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
- 60 LFX Mentorship
- 113 LFX Mentorship: Linux Kernel
- 618 Linux Foundation IT Professional Programs
- 321 Cloud Engineer IT Professional Program
- 142 Advanced Cloud Engineer IT Professional Program
- 55 DevOps Engineer IT Professional Program
- 68 Cloud Native Developer IT Professional Program
- 6 Express Training Courses
- 6 Express Courses - Discussion Forum
- 2.3K Training Courses
- 19 LFC110 Class Forum - Discontinued
- 9 LFC131 Class Forum
- 31 LFD102 Class Forum
- 176 LFD103 Class Forum
- 22 LFD121 Class Forum
- 2 LFD137 Class Forum
- 61 LFD201 Class Forum
- 2 LFD210 Class Forum
- 1 LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum - Discontinued
- LFD237 Class Forum
- 23 LFD254 Class Forum
- 653 LFD259 Class Forum
- 108 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 4 LFD273 Class Forum
- 2 LFS145 Class Forum
- 28 LFS200 Class Forum
- 740 LFS201 Class Forum - Discontinued
- 1 LFS201-JP クラス フォーラム
- 12 LFS203 Class Forum
- 92 LFS207 Class Forum
- 301 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 37 LFS243 Class Forum
- 12 LFS244 Class Forum
- 41 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 142 LFS253 Class Forum
- LFS254 Class Forum
- LFS255 Class Forum
- LFS256 Class Forum
- LFS257 Class Forum
- 1.2K LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 106 LFS260 Class Forum
- 145 LFS261 Class Forum
- 39 LFS262 Class Forum
- 83 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
- 204 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS274 Class Forum
- 3 LFS281 Class Forum
- 249 LFW211 Class Forum
- 177 LFW212 Class Forum
- 9 SKF100 Class Forum
- SKF200 Class Forum
- 907 Hardware
- 220 Drivers
- 74 I/O Devices
- 44 Monitors
- 116 Multimedia
- 210 Networking
- 102 Printers & Scanners
- 86 Storage
- 764 Linux Distributions
- 88 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 24 openSUSE
- 143 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 357 Ubuntu
- 482 Linux System Administration
- 40 Cloud Computing
- 70 Command Line/Scripting
- Github systems admin projects
- 95 Linux Security
- 80 Network Management
- 108 System Management
- 51 Web Management
- 72 Mobile Computing
- 25 Android
- 32 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 545 Off Topic
- 132 Introductions
- 223 Small Talk
- 22 Study Material
- 831 Programming and Development
- 282 Kernel Development
- 515 Software Development
- 974 Software
- 260 Applications
- 185 Command Line
- 3 Compiling/Installing
- 119 Games
- 318 Installation
- 65 All In Program
- 65 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)