Refactor DB notifications listener to support large payloads.

The listener will automatically retrieve the full payload
before passing it on to event handlers.

lib/www/server/lib/db/notify.js

@@ -1,5 +1,31 @@
-const { makeSubscriber } = require('./connection');
+const { makeSubscriber, pool } = require('./connection');
+const { ALERT, ERROR, WARNING, NOTICE, INFO, DEBUG } = require('DOUGAL_ROOT/debug')(__filename);
 
+async function fullPayload (payload) {
+
+	if (!payload.payload_id) {
+		return payload;
+	} else {
+		let client, res;
+		try {
+			client = await pool.connect();
+			const text = `SELECT payload FROM notify_payloads WHERE id = $1;`;
+			const values = [ payload.payload_id ];
+			res = await client.query(text, values);
+			res = res?.rows[0]?.payload;
+			DEBUG(`Oversize notification payload retrieved with id ${payload.payload_id} and size ${res.length}`);
+			// DEBUG(res);
+			res = JSON.parse(res);
+		} catch (err) {
+			ERROR(err);
+		} finally {
+			if (client) {
+				client.release();
+			}
+		}
+		return res;
+	}
+}
 
 async function listen (addChannels, callback) {
 
@@ -18,11 +44,11 @@ async function listen (addChannels, callback) {
 
 	for (const channel of addChannels) {
 		await client.listenTo(channel);
-		client.notifications.on(channel, (payload) => {
+		client.notifications.on(channel, async (payload) => {
 			const data = {
 				channel,
 				_received: new Date(),
-				payload
+				payload: await fullPayload(payload)
 			};
 			callback(data);
 		});