Add support to pre-epoch Unix time (JamesNK#2614)

Co-authored-by: Max A. Kiselev <[email protected]>
Co-authored-by: James Newton-King <[email protected]>

Src/Newtonsoft.Json.Tests/Converters/UnixDateTimeConverterTests.cs

@@ -25,6 +25,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 #if DNXCORE50
 using Xunit;
 using Test = Xunit.FactAttribute;
@@ -71,6 +72,17 @@ public void SerializeInvalidDate()
             );
         }
 
+        [Test]
+        public void SerializeDateBeforeEpoch()
+        {
+            DateTime date = new DateTime(1964, 2, 7);
+            long dateSeconds = (long)(date.ToUniversalTime() - new DateTime(1970, 1, 1)).TotalSeconds;
+
+            string result = JsonConvert.SerializeObject(date, new UnixDateTimeConverter { AllowPreEpoch = true });
+
+            Assert.AreEqual(dateSeconds.ToString(CultureInfo.InvariantCulture), result);
+        }
+
         [Test]
         public void WriteJsonInvalidType()
         {
@@ -159,6 +171,19 @@ public void DeserializeInvalidStringToDateTimeOffset()
                 "Cannot convert invalid value to System.DateTimeOffset. Path '', line 1, position 5."
             );
         }
+
+        [Test]
+        public void DeserializeDateTimeOffsetBeforeEpoch()
+        {
+            UnixDateTimeConverter converter = new UnixDateTimeConverter(true);
+            DateTimeOffset d = new DateTimeOffset(1969, 2, 1, 20, 6, 18, TimeSpan.Zero);
+
+            string json = JsonConvert.SerializeObject(d, converter);
+
+            DateTimeOffset result = JsonConvert.DeserializeObject<DateTimeOffset>(json, converter);
+
+            Assert.AreEqual(new DateTimeOffset(1969, 2, 1, 20, 6, 18, TimeSpan.Zero), result);
+        }
 #endif
 
         [Test]
@@ -186,6 +211,14 @@ public void DeserializeInvalidValue()
             );
         }
 
+        [Test]
+        public void DeserializeNegativeIntegerToDateTimeBeforeEpoch()
+        {
+            DateTime result = JsonConvert.DeserializeObject<DateTime>("-1514840476", new UnixDateTimeConverter(true));
+
+            Assert.AreEqual(new DateTime(1921, 12, 31, 02, 58, 44, DateTimeKind.Utc), result);
+        }
+
         [Test]
         public void DeserializeInvalidValueType()
         {
@@ -263,6 +296,49 @@ public void ConverterObject()
             Assert.IsNull(obj2.Object2);
             Assert.AreEqual(new DateTime(2018, 1, 1, 21, 1, 16, DateTimeKind.Utc), obj2.ObjectNotHandled);
         }
+
+#if !NET20
+        [Test]
+        public void ConverterObjectWithDatesBeforeEpoch()
+        {
+            PreEpochUnixConverterObject obj1 = new PreEpochUnixConverterObject
+            {
+                Date1 = new DateTime(1969, 1, 1, 0, 0, 3, DateTimeKind.Utc),
+                Date2 = new DateTimeOffset(1969, 1, 1, 0, 0, 3, TimeSpan.Zero)
+            };
+
+            string json = JsonConvert.SerializeObject(obj1, Formatting.Indented);
+            StringAssert.AreEqual(@"{
+  ""Date1"": -31535997,
+  ""Date2"": -31535997
+}", json);
+
+            PreEpochUnixConverterObject obj2 = JsonConvert.DeserializeObject<PreEpochUnixConverterObject>(json);
+            Assert.IsNotNull(obj2);
+
+            Assert.AreEqual(new DateTime(1969, 1, 1, 0, 0, 3, DateTimeKind.Utc), obj2.Date1);
+            Assert.AreEqual(new DateTimeOffset(1969, 1, 1, 0, 0, 3, TimeSpan.Zero), obj2.Date2);
+        }
+#else
+        [Test]
+        public void ConverterObjectWithDatesBeforeEpoch()
+        {
+            PreEpochUnixConverterObject obj1 = new PreEpochUnixConverterObject
+            {
+                Date1 = new DateTime(1969, 1, 1, 0, 0, 3, DateTimeKind.Utc)
+            };
+
+            string json = JsonConvert.SerializeObject(obj1, Formatting.Indented);
+            StringAssert.AreEqual(@"{
+  ""Date1"": -31535997
+}", json);
+
+            PreEpochUnixConverterObject obj2 = JsonConvert.DeserializeObject<PreEpochUnixConverterObject>(json);
+            Assert.IsNotNull(obj2);
+
+            Assert.AreEqual(new DateTime(1969, 1, 1, 0, 0, 3, DateTimeKind.Utc), obj2.Date1);
+        }
+#endif
     }
 
     [JsonArray(ItemConverterType = typeof(UnixDateTimeConverter))]
@@ -281,4 +357,15 @@ public class UnixConverterObject
         [JsonConverter(typeof(UnixDateTimeConverter))]
         public object ObjectNotHandled { get; set; }
     }
+
+    public class PreEpochUnixConverterObject
+    {
+        [JsonConverter(typeof(UnixDateTimeConverter), true)]
+        public DateTime Date1 { get; set; }
+
+#if !NET20
+        [JsonConverter (typeof(UnixDateTimeConverter), true)]
+        public DateTimeOffset Date2 { get; set; }
+#endif
+    }
 }

Src/Newtonsoft.Json/Converters/UnixDateTimeConverter.cs

@@ -36,6 +36,37 @@ public class UnixDateTimeConverter : DateTimeConverterBase
     {
         internal static readonly DateTime UnixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
 
+        /// <summary>
+        /// Gets or sets a value indicating whether the dates before Unix epoch
+        /// should converted to and from JSON.
+        /// </summary>
+        /// <value>
+        /// <c>true</c> to allow converting dates before Unix epoch to and from JSON;
+        /// <c>false</c> to throw an exception when a date being converted to or from JSON
+        /// occurred before Unix epoch. The default value is <c>false</c>.
+        /// </value>
+        public bool AllowPreEpoch { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="UnixDateTimeConverter"/> class.
+        /// </summary>
+        public UnixDateTimeConverter() : this(false)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="UnixDateTimeConverter"/> class.
+        /// </summary>
+        /// <param name="allowPreEpoch">
+        /// <c>true</c> to allow converting dates before Unix epoch to and from JSON;
+        /// <c>false</c> to throw an exception when a date being converted to or from JSON
+        /// occurred before Unix epoch. The default value is <c>false</c>.
+        /// </param>
+        public UnixDateTimeConverter(bool allowPreEpoch)
+        {
+            AllowPreEpoch = allowPreEpoch;
+        }
+
         /// <summary>
         /// Writes the JSON representation of the object.
         /// </summary>
@@ -61,7 +92,7 @@ public override void WriteJson(JsonWriter writer, object? value, JsonSerializer
                 throw new JsonSerializationException("Expected date object value.");
             }
 
-            if (seconds < 0)
+            if (!AllowPreEpoch && seconds < 0)
             {
                 throw new JsonSerializationException("Cannot convert date value that is before Unix epoch of 00:00:00 UTC on 1 January 1970.");
             }
@@ -108,7 +139,7 @@ public override void WriteJson(JsonWriter writer, object? value, JsonSerializer
                 throw JsonSerializationException.Create(reader, "Unexpected token parsing date. Expected Integer or String, got {0}.".FormatWith(CultureInfo.InvariantCulture, reader.TokenType));
             }
 
-            if (seconds >= 0)
+            if (AllowPreEpoch || seconds >= 0)
             {
                 DateTime d = UnixEpoch.AddSeconds(seconds);