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@mesg/application

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This library lets you connect to the MESG engine to listen for any event or result that you might be interested too. It also allows you to execute a task, either synchronously or asynchronously.

Contents

• Installation
• Application
  • Resolve SID
  • Listen events
  • Listen results
  • Execute task
  • Execute task and wait result

Installation

npm install @mesg/application

Application

Require mesg-js as an application:

const Application = require('@mesg/application')

const mesg = new Application()

MESG Engine endpoint

By default, the library connects to the MESG Engine from the endpoint localhost:50052.

Resolve SID

Instead of hard-coding runnerHash in your application's env, your application can resolve dynamically using the service's SID.

const runnerHash = await mesg.resolveRunner('SID_OF_THE_SERVICE')

const result = await mesg.executeTaskAndWaitResult({
  executorHash: runnerHash,
  .....
})

Listen events

Listen events from a service.

const instanceHash = await mesg.resolve('SID_OF_THE_SERVICE')

mesg.listenEvent({
  filter: {
    instanceHash: instanceHash,
    key: 'EVENT_KEY' // optional
  }
})
.on('data', (event) => {
  console.log('an event received:', event.key, mesg.decodeData(event.data))
})

Listen results

Listen results from a service.

const runnerHash = await mesg.resolveRunner('SID_OF_THE_SERVICE')

mesg.listenResult({
  filter: {
    executorHash: runnerHash,
    taskKey: 'TASK_KEY_FILTER', // optional
    tags: ['TAG_FILTER'] // optional
  }
})
.on('data', (result) => {
  if (result.error) {
    console.error('an error has occurred:', result.error)
    return
  }
  console.log('a result received:', mesg.decodeData(result.outputs))
})

Execute task

Execute task on a service.

const runnerHash = await mesg.resolveRunner('SID_OF_THE_SERVICE')

const execution = await mesg.executeTask({
  executorHash: runnerHash,
  eventHash: event.hash,
  taskKey: 'TASK_KEY',
  inputs: mesg.encodeData({ key: 'INPUT_DATA' }),
  tags: ['ASSOCIATE_TAG'] // optional
})
console.log('task in progress with execution:', execution.hash)

Execute task and wait result

Execute task on a service and wait for its result. This can be considered as a shortcut for using both executeTask() and listenResult() at same time.

const runnerHash = await mesg.resolveRunner('SID_OF_THE_SERVICE')

const result = await mesg.executeTaskAndWaitResult({
  executorHash: runnerHash,
  eventHash: event.hash,
  taskKey: 'TASK_KEY',
  inputs: mesg.encodeData({ key: 'INPUT_DATA' }),
  tags: ['ASSOCIATE_TAG'] // optional
})
if (result.error) {
  console.error('an error has occurred:', result.error)
  throw new Error(result.error)
}
console.log('a result received:', mesg.decodeData(result.outputs))