Method: ZipKit::ZipWriter#write_central_directory_file_header

Defined in:

lib/zip_kit/zip_writer.rb

#write_central_directory_file_header(io:, local_file_header_location:, gp_flags:, storage_mode:, compressed_size:, uncompressed_size:, mtime:, crc32:, filename:, unix_permissions: nil) ⇒ void

This method returns an undefined value.

Writes the file header for the central directory, for a particular file in the archive. When writing out this data, ensure that the CRC32 and both sizes (compressed/uncompressed) are correct for the entry in question.

Parameters:

• io (#<<) —

  the buffer to write the local file header to

• filename (String) —

  the name of the file in the archive

• compressed_size (Integer) —

  The size of the compressed (or stored) data - how much space it uses in the ZIP

• uncompressed_size (Integer) —

  The size of the file once extracted

• crc32 (Integer) —

  The CRC32 checksum of the file

• mtime (Time) —

  the modification time to be recorded in the ZIP

• gp_flags (Integer) —

  bit-packed general purpose flags

• unix_permissions (Integer) (defaults to: nil) —

  the permissions for the file, or nil for the default to be used

# File 'lib/zip_kit/zip_writer.rb', line 146

def write_central_directory_file_header(io:,
  local_file_header_location:,
  gp_flags:,
  storage_mode:,
  compressed_size:,
  uncompressed_size:,
  mtime:,
  crc32:,
  filename:,
  unix_permissions: nil)
  # At this point if the header begins somewhere beyound 0xFFFFFFFF we _have_ to record the offset
  # of the local file header as a zip64 extra field, so we give up, give in, you loose, love will always win...
  add_zip64 = (local_file_header_location > FOUR_BYTE_MAX_UINT) ||
    (compressed_size > FOUR_BYTE_MAX_UINT) || (uncompressed_size > FOUR_BYTE_MAX_UINT)

  # central file header signature   4 bytes  (0x02014b50)
  io << [0x02014b50].pack(C_UINT4)
  # version made by                 2 bytes
  io << MADE_BY_SIGNATURE

  # version needed to extract       2 bytes
  io << if add_zip64
    [VERSION_NEEDED_TO_EXTRACT_ZIP64].pack(C_UINT2)
  else
    [VERSION_NEEDED_TO_EXTRACT].pack(C_UINT2)
  end

  # general purpose bit flag        2 bytes
  io << [gp_flags].pack(C_UINT2)
  # compression method              2 bytes
  io << [storage_mode].pack(C_UINT2)
  # last mod file time              2 bytes
  io << [to_binary_dos_time(mtime)].pack(C_UINT2)
  # last mod file date              2 bytes
  io << [to_binary_dos_date(mtime)].pack(C_UINT2)
  # crc-32                          4 bytes
  io << [crc32].pack(C_UINT4)

  # compressed size              4 bytes
  # uncompressed size            4 bytes
  if add_zip64
    io << [FOUR_BYTE_MAX_UINT].pack(C_UINT4)
    io << [FOUR_BYTE_MAX_UINT].pack(C_UINT4)
  else
    io << [compressed_size].pack(C_UINT4)
    io << [uncompressed_size].pack(C_UINT4)
  end

  # Filename should not be longer than 0xFFFF otherwise this wont fit here
  # file name length                2 bytes
  io << [filename.bytesize].pack(C_UINT2)

  extra_fields = StringIO.new
  if add_zip64
    extra_fields << zip_64_extra_for_central_directory_file_header(local_file_header_location: local_file_header_location,
      compressed_size: compressed_size,
      uncompressed_size: uncompressed_size)
  end
  extra_fields << timestamp_extra_for_central_directory_entry(mtime)

  # extra field length              2 bytes
  io << [extra_fields.size].pack(C_UINT2)
  # file comment length             2 bytes
  io << [0].pack(C_UINT2)

  # For The Unarchiver < 3.11.1 this field has to be set to the overflow value if zip64 is used
  # because otherwise it does not properly advance the pointer when reading the Zip64 extra field
  # https://bitbucket.org/WAHa_06x36/theunarchiver/pull-requests/2/bug-fix-for-zip64-extra-field-parser/diff
  # disk number start               2 bytes
  io << if add_zip64
    [TWO_BYTE_MAX_UINT].pack(C_UINT2)
  else
    [0].pack(C_UINT2)
  end
  # internal file attributes        2 bytes
  io << [0].pack(C_UINT2)

  # Because the add_empty_directory method will create a directory with a trailing "/",
  # this check can be used to assign proper permissions to the created directory.
  external_attrs = if filename.end_with?("/")
    unix_permissions ||= DEFAULT_DIRECTORY_UNIX_PERMISSIONS
    generate_external_attrs(unix_permissions, FILE_TYPE_DIRECTORY)
  else
    unix_permissions ||= DEFAULT_FILE_UNIX_PERMISSIONS
    generate_external_attrs(unix_permissions, FILE_TYPE_FILE)
  end

  # external file attributes        4 bytes
  io << [external_attrs].pack(C_UINT4)

  # relative offset of local header 4 bytes
  io << if add_zip64
    [FOUR_BYTE_MAX_UINT].pack(C_UINT4)
  else
    [local_file_header_location].pack(C_UINT4)
  end

  # file name (variable size)
  io << filename
  # extra field (variable size)
  io << extra_fields.string
  # file comment (variable size)
  # (empty)
end