Fix enum string conversion on url formatter

src/Elastic.Transport/Extensions/Extensions.cs

@@ -7,10 +7,24 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Runtime.Serialization;
 using System.Text;
 
 namespace Elastic.Transport.Extensions;
 
+internal static class EnumExtensions
+{
+	public static string GetEnumName(this Enum e)
+	{
+		var attributes = e.GetType().GetField(e.ToString())?.GetCustomAttributes(typeof(EnumMemberAttribute), false);
+		if (attributes is null || attributes.Length == 0)
+			return e.ToString();
+
+		var enumMember = attributes[0] as EnumMemberAttribute;
+		return enumMember?.Value ?? e.ToString();
+	}
+}
+
 internal static class Extensions
 {
 	[Obsolete("Please use the overload placing the enumerated array as out")]

src/Elastic.Transport/Requests/UrlFormatter.cs

@@ -49,7 +49,7 @@ public static string CreateString(object? value, ITransportConfiguration setting
 			null => string.Empty,
 			string s => s,
 			string[] ss => string.Join(",", ss),
-			Enum e => e.ToString(),
+			Enum e => e.GetEnumName(),
 			bool b => b ? "true" : "false",
 			DateTimeOffset offset => offset.ToString("o"),
 			TimeSpan timeSpan => timeSpan.ToTimeUnit(),

tests/Elastic.Transport.Tests/UsageTests.cs

@@ -3,6 +3,8 @@
 // See the LICENSE file in the project root for more information
 
 using System;
+using System.Collections.Generic;
+using System.Runtime.Serialization;
 using Elastic.Transport.Products;
 using Elastic.Transport.Products.Elasticsearch;
 using FluentAssertions;
@@ -15,6 +17,31 @@ namespace Elastic.Transport.Tests;
 
 public class UsageTests
 {
+	private enum MyEnum
+	{
+		[EnumMember(Value = "different")]
+		Value
+	}
+
+	[Fact]
+	public void EnumsUseEnumMemberAttribute()
+	{
+		var pool = new StaticNodePool([new Node(new Uri("http://localhost:9200"))]);
+		var requestInvoker = new InMemoryRequestInvoker();
+		var serializer = LowLevelRequestResponseSerializer.Instance;
+		var product = ElasticsearchProductRegistration.Default;
+
+		var settings = new TransportConfiguration(pool, requestInvoker, serializer, product);
+		var transport = new DistributedTransport<TransportConfiguration>(settings);
+
+		var requestParameters = new DefaultRequestParameters { QueryString =
+			new Dictionary<string, object>{ { "enum", MyEnum.Value } } };
+		var path = requestParameters.CreatePathWithQueryStrings("/", settings);
+		var response = transport.Request<StringResponse>(new EndpointPath(HttpMethod.GET, path), null, null, null);
+
+		response.ApiCallDetails.Uri.Should().Be(new Uri("http://localhost:9200?enum=different"));
+	}
+
 	[Fact]
 	public void TransportVersionIsSet()
 	{