fix(http/file_server): throw error inside of serveFile if filePath is a directory

[timonson]

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This behavior was unintentionally changed after 0.114.0. The function serveFile only serves files (no directories).

[kt3k]

Note: #1479 changed the timing of throwing when the directory path is given as filePath parameter. It used to immediately throw, but now it throws when the response body is read

This PR tries to restore the previous behavior

BTW in file_server.ts, fileInfo.isDirectory is already checked before passing filepath to serveFile. So this change only affects users who use serveFile API directly.

[timonson]

So this change only affects users who use serveFile API directly.

Yes, exactly. I should have made this clear.

[kt3k]

@timonson I've looked at test cases of serveFile, and in some cases it returns Response object with error status code. Does it make sense to your use cases to return 404 Response object instead of throwing?

[timonson]

That's a great point and I agree there should be consistent behavior with regards to error handling inside the function. For my specific use case it would work. We could put everything inside a try block and invoke serveFallback inside the catch block.

[kt3k]

Note: #2529 partially did what we planned

[cjihrig]

Closing as https://github.com/denoland/deno_std/pull/2659 supersedes this PR.