@springernature/backend-proxy

backend-proxy

Express/Connect middleware that proxies requests to a backend and renders the result.

This library has only devDependencies, and is no longer being developed.

Requirements

Supported & tested on node versions 14 - 22. Should run fine on 8.3.0+

Installation

To add backend-proxy to your project run

npm install --save @springernature/backend-proxy

Middleware

backendProxy(options)

The backend-proxy middleware will take all incoming HTTP requests and forward them to a backend service. The backend response will then be stored on the original HTTP request to be used by your application, or automatically rendered using render-backend-response. The status code from the backend will also be returned.

By default, client errors (400 - 499) are proxied to the client and server errors (500 - 599) will result in an error being raised. This behaviour can be amended by setting the interceptErrors option to true or a custom function. Using a custom function as value for the interceptErrors option; you can, for a subset of 4XX - 5XX errors, raise them rather than have them proxied to the client.

const {backendProxy} = require('@springernature/backend-proxy');

// Proxy all requests to a backend
app.use('*', backendProxy({backend: 'http://my.backend'}));
app.get('*', (req, res) => res.json(req.backendResponse));

// Proxy a specific route to a specific backend
app.use('/login', backendProxy({
    backend: 'http://other.backebd/login',
    usePath: false,
    interceptErrors: true,
    backendHeaders: ['set-cookie']
}), (req, res) => {
	res.render('login', req.backendResponse);
});

The following table describe the properties of the options object.

Property	Description	Type	Default
backend	Backend service to proxy requests to	string
requiredContentType	Backend response content type thats required to allow interception and deserialization	string	application/json
usePath	Should the incoming HTTP request's path be appended to the backend URL	boolean	true
interceptErrors	Should backend responses with HTTP 400 - 599 be intercepted and raised as express errors. If provided as a function, it takes the backendResponse as parameter and returns a boolean. This gives the frontend the flexibility to decided on a per-response status code basis.	undefined, boolean or function	undefined
key	The property on the request object that the backend response will be stored under.	string	backendResponse
backendHeaders	List of headers to copy from a Backend response to the outgoing client response (e.g. Set-Cookie...)	string[]

renderBackendResponse(options)

The renderBackendResponse renders any request which has a backendResponse on it. The backend response needs to contain a field named $config (the name can be changed) which contains the template to render, and layout if needed.

const {backendProxy, renderBackendResponse} = require('@springernature/backend-proxy');

app.use('*', backendProxy({
    backend: 'http://my.backend'
}));
app.use(renderBackendResponse());

Example backend response from http://my.backend to render the home template.

{
  "$config": {
    "template": "home"
  },
  "someField": "some value"
}

The following table describe the properties of the options object.

Property	Description	Type	Default
templateKey	The property on the backend response that contains the template named (and layout)	string	$config
key	The property on the request object that the backend response will be stored under.	string	backendResponse

mockBackendResponse(options)

Development only middleware that will match incoming requests to a json file, and if found will store it on the request under backendResponse simulating what backendProxy achieves. Note: This middleware will throw an exception if it is run in production

const {mockBackendResponse, renderBackendResponse} = require('@springernature/backend-proxy');
app.use(mockBackendResponse({
    directory: path.resolve(__dirname, 'backend-mocks')
}));
app.use(renderBackendResponse());

The following table describe the properties of the options object.

Property	Description	Type	Default
directory	Directory to look for mock files in	string
key	The property on the request object that the backend response will be stored under.	string	backendResponse

File structure

The mockBackendResponse middleware will match incoming requests to files that match $PATH_$METHOD.js or $PATH_$METHOD.json. If both a .js and .json file exist then the .js file will be used.

.
|___ get.json  # Matches the root request of http://localhost:8080/
|___ login-get.json # Matches an HTTP GET to http://localhost:8080/login
|___ logout-get.js # Matches an HTTP GET to http://localhost:8080/logout
|___ login-post.json # Matches an HTTP POST to http://localhost:8080/login
|___ sub-directory
  |____ other-get.json # Matches an HTTP GET to http://localhost:8080/sub-directory/other

Examples

A set of examples can be found can be examples directory.

Change Log

History

Support

You can have a look at the Springer Nature Frontend Playbook for an explanation of how we support our open source projects.

License

MIT

Copyright © 2019 Springer Nature

Changelog

3.0.0

17/04/2025

No change to source code.

• Now only tested on node versions 14 - 22.
• Should still run fine on 8.3.0+ but no longer tested on 8-12 so we can update testing-related dependencies.