Fix RuntimeError in REXML::Parsers::BaseParser for valid feeds (#199)

GitHub: fix GH-198

Change `#entity` to not match against default entities

After this change, the following example will not raise a RuntimeError:

```ruby
# rexml/refactor_entity_example.rb

$LOAD_PATH.unshift(File.expand_path("lib"))

require "rexml/parsers/baseparser"

valid_feed = "<p>#{'A' * 10_240}</p>"

base_parser = REXML::Parsers::BaseParser.new("")
base_parser.unnormalize(valid_feed) # => "<p>" + "A" * 10_240 + "</p>"
```

Default entities now gets substituted by this block instead


https://github.com/ruby/rexml/blob/e14847cee53d26eb162ad786ba12e3cd7a86fce0/lib/rexml/parsers/baseparser.rb#L560-L563

---------

Co-authored-by: Sutou Kouhei <kou@clear-code.com>
Co-authored-by: NAITOH Jun <naitoh@gmail.com>

lib/rexml/parsers/baseparser.rb

@@ -521,15 +521,13 @@ def pull_event
       private :pull_event
 
       def entity( reference, entities )
-        value = nil
-        value = entities[ reference ] if entities
-        if value
-          record_entity_expansion
-        else
-          value = DEFAULT_ENTITIES[ reference ]
-          value = value[2] if value
-        end
-        unnormalize( value, entities ) if value
+        return unless entities
+
+        value = entities[ reference ]
+        return if value.nil?
+
+        record_entity_expansion
+        unnormalize( value, entities )
       end
 
       # Escapes all possible entities

test/test_pullparser.rb

@@ -254,6 +254,36 @@ def test_with_default_entity
           end
         end
 
+        def test_with_only_default_entities
+          member_value = "<p>#{'A' * @default_entity_expansion_text_limit}</p>"
+          source = <<-XML
+<?xml version="1.0" encoding="UTF-8"?>
+<member>
+#{member_value}
+</member>
+          XML
+
+          parser = REXML::Parsers::PullParser.new(source)
+          events = {}
+          element_name = ''
+          while parser.has_next?
+            event = parser.pull
+            case event.event_type
+            when :start_element
+              element_name = event[0]
+            when :text
+              events[element_name] = event[1]
+            end
+          end
+
+          expected_value = "<p>#{'A' * @default_entity_expansion_text_limit}</p>"
+          assert_equal(expected_value, events['member'].strip)
+          assert_equal(0, parser.entity_expansion_count)
+          assert do
+            events['member'].bytesize > @default_entity_expansion_text_limit
+          end
+        end
+
         def test_entity_expansion_text_limit
           source = <<-XML
 <!DOCTYPE member [

test/test_sax.rb

@@ -187,6 +187,30 @@ def test_with_default_entity
           end
         end
 
+        def test_with_only_default_entities
+          member_value = "<p>#{'A' * @default_entity_expansion_text_limit}</p>"
+          source = <<-XML
+<?xml version="1.0" encoding="UTF-8"?>
+<member>
+#{member_value}
+</member>
+          XML
+
+          sax = REXML::Parsers::SAX2Parser.new(source)
+          text_value = nil
+          sax.listen(:characters, ["member"]) do |text|
+            text_value = text
+          end
+          sax.parse
+
+          expected_value = "<p>#{'A' * @default_entity_expansion_text_limit}</p>"
+          assert_equal(expected_value, text_value.strip)
+          assert_equal(0, sax.entity_expansion_count)
+          assert do
+            text_value.bytesize > @default_entity_expansion_text_limit
+          end
+        end
+
         def test_entity_expansion_text_limit
           source = <<-XML
 <!DOCTYPE member [

test/test_stream.rb

@@ -89,6 +89,43 @@ def entity(content)
     end
   end
 
+  class EntityExpansionLimitTest < Test::Unit::TestCase
+    def setup
+      @default_entity_expansion_limit = REXML::Security.entity_expansion_limit
+      @default_entity_expansion_text_limit = REXML::Security.entity_expansion_text_limit
+    end
+
+    def teardown
+      REXML::Security.entity_expansion_limit = @default_entity_expansion_limit
+      REXML::Security.entity_expansion_text_limit = @default_entity_expansion_text_limit
+    end
+
+    def test_with_only_default_entities
+      member_value = "&lt;p&gt;#{'A' * @default_entity_expansion_text_limit}&lt;/p&gt;"
+      source = <<-XML
+<?xml version="1.0" encoding="UTF-8"?>
+<member>
+#{member_value}
+</member>
+      XML
+
+      listener = MyListener.new
+      class << listener
+        attr_accessor :text_value
+        def text(text)
+          @text_value << text
+        end
+      end
+      listener.text_value = ""
+      REXML::Document.parse_stream(source, listener)
+
+      expected_value = "<p>#{'A' * @default_entity_expansion_text_limit}</p>"
+      assert_equal(expected_value, listener.text_value.strip)
+      assert do
+        listener.text_value.bytesize > @default_entity_expansion_text_limit
+      end
+    end
+  end
 
   # For test_listener
   class RequestReader