private static string TryExpandShortFileName(ref StringBuffer outputBuffer, string originalPath)
{
// We guarantee we'll expand short names for paths that only partially exist. As such, we need to find the part of the path that actually does exist. To
// avoid allocating like crazy we'll create only one input array and modify the contents with embedded nulls.
Debug.Assert(!PathInternal.IsPartiallyQualified(outputBuffer.AsSpan()), "should have resolved by now");
// We'll have one of a few cases by now (the normalized path will have already:
//
// 1. Dos path (C:\)
// 2. Dos UNC (\\Server\Share)
// 3. Dos device path (\\.\C:\, \\?\C:\)
//
// We want to put the extended syntax on the front if it doesn't already have it, which may mean switching from \\.\.
//
// Note that we will never get \??\ here as GetFullPathName() does not recognize \??\ and will return it as C:\??\ (or whatever the current drive is).
int rootLength = PathInternal.GetRootLength(outputBuffer.AsSpan());
bool isDevice = PathInternal.IsDevice(outputBuffer.AsSpan());
StringBuffer inputBuffer = new StringBuffer(0);
try
{
bool isDosUnc = false;
int rootDifference = 0;
bool wasDotDevice = false;
// Add the extended prefix before expanding to allow growth over MAX_PATH
if (isDevice)
{
// We have one of the following (\\?\ or \\.\)
inputBuffer.Append(ref outputBuffer);
if (outputBuffer[2] == '.')
{
wasDotDevice = true;
inputBuffer[2] = '?';
}
}
else
{
isDosUnc = !PathInternal.IsDevice(outputBuffer.AsSpan()) && outputBuffer.Length > 1 && outputBuffer[0] == '\\' && outputBuffer[1] == '\\';
rootDifference = GetInputBuffer(ref outputBuffer, isDosUnc, ref inputBuffer);
}
rootLength += rootDifference;
int inputLength = inputBuffer.Length;
bool success = false;
int foundIndex = inputBuffer.Length - 1;
while (!success)
{
uint result = Interop.Kernel32.GetLongPathNameW(inputBuffer.UnderlyingArray, outputBuffer.UnderlyingArray, (uint)outputBuffer.Capacity);
// Replace any temporary null we added
if (inputBuffer[foundIndex] == '\0')
{
inputBuffer[foundIndex] = '\\';
}
if (result == 0)
{
// Look to see if we couldn't find the file
int error = Marshal.GetLastWin32Error();
if (error != Interop.Errors.ERROR_FILE_NOT_FOUND && error != Interop.Errors.ERROR_PATH_NOT_FOUND)
{
// Some other failure, give up
break;
}
// We couldn't find the path at the given index, start looking further back in the string.
foundIndex--;
for (; foundIndex > rootLength && inputBuffer[foundIndex] != '\\'; foundIndex--)
{
;
}
if (foundIndex == rootLength)
{
// Can't trim the path back any further
break;
}
else
{
// Temporarily set a null in the string to get Windows to look further up the path
inputBuffer[foundIndex] = '\0';
}
}
else if (result > outputBuffer.Capacity)
{
// Not enough space. The result count for this API does not include the null terminator.
outputBuffer.EnsureCapacity(checked ((int)result));
result = Interop.Kernel32.GetLongPathNameW(inputBuffer.UnderlyingArray, outputBuffer.UnderlyingArray, (uint)outputBuffer.Capacity);
}
else
{
// Found the path
success = true;
outputBuffer.Length = checked ((int)result);
if (foundIndex < inputLength - 1)
{
// It was a partial find, put the non-existent part of the path back
outputBuffer.Append(ref inputBuffer, foundIndex, inputBuffer.Length - foundIndex);
}
}
}
// Strip out the prefix and return the string
ref StringBuffer bufferToUse = ref Choose(success, ref outputBuffer, ref inputBuffer);
// Switch back from \\?\ to \\.\ if necessary
if (wasDotDevice)
{
bufferToUse[2] = '.';
}
string returnValue = null;
int newLength = bufferToUse.Length - rootDifference;
if (isDosUnc)
{
// Need to go from \\?\UNC\ to \\?\UN\\
bufferToUse[PathInternal.UncExtendedPrefixLength - PathInternal.UncPrefixLength] = '\\';
}
// We now need to strip out any added characters at the front of the string
if (bufferToUse.SubstringEquals(originalPath, rootDifference, newLength))
{
// Use the original path to avoid allocating
returnValue = originalPath;
}
else
{
returnValue = bufferToUse.Substring(rootDifference, newLength);
}
return(returnValue);
}
