Address PR feedback

src/Microsoft.Diagnostics.Monitoring.WebApi/EventMonitoringPassthroughStream.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Diagnostics.Monitoring.WebApi
     /// A stream that can monitor an event stream which is compatible with <see cref="EventPipeEventSource"/>
     /// for a specific event while also passing along the event data to a destination stream.
     /// </summary>
-    public class EventMonitoringPassthroughStream : Stream
+    public sealed class EventMonitoringPassthroughStream : Stream
     {
         private readonly Action<TraceEvent> _onPayloadFilterMismatch;
         private readonly Action<TraceEvent> _onEvent;
@@ -47,7 +47,7 @@ public class EventMonitoringPassthroughStream : Stream
         /// <param name="onEvent">A callback that will be invoked each time the requested event has been observed.</param>
         /// <param name="onPayloadFilterMismatch">A callback that will be invoked if the field names specified in <paramref name="payloadFilter"/> do not match those in the event's manifest.</param>
         /// <param name="sourceStream">The source event stream which is compatible with <see cref="EventPipeEventSource"/>.</param>
-        /// <param name="destinationStream">The destination stream to write events.</param>
+        /// <param name="destinationStream">The destination stream to write events. It must either be full duplex or be write-only.</param>
         /// <param name="bufferSize">The size of the buffer to use when writing to the <paramref name="destinationStream"/>.</param>
         /// <param name="callOnEventOnlyOnce">If true, the provided <paramref name="onEvent"/> will only be called for the first matching event.</param>
         /// <param name="leaveDestinationStreamOpen">If true, the provided <paramref name="destinationStream"/> will not be automatically closed when this class is.</param>
@@ -102,19 +102,11 @@ public Task ProcessAsync(CancellationToken token)
         /// <summary>
         /// Stops monitoring for the specified stopping event. Data will continue to be written to the provided destination stream.
         /// </summary>
-        public void StopMonitoringForEvent()
+        private void StopMonitoringForEvent()
         {
             _eventSource?.Dynamic.RemoveCallback<TraceEvent>(TraceEventCallback);
         }
 
-        /// <summary>
-        /// Stops processing the event data, data will no longer be written to the provided destination stream.
-        /// </summary>
-        public void StopProcessing()
-        {
-            _eventSource?.StopProcessing();
-        }
-
         private void TraceEventCallback(TraceEvent obj)
         {
             if (_payloadFilterIndexCache == null && !HydratePayloadFilterCache(obj))
@@ -140,19 +132,28 @@ private void TraceEventCallback(TraceEvent obj)
             _onEvent(obj);
         }
 
+        /// <summary>
+        /// Hydrates the payload filter cache.
+        /// </summary>
+        /// <param name="obj">An instance of the stopping event (matching provider, task name, and opcode), but without checking the payload yet.</param>
+        /// <returns></returns>
         private bool HydratePayloadFilterCache(TraceEvent obj)
         {
             if (_payloadFilterIndexCache != null)
             {
                 return true;
             }
 
+            // If there's no payload filter, there's nothing to do.
             if (_payloadFilter == null || _payloadFilter.Count == 0)
             {
                 _payloadFilterIndexCache = new(capacity: 0);
                 return true;
             }
 
+            // If the payload has fewer fields than the requested filter, we can never match it.
+            // NOTE: this function will only ever be called with an instance of the stopping event
+            // (matching provider, task name, and opcode) but without checking the payload yet.
             if (obj.PayloadNames.Length < _payloadFilter.Count)
             {
                 return false;
@@ -167,6 +168,7 @@ private bool HydratePayloadFilterCache(TraceEvent obj)
                 }
             }
 
+            // Check if one or more of the requested filter field names did not exist on the actual payload.
             if (_payloadFilter.Count != payloadFilterCache.Count)
             {
                 return false;

src/Microsoft.Diagnostics.Monitoring.WebApi/StreamLeaveOpenWrapper.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Diagnostics.Monitoring.WebApi
     /// <summary>
     /// Wraps a given stream but leaves it open on Dispose.
     /// </summary>
-    public class StreamLeaveOpenWrapper : Stream
+    public sealed class StreamLeaveOpenWrapper : Stream
     {
         private readonly Stream _baseStream;