fix(journal-parse): Improve idle CPU performance ZMS-109 (#597)

* optimize CPU performance, reduce amount of calls to JSON.parse

* default to needFullParse, otherwise do not do full parse

lib/imap-notifier.js

@@ -78,17 +78,39 @@ class ImapNotifier extends EventEmitter {
         this.subscriber.on('message', (channel, message) => {
             if (channel === 'wd_events') {
                 let data;
-                try {
-                    data = JSON.parse(message);
-                } catch (E) {
-                    return;
+                // if e present at beginning, check if p also is present
+                // if no p -> no json parse
+                // if p -> json parse ONLY p
+                // if e not in beginning but p is -> json parse whole
+
+                let needFullParse = true;
+
+                if (message.length === 32 && message[2] === 'e' && message[5] === '"' && message[6 + 24] === '"') {
+                    // there is only e, no p -> no need for full parse
+                    needFullParse = false;
+                }
+
+                if (!needFullParse) {
+                    // get e and continue
+                    data = { e: message.slice(6, 6 + 24) };
+                } else {
+                    // full parse
+                    try {
+                        data = JSON.parse(message);
+                    } catch (E) {
+                        return;
+                    }
                 }
-                if (data.e && !data.p) {
-                    // events without payload are scheduled, these are notifications about changes in journal
-                    scheduleDataEvent(data.e);
-                } else if (data.e) {
-                    // events with payload are triggered immediatelly, these are actions for doing something
-                    this._listeners.emit(data.e, data.p);
+
+                if (this._listeners._events[data.e]?.length > 0) {
+                    // do not schedule or fire/emit empty events
+                    if (data.e && !data.p) {
+                        // events without payload are scheduled, these are notifications about changes in journal
+                        scheduleDataEvent(data.e);
+                    } else if (data.e) {
+                        // events with payload are triggered immediatelly, these are actions for doing something
+                        this._listeners.emit(data.e, data.p);
+                    }
                 }
             }
         });