[csharp] Fix oneOf/anyOf response deserialization in httpclient library (#25080)

* [csharp] Fix oneOf/anyOf response deserialization in httpclient library

In the httpclient library's ApiClient.ExecAsync, responses whose schema
is oneOf/anyOf (types derived from AbstractOpenAPISchema) are deserialized
by reflectively invoking the model's static FromJson(string) method.

The call passed response.Content (an HttpContent) instead of the JSON
string FromJson expects. Because the invocation is reflective it compiled
but threw ArgumentException at runtime ("object of type
HttpConnectionResponseContent cannot be converted to type String") on
every oneOf/anyOf response.

Read the response body as a string first and pass that to FromJson. The
content is already buffered by the preceding Deserialize call, so
re-reading it is safe. Regenerated the affected csharp httpclient samples.

Fixes #25079

* [csharp] Add regression test for oneOf/anyOf httpclient response deserialization

Adds a unit test to the net10, net9 and standard2.0 httpclient Petstore
samples that drives ApiClient.GetAsync<Pig> (Pig is a oneOf) through a
stub HttpMessageHandler and asserts the response is deserialized to the
correct concrete type. Without the fix this throws the ArgumentException
reported in #25079.

Refs #25079

* [csharp] Dispose HttpClient/ApiClient in oneOf regression test

ApiClient does not own an injected HttpClient, so the test must dispose it
itself. Use 'using' declarations for both the HttpClient and ApiClient.

Addresses review feedback on #25080.

Author: cguldner

modules/openapi-generator/src/main/resources/csharp/libraries/httpclient/ApiClient.mustache

@@ -563,7 +563,8 @@ namespace {{packageName}}.Client
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof({{{packageName}}}.{{modelPackage}}.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {

samples/client/petstore/csharp/httpclient/net10/Petstore-nonPublicApi/src/Org.OpenAPITools/Client/ApiClient.cs

@@ -546,7 +546,8 @@ private async Task<ApiResponse<T>> ExecAsync<T>(HttpRequestMessage req,
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof(Org.OpenAPITools.Model.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {

samples/client/petstore/csharp/httpclient/net10/Petstore/src/Org.OpenAPITools.Test/Client/OneOfResponseDeserializationTests.cs

@@ -0,0 +1,69 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * Generated by: https://github.com/openapitools/openapi-generator.git
+ */
+
+using System.Net;
+using System.Net.Http;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Org.OpenAPITools.Client;
+using Org.OpenAPITools.Model;
+using Xunit;
+
+namespace Org.OpenAPITools.Test.Client
+{
+    /// <summary>
+    /// Regression tests for deserializing oneOf/anyOf responses (types derived from
+    /// AbstractOpenAPISchema) in the httpclient library.
+    /// See https://github.com/OpenAPITools/openapi-generator/issues/25079
+    /// </summary>
+    public class OneOfResponseDeserializationTests
+    {
+        /// <summary>
+        /// Returns a canned JSON body for every request, so ExecAsync can be exercised
+        /// without a live server.
+        /// </summary>
+        private sealed class StubHttpMessageHandler : HttpMessageHandler
+        {
+            private readonly string _json;
+
+            public StubHttpMessageHandler(string json)
+            {
+                _json = json;
+            }
+
+            protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+            {
+                var response = new HttpResponseMessage(HttpStatusCode.OK)
+                {
+                    Content = new StringContent(_json, Encoding.UTF8, "application/json")
+                };
+                return Task.FromResult(response);
+            }
+        }
+
+        /// <summary>
+        /// A oneOf/anyOf response must be deserialized via the model's static
+        /// FromJson(string) method. Previously ApiClient.ExecAsync passed the
+        /// HttpContent instead of the body string, which threw an ArgumentException
+        /// at runtime for every oneOf/anyOf response.
+        /// </summary>
+        [Fact]
+        public async Task OneOfResponseIsDeserializedToConcreteType()
+        {
+            using var httpClient = new HttpClient(new StubHttpMessageHandler("{\"className\":\"BasquePig\"}"));
+            using var apiClient = new ApiClient(httpClient, "http://localhost");
+
+            ApiResponse<Pig> response = await apiClient.GetAsync<Pig>("/fake", new RequestOptions());
+
+            Assert.NotNull(response.Data);
+            Assert.IsType<BasquePig>(response.Data.ActualInstance);
+        }
+    }
+}

samples/client/petstore/csharp/httpclient/net10/Petstore/src/Org.OpenAPITools/Client/ApiClient.cs

@@ -546,7 +546,8 @@ private async Task<ApiResponse<T>> ExecAsync<T>(HttpRequestMessage req,
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof(Org.OpenAPITools.Model.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {

samples/client/petstore/csharp/httpclient/net9/Petstore-nonPublicApi/src/Org.OpenAPITools/Client/ApiClient.cs

@@ -546,7 +546,8 @@ private async Task<ApiResponse<T>> ExecAsync<T>(HttpRequestMessage req,
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof(Org.OpenAPITools.Model.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {

samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools.Test/Client/OneOfResponseDeserializationTests.cs

@@ -0,0 +1,69 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * Generated by: https://github.com/openapitools/openapi-generator.git
+ */
+
+using System.Net;
+using System.Net.Http;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Org.OpenAPITools.Client;
+using Org.OpenAPITools.Model;
+using Xunit;
+
+namespace Org.OpenAPITools.Test.Client
+{
+    /// <summary>
+    /// Regression tests for deserializing oneOf/anyOf responses (types derived from
+    /// AbstractOpenAPISchema) in the httpclient library.
+    /// See https://github.com/OpenAPITools/openapi-generator/issues/25079
+    /// </summary>
+    public class OneOfResponseDeserializationTests
+    {
+        /// <summary>
+        /// Returns a canned JSON body for every request, so ExecAsync can be exercised
+        /// without a live server.
+        /// </summary>
+        private sealed class StubHttpMessageHandler : HttpMessageHandler
+        {
+            private readonly string _json;
+
+            public StubHttpMessageHandler(string json)
+            {
+                _json = json;
+            }
+
+            protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+            {
+                var response = new HttpResponseMessage(HttpStatusCode.OK)
+                {
+                    Content = new StringContent(_json, Encoding.UTF8, "application/json")
+                };
+                return Task.FromResult(response);
+            }
+        }
+
+        /// <summary>
+        /// A oneOf/anyOf response must be deserialized via the model's static
+        /// FromJson(string) method. Previously ApiClient.ExecAsync passed the
+        /// HttpContent instead of the body string, which threw an ArgumentException
+        /// at runtime for every oneOf/anyOf response.
+        /// </summary>
+        [Fact]
+        public async Task OneOfResponseIsDeserializedToConcreteType()
+        {
+            using var httpClient = new HttpClient(new StubHttpMessageHandler("{\"className\":\"BasquePig\"}"));
+            using var apiClient = new ApiClient(httpClient, "http://localhost");
+
+            ApiResponse<Pig> response = await apiClient.GetAsync<Pig>("/fake", new RequestOptions());
+
+            Assert.NotNull(response.Data);
+            Assert.IsType<BasquePig>(response.Data.ActualInstance);
+        }
+    }
+}

samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools/Client/ApiClient.cs

@@ -546,7 +546,8 @@ private async Task<ApiResponse<T>> ExecAsync<T>(HttpRequestMessage req,
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof(Org.OpenAPITools.Model.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {

samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools.Test/Client/OneOfResponseDeserializationTests.cs

@@ -0,0 +1,69 @@
+/*
+ * OpenAPI Petstore
+ *
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * Generated by: https://github.com/openapitools/openapi-generator.git
+ */
+
+using System.Net;
+using System.Net.Http;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Org.OpenAPITools.Client;
+using Org.OpenAPITools.Model;
+using Xunit;
+
+namespace Org.OpenAPITools.Test.Client
+{
+    /// <summary>
+    /// Regression tests for deserializing oneOf/anyOf responses (types derived from
+    /// AbstractOpenAPISchema) in the httpclient library.
+    /// See https://github.com/OpenAPITools/openapi-generator/issues/25079
+    /// </summary>
+    public class OneOfResponseDeserializationTests
+    {
+        /// <summary>
+        /// Returns a canned JSON body for every request, so ExecAsync can be exercised
+        /// without a live server.
+        /// </summary>
+        private sealed class StubHttpMessageHandler : HttpMessageHandler
+        {
+            private readonly string _json;
+
+            public StubHttpMessageHandler(string json)
+            {
+                _json = json;
+            }
+
+            protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+            {
+                var response = new HttpResponseMessage(HttpStatusCode.OK)
+                {
+                    Content = new StringContent(_json, Encoding.UTF8, "application/json")
+                };
+                return Task.FromResult(response);
+            }
+        }
+
+        /// <summary>
+        /// A oneOf/anyOf response must be deserialized via the model's static
+        /// FromJson(string) method. Previously ApiClient.ExecAsync passed the
+        /// HttpContent instead of the body string, which threw an ArgumentException
+        /// at runtime for every oneOf/anyOf response.
+        /// </summary>
+        [Fact]
+        public async Task OneOfResponseIsDeserializedToConcreteType()
+        {
+            using var httpClient = new HttpClient(new StubHttpMessageHandler("{\"className\":\"BasquePig\"}"));
+            using var apiClient = new ApiClient(httpClient, "http://localhost");
+
+            ApiResponse<Pig> response = await apiClient.GetAsync<Pig>("/fake", new RequestOptions());
+
+            Assert.NotNull(response.Data);
+            Assert.IsType<BasquePig>(response.Data.ActualInstance);
+        }
+    }
+}

samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools/Client/ApiClient.cs

@@ -545,7 +545,8 @@ private async Task<ApiResponse<T>> ExecAsync<T>(HttpRequestMessage req,
                 // if the response type is oneOf/anyOf, call FromJSON to deserialize the data
                 if (typeof(Org.OpenAPITools.Model.AbstractOpenAPISchema).IsAssignableFrom(typeof(T)))
                 {
-                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { response.Content });
+                    string jsonString = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+                    responseData = (T)typeof(T).GetMethod("FromJson").Invoke(null, new object[] { jsonString });
                 }
                 else if (typeof(T).Name == "Stream") // for binary response
                 {