I have some code and when it executes, it throws a IOException, saying that
The process cannot access the file 'filename' because it is being used by
another process
What does this mean, and what can I do about it?
What is the cause?
The error message is pretty clear: you're trying to access a file, and it's not accessible because another process (or even the same process) is doing something with it (and it didn't allow any sharing).
Debugging
It may be pretty easy to solve (or pretty hard to understand), depending on your specific scenario. Let's see some.
Your process is the only one to access that file
You're sure the other process is your own process. If you know you open that file in another part of your program, then first of all you have to check that you properly close the file handle after each use. Here is an example of code with this bug:
var stream = new FileStream(path, FileAccess.Read);
var reader = new StreamReader(stream);
// Read data from this file, when I'm done I don't need it any more
File.Delete(path); // IOException: file is in use
Fortunately FileStream implements IDisposable, so it's easy to wrap all your code inside a using statement:
using (var stream = File.Open("myfile.txt", FileMode.Open)) {
// Use stream
}
// Here stream is not accessible and it has been closed (also if
// an exception is thrown and stack unrolled
This pattern will also ensure that the file won't be left open in case of exceptions (it may be the reason the file is in use: something went wrong, and no one closed it; see this post for an example).
If everything seems fine (you're sure you always close every file you open, even in case of exceptions) and you have multiple working threads, then you have two options: rework your code to serialize file access (not always doable and not always wanted) or apply a retry pattern. It's a pretty common pattern for I/O operations: you try to do something and in case of error you wait and try again (did you ask yourself why, for example, Windows Shell takes some time to inform you that a file is in use and cannot be deleted?). In C# it's pretty easy to implement (see also better examples about disk I/O, networking and database access).
private const int NumberOfRetries = 3;
private const int DelayOnRetry = 1000;
for (int i=1; i <= NumberOfRetries; ++i) {
try {
// Do stuff with file
break; // When done we can break loop
}
catch (IOException e) when (i <= NumberOfRetries) {
// You may check error code to filter some exceptions, not every error
// can be recovered.
Thread.Sleep(DelayOnRetry);
}
}
Please note a common error we see very often on StackOverflow:
var stream = File.Open(path, FileOpen.Read);
var content = File.ReadAllText(path);
In this case ReadAllText() will fail because the file is in use (File.Open() in the line before). To open the file beforehand is not only unnecessary but also wrong. The same applies to all File functions that don't return a handle to the file you're working with: File.ReadAllText(), File.WriteAllText(), File.ReadAllLines(), File.WriteAllLines() and others (like File.AppendAllXyz() functions) will all open and close the file by themselves.
Your process is not the only one to access that file
If your process is not the only one to access that file, then interaction can be harder. A retry pattern will help (if the file shouldn't be open by anyone else but it is, then you need a utility like Process Explorer to check who is doing what).
Ways to avoid
When applicable, always use using statements to open files. As said in previous paragraph, it'll actively help you to avoid many common errors (see this post for an example on how not to use it).
If possible, try to decide who owns access to a specific file and centralize access through a few well-known methods. If, for example, you have a data file where your program reads and writes, then you should box all I/O code inside a single class. It'll make debug easier (because you can always put a breakpoint there and see who is doing what) and also it'll be a synchronization point (if required) for multiple access.
Don't forget I/O operations can always fail, a common example is this:
if (File.Exists(path))
File.Delete(path);
If someone deletes the file after File.Exists() but before File.Delete(), then it'll throw an IOException in a place where you may wrongly feel safe.
Whenever it's possible, apply a retry pattern, and if you're using FileSystemWatcher, consider postponing action (because you'll get notified, but an application may still be working exclusively with that file).
Advanced scenarios
It's not always so easy, so you may need to share access with someone else. If, for example, you're reading from the beginning and writing to the end, you have at least two options.
1) share the same FileStream with proper synchronization functions (because it is not thread-safe). See this and this posts for an example.
2) use FileShare enumeration to instruct OS to allow other processes (or other parts of your own process) to access same file concurrently.
using (var stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.Read))
{
}
In this example I showed how to open a file for writing and share for reading; please note that when reading and writing overlaps, it results in undefined or invalid data. It's a situation that must be handled when reading. Also note that this doesn't make access to the stream thread-safe, so this object can't be shared with multiple threads unless access is synchronized somehow (see previous links). Other sharing options are available, and they open up more complex scenarios. Please refer to MSDN for more details.
In general N processes can read from same file all together but only one should write, in a controlled scenario you may even enable concurrent writings but this can't be generalized in few text paragraphs inside this answer.
Is it possible to unlock a file used by another process? It's not always safe and not so easy but yes, it's possible.
Using FileShare fixed my issue of opening file even if it is opened by another process.
using (var stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
}
Problem
one is tying to open file System.IO.File.Open(path, FileMode) with this method and want a shared access on file but
if u read documentation of System.IO.File.Open(path, FileMode) it is explicitly saying its does not allow sharing
Solution
use you have to use other override with FileShare
using FileStream fs = System.IO.File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
with FileShare.Read
Had an issue while uploading an image and couldn't delete it and found a solution. gl hf
//C# .NET
var image = Image.FromFile(filePath);
image.Dispose(); // this removes all resources
//later...
File.Delete(filePath); //now works
As other answers in this thread have pointed out, to resolve this error you need to carefully inspect the code, to understand where the file is getting locked.
In my case, I was sending out the file as an email attachment before performing the move operation.
So the file got locked for couple of seconds until SMTP client finished sending the email.
The solution I adopted was to move the file first, and then send the email. This solved the problem for me.
Another possible solution, as pointed out earlier by Hudson, would've been to dispose the object after use.
public static SendEmail()
{
MailMessage mMailMessage = new MailMessage();
//setup other email stuff
if (File.Exists(attachmentPath))
{
Attachment attachment = new Attachment(attachmentPath);
mMailMessage.Attachments.Add(attachment);
attachment.Dispose(); //disposing the Attachment object
}
}
I got this error because I was doing File.Move to a file path without a file name, need to specify the full path in the destination.
The error indicates another process is trying to access the file. Maybe you or someone else has it open while you are attempting to write to it. "Read" or "Copy" usually doesn't cause this, but writing to it or calling delete on it would.
There are some basic things to avoid this, as other answers have mentioned:
In FileStream operations, place it in a using block with a FileShare.ReadWrite mode of access.
For example:
using (FileStream stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
}
Note that FileAccess.ReadWrite is not possible if you use FileMode.Append.
I ran across this issue when I was using an input stream to do a File.SaveAs when the file was in use. In my case I found, I didn't actually need to save it back to the file system at all, so I ended up just removing that, but I probably could've tried creating a FileStream in a using statement with FileAccess.ReadWrite, much like the code above.
Saving your data as a different file and going back to delete the old one when it is found to be no longer in use, then renaming the one that saved successfully to the name of the original one is an option. How you test for the file being in use is accomplished through the
List<Process> lstProcs = ProcessHandler.WhoIsLocking(file);
line in my code below, and could be done in a Windows service, on a loop, if you have a particular file you want to watch and delete regularly when you want to replace it. If you don't always have the same file, a text file or database table could be updated that the service always checks for file names, and then performs that check for processes & subsequently performs the process kills and deletion on it, as I describe in the next option. Note that you'll need an account user name and password that has Admin privileges on the given computer, of course, to perform the deletion and ending of processes.
When you don't know if a file will be in use when you are trying to save it, you can close all processes that could be using it, like Word, if it's a Word document, ahead of the save.
If it is local, you can do this:
ProcessHandler.localProcessKill("winword.exe");
If it is remote, you can do this:
ProcessHandler.remoteProcessKill(computerName, txtUserName, txtPassword, "winword.exe");
where txtUserName is in the form of DOMAIN\user.
Let's say you don't know the process name that is locking the file. Then, you can do this:
List<Process> lstProcs = new List<Process>();
lstProcs = ProcessHandler.WhoIsLocking(file);
foreach (Process p in lstProcs)
{
if (p.MachineName == ".")
ProcessHandler.localProcessKill(p.ProcessName);
else
ProcessHandler.remoteProcessKill(p.MachineName, txtUserName, txtPassword, p.ProcessName);
}
Note that file must be the UNC path: \\computer\share\yourdoc.docx in order for the Process to figure out what computer it's on and p.MachineName to be valid.
Below is the class these functions use, which requires adding a reference to System.Management. The code was originally written by Eric J.:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Management;
namespace MyProject
{
public static class ProcessHandler
{
[StructLayout(LayoutKind.Sequential)]
struct RM_UNIQUE_PROCESS
{
public int dwProcessId;
public System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
}
const int RmRebootReasonNone = 0;
const int CCH_RM_MAX_APP_NAME = 255;
const int CCH_RM_MAX_SVC_NAME = 63;
enum RM_APP_TYPE
{
RmUnknownApp = 0,
RmMainWindow = 1,
RmOtherWindow = 2,
RmService = 3,
RmExplorer = 4,
RmConsole = 5,
RmCritical = 1000
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
struct RM_PROCESS_INFO
{
public RM_UNIQUE_PROCESS Process;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_APP_NAME + 1)]
public string strAppName;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_SVC_NAME + 1)]
public string strServiceShortName;
public RM_APP_TYPE ApplicationType;
public uint AppStatus;
public uint TSSessionId;
[MarshalAs(UnmanagedType.Bool)]
public bool bRestartable;
}
[DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
static extern int RmRegisterResources(uint pSessionHandle,
UInt32 nFiles,
string[] rgsFilenames,
UInt32 nApplications,
[In] RM_UNIQUE_PROCESS[] rgApplications,
UInt32 nServices,
string[] rgsServiceNames);
[DllImport("rstrtmgr.dll", CharSet = CharSet.Auto)]
static extern int RmStartSession(out uint pSessionHandle, int dwSessionFlags, string strSessionKey);
[DllImport("rstrtmgr.dll")]
static extern int RmEndSession(uint pSessionHandle);
[DllImport("rstrtmgr.dll")]
static extern int RmGetList(uint dwSessionHandle,
out uint pnProcInfoNeeded,
ref uint pnProcInfo,
[In, Out] RM_PROCESS_INFO[] rgAffectedApps,
ref uint lpdwRebootReasons);
/// <summary>
/// Find out what process(es) have a lock on the specified file.
/// </summary>
/// <param name="path">Path of the file.</param>
/// <returns>Processes locking the file</returns>
/// <remarks>See also:
/// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373661(v=vs.85).aspx
/// http://wyupdate.googlecode.com/svn-history/r401/trunk/frmFilesInUse.cs (no copyright in code at time of viewing)
///
/// </remarks>
static public List<Process> WhoIsLocking(string path)
{
uint handle;
string key = Guid.NewGuid().ToString();
List<Process> processes = new List<Process>();
int res = RmStartSession(out handle, 0, key);
if (res != 0) throw new Exception("Could not begin restart session. Unable to determine file locker.");
try
{
const int ERROR_MORE_DATA = 234;
uint pnProcInfoNeeded = 0,
pnProcInfo = 0,
lpdwRebootReasons = RmRebootReasonNone;
string[] resources = new string[] { path }; // Just checking on one resource.
res = RmRegisterResources(handle, (uint)resources.Length, resources, 0, null, 0, null);
if (res != 0) throw new Exception("Could not register resource.");
//Note: there's a race condition here -- the first call to RmGetList() returns
// the total number of process. However, when we call RmGetList() again to get
// the actual processes this number may have increased.
res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, null, ref lpdwRebootReasons);
if (res == ERROR_MORE_DATA)
{
// Create an array to store the process results
RM_PROCESS_INFO[] processInfo = new RM_PROCESS_INFO[pnProcInfoNeeded];
pnProcInfo = pnProcInfoNeeded;
// Get the list
res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, processInfo, ref lpdwRebootReasons);
if (res == 0)
{
processes = new List<Process>((int)pnProcInfo);
// Enumerate all of the results and add them to the
// list to be returned
for (int i = 0; i < pnProcInfo; i++)
{
try
{
processes.Add(Process.GetProcessById(processInfo[i].Process.dwProcessId));
}
// catch the error -- in case the process is no longer running
catch (ArgumentException) { }
}
}
else throw new Exception("Could not list processes locking resource.");
}
else if (res != 0) throw new Exception("Could not list processes locking resource. Failed to get size of result.");
}
finally
{
RmEndSession(handle);
}
return processes;
}
public static void remoteProcessKill(string computerName, string userName, string pword, string processName)
{
var connectoptions = new ConnectionOptions();
connectoptions.Username = userName;
connectoptions.Password = pword;
ManagementScope scope = new ManagementScope(#"\\" + computerName + #"\root\cimv2", connectoptions);
// WMI query
var query = new SelectQuery("select * from Win32_process where name = '" + processName + "'");
using (var searcher = new ManagementObjectSearcher(scope, query))
{
foreach (ManagementObject process in searcher.Get())
{
process.InvokeMethod("Terminate", null);
process.Dispose();
}
}
}
public static void localProcessKill(string processName)
{
foreach (Process p in Process.GetProcessesByName(processName))
{
p.Kill();
}
}
[DllImport("kernel32.dll")]
public static extern bool MoveFileEx(string lpExistingFileName, string lpNewFileName, int dwFlags);
public const int MOVEFILE_DELAY_UNTIL_REBOOT = 0x4;
}
}
I had this problem and it was solved by following the code below
var _path=MyFile.FileName;
using (var stream = new FileStream
(_path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
// Your Code! ;
}
I had a very specific situation where I was getting an "IOException: The process cannot access the file 'file path'" on the line
File.Delete(fileName);
Inside an NUnit test that looked like:
Assert.Throws<IOException>(() =>
{
using (var sr = File.OpenText(fileName) {
var line = sr.ReadLine();
}
});
File.Delete(fileName);
It turns out NUnit 3 uses something they call "isolated context" for exception assertions. This probably runs on a separate thread.
My fix was to put the File.Delete in the same context.
Assert.Throws<IOException>(() =>
{
try
{
using (var sr = File.OpenText(fileName) {
var line = sr.ReadLine();
}
}
catch
{
File.Delete(fileName);
throw;
}
});
I had the following scenario that was causing the same error:
Upload files to the server
Then get rid of the old files after they have been uploaded
Most files were small in size, however, a few were large, and so attempting to delete those resulted in the cannot access file error.
It was not easy to find, however, the solution was as simple as Waiting "for the task to complete execution":
using (var wc = new WebClient())
{
var tskResult = wc.UploadFileTaskAsync(_address, _fileName);
tskResult.Wait();
}
In my case this problem was solved by Opening the file for Shared writing/reading. Following are the sample codes for shared reading and writing:-
Stream Writer
using(FileStream fs = new FileStream("D:\\test.txt",
FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
using (StreamWriter sw = new StreamWriter(fs))
{
sw.WriteLine("any thing which you want to write");
}
Stream Reader
using (FileStream fs = new FileStream("D:\\test.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (StreamReader rr=new StreamReader(fs))
{
rr.ReadLine())
}
My below code solve this issue, but i suggest
First of all you need to understand what causing this issue and try the solution which you can find by changing code
I can give another way to solve this issue but better solution is to check your coding structure and try to analyse what makes this happen,if you do not find any solution then you can go with this code below
try{
Start:
///Put your file access code here
}catch (Exception ex)
{
//by anyway you need to handle this error with below code
if (ex.Message.StartsWith("The process cannot access the file"))
{
//Wait for 5 seconds to free that file and then start execution again
Thread.Sleep(5000);
goto Start;
}
}
I'm having a class that is using a FileStream internally using the FileOption: DeleteOnClose. The normal behavior is when I allocate the class with a filename, I do not use the DeleteOnClose, otherwise I use it.
The only problem is that I happens sometimes that I need to undo the DeleteOnClose.
I would be too lengthy to explain the deeper details here. Of course I could create a copy and copy the contents of the FileStream that have been opened with DeleteOnClose to another FileStream but the file size is too large (>= 30GB) so that this approach is impractical.
Deleting the file manually does not work, since the classes are more or less used as memory containers that need to be handled by the GC. Also when something happens it's not helpful to have dead files lying around.
So I was hoping if there is a way to undo the DeleteOnClose attribute as this can be done, e.g. with SetFileAttributes where e.g. the Temporary flag can be set/unset.
With the comments of TheGeneral and TonPlooij I created a small example to test FileDispositionInfo, but somehow this also doesn't work (copied from http://source.roslyn.codeplex.com/#Roslyn.Test.Utilities/TempFiles/DisposableFile.cs,4d5c94058d1b4cd3):
using Microsoft.Win32.SafeHandles;
using System;
using System.IO;
using System.Runtime.InteropServices;
namespace ConsoleApp11
{
class Program
{
[DllImport("kernel32.dll", PreserveSig = false)]
private static extern void SetFileInformationByHandle(SafeFileHandle handle, int fileInformationClass, ref uint fileDispositionInfoDeleteFile, int bufferSize);
private const int FileDispositionInfo = 4;
internal static void PrepareDeleteOnCloseStreamForDisposal(FileStream stream)
{
// tomat: Set disposition to "delete" on the stream, so to avoid ForeFront EndPoint
// Protection driver scanning the file. Note that after calling this on a file that's open with DeleteOnClose,
// the file can't be opened again, not even by the same process.
uint trueValue = 1;
SetFileInformationByHandle(stream.SafeFileHandle, FileDispositionInfo, ref trueValue, sizeof(uint));
}
/// <summary>
/// Marks given file for automatic deletion when all its handles are closed.
/// Note that after doing this the file can't be opened again, not even by the same process.
/// </summary>
internal static void DeleteFileOnClose(string fullPath)
{
using (var stream = new FileStream(fullPath, FileMode.Create, FileAccess.ReadWrite, FileShare.Delete| FileShare.ReadWrite, 8))
{
PrepareDeleteOnCloseStreamForDisposal(stream);
}
}
static void Main(string[] args)
{
DeleteFileOnClose("D:\\test.dat");
Console.WriteLine("Done.");
Console.ReadKey();
}
}
}
To answer you question directly, no you cant change the option mid way through. The file stream uses the winapi flag FILE_FLAG_DELETE_ON_CLOSE, this cant be changed mid way through, its essentially associated with the file handle, when the handle is closed the operating system cleans up the file, that is it and no work around.
If you want different behavior you will have to implement it yourself after the fact. ie deleting the file after its closed or not.
The best alternative I came up with was to create a hard-link to the temporary file if I want to persist it. DeleteOnClose apparently does not seem to actually delete the file, but only the link to the file, which means if we create another hard link to it before closing the file stream it will be persisted (with a new name).
This of course requires a file system that supports hard links, and I'm not sure if this will work on MacOS/Linux, but on Windows NTFS it seems to work as advertised.
So something like the following appears to work, if it is acceptable to use a temporary file name until we decide to persist it:
public class TemporaryFile : FileStream
{
[DllImport("Kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
private static extern bool CreateHardLink(string lpFileName, string lpExistingFileName, IntPtr lpSecurityAttributes);
public TemporaryFile(string path, FileMode fileMode = FileMode.Create, FileAccess fileAccess = FileAccess.ReadWrite, FileShare fileShare = FileShare.ReadWrite | FileShare.Delete, int bufferSize = 4096, FileOptions options = FileOptions.None)
: base(path, fileMode, fileAccess, fileShare, bufferSize, GetFileOptions(options))
{
}
public void PersistTo(string path)
{
if (!CreateHardLink(path, Name, IntPtr.Zero))
{
Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
}
}
private static FileOptions GetFileOptions(FileOptions options)
{
return options | FileOptions.DeleteOnClose;
}
}
Which could then be used like:
using var tempFile = new TemporaryFile(#"c:\tempFile.tmp");
// Write data to TempFile
if (shouldFileBePersisted)
tempFile.PersistTo(#"c:\permanentFileName.txt");
It isn't a perfect solution, but this worked for my purposes, so thought I'd share it.
I have a few methods which work with MemoryMappedFiles for writing/reading data. They work alright if I use simple string for file name, for example "file.mmf". However if I use full directory path the above mentioned exception is being thrown -
Exception has been thrown by the target of an invocation.
With inner exception - {"Could not find a part of the path."}. Here is how my method looks like:
public void WriteToFile(string fileName, string value)
{
string newFileName = CombineDirectory(fileName);
byte[] newValue = Encoding.UTF8.GetBytes(value);
long capacity = newValue.Length + INT_MAXVALUE_TO_BYTEARRAY_LENGTH;
using (var mmf = MemoryMappedFile.CreateFromFile(newFileName, FileMode.Create, newFileName, capacity))
{
using (var accesor = mmf.CreateViewAccessor())
{
byte[] newValueLength = BitConverter.GetBytes(value.Length);
accesor.WriteArray(0, newValueLength, 0, newValueLength.Length);
accesor.WriteArray(INT_MAXVALUE_TO_BYTEARRAY_LENGTH, newValue, 0, newValue.Length);
}
}
}
My path looks like this :
"C:\\Users\\MyUser\\Documents\\Visual Studio 2012.mmf"
And I am using
Path.Combine
The exception occurs on the first 'using' line. If I try to create a file using the same file path with
File.Create
the file is being created with no problem.
If anyone has any suggestions, that would be great.
Regards
You need to make sure that the mapName argument (i.e. the third argument in your call to CreateFromFile) is not identical to the file path. It will throw a PathNotFound exception if you do. Not really helpful in figuring out why it is failing, I agree.
So your options for choosing a map name value:
Generate some unique key, e.g. Guid.NewGuid().ToString()
Use a constant value, e.g. "MySpecialMapForThings"
Use some convention, e.g. generate a unique key that you also use for just the file name part of the mapped file.
An example for the last option:
public static Tuple<FileInfo, string> GenerateMapInfo(string mapDirectory, string fileExtension)
{
var uniqueMapName = Guid.NewGuid().ToString();
var fileName = Path.Combine(mapDirectory, Path.ChangeExtension(uniqueMapName, fileExtension));
return Tuple.Create(new FileInfo(fileName), uniqueMapName);
}
public void WriteToFile(Tuple<FileInfo, string> mapInfo, string value)
{
byte[] newValue = Encoding.UTF8.GetBytes(value);
long capacity = newValue.Length + INT_MAXVALUE_TO_BYTEARRAY_LENGTH;
using (var mmf = MemoryMappedFile.CreateFromFile(mapInfo.Item1.FullName, FileMode.Create, mapInfo.Item2, capacity))
using (var accesor = mmf.CreateViewAccessor())
{
byte[] newValueLength = BitConverter.GetBytes(value.Length);
accesor.WriteArray(0, newValueLength, 0, newValueLength.Length);
accesor.WriteArray(INT_MAXVALUE_TO_BYTEARRAY_LENGTH, newValue, 0, newValue.Length);
}
}
What is the best way to validate the file format in file-upload control in ASP.NET?
Actually I want that user only upload files with specific format. Although I validate it by checking file name but I am looking for another solution to over come this.
Try the following code which reads the first 256 bytes from the file and return the mime type of the file using an internal dll (urlmon.dll).Then compare the mime type of your file and the returned mime type after parsing.
using System.Runtime.InteropServices; ...
[DllImport(#"urlmon.dll", CharSet = CharSet.Auto)]
private extern static System.UInt32 FindMimeFromData(
System.UInt32 pBC,
[MarshalAs(UnmanagedType.LPStr)] System.String pwzUrl,
[MarshalAs(UnmanagedType.LPArray)] byte[] pBuffer,
System.UInt32 cbSize,
[MarshalAs(UnmanagedType.LPStr)] System.String pwzMimeProposed,
System.UInt32 dwMimeFlags,
out System.UInt32 ppwzMimeOut,
System.UInt32 dwReserverd
);
public string getMimeFromFile(string filename)
{
if (!File.Exists(filename))
throw new FileNotFoundException(filename + " not found");
byte[] buffer = new byte[256];
using (FileStream fs = new FileStream(filename, FileMode.Open))
{
if (fs.Length >= 256)
fs.Read(buffer, 0, 256);
else
fs.Read(buffer, 0, (int)fs.Length);
}
try
{
System.UInt32 mimetype;
FindMimeFromData(0, null, buffer, 256, null, 0, out mimetype, 0);
System.IntPtr mimeTypePtr = new IntPtr(mimetype);
string mime = Marshal.PtrToStringUni(mimeTypePtr);
Marshal.FreeCoTaskMem(mimeTypePtr);
return mime;
}
catch (Exception e)
{
return "unknown/unknown";
}
}
But check the type in different browsers, since the mimetype might be different in different browsers.
Also this will give the exact mimetype even if you changed the extension by editing the name of the file.
Hope this helps you...
The only way to be sure is to actually parse the whole file according to the specification of the file format and check that everything fits.
If you want to do just basic check, most binary file formats have some form of header or magic number at their beginning, that you can check for.
You can use a component like Uploadify that limit's the user which type of files he can choose before uploading.
I have an application that works with Enhanced Metafiles.
I am able to create them, save them to disk as .emf and load them again no problem.
I do this by using the gdi32.dll methods and the DLLImport attribute.
However, to enable Version Tolerant Serialization I want to save the metafile in an object along with other data.
This essentially means that I need to serialize the metafile data as a byte array and then deserialize it again in order to reconstruct the metafile.
The problem I have is that the deserialized data would appear to be corrupted in some way, since the method that I use to reconstruct the Metafile raises a "Parameter not valid exception".
At the very least the pixel format and resolutions have changed.
Code use is below.
[DllImport("gdi32.dll")]
public static extern uint GetEnhMetaFileBits(IntPtr hemf, uint cbBuffer, byte[] lpbBuffer);
[DllImport("gdi32.dll")]
public static extern IntPtr SetEnhMetaFileBits(uint cbBuffer, byte[] lpBuffer);
[DllImport("gdi32.dll")]
public static extern bool DeleteEnhMetaFile(IntPtr hemf);
The application creates a metafile image and passes it to the method below.
private byte[] ConvertMetaFileToByteArray(Image image)
{
byte[] dataArray = null;
Metafile mf = (Metafile)image;
IntPtr enhMetafileHandle = mf.GetHenhmetafile();
uint bufferSize = GetEnhMetaFileBits(enhMetafileHandle, 0, null);
if (enhMetafileHandle != IntPtr.Zero)
{
dataArray = new byte[bufferSize];
GetEnhMetaFileBits(enhMetafileHandle, bufferSize, dataArray);
}
DeleteEnhMetaFile(enhMetafileHandle);
return dataArray;
}
At this point the dataArray is inserted into an object and serialized using a BinaryFormatter.
The saved file is then deserialized again using a BinaryFormatter and the dataArray retrieved from the object.
The dataArray is then used to reconstruct the original Metafile using the following method.
public static Image ConvertByteArrayToMetafile(byte[] data)
{
Metafile mf = null;
try
{
IntPtr hemf = SetEnhMetaFileBits((uint)data.Length, data);
mf = new Metafile(hemf, true);
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
return (Image)mf;
}
The reconstructed metafile is then saved saved to disk as a .emf (Model) at which point it can be accessed by the Presenter for display.
private static void SaveFile(Image image, String filepath)
{
try
{
byte[] buffer = ConvertMetafileToByteArray(image);
File.WriteAllBytes(filepath, buffer); //will overwrite file if it exists
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
}
The problem is that the save to disk fails. If this same method is used to save the original Metafile before it is serialized everything is OK. So something is happening to the data during serialization/deserializtion.
Indeed if I check the Metafile properties in the debugger I can see that the ImageFlags, PropertyID, resolution and pixelformats change.
Original Format32bppRgb changes to Format32bppArgb
Original Resolution 81 changes to 96
I've trawled though google and SO and this has helped me get this far but Im now stuck.
Does any one have enough experience with Metafiles / serialization to help..?
EDIT: If I serialize/deserialize the byte array directly (without embedding in another object) I get the same problem.