Develop Reference

How to remove a file lock

I have an service to move files from a working folder to backup folder. The folders are on a network share, so at times we will open a file, using something like notepad, to look at it. People are not (well, shouldn't) be editing, just looking.
When we try to move the file, I get permission denied. I'm looking for a way in C# to force remove a file lock, so the service can move the file to the backup folder.

You have to use P/Invoke. These are the functions you care about:
[DllImport("netapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
static extern int NetFileEnum(string servername, string basepath, string username, int level, ref IntPtr bufptr, int prefmaxlen, out int entriesread, out int totalentries, IntPtr resume_handle);
[DllImport("netapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
static extern int NetFileClose(string servername, int id);
[DllImport("Netapi32.dll", SetLastError = true)]
static extern int NetApiBufferFree(IntPtr buffer);
Here's some code similar to what I've used with success:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
struct FILE_INFO_3
{
public int fi3_id;
public int fi3_permission;
public int fi3_num_locks;
[MarshalAs(UnmanagedType.LPWStr)]
public string fi3_pathname;
[MarshalAs(UnmanagedType.LPWStr)]
public string fi3_username;
}
private static FILE_INFO_3[] GetLockedFiles(string server, string path)
{
const int MAX_PREFERRED_LENGTH = -1;
int dwReadEntries;
int dwTotalEntries;
IntPtr pBuffer = IntPtr.Zero;
FILE_INFO_3 pCurrent = new FILE_INFO_3();
List<FILE_INFO_3> files = new List<FILE_INFO_3>();
int dwStatus = NetFileEnum(server, path, null, 3, ref pBuffer, MAX_PREFERRED_LENGTH, out dwReadEntries, out dwTotalEntries, IntPtr.Zero);
if (dwStatus == 0)
{
for (int dwIndex = 0; dwIndex < dwReadEntries; dwIndex++)
{
IntPtr iPtr = new IntPtr(pBuffer.ToInt32() + (dwIndex * Marshal.SizeOf(pCurrent)));
pCurrent = (FILE_INFO_3)Marshal.PtrToStructure(iPtr, typeof(FILE_INFO_3));
files.Add(pCurrent);
}
}
NetApiBufferFree(pBuffer);
return files.ToArray();
}
static void Main(string[] args)
{
FILE_INFO_3[] lockedFiles = GetLockedFiles("someservername", #"C:\somepath");
foreach (FILE_INFO_3 lockedFile in lockedFiles)
{
int dwStatus = NetFileClose(_serverName, lockedFile.fi3_id);
// Check dwStatus for success here
}
}
EDIT: As noted by the OP in the comments below, when compiling as 64-bit, you need to use ToInt64 instead of ToInt32. More information can be found here.

How do I PInvoke RpcMgmtEpEltInqNext?

The search term RpcMgmtEpEltInqNext on both Stackoverflow and PInvoke.net yields zero results, so this should be worth asking. I've been fiddling around on MSDN and looking through Win SDK *.h files all day, and feeling a bit out of my element.
I'm basically attempting to query the MSRPC endpoint mapper with managed code. Here is what I have so far:
[DllImport("Rpcrt4.dll", CharSet = CharSet.Auto)]
public static extern int RpcBindingFromStringBinding(string StringBinding, out IntPtr Binding);
[DllImport("Rpcrt4.dll")]
public static extern int RpcBindingFree(ref IntPtr Binding);
[DllImport("Rpcrt4.dll", CharSet = CharSet.Auto)]
public static extern int RpcMgmtEpEltInqBegin(IntPtr EpBinding,
int InquiryType, // 0x00000000 = RPC_C_EP_ALL_ELTS
int IfId,
int VersOption,
string ObjectUuid,
out IntPtr InquiryContext);
[DllImport("Rpcrt4.dll", CharSet = CharSet.Auto)]
public static extern int RpcMgmtEpEltInqNext(ref IntPtr InquiryContext,
out int IfId,
out IntPtr Binding,
out string ObjectUuid,
out string Annotation);
public static List<int> QueryEPM(string host)
{
List<int> ports = new List<int>();
int retCode = 0; // RPC_S_OK
IntPtr bindingHandle = IntPtr.Zero;
IntPtr inquiryContext = IntPtr.Zero;
IntPtr elementBindingHandle = IntPtr.Zero;
int elementIfId = 0;
string elementUuid = string.Empty;
string elementAnnotation = string.Empty;
try
{
retCode = RpcBindingFromStringBinding("ncacn_ip_tcp:" + host, out bindingHandle);
if (retCode != 0)
throw new Exception("RpcBindingFromStringBinding: " + retCode);
retCode = RpcMgmtEpEltInqBegin(bindingHandle, 0, 0, 0, string.Empty, out inquiryContext);
if (retCode != 0)
throw new Exception("RpcMgmtEpEltInqBegin: " + retCode);
retCode = RpcMgmtEpEltInqNext (ref inquiryContext, out elementIfId, out elementBindingHandle, out elementUuid, out elementAnnotation);
if (retCode != 0)
throw new Exception("RpcMgmtEpEltInqNext: " + retCode);
}
The above code isn't complete, but it illustrates my point. The code consistently returns:
RpcMgmtEpEltIngNext: 87
87 meaning Parameter is Incorrect according to here.
So I'm basically stumped at this point, and I'm sure it's because of my extremely crappy PInvoke code.

The p/invoke declaration is wrong. It needs to be:
[DllImport("Rpcrt4.dll", CharSet = CharSet.Auto)]
public static extern int RpcMgmtEpEltInqNext(
IntPtr InquiryContext,
out RPC_IF_ID IfId,
out IntPtr Binding,
out Guid ObjectUuid,
out IntPtr Annotation
);
The first parameter must be passed by value.
You'll need to translate the RPC_IF_ID struct. It's quite a simple one.
public struct RPC_IF_ID
{
public Guid Uuid;
public ushort VersMajor;
public ushort VersMinor;
}
The two string parameters you used were just wrong. They lead to the marshaller calling CoTaskMemFree on the returned value for Annotation. You don't want that. You will need to use Marshal.PtrToStringAnsi to read the value.
Don't forget to call RpcBindingFree and RpcStringFree as per the docs.

What's the appropriate method for marshalling an array of strings?

I'm having an issue where I get a different memory layout when debugging with ReSharper.
I have an unmanaged method that returns an array of (at most) 7-character, null-terminated strings. When executing this method without ReSharper's debugger, the start of the "next" string is 16 bytes later. When executing it with ReSharper's debugger (via ReSharper's Unit Test form choosing the "Debug Unit Tests" option), the start is 64 bytes later.
The method signature is similar to the snippet below. The string array is then "created" similar to the solution here.
[return: MarshalAs(UnmanagedType.I1)]
[DllImport("myDll.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
private static extern bool GetStrings(IntPtr sourceFile,
out IntPtr ptrToStrings,
out uint numberOfStrings);

Try using this to obtain the strings:
[return: MarshalAs(UnmanagedType.I1)]
[DllImport("myDll.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
private static unsafe extern bool GetStrings(IntPtr sourceFile,
[Out] out byte* ptrToStrings,
[Out] out uint numberOfStrings);
[SecuritySafeCritical]
private static unsafe string[] ManagedMethod(IntPtr sourceFile)
{
uint size;
byte* array;
if (!GetStrings(sourceFile, out array, out size))
{
throw new Exception("Unable to read strings.");
}
string[] retval = new string[size];
for (int i = 0, p = 0; i < size; i++, p += 8)
{
retval[i] = Marshal.PtrToStringAnsi(new IntPtr(&array[p]));
}
return retval;
}

I successfully called advapi32's LsaEnumerateAccountRights() from C#. Now how do I unmarshal the array of LSA_UNICODE_STRING it returns?

It's a pointer to an array of LSA_UNICODE_STRING structures. I found some code that does the inverse, i.e., create a LSA_UNICODE_STRING from a C# string. You can see that in the helper code section below.
What I have up to and including the call to LsaEnumerateAccountRights() seems to work just fine. Sensible values are returned for the array pointer and for the count.
I am at a loss as to how to get at those blasted strings. Help please? Pretty please?
UPDATE: nobugz's helper function in his answer below is ALMOST right, you only have to divide the length by UnicodeEncoding.CharSize. Thanks to him, I can now see the FIRST string in the array. See the updates at the end of both code sections below.
Now, how the netherworld do I do pointer arithmetic?
UPDATE 2.5: See answer for the functioning code. I lost the old, "wrong" code.

Found it! In this blog post. Now the amended code below works fully. It's even 64-bit safe!
The main code:
IntPtr sid = IntPtr.Zero;
int sidSize = 0;
StringBuilder domainName = new StringBuilder();
int nameSize = 0;
int accountType = 0;
LookupAccountName("\\\\" + tbHost.Text, tbUsername.Text, sid, ref sidSize,
domainName, ref nameSize, ref accountType);
domainName = new StringBuilder(nameSize);
sid = Marshal.AllocHGlobal(sidSize);
bool result = LookupAccountName("\\\\" + tbHost.Text, tbUsername.Text, sid, ref sidSize,
domainName, ref nameSize, ref accountType);
myResults.Text += String.Format("LookupAccountName(): Result {0}, SID {1}\n", result, sid);
LSA_UNICODE_STRING systemName = string2LSAUS("\\\\" + tbHost.Text);
IntPtr policyHandle = IntPtr.Zero;
LSA_OBJECT_ATTRIBUTES objAttrs = new LSA_OBJECT_ATTRIBUTES();
uint retVal = LsaOpenPolicy(ref systemName, ref objAttrs,
POLICY_LOOKUP_NAMES | POLICY_VIEW_LOCAL_INFORMATION, out policyHandle);
myResults.Text += String.Format("LsaOpenPolicy(): Result {0}, Policy Handle {1}\n", retVal, policyHandle);
IntPtr rightsArray = IntPtr.Zero;
ulong rightsCount = 0;
long lretVal = LsaEnumerateAccountRights(policyHandle, sid, out rightsArray, out rightsCount);
retVal = LsaNtStatusToWinError(lretVal);
if (retVal != 0)
throw new System.ComponentModel.Win32Exception((int)retVal);
myResults.Text += String.Format("LsaEnumerateAccountRights(): Result {0}, RightsArray {1}, Count {2}\n",
retVal, rightsArray, rightsCount);
LSA_UNICODE_STRING myLsaus = new LSA_UNICODE_STRING();
for (ulong i = 0; i < rightsCount; i++)
{
IntPtr itemAddr = new IntPtr(rightsArray.ToInt64() + (long)(i * (ulong) Marshal.SizeOf(myLsaus)));
myLsaus = (WinNetUtils.LSA_UNICODE_STRING)Marshal.PtrToStructure(itemAddr, myLsaus.GetType());
string thisRight = WinNetUtils.LSAUS2string(myLsaus);
NonBlockingPrint(wmiResults, "Right #{0}: {1}\n", i+1, thisRight);
}
LsaClose(policyHandle);
The helper functions, imports etc:
public const int POLICY_VIEW_LOCAL_INFORMATION = 0x1;
public const int POLICY_LOOKUP_NAMES = 0x00000800;
[DllImport("advapi32.dll", CharSet = CharSet.Unicode, PreserveSig = true)]
public static extern UInt32 LsaNtStatusToWinError(
long Status);
[DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true, PreserveSig = true)]
public static extern bool ConvertStringSidToSid(
string StringSid, out IntPtr pSid);
[DllImport("advapi32.dll", CharSet = CharSet.Unicode, SetLastError = true, PreserveSig = true)]
public static extern bool LookupAccountName(
string lpSystemName, string lpAccountName,
IntPtr psid, ref int cbsid,
StringBuilder domainName, ref int cbdomainLength,
ref int use );
[DllImport("advapi32.dll", CharSet = CharSet.Unicode, PreserveSig = true)]
public static extern UInt32 LsaOpenPolicy(
ref LSA_UNICODE_STRING SystemName,
ref LSA_OBJECT_ATTRIBUTES ObjectAttributes,
Int32 DesiredAccess,
out IntPtr PolicyHandle );
[DllImport("advapi32.dll", SetLastError = true, PreserveSig = true)]
public static extern long LsaEnumerateAccountRights(
IntPtr PolicyHandle, IntPtr AccountSid,
out /* LSA_UNICODE_STRING[] */ IntPtr UserRights,
out ulong CountOfRights);
[DllImport("advapi32.dll", SetLastError = true, PreserveSig = true)]
public static extern long LsaClose(
IntPtr PolicyHandle);
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct LSA_UNICODE_STRING
{
public UInt16 Length;
public UInt16 MaximumLength;
public IntPtr Buffer;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct LSA_OBJECT_ATTRIBUTES
{
public IntPtr RootDirectory;
public IntPtr SecurityDescriptor;
public IntPtr SecurityQualityOfService;
public LSA_UNICODE_STRING ObjectName;
public UInt32 Attributes;
public UInt32 Length;
}
public static LSA_UNICODE_STRING string2LSAUS(string myString)
{
LSA_UNICODE_STRING retStr = new LSA_UNICODE_STRING();
retStr.Buffer = Marshal.StringToHGlobalUni(myString);
retStr.Length = (UInt16)(myString.Length * UnicodeEncoding.CharSize);
retStr.MaximumLength = (UInt16)((myString.Length + 1) * UnicodeEncoding.CharSize);
return retStr;
}
public static string LSAUS2string(LSA_UNICODE_STRING lsaus)
{
char[] cvt = new char[lsaus.Length / UnicodeEncoding.CharSize];
Marshal.Copy(lsaus.Buffer, cvt, 0, lsaus.Length / UnicodeEncoding.CharSize);
return new string(cvt);
}

This ought to work for you:
private static string LSAUS2String(LSA_UNICODE_STRING lsa) {
char[] cvt = new char[lsa.Length];
Marshal.Copy(lsa.Buffer, cvt, 0, lsa.Length);
return new string(cvt);
}

Using pinvoke in c# to call sprintf and friends on 64-bit

I am having an interesting problem with using pinvoke in C# to call _snwprintf. It works for integer types, but not for floating point numbers.
This is on 64-bit Windows, it works fine on 32-bit.
My code is below, please keep in mind that this is a contrived example to show the behavior I am seeing.
class Program
{
[DllImport("msvcrt.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
private static extern int _snwprintf([MarshalAs(UnmanagedType.LPWStr)] StringBuilder str, IntPtr length, String format, int p);
[DllImport("msvcrt.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
private static extern int _snwprintf([MarshalAs(UnmanagedType.LPWStr)] StringBuilder str, IntPtr length, String format, double p);
static void Main(string[] args)
{
Double d = 1.0f;
Int32 i = 1;
Object o = (object)d;
StringBuilder str = new StringBuilder(32);
_snwprintf(str, (IntPtr)str.Capacity, "%10.1lf", (Double)o);
Console.WriteLine(str.ToString());
o = (object)i;
_snwprintf(str, (IntPtr)str.Capacity, "%10d", (Int32)o);
Console.WriteLine(str.ToString());
Console.ReadKey();
}
}
The output of this program is
0.0
1
It should print 1.0 on the first line and not 0.0, and so far I am stumped.

I'm not exactly sure why your calls do not work, but the secured versions of these methods do work properly in both x86 and x64.
The following code does work, as expected:
class Program
{
[DllImport("msvcrt.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
private static extern int _snwprintf_s([MarshalAs(UnmanagedType.LPWStr)] StringBuilder str, IntPtr bufferSize, IntPtr length, String format, int p);
[DllImport("msvcrt.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
private static extern int _snwprintf_s([MarshalAs(UnmanagedType.LPWStr)] StringBuilder str, IntPtr bufferSize, IntPtr length, String format, double p);
static void Main(string[] args)
{
// Preallocate this to a given length
StringBuilder str = new StringBuilder(100);
double d = 1.4;
int i = 7;
float s = 1.1f;
// No need for box/unbox
_snwprintf_s(str, (IntPtr)100, (IntPtr)32, "%10.1lf", d);
Console.WriteLine(str.ToString());
_snwprintf_s(str, (IntPtr)100, (IntPtr)32, "%10.1f", s);
Console.WriteLine(str.ToString());
_snwprintf_s(str, (IntPtr)100, (IntPtr)32, "%10d", i);
Console.WriteLine(str.ToString());
Console.ReadKey();
}
}

It is possible with the undocumented __arglist keyword:
using System;
using System.Text;
using System.Runtime.InteropServices;
class Program {
[DllImport("msvcrt.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
private static extern int _snwprintf(StringBuilder str, int length, String format, __arglist);
static void Main(string[] args) {
Double d = 1.0f;
Int32 i = 1;
String s = "nobugz";
StringBuilder str = new StringBuilder(666);
_snwprintf(str, str.Capacity, "%10.1lf %d %s", __arglist(d, i, s));
Console.WriteLine(str.ToString());
Console.ReadKey();
}
}
Please don't use that.

uint is 32 bits. The length parameter of snprintf is size_t, which is 64 bits in 64 bit processes. Change the second parameter to IntPtr, which is the closest .NET equivalent of size_t.
In addition, you need to preallocate your StringBuilder. Currently you have a buffer overrun.

Try MarshalAs R8 (Thats for real/floating 8 (which is double)) on last parameter in second function.

Take a look at these two articles:
http://www.codeproject.com/Messages/2840231/Alternative-using-MSVCRT-sprintf.aspx (this is actually note to CodeProject article)
http://bartdesmet.net/blogs/bart/archive/2006/09/28/4473.aspx