Inaccurate/Unhelpful MockFileSystem UNC path error message on Unix-like systems

[HarrisonTCodes]

Issue

When creating a MockFileSystem with initial files using UNC paths (Windows format) on Unix-like systems, the error handling can be contradictory to the code and inaccurate, as the error message is fixed/hardcoded to Windows paths. For example, when running the below on a Unix-like system

var filesystem = new MockFileSystem(new Dictionary<string, MockFileData>
{
 {@"\\server\share\file", "content"}
});

The error reads System.ArgumentException: The UNC path should be of the form \\server\share. (Parameter 'path'), despite the path being in that exact form, and actually requiring the form //server/share on Unix-like systems.

Cause

It seems there is handling of UNC paths with forward-slash separation following this standard in the MockFileSystem class, from this line:

var isUnc =
 StringOperations.StartsWith(fixedPath, @"\\") ||
 StringOperations.StartsWith(fixedPath, @"//");

The next line uses the platform-specific separator:

lastIndex = StringOperations.IndexOf(fixedPath, separator, 2)

Which will then lead to errors if trying to use backslash-separated UNC paths on Unix-like systems, or presumably forwardslash-separated UNC paths on Windows systems (untested). The error message however, as above, is hardcoded/fixed to the Windows paths:

// In MockFileSystem.cs
if (lastIndex < 0)
{
 throw CommonExceptions.InvalidUncPath(nameof(path));
}

// In CommonExceptions.cs
public static ArgumentException InvalidUncPath(string paramName) =>
 new ArgumentException(@"The UNC path should be of the form \\server\share.", paramName);

[vbreuss]

Thanks for reporting. Should I assign this issue to you, @HarrisonTCodes?

[HarrisonTCodes]

More than happy to take a look at implementing a solution/fix to this, please go ahead :)

Wondering what the best approach may be. Two potential solutions initially come to mind:

1. The error message is still fixed, but expand it to mention both platforms, such as: The UNC path should be of the form \\server\share on Windows systems and //server/share on Unix-like systems

2. The error message is dynamic and will be platform-specific, producing either the current message on Windows systems, or a similar one with the corrected path on Unix-like systems

Would be interested on your take here, or if there is another preferred way to go about this I may be overlooking

[vbreuss]

Wondering what the best approach may be. Two potential solutions initially come to mind:

1. The error message is still fixed, but expand it to mention both platforms, such as: The UNC path should be of the form \\server\share on Windows systems and //server/share on Unix-like systems
2. The error message is dynamic and will be platform-specific, producing either the current message on Windows systems, or a similar one with the corrected path on Unix-like systems

Would be interested on your take here, or if there is another preferred way to go about this I may be overlooking

I would go with your second suggestion. System.IO.Abstractions will always behave as the host operating system, so just having the correct message for the current operating system seems sufficient.

[HarrisonTCodes]

Great, thanks - I'll raise a PR with a fix!

[github-actions]

This is addressed in release v22.1.0.