fix: in case of error, propagate back error code of edgeHub (Azure#4929)

instead of using 0 (which is a result of uninitialized status property)

edge-hub/core/src/Microsoft.Azure.Devices.Edge.Hub.MqttBrokerAdapter/upstream/BrokeredCloudProxyDispatcher.cs

@@ -6,6 +6,7 @@ namespace Microsoft.Azure.Devices.Edge.Hub.MqttBrokerAdapter
     using System.Collections.Generic;
     using System.Dynamic;
     using System.IO;
+    using System.Net;
     using System.Text;
     using System.Text.RegularExpressions;
     using System.Threading;
@@ -306,13 +307,33 @@ void HandleDirectMethodCall(string id, string method, string rid, byte[] payload
         {
             // TODO acquire the response timeout from the message
             var callingTask = this.edgeHub.InvokeMethodAsync(rid, new DirectMethodRequest(id, method, payload, TimeSpan.FromMinutes(1)));
-            callingTask.ContinueWith(
-                    async response =>
+            _ = callingTask.ContinueWith(
+                    async responseTask =>
                     {
-                        var status = response.IsCompletedSuccessfully ? response.Result.Status : 500; // TODO check the correct status code to return
-                        var topic = string.Format(DirectMethodResponseTemplate, id, response.Result.Status, rid);
+                        // DirectMethodResponse has a 'Status' and 'HttpStatusCode'. If everything is fine, 'Status' contains
+                        // the response of the device and HttpStatusCode is 200. In this case we pass back the response of the
+                        // device. If something went wrong, then HttpStatusCode is an error (typically 404). In this case we
+                        // pass back that value. The value 500/InternalServerError is just a fallback, edgeHub is supposed to
+                        // handle errors, so 500 always should be overwritten.
+                        var responseCode = Convert.ToInt32(HttpStatusCode.InternalServerError);
+                        var responseData = this.emptyArray;
+                        if (responseTask.IsCompletedSuccessfully)
+                        {
+                            var response = responseTask.Result;
+                            responseData = response.Data ?? responseData;
+
+                            if (response.HttpStatusCode == HttpStatusCode.OK)
+                            {
+                                responseCode = response.Status;
+                            }
+                            else
+                            {
+                                responseCode = Convert.ToInt32(response.HttpStatusCode);
+                            }
+                        }
 
-                        await this.SendUpstreamMessageAsync(RpcCmdPub, topic, response.Result.Data ?? this.emptyArray);
+                        var topic = string.Format(DirectMethodResponseTemplate, id, responseCode, rid);
+                        await this.SendUpstreamMessageAsync(RpcCmdPub, topic, responseData);
                     });
         }
 

edge-hub/core/test/Microsoft.Azure.Devices.Edge.Hub.MqttBrokerAdapter.Test/BrokeredCloudProxyDispatcherTest.cs

@@ -0,0 +1,85 @@
+// Copyright (c) Microsoft. All rights reserved.
+namespace Microsoft.Azure.Devices.Edge.Hub.MqttBrokerAdapter.Test
+{
+    using System;
+    using System.IO;
+    using System.Text;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.Azure.Devices.Edge.Hub.Core;
+    using Moq;
+    using Newtonsoft.Json;
+    using Newtonsoft.Json.Bson;
+    using Newtonsoft.Json.Serialization;
+    using Xunit;
+
+    public class BrokeredCloudProxyDispatcherTest
+    {
+        [Fact]
+        public async Task SuccessfulMethodCallReturnsMethodResult()
+        {
+            var resultTopic = await this.DirectMethodCall(new DirectMethodResponse("123", new byte[] { 1, 2, 3 }, 201));
+            Assert.Contains("/res/201/", resultTopic);
+        }
+
+        [Fact]
+        public async Task FailedMethodCallReturnsHttpStatus()
+        {
+            var resultTopic = await this.DirectMethodCall(new DirectMethodResponse(new Exception("some error"), System.Net.HttpStatusCode.NotFound));
+            Assert.Contains("/res/404/", resultTopic);
+        }
+
+        public async Task<string> DirectMethodCall(DirectMethodResponse response)
+        {
+            var connector = new Mock<IMqttBrokerConnector>();
+            var edgeHub = new Mock<IEdgeHub>();
+
+            var lastPayload = default(byte[]);
+
+            var milestone = new SemaphoreSlim(0, 1);
+
+            connector.Setup(c => c.SendAsync(It.IsAny<string>(), It.IsAny<byte[]>(), It.IsAny<bool>()))
+                     .Callback<string, byte[], bool>(
+                        (_, p, __) =>
+                        {
+                            lastPayload = p;
+                            milestone.Release();
+                        })
+                     .Returns(() => Task.FromResult(true));
+
+            edgeHub.Setup(e => e.InvokeMethodAsync(It.IsAny<string>(), It.IsAny<DirectMethodRequest>()))
+                   .Returns(() => Task.FromResult(response));
+
+            var sut = new BrokeredCloudProxyDispatcher();
+
+            sut.BindEdgeHub(edgeHub.Object);
+            sut.SetConnector(connector.Object);
+
+            await sut.HandleAsync(new MqttPublishInfo("$downstream/dev_a/mod_1/methods/post/test/?$rid=123", Encoding.UTF8.GetBytes("{ \"test\":\"data\"}")));
+
+            await milestone.WaitAsync();
+
+            var packet = GetRpcPacket(lastPayload);
+
+            return packet.Topic;
+        }
+
+        RpcPacket GetRpcPacket(byte[] payload)
+        {
+            var packet = default(RpcPacket);
+            using (var reader = new BsonDataReader(new MemoryStream(payload)))
+            {
+                var serializer = new JsonSerializer
+                {
+                    ContractResolver = new DefaultContractResolver
+                    {
+                        NamingStrategy = new CamelCaseNamingStrategy()
+                    }
+                };
+
+                packet = serializer.Deserialize<RpcPacket>(reader);
+            }
+            return packet;
+        }
+    }
+}