Using the RabbitMQ consume method in conjunction with the channel.ack function

I'm currently working on a function in TypeScript to consume messages from my RabbitMQ:

  async consume(
    queue: string,
    callback: (message: ConsumeMessage | null) => void,
  ) {
    return this.channel.consume(queue, message => {
      callback(message);
      this.channel.ack(message);
    });
  }

The this.channel.consume method takes the queue and a message with type ConsumeMessage, while this.channel.ack requires a Message type parameter from the amqlib library.

However, I ran into an issue where I get an error stating:

Argument of type 'ConsumeMessage | null' is not assignable to parameter of type 'Message'. Type 'null' is not assignable to type 'Message'.ts (2345)

whenever I try to use .ack.

I also have questions about how to handle errors effectively in this scenario.

Answer №1

The reason for that error message is because you can't substitute your custom type ConsumeMessage | null where a amqplib.Message | null is required. The TypeScript compiler can only ensure that an object conforming to Message will be passed into the callback, and it cannot guarantee the presence of your additional properties.

I'm also unsure about how to handle errors in this scenario

To address this issue, it would be advisable to include an err parameter as the first argument in your callback function. This way, you can indicate a custom error if message happens to be null, which occurs when the consumer is terminated. Assuming you are utilizing amqplib/callback_api.

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