D-Bus Proxy: addListener mulitple times (3) to the same event, emits the D-Bus signal mulitple times (3 * 3)

[ManuW]

I have a simple D-Bus service. The service has only one signal called test and the service emits every ten seconds the current date.

import * as dbus from 'dbus-next';

class MyInterface extends dbus.interface.Interface {

    /* https://github.com/dbusjs/node-dbus-next/blob/master/lib/service/interface.js#L266 */
    static configureDBusIntf() {
        MyInterface.configureMembers({
            signals: {
                test: {
                    signature: 's'
                }
            }
        });
    }

    constructor() {
        super('org.test.iface');
    }

    test(msg: string) {
        return msg;
    }
}

async function main() {
    MyInterface.configureDBusIntf();
    const example = new MyInterface();

    const bus = dbus.sessionBus();
    await bus.requestName('org.test.test', 0);
    bus.export('/org/test/test', example);

    setInterval(
        () => {
            const date = new Date();
            console.log(date);
            example.test(date.toUTCString());
        },
        10000
    );
}

main().catch((err) => {
    console.log('Error:' + err);
});

/*
$ node dist/dbus_service.js 
2021-02-16T00:17:52.457Z
2021-02-16T00:18:02.469Z
2021-02-16T00:18:12.480Z
*/

The client adds a listener to the test D-Bus signal three times => Instead of receiving the signal three times the client receives the signal nine times!

import * as dbus from 'dbus-next';

async function main() {

    const log1 = (str: string) => { console.log('1  ', str) };
    const log2 = (str: string) => { console.log(' 2 ', str) };
    const log3 = (str: string) => { console.log('  3', str) };

    const bus = dbus.sessionBus();
    const obj = await bus.getProxyObject('org.test.test', '/org/test/test');
    const testIface = obj.getInterface('org.test.iface');
    testIface.on('test', log1);
    testIface.on('test', log2);
    testIface.on('test', log3);
}

main().catch((err) => {
    console.log('Error:' + err);
});

/*
$ node dist/dbus_client.js
1   Tue, 16 Feb 2021 00:17:52 GMT
 2  Tue, 16 Feb 2021 00:17:52 GMT
  3 Tue, 16 Feb 2021 00:17:52 GMT
1   Tue, 16 Feb 2021 00:17:52 GMT
 2  Tue, 16 Feb 2021 00:17:52 GMT
  3 Tue, 16 Feb 2021 00:17:52 GMT
1   Tue, 16 Feb 2021 00:17:52 GMT
 2  Tue, 16 Feb 2021 00:17:52 GMT
  3 Tue, 16 Feb 2021 00:17:52 GMT

1   Tue, 16 Feb 2021 00:18:02 GMT
 2  Tue, 16 Feb 2021 00:18:02 GMT
  3 Tue, 16 Feb 2021 00:18:02 GMT
1   Tue, 16 Feb 2021 00:18:02 GMT
 2  Tue, 16 Feb 2021 00:18:02 GMT
  3 Tue, 16 Feb 2021 00:18:02 GMT
1   Tue, 16 Feb 2021 00:18:02 GMT
 2  Tue, 16 Feb 2021 00:18:02 GMT
  3 Tue, 16 Feb 2021 00:18:02 GMT

1   Tue, 16 Feb 2021 00:18:12 GMT
 2  Tue, 16 Feb 2021 00:18:12 GMT
  3 Tue, 16 Feb 2021 00:18:12 GMT
1   Tue, 16 Feb 2021 00:18:12 GMT
 2  Tue, 16 Feb 2021 00:18:12 GMT
  3 Tue, 16 Feb 2021 00:18:12 GMT
1   Tue, 16 Feb 2021 00:18:12 GMT
 2  Tue, 16 Feb 2021 00:18:12 GMT
  3 Tue, 16 Feb 2021 00:18:12 GMT
*/

I found a fix for this issue but maybe not the best: Simply check the amount of listeners

lib/client/proxy-interface.js

...
    this.on('removeListener', (eventName, listener) => {
      // FIX
      if (this.listeners(eventName).length > 0) {
        return;
      }

      const [signal, detailedEvent] = getEventDetails(eventName);

      if (!signal) {
        return;
      }

      if (this.$object.bus._connection.stream.writable) {
        this.$object.bus._removeMatch(this._signalMatchRuleString(eventName))
          .catch(error => {
            this.$object.bus.emit('error', error);
          });
      }
      this.$object.bus._signals.removeListener(detailedEvent, this._getEventListener(signal));
    });

    this.on('newListener', (eventName, listener) => {
      // FIX
      if (this.listeners(eventName).length > 0) {
        return;
      }

      const [signal, detailedEvent] = getEventDetails(eventName);

      if (!signal) {
        return;
      }

      this.$object.bus._addMatch(this._signalMatchRuleString(eventName))
        .catch(error => {
          this.$object.bus.emit('error', error);
        });
      this.$object.bus._signals.on(detailedEvent, this._getEventListener(signal));
    });
  }
...