191 lines
6.1 KiB
Markdown
191 lines
6.1 KiB
Markdown
<!-- markdownlint-disable MD013 MD024 -->
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# MQEmitter
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[](https://snyk.io/test/github/mcollina/mqemitter)
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[](http://standardjs.com/)\
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[](https://david-dm.org/mcollina/mqemitter)
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[](https://david-dm.org/mcollina/mqemitter?type=dev)\
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[](https://www.npmjs.com/mqemitter)
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[](https://www.npmjs.com/mqemitter)
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An Opinionated Message Queue with an emitter-style API, but with callbacks.
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If you need a multi process MQEmitter, check out the table below:
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- [mqemitter-redis]: Redis-powered mqemitter
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- [mqemitter-mongodb]: Mongodb based mqemitter
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- [mqemitter-child-process]: Share the same mqemitter between a hierarchy of child processes
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- [mqemitter-cs]: Expose a MQEmitter via a simple client/server protocol
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- [mqemitter-p2p]: A P2P implementation of MQEmitter, based on HyperEmitter and a Merkle DAG
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- [mqemitter-aerospike]: Aerospike mqemitter
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## Installation
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```sh
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npm install mqemitter
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```
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## Examples
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```js
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const mq = require('mqemitter')
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const emitter = mq({ concurrency: 5 })
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const message
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emitter.on('hello world', function (message, cb) {
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// call callback when you are done
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// do not pass any errors, the emitter cannot handle it.
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cb()
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})
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// topic is mandatory
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message = { topic: 'hello world', payload: 'or any other fields' }
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emitter.emit(message, function () {
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// emitter will never return an error
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})
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```
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## API
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- [new MQEmitter ([options])](#new-mqemitter-options)
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- [emitter.emit (message, callback)](#emitteremit-message-callback)
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- [emitter.on (topic, listener, [callback])](#emitteron-topic-listener-callback)
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- [emitter.removeListener (topic, listener, [callback])](#emitterremovelistener-topic-listener-callback)
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- [emitter.close (callback)](#emitterclose-callback)
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## new MQEmitter ([options])
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- options `<object>`
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- `concurrency` `<number>` maximum number of concurrent messages that can be on concurrent delivery. __Default__: `0`
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- `wildcardOne` `<string>` a char to use for matching exactly one _non-empty_ level word. __Default__: `+`
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- `wildcardSome` `<string>` a char to use for matching multiple level wildcards. __Default__: #`
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- `matchEmptyLevels` `<boolean>` If true then `wildcardOne` also matches an empty word. __Default__: `true`
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- `separator` `<string>` a separator character to use for separating words. __Default__: `/`
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Create a new MQEmitter class.
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MQEmitter is the class and function exposed by this module.
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It can be created by `MQEmitter()` or using `new MQEmitter()`.
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For more information on wildcards, see [this explanation](#wildcards) or [Qlobber](https://www.npmjs.com/qlobber).
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## emitter.emit (message, callback)
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- `message` `<object>`
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- `callback` `<Function>` `(error) => void`
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- error `<Error>` | `null`
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Emit the given message, which must have a `topic` property, which can contain wildcards as defined on creation.
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## emitter.on (topic, listener, [callback])
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- `topic` `<string>`
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- `listener` `<Function>` `(message, done) => void`
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- `callback` `<Function>` `() => void`
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Add the given listener to the passed topic. Topic can contain wildcards, as defined on creation.
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The `listener` __must never error__ and `done` must not be called with an __`err`__ object.
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`callback` will be called when the event subscribe is done correctly.
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## emitter.removeListener (topic, listener, [callback])
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The inverse of `on`.
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## emitter.close (callback)
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- `callback` `<Function>` `() => void`
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Close the given emitter. After, all writes will return an error.
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## Wildcards
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__MQEmitter__ supports the use of wildcards: every topic is splitted according to `separator`.
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The wildcard character `+` matches exactly _non-empty_ one word:
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```js
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const mq = require('mqemitter')
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const emitter = mq()
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emitter.on('hello/+/world', function(message, cb) {
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// will ONLY capture { topic: 'hello/my/world', 'something': 'more' }
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console.log(message)
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cb()
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})
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emitter.on('hello/+', function(message, cb) {
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// will not be called
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console.log(message)
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cb()
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})
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emitter.emit({ topic: 'hello/my/world', something: 'more' })
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emitter.emit({ topic: 'hello//world', something: 'more' })
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```
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The wildcard character `+` matches one word:
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```js
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const mq = require('mqemitter')
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const emitter = mq({ matchEmptyLevels: true })
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emitter.on('hello/+/world', function(message, cb) {
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// will capture { topic: 'hello/my/world', 'something': 'more' }
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// and capture { topic: 'hello//world', 'something': 'more' }
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console.log(message)
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cb()
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})
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emitter.on('hello/+', function(message, cb) {
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// will not be called
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console.log(message)
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cb()
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})
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emitter.emit({ topic: 'hello/my/world', something: 'more' })
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emitter.emit({ topic: 'hello//world', something: 'more' })
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```
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The wildcard character `#` matches zero or more words:
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```js
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const mq = require('mqemitter')
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const emitter = mq()
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emitter.on('hello/#', function(message, cb) {
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// this will print { topic: 'hello/my/world', 'something': 'more' }
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console.log(message)
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cb()
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})
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emitter.on('#', function(message, cb) {
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// this will print { topic: 'hello/my/world', 'something': 'more' }
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console.log(message)
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cb()
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})
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emitter.on('hello/my/world/#', function(message, cb) {
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// this will print { topic: 'hello/my/world', 'something': 'more' }
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console.log(message)
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cb()
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})
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emitter.emit({ topic: 'hello/my/world', something: 'more' })
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```
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Of course, you can mix `#` and `+` in the same subscription.
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## LICENSE
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MIT
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[mqemitter-redis]: https://www.npmjs.com/mqemitter-redis
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[mqemitter-mongodb]: https://www.npmjs.com/mqemitter-mongodb
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[mqemitter-child-process]: https://www.npmjs.com/mqemitter-child-process
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[mqemitter-cs]: https://www.npmjs.com/mqemitter-cs
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[mqemitter-p2p]: https://www.npmjs.com/mqemitter-p2p
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[mqemitter-aerospike]: https://www.npmjs.com/mqemitter-aerospike
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