add support to use custom rules defined on external node packages

[wandenberg]

Add similar support to custom rules using an interface close to the one defined by anyproxy rules.

The module needs to export a class to be initialized and respond to some methods depending on if it is to be used as a before_send or an after_body rule (raw specification on the example code bellow).

const fs = require('fs');

module.exports = class RuleModule1 {
  constructor(type, config) {
    this.type = type;
    this.action = {};
    this.trigger = { test: this.test.bind(this) };
    this.config = JSON.parse(config);
  }

  // Define if the rule should be applied or not based on the received parameters.
  // if it returns true means the rule will be applied, otherwise means the rule will be skipped
  test(opt, ctx) {
    opt = opt || {};
    return true;
  }

  // Execute the custom code on the before_send step
  // if it returns null the request will be sent as usual
  // if it returns an object with the format { response: { statusCode: CODE, statusMessage: 'OPTIONAL status Message', headers: {}, body: 'default body' } },
  // the request will not be sent and the custom response will be used to respond the client request
  beforeSendRequest(req, res) {
    const _url = req.ctx.url||req.url_full||req.url;
    if (!_url.match(/svg/)) {
      return null;
    }

    return {
      response: {
        statusCode: 200,
        // statusMessage: 'OK',
        headers: {
          'Cache-Control': 'max-age=691200',
          'Connection': 'Keep-Alive',
          'Date': 'Sun, 01 Sep 2019 08:17:18 GMT',
        },
        body: fs.readFileSync('/images/empty.svg')
      }
    };
  }

  // Execute the custom code on the after_body step
  // if it returns null the default proxy response body will be forwarded
  // if it returns an object with the format { response: { body: 'new body' } }, the new body will be used instead of the original response body
  beforeSendResponse(req, res, body) {
    const _url = req.ctx.url||req.url_full||req.url;
    if (!_url.match(/json/)) {
      return null;
    }

    return {
      response: {
        body: Date.now() + ' HI ' + body
      }
    };
  }
};

UI changes

Creating a custom rule on the UI:

Defining the module name:

Setting custom configuration to the rule in json format: