Faster enum -> string resolution (#2418)

Specific enum GetStringValue extension methods for known enums
Caching of generic method of resolving string values for enums based on enum type.
Renamed KnownEnums.Resolve to GetStringValue and made an extension method.
Added GetStringValue extension method for HttpMethod - this is a hot path, called on every request.
Fixed casing issue in HttpConnection for setting ContentLength

Closes #2400

Author: russcam

src/CodeGeneration/ApiGenerator/Views/Enums.Generated.cshtml

@@ -1,8 +1,8 @@
+@using System
 @using System.Collections.Generic
 @using System.Linq
 @using ApiGenerator.Domain
 @using ApiGenerator
-
 @functions {
 	private const string RawSize = "Raw";
 	private const string SizeEnum = "Size";
@@ -14,75 +14,149 @@
 	}
 	private string CreateCase(string e, string o)
 	{
-		var enumValue = (e == SizeEnum && o == string.Empty) ? RawSize : o.ToPascalCase(true);
+		var enumValue = GetEnumValue(e, o);
 		return string.Format("case {0}.{1}: return \"{2}\";", e, enumValue, o);
 	}
 	private bool IsFlag(string name)
 	{
-		return (name.EndsWith("Metric")) || name.EndsWith("Feature");
+		return name.EndsWith("Metric") || name.EndsWith("Feature");
+	}
+
+	private string CreateEnumKeyValue(string enumName, string value, int index)
+	{
+		var enumValue = GetEnumValue(enumName, value);
+		return string.Format("{3}{{ {0}.{1}, \"{2}\" }},", enumName, enumValue, value, index == 0 ? "\t\t\t\t" : string.Empty);
+	}
+
+	private string GetEnumValue(string enumName, string value)
+	{
+		return enumName == SizeEnum && value == string.Empty 
+			? RawSize 
+			: value.ToPascalCase(true);
 	}
 }
 using System;
 using System.Collections.Generic;
+using System.Collections.Concurrent;
 using System.Linq;
 using System.Text;
+using System.Reflection;
 using System.Runtime.Serialization;
 
 ///This file contains all the typed enums that the client rest api spec exposes.
 ///This file is automatically generated from https://github.com/elastic/elasticsearch/tree/@Model.Commit/rest-api-spec
 ///Generated of commit @Model.Commit
 namespace Elasticsearch.Net
 {
-	@foreach (EnumDescription e in Model.EnumsInTheSpec)
-	{
-		var isFlag = IsFlag(e.Name);
+@foreach (EnumDescription e in Model.EnumsInTheSpec)
+{
+	var isFlag = IsFlag(e.Name);
 	<text>
-	@(isFlag ? "[Flags]" : string.Empty)public enum @e.Name 
+	@(isFlag ? "[Flags]" : string.Empty)public enum @e.Name
 	{
-		@Raw(string.Join(",\r\n\t\t", e.Options.OrderBy(s=>s == "_all" ? 1 : 0).Select((s, i) => CreateEnum(e.Name, s, isFlag ? (int?)i : null ))))
-	}
-	</text>
-	}
+	@Raw(string.Join(",\r\n\t\t", e.Options.OrderBy(s => s == "_all" ? 1 : 0).Select((s, i) => CreateEnum(e.Name, s, isFlag ? (int?)i : null))))
+	}</text>
+}
 
 	public static class KnownEnums
+    { 
+        private class EnumDictionary : @(Raw("Dictionary<Enum, string>"))
+		{	
+			public EnumDictionary(int capacity) : base(capacity) {}
+			public @(Raw("Func<Enum, string>")) Resolver { get; set; }
+		}	
+
+	@foreach (EnumDescription e in Model.EnumsInTheSpec)
 	{
-		public static string UnknownEnum { get; } = "_UNKNOWN_ENUM_";
-		public static string Resolve(Enum e)
+		var isFlag = IsFlag(e.Name);
+		<text>
+		public static string GetStringValue(this @(e.Name) enumValue)
+		{
+		</text>
+		if (isFlag)
+		{
+			var allOption = e.Options.FirstOrDefault(o => o == "_all");
+			if (allOption != null)
+			{
+	        <text>if ((enumValue & @(e.Name).All) != 0) return "_all";</text>
+			}
+			<text>var list = new @(Raw("List<string>()"));</text>
+			foreach (var option in e.Options.Where(o => o != "_all"))
+			{
+			<text>if ((enumValue & @(e.Name).@(GetEnumValue(e.Name, option))) != 0) list.Add("@(option)");</text>
+			}
+			<text>return string.Join(",", list);
+		}</text>
+		}
+		else
+		{
+			<text>switch (enumValue)
+			{
+				@Raw(string.Join("\r\n\t\t\t\t", e.Options.Select(o => CreateCase(e.Name, o))))
+			}
+			throw new ArgumentException($"'{enumValue.ToString()}' is not a valid value for enum '@(e.Name)'");		
+		}</text>
+		}
+	}
+
+		private static readonly @(Raw("ConcurrentDictionary<Type, Func<Enum, string>>")) EnumStringResolvers =
+			new @(Raw("ConcurrentDictionary<Type, Func<Enum, string>>"))();
+
+		static KnownEnums()
+		{
+		@foreach (EnumDescription e in Model.EnumsInTheSpec)
+		{
+			<text>EnumStringResolvers.TryAdd(typeof(@(e.Name)), (e) => GetStringValue((@(e.Name))e));</text>
+		}
+		}
+
+		public static string GetStringValue(this Enum e)
+		{
+			var type = e.GetType();		
+			var resolver = EnumStringResolvers.GetOrAdd(type, GetEnumStringResolver);
+			return resolver(e);
+		}
+
+		private static @Raw("Func<Enum, string>") GetEnumStringResolver(Type type)
 		{
-			@foreach (EnumDescription e in Model.EnumsInTheSpec)
+			var values = Enum.GetValues(type);
+			var dictionary = new EnumDictionary(values.Length);
+
+			for (int index = 0; index < values.Length; index++)
 			{
-			var isFlag = IsFlag(e.Name);
-			<text>if (e is @e.Name)
-			{ </text>
-			if (isFlag)
+				var value = values.GetValue(index);
+#if DOTNETCORE
+				var info = type.GetTypeInfo().GetDeclaredField(value.ToString());
+#else
+				var info = type.GetField(value.ToString());
+#endif
+				var da = (EnumMemberAttribute[])info.GetCustomAttributes(typeof(EnumMemberAttribute), false);
+				var stringValue = da.Length > 0 ? da[0].Value : Enum.GetName(type, value);
+				dictionary.Add((Enum)value, stringValue);
+			}
+
+#if DOTNETCORE
+			var isFlag = type.GetTypeInfo().GetCustomAttributes(typeof(FlagsAttribute), false).Any();
+#else
+			var isFlag = type.GetCustomAttributes(typeof(FlagsAttribute), false).Length > 0;
+#endif
+
+			return (e) => 
 			{
-				<text>var list = new @(Raw("List<string>()"));</text>
-				foreach(var option in e.Options.OrderBy(s=>s == "_all" ? 1 : 0))
+				if (isFlag)
 				{
-					if (option != "_all")
+					var list = new @(Raw("List<string>()"));
+					foreach(var kv in dictionary)
 					{
-				<text>if (e.HasFlag(@(e.Name).@(option.ToPascalCase(true)))) list.Add("@(option)");</text>
-					}
-					else 
-					{
-				<text>if (e.HasFlag(@(e.Name).@(option.ToPascalCase(true)))) return "@(option)";</text>
+						if (e.HasFlag(kv.Key)) list.Add(kv.Value);
 					}
+					return string.Join(",", list);
 				}
-				<text>return string.Join(",", list);</text>
-			}
-			else 
-			{
-				<text>switch((@e.Name)e)
+				else
 				{
-					@Raw(string.Join("\r\n\t\t\t\t\t", e.Options.Select(o =>CreateCase(e.Name,o))))
-				}</text>
-			}
-			<text>
-			}
-			</text>
-			}
-			return UnknownEnum;
+					return dictionary[e];
+				}
+			};
 		}
 	}
-}
- 
+}

src/Elasticsearch.Net/Connection/HttpConnection.cs

@@ -66,7 +66,7 @@ protected virtual HttpWebRequest CreateWebRequest(RequestData requestData)
 			//see: https://github.com/elasticsearch/elasticsearch-net/issues/562
 			var m = requestData.Method.GetStringValue();
 			request.Method = m;
-			if (m != "head" && m != "get" && (requestData.PostData == null))
+			if (m != "HEAD" && m != "GET" && (requestData.PostData == null))
 				request.ContentLength = 0;
 
 			return request;

src/Elasticsearch.Net/Connection/HttpMethod.cs

@@ -17,4 +17,4 @@ public enum HttpMethod
 		[EnumMember(Value = "HEAD")]
 		HEAD
 	}
-}
+}