render-stream.js
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/* @flow */
/**
* Original RenderStream implementation by Sasha Aickin (@aickin)
* Licensed under the Apache License, Version 2.0
* http://www.apache.org/licenses/LICENSE-2.0
*
* Modified by Evan You (@yyx990803)
*/
const stream = require('stream')
import { isTrue, isUndef } from 'shared/util'
import { createWriteFunction } from './write'
export default class RenderStream extends stream.Readable {
buffer: string;
render: (write: Function, done: Function) => void;
expectedSize: number;
write: Function;
next: Function;
end: Function;
done: boolean;
constructor (render: Function) {
super()
this.buffer = ''
this.render = render
this.expectedSize = 0
this.write = createWriteFunction((text, next) => {
const n = this.expectedSize
this.buffer += text
if (this.buffer.length >= n) {
this.next = next
this.pushBySize(n)
return true // we will decide when to call next
}
return false
}, err => {
this.emit('error', err)
})
this.end = () => {
this.emit('beforeEnd')
// the rendering is finished; we should push out the last of the buffer.
this.done = true
this.push(this.buffer)
}
}
pushBySize (n: number) {
const bufferToPush = this.buffer.substring(0, n)
this.buffer = this.buffer.substring(n)
this.push(bufferToPush)
}
tryRender () {
try {
this.render(this.write, this.end)
} catch (e) {
this.emit('error', e)
}
}
tryNext () {
try {
this.next()
} catch (e) {
this.emit('error', e)
}
}
_read (n: number) {
this.expectedSize = n
// it's possible that the last chunk added bumped the buffer up to > 2 * n,
// which means we will need to go through multiple read calls to drain it
// down to < n.
if (isTrue(this.done)) {
this.push(null)
return
}
if (this.buffer.length >= n) {
this.pushBySize(n)
return
}
if (isUndef(this.next)) {
// start the rendering chain.
this.tryRender()
} else {
// continue with the rendering.
this.tryNext()
}
}
}