Make slack webhooks discord compatible

webhookRelay.js

const express = require('express'),
	bodyParser = require('body-parser'),
	request = require('unirest'),
	app = express();

app.disable('x-powered-by');
app.set('env', 'production');

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

app.post('/relay/:id/:token', log, (req, res) => {
	if (!req.params.id || !req.params.token || !req.body)
		res.sendStatus(400);

	if (req.body.payload)
		req.body = JSON.parse(req.body.payload);

	for (let attachment of req.body.attachments) {
		if (!attachment.fields)
			continue;
		for (let field of attachment.fields) {
			field.title = field.title || '​';
			field.value = field.value || '​';
		}
	}

	console.log('Relaying data: ' + require('util').inspect(req.body, { depth: null }));

	request.post(`https://canary.discordapp.com/api/webhooks/${req.params.id}/${req.params.token}/slack?wait=true`)
		.type('application/json')
		.header('User-Agent', 'Webhook-Relay v1')
		.send(req.body)
		.end(response => {
			if (response.ok) {
				console.log('Relay Response: ' + require('util').inspect(response.body, { depth: null }));
				res.status(200).send(response.body);
			} else {
				console.error('Relay Error: ' + require('util').inspect(response.body, { depth: null }));
				res.sendStatus(500);
			}
		});
});

app.use((req, res) => {
	res.status(404);

	if (req.accepts('html'))
		res.send('<h1>' + req.url + ' not found</h1>');
	else if (req.accepts('json'))
		res.send({ error: 'Not found' });
	else
		res.type('txt').send('Not found');
});

function log(req, res, next) {
	console.log(`${req.method} ${req.path} from ${req.headers['x-forwarded-for'] || req.connection.remoteAddress || req.socket.remoteAddress || req.connection.socket.remoteAddress}`);
	return next();
}

app.listen(8080, '0.0.0.0', error => {
	if (error)
		return console.log(error)
	console.log('Webhook Relay online');
});

Here's a SystemD service unit file for this.

[Unit]
Description=webhookRelay.js - a Slack to Discord webhook relay for Grafana
Documentation=https://gist.github.com/brussell98/a865ecc2284e958226596accc852ee28
After=network.target

[Service]
Type=simple
User=nobody
ExecStart=/usr/bin/node /data/discordWebhookRelay/webhookRelay.js
Restart=on-failure

[Install]
WantedBy=multi-user.target

You don't really need this... Discord already converts Slack on their end. Just add /slack to the URL ie. https://discordapp.com/api/webhooks/XXXXX/XXXXXXXX/slack