Improve performance of JSON HTML entity escaping

Running gsub! 5 times with string arguments seems to be faster than
running it once with a regex and Hash.

When there are matches to the regex (there are characters to escape)
this is faster in part because CRuby will allocate a new match object
and string as a key to lookup in the map hash provided. It's possible
that could be optimized upstream, but at the moment this avoids those
allocations.

Surprisingly (at least to me) this is still much faster when there is no
replacement needed: in my test ~3x faster on a short ~200 byte string,
and ~5x faster on a pre-escaped ~600k twitter.json.

actionview/test/template/erb_util_test.rb

@@ -13,9 +13,15 @@ class ErbUtilTest < ActiveSupport::TestCase
     end
   end
 
-  ERB::Util::JSON_ESCAPE.each do |given, expected|
+  {
+    "&" => '\u0026',
+    ">" => '\u003e',
+    "<" => '\u003c',
+    "\u2028" => '\u2028',
+    "\u2029" => '\u2029'
+  }.each do |given, expected|
     define_method "test_json_escape_#{expected.gsub(/\W/, '')}" do
-      assert_equal ERB::Util::JSON_ESCAPE[given], json_escape(given)
+      assert_equal expected, json_escape(given)
     end
   end
 

activesupport/lib/active_support/core_ext/erb/util.rb

@@ -38,9 +38,7 @@ module ERBUtilPrivate
 class ERB
   module Util
     HTML_ESCAPE = { "&" => "&amp;",  ">" => "&gt;",   "<" => "&lt;", '"' => "&quot;", "'" => "&#39;" }
-    JSON_ESCAPE = { "&" => '\u0026', ">" => '\u003e', "<" => '\u003c', "\u2028" => '\u2028', "\u2029" => '\u2029' }
     HTML_ESCAPE_ONCE_REGEXP = /["><']|&(?!([a-zA-Z]+|(#\d+)|(#[xX][\dA-Fa-f]+));)/
-    JSON_ESCAPE_REGEXP = /[\u2028\u2029&><]/u
 
     # Following XML requirements: https://www.w3.org/TR/REC-xml/#NT-Name
     TAG_NAME_START_CODEPOINTS = "@:A-Z_a-z\u{C0}-\u{D6}\u{D8}-\u{F6}\u{F8}-\u{2FF}\u{370}-\u{37D}\u{37F}-\u{1FFF}" \
@@ -124,7 +122,12 @@ def html_escape_once(s)
     # JSON gem, do not provide this kind of protection by default; also some gems
     # might override +to_json+ to bypass Active Support's encoder).
     def json_escape(s)
-      result = s.to_s.gsub(JSON_ESCAPE_REGEXP, JSON_ESCAPE)
+      result = s.to_s.dup
+      result.gsub!(">", '\u003e')
+      result.gsub!("<", '\u003c')
+      result.gsub!("&", '\u0026')
+      result.gsub!("\u2028", '\u2028')
+      result.gsub!("\u2029", '\u2029')
       s.html_safe? ? result.html_safe : result
     end
 

activesupport/lib/active_support/json/encoding.rb

@@ -39,33 +39,21 @@ def encode(value)
             value = value.as_json(options.dup)
           end
           json = stringify(jsonify(value))
+
+          # Rails does more escaping than the JSON gem natively does (we
+          # escape \u2028 and \u2029 and optionally >, <, & to work around
+          # certain browser problems).
           if Encoding.escape_html_entities_in_json
-            json.gsub! ESCAPE_REGEX_WITH_HTML_ENTITIES, ESCAPED_CHARS
-          else
-            json.gsub! ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, ESCAPED_CHARS
+            json.gsub!(">", '\u003e')
+            json.gsub!("<", '\u003c')
+            json.gsub!("&", '\u0026')
           end
+          json.gsub!("\u2028", '\u2028')
+          json.gsub!("\u2029", '\u2029')
           json
         end
 
         private
-          # Rails does more escaping than the JSON gem natively does (we
-          # escape \u2028 and \u2029 and optionally >, <, & to work around
-          # certain browser problems).
-          ESCAPED_CHARS = {
-            "\u2028" => '\u2028',
-            "\u2029" => '\u2029',
-            ">"      => '\u003e',
-            "<"      => '\u003c',
-            "&"      => '\u0026',
-            }
-
-          ESCAPE_REGEX_WITH_HTML_ENTITIES = /[\u2028\u2029><&]/u
-          ESCAPE_REGEX_WITHOUT_HTML_ENTITIES = /[\u2028\u2029]/u
-
-          # Mark these as private so we don't leak encoding-specific constructs
-          private_constant :ESCAPED_CHARS, :ESCAPE_REGEX_WITH_HTML_ENTITIES,
-            :ESCAPE_REGEX_WITHOUT_HTML_ENTITIES
-
           # Convert an object into a "JSON-ready" representation composed of
           # primitives like Hash, Array, String, Symbol, Numeric,
           # and +true+/+false+/+nil+.