Check out https://github.com/mathiasbynens/small

Kinda silly including 0-byte files which is most of them. Now you're just building a list of things that take empty input.

They should move those to a simple list in the README and reserve the repo for non-empty files.

That is indeed a nice one, "Smallest possible syntactically valid files of different types".

Following the GitHub link (datasette-render-images) in the comment you replied to, there's a code comment with a link to the same library (small).

Doesn't a PDF detector only need to check if the first few bytes are '%PDF-1.' ?

That is, do you need a "valid PDF" detector or "more likely a PDF than anything else" detector?

Realistically, yes, but strictly speaking PDFs start with a footer and most PDF readers will accept highly corrupt files.

Depends. If you need to parse it, that might still cause errors.

Agreed.

Though when I think of "detector" I think more of https://en.wikipedia.org/wiki/File_(command) and not something which verifies the file is in the correct format.

Well...

file 'setupTests.ts' setupTests.ts: Java source, ASCII text

I wouldn't put too much trust in file.

I don’t know what you expected. File is just there to give a good guess at a file’s format. There are a ton of reasons why this problem is hard, and there are reasons to make “file” less accurate in order to make the implementation simpler and more secure.

But it will work fine for PDFs, often enough.

The heuristic used for Java source looks like this:

0 regex \^import.*;$ Java source

That use is indeed exactly what inspired the question!

I'm curious why you needed the absolute smallest PDF file for testing? As an intellectual exercise, golfing the PDF format sounds like a bit of fun, but given that https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pd... is 13KB, I would think you could load that in a test suite on pretty much any reasonable, non-embedded platform. And, why would you want to load it on an embedded platform, anyway?

Testing near/at boundary conditions is generally good practice.

A minimal size file could easily catch some cases where your code assumes some sort of structure (some flag, header, metadata structure, etc.) exists when it's possible it actually doesn't.