pg-pubsub should subscribe to listeningClient.on('error')

[benjie]

Summary

If the server disconnects us; we will only know when the next select 1 runs:

graphile-engine/packages/pg-pubsub/src/index.ts

Line 181 in 9940895

client.query("select 1").catch(e => {

We should catch this issue and reconnect earlier so we miss fewer events.

Steps to reproduce

1. Set up a PostGraphile subscription.
2. Terminate the PostgreSQL backend handling this subscription.

Expected results

pg-pubsub should reconnect quickly.

Actual results

pg-pubsub only notices when the next select 1 fails (up to 25 seconds later).

Possible Solution

client.on('error', () => {releaseClient(client); if (!pgPool.ending) setupClient()})