express-mung
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Express response transformations (or make until no good)
express-mung ![Build Status](https://travis-ci.org/richardschneider/express-prefer.svg)
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 version](https://badge.fury.io/js/express-mung.svg)
$ 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'))
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 thecontent-type
is switchedtext-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. ifres.end
has been called), it will abort. -
calling
res.json
orres.send
frommung.write
can lead to unexpected behavior since they end the response internally.
options
-
mungError
, whentrue
the munger function is always invoked. Whenfalse
(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 ([email protected])