"uname":      strings.Repeat("long", 10),
			},
			Format: FormatPAX,
		}},
	}, {
		file: "testdata/pax-global-records.tar",
		headers: []*Header{{
			Typeflag:   TypeXGlobalHeader,
			Name:       "global1",
			PAXRecords: map[string]string{"path": "global1", "mtime": "1500000000.0"},
			Format:     FormatPAX,
		}, {
			Typeflag: TypeReg,
			Name:     "file1",
			ModTime:  time.Unix(0, 0),

		format.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 {

	// normally be visible to the outside. As such, this loop iterates through
	// one or more "header files" until it finds a "normal file".
	format := FormatUSTAR | FormatPAX | FormatGNU
	for {
		// Discard the remainder of the file and any padding.
		if err := discard(tr.r, tr.curr.physicalRemaining()); err != nil {
			return nil, err
		}