Lab 12
Hey guys,
I'm trying to solve lab 2 in chapter 12, but I always get an error when I use the transform
in the pipeline.
Does anyone know what may be causing this error:
internal/streams/pipeline.js:27 stream.on('close', () => { ^ TypeError: stream.on is not a function at destroyer (internal/streams/pipeline.js:27:10) at internal/streams/pipeline.js:79:12 at Array.map (<anonymous>) at pipeline (internal/streams/pipeline.js:76:28) at Object.<anonymous> (/Users/joao.hortale/Dev/OpenJsCertification/LFW211/labs/ch-12/labs-2/index.js:33:1) at Module._compile (internal/modules/cjs/loader.js:999:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10) at Module.load (internal/modules/cjs/loader.js:863:32) at Function.Module._load (internal/modules/cjs/loader.js:708:14) at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12)
this is my code:
'use strict' const { Readable, Writable, Transform, PassThrough, pipeline } = require('stream') const assert = require('assert') const createWritable = () => { const sink = [] const writable = new Writable({ write(chunk, enc, cb) { sink.push(chunk.toString()) cb() } }) writable.sink = sink return writable } const readable = Readable.from(['a', 'b', 'c']) const writable = createWritable() const transform = () => { return new Transform({ objectMode: true, transform (chunk, enc, next) { chunk.toString().toUpperCase() next() } }) } pipeline(readable, transform, writable, (err) => { assert.ifError(err) assert.deepStrictEqual(writable.sink, ['A', 'B', 'C']) console.log('passed!') })
Thanks in advanced for your support.
Comments
-
I updated my code but I still have the same problem:
'use strict' const { Readable, Writable, Transform, PassThrough, pipeline } = require('stream') const assert = require('assert') const createWritable = () => { const sink = [] const writable = new Writable({ write(chunk, enc, cb) { sink.push(chunk.toString()) cb() } }) writable.sink = sink return writable } const readable = Readable.from(['a', 'b', 'c']) const writable = createWritable() const transform = () => { return new Transform({ transform (chunk, enc, next) { const uppercased = chunk.toString().toUpperCase() next(null, uppercased) } }) } pipeline(readable, transform, writable, (err) => { assert.ifError(err) assert.deepStrictEqual(writable.sink, ['A', 'B', 'C']) console.log('passed!') })
0 -
@jhortale you're passing
transform
topipeline
but it's a function (and so has noon
method).fix:
pipeline(readable, transform(), writable, ...)
2 -
@davidmarkclements said:
@jhortale you're passingtransform
topipeline
but it's a function (and so has noon
method).fix:
pipeline(readable, transform(), writable, ...)
stupid error. Thank you so much @davidmarkclements
1 -
That helped @davidmarkclements . Thanks. I was perplexed.
1 -
It works, but is it correct if I do it like this... ?
const transform = new Transform({ decodeStrings: false, transform(chunk,enc,next) { const uppercased = chunk.toUpperCase() next(null, uppercased) } })
In that case no need to change pipeline call...
0 -
@k0dard yes that would work. Using a function that returns the stream is a better pattern, as it allows for re-use.
0 -
@davidmarkclements Could you explain a bit further ? I'm not sure I understand difference in re-usability, could you give example where the one could be reused and other couldn't ?
0 -
hey @k0dard
Once a stream has been consumed, it can't be re-used.
So a key example would be something like an HTTP server, where a function (the request listener function) is called for each request
const { createReadStream } = require('fs') const { createServer } = require('http') const selfRead = createReadStream(__filename) // NOTE: DON'T DO THIS! createServer((req, res) => { selfRead.pipe(res) }).listen(3000)
This above server will only stream content on the first request.
Subsequent request will be blank.
We can fix this by creating a new stream for each request:
const { createReadStream } = require('fs') const { createServer } = require('http') const selfRead = () => createReadStream(__filename) createServer((req, res) => { selfRead().pipe(res) }).listen(3000)
1 -
Wow, didn't know that a stream can't be reused.
Thanks a lot for your answer !
0 -
np @k0dard
0 -
@davidmarkclements You saved my time, Thanks bro
0
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