Improve JSON RPC message deserialization

This change improves JSON RPC message deserialization to tolerate requests
and events lacking a 'params' object.  This appeared while using
vscode-languageclient and attempting the language server using its stop()
method.

Author: daviwil

src/PowerShellEditorServices.Protocol/MessageProtocol/Serializers/JsonRpcMessageSerializer.cs

@@ -62,51 +62,41 @@ public Message DeserializeMessage(JObject messageJson)
                 // Message is a Request or Response
                 string messageId = token.ToString();
 
-                if (messageJson.TryGetValue("params", out token))
-                {
-                    JToken messageParams = token;
-
-                    if (!messageJson.TryGetValue("method", out token))
-                    {
-                        // TODO: Throw parse error
-                    }
-
-                    return Message.Request(messageId, token.ToString(), messageParams);
-                }
-                else if(messageJson.TryGetValue("result", out token))
+                if (messageJson.TryGetValue("result", out token))
                 {
                     return Message.Response(messageId, null, token);
                 }
-                else if(messageJson.TryGetValue("error", out token))
+                else if (messageJson.TryGetValue("error", out token))
                 {
                     return Message.ResponseError(messageId, null, token);
                 }
                 else
                 {
-                    return Message.Unknown();
-                }
-            }
-            else
-            {
-                // Messages without an id are events
-                if (messageJson.TryGetValue("params", out token))
-                {
-                    JToken messageParams = token;
+                    JToken messageParams = null;
+                    messageJson.TryGetValue("params", out messageParams);
 
                     if (!messageJson.TryGetValue("method", out token))
                     {
                         // TODO: Throw parse error
                     }
 
-                    return Message.Event(token.ToString(), messageParams);
+                    return Message.Request(messageId, token.ToString(), messageParams);
                 }
-                else
+            }
+            else
+            {
+                // Messages without an id are events
+                JToken messageParams = token;
+                messageJson.TryGetValue("params", out messageParams);
+
+                if (!messageJson.TryGetValue("method", out token))
                 {
-                    return Message.Unknown();
+                    // TODO: Throw parse error
                 }
+
+                return Message.Event(token.ToString(), messageParams);
             }
         }
     }
-
 }
 

src/PowerShellEditorServices.Protocol/Server/ProtocolServer.cs

@@ -63,12 +63,14 @@ public void Stop()
         {
             if (this.isStarted)
             {
+                // Make sure no future calls try to stop the server during shutdown
+                this.isStarted = false;
+
                 // Stop the implementation first
                 this.OnStop();
 
                 this.serverChannel.Stop();
                 this.serverExitedTask.SetResult(true);
-                this.isStarted = false;
             }
         }