From da7a95f563fe78ef06eff17a9394ebf806edb9e2 Mon Sep 17 00:00:00 2001
From: James Newton-King <james@newtonking.com>
Date: Fri, 4 May 2018 16:08:06 -0700
Subject: [PATCH] Handle null collections when writing NegotiateResponse
 (#2202)

---
 .../NegotiateProtocol.cs                      | 30 +++++++++------
 .../NegotiateProtocolTests.cs                 | 38 ++++++++++++++++++-
 2 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Http.Connections.Common/NegotiateProtocol.cs b/src/Microsoft.AspNetCore.Http.Connections.Common/NegotiateProtocol.cs
index b23dcb4be6..0102da6ae2 100644
--- a/src/Microsoft.AspNetCore.Http.Connections.Common/NegotiateProtocol.cs
+++ b/src/Microsoft.AspNetCore.Http.Connections.Common/NegotiateProtocol.cs
@@ -49,21 +49,27 @@ namespace Microsoft.AspNetCore.Http.Connections
                     jsonWriter.WritePropertyName(AvailableTransportsPropertyName);
                     jsonWriter.WriteStartArray();
 
-                    foreach (var availableTransport in response.AvailableTransports)
+                    if (response.AvailableTransports != null)
                     {
-                        jsonWriter.WriteStartObject();
-                        jsonWriter.WritePropertyName(TransportPropertyName);
-                        jsonWriter.WriteValue(availableTransport.Transport);
-                        jsonWriter.WritePropertyName(TransferFormatsPropertyName);
-                        jsonWriter.WriteStartArray();
-
-                        foreach (var transferFormat in availableTransport.TransferFormats)
+                        foreach (var availableTransport in response.AvailableTransports)
                         {
-                            jsonWriter.WriteValue(transferFormat);
-                        }
+                            jsonWriter.WriteStartObject();
+                            jsonWriter.WritePropertyName(TransportPropertyName);
+                            jsonWriter.WriteValue(availableTransport.Transport);
+                            jsonWriter.WritePropertyName(TransferFormatsPropertyName);
+                            jsonWriter.WriteStartArray();
 
-                        jsonWriter.WriteEndArray();
-                        jsonWriter.WriteEndObject();
+                            if (availableTransport.TransferFormats != null)
+                            {
+                                foreach (var transferFormat in availableTransport.TransferFormats)
+                                {
+                                    jsonWriter.WriteValue(transferFormat);
+                                }
+                            }
+
+                            jsonWriter.WriteEndArray();
+                            jsonWriter.WriteEndObject();
+                        }
                     }
 
                     jsonWriter.WriteEndArray();
diff --git a/test/Microsoft.AspNetCore.Http.Connections.Tests/NegotiateProtocolTests.cs b/test/Microsoft.AspNetCore.Http.Connections.Tests/NegotiateProtocolTests.cs
index 85bbd0bf47..b959e3b44e 100644
--- a/test/Microsoft.AspNetCore.Http.Connections.Tests/NegotiateProtocolTests.cs
+++ b/test/Microsoft.AspNetCore.Http.Connections.Tests/NegotiateProtocolTests.cs
@@ -1,7 +1,11 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Text;
-using Microsoft.AspNetCore.Http.Connections.Internal;
+using Microsoft.AspNetCore.Internal;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Http.Connections.Tests
@@ -50,5 +54,37 @@ namespace Microsoft.AspNetCore.Http.Connections.Tests
 
             Assert.Equal(expectedMessage, exception.InnerException.Message);
         }
+
+        [Fact]
+        public void WriteNegotiateResponseWithNullAvailableTransports()
+        {
+            using (MemoryBufferWriter writer = new MemoryBufferWriter())
+            {
+                NegotiateProtocol.WriteResponse(new NegotiationResponse(), writer);
+
+                string json = Encoding.UTF8.GetString(writer.ToArray());
+
+                Assert.Equal("{\"availableTransports\":[]}", json);
+            }
+        }
+
+        [Fact]
+        public void WriteNegotiateResponseWithNullTransferFormats()
+        {
+            using (MemoryBufferWriter writer = new MemoryBufferWriter())
+            {
+                NegotiateProtocol.WriteResponse(new NegotiationResponse
+                {
+                    AvailableTransports = new List<AvailableTransport>
+                    {
+                        new AvailableTransport()
+                    }
+                }, writer);
+
+                string json = Encoding.UTF8.GetString(writer.ToArray());
+
+                Assert.Equal("{\"availableTransports\":[{\"transport\":null,\"transferFormats\":[]}]}", json);
+            }
+        }
     }
 }