Problem

Accessing a path like static/a/abc will throw an error and respond with status code 500 if a is a file. This is because this generates an ENOTDIR error, instead of ENOENT.

We discovered this since we serve images at static/*.jpg and paths like static/*.jpg/abc returned 500 instead of 404.

Expectation

Should respond with status code 404 and show the 404 page.

Solution

In the code you check forif (err.code !== 'ENOENT'). Adding && err.code !== 'ENOTDIR' for example here makes it correctly respond with 404 instead of 500:

https://github.com/zeit/serve-handler/blob/d1368bf5ece565b27850ceaab2758a5ae0a4579d/src/index.js#L611