node express not executing dynamically added middleware-CodePudding

I am configuring rate-limit in my node express application. I am fetching rate limit configurations from external API and trying to configure the rate-limit middleware or trying to update middleware after getting config data but not getting success.

In app._router.stack, I can see my middleware added but express is not triggering/executing it once I call route/service.

I made one below sample so that you can try to reproduce the problem.

const app = express()

app.get('/', (req, res) => {
  res.send({msg: 'success'})
})

app.listen(4200, () => {
  
  app.use(function testMiddleware (req, res, next) { // this middleware is not executing
    console.log('hello....')
    next()
  })

  console.log(app._router.stack) // above middleware added in stack.
  console.log('Server started successfully!, Open this URL http://localhost:4200')
})

In the above example, It is the same case. If I add middleware after the server start then it is not working. and of course, it is working if I added it before the server started but this is not the case that I am trying to achieve.

Note: I want to add it after the server start. Because fetching config from external API and I have background job that fetches config in 1-5 min and if any changes then apply the setting. All things are automated and don't want to restart the server manually.

CodePudding user response：

It is adding in the stack but the stack is the real problem here. It executes the middleware in the same order which is available in the stack.

// output of console.log(app._router.stack)

Layer {
    handle: [Function: bound dispatch],
    name: 'bound dispatch',
    params: undefined,
    path: undefined,
    keys: [],
    regexp: /^\/?$/i { fast_star: false, fast_slash: false },
    route: Route { path: '/', stack: [Array], methods: [Object] }
  },
  Layer {
    handle: [Function: testMiddleware],
    name: 'testMiddleware',
    params: undefined,
    path: undefined,
    keys: [],
    regexp: /^\/?(?=\/|$)/i { fast_star: false, fast_slash: true },
    route: undefined
  }

It triggers first / routes and there is no next() that is why it is completely unreachable to testMiddleware middleware. If you add next() in / routes body then it will be able to reach middleware but that does not make sense because we need to call middleware first and then route.

so it is creating a new question, how to add dynamic middleware at the top of the route stack and I found something related to https://stackoverflow.com/a/13691542/11286367 https://stackoverflow.com/a/60332223/11286367

CodePudding user response：

You don't call next() on your first middleware, including it fixes the issue.

Could you not also just create the middleware to call a function which is redefined when you want, like so:

const app = require('express')()

var my_func = function(req, res){
  return
}

app.use(function testMiddleware (req, res, next) {
  my_func(req, res)
  next()
})

app.get('/', (req, res, next) => {
  res.send({msg: 'success'})
})

app.listen(4200, () => {
  
  my_func = function(req, res){
    console.log('hello....')
  }

  console.log(app._router.stack)
  console.log('Server started successfully!, Open this URL http://localhost:4200')
})