64 lines
1.6 KiB
Markdown
64 lines
1.6 KiB
Markdown
# first-chunk-stream [](https://travis-ci.org/sindresorhus/first-chunk-stream)
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> Buffer and transform the n first bytes of a stream
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## Install
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```
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$ npm install --save first-chunk-stream
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```
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## Usage
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```js
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const fs = require('fs');
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const concatStream = require('concat-stream');
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const firstChunkStream = require('first-chunk-stream');
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// unicorn.txt => unicorn rainbow
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fs.createReadStream('unicorn.txt')
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.pipe(firstChunkStream({chunkLength: 7}, function (chunk, enc, cb) {
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this.push(chunk.toUpperCase());
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cb();
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}))
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.pipe(concatStream(function (data) {
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if (data.length < 7) {
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throw new Error('Couldn\'t get the minimum required first chunk length');
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}
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console.log(data);
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//=> 'UNICORN rainbow'
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}));
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```
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## API
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### firstChunkStream([options], transform)
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Returns a `FirstChunkStream` instance.
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#### options
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The options object is passed to the [`Duplex` stream](https://nodejs.org/api/stream.html#stream_class_stream_duplex) constructor allowing you to customize your stream behavior. In addition you can specify the following option:
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##### chunkLength
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Type: `number`
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How many bytes you want to buffer.
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#### transform(chunk, encoding, callback)
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Type: `function`
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The function that gets the required `options.chunkLength` bytes.
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Note that the buffer can have a smaller length than the required one. In that case, it will be due to the fact that the complete stream contents has a length less than the `òptions.chunkLength` value. You should check for this yourself if you strictly depend on the length.
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## License
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MIT © [Sindre Sorhus](http://sindresorhus.com)
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