Add Redis request caching to Node.js with Express.js.

node-express-redis-cache.js

var zlib = require('zlib');
var redis = require('redis');
var redisClient = redis.createClient();
var crypto = require('crypto');

// Our custom caching write function
function cached(body, lifetime, type) {
  var key = this.req.originalUrl;
  var res = this;
  var etag, len;

  if (typeof body === 'object') {
    body = JSON.stringify(body);
  }
  zlib.gzip(body, function(err, result) {
    if (err) return;
    len = result.length;
    etag = crypto.createHash('md5').update(result).digest('hex');

    // Send the result to the client first
    res.setHeader('ETag', etag); 
    res.setHeader('Cache-Control', 'max-age=' + lifetime); 
    res.setHeader('Content-Encoding', 'gzip'); 
    res.setHeader('Content-Length', len); 
    res.setHeader('Content-Type', type); 
    res.end(result, 'binary');

    // Add the result to the Redis cache
    var hash = {
      etag: etag,
      max_age: lifetime,
      content_type: type,
      content_length: len,
      content_encoding: 'gzip'
    };

    redisClient.hmset(key + '-meta', hash, redis.print);
    redisClient.set(key + '-content', result, redis.print);
    redisClient.expire(key + '-meta', lifetime);
    redisClient.expire(key + '-content', lifetime);
  });
};

// Now configure Express to know about the caching function
var express = require('express');
var response = express.response;
response.cached = cached;

// An example of using this for a request, 300 being the number of seconds that Redis will keep it for.
function someRoute(req, res) {
  var content = "blah, blah, blah";
  res.cached(content, 300, 'text/html');
}

is this guaranteed? I'm trying to cache tweet results and the script looks neat and globally accessible.