139 lines
4.4 KiB
Markdown
139 lines
4.4 KiB
Markdown
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# combined-stream
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A stream that emits multiple other streams one after another.
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**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`.
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- [combined-stream2](https://www.npmjs.com/package/combined-stream2): A drop-in streams2-compatible replacement for the combined-stream module.
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- [multistream](https://www.npmjs.com/package/multistream): A stream that emits multiple other streams one after another.
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## Installation
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``` bash
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npm install combined-stream
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```
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## Usage
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Here is a simple example that shows how you can use combined-stream to combine
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two files into one:
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``` javascript
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var CombinedStream = require('combined-stream');
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var fs = require('fs');
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var combinedStream = CombinedStream.create();
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combinedStream.append(fs.createReadStream('file1.txt'));
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combinedStream.append(fs.createReadStream('file2.txt'));
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combinedStream.pipe(fs.createWriteStream('combined.txt'));
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```
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While the example above works great, it will pause all source streams until
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they are needed. If you don't want that to happen, you can set `pauseStreams`
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to `false`:
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``` javascript
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var CombinedStream = require('combined-stream');
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var fs = require('fs');
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var combinedStream = CombinedStream.create({pauseStreams: false});
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combinedStream.append(fs.createReadStream('file1.txt'));
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combinedStream.append(fs.createReadStream('file2.txt'));
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combinedStream.pipe(fs.createWriteStream('combined.txt'));
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```
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However, what if you don't have all the source streams yet, or you don't want
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to allocate the resources (file descriptors, memory, etc.) for them right away?
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Well, in that case you can simply provide a callback that supplies the stream
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by calling a `next()` function:
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``` javascript
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var CombinedStream = require('combined-stream');
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var fs = require('fs');
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var combinedStream = CombinedStream.create();
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combinedStream.append(function(next) {
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next(fs.createReadStream('file1.txt'));
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});
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combinedStream.append(function(next) {
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next(fs.createReadStream('file2.txt'));
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});
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combinedStream.pipe(fs.createWriteStream('combined.txt'));
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```
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## API
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### CombinedStream.create([options])
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Returns a new combined stream object. Available options are:
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* `maxDataSize`
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* `pauseStreams`
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The effect of those options is described below.
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### combinedStream.pauseStreams = `true`
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Whether to apply back pressure to the underlaying streams. If set to `false`,
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the underlaying streams will never be paused. If set to `true`, the
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underlaying streams will be paused right after being appended, as well as when
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`delayedStream.pipe()` wants to throttle.
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### combinedStream.maxDataSize = `2 * 1024 * 1024`
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The maximum amount of bytes (or characters) to buffer for all source streams.
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If this value is exceeded, `combinedStream` emits an `'error'` event.
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### combinedStream.dataSize = `0`
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The amount of bytes (or characters) currently buffered by `combinedStream`.
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### combinedStream.append(stream)
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Appends the given `stream` to the combinedStream object. If `pauseStreams` is
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set to `true, this stream will also be paused right away.
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`streams` can also be a function that takes one parameter called `next`. `next`
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is a function that must be invoked in order to provide the `next` stream, see
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example above.
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Regardless of how the `stream` is appended, combined-stream always attaches an
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`'error'` listener to it, so you don't have to do that manually.
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Special case: `stream` can also be a String or Buffer.
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### combinedStream.write(data)
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You should not call this, `combinedStream` takes care of piping the appended
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streams into itself for you.
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### combinedStream.resume()
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Causes `combinedStream` to start drain the streams it manages. The function is
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idempotent, and also emits a `'resume'` event each time which usually goes to
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the stream that is currently being drained.
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### combinedStream.pause();
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If `combinedStream.pauseStreams` is set to `false`, this does nothing.
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Otherwise a `'pause'` event is emitted, this goes to the stream that is
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currently being drained, so you can use it to apply back pressure.
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### combinedStream.end();
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Sets `combinedStream.writable` to false, emits an `'end'` event, and removes
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all streams from the queue.
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### combinedStream.destroy();
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Same as `combinedStream.end()`, except it emits a `'close'` event instead of
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`'end'`.
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## License
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combined-stream is licensed under the MIT license.
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