Add PluginProtocol message type.

- Returns the current Protocol.
- Added a test to validate that the Protocol is being returned.

#13

Author: N. Taylor Mullen

src/Microsoft.AspNet.Tooling.Razor/Models/OutgoingMessages/PluginProtocolMessage.cs

@@ -0,0 +1,15 @@
+// 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;
+
+namespace Microsoft.AspNet.Tooling.Razor.Models.OutgoingMessages
+{
+    public class PluginProtocolMessage : RazorPluginMessage<string>
+    {
+        public PluginProtocolMessage(Version protocol)
+            : base(messageType: RazorPluginMessageTypes.PluginProtocol, data: protocol.ToString())
+        {
+        }
+    }
+}

src/Microsoft.AspNet.Tooling.Razor/RazorPlugin.cs

@@ -15,6 +15,7 @@ namespace Microsoft.AspNet.Tooling.Razor
 {
     public class RazorPlugin : IPlugin
     {
+        private static readonly Version Protocol = new Version(1, 0, 0);
         private readonly IPluginMessageBroker _messageBroker;
 
         public RazorPlugin(IPluginMessageBroker messageBroker)
@@ -34,17 +35,20 @@ public void ProcessMessage(JObject data, IAssemblyLoadContext assemblyLoadContex
                         nameof(RazorPluginRequestMessage)));
             }
 
-            if (message.Data == null)
-            {
-                throw new InvalidOperationException(
-                    Resources.FormatValueMustBeProvidedInMessage(
-                        nameof(message.Data),
-                        nameof(RazorPluginRequestMessage)));
-            }
-
             switch (message.MessageType)
             {
+                case RazorPluginMessageTypes.PluginProtocol:
+                    _messageBroker.SendMessage(new PluginProtocolMessage(Protocol));
+                    break;
                 case RazorPluginMessageTypes.ResolveTagHelperDescriptors:
+                    if (message.Data == null)
+                    {
+                        throw new InvalidOperationException(
+                            Resources.FormatValueMustBeProvidedInMessage(
+                                nameof(message.Data),
+                                RazorPluginMessageTypes.ResolveTagHelperDescriptors));
+                    }
+
                     var messageData = message.Data.ToObject<ResolveTagHelperDescriptorsRequestData>();
 
                     if (messageData.AssemblyName == null)

src/Microsoft.AspNet.Tooling.Razor/RazorPluginMessageTypes.cs

@@ -5,6 +5,7 @@ namespace Microsoft.AspNet.Tooling.Razor
 {
     public static class RazorPluginMessageTypes
     {
-        public const string ResolveTagHelperDescriptors = "ResolveTagHelperDescriptors";
+        public const string ResolveTagHelperDescriptors = nameof(ResolveTagHelperDescriptors);
+        public const string PluginProtocol = nameof(PluginProtocol);
     }
 }

test/Microsoft.AspNet.Tooling.Razor.Tests/RazorPluginTest.cs

@@ -58,7 +58,8 @@ public void ProcessMessage_ThrowsWhenNoData()
             var messageBroker = new TestPluginMessageBroker();
             var assemblyLoadContext = new TestAssemblyLoadContext();
             var plugin = new RazorPlugin(messageBroker);
-            var expectedMessage = "'Data' must be provided for a 'RazorPluginRequestMessage' message.";
+            var expectedMessage = "'Data' must be provided for a '" +
+                RazorPluginMessageTypes.ResolveTagHelperDescriptors + "' message.";
 
             // Act & Assert
             var error = Assert.Throws<InvalidOperationException>(
@@ -130,6 +131,29 @@ public void ProcessMessage_ResolveTagHelperDescriptors_ThrowsWhenNoSourceLocatio
             Assert.Equal(expectedMessage, error.Message, StringComparer.Ordinal);
         }
 
+        [Fact]
+        public void ProcessMessage_PluginProtocol_ResolvesCurrentProtocol()
+        {
+            // Arrange
+            var message = new JObject
+            {
+                { "MessageType", RazorPluginMessageTypes.PluginProtocol },
+            };
+            PluginProtocolMessage responseMessage = null;
+            var messageBroker = new TestPluginMessageBroker(data => responseMessage = (PluginProtocolMessage)data);
+            var assemblyLoadContext = new TestAssemblyLoadContext();
+            var plugin = new RazorPlugin(messageBroker);
+
+            // Act
+            plugin.ProcessMessage(message, assemblyLoadContext);
+
+            // Assert
+            Assert.NotNull(responseMessage);
+            Assert.Equal(RazorPluginMessageTypes.PluginProtocol, responseMessage.MessageType, StringComparer.Ordinal);
+            var responseData = responseMessage.Data;
+            Assert.Equal("1.0.0", responseData, StringComparer.Ordinal);
+        }
+
         [Fact]
         public void ProcessMessage_ResolveTagHelperDescriptors_ResolvesTagHelperDescriptors()
         {