> An error is an event that someone should act on. Not necessarily you.

Personally, I'd further qualify that. It should be logged as an error if the person who reads the logs would be responsible for fixing it.

Suppose you run a photo gallery web site. If a user uploads a corrupt JPEG, and the server detects that it's corrupt and rejects it, then someone needs to do something, but from the point of view of the person who runs the web site, the web site behaved correctly. It can't control whether people's JPEGs are corrupt. So this shouldn't be categorized as an error in the server logs.

But if you let users upload a batch of JPEG files (say a ZIP file full of them), you might produce a log file for the user to view. And in that log file, it's appropriate to categorize it as an error.

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Arrowmaster a day ago | parent | next [-]

Counter argument. How do you know the user uploaded a corrupted image and it didn't get corrupted by your internet connection, server hardware, or a bug in your software stack?

You cannot accurately assign responsibility until you understand the problem.

	▲	jeremyjh 17 hours ago \| parent [-]
		This is just trolling. The JPEG is corrupt if the library that reads it says it is corrupt. You log it as a warning. If you upgrade the library or change your upstream reverse proxy, and starting getting 1000x the number of warnings, you can still recognize that and take action without personally inspecting each failed upload to be sure you haven't yet stumbled on the one edge case where the JPEG library is out of spec.

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colechristensen a day ago | parent | prev [-]

That's the difference between an HTTP 4xx and 5xx

4xx is for client side errors, 5xx is for server side errors.

For your situation you'd respond with an HTTP 400 "Bad Request" and not an HTTP 500 "Internal Server Error" because the problem was with the request not with the server.