1# combined-stream 2 3A stream that emits multiple other streams one after another. 4 5**NB** Currently `combined-stream` works with streams version 1 only. There is ongoing effort to switch this library to streams version 2. Any help is welcome. :) Meanwhile you can explore other libraries that provide streams2 support with more or less compatibility with `combined-stream`. 6 7- [combined-stream2](https://www.npmjs.com/package/combined-stream2): A drop-in streams2-compatible replacement for the combined-stream module. 8 9- [multistream](https://www.npmjs.com/package/multistream): A stream that emits multiple other streams one after another. 10 11## Installation 12 13``` bash 14npm install combined-stream 15``` 16 17## Usage 18 19Here is a simple example that shows how you can use combined-stream to combine 20two files into one: 21 22``` javascript 23var CombinedStream = require('combined-stream'); 24var fs = require('fs'); 25 26var combinedStream = CombinedStream.create(); 27combinedStream.append(fs.createReadStream('file1.txt')); 28combinedStream.append(fs.createReadStream('file2.txt')); 29 30combinedStream.pipe(fs.createWriteStream('combined.txt')); 31``` 32 33While the example above works great, it will pause all source streams until 34they are needed. If you don't want that to happen, you can set `pauseStreams` 35to `false`: 36 37``` javascript 38var CombinedStream = require('combined-stream'); 39var fs = require('fs'); 40 41var combinedStream = CombinedStream.create({pauseStreams: false}); 42combinedStream.append(fs.createReadStream('file1.txt')); 43combinedStream.append(fs.createReadStream('file2.txt')); 44 45combinedStream.pipe(fs.createWriteStream('combined.txt')); 46``` 47 48However, what if you don't have all the source streams yet, or you don't want 49to allocate the resources (file descriptors, memory, etc.) for them right away? 50Well, in that case you can simply provide a callback that supplies the stream 51by calling a `next()` function: 52 53``` javascript 54var CombinedStream = require('combined-stream'); 55var fs = require('fs'); 56 57var combinedStream = CombinedStream.create(); 58combinedStream.append(function(next) { 59 next(fs.createReadStream('file1.txt')); 60}); 61combinedStream.append(function(next) { 62 next(fs.createReadStream('file2.txt')); 63}); 64 65combinedStream.pipe(fs.createWriteStream('combined.txt')); 66``` 67 68## API 69 70### CombinedStream.create([options]) 71 72Returns a new combined stream object. Available options are: 73 74* `maxDataSize` 75* `pauseStreams` 76 77The effect of those options is described below. 78 79### combinedStream.pauseStreams = `true` 80 81Whether to apply back pressure to the underlaying streams. If set to `false`, 82the underlaying streams will never be paused. If set to `true`, the 83underlaying streams will be paused right after being appended, as well as when 84`delayedStream.pipe()` wants to throttle. 85 86### combinedStream.maxDataSize = `2 * 1024 * 1024` 87 88The maximum amount of bytes (or characters) to buffer for all source streams. 89If this value is exceeded, `combinedStream` emits an `'error'` event. 90 91### combinedStream.dataSize = `0` 92 93The amount of bytes (or characters) currently buffered by `combinedStream`. 94 95### combinedStream.append(stream) 96 97Appends the given `stream` to the combinedStream object. If `pauseStreams` is 98set to `true, this stream will also be paused right away. 99 100`streams` can also be a function that takes one parameter called `next`. `next` 101is a function that must be invoked in order to provide the `next` stream, see 102example above. 103 104Regardless of how the `stream` is appended, combined-stream always attaches an 105`'error'` listener to it, so you don't have to do that manually. 106 107Special case: `stream` can also be a String or Buffer. 108 109### combinedStream.write(data) 110 111You should not call this, `combinedStream` takes care of piping the appended 112streams into itself for you. 113 114### combinedStream.resume() 115 116Causes `combinedStream` to start drain the streams it manages. The function is 117idempotent, and also emits a `'resume'` event each time which usually goes to 118the stream that is currently being drained. 119 120### combinedStream.pause(); 121 122If `combinedStream.pauseStreams` is set to `false`, this does nothing. 123Otherwise a `'pause'` event is emitted, this goes to the stream that is 124currently being drained, so you can use it to apply back pressure. 125 126### combinedStream.end(); 127 128Sets `combinedStream.writable` to false, emits an `'end'` event, and removes 129all streams from the queue. 130 131### combinedStream.destroy(); 132 133Same as `combinedStream.end()`, except it emits a `'close'` event instead of 134`'end'`. 135 136## License 137 138combined-stream is licensed under the MIT license. 139