SerilogWebHostBuilderExtensions.cs

// Copyright 2017-2019 Serilog Contributors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

using System;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Logging;
using Serilog.Extensions.Logging;
using Microsoft.Extensions.DependencyInjection;
using Serilog.Extensions.Hosting;

namespace Serilog
{
    /// <summary>
    /// Extends <see cref="IWebHostBuilder"/> with Serilog configuration methods.
    /// </summary>
    public static class SerilogWebHostBuilderExtensions
    {
        /// <summary>
        /// Sets Serilog as the logging provider.
        /// </summary>
        /// <param name="builder">The web host builder to configure.</param>
        /// <param name="logger">The Serilog logger; if not supplied, the static <see cref="Serilog.Log"/> will be used.</param>
        /// <param name="dispose">When true, dispose <paramref name="logger"/> when the framework disposes the provider. If the
        /// logger is not specified but <paramref name="dispose"/> is true, the <see cref="Log.CloseAndFlush()"/> method will be
        /// called on the static <see cref="Log"/> class instead.</param>
        /// <param name="providers">A <see cref="LoggerProviderCollection"/> registered in the Serilog pipeline using the
        /// <c>WriteTo.Providers()</c> configuration method, enabling other <see cref="ILoggerProvider"/>s to receive events. By
        /// default, only Serilog sinks will receive events.</param>
        /// <returns>The web host builder.</returns>
        public static IWebHostBuilder UseSerilog(
            this IWebHostBuilder builder, 
            ILogger logger = null, 
            bool dispose = false,
            LoggerProviderCollection providers = null)
        {
            if (builder == null) throw new ArgumentNullException(nameof(builder));

            builder.ConfigureServices(collection =>
            {
                if (providers != null)
                {
                    collection.AddSingleton<ILoggerFactory>(services =>
                    {
                        var factory = new SerilogLoggerFactory(logger, dispose, providers);

                        foreach (var provider in services.GetServices<ILoggerProvider>())
                            factory.AddProvider(provider);

                        return factory;
                    });
                }
                else
                {
                    collection.AddSingleton<ILoggerFactory>(services => new SerilogLoggerFactory(logger, dispose));
                }

                ConfigureServices(collection, logger);
            });

            return builder;
        }

        /// <summary>Sets Serilog as the logging provider.</summary>
        /// <remarks>
        /// A <see cref="WebHostBuilderContext"/> is supplied so that configuration and hosting information can be used.
        /// The logger will be shut down when application services are disposed.
        /// </remarks>
        /// <param name="builder">The web host builder to configure.</param>
        /// <param name="configureLogger">The delegate for configuring the <see cref="LoggerConfiguration" /> that will be used to construct a <see cref="Logger" />.</param>
        /// <param name="preserveStaticLogger">Indicates whether to preserve the value of <see cref="Log.Logger"/>.</param>
        /// <param name="writeToProviders">By default, Serilog does not write events to <see cref="ILoggerProvider"/>s registered through
        /// the Microsoft.Extensions.Logging API. Normally, equivalent Serilog sinks are used in place of providers. Specify
        /// <c>true</c> to write events to all providers.</param>
        /// <returns>The web host builder.</returns>
        public static IWebHostBuilder UseSerilog(
            this IWebHostBuilder builder,
            Action<WebHostBuilderContext, LoggerConfiguration> configureLogger,
            bool preserveStaticLogger = false,
            bool writeToProviders = false)
        {
            if (builder == null) throw new ArgumentNullException(nameof(builder));
            if (configureLogger == null) throw new ArgumentNullException(nameof(configureLogger));

            builder.ConfigureServices((context, collection) =>
            {
                var loggerConfiguration = new LoggerConfiguration();

                LoggerProviderCollection loggerProviders = null;
                if (writeToProviders)
                {
                    loggerProviders = new LoggerProviderCollection();
                    loggerConfiguration.WriteTo.Providers(loggerProviders);
                }

                configureLogger(context, loggerConfiguration);
                var logger = loggerConfiguration.CreateLogger();
                
                ILogger registeredLogger = null;
                if (preserveStaticLogger)
                {
                    registeredLogger = logger;
                }
                else
                {
                    // Passing a `null` logger to `SerilogLoggerFactory` results in disposal via
                    // `Log.CloseAndFlush()`, which additionally replaces the static logger with a no-op.
                    Log.Logger = logger;
                }

                collection.AddSingleton<ILoggerFactory>(services =>
                {
                    var factory = new SerilogLoggerFactory(registeredLogger, true, loggerProviders);

                    if (writeToProviders)
                    {
                        foreach (var provider in services.GetServices<ILoggerProvider>())
                            factory.AddProvider(provider);
                    }

                    return factory;
                });

                ConfigureServices(collection, logger);
            });
            return builder;
        }
        
        static void ConfigureServices(IServiceCollection collection, ILogger logger)
        {
            if (collection == null) throw new ArgumentNullException(nameof(collection));

            if (logger != null)
            {
                // This won't (and shouldn't) take ownership of the logger. 
                collection.AddSingleton(logger);
            }

            // Registered to provide two services...
            var diagnosticContext = new DiagnosticContext(logger);

            // Consumed by e.g. middleware
            collection.AddSingleton(diagnosticContext);

            // Consumed by user code
            collection.AddSingleton<IDiagnosticContext>(diagnosticContext);
        }
    }
}