https://github.com/emilbayes/pg-ipc

IPC over PostgreSQL LISTEN/NOTIFY/UNLISTEN exposed as an EventEmitter
https://github.com/emilbayes/pg-ipc

database ipc postgres pubsub

Last synced: about 2 months ago
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IPC over PostgreSQL LISTEN/NOTIFY/UNLISTEN exposed as an EventEmitter

• Host: GitHub
• URL: https://github.com/emilbayes/pg-ipc
• Owner: emilbayes
• Created: 2017-02-01T08:52:49.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2022-04-05T08:32:30.000Z (over 2 years ago)
• Last Synced: 2024-10-17T16:31:37.070Z (2 months ago)
• Topics: database, ipc, postgres, pubsub
• Language: JavaScript
• Size: 9.77 KB
• Stars: 31
• Watchers: 2
• Forks: 4
• Open Issues: 2
• Metadata Files:
  • Readme: README.md

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README

        
# `pg-ipc`

> IPC over PostgreSQL LISTEN/NOTIFY/UNLISTEN exposed as an EventEmitter

## Usage

```js

var pgIPC = require('pg-ipc')

var client = new require('pg').Client({ ... })

var ipc = pgIPC(client)

ipc.on('error', console.error)

ipc.on('end', function () {

  client.end()

})

ipc.on('someChannel', function (msg) {

  // Ignore messages from this process

  if (msg.processId === client.processID) return

  console.log(msg.payload.currentTime)

})

ipc.notify('someChannel', {currentTime: Date.now()})

// some time later ...

ipc.end()

```

## API

### `pgIPC(client)`

Instantiates a new `EventEmitter` with the appropriate hooks to automatically

`LISTEN`/`NOTIFY`/`UNLISTEN`. Note that `client` must be a `pg.Client` instance

and not a `pg.Pool`, as a single connection is required.

### `ipc.on(channel, listener)`

All the standard `EventEmitter` methods are exposed. When a listener is added to

`channel`, a `LISTEN` command is automatically issued, and `UNLISTEN` when the

number of listeners reach zero. The listener will receive the message as its

first argument. Notable properties being `channel`, `payload`, `processId`. Each

postgres `connection` is assigned a unique `processId`, which can be used to

ignore messages from the same process.

See [`EventEmitter`](https://nodejs.org/api/events.html) for more details.

Reserved channels are:

`['newListener', 'removeListener', 'notify', 'unlisten', 'listen', 'error', 'end']`

### `ipc.notify(channel[, payload])`

Alias: `ipc.send(channel[, payload])`. Send a message to `channel` with optional

`payload`. `payload` is transparently converted to JSON where appropriate.

### `ipc.end()`

Issue `UNLISTEN *` if connected, emit `end` and detach all event listeners.

Does not call `client.end()` so you can continue using the client. However,

any listeners you've issued outside outside of this module will also be detached

### Event: `listen`

Emitted when a `LISTEN` has been successfully issued. Passed `channel`

### Event: `notify`

Emitted after a notification has been successfully sent. Passed `channel` and `payload`

### Event: `unlisten`

Emitted when a `UNLISTEN` has been successfully issued. Passed `channel`

### Event: `end`

Emitted when all `LISTEN`s have been removed, but before all event listeners are removed.

### Event: `error`

Propagates any errors caused by queries on `Client`. Passed the `err` argument from

the query callback.

## Install

```sh

npm install pg-ipc

```

## License

[ISC](LICENSE.md)