Json writer, only emit floating point finite numbers, ignore INF/NaN

My interpretation of RFC4627, Section 2.4 "Numbers" of:
  Numeric values that cannot be represented as sequences of digits
   (such as Infinity and NaN) are not permitted.

I have also verified this matter with NodeJS JSON.stringify() that
emitting a null is consistent behavior with a JSON implementation
written in JavaScript.

Previously Qt would emit:
{
 plusInfinity: inf,
 minusInfinity: -inf,
 notANumber: nan
}

Which maybe turned into a string values of "inf", "-inf", "nan" by
the receiving parser.  Now it returns the JSON null value just like
NodeJS JSON.stringify().

Change-Id: I9f9c17f12b2606280806c47a9d90465c4ba5f786
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/corelib/json/qjsonwriter.cpp b/src/corelib/json/qjsonwriter.cpp
index 76f62241e3..c284f76cbb 100644
--- a/src/corelib/json/qjsonwriter.cpp
+++ b/src/corelib/json/qjsonwriter.cpp
@@ -169,9 +169,14 @@ static void valueToJson(const QJsonPrivate::Base *b, const QJsonPrivate::Value &
     case QJsonValue::Bool:
         json += v.toBoolean() ? "true" : "false";
         break;
-    case QJsonValue::Double:
-        json += QByteArray::number(v.toDouble(b));
+    case QJsonValue::Double: {
+        const double d = v.toDouble(b);
+        if (qIsFinite(d))
+            json += QByteArray::number(d);
+        else
+            json += "null"; // +INF || -INF || NaN (see RFC4627#section2.4)
         break;
+    }
     case QJsonValue::String:
         json += '"';
         json += escapedString(v.toString(b));