get error response as dynamic with Newtonsoft

missed in earlier back-ports from 3.x

src/Flurl.Http.Newtonsoft/ExtensionMethods.cs

@@ -13,7 +13,7 @@ namespace Flurl.Http.Newtonsoft
 	public static class ExtensionMethods
 	{
 		/// <summary>
-		/// Deserializes JSON-formatted HTTP response body to a dynamic object.
+		/// Deserializes a JSON-formatted HTTP response body to a dynamic object.
 		/// </summary>
 		/// <returns>A Task whose result is a dynamic object containing data in the response body.</returns>
 		public static async Task<dynamic> GetJsonAsync(this IFlurlResponse resp) {
@@ -22,7 +22,7 @@ public static async Task<dynamic> GetJsonAsync(this IFlurlResponse resp) {
 		}
 
 		/// <summary>
-		/// Deserializes JSON-formatted HTTP response body to a list of dynamic objects.
+		/// Deserializes a JSON-formatted HTTP response body to a list of dynamic objects.
 		/// </summary>
 		/// <returns>A Task whose result is a list of dynamic objects containing data in the response body.</returns>
 		public static async Task<IList<dynamic>> GetJsonListAsync(this IFlurlResponse resp) {
@@ -31,7 +31,7 @@ public static async Task<IList<dynamic>> GetJsonListAsync(this IFlurlResponse re
 		}
 
 		/// <summary>
-		/// Deserializes JSON-formatted HTTP response body to a dynamic object. Intended to chain off an async call.
+		/// Deserializes a JSON-formatted HTTP response body to a dynamic object. Intended to chain off an async call.
 		/// </summary>
 		/// <returns>A Task whose result is a dynamic object containing data in the response body.</returns>
 		public static async Task<dynamic> ReceiveJson(this Task<IFlurlResponse> response) {
@@ -41,7 +41,7 @@ public static async Task<dynamic> ReceiveJson(this Task<IFlurlResponse> response
 		}
 
 		/// <summary>
-		/// Deserializes JSON-formatted HTTP response body to a list of dynamic objects. Intended to chain off an async call.
+		/// Deserializes a JSON-formatted HTTP response body to a list of dynamic objects. Intended to chain off an async call.
 		/// </summary>
 		/// <returns>A Task whose result is a list of dynamic objects containing data in the response body.</returns>
 		public static async Task<IList<dynamic>> ReceiveJsonList(this Task<IFlurlResponse> response) {
@@ -50,6 +50,13 @@ public static async Task<IList<dynamic>> ReceiveJsonList(this Task<IFlurlRespons
 			return await resp.GetJsonListAsync().ConfigureAwait(false);
 		}
 
+		/// <summary>
+		/// Deserializes a JSON-formatted error response body to a dynamic object.
+		/// </summary>
+		/// <returns>A Task whose result is a dynamic object containing data in the response body.</returns>
+		public static async Task<dynamic> GetResponseJsonAsync(this FlurlHttpException flurlException) =>
+			(flurlException.Call?.Response == null) ? null : await flurlException.Call.Response.GetJsonAsync().ConfigureAwait(false);
+
 		/// <summary>
 		/// Shortcut to use NewtonsoftJsonSerializer with this IFlurlClientBuilder.
 		/// </summary>

test/Flurl.Test/Http/NewtonsoftTests.cs

@@ -56,6 +56,24 @@ public async Task null_response_returns_null_dynamic() {
 			var list = await resp.ReceiveJsonList();
 			Assert.IsNull(list);
 		}
+
+		[TestCase(false)]
+		[TestCase(true)]
+		public async Task can_get_error_json_untyped(bool useShortcut) {
+			HttpTest.RespondWithJson(new { code = 999, message = "our server crashed" }, 500);
+
+			try {
+				await "http://api.com".GetStringAsync();
+			}
+			catch (FlurlHttpException ex) {
+				var error = useShortcut ? // error is a dynamic this time
+					await ex.GetResponseJsonAsync() :
+					await ex.Call.Response.GetJsonAsync();
+				Assert.IsNotNull(error);
+				Assert.AreEqual(999, error.code);
+				Assert.AreEqual("our server crashed", error.message);
+			}
+		}
 	}
 
 	[TestFixture, Parallelizable]