CSHARP-963: Support $date with ISO8601 string in extended JSON.

Author: rstam

MongoDB.Bson/IO/JsonReader.cs

@@ -923,13 +923,30 @@ private BsonValue ParseDateTimeExtendedJson()
         {
             VerifyToken(":");
             var valueToken = PopToken();
-            if (valueToken.Type != JsonTokenType.Int32 && valueToken.Type != JsonTokenType.Int64)
+
+            long millisecondsSinceEpoch;
+            if (valueToken.Type == JsonTokenType.Int32 || valueToken.Type == JsonTokenType.Int64)
             {
-                var message = string.Format("JSON reader expected an integer but found '{0}'.", valueToken.Lexeme);
+                millisecondsSinceEpoch = valueToken.Int64Value;
+            }
+            else if (valueToken.Type == JsonTokenType.String)
+            {
+                DateTime dateTime;
+                if (!DateTime.TryParse(valueToken.StringValue, out dateTime))
+                {
+                    var message = string.Format("Invalid $date string: '{0}'.", valueToken.StringValue);
+                    throw new FileFormatException(message);
+                }
+                millisecondsSinceEpoch = BsonUtils.ToMillisecondsSinceEpoch(dateTime);
+            }
+            else
+            {
+                var message = string.Format("JSON reader expected an integer or an ISO 8601 string for $date but found a '{0}'.", valueToken.Lexeme);
                 throw new FileFormatException(message);
             }
+
             VerifyToken("}");
-            return new BsonDateTime(valueToken.Int64Value);
+            return new BsonDateTime(millisecondsSinceEpoch);
         }
 
         private BsonValue ParseDateTimeConstructor(bool withNew)

MongoDB.BsonUnitTests/IO/JsonReaderTests.cs

@@ -223,6 +223,21 @@ public void TestDateTimeStrict()
             Assert.AreEqual(json, BsonSerializer.Deserialize<DateTime>(new StringReader(json)).ToJson(jsonSettings));
         }
 
+        [Test]
+        public void TestDateTimeStrictIso8601()
+        {
+            var json = "{ \"$date\" : \"1970-01-01T00:00:00Z\" }";
+            using (_bsonReader = BsonReader.Create(json))
+            {
+                Assert.AreEqual(BsonType.DateTime, _bsonReader.ReadBsonType());
+                Assert.AreEqual(0, _bsonReader.ReadDateTime());
+                Assert.AreEqual(BsonReaderState.Done, _bsonReader.State);
+            }
+            var expected = "{ \"$date\" : 0 }"; // it's still not ISO8601 on the way out
+            var jsonSettings = new JsonWriterSettings { OutputMode = JsonOutputMode.Strict };
+            Assert.AreEqual(expected, BsonSerializer.Deserialize<DateTime>(new StringReader(json)).ToJson(jsonSettings));
+        }
+
         [Test]
         public void TestDateTimeTengen()
         {