Rolling text file to GZip Trace Listener

public class CustomTraceListener
    : TraceListener
{
    private readonly string _fullFileName;
    private readonly int _maxFileSize;
    private FileStream _fileStream;
    private int _numBytes;
    private string _currentLogFileFullName;
         
    public CustomTraceListener(string fullFileName, int maxFileSize = 10 * 1024 * 1024)
    {
        var fileInfo = new FileInfo(fullFileName);
        if (!fileInfo.Directory.Exists)
        {
            throw new ApplicationException("Invalid directory for trace file");
        }
        _fullFileName = fullFileName;
        _maxFileSize = maxFileSize;
        InitializeFile();
    }
 
    private void InitializeFile()
    {
        if (_fileStream != null)
        {
            _fileStream.Dispose(); 
            _fileStream = null;
 
            using (var inputStream = File.OpenRead(_currentLogFileFullName))
            {
                using var outputFileStream = File.OpenWrite($"{_currentLogFileFullName}.gz");
                using var gzipStream = new GZipStream(outputFileStream, CompressionLevel.Optimal);
                byte[] buffer = new byte[1024 * 32];
                int count;
                while ((count = inputStream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    gzipStream.Write(buffer, 0, count);
                }
            }
            File.Delete(_currentLogFileFullName);
        }
 
        var fileInfo = new FileInfo(_fullFileName);
        _currentLogFileFullName = Path.Combine(fileInfo.DirectoryName, $"{Path.GetFileNameWithoutExtension(_fullFileName)}_{DateTime.Now:yyyyMMddHHmmssfff}{fileInfo.Extension}");
        _fileStream = new FileStream(_currentLogFileFullName, FileMode.Create, FileAccess.Write, FileShare.Read);
        _numBytes = 0;
    }
 
    public override void Write(string message)
    {
        RefreshFile();
        byte[] bytes = Encoding.UTF8.GetBytes(message);
        _numBytes += bytes.Length;
        _fileStream.Write(bytes, 0, bytes.Length);
        _fileStream.Flush();
    }
 
    public override void WriteLine(string message)
    {
        RefreshFile();
        byte[] bytes = Encoding.UTF8.GetBytes($"{message}{Environment.NewLine}");
        _numBytes += bytes.Length;
        _fileStream.Write(bytes, 0, bytes.Length);
        _fileStream.Flush();
    }
 
    private void RefreshFile()
    {
        lock (this)
        {
            if (_numBytes > _maxFileSize) { InitializeFile(); }
        }
    }
 
    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);
        if (_fileStream != null) { _fileStream.Dispose(); _fileStream = null; }
    }
}

using var customListener = new CustomTraceListener(@"C:\temp\myfile.log");
Trace.Listeners.Add(new ConsoleTraceListener());
Trace.Listeners.Add(customListener);

This writes to a text file, then after 10MB is written, the log file is gzipped and a new one is created. This is a blocking operation, so be aware you may get the occasional short delay.

If the app is interrupted the file contents will be there in plain text up to that point, so it would need to be compressed manually.