How to Download log files generated from log4Net

Question

I'm using log4net in a ASP.NET MVC 4 application and I'm trying to download the generated log file from log4Net.

I have in mind to download the log file with a FileResult, like:

[Authorize(Roles = "Admin")]
public FileResult DownloadUserInterfaceLog()
{
    // Get the path of the log file
    string path = (LogManager.GetCurrentLoggers()[0].Logger.Repository.GetAppenders()[0] as FileAppender).File;
    // Get the file
    byte[] fileBytes = System.IO.File.ReadAllBytes(path);
    string fileName = "Log.txt";
    // Return the expected file
    return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Octet, fileName);
}

My problem is that when I call System.IO.File.ReadAllBytes(path);I get an Exception, cause the log file is already used by another process.

I'm already put <lockingModel value="log4net.Appender.FileAppender+MinimalLock" /> (which should release the file after any modification) in my Web.Config with no success.

Begin of log4Net configuration in Web.Config:

<log4net>
    <appender name="Appender-root" type="log4net.Appender.RollingFileAppender">
        <lockingModel value="log4net.Appender.FileAppender+MinimalLock" />
        <file value="Path..." />
        <appendToFile value="true" />

score 3 · Accepted Answer · answered Jan 14 '15 at 10:15

Here is an article about similar trouble.

File.ReadAllBytes() function is written such that it uses a call like the following to instantiate a FileStream:
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read)
Notice that the FileShare is specified as Read. That means if you have another piece of code writing to the same file at the same time, you will get an error even if the other piece of code created the FileStream by specifying the share mode as “ReadWrite” like so:
FileStream fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.ReadWrite)

Solution is to write your own custom ReadAllBytes:

public static byte[] ReadAllBytes(String path)
{
    byte[] bytes;
    using (FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        int index = 0;
        long fileLength = fs.Length;
        if (fileLength > Int32.MaxValue)
            throw new IOException(“File too long”);
        int count = (int)fileLength;
        bytes = new byte[count];
        while (count > 0)
        {
            int n = fs.Read(bytes, index, count);
            if (n == 0)
                throw new InvalidOperationException(“End of file reached before expected”);
            index += n;
            count -= n;
        }
    }
return bytes;
}

score 2 · Answer 2 · answered Jan 14 '15 at 10:11

2

you need to close the Appender before accessing the file:

((FileAppender)LogManager.GetCurrentLoggers()[0].Logger.Repository.GetAppenders()[0]).Close()

answered Jan 14 '15 at 10:11

Alexis Peters

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1

Seems to work ! Thank you so much !! Do you know also, how can I restablish the log4net tracer ? (after I close the Appender) – Yordan Asenov Jan 14 '15 at 10:20

score 0 · Answer 3 · answered Dec 10 '21 at 13:36

This worked for me

            var logFile = System.Web.HttpContext.Current.Server.MapPath("/Log.txt");
            if (System.IO.File.Exists(logFile))
            {
                var copyFile = logFile.Replace(".txt", "");
                System.IO.File.Copy(logFile, copyFile);
                var bytes = System.IO.File.ReadAllBytes(copyFile);
                System.IO.File.Delete(copyFile);
                return bytes;

            }

score 0 · Answer 4 · answered Apr 22 '22 at 07:32

However, below code can be used to open the file without throwing exception

using (var stream = File.Open(selectedItem.FileFullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
            {
                using (var streamReader = new StreamReader(stream))
                {
                    while (streamReader.Peek() > -1)
                    {
                        var line = streamReader.ReadLine();
                        // . . .
                    }
                }
            }

How to Download log files generated from log4Net

4 Answers4