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
Categories
- All Categories
- 112 LFX Mentorship
- 112 LFX Mentorship: Linux Kernel
- 604 Linux Foundation IT Professional Programs
- 315 Cloud Engineer IT Professional Program
- 139 Advanced Cloud Engineer IT Professional Program
- 52 DevOps Engineer IT Professional Program
- 67 Cloud Native Developer IT Professional Program
- 3 Express Training Courses
- 3 Express Courses - Discussion Forum
- 5.3K Training Courses
- 17 LFC110 Class Forum - Discontinued
- 8 LFC131 Class Forum
- 30 LFD102 Class Forum
- 178 LFD103 Class Forum
- LFD110 Class Forum
- 24 LFD121 Class Forum
- LFD133 Class Forum
- 2 LFD137 Class Forum
- 62 LFD201 Class Forum
- 2 LFD210 Class Forum
- 1 LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 127 LFD232 Class Forum - Discontinued
- LFD233 Class Forum
- LFD237 Class Forum
- 22 LFD254 Class Forum
- 643 LFD259 Class Forum
- 107 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 4 LFD273 Class Forum
- 1 LFS101 Class Forum
- LFS112 Class Forum
- LFS116 Class Forum
- LFS118 Class Forum
- LFS144 Class Forum
- 2 LFS145 Class Forum
- LFS151 Class Forum
- LFS157 Class Forum
- LFS158 Class Forum
- LFS162 Class Forum
- LFS167 Class Forum
- 28 LFS200 Class Forum
- 735 LFS201 Class Forum - Discontinued
- 1 LFS201-JP クラス フォーラム
- 13 LFS203 Class Forum
- 98 LFS207 Class Forum
- 299 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 36 LFS243 Class Forum
- 12 LFS244 Class Forum
- LFS245 Class Forum
- 41 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 141 LFS253 Class Forum
- LFS254 Class Forum
- LFS255 Class Forum
- 2 LFS256 Class Forum
- LFS257 Class Forum
- 1.2K LFS258 Class Forum
- 9 LFS258-JP クラス フォーラム
- 109 LFS260 Class Forum
- 144 LFS261 Class Forum
- 39 LFS262 Class Forum
- 82 LFS263 Class Forum - Discontinued
- 15 LFS264 Class Forum - Discontinued
- 11 LFS266 Class Forum - Discontinued
- 20 LFS267 Class Forum
- 18 LFS268 Class Forum
- 26 LFS269 Class Forum
- 198 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS274 Class Forum
- 3 LFS281 Class Forum
- 254 LFW211 Class Forum
- 173 LFW212 Class Forum
- 9 SKF100 Class Forum
- SKF200 Class Forum
- 781 Hardware
- 198 Drivers
- 68 I/O Devices
- 37 Monitors
- 95 Multimedia
- 174 Networking
- 87 Printers & Scanners
- 83 Storage
- 742 Linux Distributions
- 80 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 23 openSUSE
- 143 Red Hat Enterprise
- 31 Slackware
- 13 SUSE Enterprise
- 347 Ubuntu
- 450 Linux System Administration
- 31 Cloud Computing
- 69 Command Line/Scripting
- Github systems admin projects
- 89 Linux Security
- 76 Network Management
- 101 System Management
- 46 Web Management
- 51 Mobile Computing
- 18 Android
- 23 Development
- 1.2K New to Linux
- 1K Getting Started with Linux
- 355 Off Topic
- 109 Introductions
- 167 Small Talk
- 18 Study Material
- 504 Programming and Development
- 283 Kernel Development
- 203 Software Development
- 844 Software
- 210 Applications
- 180 Command Line
- 3 Compiling/Installing
- 107 Games
- 308 Installation
- 51 All In Program
- 51 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)