Sails WebCache service

WebCache.js

/**
 * WebCache service.
 */

const crypto    = require('crypto');
const fs        = require('fs');
const mkdirp    = require('mkdirp');
const request   = require('request');
const urlParser = require('url');
const zlib      = require('zlib');

module.exports = {

  cacheRoot: '.tmp/webcache',

  request: function (params, callback) {

    // Extract and validate parameters.
    var url = params.url;
    var reset = !!params.reset;
    var followRedirect = !!params.followRedirect;
    if (typeof url !== 'string') return callback(new Error("Parameter 'url' must be a string."));

    // Determine cache file name from hostname and url's md5 hash,
    var hostname = urlParser.parse(url).hostname;
    var urlHash = crypto.createHash('md5').update(url, 'utf8').digest('hex');
    var cacheFileName = this.cacheRoot + '/' + hostname + '/' + urlHash + '.gz';

    // Make sure directory exists.
    mkdirp(this.cacheRoot + '/' + hostname, function (err) {
      if (err) return callback(err);
      // Check for existing cache entry.
      fs.access(cacheFileName, fs.R_OK, function (err) {
        if (err || reset) {
          // Perform actual request.
          request({
            url: url,
            followRedirect: followRedirect
          }, function (err, response, body) {
            if (err) return callback(err);
            if (!body) return callback(new Error('Empty response body'));
            // Compress response body.
            zlib.gzip(body, function (err, compressed) {
              if (err) return callback(err);
              // Write new cache entry.
              fs.writeFile(cacheFileName, compressed, function (err) {
                if (err) return callback(err);
                // Return uncompressed response body.
                return callback(null, body);
              });
            });
          });
        }
        else {
          // Read existing cache entry.
          fs.readFile(cacheFileName, function (err, compressed) {
            if (err) return callback(err);
            // Uncompress response body.
            zlib.gunzip(compressed, function (err, body) {
              if (err) return callback(err);
              // Return uncompressed response body.
              return callback(null, body);
            });
          });
        }
      });
    });

  }

};

The WebCache.request method stores the response body of HTTP requests in compressed files named .tmp/webcache/{hostname}/{urlHash}.gz