It is not possible to use RegEx for event matching on the @EventPattern() adn @MessagePattern()

[alfredoperez]

Bug Report

.

Current behavior

It is not possible to use a RegEx for event and message patterns. This is possible when using KafkaJS library but is not possible in NestJS

Input Code

Having a controller emitting a message 'pre-notify-post'

@Post('notify-with-regex')
  async sendNotificationForRegExMatching(): Promise<any> {
    return this.client.emit('pre-notify-post', { notify: true });
  }

Also having a controller with the event handler and expecting messages that match the regular expression of /.*notify.*/ :

 @EventPattern(/.*notify.*/)
  secondEventHandler(data: any) {
    KafkaController.IS_NOTIFIED_WITH_REGEX = data.value.notify;
  }

Currently, the event handler never gets called, because the handler is not matched using regular expressions.

Expected behavior

It is expected to listen to events and messages by using RegEx patterns. This is possible in KafkaJS library and it is useful when having a set of a topic that the consumer wants to listen to.

Alternatively, you can subscribe to multiple topics at once using a RegExp:

await consumer.connect()
await consumer.subscribe({ topic: /topic-(eu|us)-.*/i })

https://kafka.js.org/docs/consuming

Possible Solution

This could be fixed by getting the matching routes.

Environment

Nest version: 6.7

[alfredoperez]

I can work on the fix for this, but I want to get your opinion first.

[kamilmysliwiec]

I'd love to see the draft PR. Would you like to create one with your idea?

[Vetm]

Any updates on this? Without this feature kafka is pretty much useless for us.

[inmativ]

I also need this feature. Some microservices need to handle different kafka topics in the same way. We have to write a separate listener for each topic.

[vviital]

Hello! Any updates? We also stuck with this.

[kuskoman]

I'm just a random with some experience in creating own microservice transport (actually at work we replaced nearly whole nest/microservices to match our needs), but i can try to implement it in free time.
@alfredoperez if i understand it correctly, this kind of pattern matching would require an array of regexes checking if given event has a regex matching it pattern.
However, unlike for string matching, which is exact, more than one regex can match one string.
What should happen (/what is currently happening in kafka in implementation you mentioned) when it is happening?

For example in case when the event is "someString", and there are 2 handlers: someHandler matching /some.*/ and string handler matching for /.*string/i. Should the first (which is first?) handler be executed, or both of them?

Sorry for mentioning, but @kamilmysliwiec how would you handle this situation? Is there any place in code when there is similiar (regex based) patter matching?

[Idan747]

Hi, any update on this?

[Jaikant]

We have a similar requirement, either the MessagePattern decorator takes in an array of strings or a regex could also work.