dotnet/runtime

Reconsider the exception type thrown when trying to open a directory as file

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#70,275 opened on Jun 6, 2022

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area-System.IOhelp wanted

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Description

In FileSystem.Windows, as well as SafeFileHandle.Windows we have this comment:

https://github.com/dotnet/runtime/blob/6a56aa3512c912df602bf074dc925b77f3895b24/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs#L216-L224

However, when testing with native code on Windows 10, calling CreateFileA returns ERROR_PATH_NOT_FOUND for either C:\ or other normal directories.

So this causing behavior inconsistency on managed API again: when calling File.Open on C:\, it throws UnauthorizedException. When calling with other directories, it throws PathNotFoundException.

I didn't find any test for exceptions in System.IO.FileSystem.

Changing the exception thrown is technically breaking, but helps for consistency. Changing to an exception is already used for other circumstances won't break much.

We need to also examine Windows 7 and 8 behavior and the behavior of CreateFile2 and NtCreateFile. (Or if you can directly check it through Windows source code)

Contributor guide

Research direction
Test CreateFile, CreateFile2, NtCreateFile on Windows 7, 8, 10 to determine the actual error codes when opening a directory as a file, then implement consistent exception throwing.
Tech stack
csharp
Domain
backendapiinfrastructure
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C#Windows API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45