Method: ZipTricks::ZipWriter#write_local_file_header

Defined in:
lib/zip_tricks/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 (Fixnum) —

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

  • uncompressed_size (Fixnum) —

    The size of the file once extracted

  • crc32 (Fixnum) —

    The CRC32 checksum of the file

  • mtime (Time) —

    the modification time to be recorded in the ZIP

  • gp_flags (Fixnum) —

    bit-packed general purpose flags

  • storage_mode (Fixnum) —

    8 for deflated, 0 for stored...



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# File 'lib/zip_tricks/zip_writer.rb', line 85

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)

  io << [0x04034b50].pack(C_UINT4)                        # local file header signature     4 bytes  (0x04034b50)
  io << if requires_zip64                                 # version needed to extract       2 bytes
    [VERSION_NEEDED_TO_EXTRACT_ZIP64].pack(C_UINT2)
  else
    [VERSION_NEEDED_TO_EXTRACT].pack(C_UINT2)
  end

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

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

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

  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)

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

  io << filename                                     # file name (variable size)
  io << extra_fields.string
end