Some thoughts on how to make Transform streams faster.
Part of the overhead of Transform (and PassThrough) is that it is actually 2 streams, one Writable and one Readable, both with buffering and state management, which are connected together.
We could try to skip this and implement Transform as a Readable which implements the Writable interface and proxies the naming.
e.g.
class FastTransform extends Readable {
constructor(options) {
super(options)
this._writableState = {
length: 0,
needDrain: false,
ended: false,
finished: false
}
}
get writableEnded () {
return this._writableState.ended
}
get writableFinished () {
return this._writableState.finished
}
_read () {
const rState = this._readableState
const wState = this._writableState
if (!wState.needDrain) {
return
}
if (wState.length + rState.length > rState.highWaterMark) {
return
}
wState.needDrain = false
this.emit('drain')
}
write (chunk) {
const rState = this._readableState
const wState = this._writableState
const len = chunk.length
wState.length += len
this._transform(chunk, null, (err, data) => {
wState.length -= len
if (err) {
this.destroy(err)
} else if (data != null) {
this.push(data)
}
this._read()
})
wState.needDrain = wState.length + rState.length > rState.highWaterMark
return wState.needDrain
}
end () {
const wState = this._writableState
wState.ended = true
if (this._flush) {
this._flush(chunk, (err, data) => {
const wState = this._writableState
if (err) {
this.destroy(err)
} else {
if (data != null) {
this.push(data)
}
this.push(null)
wState.finished = true
this.emit('finish')
}
})
} else {
this.push(null)
wState.finished = true
this.emit('finish')
}
}
}
// TODO: Make Writable[Symbol.hasInstance] recognize `FastTransform`.Making this fully backwards compatible with Transform might be difficult.
Some thoughts on how to make
Transformstreams faster.Part of the overhead of
Transform(andPassThrough) is that it is actually 2 streams, oneWritableand oneReadable, both with buffering and state management, which are connected together.We could try to skip this and implement
Transformas aReadablewhich implements theWritableinterface and proxies the naming.e.g.
Making this fully backwards compatible with
Transformmight be difficult.