EVM event does not emits correctly same Event called twice on same function call

[eduardonunesp]

The issue was reported by E11, according to Allejo

Bug

The bug happens when a Contract with an Event is called twice inside a function body, the Event is only emitted one time, let's say we have a Contract like the following:

contract SimpleStore {
  uint256 public value;

  event NewValueSet(uint256 indexed _value);

  function set(uint256 _value) public {
    value = _value;
    emit NewValueSet(value);
    emit NewValueSet(value + 1);
  }
}

If a transaction was sent to the SimpleStore contract on function set with value equals 1, only one event will be emitted with the value equals 1, and the second event with value equals 2 isn't emitted

Expected

If a transaction was sent to the SimpleStore contract on function set with a value equals 1, two events should be emitted a first one with the value of 1 and a second with the value of 2

A proof of concept can be found at: loomnetwork/loom-js#194

[enlight]

I'm 90% sure the issue is here:

func (h *EthResetHub) Publish(message pubsub.Message) int {
	h.mutex.RLock()
	defer h.mutex.RUnlock()

	count := 0
	// iterate over all subscribers, and publish messages
	for sub, unsent := range h.registry {
		if unsent {
			if sub.Match(message.Topic()) {
				count += sub.Publish(message)
				h.registry[sub] = false
			}
		}
	}

	return count
}

So once EthResetHub.Publish sends a message to a particular subscriber it won't send any other message to the subscriber until EthResetHub.Reset is called and h.registry[sub] is set to true again to indicate it hasn't received a message.

The event handler does attempt to dispatch all events:

func (ed *DefaultEventHandler) EmitBlockTx(height uint64) (err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("caught panic publishing event: %v", r)
		}
	}()
	msgs, err := ed.stash.fetch(height)
	if err != nil {
		return err
	}
	ed.ethSubscriptions.Reset()
	for _, msg := range msgs {
		emitMsg, err := json.Marshal(&msg)
		if err != nil {
			log.Default.Error("Error in event marshalling for event: %v", emitMsg)
		}
		eventData := types.EventData(*msg)
		ethMsg, err := proto.Marshal(&eventData)
		if err != nil {
			log.Default.Error("Error in event marshalling for event: %v", emitMsg)
		}

		log.Debug("sending event:", "height", height, "contract", msg.PluginName)
		if err := ed.dispatcher.Send(height, emitMsg); err != nil {
			log.Default.Error("Error sending event: height: %d; msg: %+v\n", height, msg)
		}
		contractTopic := "contract:" + msg.PluginName
		ed.subscriptions.Publish(pubsub.NewMessage(contractTopic, emitMsg))
		ed.ethSubscriptions.Publish(pubsub.NewMessage(string(ethMsg), emitMsg))
		for _, topic := range msg.Topics {
			ed.subscriptions.Publish(pubsub.NewMessage(topic, emitMsg))
			log.Debug("published WS event", "topic", topic)
		}
	}
	ed.stash.purge(height)
	return nil
}

[Sriep]

I believe this feature was introduced to fix a previous issue where the same event was being emitted for matching both account and topics. Should be able to add to #463 or fix in current master.

[eduardonunesp]

The issue above also happens when the function emits more than one event on the same function, like the issue described on loomnetwork/loom-js#146 also reproduced on loomnetwork/loom-js#194

[eduardonunesp]

Thanks for the fix @pathornteng, the loomjs PR is ready to merge loomnetwork/loom-js#194