express-mung

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 or res.json 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) {
    // ...
    return body;
}

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) 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) 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) transform the HTTP headers of the response. fn(req, res) receives the req and res. It returns a promise to modify the header(s).

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

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

NOTE sending a response while in mung.headers* is undefined behaviour and will most likely result in an 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 ([e-mail])