GelfLoggerDecorator.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Configuration;
using Microsoft.Extensions.Options;

namespace Gelf.Extensions.Logging.Samples.AspNetCore2
{
    public class LoggerDecorator : ILogger
    {
        private readonly ILogger _logger;

        public LoggerDecorator(ILogger logger)
        {
            _logger = logger;
        }

        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
        {
            var additionalFields = new Dictionary<string, object>(2)
            {
                ["log_level"] = logLevel.ToString()
            };

            if (state is IEnumerable<KeyValuePair<string, object>> logValues)
            {
                additionalFields["message_template"] = logValues.Last().Value;
            }

            using (_logger.BeginScope(additionalFields))
            {
                _logger.Log(logLevel, eventId, state, exception, formatter);
            }
        }

        public bool IsEnabled(LogLevel logLevel)
        {
            return _logger.IsEnabled(logLevel);
        }

        public IDisposable BeginScope<TState>(TState state)
        {
            return _logger.BeginScope(state);
        }
    }

    [ProviderAlias("GELF")]
    public class GelfLoggerProviderDecorator : ILoggerProvider
    {
        private readonly GelfLoggerProvider _loggerProvider;

        public GelfLoggerProviderDecorator(GelfLoggerProvider loggerProvider)
        {
            _loggerProvider = loggerProvider;
        }

        public ILogger CreateLogger(string categoryName)
        {
            var logger = _loggerProvider.CreateLogger(categoryName);
            return new LoggerDecorator(logger);
        }

        public void Dispose()
        {
            _loggerProvider.Dispose();
        }
    }

    public static class LoggerBuilderExtensions
    {
        public static ILoggingBuilder AddDecoratedGelf(this ILoggingBuilder builder, Action<GelfLoggerOptions> configure)
        {
            builder.AddConfiguration();
            builder.Services.AddSingleton<GelfLoggerProvider>();
            builder.Services.AddSingleton<ILoggerProvider, GelfLoggerProviderDecorator>();
            builder.Services.TryAddSingleton<IConfigureOptions<GelfLoggerOptions>, GelfLoggerOptionsSetup>();
            builder.Services.Configure(configure);

            return builder;
        }
    }
}