Spusher API

Messages can easily be sent through the Spusher API.

To add a subscribe link, HMAC is used with SHA256 encrypted link signing.

You can create a QR code for non-mobile devices or link to it directly on mobile devices.

import { createHmac } from 'crypto';
import { URL } from 'url';
import { stringify } from 'querystring';

/**
 * Get a signed url for subscribing to a channel
 * @param {String} secret The secret for the channel
 * @param {String} channel The id of the channel
 * @param {String} [userId] Optionally link an id of the user for direct messaging
 * @param {Number} validTo The time until which this link will be valid in milliseconds elapsed since January 1, 1970
 * @returns {String}
 */
function getSignedUrl({
  secret,
  channel,
  userId,
  validTo
}) {
  const params = {
    validTo,
    ...(userId ? { userId } : {})
  };

  const digest = createHmac('sha256', secret)
  .update(channel)
  .update(Object.keys(params)
    .filter(key => key !== 'digest')
    .sort((a, b) => a.localeCompare(b))
    .map(key => params[key])
    .join('')
  )
  .digest('hex');

  const url = new URL(`/channels/${channel}`, 'https://spusher.nl');
  url.hash = '#' + stringify({
    ...params,
    digest
  });

  return url.toString();
}

Sending messages

Sending messages can be done by posting a JSON payload to the url

https://europe-west1-spusher-781ad.cloudfunctions.net/v1

import axios from 'axios';

async function sendMessage() {
  const channel = process.env.SPUSHER_CHANNEL;
  const secret = process.env.SPUSHER_SECRET;

  const api = axios.create({
    baseURL: 'https://europe-west1-spusher-781ad.cloudfunctions.net/v1',
    headers: {
      authorization: `Bearer ${secret}`
    }
  });

  try {
    await api.post(`/${channel}/post`, {
      body: 'Hello world!',
      link: '/'
    });
  }
  catch (e) {
    if (e.isAxiosError) {
      throw `Axios request to ${e.config.url} failed with ${e.toString()}`;
    } else {
      throw e;
    }
  }
}