Proxy service to record requests and filter unwanted requests

proxy-record.js

var express = require('express');
var expressProxy = require('express-http-proxy');
var yakbak = require('yakbak');

/**
 * Create proxy service that caches calls
 * @param { Object } config
 * @param { string } config.serverHost - host of destination service
 * @param { number } config.port - port to provide the proxy on localhost
 * @param { string } [config.recordDir] - directory to store recordings within (default is /responses)
 * @param { string[] } [config.filteredPaths] - paths to pass-through to the destination without recording (default is [])
 * @param { boolean } [config.alwaysCallApi] - flag to pass-through all requests to destination without recording (default is false)
 */
function proxyRecorder({ serverHost, port, recordDir = '/responses', filteredPaths = [], alwaysCallApi = false }) {
  var server = yakbak(serverHost, {
    dirname: __dirname + '/' + recordDir,
    hash: hashMethod
  });

  return express()
    .use(function(req, res, next) {
      const isFiltered = filteredPaths.reduce((prev, curr) => prev || req.path.indexOf(curr) !== -1, false);
      if (isFiltered || alwaysCallApi) {
        console.info('proxy - no record, real call');
        return expressProxy(serverHost)(req, res, next);
      }
      console.info('proxy - cache record');
      return server(req, res);
    })
    .listen(port, () => {
      console.log('Running proxy for ', serverHost, ' on port ', port);
    });
}

proxyRecorder({ serverHost: 'https://aws.random.cat', port: 1236, recordDir: 'cat', filteredPaths: ['/cat'] });
proxyRecorder({ serverHost: 'https://randomfox.ca', port: 1237 });

// hashing algorithm for requests
// source: https://github.com/flickr/incoming-message-hash/
var crypto = require('crypto');
var url = require('url');

function hashMethod(req, body, algorithm, encoding) {
  var hash = createHash(algorithm);

  updateHash(hash, req);

  hash.write(body);

  return hash.digest(encoding || 'hex');
}

function createHash(algorithm) {
  return crypto.createHash(algorithm || 'md5');
}

function updateHash(hash, req) {
  var parts = url.parse(req.url, true);

  hash.update(req.httpVersion);
  hash.update(req.method);
  hash.update(parts.pathname);
  hash.update(JSON.stringify(sort(parts.query)));
  // hash.update(JSON.stringify(sort(req.headers)));
  hash.update(JSON.stringify(sort(req.trailers)));
}

function sort(obj) {
  var ret = {};

  Object.keys(obj)
    .sort()
    .forEach(function(key) {
      ret[key] = obj[key];
    });

  return ret;
}