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148 lines
3.9 KiB
148 lines
3.9 KiB
# pino-abstract-transport
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[](https://www.npmjs.com/package/pino-abstract-transport)
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[](https://github.com/pinojs/pino-abstract-transport/actions)
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[](https://coveralls.io/github/pinojs/pino-abstract-transport?branch=master)
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[](https://standardjs.com/)
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Write Pino transports easily.
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## Install
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```
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npm i pino-abstract-transport
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```
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## Usage
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```js
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import build from 'pino-abstract-transport'
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export default async function (opts) {
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return build(async function (source) {
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for await (let obj of source) {
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console.log(obj)
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}
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})
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}
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```
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or in CommonJS and streams:
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```js
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'use strict'
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const build = require('pino-abstract-transport')
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module.exports = function (opts) {
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return build(function (source) {
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source.on('data', function (obj) {
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console.log(obj)
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})
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})
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}
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```
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## Typescript usage
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Install the type definitions for node. Make sure the major version of the type definitions matches the node version you are using.
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#### Node 16
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```
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npm i -D @types/node@16
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```
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## API
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### build(fn, opts) => Stream
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Create a [`split2`](http://npm.im/split2) instance and returns it.
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This same instance is also passed to the given function, which is called
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synchronously.
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If `opts.transform` is `true`, `pino-abstract-transform` will
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wrap the split2 instance and the returned stream using [`duplexify`](https://www.npmjs.com/package/duplexify),
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so they can be concatenated into multiple transports.
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#### Events emitted
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In addition to all events emitted by a [`Readable`](https://nodejs.org/api/stream.html#stream_class_stream_readable)
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stream, it emits the following events:
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* `unknown` where an unparsable line is found, both the line and optional error is emitted.
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#### Options
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* `parse` an option to change to data format passed to build function. When this option is set to `lines`,
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the data is passed as a string, otherwise the data is passed as an object. Default: `undefined`.
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* `close(err, cb)` a function that is called to shutdown the transport. It's called both on error and non-error shutdowns.
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It can also return a promise. In this case discard the the `cb` argument.
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* `parseLine(line)` a function that is used to parse line received from `pino`.
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## Example
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### custom parseLine
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You can allow custom `parseLine` from users while providing a simple and safe default parseLine.
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```js
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'use strict'
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const build = require('pino-abstract-transport')
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function defaultParseLine (line) {
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const obj = JSON.parse(line)
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// property foo will be added on each line
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obj.foo = 'bar'
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return obj
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}
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module.exports = function (opts) {
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const parseLine = typeof opts.parseLine === 'function' ? opts.parseLine : defaultParseLine
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return build(function (source) {
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source.on('data', function (obj) {
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console.log(obj)
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})
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}, {
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parseLine: parseLine
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})
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}
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```
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### Stream concatenation / pipeline
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You can pipeline multiple transports:
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```js
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const build = require('pino-abstract-transport')
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const { Transform, pipeline } = require('stream')
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function buildTransform () {
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return build(function (source) {
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return new Transform({
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objectMode: true,
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autoDestroy: true,
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transform (line, enc, cb) {
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line.service = 'bob'
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cb(null, JSON.stringify(line))
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}
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})
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}, { enablePipelining: true })
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}
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function buildDestination () {
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return build(function (source) {
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source.on('data', function (obj) {
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console.log(obj)
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})
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})
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}
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pipeline(process.stdin, buildTransform(), buildDestination(), function (err) {
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console.log('pipeline completed!', err)
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})
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```
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## License
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MIT
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