ctx.originalUrl invalid when used as express route about discussions

[matthieusieben]

Thanks for your answer.

I have several use-cases for this:

1. At my company we currently use Express. I want to push Koa because I think it is a more modern and overall better way to implement the middleware pattern. But my company cannot afford a full re-write. So the only solution is to push Koa as the replacement, and slowly migrate endpoints 1 by 1 to Koa. Doing this requires to use Koa as an Express middleware.

2. Some libraries use Express under the hood. For example, Nuxt.js uses Express for its serverMiddlewares. As I said, I prefer using Koa to implement my middlewares.

3. This is not coming from me, really. Here is an extract of Koa doc on koajs.com:

app.callback()
Return a callback function suitable for the http.createServer() method to handle a request. You may also use this callback function to mount your Koa app in a Connect/Express app.

The project's own doc recommend using callback() to mount a koa app into an express app. But this integration is currently broken due to this originalUrl problem.

Now I understand that you don't want to make changes to the Application's createContext() methods. And, to be honest, I don't think it is the right way either.

If there is one place where Koa's code should care about integration with another lib, it should be in the one place build for that purpose: the callback() method. Of course you can argue that this can be done in user-land, or even in yet another (one liner) NPM module. But then, you should remove any mention to Express from the doc, or at least mention that the integration with Express is broken in some cases. And I don't think that that is going to help Koa become a replacement for Express.

[fl0w]

I don't see the point, why would you run Koa as a middleware for express? In addition, modify Koa source for an unsupported/unintended use-case?

[matthieusieben]

A less breaking solution would be to add an option to restore the originalUrl when generating a callback:

  callback(options = {}) {
    const fn = compose(this.middleware)

    if (!this.listenerCount('error')) this.on('error', this.onerror)

    const handleRequest = (req, res) => {
      if (options.restoreUrl) req.url = req.originalUrl || req.url
      const ctx = this.createContext(req, res)
      return this.handleRequest(ctx, fn)
    }

    return handleRequest
  }

[matthieusieben]

My current "hack" is to monkey patch the callback():

  const koaMiddleware = koaApp.callback()

  expressApp.use('/api', (req, res) => {
    req.url = req.originalUrl || req.url
    handleRequest(req, res)
  })

[matthieusieben]

A more complex (?) alternative would be to make use of the req.baseUrl that the express router adds, when computing the originalUrl.

[Frondor]

Hello! Is this still an issue? I see the source code looks like the changes suggested are already implemented.

I'm actually experiencing the same limitation while doing a forward rewrite.