Class: FsCache::Attributes::Crc

Inherits:
FsCache::Attribute show all
Defined in:
lib/fs_cache/attributes/crc.rb

Overview

CRC attribute. Can be:

  • String: Internal CRC computed from files by blocks

Defined Under Namespace

Modules: Helpers

Constant Summary collapse

CRC_BLOCK_SIZE =

Size of blocks to compute CRCs in bytes. Changing this value will invalidate previously computed CRCs.

32 * 1024 * 1024

Instance Method Summary collapse

Instance Method Details

#attribute_for(file) ⇒ Object

Get the attribute for a given file

Parameters

  • file (String): File to get the attribute for

Result

  • Object: Corresponding attribute value



20
21
22
23
24
25
26
27
28
29
 
# File 'lib/fs_cache/attributes/crc.rb', line 20

def attribute_for(file)
  blocks_crc = ''
  File.open(file, 'rb') do |file_io|
    buffer = nil
    while (buffer = file_io.read(CRC_BLOCK_SIZE))
      blocks_crc << Zlib.crc32(buffer, 0).to_s(16).upcase
    end
  end
  Zlib.crc32(blocks_crc, 0).to_s(16).upcase
end

#invalidated_on_change_of ⇒ Object

Get the list of other attributes that invalidate this one. If any of those attributes is chaning on a file, then reset our attribute for the file.

Result

  • Array<Symbol>: List of dependent attributes



36
37
38
 
# File 'lib/fs_cache/attributes/crc.rb', line 36

def invalidated_on_change_of
  [:size]
end