MM-34878: Add metrics for websocket reconnects (#17522)

* MM-34878: Add metrics for websocket reconnects

Added two new metrics to track successful websocket drain
and dead queue misses.

```release-note
NONE
```

https://mattermost.atlassian.net/browse/MM-34878

* remove TODO line

app/web_conn.go

@@ -34,6 +34,12 @@ const (
 	deadQueueSize          = 128            // Approximated from /proc/sys/net/core/wmem_default / 2048 (avg msg size)
 )
 
+const (
+	reconnectFound    = "success"
+	reconnectNotFound = "failure"
+	reconnectLossless = "lossless"
+)
+
 type WebConnConfig struct {
 	WebSocket    *websocket.Conn
 	Session      model.Session
@@ -304,11 +310,13 @@ func (wc *WebConn) writePump() {
 				wc.logSocketErr("websocket.drainDeadQueue", err)
 				return
 			}
+			if m := wc.App.Metrics(); m != nil {
+				m.IncrementWebsocketReconnectEvent(reconnectFound)
+			}
 		} else if wc.hasMsgLoss() {
 			// If the seq number is not in dead queue, but it was supposed to be,
 			// then generate a different connection ID,
 			// and set sequence to 0, and clear dead queue.
-			// TODO: Add metrics for this. (both true and false cases)
 			wc.clearDeadQueue()
 			wc.SetConnectionID(model.NewId())
 			wc.Sequence = 0
@@ -320,6 +328,13 @@ func (wc *WebConn) writePump() {
 				wc.logSocketErr("websocket.sendHello", err)
 				return
 			}
+			if m := wc.App.Metrics(); m != nil {
+				m.IncrementWebsocketReconnectEvent(reconnectNotFound)
+			}
+		} else {
+			if m := wc.App.Metrics(); m != nil {
+				m.IncrementWebsocketReconnectEvent(reconnectLossless)
+			}
 		}
 	}
 

einterfaces/metrics.go

@@ -43,6 +43,7 @@ type MetricsInterface interface {
 	DecrementWebSocketBroadcastBufferSize(hub string, amount float64)
 	IncrementWebSocketBroadcastUsersRegistered(hub string, amount float64)
 	DecrementWebSocketBroadcastUsersRegistered(hub string, amount float64)
+	IncrementWebsocketReconnectEvent(eventType string)
 
 	AddMemCacheHitCounter(cacheName string, amount float64)
 	AddMemCacheMissCounter(cacheName string, amount float64)

einterfaces/mocks/MetricsInterface.go

@@ -230,6 +230,11 @@ func (_m *MetricsInterface) IncrementWebsocketEvent(eventType string) {
 	_m.Called(eventType)
 }
 
+// IncrementWebsocketReconnectEvent provides a mock function with given fields: eventType
+func (_m *MetricsInterface) IncrementWebsocketReconnectEvent(eventType string) {
+	_m.Called(eventType)
+}
+
 // ObserveApiEndpointDuration provides a mock function with given fields: endpoint, method, statusCode, elapsed
 func (_m *MetricsInterface) ObserveApiEndpointDuration(endpoint string, method string, statusCode string, elapsed float64) {
 	_m.Called(endpoint, method, statusCode, elapsed)