Skip MIME type validation when no body (#5735)

This skips MIME type validation for 204 responses and responses to HEAD requests. Elastic Cloud responses to HEAD requests strip the content-type header and this causes validation issues.

We also skip setting the body based on this same check.

Author: stevejgordon

src/Elasticsearch.Net/Transport/Pipeline/ResponseBuilder.cs

@@ -17,7 +17,9 @@ public static class ResponseBuilder
 		public const int BufferSize = 81920;
 
 		private static readonly Type[] SpecialTypes =
-			{ typeof(StringResponse), typeof(BytesResponse), typeof(VoidResponse), typeof(DynamicResponse) };
+		{
+			typeof(StringResponse), typeof(BytesResponse), typeof(VoidResponse), typeof(DynamicResponse)
+		};
 
 		public static TResponse ToResponse<TResponse>(
 			RequestData requestData,
@@ -31,8 +33,17 @@ public static TResponse ToResponse<TResponse>(
 		{
 			responseStream.ThrowIfNull(nameof(responseStream));
 			var details = Initialize(requestData, ex, statusCode, warnings, mimeType);
+
 			//TODO take ex and (responseStream == Stream.Null) into account might not need to flow to SetBody in that case
-			var response = SetBody<TResponse>(details, requestData, responseStream, mimeType) ?? new TResponse();
+
+			TResponse response = null;
+
+			// Only attempt to set the body if the response may have content
+			if (MayHaveBody(statusCode, requestData.Method))
+				response = SetBody<TResponse>(details, requestData, responseStream, mimeType);
+
+			response ??= new TResponse();
+
 			response.ApiCall = details;
 			return response;
 		}
@@ -50,12 +61,25 @@ public static async Task<TResponse> ToResponseAsync<TResponse>(
 		{
 			responseStream.ThrowIfNull(nameof(responseStream));
 			var details = Initialize(requestData, ex, statusCode, warnings, mimeType);
-			var response = await SetBodyAsync<TResponse>(details, requestData, responseStream, mimeType, cancellationToken).ConfigureAwait(false)
-				?? new TResponse();
+
+			TResponse response = null;
+
+			// Only attempt to set the body if the response may have content
+			if (MayHaveBody(statusCode, requestData.Method))
+				response = await SetBodyAsync<TResponse>(details, requestData, responseStream, mimeType, cancellationToken).ConfigureAwait(false);
+
+			response ??= new TResponse();
+
 			response.ApiCall = details;
 			return response;
 		}
 
+		/// <summary>
+		/// A helper which returns true if the response could potentially have a body.
+		/// </summary>
+		private static bool MayHaveBody(int? statusCode, HttpMethod httpMethod) =>
+			!statusCode.HasValue || (statusCode.Value != 204 && httpMethod != HttpMethod.HEAD);
+
 		private static ApiCallDetails Initialize(
 			RequestData requestData, Exception exception, int? statusCode, IEnumerable<string> warnings, string mimeType
 		)
@@ -70,7 +94,10 @@ private static ApiCallDetails Initialize(
 					success = requestData.ConnectionSettings
 						.StatusCodeToResponseSuccess(requestData.Method, statusCode.Value);
 			}
-			if (!RequestData.ValidResponseContentType(requestData.Accept, mimeType))
+
+			// We don't validate the content-type (MIME type) for HEAD requests or responses that have no content (204 status code).
+			// Elastic Cloud responses to HEAD requests strip the content-type header so we want to avoid validation in that case.
+			if (MayHaveBody(statusCode, requestData.Method) && !RequestData.ValidResponseContentType(requestData.Accept, mimeType))
 				success = false;
 
 			var details = new ApiCallDetails
@@ -143,7 +170,8 @@ private static async Task<TResponse> SetBodyAsync<TResponse>(
 
 				var serializer = requestData.ConnectionSettings.RequestResponseSerializer;
 				if (requestData.CustomResponseBuilder != null)
-					return await requestData.CustomResponseBuilder.DeserializeResponseAsync(serializer, details, responseStream, cancellationToken).ConfigureAwait(false) as TResponse;
+					return await requestData.CustomResponseBuilder.DeserializeResponseAsync(serializer, details, responseStream, cancellationToken)
+						.ConfigureAwait(false) as TResponse;
 
 				return !RequestData.ValidResponseContentType(requestData.Accept, mimeType)
 					? null
@@ -171,8 +199,7 @@ private static bool SetSpecialTypes<TResponse>(string mimeType, byte[] bytes, IM
 				//if not json store the result under "body"
 				if (!RequestData.IsJsonMimeType(mimeType))
 				{
-					var dictionary = new DynamicDictionary();
-					dictionary["body"] = new DynamicValue(bytes.Utf8String());
+					var dictionary = new DynamicDictionary { ["body"] = new(bytes.Utf8String()) };
 					cs = new DynamicResponse(dictionary) as TResponse;
 				}
 				else

tests/Tests.Reproduce/GitHubIssue5730.cs

@@ -0,0 +1,56 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Elastic.Elasticsearch.Xunit.XunitPlumbing;
+using Elasticsearch.Net;
+using FluentAssertions;
+using Nest;
+using Tests.Core.Client;
+
+namespace Tests.Reproduce
+{
+	public class GitHubIssue5730
+	{
+		[U]
+		public void IndexExistsIsValidForBothLocalAndCloudResponses()
+		{
+			var client = TestClient.FixedInMemoryClient(Array.Empty<byte>());
+
+			var response = client.Indices.Exists("an-index");
+
+			response.IsValid.Should().BeTrue();
+			response.Exists.Should().BeTrue();
+
+			// Elastic Cloud responses for HEAD requests do not include the `content-type` header.
+			// This test ensures that our validation handles this.
+
+			var cloudClient = new ElasticClient(new ConnectionSettings(new SingleNodeConnectionPool(new Uri("http://localhost:9200")),
+				new CloudIndexExistsInMemoryConnection()));
+
+			response = cloudClient.Indices.Exists("an-index");
+
+			response.IsValid.Should().BeTrue();
+			response.Exists.Should().BeTrue();
+		}
+
+		/// <summary>
+		/// Simulates not returning the content-type header so passes null mimeType to the <see cref="ResponseBuilder" />.
+		/// </summary>
+		private class CloudIndexExistsInMemoryConnection : IConnection
+		{
+			public TResponse Request<TResponse>(RequestData requestData) where TResponse : class, IElasticsearchResponse, new() =>
+				ResponseBuilder.ToResponse<TResponse>(requestData, null, 200, null, Stream.Null, null);
+
+			public Task<TResponse> RequestAsync<TResponse>(RequestData requestData, CancellationToken cancellationToken)
+				where TResponse : class, IElasticsearchResponse, new() =>
+				Task.FromResult(ResponseBuilder.ToResponse<TResponse>(requestData, null, 200, null, Stream.Null, null));
+
+			public void Dispose() { }
+		}
+	}
+}