A Publish/Subscribe implementation on top of PostgreSQL NOTIFY/LISTEN
npm install pg-pubsub --saveNode.js >= 10.x Postgres >= 9.4
const PGPubsub = require('pg-pubsub');
const pubsubInstance = new PGPubsub(uri[, options]);{
[log]: Function // default: silent when NODE_ENV=production, otherwise defaults to console.log(...)
}- addChannel(channelName[, eventListener]) – starts listening on a channel and optionally adds an event listener for that event. As
PGPubsubinherits fromEventEmitterone also add it oneself. - removeChannel(channelName[, eventListener]) – either removes all event listeners and stops listeneing on the channel or removes the specified event listener and stops listening on the channel if that was the last listener attached.
- publish(channelName, data) – publishes the specified data JSON-encoded to the specified channel. It may be better to do this by sending the
NOTIFY channelName, '{"hello":"world"}'query yourself using your ordinary Postgres pool, rather than relying on the single connection of this module. Returns a Promise that will become rejected or resolved depending on the success of the Postgres call. - close(): Promise – closes down the database connection and removes all listeners. Useful for graceful shutdowns.
- All EventEmitter methods are inherited from
EventEmitter
const pubsubInstance = new PGPubsub('postgres://username@localhost/database');
pubsubInstance.addChannel('channelName', function (channelPayload) {
// Process the payload – if it was JSON that JSON has been parsed into an object for you
});
pubsubInstance.publish('channelName', { hello: "world" });The above sends NOTIFY channelName, '{"hello":"world"}' to PostgreSQL, which will trigger the above listener with the parsed JSON in channelPayload.
const pubsubInstance = new PGPubsub('postgres://username@localhost/database');
pubsubInstance.addChannel('channelName');
// pubsubInstance is a full EventEmitter object that sends events on channel names
pubsubInstance.once('channelName', function (channelPayload) {
// Process the payload
});Creating a PGPubsub instance will not do much up front. It will prepare itself to start a Postgres connection once the first channel is added and then it will keep a connection open until its shut down, reconnecting it if it gets lost, so that it can constantly listen for new notifications.
The easiest way to run tests is via Makefile on a Linux compatible environment:
make testIn case you want to run the tests manually, you first need to be able to access a PostgreSQL instance. You can do that in 2 ways:
docker run --rm -it -p 5432:5432 -e \
POSTGRES_DB=pgpubsub_test -e \
POSTGRES_PASSWORD=postgres postgresYou can create an environment file in test/.env:
DATABASE_TEST_URL=postgres://postgres:postgres@localhost:5432/postgres
DATABASE_TEST_URL_INVALID_USER=postgres://invalidUser:postgres@localhost:5432/postgres
DATABASE_TEST_URL_INVALID_PASSWORD=postgres://postgres:invalidPassword@localhost:5432/postgresOnce the PostgreSQL setup is done, you can run the test with your Node environment:
npm i
npm test