Add DateTimeOffset converter to handle UTC serialization

src/NATS.Client.JetStream/Models/StreamSource.cs

@@ -35,6 +35,7 @@ public record StreamSource
     /// </summary>
     [System.Text.Json.Serialization.JsonPropertyName("opt_start_time")]
     [System.Text.Json.Serialization.JsonIgnore(Condition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingDefault)]
+    [System.Text.Json.Serialization.JsonConverter(typeof(NatsJSJsonDateTimeOffsetConverter))]
     public DateTimeOffset OptStartTime { get; set; }
 
     /// <summary>

src/NATS.Client.JetStream/NatsJSJsonSerializer.cs

@@ -1,3 +1,4 @@
+using System.Buffers.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using NATS.Client.Core;
@@ -393,3 +394,24 @@ public override void Write(Utf8JsonWriter writer, TimeSpan? value, JsonSerialize
         }
     }
 }
+
+internal class NatsJSJsonDateTimeOffsetConverter : JsonConverter<DateTimeOffset>
+{
+    public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        if (reader.TokenType == JsonTokenType.Null)
+        {
+            return default;
+        }
+
+        return reader.GetDateTimeOffset();
+    }
+
+    public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
+    {
+        // Write the date time in the format e.g. "2024-01-01T00:00:00Z"
+        // instead of the default DateTimeOffset format e.g. "2024-01-01T00:00:00+00:00"
+        // which is confusing the server.
+        writer.WriteStringValue(value.UtcDateTime);
+    }
+}

tests/NATS.Client.JetStream.Tests/TimeSpanJsonTests.cs

@@ -1,12 +1,27 @@
 using System.Buffers;
 using System.Text;
+using System.Text.Json;
 using NATS.Client.JetStream.Internal;
 using NATS.Client.JetStream.Models;
 
 namespace NATS.Client.JetStream.Tests;
 
 public class TimeSpanJsonTests
 {
+    [Fact]
+    public void NatsJSJsonDateTimeOffsetConverter_serialize_UTC_offset_as_Z()
+    {
+        var streamSource = new StreamSource
+        {
+            Name = "events",
+            OptStartTime = DateTimeOffset.Parse("2024-01-01T00:00:00+00:00"),
+        };
+
+        var json = JsonSerializer.Serialize(streamSource, NatsJSJsonSerializerContext.Default.StreamSource);
+
+        Assert.Equal("""{"name":"events","opt_start_time":"2024-01-01T00:00:00Z"}""", json);
+    }
+
     [Theory]
     [InlineData("00:00:00.001", "\"ack_wait\":1000000\\b")]
     [InlineData("00:00:01.000", "\"ack_wait\":1000000000\\b")]