Merge pull request #26932 from dmcgowan/update-tar-split

Update tar split

hack/vendor.sh

@@ -92,7 +92,7 @@ clone git github.com/miekg/dns 75e6e86cc601825c5dbcd4e0c209eab180997cd7
 
 # get graph and distribution packages
 clone git github.com/docker/distribution 77b9d2997abcded79a5314970fe69a44c93c25fb
-clone git github.com/vbatts/tar-split v0.9.11
+clone git github.com/vbatts/tar-split v0.10.1
 
 # get go-zfs packages
 clone git github.com/mistifyio/go-zfs 22c9b32c84eb0d0c6f4043b6e90fc94073de92fa

vendor/src/github.com/vbatts/tar-split/LICENSE

@@ -1,19 +1,28 @@
 Copyright (c) 2015 Vincent Batts, Raleigh, NC, USA
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
+All rights reserved.
 
-The above copyright notice and this permission notice shall be included in
-all copies or substantial portions of the Software.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-THE SOFTWARE.
+1. Redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+this list of conditions and the following disclaimer in the documentation
+and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its contributors
+may be used to endorse or promote products derived from this software without
+specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/src/github.com/vbatts/tar-split/archive/tar/common.go

@@ -327,3 +327,14 @@ func toASCII(s string) string {
 	}
 	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 {
+	switch flag {
+	case TypeLink, TypeSymlink, TypeChar, TypeBlock, TypeDir, TypeFifo:
+		return true
+	default:
+		return false
+	}
+}

vendor/src/github.com/vbatts/tar-split/archive/tar/reader.go

@@ -12,6 +12,7 @@ import (
 	"errors"
 	"io"
 	"io/ioutil"
+	"math"
 	"os"
 	"strconv"
 	"strings"
@@ -39,6 +40,10 @@ type Reader struct {
 	rawBytes      *bytes.Buffer // last raw bits
 }
 
+type parser struct {
+	err error // Last error seen
+}
+
 // RawBytes accesses the raw bytes of the archive, apart from the file payload itself.
 // This includes the header and padding.
 //
@@ -70,12 +75,36 @@ type regFileReader struct {
 	nb int64     // number of unread bytes for current file entry
 }
 
-// A sparseFileReader is a numBytesReader for reading sparse file data from a tar archive.
+// A sparseFileReader is a numBytesReader for reading sparse file data from a
+// tar archive.
 type sparseFileReader struct {
-	rfr *regFileReader // reads the sparse-encoded file data
-	sp  []sparseEntry  // the sparse map for the file
-	pos int64          // keeps track of file position
-	tot int64          // total size of the file
+	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
+}
+
+// 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
@@ -109,7 +138,6 @@ func NewReader(r io.Reader) *Reader { return &Reader{r: r} }
 //
 // io.EOF is returned at the end of the input.
 func (tr *Reader) Next() (*Header, error) {
-	var hdr *Header
 	if tr.RawAccounting {
 		if tr.rawBytes == nil {
 			tr.rawBytes = bytes.NewBuffer(nil)
@@ -117,98 +145,88 @@ func (tr *Reader) Next() (*Header, error) {
 			tr.rawBytes.Reset()
 		}
 	}
-	if tr.err == nil {
-		tr.skipUnread()
-	}
+
 	if tr.err != nil {
-		return hdr, tr.err
-	}
-	hdr = tr.readHeader()
-	if hdr == nil {
-		return hdr, tr.err
+		return nil, tr.err
 	}
-	// Check for PAX/GNU header.
-	switch hdr.Typeflag {
-	case TypeXHeader:
-		//  PAX extended header
-		headers, err := parsePAX(tr)
-		if err != nil {
-			return nil, err
-		}
-		// We actually read the whole file,
-		// but this skips alignment padding
-		tr.skipUnread()
+
+	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:
+	for {
+		tr.err = tr.skipUnread()
 		if tr.err != nil {
 			return nil, tr.err
 		}
+
 		hdr = tr.readHeader()
-		if hdr == nil {
+		if tr.err != nil {
 			return nil, tr.err
 		}
-		mergePAX(hdr, headers)
+		// 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
+			}
+			continue loop // 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
+			}
 
-		// Check for a PAX format sparse file
-		sp, err := tr.checkForGNUSparsePAXHeaders(hdr, headers)
-		if err != nil {
-			tr.err = err
-			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 = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
-		}
-		return hdr, nil
-	case TypeGNULongName:
-		// We have a GNU long name header. Its contents are the real file name.
-		realname, err := ioutil.ReadAll(tr)
-		if err != nil {
-			return nil, err
-		}
-		var buf []byte
-		if tr.RawAccounting {
-			if _, err = tr.rawBytes.Write(realname); err != nil {
-				return nil, err
+			if tr.RawAccounting {
+				if _, tr.err = tr.rawBytes.Write(realname); tr.err != nil {
+					return nil, tr.err
+				}
 			}
-			buf = make([]byte, tr.rawBytes.Len())
-			copy(buf[:], tr.RawBytes())
-		}
-		hdr, err := tr.Next()
-		// since the above call to Next() resets the buffer, we need to throw the bytes over
-		if tr.RawAccounting {
-			buf = append(buf, tr.RawBytes()...)
-			if _, err = tr.rawBytes.Write(buf); err != nil {
-				return nil, err
+
+			// Convert GNU extensions to use PAX headers.
+			if extHdrs == nil {
+				extHdrs = make(map[string]string)
 			}
-		}
-		hdr.Name = cString(realname)
-		return hdr, err
-	case TypeGNULongLink:
-		// We have a GNU long link header.
-		realname, err := ioutil.ReadAll(tr)
-		if err != nil {
-			return nil, err
-		}
-		var buf []byte
-		if tr.RawAccounting {
-			if _, err = tr.rawBytes.Write(realname); err != nil {
-				return nil, err
+			var p parser
+			switch hdr.Typeflag {
+			case TypeGNULongName:
+				extHdrs[paxPath] = p.parseString(realname)
+			case TypeGNULongLink:
+				extHdrs[paxLinkpath] = p.parseString(realname)
 			}
-			buf = make([]byte, tr.rawBytes.Len())
-			copy(buf[:], tr.RawBytes())
-		}
-		hdr, err := tr.Next()
-		// since the above call to Next() resets the buffer, we need to throw the bytes over
-		if tr.RawAccounting {
-			buf = append(buf, tr.RawBytes()...)
-			if _, err = tr.rawBytes.Write(buf); err != nil {
+			if p.err != nil {
+				tr.err = p.err
+				return nil, tr.err
+			}
+			continue loop // This is a meta header affecting the next header
+		default:
+			mergePAX(hdr, extHdrs)
+
+			// Check for a PAX format sparse file
+			sp, err := tr.checkForGNUSparsePAXHeaders(hdr, extHdrs)
+			if err != nil {
+				tr.err = err
 				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
+				}
+			}
+			break loop // This is a file, so stop
 		}
-		hdr.Linkname = cString(realname)
-		return hdr, err
 	}
-	return hdr, tr.err
+	return hdr, nil
 }
 
 // checkForGNUSparsePAXHeaders checks the PAX headers for GNU sparse headers. If they are found, then
@@ -385,6 +403,7 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 			return nil, err
 		}
 	}
+	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.
@@ -393,35 +412,17 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 	headers := make(map[string]string)
 	// Each record is constructed as
 	//     "%d %s=%s\n", length, keyword, value
-	for len(buf) > 0 {
-		// or the header was empty to start with.
-		var sp int
-		// The size field ends at the first space.
-		sp = bytes.IndexByte(buf, ' ')
-		if sp == -1 {
-			return nil, ErrHeader
-		}
-		// Parse the first token as a decimal integer.
-		n, err := strconv.ParseInt(string(buf[:sp]), 10, 0)
-		if err != nil || n < 5 || int64(len(buf)) < n {
-			return nil, ErrHeader
-		}
-		// Extract everything between the decimal and the n -1 on the
-		// beginning to eat the ' ', -1 on the end to skip the newline.
-		var record []byte
-		record, buf = buf[sp+1:n-1], buf[n:]
-		// The first equals is guaranteed to mark the end of the key.
-		// Everything else is value.
-		eq := bytes.IndexByte(record, '=')
-		if eq == -1 {
+	for len(sbuf) > 0 {
+		key, value, residual, err := parsePAXRecord(sbuf)
+		if err != nil {
 			return nil, ErrHeader
 		}
-		key, value := record[:eq], record[eq+1:]
+		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.Write(value)
+			sparseMap.WriteString(value)
 			sparseMap.Write([]byte{','})
 		} else {
 			// Normal key. Set the value in the headers map.
@@ -436,9 +437,42 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 	return headers, nil
 }
 
-// cString parses bytes as a NUL-terminated C-style string.
+// 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 cString(b []byte) string {
+func (*parser) parseString(b []byte) string {
 	n := 0
 	for n < len(b) && b[n] != 0 {
 		n++
@@ -446,19 +480,51 @@ func cString(b []byte) string {
 	return string(b[0:n])
 }
 
-func (tr *Reader) octal(b []byte) int64 {
-	// Check for binary format first.
+// 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 {
-		var x int64
+		// 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
+				c &= 0x7f // Ignore signal bit in first byte
 			}
-			x = x<<8 | int64(c)
+			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 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.
@@ -469,27 +535,55 @@ func (tr *Reader) octal(b []byte) int64 {
 	if len(b) == 0 {
 		return 0
 	}
-	x, err := strconv.ParseUint(cString(b), 8, 64)
-	if err != nil {
-		tr.err = err
+	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.
-func (tr *Reader) skipUnread() {
-	nr := tr.numBytes() + tr.pad // number of bytes to skip
+// 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, nr)
-		return
+		_, tr.err = io.CopyN(tr.rawBytes, tr.r, totalSkip)
+		return tr.err
 	}
-	if sr, ok := tr.r.(io.Seeker); ok {
-		if _, err := sr.Seek(nr, os.SEEK_CUR); err == nil {
-			return
+	// 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
 		}
 	}
-	_, tr.err = io.CopyN(ioutil.Discard, tr.r, nr)
+
+	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
+	}
+	return tr.err
 }
 
 func (tr *Reader) verifyChecksum(header []byte) bool {
@@ -497,23 +591,32 @@ func (tr *Reader) verifyChecksum(header []byte) bool {
 		return false
 	}
 
-	given := tr.octal(header[148:156])
+	var p parser
+	given := p.parseOctal(header[148:156])
 	unsigned, signed := checksum(header)
-	return given == unsigned || given == signed
+	return p.err == nil && (given == unsigned || given == signed)
 }
 
+// readHeader reads the next block header and assumes that the underlying reader
+// is already aligned to a block boundary.
+//
+// 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 _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
+	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 _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
-				return nil
+			if _, err := tr.rawBytes.Write(header[:n]); err != nil {
+				tr.err = err
 			}
 		}
-		return nil
+		return nil // io.EOF is okay here
 	}
 	if tr.RawAccounting {
 		if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
@@ -523,14 +626,15 @@ func (tr *Reader) readHeader() *Header {
 
 	// Two blocks of zero bytes marks the end of the archive.
 	if bytes.Equal(header, zeroBlock[0:blockSize]) {
-		if _, tr.err = io.ReadFull(tr.r, header); tr.err != nil {
+		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 _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
-					return nil
+				if _, err := tr.rawBytes.Write(header[:n]); err != nil {
+					tr.err = err
 				}
 			}
-			return nil
+			return nil // io.EOF is okay here
 		}
 		if tr.RawAccounting {
 			if _, tr.err = tr.rawBytes.Write(header); tr.err != nil {
@@ -551,22 +655,19 @@ func (tr *Reader) readHeader() *Header {
 	}
 
 	// Unpack
+	var p parser
 	hdr := new(Header)
 	s := slicer(header)
 
-	hdr.Name = cString(s.next(100))
-	hdr.Mode = tr.octal(s.next(8))
-	hdr.Uid = int(tr.octal(s.next(8)))
-	hdr.Gid = int(tr.octal(s.next(8)))
-	hdr.Size = tr.octal(s.next(12))
-	if hdr.Size < 0 {
-		tr.err = ErrHeader
-		return nil
-	}
-	hdr.ModTime = time.Unix(tr.octal(s.next(12)), 0)
+	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 = cString(s.next(100))
+	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,
@@ -586,70 +687,76 @@ func (tr *Reader) readHeader() *Header {
 
 	switch format {
 	case "posix", "gnu", "star":
-		hdr.Uname = cString(s.next(32))
-		hdr.Gname = cString(s.next(32))
+		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 = tr.octal(devmajor)
-			hdr.Devminor = tr.octal(devminor)
+			hdr.Devmajor = p.parseNumeric(devmajor)
+			hdr.Devminor = p.parseNumeric(devminor)
 		}
 		var prefix string
 		switch format {
 		case "posix", "gnu":
-			prefix = cString(s.next(155))
+			prefix = p.parseString(s.next(155))
 		case "star":
-			prefix = cString(s.next(131))
-			hdr.AccessTime = time.Unix(tr.octal(s.next(12)), 0)
-			hdr.ChangeTime = time.Unix(tr.octal(s.next(12)), 0)
+			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)
 		}
 		if len(prefix) > 0 {
 			hdr.Name = prefix + "/" + hdr.Name
 		}
 	}
 
-	if tr.err != nil {
-		tr.err = ErrHeader
+	if p.err != nil {
+		tr.err = p.err
 		return nil
 	}
 
-	// Maximum value of hdr.Size is 64 GB (12 octal digits),
-	// so there's no risk of int64 overflowing.
-	nb := int64(hdr.Size)
-	tr.pad = -nb & (blockSize - 1) // blockSize is a power of two
+	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 = tr.octal(header[483:495])
+		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 = &sparseFileReader{rfr: tr.curr.(*regFileReader), sp: sp, tot: hdr.Size}
+		tr.curr, tr.err = newSparseFileReader(tr.curr, sp, hdr.Size)
+		if tr.err != nil {
+			return nil
+		}
 	}
 
 	return hdr
 }
 
-// A sparseEntry holds a single entry in a sparse file's sparse map.
-// A sparse entry indicates the offset and size in a sparse file of a
-// block of data.
-type sparseEntry struct {
-	offset   int64
-	numBytes int64
-}
-
 // 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 {
@@ -660,10 +767,10 @@ func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
 
 	// Read the four entries from the main tar header
 	for i := 0; i < oldGNUSparseMainHeaderNumEntries; i++ {
-		offset := tr.octal(s.next(oldGNUSparseOffsetSize))
-		numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
-		if tr.err != nil {
-			tr.err = ErrHeader
+		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 {
@@ -687,10 +794,10 @@ func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
 		isExtended = sparseHeader[oldGNUSparseExtendedHeaderIsExtendedOffset] != 0
 		s = slicer(sparseHeader)
 		for i := 0; i < oldGNUSparseExtendedHeaderNumEntries; i++ {
-			offset := tr.octal(s.next(oldGNUSparseOffsetSize))
-			numBytes := tr.octal(s.next(oldGNUSparseNumBytesSize))
-			if tr.err != nil {
-				tr.err = ErrHeader
+			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 {
@@ -702,134 +809,111 @@ func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
 	return sp
 }
 
-// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format version 1.0.
-// The sparse map is stored just before the file data and padded out to the nearest block boundary.
+// 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
+// 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) {
-	buf := make([]byte, 2*blockSize)
-	sparseHeader := buf[:blockSize]
-
-	// readDecimal is a helper function to read a decimal integer from the sparse map
-	// while making sure to read from the file in blocks of size blockSize
-	readDecimal := func() (int64, error) {
-		// Look for newline
-		nl := bytes.IndexByte(sparseHeader, '\n')
-		if nl == -1 {
-			if len(sparseHeader) >= blockSize {
-				// This is an error
-				return 0, ErrHeader
-			}
-			oldLen := len(sparseHeader)
-			newLen := oldLen + blockSize
-			if cap(sparseHeader) < newLen {
-				// There's more header, but we need to make room for the next block
-				copy(buf, sparseHeader)
-				sparseHeader = buf[:newLen]
-			} else {
-				// There's more header, and we can just reslice
-				sparseHeader = sparseHeader[:newLen]
-			}
-
-			// Now that sparseHeader is large enough, read next block
-			if _, err := io.ReadFull(r, sparseHeader[oldLen:newLen]); err != nil {
-				return 0, err
-			}
-			// leaving this function for io.Reader makes it more testable
-			if tr, ok := r.(*Reader); ok && tr.RawAccounting {
-				if _, err := tr.rawBytes.Write(sparseHeader[oldLen:newLen]); err != nil {
-					return 0, err
+	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
+	// 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
 				}
+				return err
 			}
-
-			// Look for a newline in the new data
-			nl = bytes.IndexByte(sparseHeader[oldLen:newLen], '\n')
-			if nl == -1 {
-				// This is an error
-				return 0, ErrHeader
+			buf.Write(blk)
+			for _, c := range blk {
+				if c == '\n' {
+					cntNewline++
+				}
 			}
-			nl += oldLen // We want the position from the beginning
-		}
-		// Now that we've found a newline, read a number
-		n, err := strconv.ParseInt(string(sparseHeader[:nl]), 10, 0)
-		if err != nil {
-			return 0, ErrHeader
 		}
+		return nil
+	}
 
-		// Update sparseHeader to consume this number
-		sparseHeader = sparseHeader[nl+1:]
-		return n, nil
+	// nextToken gets the next token delimited by a newline. This assumes that
+	// at least one newline exists in the buffer.
+	var nextToken = func() string {
+		cntNewline--
+		tok, _ := buf.ReadString('\n')
+		return tok[:len(tok)-1] // Cut off newline
 	}
 
-	// Read the first block
-	if _, err := io.ReadFull(r, sparseHeader); err != nil {
+	// Parse for the number of entries.
+	// Use integer overflow resistant math to check this.
+	if err := feedTokens(1); err != nil {
 		return nil, err
 	}
-	// leaving this function for io.Reader makes it more testable
-	if tr, ok := r.(*Reader); ok && tr.RawAccounting {
-		if _, err := tr.rawBytes.Write(sparseHeader); err != nil {
-			return nil, err
-		}
+	numEntries, err := strconv.ParseInt(nextToken(), 10, 0) // Intentionally parse as native int
+	if err != nil || numEntries < 0 || int(2*numEntries) < int(numEntries) {
+		return nil, ErrHeader
 	}
 
-	// The first line contains the number of entries
-	numEntries, err := readDecimal()
-	if err != nil {
+	// Parse for all member entries.
+	// numEntries is trusted after this since a potential attacker must have
+	// committed resources proportional to what this library used.
+	if err := feedTokens(2 * numEntries); err != nil {
 		return nil, err
 	}
-
-	// Read all the entries
 	sp := make([]sparseEntry, 0, numEntries)
 	for i := int64(0); i < numEntries; i++ {
-		// Read the offset
-		offset, err := readDecimal()
+		offset, err := strconv.ParseInt(nextToken(), 10, 64)
 		if err != nil {
-			return nil, err
+			return nil, ErrHeader
 		}
-		// Read numBytes
-		numBytes, err := readDecimal()
+		numBytes, err := strconv.ParseInt(nextToken(), 10, 64)
 		if err != nil {
-			return nil, err
+			return nil, ErrHeader
 		}
-
 		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
 	}
-
 	return sp, 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(headers map[string]string) ([]sparseEntry, error) {
-	// Get number of entries
-	numEntriesStr, ok := headers[paxGNUSparseNumBlocks]
-	if !ok {
+// 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) {
+	// Get number of entries.
+	// Use integer overflow resistant math to check this.
+	numEntriesStr := extHdrs[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
 	}
-	numEntries, err := strconv.ParseInt(numEntriesStr, 10, 0)
-	if err != nil {
-		return nil, ErrHeader
-	}
-
-	sparseMap := strings.Split(headers[paxGNUSparseMap], ",")
 
-	// There should be two numbers in sparseMap for each entry
+	// There should be two numbers in sparseMap for each entry.
+	sparseMap := strings.Split(extHdrs[paxGNUSparseMap], ",")
 	if int64(len(sparseMap)) != 2*numEntries {
 		return nil, ErrHeader
 	}
 
-	// Loop through the entries in the sparse map
+	// 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, 0)
+		offset, err := strconv.ParseInt(sparseMap[2*i], 10, 64)
 		if err != nil {
 			return nil, ErrHeader
 		}
-		numBytes, err := strconv.ParseInt(sparseMap[2*i+1], 10, 0)
+		numBytes, err := strconv.ParseInt(sparseMap[2*i+1], 10, 64)
 		if err != nil {
 			return nil, ErrHeader
 		}
 		sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
 	}
-
 	return sp, nil
 }
 
@@ -846,10 +930,18 @@ func (tr *Reader) numBytes() int64 {
 // 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.
+//
+// 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) {
+	if tr.err != nil {
+		return 0, tr.err
+	}
 	if tr.curr == nil {
 		return 0, io.EOF
 	}
+
 	n, err = tr.curr.Read(b)
 	if err != nil && err != io.EOF {
 		tr.err = err
@@ -879,9 +971,33 @@ func (rfr *regFileReader) numBytes() int64 {
 	return rfr.nb
 }
 
-// readHole reads a sparse file hole ending at offset toOffset
-func (sfr *sparseFileReader) readHole(b []byte, toOffset int64) int {
-	n64 := toOffset - sfr.pos
+// 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
+	}
+
+	// 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
+		}
+	}
+	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))
 	}
@@ -895,49 +1011,54 @@ func (sfr *sparseFileReader) readHole(b []byte, toOffset int64) int {
 
 // 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:]
+	}
+
+	// If there are no more fragments, then it is possible that there
+	// is one last sparse hole.
 	if len(sfr.sp) == 0 {
-		// No more data fragments to read from.
-		if sfr.pos < sfr.tot {
-			// We're in the last hole
-			n = sfr.readHole(b, sfr.tot)
-			return
+		// 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
 		}
-		// Otherwise, we're at the end of the file
 		return 0, io.EOF
 	}
-	if sfr.tot < sfr.sp[0].offset {
-		return 0, io.ErrUnexpectedEOF
-	}
+
+	// In front of a data fragment, so read a hole.
 	if sfr.pos < sfr.sp[0].offset {
-		// We're in a hole
-		n = sfr.readHole(b, sfr.sp[0].offset)
-		return
+		return sfr.readHole(b, sfr.sp[0].offset), nil
 	}
 
-	// We're not in a hole, so we'll read from the next data fragment
-	posInFragment := sfr.pos - sfr.sp[0].offset
-	bytesLeft := sfr.sp[0].numBytes - posInFragment
+	// 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[0:bytesLeft]
+		b = b[:bytesLeft]
 	}
 
 	n, err = sfr.rfr.Read(b)
 	sfr.pos += int64(n)
-
-	if int64(n) == bytesLeft {
-		// We're done with this fragment
-		sfr.sp = sfr.sp[1:]
+	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
+		}
 	}
 
-	if err == io.EOF && sfr.pos < sfr.tot {
-		// We reached the end of the last fragment's data, but there's a final hole
-		err = nil
+	if sfr.pos == endPos {
+		sfr.sp = sfr.sp[1:] // We are done with this fragment, so pop it
 	}
-	return
+	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.nb
+	return sfr.rfr.numBytes()
 }

vendor/src/github.com/vbatts/tar-split/archive/tar/writer.go

@@ -12,8 +12,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"os"
 	"path"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -23,7 +23,6 @@ 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")
-	errNameTooLong     = errors.New("archive/tar: name too long")
 	errInvalidHeader   = errors.New("archive/tar: header field too long or contains invalid values")
 )
 
@@ -43,6 +42,10 @@ type Writer struct {
 	paxHdrBuff [blockSize]byte // buffer to use in writeHeader when writing a pax header
 }
 
+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} }
 
@@ -69,17 +72,9 @@ func (tw *Writer) Flush() error {
 }
 
 // Write s into b, terminating it with a NUL if there is room.
-// If the value is too long for the field and allowPax is true add a paxheader record instead
-func (tw *Writer) cString(b []byte, s string, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
-	needsPaxHeader := allowPax && len(s) > len(b) || !isASCII(s)
-	if needsPaxHeader {
-		paxHeaders[paxKeyword] = s
-		return
-	}
+func (f *formatter) formatString(b []byte, s string) {
 	if len(s) > len(b) {
-		if tw.err == nil {
-			tw.err = ErrFieldTooLong
-		}
+		f.err = ErrFieldTooLong
 		return
 	}
 	ascii := toASCII(s)
@@ -90,40 +85,40 @@ func (tw *Writer) cString(b []byte, s string, allowPax bool, paxKeyword string,
 }
 
 // Encode x as an octal ASCII string and write it into b with leading zeros.
-func (tw *Writer) octal(b []byte, x int64) {
+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
 	}
-	tw.cString(b, s, false, paxNone, nil)
+	f.formatString(b, s)
 }
 
-// Write x into b, either as octal or as binary (GNUtar/star extension).
-// If the value is too long for the field and writingPax is enabled both for the field and the add a paxheader record instead
-func (tw *Writer) numeric(b []byte, x int64, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
-	// Try octal first.
-	s := strconv.FormatInt(x, 8)
-	if len(s) < len(b) {
-		tw.octal(b, x)
-		return
-	}
+// 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)
+}
 
-	// If it is too long for octal, and pax is preferred, use a pax header
-	if allowPax && tw.preferPax {
-		tw.octal(b, 0)
-		s := strconv.FormatInt(x, 10)
-		paxHeaders[paxKeyword] = s
+// 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
 	}
 
-	// Too big: use binary (big-endian).
-	tw.usedBinary = true
-	for i := len(b) - 1; x > 0 && i >= 0; i-- {
-		b[i] = byte(x)
-		x >>= 8
-	}
-	b[0] |= 0x80 // highest bit indicates binary format
+	f.formatOctal(b, 0) // Last resort, just write zero
+	f.err = ErrFieldTooLong
 }
 
 var (
@@ -162,6 +157,7 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 	// subsecond time resolution, but for now let's just capture
 	// too long fields or non ascii characters
 
+	var f formatter
 	var header []byte
 
 	// We need to select which scratch buffer to use carefully,
@@ -176,10 +172,40 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 	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
+		}
+		f.formatString(b, s)
+	}
+	var formatNumeric = func(b []byte, x int64, paxKeyword string) {
+		// Try octal first.
+		s := strconv.FormatInt(x, 8)
+		if len(s) < len(b) {
+			f.formatOctal(b, x)
+			return
+		}
+
+		// If it is too long for octal, and PAX is preferred, use a PAX header.
+		if paxKeyword != paxNone && tw.preferPax {
+			f.formatOctal(b, 0)
+			s := strconv.FormatInt(x, 10)
+			paxHeaders[paxKeyword] = s
+			return
+		}
+
+		tw.usedBinary = true
+		f.formatNumeric(b, x)
+	}
+
 	// 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)
 
-	tw.cString(pathHeaderBytes, hdr.Name, true, paxPath, paxHeaders)
+	formatString(pathHeaderBytes, hdr.Name, paxPath)
 
 	// Handle out of range ModTime carefully.
 	var modTime int64
@@ -187,25 +213,25 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 		modTime = hdr.ModTime.Unix()
 	}
 
-	tw.octal(s.next(8), hdr.Mode)                                   // 100:108
-	tw.numeric(s.next(8), int64(hdr.Uid), true, paxUid, paxHeaders) // 108:116
-	tw.numeric(s.next(8), int64(hdr.Gid), true, paxGid, paxHeaders) // 116:124
-	tw.numeric(s.next(12), hdr.Size, true, paxSize, paxHeaders)     // 124:136
-	tw.numeric(s.next(12), modTime, false, paxNone, nil)            // 136:148 --- consider using pax for finer granularity
-	s.next(8)                                                       // chksum (148:156)
-	s.next(1)[0] = hdr.Typeflag                                     // 156:157
+	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
 
-	tw.cString(s.next(100), hdr.Linkname, true, paxLinkpath, paxHeaders)
+	formatString(s.next(100), hdr.Linkname, paxLinkpath)
 
-	copy(s.next(8), []byte("ustar\x0000"))                        // 257:265
-	tw.cString(s.next(32), hdr.Uname, true, paxUname, paxHeaders) // 265:297
-	tw.cString(s.next(32), hdr.Gname, true, paxGname, paxHeaders) // 297:329
-	tw.numeric(s.next(8), hdr.Devmajor, false, paxNone, nil)      // 329:337
-	tw.numeric(s.next(8), hdr.Devminor, false, paxNone, nil)      // 337:345
+	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)
-	tw.cString(prefixHeaderBytes, "", false, paxNone, nil) // 345:500  prefix
+	formatString(prefixHeaderBytes, "", paxNone) // 345:500  prefix
 
 	// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
 	if tw.usedBinary {
@@ -215,37 +241,26 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 	_, paxPathUsed := paxHeaders[paxPath]
 	// try to use a ustar header when only the name is too long
 	if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
-		suffix := hdr.Name
-		prefix := ""
-		if len(hdr.Name) > fileNameSize && isASCII(hdr.Name) {
-			var err error
-			prefix, suffix, err = tw.splitUSTARLongName(hdr.Name)
-			if err == nil {
-				// ok we can use a ustar long name instead of pax, now correct the fields
-
-				// remove the path field from the pax header. this will suppress the pax header
-				delete(paxHeaders, paxPath)
-
-				// update the path fields
-				tw.cString(pathHeaderBytes, suffix, false, paxNone, nil)
-				tw.cString(prefixHeaderBytes, prefix, false, paxNone, nil)
-
-				// Use the ustar magic if we used ustar long names.
-				if len(prefix) > 0 && !tw.usedBinary {
-					copy(header[257:265], []byte("ustar\x00"))
-				}
-			}
+		prefix, suffix, ok := splitUSTARPath(hdr.Name)
+		if ok {
+			// Since we can encode in USTAR format, disable PAX header.
+			delete(paxHeaders, paxPath)
+
+			// Update the path fields
+			formatString(pathHeaderBytes, suffix, paxNone)
+			formatString(prefixHeaderBytes, prefix, paxNone)
 		}
 	}
 
 	// The chksum field is terminated by a NUL and a space.
 	// This is different from the other octal fields.
 	chksum, _ := checksum(header)
-	tw.octal(header[148:155], chksum)
+	f.formatOctal(header[148:155], chksum) // Never fails
 	header[155] = ' '
 
-	if tw.err != nil {
-		// problem with header; probably integer too big for a field.
+	// Check if there were any formatting errors.
+	if f.err != nil {
+		tw.err = f.err
 		return tw.err
 	}
 
@@ -270,28 +285,25 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 	return tw.err
 }
 
-// writeUSTARLongName splits a USTAR long name hdr.Name.
-// name must be < 256 characters. errNameTooLong is returned
-// if hdr.Name can't be split. The splitting heuristic
-// is compatible with gnu tar.
-func (tw *Writer) splitUSTARLongName(name string) (prefix, suffix string, err error) {
+// 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 > fileNamePrefixSize+1 {
+	if length <= fileNameSize || !isASCII(name) {
+		return "", "", false
+	} else if length > fileNamePrefixSize+1 {
 		length = fileNamePrefixSize + 1
 	} else if name[length-1] == '/' {
 		length--
 	}
+
 	i := strings.LastIndex(name[:length], "/")
-	// nlen contains the resulting length in the name field.
-	// plen contains the resulting length in the prefix field.
-	nlen := len(name) - i - 1
-	plen := i
+	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 {
-		err = errNameTooLong
-		return
+		return "", "", false
 	}
-	prefix, suffix = name[:i], name[i+1:]
-	return
+	return name[:i], name[i+1:], true
 }
 
 // writePaxHeader writes an extended pax header to the
@@ -304,11 +316,11 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
 	// succeed, and seems harmless enough.
 	ext.ModTime = hdr.ModTime
 	// The spec asks that we namespace our pseudo files
-	// with the current pid.
-	pid := os.Getpid()
+	// 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,
-		fmt.Sprintf("PaxHeaders.%d", pid), file)
+	fullName := path.Join(dir, "PaxHeaders.0", file)
 
 	ascii := toASCII(fullName)
 	if len(ascii) > 100 {
@@ -318,8 +330,15 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
 	// Construct the body
 	var buf bytes.Buffer
 
-	for k, v := range paxHeaders {
-		fmt.Fprint(&buf, paxHeader(k+"="+v))
+	// 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()))
@@ -335,17 +354,18 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
 	return nil
 }
 
-// paxHeader formats a single pax record, prefixing it with the appropriate length
-func paxHeader(msg string) string {
-	const padding = 2 // Extra padding for space and newline
-	size := len(msg) + padding
+// 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\n", size, msg)
+	record := fmt.Sprintf("%d %s=%s\n", size, k, v)
+
+	// Final adjustment if adding size field increased the record size.
 	if len(record) != size {
-		// Final adjustment if adding size increased
-		// the number of digits in size
 		size = len(record)
-		record = fmt.Sprintf("%d %s\n", size, msg)
+		record = fmt.Sprintf("%d %s=%s\n", size, k, v)
 	}
 	return record
 }