Adding support for deserializing ISO 8601 durations as TimeSpan in JSON

RestSharp.Tests/JsonTests.cs

@@ -539,6 +539,14 @@ public void Can_Deserialize_TimeSpan()
             Assert.Null(payload.NullableWithoutValue);
             Assert.NotNull(payload.NullableWithValue);
             Assert.Equal(new TimeSpan(21, 30, 7), payload.NullableWithValue.Value);
+            Assert.Equal(new TimeSpan(0, 0, 10), payload.IsoSecond);
+            Assert.Equal(new TimeSpan(0, 3, 23), payload.IsoMinute);
+            Assert.Equal(new TimeSpan(5, 4, 9), payload.IsoHour);
+            Assert.Equal(new TimeSpan(1, 19, 27, 13), payload.IsoDay);
+            // 2 months + 4 days = 64 days
+            Assert.Equal(new TimeSpan(64, 3, 14, 19), payload.IsoMonth);
+            // 1 year = 365 days
+            Assert.Equal(new TimeSpan(365, 9, 27, 48), payload.IsoYear);
         }
 
         [Fact]

RestSharp.Tests/SampleClasses/misc.cs

@@ -233,6 +233,18 @@ public class TimeSpanTestStructure
         public TimeSpan? NullableWithoutValue { get; set; }
 
         public TimeSpan? NullableWithValue { get; set; }
+
+        public TimeSpan? IsoSecond { get; set; }
+
+        public TimeSpan? IsoMinute { get; set; }
+
+        public TimeSpan? IsoHour { get; set; }
+
+        public TimeSpan? IsoDay { get; set; }
+
+        public TimeSpan? IsoMonth { get; set; }
+
+        public TimeSpan? IsoYear { get; set; }
     }
 
     public class JsonEnumsTestStructure

RestSharp.Tests/SampleData/timespans.txt

@@ -6,4 +6,10 @@
     "Hour": "21:30:07.0000000",
     "NullableWithoutValue": null,
     "NullableWithValue": "21:30:07.0000000",
+    "IsoSecond": "PT10S",
+    "IsoMinute": "PT3M23S",
+    "IsoHour": "PT5H4M9S",
+    "IsoDay": "P1DT19H27M13S",
+    "IsoMonth": "P2M4DT3H14M19S",
+    "IsoYear": "P1YT9H27M48S"
 }

RestSharp/Deserializers/JsonDeserializer.cs

@@ -7,6 +7,8 @@
 
 namespace RestSharp.Deserializers
 {
+    using System.Xml;
+
     public class JsonDeserializer : IDeserializer
     {
         public string RootElement { get; set; }
@@ -270,7 +272,14 @@ private object ConvertValue(Type type, object value)
             }
             else if (type == typeof(TimeSpan))
             {
-                return TimeSpan.Parse(stringValue);
+                TimeSpan timeSpan;
+                if (TimeSpan.TryParse(stringValue, out timeSpan))
+                {
+                    return timeSpan;
+                }
+
+                // This should handle ISO 8601 durations
+                return XmlConvert.ToTimeSpan(stringValue);
             }
             else if (type.IsGenericType)
             {