pump & concat error handler question

[max-mapper]

pump & concat error handler question

[bcomnes]

The challenge with concat and pump is that you a split callback paths with pump and concat.

Remember the callback on pump isn't just the error handler, it's more accurately dubbed the 'stream ended' or 'stream finished' handler, where you handle the first error thrown by the pipeline, but also handle any outer callbacks with pipeline results or info.

Any in-memory writable segment should (can?) capture the result on the scope outside of the pipeline and then callback from the pump callback with it. Callbacks/events/properties of the pipeline segments should always be process in the pump callback, and never act as the exit path of the pipeline. These callbacks should always be though of, resolve and behave as if they are nested inside the pump operation.

var fs = require('fs')
var miss = require('mississippi')

let results
miss.pipe(
  fs.createReadStream('./nofile'),
  miss.concat(function (result) {
    console.log('concat', result)
    results = result
  }),
  function (err) {
    if (err) throw err
    console.log('stream ended')
    console.log(results)
  }
)

[bcomnes]

One could wire up concat stream and pump to somehow automatically pass results, but this would probably be a non-standard convention on top of the stream API. Perhaps it could be defined by pump?

[bcomnes]

Closing, but we can re-open if there are more questions.

[laduke]

Callbacks/events/properties of the pipeline segments should always be process in the pump callback, and never act as the exit path of the pipeline.

that's the answer!