Improve Performance with Nested CDATA

[Masamuneee]

I think we should improve the implementation to handle nested CDATA more efficiently.

require "rexml/document"

include REXML  

(1..1000000000).step(10000000) do |depth|
  puts "Trying depth #{depth}"
  string = "<?xml version=\"1.0\"?>\n" +
           "<root>Test</root>\n" +
           "<!" + "[CDATA[" * depth + "]]>\n"
  
  start = Time.now
  begin
    doc = Document.new(string)
  rescue Exception => e
    puts "Error at depth #{depth}: #{e}"
    break
  end
  elapsed_time = Time.now - start
  puts "Elapsed time: #{elapsed_time} seconds"
end

Result:

Elapsed time: 24.994068928 seconds
Trying depth 200000001
Elapsed time: 27.070803532 seconds
Trying depth 210000001
Elapsed time: 27.870487966 seconds
Trying depth 220000001
Elapsed time: 28.787843908 seconds
Trying depth 230000001
[1]    4336 killed     ruby test.rb

[tompng]

I don't think it is a problem. Large data takes time. Not related to nested cdata.

size = 1000000
nested_cdata = "<?xml version=\"1.0\"?><root>Test</root><!" + "[CDATA[" * size + "]]>"
normal_cdata = "<?xml version=\"1.0\"?><root>Test</root><![CDATA[" + 'aaaaaaa' * size + "]]>"
normal_text = "<?xml version=\"1.0\"?><root>Test" + 'aaaaaaa' * size + "</root>"
normal_tags = "<?xml version=\"1.0\"?><root>Test" + '<b></b>' * size + "</root>"

# Size are almost the same.
[nested_cdata, normal_cdata, normal_text, normal_tags].map(&:size)
# => [7000043, 7000050, 7000038, 7000038]

REXML::Document.new(nested_cdata);
# processing time: 0.130978s
REXML::Document.new(normal_cdata);
# processing time: 0.109913s
REXML::Document.new(normal_text);
# processing time: 0.144391s
REXML::Document.new(normal_tags);
# processing time: 5.863289s

The slowness is just caused by the input size. Time consumption of parsing nested cdata, non-nested normal cdata, normal text node is almost the same.

Trying depth 220000001
Elapsed time: 28.787843908 seconds
# depth=1000000 takes 0.13s
# estimated time 220000001/1000000 * 0.13 => 28.6