Introducing Nodecap

28 Mar 2014

nodecap is a node.js implementation of the ICAP protocol for dynamic HTTP proxy filtering. Configure it with a proxy such as squid to accept, reject, or modify HTTP traffer on a per-request basis.

Use Case

Squid and other HTTP proxy servers typically provide only basic levels of filtering. nodecap implements the ICAP protocol, allowing for dynamic, per-request filtering and modification of requests and responses.

Examples:

Whitelist some domains (eg http://example.com) and then dynamically graylist domains that appear frequently in the response HTML (eg example.com’s asset CDN, http://cdn.example.net).
Rewrite response content
Verify MIME types of requests/responses
Perform request-time validation against other services (anything you can do in node)

Usage

See examples/example.js for a full example.

The basics:

# server.js
var ICAPServer = require('nodecap').ICAPServer;

//  run the server
var server = new ICAPServer({
  debug: false
});
console.log('Starting ICAP server...');
server.listen(function(port) {
  console.log('ICAP server listening on port ' + port);
});

Configuration & Getting Started

Consult your proxy’s documentation to understand how to configure the proxy to talk to your ICAP server. It is recommended that you configure requests and responses to be sent to different paths (resource endpoints) on your ICAP server.

The best documentation is the example and tests, which demonstrate example ICAP requests, ICAP handling, and ICAP responses.

API Configuration

`server.options(path, next)`

Allows configuration of a given ICAP endpoint. To set the options for endpoint /squid/configured/request-path, you could use:

# server.js
server.options('/squid/configured/request-path', function(icapReq, icapRes, next) {
  icapRes.setIcapStatusCode(200);
  icapRes.setIcapHeaders({
    'Methods': 'REQMOD',
    'Preview': '128'
  });
  icapRes.writeHeaders(false);
  icapRes.end();
});

API Routing

nodecap presents an expressjs-style API where middleware can be declared and matched to requests. Instead of request URI/method combinations, the unit of matching is domains through the DomainList class, which implements an efficient matcher for squid3 whitelist/blacklist syntax. Middlware is attached to handle requests to / responses from lists of domains:

`server.request(domainList, callback)`

Adds middleware to handle a REQMOD (HTTP request modification). The callback signature is callback(icapRequest, icapResponse, httpRequest, httpResponse, next). Calling next() is optional and will continue to the next handler. Be sure to have a catch-all handler at the end. domainList can be either a DomainList instance - which allows matching request domains against a configured list - or the literal string"*" to match all requests.

server.request(whitelist, function(icapReq, icapRes, req, res) {
  if (!icapRes.hasFilter() && icapReq.hasPreview()) {
    icapRes.allowUnchanged();
    return;
  }
  icapRes.setIcapStatusCode(200);
  icapRes.setIcapHeaders(icapReq.headers);
  icapRes.setHttpMethod(req);
  icapRes.setHttpHeaders(req.headers);
  icapRes.writeHeaders(icapReq.hasBody());
  icapReq.pipe(icapRes);
})

`server.response(domainList, callback)`

Adds middleware to handle a RESPMOD (HTTP response modification). Example:

server.response(whitelist, function(icapReq, icapRes, req, res) {
  if (!icapRes.hasFilter() && icapReq.hasPreview()) {
    icapRes.allowUnchanged();
    return;
  }
  icapRes.setIcapStatusCode(200);
  icapRes.setIcapHeaders(icapReq.headers);
  icapRes.setHttpStatus(res.code);
  icapRes.setHttpHeaders(res.headers);
  icapRes.writeHeaders(icapReq.hasBody());
  icapReq.pipe(icapRes);
})

`server.error(callback)`

Adds middleware to handle errors that occur either at the protocol level or within any options/request/response middleware. Example:

server.error(function(err, icapReq, icapRes, next) {
  console.error(err);
  if (!icapRes.done) {
    icapRes.setIcapStatusCode(500);
    icapRes.writeHeaders(false);
    icapRes.end();
  }
  next();
});

License

The MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Nodecap2