# stream-json [![NPM version][npm-image]][npm-url]
[npm-image]: https://img.shields.io/npm/v/stream-json.svg
[npm-url]: https://npmjs.org/package/stream-json
`stream-json` is a micro-library of node.js stream components with minimal dependencies for creating custom data processors oriented on processing huge JSON files while requiring a minimal memory footprint. It can parse JSON files far exceeding available memory. Even individual primitive data items (keys, strings, and numbers) can be streamed piece-wise. Streaming SAX-inspired event-based API is included as well.
Available components:
* Streaming JSON [Parser](https://github.com/uhop/stream-json/wiki/Parser).
* It produces a SAX-like token stream.
* Optionally it can pack keys, strings, and numbers (controlled separately).
* The [main module](https://github.com/uhop/stream-json/wiki/Main-module) provides helpers to create a parser.
* Filters to edit a token stream:
* [Pick](https://github.com/uhop/stream-json/wiki/Pick) selects desired objects.
* It can produces multiple top-level objects just like in [JSON Streaming](https://en.wikipedia.org/wiki/JSON_Streaming) protocol.
* Don't forget to use [StreamValues](https://github.com/uhop/stream-json/wiki/StreamValues) when picking several subobjects!
* [Replace](https://github.com/uhop/stream-json/wiki/Replace) substitutes objects with a replacement.
* [Ignore](https://github.com/uhop/stream-json/wiki/Ignore) removes objects.
* [Filter](https://github.com/uhop/stream-json/wiki/Filter) filters tokens maintaining stream's validity.
* Streamers to produce a stream of JavaScript objects.
* [StreamValues](https://github.com/uhop/stream-json/wiki/StreamValues) can handle a stream of JSON objects.
* Useful to stream objects selected by `Pick`, or generated by other means.
* It supports [JSON Streaming](https://en.wikipedia.org/wiki/JSON_Streaming) protocol, where individual values are separated semantically (like in `"{}[]"`), or with white spaces (like in `"true 1 null"`).
* [StreamArray](https://github.com/uhop/stream-json/wiki/StreamArray) takes an array of objects and produces a stream of its components.
* It streams array components individually taking care of assembling them automatically.
* Created initially to deal with JSON files similar to [Django](https://www.djangoproject.com/)-produced database dumps.
* Only one top-level array per stream is valid!
* [StreamObject](https://github.com/uhop/stream-json/wiki/StreamObject) takes an object and produces a stream of its top-level properties.
* Only one top-level object per stream is valid!
* Essentials:
* [Assembler](https://github.com/uhop/stream-json/wiki/Assembler) interprets a token stream creating JavaScript objects.
* [Disassembler](https://github.com/uhop/stream-json/wiki/Disassembler) produces a token stream from JavaScript objects.
* [Stringer](https://github.com/uhop/stream-json/wiki/Stringer) converts a token stream back into a JSON text stream.
* [Emitter](https://github.com/uhop/stream-json/wiki/Emitter) reads a token stream and emits each token as an event.
* It can greatly simplify data processing.
* Utilities:
* [emit()](https://github.com/uhop/stream-json/wiki/emit()) makes any stream component to emit tokens as events.
* [withParser()](https://github.com/uhop/stream-json/wiki/withParser()) helps to create stream components with a parser.
* [Batch](https://github.com/uhop/stream-json/wiki/Batch) batches items into arrays to simplify their processing.
* [Verifier](https://github.com/uhop/stream-json/wiki/Verifier) reads a stream and verifies that it is a valid JSON.
* [Utf8Stream](https://github.com/uhop/stream-json/wiki/Utf8Stream) sanitizes multibyte `utf8` text input.
* Special helpers:
* JSONL AKA [JSON Lines](http://jsonlines.org/) AKA [NDJSON](http://ndjson.org/):
* [jsonl/Parser](https://github.com/uhop/stream-json/wiki/jsonl-Parser) parses a JSONL file producing objects similar to `StreamValues`.
* Useful when we know that individual items can fit in memory.
* Generally it is faster than the equivalent combination of `Parser({jsonStreaming: true})` + `StreamValues`.
* [jsonl/Stringer](https://github.com/uhop/stream-json/wiki/jsonl-Stringer) produces a JSONL file from a stream of JavaScript objects.
* Generally it is faster than the equivalent combination of `Disassembler` + `Stringer`.
All components are meant to be building blocks to create flexible custom data processing pipelines. They can be extended and/or combined with custom code. They can be used together with [stream-chain](https://www.npmjs.com/package/stream-chain) to simplify data processing.
This toolkit is distributed under New BSD license.
## Introduction
```js
const {chain} = require('stream-chain');
const {parser} = require('stream-json');
const {pick} = require('stream-json/filters/Pick');
const {ignore} = require('stream-json/filters/Ignore');
const {streamValues} = require('stream-json/streamers/StreamValues');
const fs = require('fs');
const zlib = require('zlib');
const pipeline = chain([
fs.createReadStream('sample.json.gz'),
zlib.createGunzip(),
parser(),
pick({filter: 'data'}),
ignore({filter: /\b_meta\b/i}),
streamValues(),
data => {
const value = data.value;
// keep data only for the accounting department
return value && value.department === 'accounting' ? data : null;
}
]);
let counter = 0;
pipeline.on('data', () => ++counter);
pipeline.on('end', () =>
console.log(`The accounting department has ${counter} employees.`));
```
See the full documentation in [Wiki](https://github.com/uhop/stream-json/wiki).
Companion projects:
* [stream-csv-as-json](https://www.npmjs.com/package/stream-csv-as-json) streams huge CSV files in a format compatible with `stream-json`:
rows as arrays of string values. If a header row is used, it can stream rows as objects with named fields.
## Installation
```bash
npm install --save stream-json
# or: yarn add stream-json
```
## Use
The whole library is organized as a set of small components, which can be combined to produce the most effective pipeline. All components are based on node.js
[streams](http://nodejs.org/api/stream.html), and [events](http://nodejs.org/api/events.html). They implement all required standard APIs. It is easy to add your
own components to solve your unique tasks.
The code of all components is compact and simple. Please take a look at their source code to see how things are implemented, so you can produce your own components
in no time.
Obviously, if a bug is found, or a way to simplify existing components, or new generic components are created, which can be reused in a variety of projects,
don't hesitate to open a ticket, and/or create a pull request.
## Release History
- 1.7.4 *updated dependency (`stream-chain`), bugfix: inconsistent object/array braces. Thx [Xiao Li](https://github.com/xli1000).*
- 1.7.3 *added an assembler option to treat numbers as strings.*
- 1.7.2 *added an error check for JSONL parsing. Thx [Marc-Andre Boily](https://github.com/maboily).*
- 1.7.1 *minor bugfix and improved error reporting.*
- 1.7.0 *added `utils/Utf8Stream` to sanitize `utf8` input, all parsers support it automatically. Thx [john30](https://github.com/john30) for the suggestion.*
- 1.6.1 *the technical release, no need to upgrade.*
- 1.6.0 *added `jsonl/Parser` and `jsonl/Stringer`.*
- 1.5.0 *`Disassembler` and streamers now follow `JSON.stringify()` and `JSON.parse()` protocols respectively including `replacer` and `reviver`.*
- 1.4.1 *bugfix: `Stringer` with `makeArray` should produce empty array if no input.*
- 1.4.0 *added `makeArray` functionality to `Stringer`. Thx all who asked for it!*
- 1.3.3 *bugfix: very large/infinite streams with garbage didn't fail. Thx [Arne Marschall](https://github.com/Disco1267).*
- 1.3.2 *bugfix: filters could fail with packed-only token streams. Thx [Trey Brisbane](https://github.com/treybrisbane).*
- 1.3.1 *bugfix: reverted the last bugfix in `Verifier`, a bugfix in tests, thx [Guillermo Ares](https://github.com/guillermoares).*
- 1.3.0 *added `Batch`, a bugfix in `Verifier`.*
- 1.2.1 *the technical release.*
- 1.2.0 *added `Verifier`.*
- 1.1.4 *fixed `Filter` going haywire, thx [@codebling](https://github.com/codebling).*
- 1.1.3 *fixed `Parser` streaming numbers when shouldn't, thx [Grzegorz Lachowski](https://github.com/gregolsky).*
- 1.1.2 *fixed `Stringer` not escaping some symbols, thx [Pavel Bardov](https://github.com/pbardov).*
- 1.1.1 *minor updates in docs and comments.*
- 1.1.0 *added `Disassembler`.*
- 1.0.3 *minor tweaks, added TypeScript typings and the badge.*
- 1.0.2 *minor tweaks, documentation improvements.*
- 1.0.1 *reorg to fix export problems.*
- 1.0.0 *the first 1.0 release.*
- 0.6.1 *the technical release.*
- 0.6.0 *added Stringer to convert event streams back to JSON.*
- 0.5.3 *bug fix to allow empty JSON Streaming.*
- 0.5.2 *bug fixes in `Filter`.*
- 0.5.1 *corrected README.*
- 0.5.0 *added support for [JSON Streaming](https://en.wikipedia.org/wiki/JSON_Streaming).*
- 0.4.2 *refreshed dependencies.*
- 0.4.1 *added `StreamObject` by [Sam Noedel](https://github.com/delta62).*
- 0.4.0 *new high-performant Combo component, switched to the previous parser.*
- 0.3.0 *new even faster parser, bug fixes.*
- 0.2.2 *refreshed dependencies.*
- 0.2.1 *added utilities to filter objects on the fly.*
- 0.2.0 *new faster parser, formal unit tests, added utilities to assemble objects on the fly.*
- 0.1.0 *bug fixes, more documentation.*
- 0.0.5 *bug fixes.*
- 0.0.4 *improved grammar.*
- 0.0.3 *the technical release.*
- 0.0.2 *bug fixes.*
- 0.0.1 *the initial release.*
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