Module: Pdfrb::Source::LinearizationDetection

Defined in:
lib/pdfrb/source/linearization_detection.rb

Overview

Linearization detection (s7.6.2). A linearized PDF has a Linearization dict as its first indirect object, immediately after the header. Detecting this lets readers stream pages in order (vs. waiting for the whole file to load).

Class Method Summary collapse

Class Method Details

.linearized?(io) ⇒ Boolean

Returns true if the file at io is linearized (per the heuristic from s7.6.2: first indirect object carries a /Linearized key).

Returns:

  • (Boolean) 


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# File 'lib/pdfrb/source/linearization_detection.rb', line 15

def linearized?(io)
  # Skip header.
  Pdfrb::Source::HeaderReader.read(io)
  tokenizer = Pdfrb::Source::Tokenizer.new(io)
  parser = Pdfrb::Source::Parser.new(tokenizer)
  # Parse the first indirect object we find.
  tok = tokenizer.peek
  return false unless tok&.type == :integer

  obj = parser.parse_indirect_object
  return false unless obj.value.is_a?(::Hash)

  obj.value.key?(:Linearized)
rescue StandardError
  # Malformed input isn't linearized for our purposes.
  false
end