从 System.IO.Abstractions 抛出 UnauthorizedAccessException

Question

I'm using System.IO.Abstractions ( https://github.com/System-IO-Abstractions ) to allow me to inject an IFileSystem into my class. I've recently added a piece of code to catch an UnauthorizedAccessException thrown when the user tries to create a file in a directory which they don't have write access to.

Is there a way the set the access permissions of a directory within System.IO.Abstractions ?

The following code is as close as I have come ( MockFileSystem coming from System.IO.Abstractions ). The AccessControlSections description is

Specifies which sections of a security descriptor to save or load

So it appears that I need to set up a security descriptor of some sort but I can't find any information on that - or if this is even the right approach.

var mockFileSystem = new MockFileSystem();
mockFileSystem.Directory.CreateDirectory("C:\\Test", new DirectorySecurity("C:\\Test", AccessControlSections.None));

// This should throw an UnauthorizedAccessException
mockFileSystem.File.Create("C:\\Test\\File.txt");

Answer 1

I tried something like this and failed:

const string path = @"C:\temp\incoming";
var fileSystem = new MockFileSystem();
fileSystem.AddDirectory(path);
var diFactory = fileSystem.DirectoryInfo;
var directoryInfo = diFactory.FromDirectoryName(path);
var directorySecurity = directoryInfo.GetAccessControl();
var currentUser = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
directorySecurity.AddAccessRule(new FileSystemAccessRule(currentUser , FileSystemRights.Read, AccessControlType.Allow));

I still think this is more or less the way to go, unfortunately it doesn't work :-(

Maybe the user I'm specifying for the AccessRule isn't correct, I've tried with others too but to no avail:

var adminUser = new SecurityIdentifier(WellKnownSidType.BuiltinAdministratorsSid, null);
// -> Doesn't work either..

Anyway, in the end I created this dirty workaround to test it, and that works obviously:

var mockFileSystem = new Mock<IFileSystem>();
mockFileSystem.Setup(x => x.File.Create(It.IsAny<string>())).Throws(new Exception());

Answer 2

You can create a mock for IFileSystem to setup the method you wanna throw the exception and then you create a MockFileSystem to be used only when necessary. You can setup your mock to return the "real" file system when only some methods are invoked. In my case bellow, I wanted to only use MockFileSystem when using the Path .

You will have to setup your test like this (please read the comments):

[Fact]
public async void FailWhenCopyFails()
{
   // Arrange
   var file = Substitute.For<IFile>(); // fake File to throw UnauthorizedAccessException
   file
      .When(x => x.WriteAllBytesAsync(Arg.Any<string>(), Arg.Any<byte[]>()))
      .Do(x => { throw new UnauthorizedAccessException(); });

   file.Exists("C:\\Downloads\\" + "eclipse.exe").Returns(true);

   var fileSystem = Substitute.For<IFileSystem>(); // fake file system
   var mockFileSystem = new MockFileSystem(); // "real" file system to be used only when necessary
   fileSystem.File.Returns(file); // pass the File mock which will throw the exception
   fileSystem.Path.Returns(mockFileSystem.Path); // the "real" Path is necessary to make the test pass

   var httpResponseMessage = new HttpResponseMessage() { StatusCode = HttpStatusCode.OK };
   var httpClient = new HttpClient(new MockHttpMessageHandler(httpResponseMessage));
   var downloader = new DownloadManager(httpClient, fileSystem);

   // Act
   await Assert.ThrowsAsync<UnauthorizedAccessException>(() => downloader.DownloadFile(new Uri(eclipseUrl), downloadFolder));

   // Assert
   downloader.IsSuccess().Should().BeFalse();
}

In my case I wanted to verify the download fails if the http client can't create the downloaded file in the downloads folder (it was supposed to fail if it cannot overwrite the C:\\Downloads\\eclipse.exe already there).