fix #2316 although uncommon and no longer supported in 5.x Elasticsearch 2.x allows you to also send camelCase versions of settings and these will not be normalized and returned as is, we should also support these at read time. PascalCase is not supported

Author: Mpdreamz

src/Nest/IndexModules/IndexSettings/Settings/IndexSettingsConverter.cs

@@ -207,12 +207,23 @@ private void SetKnownIndexSettings(JsonReader reader, JsonSerializer serializer,
 
 		private static void Set<T>(IIndexSettings s, IDictionary<string, JProperty> settings, string key, Action<T> assign, JsonSerializer serializer = null)
 		{
-			if (!settings.ContainsKey(key)) return;
+			if (!settings.ContainsKey(key)) key = ToCamelCase(key);
+			if (!settings.ContainsKey(key)) return;
+
 			var v = settings[key];
 			T value = serializer == null ? v.Value.ToObject<T>() : v.Value.ToObject<T>(serializer);
 			assign(value);
 			s.Add(key, value);
 			settings.Remove(key);
-		}
+		}
+		private static string ToCamelCase(string indexSettingKey) =>
+			string.Join(".", indexSettingKey
+				.Split(new[] { "." }, StringSplitOptions.RemoveEmptyEntries)
+				.Select(t=>t
+					.Split(new[] { "_" }, StringSplitOptions.RemoveEmptyEntries)
+					.Select((s,i) => i == 0 ? s : char.ToUpperInvariant(s[0]) + s.Substring(1, s.Length - 1))
+					.Aggregate(string.Empty, (s1, s2) => s1 + s2)
+				)
+			);
 	}
 }

src/Tests/IndexModules/IndexSettings/Settings/TypedIndexSettings.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using FluentAssertions;
 using Nest;
 using Tests.Framework;
 
@@ -34,7 +35,7 @@ public class Usage : PromiseUsageTestBase<IIndexSettings, IndexSettingsDescripto
 			};
 
 			/**
-			 * 
+			 *
 			 */
 			protected override Func<IndexSettingsDescriptor, IPromise<IIndexSettings>> Fluent => s => s
 				.Setting("any.setting", "can be set")
@@ -81,5 +82,24 @@ public class Usage : PromiseUsageTestBase<IIndexSettings, IndexSettingsDescripto
 					FileSystemStorageImplementation = FileSystemStorageImplementation.MMap
 				};
 		}
+
+
+		public class CamelCaseSettingsAreReadCorrectlyTests : SerializationTestBase
+		{
+			[U] public void CamelCasedTypedSettings()
+			{
+				var indexSettings = new Nest.IndexSettings
+				{
+					{ "index.numberOfShards", 2 }
+				};
+				var settings = this.Serialize(indexSettings);
+				var deserizalized = this.Deserialize<Nest.IndexSettings>(settings);
+
+				deserizalized.NumberOfShards.Should().Be(2);
+
+
+
+			}
+		}
 	}
 }