{"\x00\x00\x00", 3, nil},
+			testRemaining{3, 4},
+			testWrite{"cde", 3, errUnrefData},
+			testRemaining{0, 1},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testRemaining{7, 3},
+			testWrite{"\x00\x00abc\x00\x00", 7, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testRemaining{7, 3},
+			testReadFrom{fileOps{int64(2), "abc", int64(1), "\x00"}, 7, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, ""}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"abcdefg", 0, errWriteHole},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"\x00\x00abcde", 5, errWriteHole},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"\x00\x00abc\x00\x00z", 7, ErrWriteTooLong},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{3, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"\x00\x00", 2, nil},
+			testRemaining{5, 3},
+			testWrite{"abc", 3, nil},
+			testRemaining{2, 0},
+			testWrite{"\x00\x00", 2, nil},
+			testRemaining{0, 0},
+		},
+	}, {
+		maker: makeSparse{makeReg{2, "ab"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"\x00\x00", 2, nil},
+			testWrite{"abc", 2, errMissData},
+			testWrite{"\x00\x00", 0, errMissData},
+		},
+	}, {
+		maker: makeSparse{makeReg{4, "abc"}, sparseHoles{{0, 2}, {5, 2}}, 7},
+		tests: []testFnc{
+			testWrite{"\x00\x00", 2, nil},
+			testWrite{"abc", 3, nil},
+			testWrite{"\x00\x00", 2, errUnrefData},
+		},
+	}}
+
+	for i, v := range vectors {
+		var wantStr string
+		bb := new(bytes.Buffer)
+		w := testNonEmptyWriter{bb}
+		var fw fileWriter
+		switch maker := v.maker.(type) {
+		case makeReg:
+			fw = &regFileWriter{w, maker.size}
+			wantStr = maker.wantStr
+		case makeSparse:
+			if !validateSparseEntries(maker.sph, maker.size) {
+				t.Fatalf("invalid sparse map: %v", maker.sph)
+			}
+			spd := invertSparseEntries(maker.sph, maker.size)
+			fw = &regFileWriter{w, maker.makeReg.size}
+			fw = &sparseFileWriter{fw, spd, 0}
+			wantStr = maker.makeReg.wantStr
+		default:
+			t.Fatalf("test %d, unknown make operation: %T", i, maker)
+		}
+
+		for j, tf := range v.tests {
+			switch tf := tf.(type) {
+			case testWrite:
+				got, err := fw.Write([]byte(tf.str))
+				if got != tf.wantCnt || err != tf.wantErr {
+					t.Errorf("test %d.%d, Write(%s):\ngot  (%d, %v)\nwant (%d, %v)", i, j, tf.str, got, err, tf.wantCnt, tf.wantErr)
+				}
+			case testReadFrom:
+				f := &testFile{ops: tf.ops}
+				got, err := fw.ReadFrom(f)
+				if _, ok := err.(testError); ok {
+					t.Errorf("test %d.%d, ReadFrom(): %v", i, j, err)
+				} else if got != tf.wantCnt || err != tf.wantErr {
+					t.Errorf("test %d.%d, ReadFrom() = (%d, %v), want (%d, %v)", i, j, got, err, tf.wantCnt, tf.wantErr)
+				}
+				if len(f.ops) > 0 {
+					t.Errorf("test %d.%d, expected %d more operations", i, j, len(f.ops))
+				}
+			case testRemaining:
+				if got := fw.LogicalRemaining(); got != tf.wantLCnt {
+					t.Errorf("test %d.%d, LogicalRemaining() = %d, want %d", i, j, got, tf.wantLCnt)
+				}
+				if got := fw.PhysicalRemaining(); got != tf.wantPCnt {
+					t.Errorf("test %d.%d, PhysicalRemaining() = %d, want %d", i, j, got, tf.wantPCnt)
+				}
+			default:
+				t.Fatalf("test %d.%d, unknown test operation: %T", i, j, tf)
+			}
+		}
+
+		if got := bb.String(); got != wantStr {
+			t.Fatalf("test %d, String() = %q, want %q", i, got, wantStr)
+		}
+	}
+}