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103 lines
3.4 KiB
103 lines
3.4 KiB
4 weeks ago
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# concat-stream
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Writable stream that concatenates all the data from a stream and calls a callback with the result. Use this when you want to collect all the data from a stream into a single buffer.
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[](https://travis-ci.org/maxogden/concat-stream)
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[](https://nodei.co/npm/concat-stream/)
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### description
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Streams emit many buffers. If you want to collect all of the buffers, and when the stream ends concatenate all of the buffers together and receive a single buffer then this is the module for you.
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Only use this if you know you can fit all of the output of your stream into a single Buffer (e.g. in RAM).
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There are also `objectMode` streams that emit things other than Buffers, and you can concatenate these too. See below for details.
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## Related
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`concat-stream` is part of the [mississippi stream utility collection](https://github.com/maxogden/mississippi) which includes more useful stream modules similar to this one.
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### examples
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#### Buffers
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```js
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var fs = require('fs')
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var concat = require('concat-stream')
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var readStream = fs.createReadStream('cat.png')
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var concatStream = concat(gotPicture)
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readStream.on('error', handleError)
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readStream.pipe(concatStream)
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function gotPicture(imageBuffer) {
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// imageBuffer is all of `cat.png` as a node.js Buffer
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}
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function handleError(err) {
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// handle your error appropriately here, e.g.:
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console.error(err) // print the error to STDERR
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process.exit(1) // exit program with non-zero exit code
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}
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```
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#### Arrays
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```js
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var write = concat(function(data) {})
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write.write([1,2,3])
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write.write([4,5,6])
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write.end()
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// data will be [1,2,3,4,5,6] in the above callback
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```
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#### Uint8Arrays
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```js
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var write = concat(function(data) {})
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var a = new Uint8Array(3)
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a[0] = 97; a[1] = 98; a[2] = 99
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write.write(a)
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write.write('!')
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write.end(Buffer.from('!!1'))
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```
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See `test/` for more examples
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# methods
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```js
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var concat = require('concat-stream')
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```
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## var writable = concat(opts={}, cb)
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Return a `writable` stream that will fire `cb(data)` with all of the data that
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was written to the stream. Data can be written to `writable` as strings,
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Buffers, arrays of byte integers, and Uint8Arrays.
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By default `concat-stream` will give you back the same data type as the type of the first buffer written to the stream. Use `opts.encoding` to set what format `data` should be returned as, e.g. if you if you don't want to rely on the built-in type checking or for some other reason.
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* `string` - get a string
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* `buffer` - get back a Buffer
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* `array` - get an array of byte integers
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* `uint8array`, `u8`, `uint8` - get back a Uint8Array
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* `object`, get back an array of Objects
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If you don't specify an encoding, and the types can't be inferred (e.g. you write things that aren't in the list above), it will try to convert concat them into a `Buffer`.
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If nothing is written to `writable` then `data` will be an empty array `[]`.
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# error handling
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`concat-stream` does not handle errors for you, so you must handle errors on whatever streams you pipe into `concat-stream`. This is a general rule when programming with node.js streams: always handle errors on each and every stream. Since `concat-stream` is not itself a stream it does not emit errors.
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We recommend using [`end-of-stream`](https://npmjs.org/end-of-stream) or [`pump`](https://npmjs.org/pump) for writing error tolerant stream code.
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# license
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MIT LICENSE
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