class Gem::Package::TarTestCase

def header(type, fname, dname, length, mode, mtime, checksum = nil, linkname = "")
  checksum ||= " " * 8
  arr = [                  # struct tarfile_entry_posix
    ASCIIZ(fname, 100),    # char name[100];     ASCII + (Z unless filled)
    Z(to_oct(mode, 7)),    # char mode[8];       0 padded, octal null
    Z(to_oct(0, 7)),       # char uid[8];        ditto
    Z(to_oct(0, 7)),       # char gid[8];        ditto
    Z(to_oct(length, 11)), # char size[12];      0 padded, octal, null
    Z(to_oct(mtime, 11)),  # char mtime[12];     0 padded, octal, null
    checksum,              # char checksum[8];   0 padded, octal, null, space
    type,                  # char typeflag[1];   file: "0"  dir: "5"
    ASCIIZ(linkname, 100), # char linkname[100]; ASCII + (Z unless filled)
    "ustar\0",             # char magic[6];      "ustar\0"
    "00",                  # char version[2];    "00"
    ASCIIZ("wheel", 32),   # char uname[32];     ASCIIZ
    ASCIIZ("wheel", 32),   # char gname[32];     ASCIIZ
    Z(to_oct(0, 7)),       # char devmajor[8];   0 padded, octal, null
    Z(to_oct(0, 7)),       # char devminor[8];   0 padded, octal, null
    ASCIIZ(dname, 155), # char prefix[155];   ASCII + (Z unless filled)
  ]
  h = arr.join
  ret = h + "\0" * (512 - h.size)
  assert_equal(512, ret.size)
  ret
end