Method: ZipKit::ZipWriter#write_local_file_header

Defined in:
lib/zip_kit/zip_writer.rb

#write_local_file_header(io:, filename:, compressed_size:, uncompressed_size:, crc32:, gp_flags:, mtime:, storage_mode:) ⇒ void

This method returns an undefined value.

Writes the local file header, that precedes the actual file data.

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

  • storage_mode (Integer) —

    8 for deflated, 0 for stored...



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# File 'lib/zip_kit/zip_writer.rb', line 74

def write_local_file_header(io:, filename:, compressed_size:, uncompressed_size:, crc32:, gp_flags:, mtime:, storage_mode:)
  requires_zip64 = compressed_size > FOUR_BYTE_MAX_UINT || uncompressed_size > FOUR_BYTE_MAX_UINT

  # local file header signature     4 bytes  (0x04034b50)
  io << [0x04034b50].pack(C_UINT4)
  # version needed to extract       2 bytes
  io << if requires_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)

  if requires_zip64
    # compressed size              4 bytes
    io << [FOUR_BYTE_MAX_UINT].pack(C_UINT4)
    # uncompressed size            4 bytes
    io << [FOUR_BYTE_MAX_UINT].pack(C_UINT4)
  else
    # compressed size              4 bytes
    io << [compressed_size].pack(C_UINT4)
    # uncompressed size            4 bytes
    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

  # Interesting tidbit:
  # https://social.technet.microsoft.com/Forums/windows/en-US/6a60399f-2879-4859-b7ab-6ddd08a70948
  # TL;DR of it is: Windows 7 Explorer _will_ open Zip64 entries. However, it desires to have the
  # Zip64 extra field as _the first_ extra field.
  if requires_zip64
    extra_fields << zip_64_extra_for_local_file_header(compressed_size: compressed_size, uncompressed_size: uncompressed_size)
  end
  extra_fields << timestamp_extra_for_local_file_header(mtime)

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

  # file name (variable size)
  io << filename

  # Contents of the extra fields (variable size)
  io << extra_fields.string
end