Improve default IsValidResponseToDeserialize implementation

src/GraphQL.Client/GraphQLHttpClientOptions.cs

@@ -61,9 +61,17 @@ public class GraphQLHttpClientOptions
     /// Note that compatible to the draft graphql-over-http spec GraphQL Server MAY return 4xx status codes (401/403, etc.)
     /// with well-formed GraphQL response containing errors collection.
     /// </summary>
-    public Func<HttpResponseMessage, bool> IsValidResponseToDeserialize { get; set; } = r =>
-        // Why not application/json? See https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#processing-the-response
-        r.IsSuccessStatusCode || r.StatusCode == HttpStatusCode.BadRequest || r.Content.Headers.ContentType?.MediaType == "application/graphql+json";
+    public Func<HttpResponseMessage, bool> IsValidResponseToDeserialize { get; set; } = DefaultIsValidResponseToDeserialize;
+
+    private static readonly IReadOnlyCollection<string> _acceptedResponseContentTypes = new[] { "application/graphql+json", "application/json", "application/graphql-response+json" };
+
+    public static bool DefaultIsValidResponseToDeserialize(HttpResponseMessage r)
+    {
+        if (r.Content.Headers.ContentType?.MediaType != null && !_acceptedResponseContentTypes.Contains(r.Content.Headers.ContentType.MediaType))
+            return false;
+
+        return r.IsSuccessStatusCode || r.StatusCode == HttpStatusCode.BadRequest;
+    }
 
     /// <summary>
     /// This callback is called after successfully establishing a websocket connection but before any regular request is made.

tests/GraphQL.Client.Serializer.Tests/DefaultValidationTest.cs

@@ -0,0 +1,28 @@
+using System.Net;
+using System.Net.Http.Headers;
+using FluentAssertions;
+using GraphQL.Client.Http;
+using Xunit;
+
+namespace GraphQL.Client.Serializer.Tests;
+
+public class DefaultValidationTest
+{
+    [Theory]
+    [InlineData(HttpStatusCode.OK, "application/json", true)]
+    [InlineData(HttpStatusCode.OK, "application/graphql-response+json", true)]
+    [InlineData(HttpStatusCode.BadRequest, "application/json", true)]
+    [InlineData(HttpStatusCode.BadRequest, "text/html", false)]
+    [InlineData(HttpStatusCode.OK, "text/html", false)]
+    [InlineData(HttpStatusCode.Forbidden, "text/html", false)]
+    [InlineData(HttpStatusCode.Forbidden, "application/json", false)]
+    public void IsValidResponse_OkJson_True(HttpStatusCode statusCode, string mediaType, bool expectedResult)
+    {
+        var response = new HttpResponseMessage(statusCode);
+        response.Content.Headers.ContentType = new MediaTypeHeaderValue(mediaType);
+
+        bool isValid = new GraphQLHttpClientOptions().IsValidResponseToDeserialize(response);
+
+        isValid.Should().Be(expectedResult);
+    }
+}