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Relax LinkTarget so it always returns null when steps on an error #55668

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Jul 15, 2021
Merged

Relax LinkTarget so it always returns null when steps on an error #55668

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22 changes: 14 additions & 8 deletions src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -427,34 +427,33 @@ internal static void CreateSymbolicLink(string path, string pathToTarget, bool i
{
string? targetPath = returnFinalTarget ?
GetFinalLinkTarget(linkPath, isDirectory) :
GetImmediateLinkTarget(linkPath, isDirectory, throwOnUnreachable: true, returnFullPath: true);
GetImmediateLinkTarget(linkPath, isDirectory, throwOnError: true, returnFullPath: true);

return targetPath == null ? null :
isDirectory ? new DirectoryInfo(targetPath) : new FileInfo(targetPath);
}

internal static string? GetLinkTarget(string linkPath, bool isDirectory)
=> GetImmediateLinkTarget(linkPath, isDirectory, throwOnUnreachable: false, returnFullPath: false);
=> GetImmediateLinkTarget(linkPath, isDirectory, throwOnError: false, returnFullPath: false);

/// <summary>
/// Gets reparse point information associated to <paramref name="linkPath"/>.
/// </summary>
/// <returns>The immediate link target, absolute or relative or null if the file is not a supported link.</returns>
internal static unsafe string? GetImmediateLinkTarget(string linkPath, bool isDirectory, bool throwOnUnreachable, bool returnFullPath)
internal static unsafe string? GetImmediateLinkTarget(string linkPath, bool isDirectory, bool throwOnError, bool returnFullPath)
{
using SafeFileHandle handle = OpenSafeFileHandle(linkPath,
Interop.Kernel32.FileOperations.FILE_FLAG_BACKUP_SEMANTICS |
Interop.Kernel32.FileOperations.FILE_FLAG_OPEN_REPARSE_POINT);

if (handle.IsInvalid)
{
int error = Marshal.GetLastWin32Error();

if (!throwOnUnreachable && IsPathUnreachableError(error))
if (!throwOnError)
{
return null;
}

int error = Marshal.GetLastWin32Error();
// File not found doesn't make much sense coming from a directory.
if (isDirectory && error == Interop.Errors.ERROR_FILE_NOT_FOUND)
{
Expand All @@ -479,6 +478,11 @@ internal static void CreateSymbolicLink(string path, string pathToTarget, bool i

if (!success)
{
if (!throwOnError)
{
return null;
}

int error = Marshal.GetLastWin32Error();
// The file or directory is not a reparse point.
if (error == Interop.Errors.ERROR_NOT_A_REPARSE_POINT)
Expand Down Expand Up @@ -600,13 +604,15 @@ uint GetFinalPathNameByHandle(SafeFileHandle handle, char[] buffer)
{
// Since all these paths will be passed to CreateFile, which takes a string anyway, it is pointless to use span.
// I am not sure if it's possible to change CreateFile's param to ROS<char> and avoid all these allocations.
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Can we also follow-up to address this comment? If we can save allocations by marshaling a span instead of creating a string to then pass down, we should. You can't today pass a span directly to a DllImport method, but you can manually pin it and pass in the pointer, which is exactly what the runtime does with string.

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Will address this in a separate PR in order to get this in before the preview7 snap, thanks.

string? current = GetImmediateLinkTarget(linkPath, isDirectory, throwOnUnreachable: false, returnFullPath: true);

// We don't throw on error since we already did all the proper validations before.
string? current = GetImmediateLinkTarget(linkPath, isDirectory, throwOnError: false, returnFullPath: true);
string? prev = null;

while (current != null)
{
prev = current;
current = GetImmediateLinkTarget(current, isDirectory, throwOnUnreachable: false, returnFullPath: true);
current = GetImmediateLinkTarget(current, isDirectory, throwOnError: false, returnFullPath: true);
}

return prev;
Expand Down