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   1 # first-chunk-stream [![Build Status](https://travis-ci.org/sindresorhus/first-chunk-stream.svg?branch=master)](https://travis-ci.org/sindresorhus/first-chunk-stream)
   2
   3 > Transform the first chunk in a stream
   4
   5 Useful if you want to do something to the first chunk.
   6
   7 You can also set the minimum size of that chunk.
   8
   9
  10 ## Install
  11
  12 ```sh
  13 $ npm install --save first-chunk-stream
  14 ```
  15
  16
  17 ## Usage
  18
  19 ```js
  20 var fs = require('fs');
  21 var concat = require('concat-stream');
  22 var firstChunk = require('first-chunk-stream');
  23
  24 // unicorn.txt => unicorn rainbow
  25 // `highWaterMark: 1` means it will only read 1 byte at the time
  26 fs.createReadStream('unicorn.txt', {highWaterMark: 1})
  27         .pipe(firstChunk({minSize: 7}, function (chunk, enc, cb) {
  28                 this.push(chunk.toUpperCase());
  29                 cb();
  30         }))
  31         .pipe(concat(function (data) {
  32                 console.log(data);
  33                 //=> UNICORN rainbow
  34         }));
  35 ```
  36
  37
  38 ## API
  39
  40 ### firstChunk([options], transform)
  41
  42 #### options.minSize
  43
  44 Type: `number`
  45
  46 The minimum size of the first chunk.
  47
  48 #### transform(chunk, encoding, callback)
  49
  50 *Required*
  51 Type: `function`
  52
  53 The [function](http://nodejs.org/docs/latest/api/stream.html#stream_transform_transform_chunk_encoding_callback) that gets the first chunk.
  54
  55 ### firstChunk.ctor()
  56
  57 Instead of returning a [stream.Transform](http://nodejs.org/docs/latest/api/stream.html#stream_class_stream_transform_1) instance, `firstChunk.ctor()` returns a constructor for a custom Transform. This is useful when you want to use the same transform logic in multiple instances.
  58
  59
  60 ## License
  61
  62 MIT © [Sindre Sorhus](http://sindresorhus.com)