Get currently active logging file?

[ChristianSauer]

Hi,
is there a way to get the currently active logging File?
I want to expose it via HTTP (don't ask...) and would like to know which file I need to expose.

[cocowalla]

I guess you could scan the folder and pick out the file with the latest "last modified" time?

Otherwise, I'm not sure there a good way to do this 🤔. You could use FileLifecycleHooks, so you would know whenever a new file was opened. Something like:

public class MyHooks : FileLifecycleHooks
{
    private readonly MyDep dep;

    public MyHooks(MyDep dep)
    {
        this.dep = dep;
    }

    public override Stream OnFileOpened(Stream underlyingStream, Encoding _)
    {
        var filename = ((FileStream)underlyingStream).Name;
        myDep.Notify(filename);
        
        return base.OnFileOpened(underlyingStream, encoding);
    }
}

BUT, this will only work if your logger doesn't have fileSizeLimitBytes set, otherwise the underlying stream will be a WriteCountingStream instead of a FileStream - WriteCountingStream doesn't expose the filename, or provide access to it's own underlying stream.

@nblumhardt do you see any other way to get the current filename? I'm wondering too if WriteCountingStream should provide a means to access it's own underlying stream?

[ChristianSauer]

Thanks for the quick reply!
The idea with the folder would definitely work, altough I prefer using an inbuilt mechanism. SImply due to the fact that I don't want to guess wrong ;)
Your LiceCycleHook looks good, except the problem with the WriteCountingStream - I think I will go with the first solution and provide a hook to plugin a better function at a later time.

[Khaos66]

Based on the answer of @cocowalla I created this solution. Not super clean, as it uses reflection, but should be safe

internal class LogFileLifecycleHooks : FileLifecycleHooks
{
    public Action<string> FileNameChanged { get; set; }

    public LogFileLifecycleHooks(Action<string> fileNameChanged)
    {
        FileNameChanged = fileNameChanged;
    }

    public override Stream OnFileOpened(Stream underlyingStream, Encoding encoding)
    {
        var streamType = underlyingStream.GetType();
        if (streamType.FullName == "Serilog.Sinks.File.WriteCountingStream")
        {
            var streamField = streamType.GetField("_stream", BindingFlags.NonPublic | BindingFlags.Instance);
            underlyingStream = streamField.GetValue(underlyingStream) as Stream;
        }
        if (underlyingStream is FileStream stream)
        {
            string filename = stream.Name;
            FileNameChanged?.Invoke(filename);
        }

        return base.OnFileOpened(underlyingStream, encoding);
    }
}

[augustoproiete]

@Khaos66 There's no need to user reflection if you're using a recent version of this sink. Since Serilog.Sinks.File v5.0.0 (June 2021), FileLifecycleHooks has an alternative method you can override and capture the name of the file.

internal class CaptureFilePathHook : FileLifecycleHooks
{
    public string? Path { get; private set; }

    public override Stream OnFileOpened(string path, Stream underlyingStream, Encoding encoding)
    {
        Path = path;
        return base.OnFileOpened(path, underlyingStream, encoding);
    }
}

More details on #191 and #189

[worthapenny]

Hi,

I am struggling to understand the usage in order to get the active log file path. This is how I tried and the Path I get is null.

var logFilePath = Path.Combine(Path.GetTempPath(), "__MyApp_Log..Log");
var filePathHook = new CaptureFilePathHook();

Log.Logger = new LoggerConfiguration()
    .Enrich.FromLogContext()
    .MinimumLevel.ControlledBy(LoggingLevelSwitch) // Default's to Information 
    .WriteTo.Console(outputTemplate: logTemplate, theme: AnsiConsoleTheme.Code)
    .WriteTo.File(
        logFilePath,
        rollingInterval: RollingInterval.Day,
        retainedFileCountLimit: 7,
        flushToDiskInterval: TimeSpan.FromSeconds(5),
        outputTemplate: logTemplate,
        hooks: filePathHook)
    .CreateLogger();

LoggingLevelSwitch.MinimumLevel = logEventLevel;

var logFIleFullPath = filePathHook.Path; // <---- is null

// .....
class CaptureFilePathHook : FileLifecycleHooks
{
    public string? Path { get; private set; }

    public override Stream OnFileOpened(string path, Stream underlyingStream, Encoding encoding)
    {
        Path = path;
        return base.OnFileOpened(path, underlyingStream, encoding);
    }
}

[GeoDirk]

@worthapenny

My code which is similar to your works in returning a path. The only difference that I could see is that my code goes to a type of Serilog.Core.Logger instead of your Log.Logger.

var log = new LoggerConfiguration()
                .MinimumLevel.Is(logLevel)
                .WriteTo.File(logPath, outputTemplate: outputTemplate, rollingInterval: RollingInterval.Day, hooks: logFilePathHook)
                .WriteTo.Debug(outputTemplate: outputTemplate)
                .CreateLogger();

[augustoproiete]

@worthapenny This is because you're not writing anything to the log, and the hook was not yet initialized... You can put a breakpoint the OnFileOpened method of your hook to confirm.

Log.Information("Hello");
var logFileFullPath = filePathHook.Path; // <----should have the path of the current file

[emilaz]

What if I need to access the filepath at a different place than where I defined the filePathHook? Can I get it from Log somehow?

[augustoproiete]

@emilaz Make sure the file path hook updates a shared variable that you can access from the place you need in your app.

[hhgm]

@emilaz Make sure the file path hook updates a shared variable that you can access from the place you need in your app.

So, I have managed to get this example working, but you mention sharing the path through shared variable... how would I do this? I am creating the logger by reading a configuration file, and that works fine, but I need to be able to the read the path from my application.

[augustoproiete]

@hhgm Create a public property on the hook that you can access to retrieve the path. Like the example above #129 (comment)