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https://github.com/lependu/fastify-language-parser

A Fastify plugin to parse request language
https://github.com/lependu/fastify-language-parser

fastify-plugin i18n nodejs

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A Fastify plugin to parse request language

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# fastify-language-parser



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Language parser plugin for [fastify](https://github.com/fastify/fastify)



It decorates `req` object with `detectedLng` and adds `preHandler` hook for those language parsers which you specified in `order` option. Supports `cookie`, `header`, `query`, `path` and `session` parser.



## Install

```

$ npm i --save fastify-language-parser

```



## Versions



The plugin supports the following `Fastify` versions. Please refer to the corresponding branch in PR and issues.



Version | Branch | Fastify | End of Support

--------|--------|---------|---------------  

1.x | [1.x](https://github.com/lependu/fastify-language-parser/tree/1.x) | [1.x](https://github.com/fastify/fastify/tree/1.x) | EOL

2.x | [2.x](https://github.com/lependu/fastify-language-parser/tree/2.x) | [2.x](https://github.com/fastify/fastify/tree/2.x) | TBD  

3.x | [master](https://github.com/lependu/fastify-language-parser/tree/master) | [3.x](https://github.com/fastify/fastify/tree/master) | TBD  

  

## Example

```js

const fastify = require('fastify')()

const LP = require('fastify-language-parser')



fastify

  .register(LP, { order: ['query'] })

  .after(err => {

    if (err) throw err

    fastify.get('/', (req, reply) => {

      // GET /?lng=de will set req.detectedLng to 'de'

      reply.send({ detectedLng: req.detectedLng })

    })

  })

```



If you need different set of parsers for different routes, [scope](https://www.fastify.io/docs/latest/Plugins-Guide/) the routes and register this plugin in each scope where it needed.



## API



### General options



name | type | default | description

-----|------|---------|------------

**`fallbackLng`** | `{String}` | `'en'` | The default value of the `req.detectedLng` decorator.

**`order`** | `{Array}` | `[]` | Order and from where language should be detected. The last item wins. Supported values are: `cookie` `header` `path` `query` `session`.

**`supportedLngs`** | `{Array}` | `['en']` | Use this option to filter the parsed language code. If it is an empty array parsers will skip the filter step. The order of items only counts when you use `header` parser.



### Parser specific options and notes

#### header parser

Under the hood it uses [accept-language-parser](https://github.com/opentable/accept-language-parser). If `supportedLngs` does not contain any item it uses the [parse](https://github.com/opentable/accept-language-parser#parserparseacceptlanguageheader), otherwise the [pick](https://github.com/opentable/accept-language-parser) method. Latter is the only case when the order in `supportedLngs` array makes any difference, because parser will pass it to the pick method. If the pick method returns no value than the `detectedLng` decorator will not change. It parses `req.headers['accept-language']` value which provided by fastify and normally you don't need to change, but you can using the `headerDecorator` and `headerKey` options.



#### query & path parsers

Parses specified keys from `req.query` and `req.params` decorators which provided by Fastify's core [Request](https://www.fastify.io/docs/latest/Request/) object. Ususally you don't need to change them, but you can using the `pathDecorator` and `queryDecorator` options.



name | type | default | description

-----|------|---------|------------

**`pathDecorator`** | `{String}` | `'params'` | The object key which contains the params matching the URL.

**`pathKey`** | `{String}` | `lng` | The object key which contains the actual language within the `req[pathDecorator]` object.

**`queryDecorator`** | `{String}` | `'query'` | The object key which contains the parsed querystring.

**`queryKey`** | `{String}` | `lng` | The object key which contains the actual language within the querystring.



#### cookie & session parsers

If you intend to use these parsers you need to register [fastify-cookie](https://github.com/fastify/fastify-cookie) or [fastify-session](https://github.com/SerayaEryn/fastify-session) plugin respectively. This plugin does not retrieves or sets any cookie or session value but looks for the `req[decorator][key]` value specified in options. The fastify-cookie plugin provides `req.cookies` decorator by defult. If you use fastify-session plugin you need to set the `req[sessionDecorator][sessionKey]` before this plugin, which reflects your session store state changes and provides the language code value.



name | type | default | description

-----|------|---------|------------

**`cookieDecorator`** | `{String}` | `'cookies'` |  Looks for the key in
 `req[cookieDecorator]`.

**`cookieKey`** | `{String}` | `'fastifyLanguageParser'` | Parses the value of
 `req[cookieDecorator][cookieKey]`.

**`sessionDecorator`** | `{String}` | `'sessions'` | Looks for the key in
 `req[sessionDecorator]`.

**`sessionKey`** | `{String}` | `'fastifyLanguageParser'` | Parses the value of
 `req[sessionDecorator][sessionKey]`.



## License

Licensed under [MIT](./LICENSE).