Respond with HTTP 400 if the request body cannot be deserialized

Modules/Reflection/MethodHandler.cs

@@ -187,7 +187,15 @@ public MethodHandler(IHandler parent, MethodInfo method, MethodRouting routing,
                             throw new ProviderException(ResponseStatus.BadRequest, "Request body expected");
                         }
 
-                        targetArguments[i] = await deserializer.DeserializeAsync(request.Content, par.ParameterType);
+                        try
+                        {
+                            targetArguments[i] = await deserializer.DeserializeAsync(request.Content, par.ParameterType);
+                        }
+                        catch (Exception e) 
+                        {
+                            throw new ProviderException(ResponseStatus.BadRequest, "Failed to deserialize request body", e);
+                        }
+
                         continue;
                     }
                 }

Testing/Modules/Conversion/ErrorHandlingTests.cs

@@ -0,0 +1,48 @@
+using System.Net;
+using System.Net.Http;
+using System.Threading.Tasks;
+
+using GenHTTP.Modules.Functional;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace GenHTTP.Testing.Acceptance.Modules.Conversion
+{
+
+    [TestClass]
+    public class ErrorHandlingTests
+    {
+
+        #region Supporting data structures
+
+        record class MyEntity(string Data);
+
+        #endregion
+
+        #region Tests
+
+        [TestMethod]
+        public async Task UndeserializableBodyReturnsWithBadRequest()
+        {
+            var inline = Inline.Create()
+                               .Post("/t", (MyEntity entity) => entity.Data);
+
+            using var runner = TestRunner.Run(inline);
+
+            using var request = runner.GetRequest("/t");
+
+            request.Method = HttpMethod.Post;
+
+            request.Content = new StringContent("I cannot be deserialized", null, "application/json");
+            request.Content.Headers.ContentType = new("application/json");
+
+            using var response = await runner.GetResponse(request);
+
+            Assert.AreEqual(HttpStatusCode.BadRequest, response.StatusCode);
+        }
+
+        #endregion
+
+    }
+
+}