problem details for errors

Author: thefringeninja

src/SqlStreamStore.HAL.Tests/StreamAppendTests.cs

@@ -122,6 +122,77 @@ public async Task append_expected_version_no_stream()
             JToken.DeepEquals(JObject.Parse(page.Messages[0].JsonMetadata), jsonMetadata).ShouldBeTrue();
         }
 
+        [Theory]
+        [InlineData(new[]{ExpectedVersion.NoStream, ExpectedVersion.NoStream})]
+        [InlineData(new[]{ExpectedVersion.NoStream, 2})]
+        public async Task wrong_expected_version(int[] expectedVersions)
+        {
+            var jsonData = JObject.FromObject(new
+            {
+                property = "value"
+            });
+
+            var jsonMetadata = JObject.FromObject(new
+            {
+                property = "metaValue"
+            });
+
+            for(var i = 0; i < expectedVersions.Length - 1; i++)
+            {
+                using(await _fixture.HttpClient.PostAsync(
+                    "/streams/a-stream",
+                    new StringContent(JObject.FromObject(new
+                    {
+                        expectedVersion = expectedVersions[i],
+                        messages = new[]
+                        {
+                            new
+                            {
+                                messageId = Guid.NewGuid(),
+                                type = "type",
+                                jsonData,
+                                jsonMetadata
+                            }
+                        }
+                    }).ToString())
+                    {
+                        Headers =
+                        {
+                            ContentType = new MediaTypeHeaderValue("application/json")
+                        }
+                    }))
+                { }
+            }
+
+            using(var response = await _fixture.HttpClient.PostAsync(
+                "/streams/a-stream",
+                new StringContent(JObject.FromObject(new
+                {
+                    expectedVersion = expectedVersions[expectedVersions.Length-1],
+                    messages = new[]
+                    {
+                        new
+                        {
+                            messageId = Guid.NewGuid(),
+                            type = "type",
+                            jsonData,
+                            jsonMetadata
+                        }
+                    }
+                }).ToString())
+                {
+                    Headers =
+                    {
+                        ContentType = new MediaTypeHeaderValue("application/json")
+                    }
+                }))
+            {
+                response.StatusCode.ShouldBe(HttpStatusCode.Conflict);
+                response.Content.Headers.ContentType.ShouldBe(new MediaTypeHeaderValue("application/problem+json"));
+            }
+            
+        }
+
         public void Dispose() => _fixture.Dispose();
     }
 }

src/SqlStreamStore.HAL/AppendStreamMiddleware.cs

@@ -1,8 +1,11 @@
 namespace SqlStreamStore.HAL
 {
+    using System;
     using Microsoft.Owin;
     using Microsoft.Owin.Builder;
+    using Newtonsoft.Json.Linq;
     using Owin;
+    using SqlStreamStore.Streams;
     using MidFunc = System.Func<System.Func<System.Collections.Generic.IDictionary<string, object>,
             System.Threading.Tasks.Task
         >, System.Func<System.Collections.Generic.IDictionary<string, object>,
@@ -35,16 +38,36 @@ private static MidFunc AppendStream(StreamResource stream) => next => async env
 
             var options = await AppendStreamOptions.Create(context.Request, context.Request.CallCancelled);
 
-            var response = await stream.AppendMessages(options, context.Request.CallCancelled);
-
-            if(response.StatusCode == 201)
+            try
             {
-                context.Response.ReasonPhrase = "Created";
-                context.Response.Headers["Location"] = $"streams/{options.StreamId}";
+                var response = await stream.AppendMessages(options, context.Request.CallCancelled);
+
+                if(response.StatusCode == 201)
+                {
+                    context.Response.ReasonPhrase = "Created";
+                    context.Response.Headers["Location"] = $"streams/{options.StreamId}";
+                }
+
+                await context.WriteHalResponse(response);
+
             }
+            catch(WrongExpectedVersionException ex)
+            {
+                context.Response.StatusCode = 409;
+                context.Response.ReasonPhrase = "Conflict";
+                context.Response.ContentType = "application/problem+json";
 
-            await context.WriteHalResponse(response);
+                await context.Response.WriteAsync(ConvertToProblemDetails(ex));
+            }
         };
 
+        private static string ConvertToProblemDetails(Exception ex)
+            => JObject.FromObject(new
+            {
+                type = "WrongExpectedVersion",
+                title = "Wrong expected version.",
+                detail = ex.Message
+            }).ToString();
+
     }
 }