system-service

Provide the basic service framework to help initial service implementation. It can be easy to inject any message framework and has built-in logging mechanism.

Contents

^Install

Install via npm:

npm install system-service --save

^Definition

const systemService = require("system-service");
const { SystemService, Logger, MessageConsumer } = systemService;

MessageConsumer

MessageConsumer is base class, which uses for connecting with SystemService. The derived class can be overwritten by the following methods:

| Method | Description | | -------- | ---------------------------------------------------------------------------------------------------------------------------- | | create | Implement to connect the 3rd party consumer (e.g. RabbitMQ, kafka, etc) with callback to this.service().processMessage | | validate | Implement custom validation for any received message. If the message is invalid, then throw exception (or external handling) | | process | Implement how to prcoess the valid message | | start | Implement to start the 3rd party consumer | | stop | Implement how to stop the 3rd party consumer to pickup any message | | cleanup | Implement any cleanup after messageConsumer's stop method is triggered | | service | Get the currency SystemService instance |

SystemService

SystemService is a message engine, which handles start and terminate the consumer by the following methods:

| Method | Description | | ------ | -------------------------------- | | start | Service start to receive message | | stop | Service stop to receive message |

Logger

logger can be used in both MessageConsumer and SystemService's derived classes this.logger.log(level, message, options)

| Parameter | Description | | --------- | -------------------------------------------------------------------------------------------- | | level | Logging level representing priorities (error, warn, info, verbose, debug, silly) | | message | message | | options | optional information |

^Diagram

• General usage: Create a dervied class as ATypeConsumer from MessageConsumer. Inside ATypeConsumer, configures it using the 3rd party consumer under create() and overrides any methods fitting for your use case.

| Layout | | --------------------------------------------------------------------------------------------------- | | |

• Inside handling

| Workflow | | ----------------------------------------------------------------------------------------------- | | |

^Get Start

• Setup message cosumer

const mq = require('amqplib/callback_api')

const URI = 'amqp://guest:guest@localhost:5672//'
const QUEUENAME = 'Demo'

const systemService = require('system-service')
const { MessageConsumer } = systemService

function errHandler (err) {
  // TODO: logging or exist program ...
}

function MQConnect (conn, queueName, handler) {
  const mQConn = function (err, ch) {
    if (err !== null) {
      errHandler(err)
    } else {
      ch.assertQueue(queueName)
      ch.consume(queueName, function (msg) {
        if (msg !== null) {
          handler(msg)s
          ch.ack(msg)
        }
      })
    }
  }
  return mQConn
}

class DemoConsumer extends MessageConsumer {
  constructor () {
    super()
    this.uri = URI
    this.queueName = QUEUENAME
    this.conn = null
    this.on_open = null
  }

  create () {
    super.create()
    mq.connect(this.uri, function (err, conn) {
      if (err !== null) {
        errHandler(err)
      } else {
        this.conn = conn

        // config the mq consume to call this.service().processMessage
        this.on_open = MQConnect(conn, this.queueName, this.service().processMessage)
      }
    })
  }

  validate (message) {
    super.validate(message)
    if ((message.cId === null) || (typeof message.cId === 'undefined')) {
      this.logger.log('error', 'message is missing cId', message)
      throw new Error('Missing Correlation Id')
    }
  }

  // process will only be called, when message is valid
  process (message) {
    super.process(message)
    // TODO: Implement handle message
    this.logger.log('verbose', 'Start process', message)
  }

  start () {
    super.start()
    const ok = this.conn.createChannel(this.on_open)

    if (ok === null) {
      errHandler(new Error('Fail: To create MQ channel'))
    }
  }
}

module.exports.DemoConsumer = DemoConsumer

• Spin up Service

const systemService = require("system-service");
const { SystemService, Logger } = systemService;

const config = { log: { config: { level: Logger.Level.error } } };
const service = new SystemService(config, new DemoConsumer());

service.start();

• Stop Service

service.stop();

^Advance

Create custom system service

• Cache : Add service cache logic
• Security : Inject the security logic and apply at consumer / use between system services communication
• Multiple services : Work with other system services (TRY NOT TO by Single Responsibility Principle)

| Layout | | ------------------------------------------------------------------------------------------------------------ | | |

^License

MIT