Send pubsub metrics once the response has finished

lib/api/middlewares/pubsub-metrics.js

@@ -5,15 +5,19 @@ const MAX_LENGTH = 100;
 
 function pubSubMetrics (pubSubMetricsBackend) {
     if (!pubSubMetricsBackend.isEnabled()) {
-        return function pubSubMetricsDisabledMiddleware (req, res, next) { next(); };
+        return function pubSubMetricsDisabledMiddleware (req, res, next) {
+            next();
+        };
     }
 
     return function pubSubMetricsMiddleware (req, res, next) {
-        const data = getEventData(req, res);
+        res.on('finish', () => {
+            const { event, attributes } = getEventData(req, res);
 
-        if (data.event) {
-            pubSubMetricsBackend.sendEvent(data.event, data.attributes);
-        }
+            if (event) {
+                pubSubMetricsBackend.sendEvent(event, attributes);
+            }
+        });
 
         return next();
     };