I'm trying to build a small program to monitor my pfirewall.log, but I can't seem to open it. I found quite many (simple) answers, that all kinda say
// use FilesystemWatcher
// open FileStream
// read from last position to end
// output new lines
The problem here is: The file seems to always be opened by another process already. I guess that's the windows process writing to the file, since it's getting written to all the time, as Notepad++ shows me.
Which means, Notepad++ can for some reason do what I can not: Read the file despite it being opened already.
I initialize my monitor in the constructor:
public FirewallLogMonitor(string path)
{
if (!File.Exists(path))
throw new FileNotFoundException("Logfile not found");
this.file = path;
this.lastPosition = 0;
this.monitor = new FileSystemWatcher(Path.GetDirectoryName(path), Path.GetFileName(path));
this.monitor.NotifyFilter = NotifyFilters.Size;
}
And try to read the file on monitor.Changed event:
private void LogFileChanged(object sender, FileSystemEventArgs e)
{
using (FileStream stream = new FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read))
using (StreamReader reader = new StreamReader(stream))
{
stream.Seek(this.lastPosition, SeekOrigin.Begin);
var newLines = reader.ReadToEnd();
this.lastPosition = stream.Length;
var filteredLines = filterLines(newLines);
if (filteredLines.Count > 0)
NewLinesAvailable(this, filteredLines);
}
}
It always throws the IOException on new FileStream(...) to tell me the file is already in use.
Since Notepad++ does it, there has to be a way I can do it too, right?
**Edit: ** A button does this:
public void StartLogging()
{
this.IsRunning = true;
this.monitor.Changed += LogFileChanged;
this.monitor.EnableRaisingEvents = true;
}
**Edit2: ** This is not a duplicate of FileMode and FileAccess and IOException: The process cannot access the file 'filename' because it is being used by another process, since that one assumes I have control over the writing process. Will try the other suggestions, and report back with results.
