Class: CorpPdf::ObjStm

Inherits:
Object
  • Object
show all
Defined in:
lib/corp_pdf/objstm.rb

Class Method Summary collapse

Class Method Details

.create(patches, compress: true) ⇒ Object

Create an object stream from patches (array of [num, gen], body: String). Returns: { dictionary: String, stream_body: String, object_count: Integer } The dictionary includes /Type /ObjStm, /N (count), /First (header size), and /Filter /FlateDecode



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# File 'lib/corp_pdf/objstm.rb', line 24

def self.create(patches, compress: true)
  return nil if patches.empty?

  # Sort patches by object number for consistency
  sorted_patches = patches.sort_by { |p| p[:ref][0] }

  # Build header: "obj_num offset obj_num offset ..."
  # Offsets are relative to the start of the object data section (after header)
  header_parts = []
  body_parts = []
  current_offset = 0

  sorted_patches.each do |patch|
    obj_num, = patch[:ref]
    body = patch[:body].to_s
    # Ensure body ends with newline for proper parsing
    body += "\n" unless body.end_with?("\n")

    header_parts << obj_num.to_s
    header_parts << current_offset.to_s
    body_parts << body
    current_offset += body.bytesize
  end

  header = "#{header_parts.join(' ')}\n"
  first = header.bytesize
  object_bodies = body_parts.join

  # Combine header and bodies
  raw_data = header + object_bodies

  # Compress if requested
  stream_body = if compress
                  Zlib::Deflate.deflate(raw_data)
                else
                  raw_data
                end

  # Build dictionary
  dict = "<<\n/Type /ObjStm\n/N #{sorted_patches.length}\n/First #{first}".b
  dict << "\n/Filter /FlateDecode".b if compress
  dict << "\n/Length #{stream_body.bytesize}\n>>".b

  {
    dictionary: dict,
    stream_body: stream_body.b,
    object_count: sorted_patches.length,
    patches: sorted_patches
  }
end

.parse(bytes, n:, first:) ⇒ Object

Parse an object stream body given N and First. Returns: array like [{ ref:, body:String }, …] in order of header listing.



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# File 'lib/corp_pdf/objstm.rb', line 7

def self.parse(bytes, n:, first:)
  head = bytes[0...first]
  entries = head.strip.split(/\s+/).map!(&:to_i)
  refs = []
  n.times do |i|
    obj = entries[2 * i]
    off = entries[(2 * i) + 1]
    next_off = i + 1 < n ? entries[(2 * (i + 1)) + 1] : (bytes.bytesize - first)
    body = bytes[first + off, (first + next_off) - (first + off)]
    refs << { ref: [obj, 0], body: body }
  end
  refs
end