Improve CDATA and comment parse performance (#246)

naitoh · kou · web-flow · commit a5f31c49be10 · 2025-03-05T06:20:42.000+09:00
## Why?

Since `&lt;a&gt;&lt;!a` and `&lt;a&gt;&lt;!a&gt;` are malformed node, they do not need to be
checked before comments and CDATA.

## Benchmark : comment (after_doctype)
```
$ benchmark-driver benchmark/parse_comment.yaml
Calculating -------------------------------------
                         before       after  before(YJIT)  after(YJIT)
       after_doctype     1.306k      5.586k        1.152k       3.569k i/s -     100.000 times in 0.076563s 0.017903s 0.086822s 0.028020s

Comparison:
                    after_doctype
               after:      5585.7 i/s
         after(YJIT):      3568.9 i/s - 1.57x  slower
              before:      1306.1 i/s - 4.28x  slower
        before(YJIT):      1151.8 i/s - 4.85x  slower
```
- YJIT=ON : 3.09x faster
- YJIT=OFF : 4.28x faster

## Benchmark : CDATA
```
$ benchmark-driver benchmark/parse_cdata.yaml
Calculating -------------------------------------
                         before       after  before(YJIT)  after(YJIT)
                 dom     1.269k      5.548k        1.053k       3.072k i/s -     100.000 times in 0.078808s 0.018026s 0.094976s 0.032553s
                 sax     1.399k      8.244k        1.220k       4.460k i/s -     100.000 times in 0.071458s 0.012130s 0.081958s 0.022422s
                pull     1.411k      8.319k        1.260k       4.806k i/s -     100.000 times in 0.070883s 0.012021s 0.079335s 0.020809s
              stream     1.420k      8.320k        1.254k       4.728k i/s -     100.000 times in 0.070406s 0.012019s 0.079738s 0.021149s

Comparison:
                              dom
               after:      5547.5 i/s
         after(YJIT):      3071.9 i/s - 1.81x  slower
              before:      1268.9 i/s - 4.37x  slower
        before(YJIT):      1052.9 i/s - 5.27x  slower

                              sax
               after:      8244.0 i/s
         after(YJIT):      4459.9 i/s - 1.85x  slower
              before:      1399.4 i/s - 5.89x  slower
        before(YJIT):      1220.1 i/s - 6.76x  slower

                             pull
               after:      8318.8 i/s
         after(YJIT):      4805.6 i/s - 1.73x  slower
              before:      1410.8 i/s - 5.90x  slower
        before(YJIT):      1260.5 i/s - 6.60x  slower

                           stream
               after:      8320.2 i/s
         after(YJIT):      4728.4 i/s - 1.76x  slower
              before:      1420.3 i/s - 5.86x  slower
        before(YJIT):      1254.1 i/s - 6.63x  slower
```
- YJIT=ON : 2.91x - 3.80x faster
- YJIT=OFF : 4.37x - 5.90x faster

Co-authored-by: Sutou Kouhei &lt;kou@clear-code.com&gt;
diff --git a/lib/rexml/parsers/baseparser.rb b/lib/rexml/parsers/baseparser.rb
@@ -449,9 +449,7 @@ def pull_event
               end
               return [ :end_element, last_tag ]
             elsif @source.match?("!", true)
-              md = @source.match(/([^>]*>)/um)
               #STDERR.puts "SOURCE BUFFER = #{source.buffer}, #{source.buffer.size}"
-              raise REXML::ParseException.new("Malformed node", @source) unless md
               if @source.match?("--", true)
                 return [ :comment, process_comment ]
               elsif @source.match?("[CDATA[", true)
@@ -461,9 +459,9 @@ def pull_event
                 else
                   raise REXML::ParseException.new("Malformed CDATA: Missing end ']]>'", @source)
                 end
+              else
+                raise REXML::ParseException.new("Malformed node: Started with '<!' but not a comment nor CDATA", @source)
               end
-              raise REXML::ParseException.new( "Declarations can only occur "+
-                "in the doctype declaration.", @source)
             elsif @source.match?("?", true)
               return process_instruction
             else
diff --git a/test/parse/test_comment.rb b/test/parse/test_comment.rb
@@ -84,6 +84,19 @@ def test_doctype_malformed_comment_end
         DETAIL
       end
 
+      def test_after_doctype_malformed_node
+        exception = assert_raise(REXML::ParseException) do
+          parse("<a><!a")
+        end
+        assert_equal(<<~DETAIL.chomp, exception.to_s)
+          Malformed node: Started with '<!' but not a comment nor CDATA
+          Line: 1
+          Position: 6
+          Last 80 unconsumed characters:
+          a
+        DETAIL
+      end
+
       def test_after_doctype_unclosed_comment
         exception = assert_raise(REXML::ParseException) do
           parse("<a><!-->")
