express-mung

Middleware for express responses.

This package allows synchronous and asynchronous transformation of an express response. This is a similar concept to the express middleware for a request but for a response. Note that the middleware is executed in LIFO order. It is implemented by monkey patching (hooking) the res.end, res.json, or res.write methods.

Getting started

$ npm install express-mung --save

Then in your middleware

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

module.exports = mung.json(my_transform);

Usage

Sample middleware (redact.js) to remove classified information.

'use strict';
const mung = require('express-mung');

/* Remove any classified information from the response. */
function redact(body, req, res) {
    if (body.secret) body.secret = '****';
    // ...
    return body;
}

module.exports = mung.json(redact);

then add to your app.js file (before the route handling middleware)

app.use(require('./redact'))

and That's all folks!

See the mocha tests for some more examples.

Reference

mung.json(fn, [options])

Transform the JSON body of the response.

fn(json, req, res) receives the JSON as an object, the req and res. It returns the modified body. If undefined is returned (i.e. nothing) then the original JSON is assumed to be modified. If null is returned, then a 204 No Content HTTP status is returned to client.

mung.jsonAsync(fn, [options])

Asynchronously transform the JSON body of the response.

fn(json, req, res) receives the JSON as an object, the req and res. It returns a promise to a modified body. The promise returns an object. If it is null then a 204 No Content is sent to the client.

mung.headers(fn)

Transform the HTTP headers of the response.

fn(req, res) receives the req and res. It should modify the header(s) and then return.

mung.headersAsync(fn)

Asynchronously transform the HTTP headers of the response.

fn(req, res) receives the req and res. It returns a promise to modify the header(s).

mung.write(fn, [options])

fn(chunk, encoding, req, res) receives the string or buffer as chunk, its encoding if applicable (null otherwise), req and res. It returns the modified body. If undefined is returned (i.e. nothing) then the original unmodified chunk is used.

Notes

• when mung.json* receives a scalar value then the content-type is switched text-plain.

• when mung.json* detects that a response has been sent, it will abort.

• sending a response while in mung.headers* is undefined behaviour and will most likely result in an error.

• when mung.write detects that a response has completed (i.e. if res.end has been called), it will abort.

• calling res.json or res.send from mung.write can lead to unexpected behavior since they end the response internally.

options

• mungError, when true the munger function is always invoked. When false (the default) the munger function is only invoked when the response is not in error.

Exception handling

mung catches any exception (synchronous, asynchronous or Promise reject) and sends an HTTP 500 response with the exception message. This is done by mung.onError(err, req, res), feel free to redefine it to your needs.

License

The MIT license

Copyright © 2015 Richard Schneider (makaretu@gmail.com)