Middleware shouldn't be async

Middleware created by this module is an async function. That is incorrect because connect framework doesn’t await middleware it runs so any exception within the middleware won’t be caught and propagated properly.

I don’t see a good way to fix it besides dropping support for async to functions.

I’ve noticed this problem while investigating error that can trigger on res.setHeader with URL with invalid characters (error TypeError [ERR_INVALID_CHAR]: Invalid character in header content ["Location"]).

[rchl]

Per my last comment, async middleware is not really a problem. Problem is if some of the exceptions are not caught but after #52 all are handled so this is fixed.

[rchl]

Actually, now that I think about it, it’s not really a problem to have an async middleware as long as you are catching errors and passing to next() function.

You can add big try/catch on whole code or something cleaner like an async wrapper function:

function asyncMiddleware(endpointHandlerFunction) {
    return function(req, res, next) {
        Promise.resolve(endpointHandlerFunction(req, res, next)).catch(next);
    };
};

and then wrap original middleware function like:

return  asyncMiddleware(async function (req, res, next) {
   ...
})