125 lines
3.5 KiB
Markdown
125 lines
3.5 KiB
Markdown
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# minipass
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A _very_ minimal implementation of a [PassThrough
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stream](https://nodejs.org/api/stream.html#stream_class_stream_passthrough)
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[It's very
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fast](https://docs.google.com/spreadsheets/d/1oObKSrVwLX_7Ut4Z6g3fZW-AX1j1-k6w-cDsrkaSbHM/edit#gid=0)
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for objects, strings, and buffers.
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Supports pipe()ing (including multi-pipe() and backpressure
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transmission), buffering data until either a `data` event handler or
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`pipe()` is added (so you don't lose the first chunk), and most other
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cases where PassThrough is a good idea.
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There is a `read()` method, but it's much more efficient to consume
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data from this stream via `'data'` events or by calling `pipe()` into
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some other stream. Calling `read()` requires the buffer to be
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flattened in some cases, which requires copying memory.
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There is also no `unpipe()` method. Once you start piping, there is
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no stopping it!
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If you set `objectMode: true` in the options, then whatever is written
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will be emitted. Otherwise, it'll do a minimal amount of Buffer
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copying to ensure proper Streams semantics when `read(n)` is called.
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This is not a `through` or `through2` stream. It doesn't transform
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the data, it just passes it right through. If you want to transform
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the data, extend the class, and override the `write()` method. Once
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you're done transforming the data however you want, call
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`super.write()` with the transform output.
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For an example of a stream that extends MiniPass to provide transform
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capabilities, check out [minizlib](http://npm.im/minizlib).
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## USAGE
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```js
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const MiniPass = require('minipass')
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const mp = new MiniPass(options) // optional: { encoding }
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mp.write('foo')
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mp.pipe(someOtherStream)
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mp.end('bar')
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```
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### collecting
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```js
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mp.collect().then(all => {
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// all is an array of all the data emitted
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// encoding is supported in this case, so
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// so the result will be a collection of strings if
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// an encoding is specified, or buffers/objects if not.
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//
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// In an async function, you may do
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// const data = await stream.collect()
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})
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```
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### iteration
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You can iterate over streams synchronously or asynchronously in
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platforms that support it.
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Synchronous iteration will end when the currently available data is
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consumed, even if the `end` event has not been reached. In string and
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buffer mode, the data is concatenated, so unless multiple writes are
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occurring in the same tick as the `read()`, sync iteration loops will
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generally only have a single iteration.
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To consume chunks in this way exactly as they have been written, with
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no flattening, create the stream with the `{ objectMode: true }`
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option.
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```js
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const mp = new Minipass({ objectMode: true })
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mp.write('a')
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mp.write('b')
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for (let letter of mp) {
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console.log(letter) // a, b
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}
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mp.write('c')
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mp.write('d')
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for (let letter of mp) {
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console.log(letter) // c, d
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}
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mp.write('e')
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mp.end()
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for (let letter of mp) {
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console.log(letter) // e
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}
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for (let letter of mp) {
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console.log(letter) // nothing
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}
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```
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Asynchronous iteration will continue until the end event is reached,
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consuming all of the data.
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```js
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const mp = new Minipass({ encoding: 'utf8' })
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// some source of some data
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let i = 5
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const inter = setInterval(() => {
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if (i --> 0)
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mp.write(Buffer.from('foo\n', 'utf8'))
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else {
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mp.end()
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clearInterval(inter)
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}
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}, 100)
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// consume the data with asynchronous iteration
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async function consume () {
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for await (let chunk of mp) {
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console.log(chunk)
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}
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return 'ok'
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}
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consume().then(res => console.log(res))
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// logs `foo\n` 5 times, and then `ok`
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```
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