# File ruby/lib/rubygems/package/tar_header.rb, line 103
def self.from(stream)
  header = stream.read 512
  return EMPTY if header == EMPTY_HEADER

  fields = header.unpack UNPACK_FORMAT

  new name: fields.shift,
      mode: strict_oct(fields.shift),
      uid: oct_or_256based(fields.shift),
      gid: oct_or_256based(fields.shift),
      size: strict_oct(fields.shift),
      mtime: strict_oct(fields.shift),
      checksum: strict_oct(fields.shift),
      typeflag: fields.shift,
      linkname: fields.shift,
      magic: fields.shift,
      version: strict_oct(fields.shift),
      uname: fields.shift,
      gname: fields.shift,
      devmajor: strict_oct(fields.shift),
      devminor: strict_oct(fields.shift),
      prefix: fields.shift,

      empty: false
end

# File ruby/lib/rubygems/package/tar_header.rb, line 149
def initialize(vals)
  unless vals[:name] && vals[:size] && vals[:prefix] && vals[:mode]
    raise ArgumentError, ":name, :size, :prefix and :mode required"
  end

  @checksum = vals[:checksum] || ""
  @devmajor = vals[:devmajor] || 0
  @devminor = vals[:devminor] || 0
  @gid = vals[:gid] || 0
  @gname = vals[:gname] || "wheel"
  @linkname = vals[:linkname]
  @magic = vals[:magic] || "ustar"
  @mode = vals[:mode]
  @mtime = vals[:mtime] || 0
  @name = vals[:name]
  @prefix = vals[:prefix]
  @size = vals[:size]
  @typeflag = vals[:typeflag]
  @typeflag = "0" if @typeflag.nil? || @typeflag.empty?
  @uid = vals[:uid] || 0
  @uname = vals[:uname] || "wheel"
  @version = vals[:version] || "00"

  @empty = vals[:empty]
end

# File ruby/lib/rubygems/package/tar_header.rb, line 136
def self.oct_or_256based(str)
  # \x80 flags a positive 256-based number
  # \ff flags a negative 256-based number
  # In case we have a match, parse it as a signed binary value
  # in big-endian order, except that the high-order bit is ignored.

  return str.unpack1("@4N") if /\A[\x80\xff]/n.match?(str)
  strict_oct(str)
end

# File ruby/lib/rubygems/package/tar_header.rb, line 129
def self.strict_oct(str)
  str.strip!
  return str.oct if /\A[0-7]*\z/.match?(str)

  raise ArgumentError, "#{str.inspect} is not an octal string"
end

# File ruby/lib/rubygems/package/tar_header.rb, line 194
def empty?
  @empty
end

# File ruby/lib/rubygems/package/tar_header.rb, line 226
def update_checksum
  header = header " " * 8
  @checksum = oct calculate_checksum(header), 6
end