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mswjs / http-middleware

Spawn an HTTP server from your request handlers or apply them to an existing server using a middleware.
https://npm.im/@mswjs/http-middleware
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`createMiddleware` Fails to Capture/Present `request.body` #9

Closed nbibler closed 2 years ago

nbibler commented 2 years ago

When using this library, I've noticed a behavior difference between createServer and createMiddleware. I think it's a bug in createMiddleware.

Using identical handlers, the createServer implementation will provide a request.body to the handler function, but createMiddleware will always return undefined for request.body.

There is a minimum-viable example gist here: https://gist.github.com/nbibler/5f08424bc8411b87acc8e8f906dfdf5d

nbibler commented 2 years ago

Oh... hrm... big difference between the createServer implementation and my minimum-viable middleware implementation is the missing app.use(express.json()). That seems to make a significant difference... if that middleware is prepended before the createMiddleware call, then the request handler gets request.body data. Without it, the route handler gets undefined.

kettanaito commented 2 years ago

Hey, @nbibler.

I believe that the intention behind createMiddleware is to delegate any request/response body parsing to you, as you're integrating it into an existing server. This library shouldn't make assumptions about how to parse bodies.

That being said, if we can prepend an express.json() parser middleware to the middleware function returned from createMiddleware, it'd be great. I don't think that's possible with the Express API, is it? Unless we return a list of middleware and ask the consumer to spread it:

app.use(...createMiddleware(...handlers))

But, honestly, if you're expecting request/response JSON bodies, you should be using a JSON parser middleware anyway. 

app.use(express.json())
app.use(createMiddleware(...handlers))

In the same way you may be handling different response body types, which would require a custom parser middleware on your side.

I'm not convinced that this is an issue on our end but I'm happy to continue the discussion.