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
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