Allow services to access Syncer objects

[anoadragon453]

Currently there is no way for services/plugins to react to events in the sync stream. We currently do so in some parts of Go-NEB, but services are not able to access it.

Passing a pointer to the syncer object to the service would allow it to listen and process any event on demand. Is this possible with the current architecture?

[alextov]

@anoadragon453 Here is how I solved this issue:

1. I forked this repository.
2. I added EventTypeHandlers(cli *gomatrix.Client) map[string]func(*gomatrix.Event) method to types.Service interface and its default no-op implementation to types.DefaultService struct.

3. In clients.go file, right after the block you referred to in your comment, I added the following:

   services, err := c.db.LoadServicesForUser(client.UserID)
   if err != nil {
       log.WithFields(log.Fields{
           log.ErrorKey:      err,
           "service_user_id": client.UserID,
       }).Warn("Error loading services")
   }
   
   for _, service := range services {
       for eventType, handler := range service.EventTypeHandlers(client) {
           syncer.OnEventType(eventType, handler)
       }
   }

4. In my main service file, I added EventTypeHandlers method implementation to my Service struct:

   // EventTypeHandlers returns custom handlers for Matrix event types.
   func (s *Service) EventTypeHandlers(client *gomatrix.Client) map[string]func(*gomatrix.Event) {
   return map[string]func(*gomatrix.Event){
       "m.room.message": func(event *gomatrix.Event) {
           // custom event handling logic goes here
       },
   }
   }

This solution works for my particular use case, but I didn’t look through the code very thoroughly and I can’t guarantee that it doesn’t break anything. Also, I have very little experience with Go. For these reasons, I didn’t want to make a pull request directly, but I hope that my snippets can be useful to someone.

[anoadragon453]

Great, good to know thanks!