cocowalla / serilog-sinks-file-header

Plugin for the Serilog File sink that writes a header at the start of each log file

Serilog.Sinks.File.Header

A FileLifecycleHooks-based plugin for the Serilog File Sink that writes a configurable header at the start of each log file.

Getting started

To get started, install the latest Serilog.Sinks.File.Header package from NuGet:

Install-Package Serilog.Sinks.File.Header -Version 1.0.1

To enable writing a header, use one of the new LoggerSinkConfiguration extensions that has a FileLifecycleHooks argument, and create a new HeaderWriter:

Log.Logger = new LoggerConfiguration()
    .WriteTo.File("log.txt", hooks: new HeaderWriter("Timestamp,Level,Message"))
    .CreateLogger();

Note this also works if you enable rolling log files.

Instead of writing a static string, you can instead provide a factory method that resolves the header at runtime:

Func<string> headerFactory = () => $"My dynamic header {DateTime.UtcNow}";

Log.Logger = new LoggerConfiguration()
    .WriteTo.File("log.txt", hooks: new HeaderWriter(headerFactory))
    .CreateLogger();

JSON appsettings.json configuration

It's also possible to enable log file headers when configuring Serilog from a configuration file using Serilog.Settings.Configuration. To do this, you will first need to create a class with a public static member that can provide the configuration system with a configured instance of HeaderWriter:

using Serilog.Sinks.File.Header;

namespace MyApp.Logging
{
    public class SerilogHooks
    {
        public static HeaderWriter MyHeaderWriter => new HeaderWriter("Timestamp,Level,Message");
    }
}

The hooks argument in Your appsettings.json file should be configured as follows:

{
  "Serilog": {
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "log.csv",
          "hooks": "MyApp.Logging.SerilogHooks::MyHeaderWriter, MyApp"
        }
      }
    ]
  }
}

To break this down a bit, what you are doing is specifying the fully qualified type name of the class that provides your HeaderWriter, using Serilog.Settings.Configuration's special :: syntax to point to the MyHeaderWriter member.

Sample applications

2 basic console apps are provided as samples:

• Serilog.Sinks.File.Header.Sample: demonstrates writing tab-delimited logs with a header row, configured programmatically
• Serilog.Sinks.File.Header.ConfigSample: demonstrates writing CSV-formatted logs with a header row, configured from appsettings.json

In both projects, logs are written to files in .\Logs.

About FileLifecycleHooks

FileLifecycleHooks is a Serilog File Sink mechanism that allows hooking into log file lifecycle events, enabling scenarios such as wrapping the Serilog output stream in another stream, or capturing files before they are deleted by Serilog's retention mechanism.

Other available hooks include:

• serilog-sinks-file-gzip: compresses logs as they are written, using streaming GZIP compression
• serilog-sinks-file-archive: archives completed log files before they are deleted by Serilog's retention mechanism