@zijin-m/Rascal

@zijin-m/Rascal wrapper for rascal to support default publication, subscription handlers, auto republish message when confirm failed, auto ackOrNack when no error emit from your handler. only support es6+;


About

Rascal is a rich pub/sub wrapper for the excellent amqplib. One of the best things about Rascal is that make amqplib easier.

This project want to add more default features for rascal that:

* default broker error handler
* default publication event handler for success, return and error
* republish message when confirm error from rabbitMQ
* default subscription event handler for message, error and so on
* auto ackOrNack message when no error throw form handler
* ts support

Examples

$3

With a Rascal config, read more

``js
module.exports = {
vhosts: {
"/": {
connection: {
protocol: "amqp",
hostname: "127.0.0.1",
port: 5672,
user: "guest",
password: "guest",
},
queues: {
"order.save.service_b": {
assert: true,
options:{
arguments: {
"x-dead-letter-exchange": "dead_letters",
"x-dead-letter-routing-key": "order.save",
}
}
},
"dead_letters.order.save.service_b": {
assert: true
}
},
exchanges: {
order: {
type: "direct",
assert: true
},
dead_letters: {
type: "direct",
assert: true,
}
},
bindings: {
"order.save.service_b": {
source: "order",
bindingKey: "save",
destination: "order.save.service_b",
destinationType: "queue"
},
"dead_letters.order.save.service_b": {
source: "dead_letters",
bindingKey: "order.save",
destination: "dead_letters.order.save.service_b",
destinationType: "queue"
},
},
publications: {
"order.save": {
vhost: "/",
exchange: "order",
routingKey: "save"
},
},
subscriptions: {
"order.save": {
queue: "order.save.service_b",
prefetch: 1,
vhost: "/",
recovery: "deferred_retry",
redeliveries: {
limit: 10,
counter: "shared"
}
},
}
}
},
recovery: {
deferred_retry: [
{
strategy: "nack",
requeue: true,
defer: 10 * 1000
}
]
},
redeliveries: {
counters: {
shared: {
type: "inMemory",
}
}
}
};
`

$3

`js
import { Broker, Consumer } from "@zijin-m/rascal";
import config from "./config";

const broker = await Broker.create(config)
const publication = await broker.publish('order.save', 'some message')
`

when you publish message, Publication will use a failedQueue that save all failed confirm message, to retry failed messages when connection recovery event emit or interval timer success publish message that is head of failedQueue .

Note

* message push to failedQueue only rabbitMQ return error confirm event, when return return confirm event, Publication will nack message, leading to message loss if you have not configured a dead letter exchange/queue.

you can also add your event handlers by listen broker.publish returned eventemitter :

`js
publication.on('error', console.error);
publication.on('return', console.log);
publication.on('success', console.log);
`

$3

`js
import { Broker, Consumer, Message } from "@zijin-m/rascal";
import config from "./config";

class OrderSaveCousumer extends Consumer {

public readonly name = "order.save"; // set subscribe name or use new OrderSaveCousumer("order.save")

async onMessage(content: any, message: Message) {
// your code
// no need to call ackOrNack if your code success, Consumer will do this for you
}
}

const broker = await Broker.create(config)
await broker.addConsumer(new OrderSaveCousumer())

`

$3

you can write your message handler code in onMessage method,
here are a few things that can happen:

#### onMessage call completed normally

Consumer will call ackOrNack() to ack message.

#### onMessage call throw error

Consumer will call ackOrNack(error) to not ack message, leading to message loss if you have not configured a dead letter exchange/queue.

$3

if you do want to retry some times when your code throw error for network failed and other reason that can success handle this message after retry, you can config redeliveries in config file that named config.json or config.ts like examples,

`js
subscriptions: {
"order.save": {
queue: "order.save.service_b",
prefetch: 1,
vhost: "/",
recovery: "deferred_retry", // use recovery
redeliveries: {
limit: 10, // max retry time
counter: "shared"
}
},
},
// define recovery
recovery: {
deferred_retry: [
{
strategy: "nack", // nack message
requeue: true, // tell rabbitMQ to requeue requeue message
defer: 10 1000 // defer 10 1000 ms to nack message for wait other service or network to restore 。
}
]
},
redeliveries: {
counters: {
shared: {
type: "inMemory", // save timer in memory
}
}
}
`
after config, Consumer will use recovery deferred_retry to retry 10 time, each time defer 10 * 1000 ms to wait network or other make message failed reason recover. and if all 10 time failed, Consumer will ackOrNack(err) by listen redeliveries_exceeded that emitted by rascal redeliveries_exceeded, leading to message loss if you have not configured a dead letter exchange/queue.

#### Implementing your own counter

inMemory counter only save timer in memory, it will loss when restart you app,
and not so accurate in cluster mode 。If want to protect yourself from redeliveries, you need to implement your own counter backed by something like redis. read more implementing-your-own-counter.

$3

if you want to custom message by call ackOrNack your self, you can do like :

`js
class OrderSaveConsumer extends Consumer {
async onMessage(content: any, message: Message, ackOrNack: AckOrNackFn) {
// your code
// see https://github.com/guidesmiths/rascal#message-acknowledgement-and-recovery-strategies
ackOrNack(err, { strategy: 'republish', defer: 1000 });
}
}
`
when you manual call ackOrNack , Consumer` will not call it more.