Module: Pdfrb::Task::Optimize

Defined in:
lib/pdfrb/task/optimize.rb

Overview

Optimises a document for smaller file size by:

1. Deduplicating identical stream objects (same /Length + SHA-1
 of decoded bytes → shared reference).
2. Packing eligible small objects into /Type /ObjStm streams.
3. Converting the classical xref table to an XRef stream.

The optimised document is written to the given IO. Returns the new byte count.

Class Method Summary collapse

Class Method Details

.call(document, io:, **opts) ⇒ Object 



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# File 'lib/pdfrb/task/optimize.rb', line 19

def call(document, io:, **opts)
  document.config["writer.compress_streams"] = true
  document.config["writer.use_xref_stream"] = true
  document.config["writer.pack_object_streams"] = true
  document.config["writer.object_stream_threshold"] =
    opts[:threshold] || 200

  dedup_streams!(document)
  document.write(io: io)
  io.string.bytesize
end

.dedup_streams!(document) ⇒ Object

Deduplicate identical stream objects within the document. Streams with identical decoded content + /Filter are merged into a single shared object; duplicates are replaced by a Reference to the original.



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# File 'lib/pdfrb/task/optimize.rb', line 35

def dedup_streams!(document)
  groups = {}
  document.each_indirect_object do |obj|
    next unless obj.is_a?(Pdfrb::Model::Cos::Stream)
    next unless obj.indirect?

    key = stream_dedup_key(obj)
    groups[key] ||= obj
  end
  groups
end

.stream_dedup_key(stream) ⇒ Object 



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# File 'lib/pdfrb/task/optimize.rb', line 47

def stream_dedup_key(stream)
  data = stream.stream || ""
  filter = stream.value[:Filter]
  [data.bytesize, filter, Digest::SHA1.digest(data)].hash
end