Class: PDF::Reader::Filter

Inherits:
Object
  • Object
show all
Defined in:
lib/pdf/reader/filter.rb

Overview

Various parts of a PDF file can be passed through a filter before being stored to provide support for features like compression and encryption. This class is for decoding that content.

Currently only 1 filter type is supported. Hopefully support for others will be added in the future.

Instance Method Summary collapse

Constructor Details

#initialize(name, options) ⇒ Filter

creates a new filter for decoding content



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# File 'lib/pdf/reader/filter.rb', line 38

def initialize (name, options)
  @options = options

  case name.to_sym
  when :FlateDecode    then @filter = :flate
  #else                raise UnsupportedFeatureError, "Unknown filter: #{name}"
  end
end

Instance Method Details

#filter(data) ⇒ Object

attempts to decode the specified data with the current filter



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# File 'lib/pdf/reader/filter.rb', line 48

def filter (data)
  # leave the data untouched if we don't support the required filter
  return data if @filter.nil?

  # decode the data
  self.send(@filter, data)
end

#flate(data) ⇒ Object

Decode the specified data with the Zlib compression algorithm



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# File 'lib/pdf/reader/filter.rb', line 57

def flate (data)
  begin
    Zlib::Inflate.new.inflate(data)
  rescue Zlib::DataError => e
    # by default, Ruby's Zlib assumes the data it's inflating
    # is RFC1951 deflated data, wrapped in a RFC1951 zlib container.
    # If that fails, then use an undocumented 'feature' to attempt to inflate
    # the data as a raw RFC1951 stream.
    #
    # See 
    # - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/243545
    # - http://www.gzip.org/zlib/zlib_faq.html#faq38
    Zlib::Inflate.new(-Zlib::MAX_WBITS).inflate(data)
  end
rescue Exception => e
  # Oops, there was a problem inflating the stream
  raise MalformedPDFError, "Error occured while inflating a compressed stream (#{e.class.to_s}: #{e.to_s})"
end