opendirSync vs opendir
Hello everyone. In ch-13, in the streaming directory content example, opendirSync(__dirname) is used as input for Readable.from() method. I wonder why it was used instead of the async opendir method? As I understand it's not recommended to use sync methods when serving HTTP responses. Was it just for demonstrative purposes? Maybe I missed something? Thanks
'use strict'
const { createServer } = require('http')
const { Readable, Transform, pipeline } = require('stream')
const { opendirSync } = require('fs')
const createEntryStream = () => {
let syntax = '[\n'
return new Transform({
writableObjectMode: true,
readableObjectMode: false,
transform (entry, enc, next) {
next(null, ${syntax} "${entry.name}"
)
syntax = ',\n'
},
final (cb) {
this.push('\n]\n')
cb()
}
})
}
createServer((req, res) => {
if (req.url !== '/') {
res.statusCode = 404
res.end('Not Found')
return
}
const dirStream = Readable.from(opendirSync(__dirname))
const entryStream = createEntryStream()
res.setHeader('Content-Type', 'application/json')
pipeline(dirStream, entryStream, res, (err) => {
if (err) console.error(err)
})
}).listen(3000)
Comments
-
hi @mmd391
As I understand it's not recommended to use sync methods when serving HTTP responses.
This is correct, and we are not using sync methods when serving HTTP responses. We're using a sync method on initialization - which is what sync methods are for - convenient init stuff.
It returns a stream (which is an asynchronous abstraction) which is then used during the request/response phase.
0 -
Hello @davidmarkclements
thank you for your reply! So, if I would use
const dirStream = Readable.from(await opendir(__dirname))
, I would not gain much and only increase the complexity of the code? Sorry, if it's a silly question.0 -
@mmd391 actually I have this wrong, I misread it. The sync op is in a request hot path - you're absolutely right
I'm updated the code to the following:
'use strict' const { createServer } = require('http') const { Readable, Transform, pipeline } = require('stream') const { opendir } = require('fs') const createEntryStream = () => { let syntax = '[\n' return new Transform({ writableObjectMode: true, readableObjectMode: false, transform (entry, enc, next) { next(null, `${syntax} "${entry.name}"`) syntax = ',\n' }, final (cb) { this.push('\n]\n') cb() } }) } createServer((req, res) => { if (req.url !== '/') { res.statusCode = 404 res.end('Not Found') return } opendir(__dirname, (err, dir) => { if (err) { res.statusCode = 500 res.end('Server Error') return } const dirStream = Readable.from(dir) const entryStream = createEntryStream() res.setHeader('Content-Type', 'application/json') pipeline(dirStream, entryStream, res, (err) => { if (err) console.error(err) }) }) }).listen(3000)
You could also use the following:
'use strict' const { createServer } = require('http') const { Readable, Transform, pipeline } = require('stream') const { opendir } = require('fs').promises const createEntryStream = () => { let syntax = '[\n' return new Transform({ writableObjectMode: true, readableObjectMode: false, transform (entry, enc, next) { next(null, `${syntax} "${entry.name}"`) syntax = ',\n' }, final (cb) { this.push('\n]\n') cb() } }) } createServer(async (req, res) => { if (req.url !== '/') { res.statusCode = 404 res.end('Not Found') return } try { const dirStream = Readable.from(await opendir(__dirname)) const entryStream = createEntryStream() res.setHeader('Content-Type', 'application/json') pipeline(dirStream, entryStream, res, (err) => { if (err) console.error(err) }) } catch (err) { res.statusCode = 500 res.end('Server Error') return } }).listen(3000)
Thanks for calling this out!
0 -
Thank you @davidmarkclements!
0
Categories
- All Categories
- 219 LFX Mentorship
- 219 LFX Mentorship: Linux Kernel
- 793 Linux Foundation IT Professional Programs
- 354 Cloud Engineer IT Professional Program
- 179 Advanced Cloud Engineer IT Professional Program
- 82 DevOps Engineer IT Professional Program
- 147 Cloud Native Developer IT Professional Program
- 138 Express Training Courses
- 138 Express Courses - Discussion Forum
- 6.2K Training Courses
- 47 LFC110 Class Forum - Discontinued
- 71 LFC131 Class Forum
- 42 LFD102 Class Forum
- 227 LFD103 Class Forum
- 19 LFD110 Class Forum
- 38 LFD121 Class Forum
- 18 LFD133 Class Forum
- 7 LFD134 Class Forum
- 18 LFD137 Class Forum
- 71 LFD201 Class Forum
- 5 LFD210 Class Forum
- 5 LFD210-CN Class Forum
- 2 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum - Discontinued
- 2 LFD233 Class Forum
- 4 LFD237 Class Forum
- 24 LFD254 Class Forum
- 697 LFD259 Class Forum
- 111 LFD272 Class Forum
- 4 LFD272-JP クラス フォーラム
- 12 LFD273 Class Forum
- 151 LFS101 Class Forum
- 1 LFS111 Class Forum
- 3 LFS112 Class Forum
- 2 LFS116 Class Forum
- 4 LFS118 Class Forum
- LFS120 Class Forum
- 7 LFS142 Class Forum
- 5 LFS144 Class Forum
- 4 LFS145 Class Forum
- 3 LFS146 Class Forum
- 3 LFS147 Class Forum
- 1 LFS148 Class Forum
- 15 LFS151 Class Forum
- 2 LFS157 Class Forum
- 31 LFS158 Class Forum
- 7 LFS162 Class Forum
- 2 LFS166 Class Forum
- 4 LFS167 Class Forum
- 3 LFS170 Class Forum
- 2 LFS171 Class Forum
- 3 LFS178 Class Forum
- 3 LFS180 Class Forum
- 2 LFS182 Class Forum
- 5 LFS183 Class Forum
- 32 LFS200 Class Forum
- 737 LFS201 Class Forum - Discontinued
- 3 LFS201-JP クラス フォーラム
- 18 LFS203 Class Forum
- 134 LFS207 Class Forum
- 2 LFS207-DE-Klassenforum
- 1 LFS207-JP クラス フォーラム
- 302 LFS211 Class Forum
- 56 LFS216 Class Forum
- 52 LFS241 Class Forum
- 48 LFS242 Class Forum
- 38 LFS243 Class Forum
- 15 LFS244 Class Forum
- 2 LFS245 Class Forum
- LFS246 Class Forum
- 49 LFS250 Class Forum
- 2 LFS250-JP クラス フォーラム
- 1 LFS251 Class Forum
- 153 LFS253 Class Forum
- 1 LFS254 Class Forum
- 1 LFS255 Class Forum
- 9 LFS256 Class Forum
- 1 LFS257 Class Forum
- 1.3K LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 119 LFS260 Class Forum
- 159 LFS261 Class Forum
- 42 LFS262 Class Forum
- 82 LFS263 Class Forum - Discontinued
- 15 LFS264 Class Forum - Discontinued
- 11 LFS266 Class Forum - Discontinued
- 24 LFS267 Class Forum
- 24 LFS268 Class Forum
- 30 LFS269 Class Forum
- LFS270 Class Forum
- 202 LFS272 Class Forum
- 2 LFS272-JP クラス フォーラム
- 1 LFS274 Class Forum
- 4 LFS281 Class Forum
- 9 LFW111 Class Forum
- 259 LFW211 Class Forum
- 181 LFW212 Class Forum
- 13 SKF100 Class Forum
- 1 SKF200 Class Forum
- 1 SKF201 Class Forum
- 796 Hardware
- 199 Drivers
- 68 I/O Devices
- 37 Monitors
- 103 Multimedia
- 174 Networking
- 91 Printers & Scanners
- 85 Storage
- 758 Linux Distributions
- 82 Debian
- 67 Fedora
- 17 Linux Mint
- 13 Mageia
- 23 openSUSE
- 148 Red Hat Enterprise
- 31 Slackware
- 13 SUSE Enterprise
- 353 Ubuntu
- 468 Linux System Administration
- 39 Cloud Computing
- 71 Command Line/Scripting
- Github systems admin projects
- 93 Linux Security
- 78 Network Management
- 102 System Management
- 47 Web Management
- 63 Mobile Computing
- 18 Android
- 33 Development
- 1.2K New to Linux
- 1K Getting Started with Linux
- 371 Off Topic
- 114 Introductions
- 174 Small Talk
- 22 Study Material
- 805 Programming and Development
- 303 Kernel Development
- 484 Software Development
- 1.8K Software
- 263 Applications
- 183 Command Line
- 3 Compiling/Installing
- 987 Games
- 317 Installation
- 97 All In Program
- 97 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)