IFileSystemInfo.ResolveLinkTarget throws exception instead of returning null if the path is not a link #981
Description
Describe the bug
System.IO.FileSystemInfo.ResolveLinkTarget returns null when the directory is not a link.
IFileSystemInfo.ResolveLinkTarget ends up crashing with a null reference exception.
ResolveLinkTarget implementation in DirectoryInfoWrapper.cs
public override IFileSystemInfo ResolveLinkTarget(bool returnFinalTarget)
{
return instance.ResolveLinkTarget(returnFinalTarget)
.WrapFileSystemInfo(FileSystem);
}WrapFileSystemInfo implementation in Converters.cs
private static FileSystemInfoBase WrapFileSystemInfo(IFileSystem fileSystem, FileSystemInfo item)
{
if (item is FileInfo fileInfo)
{
return WrapFileInfo(fileSystem, fileInfo);
}
else if (item is DirectoryInfo directoryInfo)
{
return WrapDirectoryInfo(fileSystem, directoryInfo);
}
else
{
throw new NotImplementedException(string.Format(
CultureInfo.InvariantCulture,
"The type {0} is not recognized by the System.IO.Abstractions library.",
item.GetType().AssemblyQualifiedName
));
}
}The null reference we end up hitting is because item is null in WrapFileSystemInfo.
System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=System.Private.CoreLib
StackTrace:
at System.Object.GetType()
at System.IO.Abstractions.Converters.WrapFileSystemInfo(IFileSystem fileSystem, FileSystemInfo item) in /home/runner/work/System.IO.Abstractions/System.IO.Abstractions/src/TestableIO.System.IO.Abstractions.Wrappers/Converters.cs:line 42
To Reproduce
IFileSystem fs = new FileSystem();
IDirectoryInfo dirinfo = fs.Directory.CreateDirectory(@"C:\Some\Dir");
IFileSystemInfo? target = dirinfo.ResolveLinkTarget(true); //CrashExpected behavior
ResolveLinkTarget should propagate the null return of the underlying System.IO API one way or another.
That API could do it directly, though it seems like WrapFileSystemInfo really ought to do the propagation itself.
Fix option 1:
private static FileSystemInfoBase WrapFileSystemInfo(IFileSystem fileSystem, FileSystemInfo item)
{
if (item == null)
{
return null;
}
...
}Fix option 2:
public override IFileSystemInfo ResolveLinkTarget(bool returnFinalTarget)
{
return instance.ResolveLinkTarget(returnFinalTarget)
?.WrapFileSystemInfo(FileSystem);
}