Fixes JSON down converter invalid decimal issue. (#134)

Author: cheqianh

Amazon.IonDotnet.Tests/Internals/TextWriterJsonTest.cs

@@ -46,6 +46,21 @@ public void Cleanup()
             this.sw.Dispose();
         }
 
+        [TestMethod]
+        [DataRow("0.2")]
+        [DataRow("2.d-1")]
+        [DataRow("2d-1")]
+        public void TestInvalidJsonDecimalFromIon(string decimalString)
+        {
+            var bigDecimal = BigDecimal.Parse(decimalString);
+            
+            value.SetField("value", factory.NewDecimal(bigDecimal));
+            var reader = IonReaderBuilder.Build(value);
+            jsonWriter.WriteValues(reader);
+            
+            Assert.AreEqual("{\"value\":2e-1}", this.sw.ToString());
+        }
+
         [TestMethod]
         public void TestGenericNull()
         {

Amazon.IonDotnet/Internals/Text/IonTextWriter.cs

@@ -218,6 +218,16 @@ public override void WriteDecimal(BigDecimal value)
             {
                 var decimalString = value.ToString();
                 decimalString = decimalString.Replace('d', 'e');
+
+                // Since Ion Decimal allows an exponent integer following '.' (e.g. 2.d-1) while JSON doesn't, we
+                // should make sure JSON down converter doesn't write any decimal number with '.' immediately
+                // followed by 'e'.
+                var index = decimalString.IndexOf(".e", 0);
+                if (index != -1)
+                {
+                    decimalString = decimalString.Remove(index, 1);
+                }
+
                 this.textWriter.Write(decimalString);
             }
             else