Developing a sink

The following example uses the dotnet command to create a project.

Create the project

mkdir SimpleSink
cd SimpleSink
dotnet new console

Add Dependencies

• Add the Serilog Package from NuGet

dotnet add package serilog

Building a Simple Sink

Include the following using statements. These are used by the sink class and also the configuring Serilog.

using Serilog;
using Serilog.Core;
using Serilog.Events;
using Serilog.Configuration;

Create the Sink

A sink is simply a class that implements the ILogEventSink interface. The following example renders every message regardless of log level to the console.

public class MySink : ILogEventSink
{
    private readonly IFormatProvider _formatProvider;

    public MySink(IFormatProvider formatProvider)
    {
        _formatProvider = formatProvider;
    }

    public void Emit(LogEvent logEvent)
    {
        var message = logEvent.RenderMessage(_formatProvider);
        Console.WriteLine(DateTimeOffset.Now.ToString() + " "  + message);
    }
}

Extensions for configuration

A pattern often used when configuring a sink, is to provide an extension method class for the LoggerSinkConfiguration. The following code illustrates this approach by exposing a MySink option when configuring Serilog.

public static class MySinkExtensions
{
    public static LoggerConfiguration MySink(
              this LoggerSinkConfiguration loggerConfiguration,
              IFormatProvider formatProvider = null)
    {
        return loggerConfiguration.Sink(new MySink(formatProvider));
    }
}

These extension methods also drive JSON configuration. When configuring from e.g. appsettings.json, some deployment models require adding the assembly containing the extension method class to the Using directive:

{
  "Serilog": {
    "MinimumLevel": "Information",
    "Using": [ "Example.SimpleSink" ],
    "WriteTo":
      [
        { "Name": "MySink" }
      ]
  }
}

Using the sink

As seen in Configuration Basics the new sink can be configured as follows.

var log = new LoggerConfiguration()
    .MinimumLevel.Information()
    .WriteTo.MySink()
    .CreateLogger();

Releasing resources

If the sink implements IDisposable, Serilog will call its Dispose() method when either Log.CloseAndFlush() is called (when using the static Log class), or the Logger writing to the sink is disposed directly.

Handling errors and exceptions

If a sink cannot accept/successfully process an event, it can (and should) throw an exception from Emit() to notify Serilog of this. Serilog will suppress the exception and write a standard diagnostic message to SelfLog, unless the sink is configured explicitly for auditing.

Sinks can additionally write diagnostic messages to SelfLog, however this should be done sparingly to avoid adverse performance impact.

Threading

Sinks must be completely thread-safe once constructed, and accept calls to Emit() on any thread. Serilog will invoke Emit() concurrently.

Full Sample

Below is the full example code as a console app.

using System;
using Serilog;
using Serilog.Core;
using Serilog.Events;
using Serilog.Configuration;

namespace SimpleSink
{
    class Program
    {
        static void Main(string[] args)
        {
            var log = new LoggerConfiguration()
                .MinimumLevel.Information()
                .WriteTo.MySink()
                .CreateLogger();
            
            var position = new { Latitude = 25, Longitude = 134 };
            var elapsedMs = 34;

            log.Information("Processed {@Position} in {Elapsed:000} ms.", position, elapsedMs);

        }
    }

    public class MySink : ILogEventSink
    {
        private readonly IFormatProvider _formatProvider;

        public MySink(IFormatProvider formatProvider)
        {
            _formatProvider = formatProvider;
        }

        public void Emit(LogEvent logEvent)
        {
            var message = logEvent.RenderMessage(_formatProvider);
            Console.WriteLine(DateTimeOffset.Now.ToString() + " "  + message);
        }
    }

    public static class MySinkExtensions
    {
        public static LoggerConfiguration MySink(
                  this LoggerSinkConfiguration loggerConfiguration,
                  IFormatProvider formatProvider = null)
        {
            return loggerConfiguration.Sink(new MySink(formatProvider));
        }
    }
}

Example Output

17/01/2017 3:10:26 PM +10:00 Processed { Latitude: 25, Longitude: 134 } in 034 ms.