This section will explain a lot of details about the events and subscriptions mechanisms. It uses only the Goblin API. But note that it’s possible to use the Xcraft API as well and in this case, you can find some informations at this section.
When subscribing to a topic for events, a simple syntax can be used in order to group multiple events to one subscription and without the use of regexes.
quest.sub(`*::${somethingId}.(added|updated)`, () => {});
This is a complete example which shows all possibilities. The character * is a
joker for [0..n] characters. The parenthesis can be used for OR condition
(with the pipe |) a bit like with a regex.
A troll can hide another
The topics are converted to regexes in the low lever layers. These regexes have
a cost because there are thousand of subscriptions and we must be sure that
every received messages are not tested against all registered regexes. A cache
organizes the regexes by small groups in order to reduce drastically the number
of calls on regex.test.
In order to have a working cache, it’s necessary that the topics use one or more IDs which will match:
/([^.:]+@[^.:]+|\.[a-z0-9]+-[a-z0-9]+-[a-z0-9]+-[a-z0-9]+-[a-z0-9]+\.)/g;
The first part of this regex looks like to a goblin ID (high level), and the second part is corresponding (in principle) to an Xcraft messages ID (low level).
The cache accesses are done in a map where the keys are the extracted IDs.
There is a particular key _ which contains all regexes that can be potentially
be called by topics with ID too. It’s specially the case when a subscription
topic begins with *. But note that there is a specific order for the regex
execution in order to prevent to fall too often in the _ case.