Add middleware for outgoing messages

[slackapi]

Add middleware for outgoing messages

[curtisallen]

It would be useful to define middleware on a per matcher basis similar to express.js

router.METHOD(path, [callback, ...] callback)
You can provide multiple callbacks, and all are treated equally, and behave just like middleware

This way you could

slapp.command('/foo', myMiddleware, (msg) => {
  // do stuff
})

slapp.action('someaction', 'answer', myMiddleware, (msg) => {
 // do stuff
})

function myMiddleware(msg, next} {
  // do stuff
  next()
}

[mbrevoort]

If we would add middleware for outgoing messages, how would we distinguish from incoming middleware which is currently slapp.use.

Something like this?

slapp.useIn and slapp.useOut
or
slapp.useIncoming and slapp.useOutgoing

[mbrevoort]

Also, would this be triggered off of msg.say and msg.respond or a wrapper around slapp.client so that any call would proxy through the middleware allowing you to match in any criteria that matches certain API calls like chat.postMessage or reactions.add. If it was a proxy to slapp.client it would be a good way to capture and track metrics. Also, incoming middleware has access everything incoming as well.

[selfcontained]

more options: slapp.in() and slapp.out() - might be too vague?

[shaydewael]

In Bolt v1, we added the ability to pass a post-processing function into next() (which must call done()). Post-processing functions are called after all of the listener middleware on the way back up the execution chain (to do things like handle propagated errors)