Fix deserialization of S3 snapshot repository without settings

CHANGELOG.md

@@ -13,6 +13,9 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Removed the `Features` API which is not supported by OpenSearch from the low-level client ([#331](https://github.com/opensearch-project/opensearch-net/pull/331))
 - Removed the deprecated low-level `IndexTemplateV2` APIs in favour of the `ComposableIndexTemplate` APIs ([#437](https://github.com/opensearch-project/opensearch-net/pull/437))
 
+### Fixed
+- Fixed the deserialization of S3 snapshot repositories without settings ([#587](https://github.com/opensearch-project/opensearch-net/pull/587)) 
+
 ### Dependencies
 - Bumps `System.Diagnostics.DiagnosticSource` from 6.0.1 to 8.0.0
 - Bumps `System.Text.Json` from 8.0.1 to 8.0.3
@@ -162,4 +165,4 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 [1.6.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.5.0...v1.6.0
 [1.5.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.4.0...v1.5.0
 [1.4.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.3.0...v1.4.0
-[1.3.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.2.0...v1.3.0
+[1.3.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.2.0...v1.3.0

src/OpenSearch.Client/Snapshot/Repositories/S3Repository.cs

@@ -42,6 +42,8 @@ public interface IS3Repository : IRepository<IS3RepositorySettings> { }
 	/// <inheritdoc />
 	public class S3Repository : IS3Repository
 	{
+		public S3Repository() { }
+
 		public S3Repository(IS3RepositorySettings settings) => Settings = settings;
 
 		public IS3RepositorySettings Settings { get; set; }

tests/Tests.Reproduce/GitHubIssue573.cs

@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: Apache-2.0
+*
+* The OpenSearch Contributors require contributions made to
+* this file be licensed under the Apache-2.0 license or a
+* compatible open source license.
+*/
+
+using System;
+using System.Text;
+using FluentAssertions;
+using OpenSearch.Client;
+using OpenSearch.Net;
+using OpenSearch.OpenSearch.Xunit.XunitPlumbing;
+using Tests.Core.Extensions;
+
+namespace Tests.Reproduce;
+
+/// <summary>
+/// S3 Snapshot Repository Without Settings Fails to Deserialize: <a href="https://github.com/opensearch-project/opensearch-net/issues/573">Issue #573</a>
+/// </summary>
+public class GitHubIssue573
+{
+	[U] public void DeserializingS3SnapshotRepositoryWithoutSettingsShouldSucceed()
+	{
+		var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
+
+		const string json = @"{
+				""cs-automated"": {
+					""type"": ""s3""
+				},
+				""authoring-service-snapshots"": {
+					""type"": ""s3"",
+					""settings"": {
+						""bucket"": ""some-bucket"",
+						""region"": ""us-west-2"",
+						""role_arn"": ""arn:aws:iam::123456789:role/SomeRole""
+					}
+				}
+			}";
+
+		var connection = new InMemoryConnection(Encoding.UTF8.GetBytes(json), 200);
+		var settings = new ConnectionSettings(pool, connection);
+		var client = new OpenSearchClient(settings);
+
+		var response = client.Snapshot.GetRepository();
+		response.ShouldBeValid();
+		response.Repositories
+			.Should()
+			.NotBeNull()
+			.And.HaveCount(2)
+			.And.ContainKeys("cs-automated", "authoring-service-snapshots")
+			.And.AllSatisfy(p => p.Value.Should().BeOfType<S3Repository>());
+
+		((S3Repository) response.Repositories["cs-automated"]).Settings.Should().BeNull();
+
+		((S3Repository) response.Repositories["authoring-service-snapshots"]).Settings.Should().NotBeNull();
+	}
+}