fix: memory leak on account of pending dials

Due to whatever reason if the endpoint is not respondind and the server
isn't able to establish a tunnelm the pending dials keep accumulating
and never get cleared.

Signed-off-by: Imran Pochi <[email protected]>

Author: ipochi

pkg/server/tunnel.go

@@ -102,6 +102,8 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	t.Server.PendingDial.Add(random, connection)
 	if err := backend.Send(dialRequest); err != nil {
 		klog.ErrorS(err, "failed to tunnel dial request", "host", r.Host, "dialID", connection.dialID, "agentID", connection.agentID)
+		t.Server.PendingDial.Remove(random)
+		metrics.Metrics.ObserveDialFailure(metrics.DialFailureBackendClose)
 		// Send proper HTTP error response
 		conn.Write([]byte(fmt.Sprintf("HTTP/1.1 502 Bad Gateway\r\nContent-Type: text/plain; charset=utf-8\r\n\r\nFailed to tunnel dial request: %v\r\n", err)))
 		conn.Close()
@@ -110,6 +112,9 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctxt := backend.Context()
 	if ctxt.Err() != nil {
 		klog.ErrorS(ctxt.Err(), "context reports failure")
+		t.Server.PendingDial.Remove(random)
+		metrics.Metrics.ObserveDialFailure(metrics.DialFailureBackendClose)
+		// Send proper HTTP error response
 		conn.Write([]byte(fmt.Sprintf("HTTP/1.1 502 Bad Gateway\r\nContent-Type: text/plain; charset=utf-8\r\n\r\nBackend context error: %v\r\n", ctxt.Err())))
 		conn.Close()
 		return
@@ -133,6 +138,10 @@ func (t *Tunnel) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		klog.V(3).InfoS("Connection established, sent 200 OK", "host", r.Host, "agentID", connection.agentID, "connectionID", connection.connectID)
 
 	case <-closed: // Connection was closed before being established
+		if t.Server.PendingDial.Remove(random) != nil {
+			metrics.Metrics.ObserveDialFailure(metrics.DialFailureFrontendClose)
+		}
+		return
 	}
 
 	defer func() {