yBytes := Repeat(y, growLen)
			allocs := testing.AllocsPerRun(100, func() {
				buf.Grow(growLen)
				buf.Write(yBytes)
			})
			// Check no allocation occurs in write, as long as we're single-threaded.
			if allocs != 0 {
				t.Errorf("allocation occurred during write")
			}
			// Check that buffer has correct data.
			if !Equal(buf.Bytes()[0:startLen-readBytes], xBytes[readBytes:]) {

	}
	return tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag)
}

func (tw *Writer) writePAXHeader(hdr *Header, paxHdrs map[string]string) error {
	realName, realSize := hdr.Name, hdr.Size

	// TODO(dsnet): Re-enable this when adding sparse support.
	// See https://golang.org/issue/22735
	/*
		// Handle sparse files.
		var spd sparseDatas
		var spb []byte
		if len(hdr.SparseHoles) > 0 {

	}
}

func (in *Input) Next() ScanToken {
	if in.peek {
		in.peek = false
		tok := in.peekToken
		in.text = in.peekText
		return tok
	}
	// If we cannot generate a token after 100 macro invocations, we're in trouble.
	// The usual case is caught by Push, below, but be safe.
	for nesting := 0; nesting < 100; {
		tok := in.Stack.Next()
		switch tok {
		case '#':
			if !in.beginningOfLine {

	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	if i := bytes.IndexByte(data, '\n'); i >= 0 {
		// We have a full newline-terminated line.
		return i + 1, dropCR(data[0:i]), nil
	}
	// If we're at EOF, we have a final, non-terminated line. Return it.
	if atEOF {
		return len(data), dropCR(data), nil
	}
	// Request more data.
	return 0, nil, nil
}

			return TrimFunc(s[start:stop], unicode.IsSpace)
		}
		if asciiSpace[c] == 0 {
			break
		}
	}

	// At this point s[start:stop] starts and ends with an ASCII
	// non-space bytes, so we're done. Non-ASCII cases have already
	// been handled above.
	if start == stop {
		// Special case to preserve previous TrimLeftFunc behavior,
		// returning nil instead of empty slice if all spaces.
		return nil

		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) {

	if err != nil {
		return 0, err
	}
	defer lock.Close()
	if err := syscall.Flock(int(lock.Fd()), syscall.LOCK_EX); err != nil {
		return 0, err
	}

	// In case we're booting a device or emulator alongside all.bash, wait for
	// it to be ready. adb wait-for-device is not enough, we have to
	// wait for sys.boot_completed.

			return nil, err
		}
		fw.rawCount = &countWriter{w: fw.comp}
		fw.header = h
		ow = fw
	}
	w.dir = append(w.dir, h)
	if err := writeHeader(w.cw, h); err != nil {
		return nil, err
	}
	// If we're creating a directory, fw is nil.
	w.last = fw
	return ow, nil
}

func writeHeader(w io.Writer, h *header) error {
	const maxUint16 = 1<<16 - 1
	if len(h.Name) > maxUint16 {
		return errLongName
	}

// then writeTo uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are filled with NULs.
// This always writes the last byte to ensure w is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735
func (tr *Reader) writeTo(w io.Writer) (int64, error) {
	if tr.err != nil {
		return 0, tr.err
	}
	n, err := tr.curr.WriteTo(w)

				Uid:      1000,
				Gid:      1000,
				Uname:    "rawr",
				Gname:    "dsnet",
				ModTime:  time.Unix(0, 0),
				Format:   FormatGNU,
			}, nil},
			testClose{nil},
		},
		// TODO(dsnet): Re-enable this test when adding sparse support.
		// See https://golang.org/issue/22735
		/*
			}, {
				file: "testdata/gnu-nil-sparse-data.tar",
				tests: []testFnc{
					testHeader{Header{