Method: ZipTricks::ZipWriter#write_data_descriptor

Defined in:
lib/zip_tricks/zip_writer.rb

#write_data_descriptor(io:, compressed_size:, uncompressed_size:, crc32:) ⇒ void

This method returns an undefined value.

Writes the data descriptor following the file data for a file whose local file header was written with general-purpose flag bit 3 set. If the one of the sizes exceeds the Zip64 threshold, the data descriptor will have the sizes written out as 8-byte values instead of 4-byte values.

Parameters:

  • io (#<<) —

    the buffer to write the local file header to

  • crc32 (Fixnum) —

    The CRC32 checksum of the file

  • 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



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# File 'lib/zip_tricks/zip_writer.rb', line 229

def write_data_descriptor(io:, compressed_size:, uncompressed_size:, crc32:)
  io << [0x08074b50].pack(C_UINT4)  # Although not originally assigned a signature, the value
  # 0x08074b50 has commonly been adopted as a signature value
  # for the data descriptor record.
  io << [crc32].pack(C_UINT4)                             # crc-32                          4 bytes

  # If one of the sizes is above 0xFFFFFFF use ZIP64 lengths (8 bytes) instead. A good unarchiver
  # will decide to unpack it as such if it finds the Zip64 extra for the file in the central directory.
  # So also use the opportune moment to switch the entry to Zip64 if needed
  requires_zip64 = (compressed_size > FOUR_BYTE_MAX_UINT || uncompressed_size > FOUR_BYTE_MAX_UINT)
  pack_spec = requires_zip64 ? C_UINT8 : C_UINT4

  io << [compressed_size].pack(pack_spec)       # compressed size                 4 bytes, or 8 bytes for ZIP64
  io << [uncompressed_size].pack(pack_spec)     # uncompressed size               4 bytes, or 8 bytes for ZIP64
end