add tracking for "now" and "next" messages when recording message timeouts

src/StackExchange.Redis/ExceptionFactory.cs

@@ -217,7 +217,7 @@ void add(string lk, string sk, string v)
                     if (message.QueuePosition >= 0) add("QueuePosition", null, message.QueuePosition.ToString()); // the position the item was when added to the queue
                     if ((int)message.ConnectionWriteState >= 0) add("WriteState", null, message.ConnectionWriteState.ToString()); // what the physical was doing when it was added to the queue
 #endif
-                    if (message.TryGetPhysicalState(out var ws, out var rs, out var sentDelta, out var receivedDelta))
+                    if (message != null && message.TryGetPhysicalState(out var ws, out var rs, out var sentDelta, out var receivedDelta))
                     {
                         add("Write-State", null, ws.ToString());
                         add("Read-State", null, rs.ToString());
@@ -235,6 +235,13 @@ void add(string lk, string sk, string v)
                 catch { }
             }
 
+            if (message != null)
+            {
+                message.TryGetHeadMessages(out var now, out var next);
+                if (now != null) add("Message-Current", "active", mutiplexer.IncludeDetailInExceptions ? now.CommandAndKey : now.Command.ToString());
+                if (next != null) add("Message-Next", "next", mutiplexer.IncludeDetailInExceptions ? next.CommandAndKey : next.Command.ToString());
+            }
+
             // Add server data, if we have it
             if (server != null)
             {

src/StackExchange.Redis/Message.cs

@@ -647,7 +647,15 @@ internal void SetEnqueued(PhysicalConnection connection)
             }
         }
 
-        internal bool TryGetPhysicalState(out PhysicalConnection.WriteStatus ws, out PhysicalConnection.ReadStatus rs, out long sentDelta, out long receivedDelta)
+        internal void TryGetHeadMessages(out Message now, out Message next)
+        {
+            var connection = _enqueuedTo;
+            now = next = null;
+            if (connection != null) connection.GetHeadMessages(out now, out next);
+        }
+
+        internal bool TryGetPhysicalState(out PhysicalConnection.WriteStatus ws, out PhysicalConnection.ReadStatus rs,
+            out long sentDelta, out long receivedDelta)
         {
             var connection = _enqueuedTo;
             sentDelta = receivedDelta = -1;

src/StackExchange.Redis/PhysicalConnection.cs

@@ -1414,6 +1414,7 @@ private void MatchResult(in RawResult result)
                     throw new InvalidOperationException("Received response with no message waiting: " + result.ToString());
                 msg = _writtenAwaitingResponse.Dequeue();
             }
+            _activeMessage = msg;
 
             Trace("Response to: " + msg);
             _readStatus = ReadStatus.ComputeResult;
@@ -1422,6 +1423,19 @@ private void MatchResult(in RawResult result)
                 _readStatus = ReadStatus.CompletePendingMessage;
                 msg.Complete();
             }
+
+            _activeMessage = null;
+        }
+
+        private volatile Message _activeMessage;
+
+        internal void GetHeadMessages(out Message now, out Message next)
+        {
+            now = _activeMessage;
+            lock(_writtenAwaitingResponse)
+            {
+                next = _writtenAwaitingResponse.Count == 0 ? null : _writtenAwaitingResponse.Peek();
+            }
         }
 
         partial void OnCloseEcho();