Optimize JSON escaping

Instead of using multiple gsub! calls, this uses binary encoding to do
the regexp gsub with map, then forces encoding back to UTF-8.

This uses the same approach as before
ebe0c40, with binary encoding, which
performs better.

Co-authored-by: Jean Boussier <[email protected]>

activesupport/lib/active_support/json/encoding.rb

@@ -30,6 +30,20 @@ def encode(value, options = nil)
     end
 
     module Encoding # :nodoc:
+      U2028 = -"\u2028".b
+      U2029 = -"\u2029".b
+
+      ESCAPED_CHARS = {
+        U2028 => '\u2028'.b,
+        U2029 => '\u2029'.b,
+        ">".b => '\u003e'.b,
+        "<".b => '\u003c'.b,
+        "&".b => '\u0026'.b,
+      }
+
+      ESCAPE_REGEX_WITH_HTML_ENTITIES = Regexp.union(*ESCAPED_CHARS.keys)
+      ESCAPE_REGEX_WITHOUT_HTML_ENTITIES = Regexp.union(U2028, U2029)
+
       class JSONGemEncoder # :nodoc:
         attr_reader :options
 
@@ -47,14 +61,13 @@ def encode(value)
           # Rails does more escaping than the JSON gem natively does (we
           # escape \u2028 and \u2029 and optionally >, <, & to work around
           # certain browser problems).
+          json.force_encoding(::Encoding::BINARY)
           if @options.fetch(:escape_html_entities, Encoding.escape_html_entities_in_json)
-            json.gsub!(">", '\u003e')
-            json.gsub!("<", '\u003c')
-            json.gsub!("&", '\u0026')
+            json.gsub!(ESCAPE_REGEX_WITH_HTML_ENTITIES, ESCAPED_CHARS)
+          else
+            json.gsub!(ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, ESCAPED_CHARS)
           end
-          json.gsub!("\u2028", '\u2028')
-          json.gsub!("\u2029", '\u2029')
-          json
+          json.force_encoding(::Encoding::UTF_8)
         end
 
         private
@@ -130,14 +143,13 @@ def encode(value)
             # Rails does more escaping than the JSON gem natively does (we
             # escape \u2028 and \u2029 and optionally >, <, & to work around
             # certain browser problems).
+            json.force_encoding(::Encoding::BINARY)
             if @options.fetch(:escape_html_entities, Encoding.escape_html_entities_in_json)
-              json.gsub!(">", '\u003e')
-              json.gsub!("<", '\u003c')
-              json.gsub!("&", '\u0026')
+              json.gsub!(ESCAPE_REGEX_WITH_HTML_ENTITIES, ESCAPED_CHARS)
+            else
+              json.gsub!(ESCAPE_REGEX_WITHOUT_HTML_ENTITIES, ESCAPED_CHARS)
             end
-            json.gsub!("\u2028", '\u2028')
-            json.gsub!("\u2029", '\u2029')
-            json
+            json.force_encoding(::Encoding::UTF_8)
           end
         end
       end