express-interceptor

raison d'etre

Born out of the need for a reliable, customized and maintenable middleware we need for Sesame CMS.

Some use cases include:

• conditionally transform any kind of response
• have access to responses after they are sent

API

npm i --save express-interceptor

var interceptor = require('express-interceptor');

app.use(interceptor(function(req,res){
  return {
    // define your custom condition to intercept this response
    //   returning `true` cause to buffer this request, and activate methods below
    //   otherwise we ignore it completely
    initerceptPredicate: function(){

    },
    // can transform the body, it's a properly encoded String, 
    //   done(err, string) param[1] will become the new response
    //   may omit secrets, erase words, append stuff, etc.
    send: function(body, done) {

    },
    // useful for caching, keeping stats, etc.
    afterSend: function(oldBody, newBody) {

    }
  };
}));

You can find many other examples at /examples folder - which also happen to be the tests.

technicalities

Express extends Node.js functionalities, that by default:

• allow setting and modifying of headers until the moment there is a write to the socket, this will submit headers.
• when initerceptPredicate returns true, we will buffer the contents, preventing .write to be called
• the whole buffer is presented to send function that can modify response headers right there, as well as return a new body that will be sent right away.
• afterSend is optional and happens on next tick.
• this package tries to be minimally obtrusive on the way Node or Express works, original write and end methods hijacked but then at the end.

similar to

• tamper Similar functionality, with different APIs.

• express-hijackresponse Have issues with cache, code is hard to maintain.

words of advice

This module is new, tests are appreciated. There might be edge cases that need fix.

Not recommended to intercept and transform big responses.

Activate debug with DEBUG=express-interceptor npm test