Fix race during proxy closing (#13283)

p.service is written to within the Serve method. The Serve method also waits for the stopChan to be closed.

The race was between Close being called on the proxy causing Close on the service which was written to around the same time in the Serve method.

The fix is to have Serve be responsible for closing p.service.

connect/proxy/proxy.go

@@ -123,6 +123,9 @@ func (p *Proxy) Serve() error {
 			cfg = newCfg
 
 		case <-p.stopChan:
+			if p.service != nil {
+				p.service.Close()
+			}
 			return nil
 		}
 	}
@@ -153,7 +156,4 @@ func (p *Proxy) startListener(name string, l *Listener) error {
 // called only once.
 func (p *Proxy) Close() {
 	close(p.stopChan)
-	if p.service != nil {
-		p.service.Close()
-	}
 }