Is there any way to read data from a locked file?

Question

Here's what I have in mind:

        var file = @"myfile";
        File.Open(file,
                  FileMode.Open, FileAccess.ReadWrite, FileShare.None);

        using (StreamReader rdr = new StreamReader(File.Open(file, FileMode.Open, FileAccess.Read, FileShare.Read)))
        {
            rdr.ReadToEnd();
        }
        var t = File.ReadAllBytes(file);

Neigther File.Open(file, FileMode.Open, FileAccess.Read, FileShare.Read) nor File.ReadAllBytes can read file data.

From my old c++ and winapi days, I do remember, that there used to be a good way to read locked files, if you have backup priviledges, but I have no idea how obtain and use those in c#.

Can anyone provide me with a sample on how to read a file after it has been locked?

Answer 1

Well, if the file is totally locked (no sharing ) you will not be able to read it. If the file was opened to share read , you will be able to read using a non intrusive method:

string fileName = @"myfile";
using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (StreamReader fileReader = new StreamReader(fileStream ))
{
    while (!fileReader .EndOfStream)
    {
        string line = fileReader .ReadLine();
        // Your code here
    }
}

Answer 2

What I was trying to do in fact is impossible, and backup privilege doesn't help either:

       [DllImport("kernel32.dll", CharSet = CharSet.Auto,
        CallingConvention = CallingConvention.StdCall,
        SetLastError = true)]
            public static extern SafeFileHandle CreateFile(
                string lpFileName,
                uint dwDesiredAccess,
                uint dwShareMode,
                IntPtr SecurityAttributes,
                uint dwCreationDisposition,
                uint dwFlagsAndAttributes,
                IntPtr hTemplateFile
            );

    private static uint READ_CONTROL = 0x00020000;
    private static uint OPEN_EXISTING = 3;
    private static uint FILE_FLAG_BACKUP_SEMANTICS = 0x02000000;


        var file = @"myfile";
        File.Open(file,
                  FileMode.Open, FileAccess.ReadWrite, FileShare.None);

        using(PrivilegeEnabler pe = new PrivilegeEnabler(Process.GetCurrentProcess(), Privilege.Backup))
        {
            var hFile = CreateFile(file,           // lpFileName
                       READ_CONTROL,               // dwDesiredAccess
                       0,                          // dwShareMode
                       IntPtr.Zero,                // lpSecurityAttributes
                       OPEN_EXISTING,              // dwCreationDisposition
                       FILE_FLAG_BACKUP_SEMANTICS, // dwFlagsAndAttributes
                       IntPtr.Zero);               // hTemplateFile
            using (var fs=new  FileStream(hFile.DangerousGetHandle(),FileAccess.Read))
            {
                using (StreamReader rdr=new StreamReader(fs))
                {
                    rdr.ReadToEnd();
                }
            }
        }

will still result in an error.