Skip already set headers on server initialization

[hpawe01]

Hello,

I use the possibility to modify the Express server before starting it as described in https://github.com/holidayextras/jsonapi-server/blob/master/documentation/configuring.md#gaining-access-to-the-express-server

For example, I need cookie-authentication and have to add some headers:

 const app = jsonApi.getExpressServer();
 app.use(function(req, res, next) {
   res.set('Access-Control-Allow-Origin', 'http://localhost:4200');
   res.set('Access-Control-Allow-Credentials', 'true');
   return next();
 });

But the header Access-Control-Allow-Origin gets overwritten during the initialization of the json api server:

jsonapi-server/lib/router.js

Lines 23 to 30 in 368ad6b

	res.set({
	'Content-Type': 'application/vnd.api+json',
	'Access-Control-Allow-Origin': '*',
	'Access-Control-Allow-Methods': 'GET, POST, PATCH, DELETE, OPTIONS',
	'Access-Control-Allow-Headers': req.headers['access-control-request-headers'] || '',
	'Cache-Control': 'private, must-revalidate, max-age=0',
	'Expires': 'Thu, 01 Jan 1970 00:00:00'
	})

I changed it locally, so that the header is only set, when it is not already present:

if (!res.get('Access-Control-Allow-Origin')) {
  res.set('Access-Control-Allow-Origin', '*');
}

Should I prepare a pull request with this change? Or does this break something I am not aware of?

Cheers,
Friedrich

[paparomeo]

It makes sense that already set headers are not overwritten. Please feel free to submit a PR, it would be appreciated.

[hpawe01]

@paparomeo, I created a fork, implemented the check and added a test ( tests/custom-middleware.js): hpawe01@e6d3b77.

The single test succeeds (npm test -- --grep headers), but not together with the others (npm test). When I change the filename of the test to 0custom-middleware.js, the test is executed at first and it succeeds, but now the test options.js fails. It seems like all tests are using the same instance of the jsonApiTestServer, and that I cannot change the underlying express-server just for a single test. Do you have an idea how to achieve this?

[paparomeo]

Thanks for the PR @hpawe01. I'm trying to solve some other more urgent issues, but I'll have a look at it as soon as possible.