Added option to do entity encoding

This adds a feature to support entity encoding to escape characters that
can be used XSS attacks. This is to match the behavior in
ActiveSupport::JSON. The purpose of matching AS::JSON behavior is so we
can replace it with Yajl so we can use the faster version.

Co-authored-by: Aaron Patterson <aaron.patterson@gmail.com>

ext/yajl/yajl_encode.c

@@ -59,12 +59,18 @@ yajl_string_encode2(const yajl_print_t print,
                     unsigned int htmlSafe)
 {
     unsigned int beg = 0;
-    unsigned int end = 0;    
+    unsigned int end = 0;
+    unsigned int increment = 0;
     char hexBuf[7];
+    char entityBuffer[7];
     hexBuf[0] = '\\'; hexBuf[1] = 'u'; hexBuf[2] = '0'; hexBuf[3] = '0';
     hexBuf[6] = 0;
 
+    entityBuffer[0] = '\\'; entityBuffer[1] = 'u'; entityBuffer[2] = '2'; entityBuffer[3] = '0';
+    entityBuffer[6] = 0;
+
     while (end < len) {
+        increment = 1;
         const char * escaped = NULL;
         switch (str[end]) {
             case '\r': escaped = "\\r"; break;
@@ -76,10 +82,39 @@ yajl_string_encode2(const yajl_print_t print,
             case '\b': escaped = "\\b"; break;
             case '\t': escaped = "\\t"; break;
             case '/':
-              if (htmlSafe) {
+              if (htmlSafe == 1) {
                 escaped = "\\/";
               }
               break;
+            /* Escaping 0xe280a8 0xe280a9 */
+            case 0xe2:
+              if (htmlSafe == 2) {
+                  if (len - end >= 2 && str[end + 1] == 0x80) {
+                      if (str[end + 2] == 0xa8) {
+                          increment = 3;
+                          entityBuffer[4] = '2';
+                          entityBuffer[5] = '8';
+                          escaped = entityBuffer;
+                          break;
+                      }
+
+                      if (str[end + 2] == 0xa9) {
+                          increment = 3;
+                          entityBuffer[4] = '2';
+                          entityBuffer[5] = '9';
+                          escaped = entityBuffer;
+                          break;
+                      }
+                  }
+              }
+            case '<':
+            case '>':
+            case '&':
+              if (htmlSafe == 2) {
+                  CharToHex(str[end], hexBuf + 4);
+                  escaped = hexBuf;
+              }
+              break;
             default:
                 if ((unsigned char) str[end] < 32) {
                     CharToHex(str[end], hexBuf + 4);
@@ -90,7 +125,8 @@ yajl_string_encode2(const yajl_print_t print,
         if (escaped != NULL) {
             print(ctx, (const char *) (str + beg), end - beg);
             print(ctx, escaped, (unsigned int)strlen(escaped));
-            beg = ++end;
+            end += increment;
+            beg = end;
         } else {
             ++end;
         }

ext/yajl/yajl_ext.c

@@ -1030,9 +1030,14 @@ static VALUE rb_yajl_encoder_new(int argc, VALUE * argv, VALUE klass) {
                 actualIndent = indentString;
             }
         }
+
         if (rb_hash_aref(opts, sym_html_safe) == Qtrue) {
           htmlSafe = 1;
         }
+
+        if (rb_hash_aref(opts, sym_entities) == Qtrue) {
+          htmlSafe = 2;
+        }
     }
     if (!indentString) {
       indentString = defaultIndentString;
@@ -1356,6 +1361,7 @@ void Init_yajl() {
     sym_pretty = ID2SYM(rb_intern("pretty"));
     sym_indent = ID2SYM(rb_intern("indent"));
     sym_html_safe = ID2SYM(rb_intern("html_safe"));
+    sym_entities = ID2SYM(rb_intern("entities"));
     sym_terminator = ID2SYM(rb_intern("terminator"));
     sym_symbolize_keys = ID2SYM(rb_intern("symbolize_keys"));
     sym_symbolize_names = ID2SYM(rb_intern("symbolize_names"));

ext/yajl/yajl_ext.h

@@ -56,7 +56,7 @@ static rb_encoding *utf8Encoding;
 static VALUE cStandardError, cParseError, cEncodeError, mYajl, cParser, cProjector, cEncoder;
 static ID intern_io_read, intern_call, intern_keys, intern_to_s,
             intern_to_json, intern_has_key, intern_to_sym, intern_as_json;
-static ID sym_allow_comments, sym_check_utf8, sym_pretty, sym_indent, sym_terminator, sym_symbolize_keys, sym_symbolize_names, sym_html_safe;
+static ID sym_allow_comments, sym_check_utf8, sym_pretty, sym_indent, sym_terminator, sym_symbolize_keys, sym_symbolize_names, sym_html_safe, sym_entities;
 
 #define GetParser(obj, sval) Data_Get_Struct(obj, yajl_parser_wrapper, sval);
 #define GetEncoder(obj, sval) Data_Get_Struct(obj, yajl_encoder_wrapper, sval);

spec/encoding/encoding_spec.rb

@@ -275,6 +275,14 @@ def to_s
     expect(safe_encoder.encode("</script>")).to eql("\"<\\/script>\"")
   end
 
+  it "should not encode characters with entities by default" do
+    expect(Yajl.dump("\u2028\u2029><&")).to eql("\"\u2028\u2029><&\"")
+  end
+
+  it "should encode characters with entities when enabled" do
+    expect(Yajl.dump("\u2028\u2029><&", entities: true)).to eql("\"\\u2028\\u2029\\u003E\\u003C\\u0026\"")
+  end
+
   it "should default to *not* escaping / characters" do
     unsafe_encoder = Yajl::Encoder.new
     expect(unsafe_encoder.encode("</script>")).not_to eql("\"<\\/script>\"")