#nats #relay #proxy #forward #nats-io

bin+lib naps

NATS server proxy service to relay and forward custom topics and subjects

3 unstable releases

0.2.1 Feb 27, 2022
0.1.1 Jan 30, 2022
0.1.0 Jan 26, 2022

#2201 in Command line utilities

MIT license

666 lines

NATS proxy service

Simple tool to forward specific topics from one nats.io cluster to the same server or another. Provides support to process messages with deno Javascript or TypeScript code.


Imagine that we use nats.io to relay events for every confirmed or canceled order in our shopping platform:

./naps --source nats://aws:4222 --destination nats://aks:4222 --topics "orders.>"

If the --script flag is present, naps will spawn a Deno runtime with all v8 capabilities plus promises and all event loop goodies, allowing you to, for example, only keep the confirmed ones and relay them to the myapp.orders.confirmed. You only have to code a recv function with the following signature:

interface RecvResult {
    topic: string,
    msg: string

function recv(topic: string, data: Uint8Array): boolean | RecvResult {
    //... your code here...
  • If the function returns true, the message will be simply forwarded to the same topic. Do note that the message will end up twice in the topic
  • If the function returns false, this message will be discarded
  • Finally, when RecvResult is returned, that data will be sent over the nats wire.

Processing Example

./naps --source nats://aws:4222 --destination nats://aks:4222 --topics "myapp.v1.orders" --script "
    import { Buffer } from 'http://deno.land/x/node_buffer/index.ts';
    interface Order {
        status: 'confirmed' | 'canceled',
        user: string,
        amount: number,
        item: any
    function processOrder(data: Buffer): RecvResult {
        const orderRaw = data.toString();
        const order = JSON.parse(orderRaw) as Order;
        // Skip orders that are not confirmed
        if (order.status !== 'confirmed') {
            return false;
        return {
            topic: 'myapp.v1.orders.confirmed',
            msg: orderRaw

    function recv(topic, uint8array) {
        switch (topic) {
            case "myapp.v1.orders":
                return processOrder(Buffer.from(uint8array))
                // nothing to do...


  • Thanks to the rust community for such a good documentation and wide range of libraries which have made this journey far easier.
  • Thanks to the denoland community for pointing me into the right direction. Specially Andreu Botella, denoland contributor who patiently answered all my questions and guided me to a decent solution. Many thanks, man!


  • Support for NATS TLS connections
  • JetStream
  • Feature Sagas by allowing to return multiple RecvResult when employing deno runtime


~4.5M SLoC