I was reviewing some code, and I ran into the following snippet. Take a look at it:public void AddAttachment(string fileName, Stream stream)
   {
       Va...

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When designing public APIs for libraries, avoid trying to guess user intent by inferring behavior from limited information. A code example shows an AddAttachment method that automatically determines content type from file extensions, which limits flexibility and forces library updates for new file types. Instead, let callers explicitly provide the information they already know. This approach prevents blocking users from doing what they need and reduces the need for library changes, especially important for externally shipped libraries where updates are slow to deploy.

API Design: Don't try to guess

Great catch! I liked the article a lot. The only thing I would mention is how vulnerable it is to infer file types from a cyber security perspective. Good development habits should always lean towards zero trust.

I was always of the opinion that any general purpose library should give you access to the layer below. The simplest example is an ORM that lets you write plain SQL. You know, just in case.

I get the point, but often this kind of code cleaning leads to unwanted errors for clients. In the school they taught us that every function and every program we write has to be absolutely unbreakable, for example with files: have extension limitation, check magic bytes if file is really what it looks like, check file size to not shut down our server and so on…I don’t say it should be all in 1 function, but I just feel it should be a common sense in use everywhere to not blindly listen only 1 preference of 1 godly programmer 🙈

What will happen if my file is exe file, but I pass jpg into the method?