- MonitorEvent: added ConvertArg method

- NetMQMonitor: use above
- NetMQMonitorEventArgs: added nullable indicator
- NetMQMonitorTests: added tests for ConvertArg method

Author: mmillerbe

src/NetMQ.Tests/NetMQMonitorTests.cs

@@ -2,6 +2,8 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using AsyncIO;
+using NetMQ.Core;
 using NetMQ.Monitoring;
 using NetMQ.Sockets;
 using Xunit;
@@ -157,5 +159,31 @@ public void MonitorDisposeProperlyWhenDisposedAfterMonitoredTcpSocket()
             }
             // NOTE If this test fails, it will hang because context.Dispose will block
         }
+
+        [Fact]
+        public void ConvertArgDoesNotThrowForNullSocket()
+        {
+            AsyncSocket? socket = null;
+            MonitorEvent monitorEvent = new MonitorEvent(SocketEvents.All, addr: "", arg: socket!);
+            Assert.Null(monitorEvent.ConvertArg<AsyncSocket>());
+        }
+
+        [Fact]
+        public void ConvertArgDoesNotThrowForNonNullSocket()
+        {
+            using (AsyncSocket socket = AsyncSocket.CreateIPv4Tcp())
+            {
+                MonitorEvent monitorEvent = new MonitorEvent(SocketEvents.All, addr: "", arg: socket);
+                Assert.Equal(socket, monitorEvent.ConvertArg<AsyncSocket>());
+            }
+        }
+
+        [Fact]
+        public void ConvertArgThrowsForInvalidType()
+        {
+            AsyncSocket? socket = null;
+            MonitorEvent monitorEvent = new MonitorEvent(SocketEvents.All, addr: "", arg: socket!);
+            Assert.Throws<ArgumentException>(() => monitorEvent.ConvertArg<int>());
+        }
     }
 }

src/NetMQ/Core/MonitorEvent.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using AsyncIO;
 using NetMQ.Core.Transports;
@@ -159,5 +160,17 @@ public static MonitorEvent Read(SocketBase s)
 
             return new MonitorEvent(@event, addr, arg);
         }
+
+        [return: MaybeNull]
+        public T ConvertArg<T>()
+        {
+            if (Arg is T v)
+                return v;
+
+            if (Arg is null && default(T) is null)
+                return default;
+
+            throw new ArgumentException($"Command argument must be of type {typeof(T).Name}.");
+        }
     }
 }

src/NetMQ/Monitoring/NetMQMonitor.cs

@@ -156,48 +156,37 @@ private void Handle(object sender, NetMQSocketEventArgs socketEventArgs)
         {
             var monitorEvent = MonitorEvent.Read(m_monitoringSocket.SocketHandle);
 
-            T GetArg<T>()
-            {
-                if (monitorEvent.Arg is T v)
-                    return v;
-
-                if (monitorEvent.Arg == null && default(T) == null)
-                    return default(T);
-
-                throw new ArgumentException($"Command argument must be of type {typeof(T).Name}.");
-            }
-
             switch (monitorEvent.Event)
             {
                 case SocketEvents.Connected:
-                    InvokeEvent(Connected, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, GetArg<AsyncSocket>(), SocketEvents.Connected));
+                    InvokeEvent(Connected, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<AsyncSocket>(), SocketEvents.Connected));
                     break;
                 case SocketEvents.ConnectDelayed:
-                    InvokeEvent(ConnectDelayed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)GetArg<int>(), SocketEvents.ConnectDelayed));
+                    InvokeEvent(ConnectDelayed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)monitorEvent.ConvertArg<int>(), SocketEvents.ConnectDelayed));
                     break;
                 case SocketEvents.ConnectRetried:
-                    InvokeEvent(ConnectRetried, new NetMQMonitorIntervalEventArgs(this, monitorEvent.Addr, GetArg<int>(), SocketEvents.ConnectRetried));
+                    InvokeEvent(ConnectRetried, new NetMQMonitorIntervalEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<int>(), SocketEvents.ConnectRetried));
                     break;
                 case SocketEvents.Listening:
-                    InvokeEvent(Listening, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, GetArg<AsyncSocket>(), SocketEvents.Listening));
+                    InvokeEvent(Listening, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<AsyncSocket>(), SocketEvents.Listening));
                     break;
                 case SocketEvents.BindFailed:
-                    InvokeEvent(BindFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)GetArg<int>(), SocketEvents.BindFailed));
+                    InvokeEvent(BindFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)monitorEvent.ConvertArg<int>(), SocketEvents.BindFailed));
                     break;
                 case SocketEvents.Accepted:
-                    InvokeEvent(Accepted, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, GetArg<AsyncSocket>(), SocketEvents.Accepted));
+                    InvokeEvent(Accepted, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<AsyncSocket>(), SocketEvents.Accepted));
                     break;
                 case SocketEvents.AcceptFailed:
-                    InvokeEvent(AcceptFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)GetArg<int>(), SocketEvents.AcceptFailed));
+                    InvokeEvent(AcceptFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)monitorEvent.ConvertArg<int>(), SocketEvents.AcceptFailed));
                     break;
                 case SocketEvents.Closed:
-                    InvokeEvent(Closed, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, GetArg<AsyncSocket>(), SocketEvents.Closed));
+                    InvokeEvent(Closed, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<AsyncSocket>(), SocketEvents.Closed));
                     break;
                 case SocketEvents.CloseFailed:
-                    InvokeEvent(CloseFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)GetArg<int>(), SocketEvents.CloseFailed));
+                    InvokeEvent(CloseFailed, new NetMQMonitorErrorEventArgs(this, monitorEvent.Addr, (ErrorCode)monitorEvent.ConvertArg<int>(), SocketEvents.CloseFailed));
                     break;
                 case SocketEvents.Disconnected:
-                    InvokeEvent(Disconnected, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, GetArg<AsyncSocket>(), SocketEvents.Disconnected));
+                    InvokeEvent(Disconnected, new NetMQMonitorSocketEventArgs(this, monitorEvent.Addr, monitorEvent.ConvertArg<AsyncSocket>(), SocketEvents.Disconnected));
                     break;
                 default:
                     throw new Exception("unknown event " + monitorEvent.Event);

src/NetMQ/Monitoring/NetMQMonitorEventArgs.cs

@@ -49,7 +49,7 @@ public class NetMQMonitorSocketEventArgs : NetMQMonitorEventArgs
         /// <param name="address">The address of the event.</param>
         /// <param name="socketEvent">The type of socket event that occurred.</param>
         /// <param name="socket">The socket upon which this event occurred.</param>
-        public NetMQMonitorSocketEventArgs(NetMQMonitor monitor, string address, AsyncSocket socket, SocketEvents socketEvent)
+        public NetMQMonitorSocketEventArgs(NetMQMonitor monitor, string address, AsyncSocket? socket, SocketEvents socketEvent)
             : base(monitor, address, socketEvent)
         {
             Socket = socket;
@@ -58,7 +58,7 @@ public NetMQMonitorSocketEventArgs(NetMQMonitor monitor, string address, AsyncSo
         /// <summary>
         /// Gets the socket upon which this event occurred.
         /// </summary>
-        public AsyncSocket Socket { get; }
+        public AsyncSocket? Socket { get; }
     }
 
     /// <summary>