vendor: update everything

* If possible, update each dependency to the latest available version.

* Use releases over commit IDs and avoid vendoring branches.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

8 files changed, 2405 insertions, 1233 deletions

diff --git a/vendor/github.com/vbatts/tar-split/archive/tar/common.go b/vendor/github.com/vbatts/tar-split/archive/tar/common.go
index 36f4e2398..dee9e47e4 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/common.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/common.go
@@ -3,70 +3,528 @@
 // license that can be found in the LICENSE file.
 
 // Package tar implements access to tar archives.
-// It aims to cover most of the variations, including those produced
-// by GNU and BSD tars.
 //
-// References:
-//   http://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5
-//   http://www.gnu.org/software/tar/manual/html_node/Standard.html
-//   http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html
+// 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 (
-	"bytes"
 	"errors"
 	"fmt"
+	"math"
 	"os"
 	"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 (
-	blockSize = 512
-
-	// Types
-	TypeReg           = '0'    // regular file
-	TypeRegA          = '\x00' // regular file
-	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
-	TypeCont          = '7'    // reserved
-	TypeXHeader       = 'x'    // extended header
-	TypeXGlobalHeader = 'g'    // global extended header
-	TypeGNULongName   = 'L'    // Next file has a long name
-	TypeGNULongLink   = 'K'    // Next file symlinks to a file w/ a long name
-	TypeGNUSparse     = 'S'    // sparse file
+	// 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 {
-	Name       string    // name of header file entry
-	Mode       int64     // permission and mode bits
-	Uid        int       // user id of owner
-	Gid        int       // group id of owner
-	Size       int64     // length in bytes
-	ModTime    time.Time // modified time
-	Typeflag   byte      // type of header entry
-	Linkname   string    // target name of link
-	Uname      string    // user name of owner
-	Gname      string    // group name of owner
-	Devmajor   int64     // major number of character or block device
-	Devminor   int64     // minor number of character or block device
-	AccessTime time.Time // access time
-	ChangeTime time.Time // status change time
-	Xattrs     map[string]string
+	// 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
 }
 
-// File name constants from the tar spec.
-const (
-	fileNameSize       = 100 // Maximum number of bytes in a standard tar name.
-	fileNamePrefixSize = 155 // Maximum number of ustar extension bytes.
+// 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 os.FileInfo for the Header.
 func (h *Header) FileInfo() os.FileInfo {
 	return headerFileInfo{h}
@@ -97,63 +555,43 @@ func (fi headerFileInfo) Mode() (mode os.FileMode) {
 
 	// Set setuid, setgid and sticky bits.
 	if fi.h.Mode&c_ISUID != 0 {
-		// setuid
 		mode |= os.ModeSetuid
 	}
 	if fi.h.Mode&c_ISGID != 0 {
-		// setgid
 		mode |= os.ModeSetgid
 	}
 	if fi.h.Mode&c_ISVTX != 0 {
-		// sticky
 		mode |= os.ModeSticky
 	}
 
-	// Set file mode bits.
-	// clear perm, setuid, setgid and sticky bits.
-	m := os.FileMode(fi.h.Mode) &^ 07777
-	if m == c_ISDIR {
-		// directory
+	// Set file mode bits; clear perm, setuid, setgid, and sticky bits.
+	switch m := os.FileMode(fi.h.Mode) &^ 07777; m {
+	case c_ISDIR:
 		mode |= os.ModeDir
-	}
-	if m == c_ISFIFO {
-		// named pipe (FIFO)
+	case c_ISFIFO:
 		mode |= os.ModeNamedPipe
-	}
-	if m == c_ISLNK {
-		// symbolic link
+	case c_ISLNK:
 		mode |= os.ModeSymlink
-	}
-	if m == c_ISBLK {
-		// device file
+	case c_ISBLK:
 		mode |= os.ModeDevice
-	}
-	if m == c_ISCHR {
-		// Unix character device
+	case c_ISCHR:
 		mode |= os.ModeDevice
 		mode |= os.ModeCharDevice
-	}
-	if m == c_ISSOCK {
-		// Unix domain socket
+	case c_ISSOCK:
 		mode |= os.ModeSocket
 	}
 
 	switch fi.h.Typeflag {
 	case TypeSymlink:
-		// symbolic link
 		mode |= os.ModeSymlink
 	case TypeChar:
-		// character device node
 		mode |= os.ModeDevice
 		mode |= os.ModeCharDevice
 	case TypeBlock:
-		// block device node
 		mode |= os.ModeDevice
 	case TypeDir:
-		// directory
 		mode |= os.ModeDir
 	case TypeFifo:
-		// fifo node
 		mode |= os.ModeNamedPipe
 	}
 
@@ -163,11 +601,15 @@ func (fi headerFileInfo) Mode() (mode os.FileMode) {
 // sysStat, if non-nil, populates h from system-dependent fields of fi.
 var sysStat func(fi os.FileInfo, h *Header) error
 
-// Mode constants from the tar spec.
 const (
-	c_ISUID  = 04000   // Set uid
-	c_ISGID  = 02000   // Set gid
-	c_ISVTX  = 01000   // Save text (sticky bit)
+	// 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
@@ -177,33 +619,16 @@ const (
 	c_ISSOCK = 0140000 // Socket
 )
 
-// Keywords for the PAX Extended Header
-const (
-	paxAtime    = "atime"
-	paxCharset  = "charset"
-	paxComment  = "comment"
-	paxCtime    = "ctime" // please note that ctime is not a valid pax header.
-	paxGid      = "gid"
-	paxGname    = "gname"
-	paxLinkpath = "linkpath"
-	paxMtime    = "mtime"
-	paxPath     = "path"
-	paxSize     = "size"
-	paxUid      = "uid"
-	paxUname    = "uname"
-	paxXattr    = "SCHILY.xattr."
-	paxNone     = ""
-)
-
 // 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.
-// Because os.FileInfo's Name method returns only the base name of
-// the file it describes, it may be necessary to modify the Name field
-// of the returned header to provide the full path name of the file.
+//
+// Since os.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 os.FileInfo, link string) (*Header, error) {
 	if fi == nil {
-		return nil, errors.New("tar: FileInfo is nil")
+		return nil, errors.New("archive/tar: FileInfo is nil")
 	}
 	fm := fi.Mode()
 	h := &Header{
@@ -213,30 +638,24 @@ func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 	}
 	switch {
 	case fm.IsRegular():
-		h.Mode |= c_ISREG
 		h.Typeflag = TypeReg
 		h.Size = fi.Size()
 	case fi.IsDir():
 		h.Typeflag = TypeDir
-		h.Mode |= c_ISDIR
 		h.Name += "/"
 	case fm&os.ModeSymlink != 0:
 		h.Typeflag = TypeSymlink
-		h.Mode |= c_ISLNK
 		h.Linkname = link
 	case fm&os.ModeDevice != 0:
 		if fm&os.ModeCharDevice != 0 {
-			h.Mode |= c_ISCHR
 			h.Typeflag = TypeChar
 		} else {
-			h.Mode |= c_ISBLK
 			h.Typeflag = TypeBlock
 		}
 	case fm&os.ModeNamedPipe != 0:
 		h.Typeflag = TypeFifo
-		h.Mode |= c_ISFIFO
 	case fm&os.ModeSocket != 0:
-		h.Mode |= c_ISSOCK
+		return nil, fmt.Errorf("archive/tar: sockets not supported")
 	default:
 		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
 	}
@@ -272,6 +691,12 @@ func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 			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)
@@ -279,55 +704,6 @@ func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 	return h, nil
 }
 
-var zeroBlock = make([]byte, blockSize)
-
-// POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.
-// We compute and return both.
-func checksum(header []byte) (unsigned int64, signed int64) {
-	for i := 0; i < len(header); i++ {
-		if i == 148 {
-			// The chksum field (header[148:156]) is special: it should be treated as space bytes.
-			unsigned += ' ' * 8
-			signed += ' ' * 8
-			i += 7
-			continue
-		}
-		unsigned += int64(header[i])
-		signed += int64(int8(header[i]))
-	}
-	return
-}
-
-type slicer []byte
-
-func (sp *slicer) next(n int) (b []byte) {
-	s := *sp
-	b, *sp = s[0:n], s[n:]
-	return
-}
-
-func isASCII(s string) bool {
-	for _, c := range s {
-		if c >= 0x80 {
-			return false
-		}
-	}
-	return true
-}
-
-func toASCII(s string) string {
-	if isASCII(s) {
-		return s
-	}
-	var buf bytes.Buffer
-	for _, c := range s {
-		if c < 0x80 {
-			buf.WriteByte(byte(c))
-		}
-	}
-	return buf.String()
-}
-
 // 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 {
@@ -338,3 +714,10 @@ func isHeaderOnlyType(flag byte) bool {
 		return false
 	}
 }
+
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
diff --git a/vendor/github.com/vbatts/tar-split/archive/tar/format.go b/vendor/github.com/vbatts/tar-split/archive/tar/format.go
new file mode 100644
index 000000000..1f89d0c59
--- /dev/null
+++ b/vendor/github.com/vbatts/tar-split/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/vendor/github.com/vbatts/tar-split/archive/tar/reader.go b/vendor/github.com/vbatts/tar-split/archive/tar/reader.go
index adf32122e..ea64a3820 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/reader.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/reader.go
@@ -4,44 +4,38 @@
 
 package tar
 
-// TODO(dsymonds):
-//   - pax extensions
-
 import (
 	"bytes"
-	"errors"
 	"io"
 	"io/ioutil"
-	"math"
-	"os"
 	"strconv"
 	"strings"
 	"time"
 )
 
-var (
-	ErrHeader = errors.New("archive/tar: invalid tar header")
-)
-
-const maxNanoSecondIntSize = 9
-
-// A Reader provides sequential access to the contents of a tar archive.
-// A tar archive consists of a sequence of files.
-// The Next method advances to the next file in the archive (including the first),
-// and then it can be treated as an io.Reader to access the file's data.
+// 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
-	err     error
-	pad     int64           // amount of padding (ignored) after current file entry
-	curr    numBytesReader  // reader for current file entry
-	hdrBuff [blockSize]byte // buffer to use in readHeader
+	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
 
 	RawAccounting bool          // Whether to enable the access needed to reassemble the tar from raw bytes. Some performance/memory hit for this.
 	rawBytes      *bytes.Buffer // last raw bits
 }
 
-type parser struct {
-	err error // Last error seen
+type fileReader interface {
+	io.Reader
+	fileState
+
+	WriteTo(io.Writer) (int64, error)
 }
 
 // RawBytes accesses the raw bytes of the archive, apart from the file payload itself.
@@ -57,87 +51,35 @@ func (tr *Reader) RawBytes() []byte {
 	if tr.rawBytes == nil {
 		tr.rawBytes = bytes.NewBuffer(nil)
 	}
-	// if we've read them, then flush them.
-	defer tr.rawBytes.Reset()
-	return tr.rawBytes.Bytes()
-}
+	defer tr.rawBytes.Reset() // if we've read them, then flush them.
 
-// A numBytesReader is an io.Reader with a numBytes method, returning the number
-// of bytes remaining in the underlying encoded data.
-type numBytesReader interface {
-	io.Reader
-	numBytes() int64
-}
-
-// A regFileReader is a numBytesReader for reading file data from a tar archive.
-type regFileReader struct {
-	r  io.Reader // underlying reader
-	nb int64     // number of unread bytes for current file entry
-}
-
-// A sparseFileReader is a numBytesReader for reading sparse file data from a
-// tar archive.
-type sparseFileReader struct {
-	rfr   numBytesReader // Reads the sparse-encoded file data
-	sp    []sparseEntry  // The sparse map for the file
-	pos   int64          // Keeps track of file position
-	total int64          // Total size of the file
-}
+	return tr.rawBytes.Bytes()
 
-// A sparseEntry holds a single entry in a sparse file's sparse map.
-//
-// Sparse files are represented using a series of sparseEntrys.
-// Despite the name, a sparseEntry represents an actual data fragment that
-// references data found in the underlying archive stream. All regions not
-// covered by a sparseEntry are logically filled with zeros.
-//
-// For example, if the underlying raw file contains the 10-byte data:
-//	var compactData = "abcdefgh"
-//
-// And the sparse map has the following entries:
-//	var sp = []sparseEntry{
-//		{offset: 2,  numBytes: 5} // Data fragment for [2..7]
-//		{offset: 18, numBytes: 3} // Data fragment for [18..21]
-//	}
-//
-// Then the content of the resulting sparse file with a "real" size of 25 is:
-//	var sparseData = "\x00"*2 + "abcde" + "\x00"*11 + "fgh" + "\x00"*4
-type sparseEntry struct {
-	offset   int64 // Starting position of the fragment
-	numBytes int64 // Length of the fragment
 }
 
-// Keywords for GNU sparse files in a PAX extended header
-const (
-	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"
-)
-
-// Keywords for old GNU sparse headers
-const (
-	oldGNUSparseMainHeaderOffset               = 386
-	oldGNUSparseMainHeaderIsExtendedOffset     = 482
-	oldGNUSparseMainHeaderNumEntries           = 4
-	oldGNUSparseExtendedHeaderIsExtendedOffset = 504
-	oldGNUSparseExtendedHeaderNumEntries       = 21
-	oldGNUSparseOffsetSize                     = 12
-	oldGNUSparseNumBytesSize                   = 12
-)
-
 // NewReader creates a new Reader reading from r.
-func NewReader(r io.Reader) *Reader { return &Reader{r: 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
+
 	if tr.RawAccounting {
 		if tr.rawBytes == nil {
 			tr.rawBytes = bytes.NewBuffer(nil)
@@ -146,248 +88,245 @@ func (tr *Reader) Next() (*Header, error) {
 		}
 	}
 
-	if tr.err != nil {
-		return nil, tr.err
-	}
-
-	var hdr *Header
-	var extHdrs map[string]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".
-loop:
+	format := FormatUSTAR | FormatPAX | FormatGNU
 	for {
-		tr.err = tr.skipUnread()
-		if tr.err != nil {
-			return nil, tr.err
+		// Discard the remainder of the file and any padding.
+		if err := discard(tr, tr.curr.PhysicalRemaining()); err != nil {
+			return nil, err
+		}
+		n, err := tryReadFull(tr.r, tr.blk[:tr.pad])
+		if err != nil {
+			return nil, err
 		}
+		if tr.RawAccounting {
+			tr.rawBytes.Write(tr.blk[:n])
+		}
+		tr.pad = 0
 
-		hdr = tr.readHeader()
-		if tr.err != nil {
-			return nil, tr.err
+		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:
-			extHdrs, tr.err = parsePAX(tr)
-			if tr.err != nil {
-				return nil, tr.err
+		case TypeXHeader, TypeXGlobalHeader:
+			format.mayOnlyBe(FormatPAX)
+			paxHdrs, err = parsePAX(tr)
+			if err != nil {
+				return nil, err
 			}
-			continue loop // This is a meta header affecting the next header
+			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:
-			var realname []byte
-			realname, tr.err = ioutil.ReadAll(tr)
-			if tr.err != nil {
-				return nil, tr.err
+			format.mayOnlyBe(FormatGNU)
+			realname, err := ioutil.ReadAll(tr)
+			if err != nil {
+				return nil, err
 			}
 
 			if tr.RawAccounting {
-				if _, tr.err = tr.rawBytes.Write(realname); tr.err != nil {
-					return nil, tr.err
-				}
+				tr.rawBytes.Write(realname)
 			}
 
-			// Convert GNU extensions to use PAX headers.
-			if extHdrs == nil {
-				extHdrs = make(map[string]string)
-			}
 			var p parser
 			switch hdr.Typeflag {
 			case TypeGNULongName:
-				extHdrs[paxPath] = p.parseString(realname)
+				gnuLongName = p.parseString(realname)
 			case TypeGNULongLink:
-				extHdrs[paxLinkpath] = p.parseString(realname)
-			}
-			if p.err != nil {
-				tr.err = p.err
-				return nil, tr.err
+				gnuLongLink = p.parseString(realname)
 			}
-			continue loop // This is a meta header affecting the next header
+			continue // This is a meta header affecting the next header
 		default:
-			mergePAX(hdr, extHdrs)
+			// The old GNU sparse format is handled here since it is technically
+			// just a regular file with additional attributes.
 
-			// Check for a PAX format sparse file
-			sp, err := tr.checkForGNUSparsePAXHeaders(hdr, extHdrs)
-			if err != nil {
-				tr.err = err
+			if err := mergePAX(hdr, paxHdrs); err != nil {
 				return nil, err
 			}
-			if sp != nil {
-				// Current file is a PAX format GNU sparse file.
-				// Set the current file reader to a sparse file reader.
-				tr.curr, tr.err = newSparseFileReader(tr.curr, sp, hdr.Size)
-				if tr.err != nil {
-					return nil, tr.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
 				}
 			}
-			break loop // This is a file, so stop
+
+			// 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
 		}
 	}
-	return hdr, nil
 }
 
-// checkForGNUSparsePAXHeaders checks the PAX headers for GNU sparse headers. If they are found, then
-// this function reads the sparse map and returns it. Unknown sparse formats are ignored, causing the file to
-// be treated as a regular file.
-func (tr *Reader) checkForGNUSparsePAXHeaders(hdr *Header, headers map[string]string) ([]sparseEntry, error) {
-	var sparseFormat string
-
-	// Check for sparse format indicators
-	major, majorOk := headers[paxGNUSparseMajor]
-	minor, minorOk := headers[paxGNUSparseMinor]
-	sparseName, sparseNameOk := headers[paxGNUSparseName]
-	_, sparseMapOk := headers[paxGNUSparseMap]
-	sparseSize, sparseSizeOk := headers[paxGNUSparseSize]
-	sparseRealSize, sparseRealSizeOk := headers[paxGNUSparseRealSize]
-
-	// Identify which, if any, sparse format applies from which PAX headers are set
-	if majorOk && minorOk {
-		sparseFormat = major + "." + minor
-	} else if sparseNameOk && sparseMapOk {
-		sparseFormat = "0.1"
-	} else if sparseSizeOk {
-		sparseFormat = "0.0"
-	} else {
-		// Not a PAX format GNU sparse file.
-		return nil, nil
+// 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
 	}
-
-	// Check for unknown sparse format
-	if sparseFormat != "0.0" && sparseFormat != "0.1" && sparseFormat != "1.0" {
-		return nil, nil
+	if nb < 0 {
+		return ErrHeader
 	}
 
-	// Update hdr from GNU sparse PAX headers
-	if sparseNameOk {
-		hdr.Name = sparseName
+	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 sparseSizeOk {
-		realSize, err := strconv.ParseInt(sparseSize, 10, 0)
-		if err != nil {
-			return nil, ErrHeader
+
+	// 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
 		}
-		hdr.Size = realSize
-	} else if sparseRealSizeOk {
-		realSize, err := strconv.ParseInt(sparseRealSize, 10, 0)
+		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 = realSize
+		hdr.Size = n
 	}
 
-	// Set up the sparse map, according to the particular sparse format in use
-	var sp []sparseEntry
-	var err error
-	switch sparseFormat {
-	case "0.0", "0.1":
-		sp, err = readGNUSparseMap0x1(headers)
-	case "1.0":
-		sp, err = readGNUSparseMap1x0(tr.curr)
+	// Read the sparse map according to the appropriate format.
+	if is1x0 {
+		return readGNUSparseMap1x0(tr.curr)
 	}
-	return sp, err
+	return readGNUSparseMap0x1(hdr.PAXRecords)
 }
 
-// mergePAX merges well known headers according to PAX standard.
-// In general headers with the same name as those found
-// in the header struct overwrite those found in the header
-// struct with higher precision or longer values. Esp. useful
-// for name and linkname fields.
-func mergePAX(hdr *Header, headers map[string]string) error {
-	for k, v := range headers {
+// 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 paxGname:
-			hdr.Gname = v
 		case paxUname:
 			hdr.Uname = v
+		case paxGname:
+			hdr.Gname = v
 		case paxUid:
-			uid, err := strconv.ParseInt(v, 10, 0)
-			if err != nil {
-				return err
-			}
-			hdr.Uid = int(uid)
+			id64, err = strconv.ParseInt(v, 10, 64)
+			hdr.Uid = int(id64) // Integer overflow possible
 		case paxGid:
-			gid, err := strconv.ParseInt(v, 10, 0)
-			if err != nil {
-				return err
-			}
-			hdr.Gid = int(gid)
+			id64, err = strconv.ParseInt(v, 10, 64)
+			hdr.Gid = int(id64) // Integer overflow possible
 		case paxAtime:
-			t, err := parsePAXTime(v)
-			if err != nil {
-				return err
-			}
-			hdr.AccessTime = t
+			hdr.AccessTime, err = parsePAXTime(v)
 		case paxMtime:
-			t, err := parsePAXTime(v)
-			if err != nil {
-				return err
-			}
-			hdr.ModTime = t
+			hdr.ModTime, err = parsePAXTime(v)
 		case paxCtime:
-			t, err := parsePAXTime(v)
-			if err != nil {
-				return err
-			}
-			hdr.ChangeTime = t
+			hdr.ChangeTime, err = parsePAXTime(v)
 		case paxSize:
-			size, err := strconv.ParseInt(v, 10, 0)
-			if err != nil {
-				return err
-			}
-			hdr.Size = int64(size)
+			hdr.Size, err = strconv.ParseInt(v, 10, 64)
 		default:
-			if strings.HasPrefix(k, paxXattr) {
+			if strings.HasPrefix(k, paxSchilyXattr) {
 				if hdr.Xattrs == nil {
 					hdr.Xattrs = make(map[string]string)
 				}
-				hdr.Xattrs[k[len(paxXattr):]] = v
+				hdr.Xattrs[k[len(paxSchilyXattr):]] = v
 			}
 		}
-	}
-	return nil
-}
-
-// parsePAXTime takes a string of the form %d.%d as described in
-// the PAX specification.
-func parsePAXTime(t string) (time.Time, error) {
-	buf := []byte(t)
-	pos := bytes.IndexByte(buf, '.')
-	var seconds, nanoseconds int64
-	var err error
-	if pos == -1 {
-		seconds, err = strconv.ParseInt(t, 10, 0)
-		if err != nil {
-			return time.Time{}, err
-		}
-	} else {
-		seconds, err = strconv.ParseInt(string(buf[:pos]), 10, 0)
 		if err != nil {
-			return time.Time{}, err
-		}
-		nano_buf := string(buf[pos+1:])
-		// Pad as needed before converting to a decimal.
-		// For example .030 -> .030000000 -> 30000000 nanoseconds
-		if len(nano_buf) < maxNanoSecondIntSize {
-			// Right pad
-			nano_buf += strings.Repeat("0", maxNanoSecondIntSize-len(nano_buf))
-		} else if len(nano_buf) > maxNanoSecondIntSize {
-			// Right truncate
-			nano_buf = nano_buf[:maxNanoSecondIntSize]
-		}
-		nanoseconds, err = strconv.ParseInt(string(nano_buf), 10, 0)
-		if err != nil {
-			return time.Time{}, err
+			return ErrHeader
 		}
 	}
-	ts := time.Unix(seconds, nanoseconds)
-	return ts, nil
+	hdr.PAXRecords = paxHdrs
+	return nil
 }
 
 // parsePAX parses PAX headers.
@@ -406,12 +345,11 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 	sbuf := string(buf)
 
 	// For GNU PAX sparse format 0.0 support.
-	// This function transforms the sparse format 0.0 headers into sparse format 0.1 headers.
-	var sparseMap bytes.Buffer
+	// 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
 
-	headers := make(map[string]string)
-	// Each record is constructed as
-	//     "%d %s=%s\n", length, keyword, value
+	paxHdrs := make(map[string]string)
 	for len(sbuf) > 0 {
 		key, value, residual, err := parsePAXRecord(sbuf)
 		if err != nil {
@@ -419,422 +357,234 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 		}
 		sbuf = residual
 
-		keyStr := string(key)
-		if keyStr == paxGNUSparseOffset || keyStr == paxGNUSparseNumBytes {
-			// GNU sparse format 0.0 special key. Write to sparseMap instead of using the headers map.
-			sparseMap.WriteString(value)
-			sparseMap.Write([]byte{','})
-		} else {
-			// Normal key. Set the value in the headers map.
-			headers[keyStr] = string(value)
-		}
-	}
-	if sparseMap.Len() != 0 {
-		// Add sparse info to headers, chopping off the extra comma
-		sparseMap.Truncate(sparseMap.Len() - 1)
-		headers[paxGNUSparseMap] = sparseMap.String()
-	}
-	return headers, nil
-}
-
-// 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.
-//
-// A PAX record is of the following form:
-//	"%d %s=%s\n" % (size, key, value)
-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
-	}
-
-	// Extract everything between the space and the final newline.
-	rec, nl, rem := s[sp+1:n-1], s[n-1: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
-	}
-	return rec[:eq], rec[eq+1:], rem, nil
-}
-
-// 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 {
-	n := 0
-	for n < len(b) && b[n] != 0 {
-		n++
-	}
-	return string(b[0:n])
-}
-
-// 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
+		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
 			}
-			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)
-}
-
-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)
-}
-
-// skipUnread skips any unread bytes in the existing file entry, as well as any
-// alignment padding. It returns io.ErrUnexpectedEOF if any io.EOF is
-// encountered in the data portion; it is okay to hit io.EOF in the padding.
-//
-// Note that this function still works properly even when sparse files are being
-// used since numBytes returns the bytes remaining in the underlying io.Reader.
-func (tr *Reader) skipUnread() error {
-	dataSkip := tr.numBytes()      // Number of data bytes to skip
-	totalSkip := dataSkip + tr.pad // Total number of bytes to skip
-	tr.curr, tr.pad = nil, 0
-	if tr.RawAccounting {
-		_, tr.err = io.CopyN(tr.rawBytes, tr.r, totalSkip)
-		return tr.err
-	}
-	// 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 tar 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 := tr.r.(io.Seeker); ok && dataSkip > 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, os.SEEK_CUR)
-		if err == nil {
-			// Seek seems supported, so perform the real Seek.
-			pos2, err := sr.Seek(dataSkip-1, os.SEEK_CUR)
-			if err != nil {
-				tr.err = err
-				return tr.err
-			}
-			seekSkipped = pos2 - pos1
+			sparseMap = append(sparseMap, value)
+		default:
+			paxHdrs[key] = value
 		}
 	}
-
-	var copySkipped int64 // Number of bytes skipped via CopyN
-	copySkipped, tr.err = io.CopyN(ioutil.Discard, tr.r, totalSkip-seekSkipped)
-	if tr.err == io.EOF && seekSkipped+copySkipped < dataSkip {
-		tr.err = io.ErrUnexpectedEOF
+	if len(sparseMap) > 0 {
+		paxHdrs[paxGNUSparseMap] = strings.Join(sparseMap, ",")
 	}
-	return tr.err
-}
-
-func (tr *Reader) verifyChecksum(header []byte) bool {
-	if tr.err != nil {
-		return false
-	}
-
-	var p parser
-	given := p.parseOctal(header[148:156])
-	unsigned, signed := checksum(header)
-	return p.err == nil && (given == unsigned || given == signed)
+	return paxHdrs, nil
 }
 
 // readHeader reads the next block header and assumes that the underlying reader
-// is already aligned to a block boundary.
+// 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 {
-	header := tr.hdrBuff[:]
-	copy(header, zeroBlock)
-
-	if n, err := io.ReadFull(tr.r, header); err != nil {
-		tr.err = err
-		// because it could read some of the block, but reach EOF first
-		if tr.err == io.EOF && tr.RawAccounting {
-			if _, err := tr.rawBytes.Write(header[:n]); err != nil {
-				tr.err = err
-			}
-		}
-		return nil // io.EOF is okay here
+func (tr *Reader) readHeader() (*Header, *block, error) {
+	// Two blocks of zero bytes marks the end of the archive.
+	n, err := io.ReadFull(tr.r, tr.blk[:])
+	if tr.RawAccounting && (err == nil || err == io.EOF) {
+		tr.rawBytes.Write(tr.blk[:n])
 	}
-	if tr.RawAccounting {
-		if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
-			return nil
-		}
+	if err != nil {
+		return nil, nil, err // EOF is okay here; exactly 0 bytes read
 	}
 
-	// Two blocks of zero bytes marks the end of the archive.
-	if bytes.Equal(header, zeroBlock[0:blockSize]) {
-		if n, err := io.ReadFull(tr.r, header); err != nil {
-			tr.err = err
-			// because it could read some of the block, but reach EOF first
-			if tr.err == io.EOF && tr.RawAccounting {
-				if _, err := tr.rawBytes.Write(header[:n]); err != nil {
-					tr.err = err
-				}
-			}
-			return nil // io.EOF is okay here
+	if bytes.Equal(tr.blk[:], zeroBlock[:]) {
+		n, err = io.ReadFull(tr.r, tr.blk[:])
+		if tr.RawAccounting && (err == nil || err == io.EOF) {
+			tr.rawBytes.Write(tr.blk[:n])
 		}
-		if tr.RawAccounting {
-			if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
-				return nil
-			}
+		if err != nil {
+			return nil, nil, err // EOF is okay here; exactly 1 block of zeros read
 		}
-		if bytes.Equal(header, zeroBlock[0:blockSize]) {
-			tr.err = io.EOF
-		} else {
-			tr.err = ErrHeader // zero block and then non-zero block
+		if bytes.Equal(tr.blk[:], zeroBlock[:]) {
+			return nil, nil, io.EOF // normal EOF; exactly 2 block of zeros read
 		}
-		return nil
+		return nil, nil, ErrHeader // Zero block and then non-zero block
 	}
 
-	if !tr.verifyChecksum(header) {
-		tr.err = ErrHeader
-		return nil
+	// Verify the header matches a known format.
+	format := tr.blk.GetFormat()
+	if format == FormatUnknown {
+		return nil, nil, ErrHeader
 	}
 
-	// Unpack
 	var p parser
 	hdr := new(Header)
-	s := slicer(header)
-
-	hdr.Name = p.parseString(s.next(100))
-	hdr.Mode = p.parseNumeric(s.next(8))
-	hdr.Uid = int(p.parseNumeric(s.next(8)))
-	hdr.Gid = int(p.parseNumeric(s.next(8)))
-	hdr.Size = p.parseNumeric(s.next(12))
-	hdr.ModTime = time.Unix(p.parseNumeric(s.next(12)), 0)
-	s.next(8) // chksum
-	hdr.Typeflag = s.next(1)[0]
-	hdr.Linkname = p.parseString(s.next(100))
-
-	// The remainder of the header depends on the value of magic.
-	// The original (v7) version of tar had no explicit magic field,
-	// so its magic bytes, like the rest of the block, are NULs.
-	magic := string(s.next(8)) // contains version field as well.
-	var format string
-	switch {
-	case magic[:6] == "ustar\x00": // POSIX tar (1003.1-1988)
-		if string(header[508:512]) == "tar\x00" {
-			format = "star"
-		} else {
-			format = "posix"
-		}
-	case magic == "ustar  \x00": // old GNU tar
-		format = "gnu"
-	}
 
-	switch format {
-	case "posix", "gnu", "star":
-		hdr.Uname = p.parseString(s.next(32))
-		hdr.Gname = p.parseString(s.next(32))
-		devmajor := s.next(8)
-		devminor := s.next(8)
-		if hdr.Typeflag == TypeChar || hdr.Typeflag == TypeBlock {
-			hdr.Devmajor = p.parseNumeric(devmajor)
-			hdr.Devminor = p.parseNumeric(devminor)
-		}
+	// 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 format {
-		case "posix", "gnu":
-			prefix = p.parseString(s.next(155))
-		case "star":
-			prefix = p.parseString(s.next(131))
-			hdr.AccessTime = time.Unix(p.parseNumeric(s.next(12)), 0)
-			hdr.ChangeTime = time.Unix(p.parseNumeric(s.next(12)), 0)
+		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 an 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
+}
 
-	if p.err != nil {
-		tr.err = p.err
-		return nil
-	}
-
-	nb := hdr.Size
-	if isHeaderOnlyType(hdr.Typeflag) {
-		nb = 0
-	}
-	if nb < 0 {
-		tr.err = ErrHeader
-		return nil
-	}
-
-	// Set the current file reader.
-	tr.pad = -nb & (blockSize - 1) // blockSize is a power of two
-	tr.curr = &regFileReader{r: tr.r, nb: nb}
-
-	// Check for old GNU sparse format entry.
-	if hdr.Typeflag == TypeGNUSparse {
-		// Get the real size of the file.
-		hdr.Size = p.parseNumeric(header[483:495])
-		if p.err != nil {
-			tr.err = p.err
-			return nil
-		}
-
-		// Read the sparse map.
-		sp := tr.readOldGNUSparseMap(header)
-		if tr.err != nil {
-			return nil
-		}
-
-		// Current file is a GNU sparse file. Update the current file reader.
-		tr.curr, tr.err = newSparseFileReader(tr.curr, sp, hdr.Size)
-		if tr.err != nil {
-			return nil
-		}
+// 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)
 
-	return hdr
-}
-
-// readOldGNUSparseMap reads the sparse map as stored in 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.
-func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
 	var p parser
-	isExtended := header[oldGNUSparseMainHeaderIsExtendedOffset] != 0
-	spCap := oldGNUSparseMainHeaderNumEntries
-	if isExtended {
-		spCap += oldGNUSparseExtendedHeaderNumEntries
-	}
-	sp := make([]sparseEntry, 0, spCap)
-	s := slicer(header[oldGNUSparseMainHeaderOffset:])
-
-	// Read the four entries from the main tar header
-	for i := 0; i < oldGNUSparseMainHeaderNumEntries; i++ {
-		offset := p.parseNumeric(s.next(oldGNUSparseOffsetSize))
-		numBytes := p.parseNumeric(s.next(oldGNUSparseNumBytesSize))
-		if p.err != nil {
-			tr.err = p.err
-			return nil
-		}
-		if offset == 0 && numBytes == 0 {
-			break
-		}
-		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+	hdr.Size = p.parseNumeric(blk.GNU().RealSize())
+	if p.err != nil {
+		return nil, p.err
 	}
-
-	for isExtended {
-		// There are more entries. Read an extension header and parse its entries.
-		sparseHeader := make([]byte, blockSize)
-		if _, tr.err = io.ReadFull(tr.r, sparseHeader); tr.err != nil {
-			return nil
-		}
-		if tr.RawAccounting {
-			if _, tr.err = tr.rawBytes.Write(sparseHeader); tr.err != nil {
-				return nil
+	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})
 		}
 
-		isExtended = sparseHeader[oldGNUSparseExtendedHeaderIsExtendedOffset] != 0
-		s = slicer(sparseHeader)
-		for i := 0; i < oldGNUSparseExtendedHeaderNumEntries; i++ {
-			offset := p.parseNumeric(s.next(oldGNUSparseOffsetSize))
-			numBytes := p.parseNumeric(s.next(oldGNUSparseNumBytesSize))
-			if p.err != nil {
-				tr.err = p.err
-				return nil
+		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
 			}
-			if offset == 0 && numBytes == 0 {
-				break
+			if tr.RawAccounting {
+				tr.rawBytes.Write(blk[:])
 			}
-			sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+			s = blk.Sparse()
+			continue
 		}
+		return spd, nil // Done
 	}
-	return sp
 }
 
 // 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, numBytes). This function must stop reading at the end
+// 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) ([]sparseEntry, error) {
-	var cntNewline int64
-	var buf bytes.Buffer
-	var blk = make([]byte, blockSize)
-
-	// feedTokens copies data in numBlock chunks from r into buf until there are
+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.
-	var feedTokens = func(cnt int64) error {
-		for cntNewline < cnt {
-			if _, err := io.ReadFull(r, blk); err != nil {
-				if err == io.EOF {
-					err = io.ErrUnexpectedEOF
-				}
+	feedTokens := func(n int64) error {
+		for cntNewline < n {
+			if _, err := mustReadFull(r, blk[:]); err != nil {
 				return err
 			}
-			buf.Write(blk)
+			buf.Write(blk[:])
 			for _, c := range blk {
 				if c == '\n' {
 					cntNewline++
@@ -846,10 +596,10 @@ func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
 
 	// nextToken gets the next token delimited by a newline. This assumes that
 	// at least one newline exists in the buffer.
-	var nextToken = func() string {
+	nextToken := func() string {
 		cntNewline--
 		tok, _ := buf.ReadString('\n')
-		return tok[:len(tok)-1] // Cut off newline
+		return strings.TrimRight(tok, "\n")
 	}
 
 	// Parse for the number of entries.
@@ -868,197 +618,306 @@ func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
 	if err := feedTokens(2 * numEntries); err != nil {
 		return nil, err
 	}
-	sp := make([]sparseEntry, 0, numEntries)
+	spd := make(sparseDatas, 0, numEntries)
 	for i := int64(0); i < numEntries; i++ {
-		offset, err := strconv.ParseInt(nextToken(), 10, 64)
-		if err != nil {
-			return nil, ErrHeader
-		}
-		numBytes, err := strconv.ParseInt(nextToken(), 10, 64)
-		if err != nil {
+		offset, err1 := strconv.ParseInt(nextToken(), 10, 64)
+		length, err2 := strconv.ParseInt(nextToken(), 10, 64)
+		if err1 != nil || err2 != nil {
 			return nil, ErrHeader
 		}
-		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+		spd = append(spd, sparseEntry{Offset: offset, Length: length})
 	}
-	return sp, nil
+	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(extHdrs map[string]string) ([]sparseEntry, error) {
+func readGNUSparseMap0x1(paxHdrs map[string]string) (sparseDatas, error) {
 	// Get number of entries.
 	// Use integer overflow resistant math to check this.
-	numEntriesStr := extHdrs[paxGNUSparseNumBlocks]
+	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(extHdrs[paxGNUSparseMap], ",")
+	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.
-	sp := make([]sparseEntry, 0, numEntries)
-	for i := int64(0); i < numEntries; i++ {
-		offset, err := strconv.ParseInt(sparseMap[2*i], 10, 64)
-		if err != nil {
+	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
 		}
-		numBytes, err := strconv.ParseInt(sparseMap[2*i+1], 10, 64)
-		if err != nil {
-			return nil, ErrHeader
-		}
-		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
+		spd = append(spd, sparseEntry{Offset: offset, Length: length})
+		sparseMap = sparseMap[2:]
 	}
-	return sp, nil
+	return spd, nil
 }
 
-// numBytes returns the number of bytes left to read in the current file's entry
-// in the tar archive, or 0 if there is no current file.
-func (tr *Reader) numBytes() int64 {
-	if tr.curr == nil {
-		// No current file, so no bytes
-		return 0
-	}
-	return tr.curr.numBytes()
-}
-
-// Read reads from the current entry in the tar archive.
-// It returns 0, io.EOF when it reaches the end of that entry,
-// until Next is called to advance to the next entry.
+// 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
+// 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) (n int, err error) {
+func (tr *Reader) Read(b []byte) (int, error) {
 	if tr.err != nil {
 		return 0, tr.err
 	}
-	if tr.curr == nil {
-		return 0, io.EOF
-	}
-
-	n, err = tr.curr.Read(b)
+	n, err := tr.curr.Read(b)
 	if err != nil && err != io.EOF {
 		tr.err = err
 	}
-	return
+	return n, err
 }
 
-func (rfr *regFileReader) Read(b []byte) (n int, err error) {
-	if rfr.nb == 0 {
-		// file consumed
-		return 0, io.EOF
+// 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
 	}
-	if int64(len(b)) > rfr.nb {
-		b = b[0:rfr.nb]
+	n, err := tr.curr.WriteTo(w)
+	if err != nil {
+		tr.err = err
 	}
-	n, err = rfr.r.Read(b)
-	rfr.nb -= int64(n)
+	return n, err
+}
 
-	if err == io.EOF && rfr.nb > 0 {
-		err = io.ErrUnexpectedEOF
+// 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
 	}
-	return
 }
 
-// numBytes returns the number of bytes left to read in the file's data in the tar archive.
-func (rfr *regFileReader) numBytes() int64 {
-	return rfr.nb
+func (fr *regFileReader) WriteTo(w io.Writer) (int64, error) {
+	return io.Copy(w, struct{ io.Reader }{fr})
 }
 
-// newSparseFileReader creates a new sparseFileReader, but validates all of the
-// sparse entries before doing so.
-func newSparseFileReader(rfr numBytesReader, sp []sparseEntry, total int64) (*sparseFileReader, error) {
-	if total < 0 {
-		return nil, ErrHeader // Total size cannot be negative
+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()]
 	}
 
-	// Validate all sparse entries. These are the same checks as performed by
-	// the BSD tar utility.
-	for i, s := range sp {
-		switch {
-		case s.offset < 0 || s.numBytes < 0:
-			return nil, ErrHeader // Negative values are never okay
-		case s.offset > math.MaxInt64-s.numBytes:
-			return nil, ErrHeader // Integer overflow with large length
-		case s.offset+s.numBytes > total:
-			return nil, ErrHeader // Region extends beyond the "real" size
-		case i > 0 && sp[i-1].offset+sp[i-1].numBytes > s.offset:
-			return nil, ErrHeader // Regions can't overlap and must be in order
+	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
 		}
 	}
-	return &sparseFileReader{rfr: rfr, sp: sp, total: total}, nil
-}
 
-// readHole reads a sparse hole ending at endOffset.
-func (sfr *sparseFileReader) readHole(b []byte, endOffset int64) int {
-	n64 := endOffset - sfr.pos
-	if n64 > int64(len(b)) {
-		n64 = int64(len(b))
-	}
-	n := int(n64)
-	for i := 0; i < n; i++ {
-		b[i] = 0
+	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
 	}
-	sfr.pos += n64
-	return n
 }
 
-// Read reads the sparse file data in expanded form.
-func (sfr *sparseFileReader) Read(b []byte) (n int, err error) {
-	// Skip past all empty fragments.
-	for len(sfr.sp) > 0 && sfr.sp[0].numBytes == 0 {
-		sfr.sp = sfr.sp[1:]
+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 there are no more fragments, then it is possible that there
-	// is one last sparse hole.
-	if len(sfr.sp) == 0 {
-		// This behavior matches the BSD tar utility.
-		// However, GNU tar stops returning data even if sfr.total is unmet.
-		if sfr.pos < sfr.total {
-			return sfr.readHole(b, sfr.total), nil
-		}
-		return 0, io.EOF
+	// 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++
 	}
 
-	// In front of a data fragment, so read a hole.
-	if sfr.pos < sfr.sp[0].offset {
-		return sfr.readHole(b, sfr.sp[0].offset), nil
+	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
 	}
+}
 
-	// In a data fragment, so read from it.
-	// This math is overflow free since we verify that offset and numBytes can
-	// be safely added when creating the sparseFileReader.
-	endPos := sfr.sp[0].offset + sfr.sp[0].numBytes // End offset of fragment
-	bytesLeft := endPos - sfr.pos                   // Bytes left in fragment
-	if int64(len(b)) > bytesLeft {
-		b = b[:bytesLeft]
+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
+}
 
-	n, err = sfr.rfr.Read(b)
-	sfr.pos += int64(n)
+// 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 {
-		if sfr.pos < endPos {
-			err = io.ErrUnexpectedEOF // There was supposed to be more data
-		} else if sfr.pos < sfr.total {
-			err = nil // There is still an implicit sparse hole at the end
-		}
+		err = io.ErrUnexpectedEOF
 	}
+	return n, err
+}
 
-	if sfr.pos == endPos {
-		sfr.sp = sfr.sp[1:] // We are done with this fragment, so pop it
+// 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
 }
 
-// numBytes returns the number of bytes left to read in the sparse file's
-// sparse-encoded data in the tar archive.
-func (sfr *sparseFileReader) numBytes() int64 {
-	return sfr.rfr.numBytes()
+// discard skips n bytes in r, reporting an error if unable to do so.
+func discard(tr *Reader, n int64) error {
+	var seekSkipped, copySkipped int64
+	var err error
+	r := tr.r
+	if tr.RawAccounting {
+
+		copySkipped, err = io.CopyN(tr.rawBytes, tr.r, n)
+		goto out
+	}
+
+	// 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.
+	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(ioutil.Discard, r, n-seekSkipped)
+out:
+	if err == io.EOF && seekSkipped+copySkipped < n {
+		err = io.ErrUnexpectedEOF
+	}
+	return err
 }
diff --git a/vendor/github.com/vbatts/tar-split/archive/tar/stat_atim.go b/vendor/github.com/vbatts/tar-split/archive/tar/stat_actime1.go
index cf9cc79c5..cf9cc79c5 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/stat_atim.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/stat_actime1.go
diff --git a/vendor/github.com/vbatts/tar-split/archive/tar/stat_atimespec.go b/vendor/github.com/vbatts/tar-split/archive/tar/stat_actime2.go
index 6f17dbe30..6f17dbe30 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/stat_atimespec.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/stat_actime2.go
diff --git a/vendor/github.com/vbatts/tar-split/archive/tar/stat_unix.go b/vendor/github.com/vbatts/tar-split/archive/tar/stat_unix.go
index cb843db4c..868105f33 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/stat_unix.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/stat_unix.go
@@ -8,6 +8,10 @@ package tar
 
 import (
 	"os"
+	"os/user"
+	"runtime"
+	"strconv"
+	"sync"
 	"syscall"
 )
 
@@ -15,6 +19,10 @@ 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 os.FileInfo, h *Header) error {
 	sys, ok := fi.Sys().(*syscall.Stat_t)
 	if !ok {
@@ -22,11 +30,67 @@ func statUnix(fi os.FileInfo, h *Header) error {
 	}
 	h.Uid = int(sys.Uid)
 	h.Gid = int(sys.Gid)
-	// TODO(bradfitz): populate username & group.  os/user
-	// doesn't cache LookupId lookups, and lacks group
-	// lookup functions.
+
+	// 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)
-	// TODO(bradfitz): major/minor device numbers?
+
+	// 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 "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":
+			// 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/vendor/github.com/vbatts/tar-split/archive/tar/strconv.go b/vendor/github.com/vbatts/tar-split/archive/tar/strconv.go
new file mode 100644
index 000000000..d144485a4
--- /dev/null
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/strconv.go
@@ -0,0 +1,326 @@
+// 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 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
+	}
+
+	// Extract everything between the space and the final newline.
+	rec, nl, rem := s[sp+1:n-1], s[n-1: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/vendor/github.com/vbatts/tar-split/archive/tar/writer.go b/vendor/github.com/vbatts/tar-split/archive/tar/writer.go
index 042638175..e80498d03 100644
--- a/vendor/github.com/vbatts/tar-split/archive/tar/writer.go
+++ b/vendor/github.com/vbatts/tar-split/archive/tar/writer.go
@@ -4,295 +4,410 @@
 
 package tar
 
-// TODO(dsymonds):
-// - catch more errors (no first header, etc.)
-
 import (
-	"bytes"
-	"errors"
 	"fmt"
 	"io"
 	"path"
 	"sort"
-	"strconv"
 	"strings"
 	"time"
 )
 
-var (
-	ErrWriteTooLong    = errors.New("archive/tar: write too long")
-	ErrFieldTooLong    = errors.New("archive/tar: header field too long")
-	ErrWriteAfterClose = errors.New("archive/tar: write after close")
-	errInvalidHeader   = errors.New("archive/tar: header field too long or contains invalid values")
-)
-
-// A Writer provides sequential writing of a tar archive in POSIX.1 format.
-// A tar archive consists of a sequence of files.
-// Call WriteHeader to begin a new file, and then call Write to supply that file's data,
-// writing at most hdr.Size bytes in total.
+// 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
-	err        error
-	nb         int64 // number of unwritten bytes for current file entry
-	pad        int64 // amount of padding to write after current file entry
-	closed     bool
-	usedBinary bool            // whether the binary numeric field extension was used
-	preferPax  bool            // use pax header instead of binary numeric header
-	hdrBuff    [blockSize]byte // buffer to use in writeHeader when writing a regular header
-	paxHdrBuff [blockSize]byte // buffer to use in writeHeader when writing a pax header
+	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
 }
 
-type formatter struct {
-	err error // Last error seen
+// NewWriter creates a new Writer writing to w.
+func NewWriter(w io.Writer) *Writer {
+	return &Writer{w: w, curr: &regFileWriter{w, 0}}
 }
 
-// NewWriter creates a new Writer writing to w.
-func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
+type fileWriter interface {
+	io.Writer
+	fileState
 
-// Flush finishes writing the current file (optional).
+	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.nb > 0 {
-		tw.err = fmt.Errorf("archive/tar: missed writing %d bytes", tw.nb)
+	if tw.err != nil {
 		return tw.err
 	}
-
-	n := tw.nb + tw.pad
-	for n > 0 && tw.err == nil {
-		nr := n
-		if nr > blockSize {
-			nr = blockSize
-		}
-		var nw int
-		nw, tw.err = tw.w.Write(zeroBlock[0:nr])
-		n -= int64(nw)
+	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.nb = 0
 	tw.pad = 0
-	return tw.err
+	return nil
 }
 
-// Write s into b, terminating it with a NUL if there is room.
-func (f *formatter) formatString(b []byte, s string) {
-	if len(s) > len(b) {
-		f.err = ErrFieldTooLong
-		return
+// 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
 	}
-	ascii := toASCII(s)
-	copy(b, ascii)
-	if len(ascii) < len(b) {
-		b[len(ascii)] = 0
+	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
+		}
 	}
-}
 
-// Encode x as an octal ASCII string and write it into b with leading zeros.
-func (f *formatter) formatOctal(b []byte, x int64) {
-	s := strconv.FormatInt(x, 8)
-	// leading zeros, but leave room for a NUL.
-	for len(s)+1 < len(b) {
-		s = "0" + s
+	// 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{}
 	}
-	f.formatString(b, s)
-}
 
-// fitsInBase256 reports whether x can be encoded into n bytes using base-256
-// encoding. Unlike octal encoding, base-256 encoding does not require that the
-// string ends with a NUL character. Thus, all n bytes are available for output.
-//
-// If operating in binary mode, this assumes strict GNU binary mode; which means
-// that the first byte can only be either 0x80 or 0xff. Thus, the first byte is
-// equivalent to the sign bit in two's complement form.
-func fitsInBase256(n int, x int64) bool {
-	var binBits = uint(n-1) * 8
-	return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
+	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
+	}
 }
 
-// Write x into b, as binary (GNUtar/star extension).
-func (f *formatter) formatNumeric(b []byte, x int64) {
-	if fitsInBase256(len(b), x) {
-		for i := len(b) - 1; i >= 0; i-- {
-			b[i] = byte(x)
-			x >>= 8
-		}
-		b[0] |= 0x80 // Highest bit indicates binary format
-		return
+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
 	}
 
-	f.formatOctal(b, 0) // Last resort, just write zero
-	f.err = ErrFieldTooLong
+	// 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)
 }
 
-var (
-	minTime = time.Unix(0, 0)
-	// There is room for 11 octal digits (33 bits) of mtime.
-	maxTime = minTime.Add((1<<33 - 1) * time.Second)
-)
-
-// WriteHeader writes hdr and prepares to accept the file's contents.
-// WriteHeader calls Flush if it is not the first header.
-// Calling after a Close will return ErrWriteAfterClose.
-func (tw *Writer) WriteHeader(hdr *Header) error {
-	return tw.writeHeader(hdr, true)
-}
+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)
+		}
 
-// WriteHeader writes hdr and prepares to accept the file's contents.
-// WriteHeader calls Flush if it is not the first header.
-// Calling after a Close will return ErrWriteAfterClose.
-// As this method is called internally by writePax header to allow it to
-// suppress writing the pax header.
-func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
-	if tw.closed {
-		return ErrWriteAfterClose
-	}
-	if tw.err == nil {
-		tw.Flush()
-	}
-	if tw.err != nil {
-		return tw.err
+		// 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
+		}
 	}
 
-	// a map to hold pax header records, if any are needed
-	paxHeaders := make(map[string]string)
+	// 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(shanemhansen): we might want to use PAX headers for
-	// subsecond time resolution, but for now let's just capture
-	// too long fields or non ascii characters
+	// 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
+}
 
-	var f formatter
-	var header []byte
-
-	// We need to select which scratch buffer to use carefully,
-	// since this method is called recursively to write PAX headers.
-	// If allowPax is true, this is the non-recursive call, and we will use hdrBuff.
-	// If allowPax is false, we are being called by writePAXHeader, and hdrBuff is
-	// already being used by the non-recursive call, so we must use paxHdrBuff.
-	header = tw.hdrBuff[:]
-	if !allowPax {
-		header = tw.paxHdrBuff[:]
-	}
-	copy(header, zeroBlock)
-	s := slicer(header)
-
-	// Wrappers around formatter that automatically sets paxHeaders if the
-	// argument extends beyond the capacity of the input byte slice.
-	var formatString = func(b []byte, s string, paxKeyword string) {
-		needsPaxHeader := paxKeyword != paxNone && len(s) > len(b) || !isASCII(s)
-		if needsPaxHeader {
-			paxHeaders[paxKeyword] = s
-			return
+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
 		}
-		f.formatString(b, s)
-	}
-	var formatNumeric = func(b []byte, x int64, paxKeyword string) {
-		// Try octal first.
-		s := strconv.FormatInt(x, 8)
-		if len(s) < len(b) {
-			f.formatOctal(b, x)
-			return
+	}
+	if len(hdr.Linkname) > nameSize {
+		data := hdr.Linkname + "\x00"
+		if err := tw.writeRawFile(longName, data, TypeGNULongLink, FormatGNU); err != nil {
+			return err
 		}
+	}
 
-		// If it is too long for octal, and PAX is preferred, use a PAX header.
-		if paxKeyword != paxNone && tw.preferPax {
-			f.formatOctal(b, 0)
-			s := strconv.FormatInt(x, 10)
-			paxHeaders[paxKeyword] = s
-			return
+	// 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)
 		}
-
-		tw.usedBinary = true
-		f.formatNumeric(b, x)
+	*/
+	blk.SetFormat(FormatGNU)
+	if err := tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag); err != nil {
+		return err
 	}
 
-	// keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
-	pathHeaderBytes := s.next(fileNameSize)
-
-	formatString(pathHeaderBytes, hdr.Name, paxPath)
-
-	// Handle out of range ModTime carefully.
-	var modTime int64
-	if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
-		modTime = hdr.ModTime.Unix()
+	// 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
+}
 
-	f.formatOctal(s.next(8), hdr.Mode)               // 100:108
-	formatNumeric(s.next(8), int64(hdr.Uid), paxUid) // 108:116
-	formatNumeric(s.next(8), int64(hdr.Gid), paxGid) // 116:124
-	formatNumeric(s.next(12), hdr.Size, paxSize)     // 124:136
-	formatNumeric(s.next(12), modTime, paxNone)      // 136:148 --- consider using pax for finer granularity
-	s.next(8)                                        // chksum (148:156)
-	s.next(1)[0] = hdr.Typeflag                      // 156:157
-
-	formatString(s.next(100), hdr.Linkname, paxLinkpath)
-
-	copy(s.next(8), []byte("ustar\x0000"))          // 257:265
-	formatString(s.next(32), hdr.Uname, paxUname)   // 265:297
-	formatString(s.next(32), hdr.Gname, paxGname)   // 297:329
-	formatNumeric(s.next(8), hdr.Devmajor, paxNone) // 329:337
-	formatNumeric(s.next(8), hdr.Devminor, paxNone) // 337:345
-
-	// keep a reference to the prefix to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
-	prefixHeaderBytes := s.next(155)
-	formatString(prefixHeaderBytes, "", paxNone) // 345:500  prefix
+type (
+	stringFormatter func([]byte, string)
+	numberFormatter func([]byte, int64)
+)
 
-	// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
-	if tw.usedBinary {
-		copy(header[257:265], []byte("ustar  \x00"))
-	}
+// 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
+}
 
-	_, paxPathUsed := paxHeaders[paxPath]
-	// try to use a ustar header when only the name is too long
-	if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
-		prefix, suffix, ok := splitUSTARPath(hdr.Name)
-		if ok {
-			// Since we can encode in USTAR format, disable PAX header.
-			delete(paxHeaders, paxPath)
+// 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()
 
-			// Update the path fields
-			formatString(pathHeaderBytes, suffix, paxNone)
-			formatString(prefixHeaderBytes, prefix, paxNone)
-		}
+	// Best effort for the filename.
+	name = toASCII(name)
+	if len(name) > nameSize {
+		name = name[:nameSize]
 	}
+	name = strings.TrimRight(name, "/")
 
-	// The chksum field is terminated by a NUL and a space.
-	// This is different from the other octal fields.
-	chksum, _ := checksum(header)
-	f.formatOctal(header[148:155], chksum) // Never fails
-	header[155] = ' '
-
-	// Check if there were any formatting errors.
+	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 {
-		tw.err = f.err
-		return tw.err
+		return f.err // Only occurs if size condition is violated
 	}
 
-	if allowPax {
-		for k, v := range hdr.Xattrs {
-			paxHeaders[paxXattr+k] = v
-		}
+	// 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
+}
 
-	if len(paxHeaders) > 0 {
-		if !allowPax {
-			return errInvalidHeader
-		}
-		if err := tw.writePAXHeader(hdr, paxHeaders); err != nil {
-			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
 	}
-	tw.nb = int64(hdr.Size)
-	tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize
-
-	_, tw.err = tw.w.Write(header)
-	return tw.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 <= fileNameSize || !isASCII(name) {
+	if length <= nameSize || !isASCII(name) {
 		return "", "", false
-	} else if length > fileNamePrefixSize+1 {
-		length = fileNamePrefixSize + 1
+	} else if length > prefixSize+1 {
+		length = prefixSize + 1
 	} else if name[length-1] == '/' {
 		length--
 	}
@@ -300,117 +415,239 @@ func splitUSTARPath(name string) (prefix, suffix string, ok bool) {
 	i := strings.LastIndex(name[:length], "/")
 	nlen := len(name) - i - 1 // nlen is length of suffix
 	plen := i                 // plen is length of prefix
-	if i <= 0 || nlen > fileNameSize || nlen == 0 || plen > fileNamePrefixSize {
+	if i <= 0 || nlen > nameSize || nlen == 0 || plen > prefixSize {
 		return "", "", false
 	}
 	return name[:i], name[i+1:], true
 }
 
-// writePaxHeader writes an extended pax header to the
-// archive.
-func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) error {
-	// Prepare extended header
-	ext := new(Header)
-	ext.Typeflag = TypeXHeader
-	// Setting ModTime is required for reader parsing to
-	// succeed, and seems harmless enough.
-	ext.ModTime = hdr.ModTime
-	// The spec asks that we namespace our pseudo files
-	// with the current pid.  However, this results in differing outputs
-	// for identical inputs.  As such, the constant 0 is now used instead.
-	// golang.org/issue/12358
-	dir, file := path.Split(hdr.Name)
-	fullName := path.Join(dir, "PaxHeaders.0", file)
-
-	ascii := toASCII(fullName)
-	if len(ascii) > 100 {
-		ascii = ascii[:100]
-	}
-	ext.Name = ascii
-	// Construct the body
-	var buf bytes.Buffer
-
-	// Keys are sorted before writing to body to allow deterministic output.
-	var keys []string
-	for k := range paxHeaders {
-		keys = append(keys, k)
-	}
-	sort.Strings(keys)
-
-	for _, k := range keys {
-		fmt.Fprint(&buf, formatPAXRecord(k, paxHeaders[k]))
-	}
-
-	ext.Size = int64(len(buf.Bytes()))
-	if err := tw.writeHeader(ext, false); err != nil {
-		return err
+// 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
 	}
-	if _, err := tw.Write(buf.Bytes()); err != nil {
-		return err
+	n, err := tw.curr.Write(b)
+	if err != nil && err != ErrWriteTooLong {
+		tw.err = err
 	}
-	if err := tw.Flush(); err != nil {
-		return 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
 	}
-	return nil
+	n, err := tw.curr.ReadFrom(r)
+	if err != nil && err != ErrWriteTooLong {
+		tw.err = err
+	}
+	return n, err
 }
 
-// formatPAXRecord formats a single PAX record, prefixing it with the
-// appropriate length.
-func formatPAXRecord(k, v string) string {
-	const padding = 3 // Extra padding for ' ', '=', and '\n'
-	size := len(k) + len(v) + padding
-	size += len(strconv.Itoa(size))
-	record := fmt.Sprintf("%d %s=%s\n", size, k, v)
+// 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
+	}
 
-	// Final adjustment if adding size field increased the record size.
-	if len(record) != size {
-		size = len(record)
-		record = fmt.Sprintf("%d %s=%s\n", size, k, v)
+	// Trailer: two zero blocks.
+	err := tw.Flush()
+	for i := 0; i < 2 && err == nil; i++ {
+		_, err = tw.w.Write(zeroBlock[:])
 	}
-	return record
+
+	// Ensure all future actions are invalid.
+	tw.err = ErrWriteAfterClose
+	return err // Report IO errors
 }
 
-// Write writes to the current entry in the tar archive.
-// Write returns the error ErrWriteTooLong if more than
-// hdr.Size bytes are written after WriteHeader.
-func (tw *Writer) Write(b []byte) (n int, err error) {
-	if tw.closed {
-		err = ErrWriteAfterClose
-		return
-	}
-	overwrite := false
-	if int64(len(b)) > tw.nb {
-		b = b[0:tw.nb]
-		overwrite = true
-	}
-	n, err = tw.w.Write(b)
-	tw.nb -= int64(n)
-	if err == nil && overwrite {
-		err = ErrWriteTooLong
-		return
-	}
-	tw.err = err
-	return
+// 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
 }
 
-// Close closes the tar archive, flushing any unwritten
-// data to the underlying writer.
-func (tw *Writer) Close() error {
-	if tw.err != nil || tw.closed {
-		return tw.err
+func (fw *regFileWriter) Write(b []byte) (n int, err error) {
+	overwrite := int64(len(b)) > fw.nb
+	if overwrite {
+		b = b[:fw.nb]
 	}
-	tw.Flush()
-	tw.closed = true
-	if tw.err != nil {
-		return tw.err
+	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)
+}
 
-	// trailer: two zero blocks
-	for i := 0; i < 2; i++ {
-		_, tw.err = tw.w.Write(zeroBlock)
-		if tw.err != nil {
-			break
+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
 		}
 	}
-	return tw.err
+
+	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
+	}
 }