Add LogEventDropped handler to the NetworkTarget (#5101)

src/NLog/Internal/NetworkSenders/INetworkSenderFactory.cs

@@ -53,6 +53,6 @@ internal interface INetworkSenderFactory
         /// <returns>
         /// A newly created network sender.
         /// </returns>
-        NetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, System.Security.Authentication.SslProtocols sslProtocols, TimeSpan keepAliveTime);
+        QueuedNetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, System.Security.Authentication.SslProtocols sslProtocols, TimeSpan keepAliveTime);
     }
 }

src/NLog/Internal/NetworkSenders/NetworkSenderFactory.cs

@@ -45,7 +45,7 @@ internal class NetworkSenderFactory : INetworkSenderFactory
         public static readonly INetworkSenderFactory Default = new NetworkSenderFactory();
 
         /// <inheritdoc/>
-        public NetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, System.Security.Authentication.SslProtocols sslProtocols, TimeSpan keepAliveTime)
+        public QueuedNetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, System.Security.Authentication.SslProtocols sslProtocols, TimeSpan keepAliveTime)
         {
             if (url.StartsWith("tcp://", StringComparison.OrdinalIgnoreCase))
             {

src/NLog/Internal/NetworkSenders/QueuedNetworkSender.cs

@@ -78,6 +78,7 @@ protected QueuedNetworkSender(string url)
         public int MaxQueueSize { get; set; }
 
         public NetworkTargetQueueOverflowAction OnQueueOverflow { get; set; }
+        public event EventHandler<NetworkLogEventDroppedEventArgs> LogEventDropped;
 
         protected override void DoSend(byte[] bytes, int offset, int length, AsyncContinuation asyncContinuation)
         {
@@ -94,6 +95,7 @@ protected override void DoSend(byte[] bytes, int offset, int length, AsyncContin
                         {
                             case NetworkTargetQueueOverflowAction.Discard:
                                 InternalLogger.Debug("NetworkQueue - Discarding single item, because queue is full");
+                                OnLogEventDropped(this, NetworkLogEventDroppedEventArgs.QueueOverflow);
                                 var dequeued = _pendingRequests.Dequeue();
                                 dequeued.AsyncContinuation?.Invoke(null);
                                 break;
@@ -299,5 +301,10 @@ private void SignalSocketFailedForPendingRequests(Exception pendingException)
                 eventArgs.AsyncContinuation?.Invoke(pendingException);
             }
         }
+
+        private void OnLogEventDropped(object sender, NetworkLogEventDroppedEventArgs logEventDroppedEventArgs)
+        {
+            LogEventDropped?.Invoke(this, logEventDroppedEventArgs);
+        }
     }
 }

src/NLog/Targets/NetworkLogEventDroppedEventArgs.cs

@@ -0,0 +1,71 @@
+// 
+// Copyright (c) 2004-2021 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without 
+// modification, are permitted provided that the following conditions 
+// are met:
+// 
+// * Redistributions of source code must retain the above copyright notice, 
+//   this list of conditions and the following disclaimer. 
+// 
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution. 
+// 
+// * Neither the name of Jaroslaw Kowalski nor the names of its 
+//   contributors may be used to endorse or promote products derived from this
+//   software without specific prior written permission. 
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
+// THE POSSIBILITY OF SUCH DAMAGE.
+// 
+
+using System;
+
+namespace NLog.Targets
+{
+    /// <summary>
+    /// Arguments for <see cref="NetworkTarget.LogEventDropped"/> events.
+    /// </summary>
+    public class NetworkLogEventDroppedEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Provides a value to use with events that do not have event data.
+        /// </summary>
+        internal static readonly NetworkLogEventDroppedEventArgs PayloadSizeOverflow = new NetworkLogEventDroppedEventArgs(NetworkLogEventDroppedReason.PayloadSizeOverflow);
+
+        /// <summary>
+        /// Provides a value to use with events that do not have event data.
+        /// </summary>
+        internal static readonly NetworkLogEventDroppedEventArgs ConnectionOverflow = new NetworkLogEventDroppedEventArgs(NetworkLogEventDroppedReason.ConnectionOverflow);
+
+        /// <summary>
+        /// Provides a value to use with events that do not have event data.
+        /// </summary>
+        internal static readonly NetworkLogEventDroppedEventArgs QueueOverflow = new NetworkLogEventDroppedEventArgs(NetworkLogEventDroppedReason.QueueOverflow);
+
+        /// <summary>
+        /// Creates new instance of NetworkTargetLogEventDroppedEventArgs
+        /// </summary>
+        public NetworkLogEventDroppedEventArgs(NetworkLogEventDroppedReason reason)
+        {
+            Reason = reason;
+        }
+
+        /// <summary>
+        /// The reason why log was dropped
+        /// </summary>
+        public NetworkLogEventDroppedReason Reason { get; }
+    }
+}

src/NLog/Targets/NetworkLogEventDroppedReason.cs

@@ -0,0 +1,54 @@
+// 
+// Copyright (c) 2004-2021 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without 
+// modification, are permitted provided that the following conditions 
+// are met:
+// 
+// * Redistributions of source code must retain the above copyright notice, 
+//   this list of conditions and the following disclaimer. 
+// 
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution. 
+// 
+// * Neither the name of Jaroslaw Kowalski nor the names of its 
+//   contributors may be used to endorse or promote products derived from this
+//   software without specific prior written permission. 
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
+// THE POSSIBILITY OF SUCH DAMAGE.
+// 
+
+namespace NLog.Targets
+{
+    /// <summary>
+    /// The reason why log event was dropped by <see cref="NetworkTarget"/>
+    /// </summary>
+    public enum NetworkLogEventDroppedReason
+    {
+        /// <summary>
+        /// Discarded LogEvent because message is bigger than <see cref="NetworkTarget.MaxMessageSize"/>
+        /// </summary>
+        PayloadSizeOverflow,
+        /// <summary>
+        /// Discarded LogEvent because message queue was bigger than <see cref="NetworkTarget.MaxQueueSize"/>
+        /// </summary>
+        QueueOverflow,
+        /// <summary>
+        /// Discarded LogEvent because attempted to open more than <see cref="NetworkTarget.MaxConnections"/> connections
+        /// </summary>
+        ConnectionOverflow
+    }
+}

src/NLog/Targets/NetworkTarget.cs

@@ -41,6 +41,7 @@ namespace NLog.Targets
     using NLog.Internal;
     using NLog.Internal.NetworkSenders;
     using NLog.Layouts;
+    using NLog.Targets.Wrappers;
 
     /// <summary>
     /// Sends log messages over the network.
@@ -186,6 +187,12 @@ public LineEndingMode LineEnding
         /// <docgen category='Connection Options' order='10' />
         public NetworkTargetQueueOverflowAction OnQueueOverflow { get; set; } = NetworkTargetQueueOverflowAction.Discard;
 
+        /// <summary>
+        /// Raise event when Target cannot store LogEvent and <see cref="OnQueueOverflow"/> equals <see cref="NetworkTargetOverflowAction.Discard"/>.
+        /// Event arg contains lost LogEvents
+        /// </summary>
+        public event EventHandler<NetworkLogEventDroppedEventArgs> LogEventDropped;
+
         /// <summary>
         /// Gets or sets the size of the connection cache (number of connections which are kept alive). Requires <see cref="KeepConnection"/> = true
         /// </summary>
@@ -360,6 +367,7 @@ private void WriteBytesToNewNetworkSender(string address, byte[] bytes, AsyncLog
                     {
                         case NetworkTargetConnectionsOverflowAction.Discard:
                             InternalLogger.Debug("{0}: Discarding message, because too many open connections.", this);
+                            OnLogEventDropped(this, NetworkLogEventDroppedEventArgs.ConnectionOverflow);
                             logEvent.Continuation(null);
                             return;
 
@@ -418,6 +426,11 @@ private void WriteBytesToNewNetworkSender(string address, byte[] bytes, AsyncLog
                 });
         }
 
+        private void OnLogEventDropped(object sender, NetworkLogEventDroppedEventArgs logEventDroppedEventArgs)
+        {
+            LogEventDropped?.Invoke(this, logEventDroppedEventArgs);
+        }
+
         /// <summary>
         /// Try to remove. 
         /// </summary>
@@ -567,6 +580,8 @@ private NetworkSender CreateNetworkSender(string address)
         {
             var sender = SenderFactory.Create(address, MaxQueueSize, OnQueueOverflow, MaxMessageSize, SslProtocols, TimeSpan.FromSeconds(KeepAliveTimeSeconds));
             sender.Initialize();
+            sender.LogEventDropped += OnLogEventDropped;
+
             return sender;
         }
 
@@ -600,13 +615,15 @@ private void WriteBytesToNetworkSender(NetworkSender sender, byte[] buffer, Asyn
                 if (OnOverflow == NetworkTargetOverflowAction.Discard)
                 {
                     InternalLogger.Debug("{0}: Discarded LogEvent because MessageSize={1} is above MaxMessageSize={2}", this, messageSize, MaxMessageSize);
+                    OnLogEventDropped(this, NetworkLogEventDroppedEventArgs.PayloadSizeOverflow);
                     continuation(null);
                     return;
                 }
 
                 if (OnOverflow == NetworkTargetOverflowAction.Error)
                 {
                     InternalLogger.Debug("{0}: Discarded LogEvent because MessageSize={1} is above MaxMessageSize={2}", this, messageSize, MaxMessageSize);
+                    OnLogEventDropped(this, NetworkLogEventDroppedEventArgs.PayloadSizeOverflow);
                     continuation(new InvalidOperationException($"NetworkTarget: Discarded LogEvent because MessageSize={messageSize} is above MaxMessageSize={MaxMessageSize}"));
                     return;
                 }

tests/NLog.UnitTests/Targets/NetworkTargetTests.cs

@@ -365,6 +365,9 @@ public void NetworkTargetMultipleConnectionsWithMessageDiscardTest()
             target.OnOverflow = NetworkTargetOverflowAction.Discard;
             target.Initialize(null);
 
+            int droppedLogs = 0;
+            target.LogEventDropped += (sender, args) => droppedLogs++;
+
             var exceptions = new List<Exception>();
             var mre = new ManualResetEvent(false);
             int remaining = 3;
@@ -399,6 +402,7 @@ public void NetworkTargetMultipleConnectionsWithMessageDiscardTest()
             Assert.True(result.IndexOf("2: send 0 5") != -1);
             Assert.True(result.IndexOf("1: close") != -1);
             Assert.True(result.IndexOf("2: close") != -1);
+            Assert.Equal(1, droppedLogs);
         }
 
         [Fact]
@@ -417,6 +421,9 @@ public void NetworkTargetMultipleConnectionsWithMessageErrorTest()
             target.OnOverflow = NetworkTargetOverflowAction.Error;
             target.Initialize(null);
 
+            int droppedLogs = 0;
+            target.LogEventDropped += (sender, args) => droppedLogs++;
+
             var exceptions = new List<Exception>();
             var mre = new ManualResetEvent(false);
             int remaining = 3;
@@ -451,6 +458,8 @@ public void NetworkTargetMultipleConnectionsWithMessageErrorTest()
             Assert.True(result.IndexOf("2: connect tcp://logger2.company.lan/") != -1);
             Assert.True(result.IndexOf("2: send 0 5") != -1);
             Assert.True(result.IndexOf("2: close") != -1);
+
+            Assert.Equal(1, droppedLogs);
         }
 
         [Fact]
@@ -813,6 +822,9 @@ public void NetworkTargetQueueDiscardTest()
             target.KeepConnection = true;
             target.Initialize(null);
 
+            int discardEventCalls = 0;
+            target.LogEventDropped += (sender, args) => discardEventCalls++;
+
             int pendingWrites = 1;
             var exceptions = new List<Exception>();
             var mre = new ManualResetEvent(false);
@@ -853,6 +865,8 @@ public void NetworkTargetQueueDiscardTest()
             {
                 Assert.True(ex == null, $"Network Write Exception: {ex?.ToString()}");
             }
+
+            Assert.True(discardEventCalls >= 5, $"LogDropped not called: {discardEventCalls}");
         }
 
         [Fact]
@@ -1200,7 +1214,7 @@ internal class MyQueudSenderFactory : INetworkSenderFactory
             internal StringWriter Log = new StringWriter();
             private int _idCounter;
 
-            public NetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, SslProtocols sslProtocols, TimeSpan keepAliveTime)
+            public QueuedNetworkSender Create(string url, int maxQueueSize, NetworkTargetQueueOverflowAction onQueueOverflow, int maxMessageSize, SslProtocols sslProtocols, TimeSpan keepAliveTime)
             {
                 var sender = new MyQueudNetworkSender(url, ++_idCounter, Log, this) { MaxQueueSize = maxQueueSize, OnQueueOverflow = onQueueOverflow };
                 Senders.Add(sender);