Connect middleware for pub/sub using server-sent events

redis-sse.js

//
// Simple pub/sub using redis and server-sent events (EventSource)
//
// Usage:
//
//   // Attach the middleware
//   redisSse = require("redis-sse");
//   app.use(redisSse({redis: yourRedisClient}));
//
//   // Set up a subscription to a channel in your route
//   app.get("/subscribe-me", function (req, res) {
//     req.subscribe("channelName");
//   });
//
// That's it! Anything you publish to the redis channel "channelName" will
// be delivered as a server-sent event to the client.
//

exports = module.exports = function(opts) {
  return function(req, res, next) {
    req.subscribe = function(channel) {
      if(!opts.redis) {
        throw new Error("You must specify a redis client when using redisSse middleware.");
      }

      var messageCount = 0;

      req.socket.setTimeout(Infinity);

      res.statusCode = 200;
      res.setHeader("Content-Type", "text/event-stream");
      res.setHeader("Cache-Control", "no-cache");
      res.setHeader("Connection", "keep-alive");

      opts.redis.subscribe(channel);
      opts.redis.on("message", function(c, message) {
        if (c !== channel) return;

        res.write("id: " + messageCount + "\n");
        res.write("data: " + message + "\n\n");

        messageCount += 1;
      });
    };
    
    next();
  };
};