implement hex-reader option

Author: Tim Aitken

include/json/reader.h

@@ -324,6 +324,8 @@ class JSON_API CharReaderBuilder : public CharReader::Factory {
    * - `"allowSpecialFloats": false or true`
    *   - If true, special float values (NaNs and infinities) are allowed and
    *     their values are lossfree restorable.
+   * - `"allowHexadecimal": false or true`
+   *   - If true, allow hexadecimal (eg 0xFFFF) to be used as unsigned integers.
    * - `"skipBom": false or true`
    *   - If true, if the input starts with the Unicode byte order mark (BOM),
    *     it is skipped.

src/lib_json/json_reader.cpp

@@ -875,6 +875,7 @@ class OurFeatures {
   bool failIfExtra_;
   bool rejectDupKeys_;
   bool allowSpecialFloats_;
+  bool allowHexadecimal_;
   bool skipBom_;
   size_t stackLimit_;
 }; // OurFeatures
@@ -914,6 +915,7 @@ class OurReader {
     tokenArrayEnd,
     tokenString,
     tokenNumber,
+    tokenHexadecimal,
     tokenTrue,
     tokenFalse,
     tokenNull,
@@ -952,11 +954,14 @@ class OurReader {
   bool readString();
   bool readStringSingleQuote();
   bool readNumber(bool checkInf);
+  bool readHexadecimal();
   bool readValue();
   bool readObject(Token& token);
   bool readArray(Token& token);
   bool decodeNumber(Token& token);
   bool decodeNumber(Token& token, Value& decoded);
+  bool decodeHexadecimal(Token& token);
+  bool decodeHexadecimal(Token& token, Value& decoded);
   bool decodeString(Token& token);
   bool decodeString(Token& token, String& decoded);
   bool decodeDouble(Token& token);
@@ -1191,6 +1196,12 @@ bool OurReader::readToken(Token& token) {
     ok = readComment();
     break;
   case '0':
+    if(match("x", 1)) {
+      token.type_ = tokenHexadecimal;
+      ok = features_.allowHexadecimal_;
+      readHexadecimal();
+      break;
+    }
   case '1':
   case '2':
   case '3':
@@ -1419,6 +1430,18 @@ bool OurReader::readNumber(bool checkInf) {
   }
   return true;
 }
+
+bool OurReader::readHexadecimal(void) {
+  Location p = current_;
+  char c = '0'; // stopgap for already consumed character
+  // integral part
+  while ((c >= '0' && c <= '9')
+    || (c >= 'a' && c <= 'f')
+    || (c >= 'A' && c <= 'F'))
+    c = (current_ = p) < end_ ? *p++ : '\0';
+  return true;
+}
+
 bool OurReader::readString() {
   Char c = 0;
   while (current_ != end_) {
@@ -1639,6 +1662,44 @@ bool OurReader::decodeNumber(Token& token, Value& decoded) {
   return true;
 }
 
+bool OurReader::decodeHexadecimal(Token& token) {
+  Value decoded;
+  if (!decodeHexadecimal(token, decoded))
+    return false;
+  currentValue().swapPayload(decoded);
+  currentValue().setOffsetStart(token.start_ - begin_);
+  currentValue().setOffsetLimit(token.end_ - begin_);
+  return true;
+}
+
+bool OurReader::decodeHexadecimal(Token& token, Value& decoded) {
+  Json::LargestUInt value = 0;
+  constexpr Json::LargestUInt top =
+    Json::LargestUInt(0xF) << (sizeof(top) * 8) - 4; 
+
+  Location current = token.start_;
+  while (current < token.end_) {
+    Char c = *current++;
+    static_assert('A' < 'a');
+    static_assert('0' < 'A');
+    if (c == 'x')
+      continue;
+    else if (c >= 'a')
+      c -= 'a' - 10;
+    else if (c >= 'A')
+      c -= 'A' - 10;
+    else if (c >= '0')
+      c -= '0';
+    else return addError(
+        "Contains non-hexadecimal digits.", token, current);
+    if (value & top) return addError(
+        "Number is too large for unsigned integer.", token, current);
+    value = value << 4 | static_cast<Value::UInt>(c);
+  }
+  decoded = value;
+  return true;
+}
+
 bool OurReader::decodeDouble(Token& token) {
   Value decoded;
   if (!decodeDouble(token, decoded))
@@ -1908,6 +1969,7 @@ CharReader* CharReaderBuilder::newCharReader() const {
   features.failIfExtra_ = settings_["failIfExtra"].asBool();
   features.rejectDupKeys_ = settings_["rejectDupKeys"].asBool();
   features.allowSpecialFloats_ = settings_["allowSpecialFloats"].asBool();
+  features.allowHexadecimal_ = settings_["allowHexacecimal"].asBool();
   features.skipBom_ = settings_["skipBom"].asBool();
   return new OurCharReader(collectComments, features);
 }
@@ -1925,6 +1987,7 @@ bool CharReaderBuilder::validate(Json::Value* invalid) const {
       "failIfExtra",
       "rejectDupKeys",
       "allowSpecialFloats",
+      "allowHexacecimal",
       "skipBom",
   };
   for (auto si = settings_.begin(); si != settings_.end(); ++si) {