Utilize NestJS to consume EventPattern exclusively when the header variable matches a specific value

Question

Utilize NestJS to consume EventPattern exclusively when the header variable matches a specific value

I've been working on a NestJS project where I'm using a Kafka server to emit events and NestJS to consume them. My goal is to create a consumer with the topic my-topic that is triggered only when a specific value is present in the header variable my-header-variable.

This is what I have in mind:

@MyEventPattern('my-pattern', { 'my-header-variable': 'secret'})
function index(@Payload() data: any) {
 // ... Do it only if 'my-header-variable' == 'secret'
}

Can someone guide me on how to achieve this behavior? Perhaps there is already some existing code or solution available for this?

typescript events apache-kafka nestjs

Answer 1

Answer №1

While I have managed to create a workaround that somewhat functions, it falls short of providing a complete solution.

@EventPattern('my-pattern')
@AdditionalDecorator()
function index(@Payload() data: any) {
 // ... Only execute if 'my-header-variable' == 'secret'
}

In this approach, I introduced an additional decorator specifically tailored to work in conjunction with @EventPattern. It will return undefined if the header does not meet the expected criteria. Here is the implementation:

export const AdditionalDecorator = () => {
   return (target: any, methodName: string, descriptor: PropertyDescriptor) => {
    const originalMethod = descriptor.value;

    descriptor.value = function (data: any, context: KafkaContext) {
      const { headers } = context.getMessage();
      if (!headers || headers['my-header-variable'] !== 'secret') return undefined;      
      return originalMethod.call(this, data, context);
    };

    return descriptor;
  };
};

Although it gets the job done to some extent, I am still actively seeking a more robust and definitive solution.

Answer 2

While I have managed to create a workaround that somewhat functions, it falls short of providing a complete solution.

@EventPattern('my-pattern')
@AdditionalDecorator()
function index(@Payload() data: any) {
 // ... Only execute if 'my-header-variable' == 'secret'
}

In this approach, I introduced an additional decorator specifically tailored to work in conjunction with @EventPattern. It will return undefined if the header does not meet the expected criteria. Here is the implementation:

export const AdditionalDecorator = () => {
   return (target: any, methodName: string, descriptor: PropertyDescriptor) => {
    const originalMethod = descriptor.value;

    descriptor.value = function (data: any, context: KafkaContext) {
      const { headers } = context.getMessage();
      if (!headers || headers['my-header-variable'] !== 'secret') return undefined;      
      return originalMethod.call(this, data, context);
    };

    return descriptor;
  };
};

Although it gets the job done to some extent, I am still actively seeking a more robust and definitive solution.

Utilize NestJS to consume EventPattern exclusively when the header variable matches a specific value

Answer №1

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