I'm trying to create a wrapper around child_process.spawn but I'm having
trouble understanding streams2. i know how to do this with the "old" streams
suppose I have a function BlackBox with the external api that looks like
this: (|s are pipes)
inputStream | BlackBox | outputStream
but as BlackBox is a wrapper for child_process.spawn, it'll look like this
internally
inputStream | BlackBox.Writable -> stdin -> stdout -> BlackBox.Readable |
outputStream
what I have so far is the following:
var Duplex = require('stream').Duplex
var spawn = require('child_process').spawn
var util = require('util')
util.inherits(BlackBox, Duplex)
function BlackBox () {
Duplex.call(this)
// Example process
this.proc = spawn('convert', ['-', ':-'])
var that = this
// .push(null) signifies the end of a stream?
this.proc.stdout.on('end', function () {
that.push(null)
})
}
BlackBox.prototype._write = function (chunk, encoding, callback) {
return this.proc.stdin.write(chunk, encoding, callback)
}
BlackBox.prototype._read = function (size) {
var that = this
this.proc.stdout.on('readable', function () {
var chunk = this.read(size)
if (chunk === null)
that.push('')
else
that.push(chunk)
})
}
My main questions are:
1. Am I doing this correctly? Streams as an emitter makes more sense to
me (data and end events, pause and resume), but if this is all you have to
do to create a readable and writable steam, then I understand streams2.
2. Am I handling all the backpressure correctly?
3. Am I handling the end event correclty?
4. How would I handle BlackBox.prototype.destroy()?
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