Class: Spritely::Cache

Inherits:
Struct
  • Object
show all
Defined in:
lib/spritely/cache.rb

Constant Summary collapse

PNG_SIGNATURE_LENGTH =

www.w3.org/TR/PNG/#5PNG-file-signature

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PNG_INFO_LENGTH =

www.w3.org/TR/PNG/#5DataRep

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PNG_CRC_LENGTH =

Cyclic Redundancy Check (CRC) byte-length; www.w3.org/TR/PNG/#5Chunk-layout

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Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#filename ⇒ Object

Returns the value of attribute filename

Returns:

  • (Object) —

    the current value of filename



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# File 'lib/spritely/cache.rb', line 4

def filename
  @filename
end

Class Method Details

.busted?(filename, expected_cache_key) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/spritely/cache.rb', line 13

def self.busted?(filename, expected_cache_key)
  new(filename).key != expected_cache_key
end

.generate(*objects) ⇒ Object 



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# File 'lib/spritely/cache.rb', line 9

def self.generate(*objects)
  Digest::MD5.hexdigest(objects.collect(&:cache_key).join)
end

Instance Method Details

#key ⇒ Object 



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# File 'lib/spritely/cache.rb', line 17

def key
  return @key if @key

  File.open(filename) do |file|
    file.read(PNG_SIGNATURE_LENGTH) # we first have to read the signature to fast-forward the IO#pos
    until file.eof?
      each_chunk(file) do |keyword, value|
        if keyword == 'cache_key'
          return @key = value
          break
        end
      end
    end
  end
end