NATS update filters on a consumer (to work around Nack bug where can't update filters on consumers)

main.go

// Change filters on a NATS consumer (workaround until nack can support this)
// No warranty. Use at your own risk. Mutates your system so do some tests before going all in.

package main

import (
	"context"
	"fmt"
	"os"
	"strings"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/nats-io/nats.go/jetstream"
)

func main() {
	// Set NATS url
	url := os.Getenv("NATS_URL")
	if url == "" {
		url = nats.DefaultURL
	}

  // Comma separated list of filters you want to change to
	filtersText := os.Getenv("FILTERS")
	if filtersText == "" {
		fmt.Println("No filters provided (comma separated list of filters)")
		return
	}

	filters := strings.Split(filtersText, ",")
	for i, filter := range filters {
		filters[i] = strings.TrimSpace(filter)
	}

	fmt.Printf("Filters: %v %v\n", filters, len(filters))

  // Connect to NATS
  nc, err := nats.Connect(url)
	if err != nil {
		panic(err)
	}
	defer nc.Drain()

	js, _ := jetstream.New(nc)

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	// Replace with your stream and consumer names
	streamName := "all-requests"
	consumerName := "specific-requests"

	// Retrieve the consumer configuration

	// Get requests stream
	stream, _ := js.Stream(ctx, streamName)

	consumer, err := stream.Consumer(ctx, consumerName)
	if err != nil {
		panic(err)
	}
	consumerInfo, err := consumer.Info(ctx)
	if err != nil {
		panic(err)
	}

	consumerConfig := consumerInfo.Config

	fmt.Printf("Consumer config        : %v\n", consumerConfig)

  // Update filters on existing consumer config
	consumerConfig.FilterSubjects = filters

	fmt.Printf("Consumer config updated: %v\n", consumerConfig)

	// Update consumer
	_, err = stream.CreateOrUpdateConsumer(ctx, consumerConfig)
	if err != nil {
		panic(err)
	}
}