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Global exception handling and custom logging in AspNet Core with MongoDB

In this, we would be looking into logging and global exception handling in the AspNet Core application with proper registration of logger and global exception handling.

Custom logging


The first step is to create a data model that we want to save into DB.

Error log Data model
These are few properties to do logging which could be extended or reduced based on need.

 public class ErrorLog  
 {  
      /// <summary>  
      /// Gets or sets the Error log identifier.  
      /// </summary>  
      /// <value>  
      /// The Error log identifier.  
      /// </value>  
      [BsonRepresentation(BsonType.ObjectId)]  
      public ObjectId Id { get; set;   
      /// <summary>  
      /// Gets or sets the date.  
      /// </summary>  
      /// <value>  
      /// The date.  
      /// </value>  
      public DateTime Date { get; set; }  
      /// <summary>  
      /// Gets or sets the thread.  
      /// </summary>  
      /// <value>  
      /// The thread.  
      /// </value>  
      public string Thread { get; set; }  
      /// <summary>  
      /// Gets or sets the level.  
      /// </summary>  
      /// <value>  
      /// The level.  
      /// </value>  
      public string Level { get; set; }  
      /// <summary>  
      /// Gets or sets the logger.  
      /// </summary>  
      /// <value>  
      /// The logger.  
      /// </value>  
      public string Logger { get; set; }  
      /// <summary>  
      /// Gets or sets the message.  
      /// </summary>  
      /// <value>  
      /// The message.  
      /// </value>  
      public string Message { get; set; }  
      /// <summary>  
      /// Gets or sets the exception.  
      /// </summary>  
      /// <value>  
      /// The exception.  
      /// </value>  
      public string Exception { get; set; }  
      /// <summary>  
      /// Gets or sets the user agent.  
      /// </summary>  
      /// <value>  
      /// The user agent.  
      /// </value>  
      public string UserAgent { get; set; }  
      /// <summary>  
      /// Gets or sets the ip address.  
      /// </summary>  
      /// <value>  
      /// The ip address.  
      /// </value>  
      public string IpAddress { get; set; }  
      /// <summary>  
      /// Gets or sets the URL.  
      /// </summary>  
      /// <value>  
      /// The URL.  
      /// </value>  
      public string Url { get; set; }  
      /// <summary>  
      /// Gets or sets the referrer.  
      /// </summary>  
      /// <value>  
      /// The referrer.  
      /// </value>  
      public string Referrer { get; set; }  
      /// <summary>  
      /// Gets or sets the name of the user.  
      /// </summary>  
      /// <value>  
      /// The name of the user.  
      /// </value>  
      public string UserName { get; set; }  
      /// <summary>  
      /// Gets or sets the name of the server.  
      /// </summary>  
      /// <value>  
      /// The name of the server.  
      /// </value>  
      public string ServerName { get; set; }  
 }  

The logger, for collecting log information and inserting into DB

It has to be extended from ILogger for implementing the definition of Logger.


 using Microsoft.AspNetCore.Http;  
 using Microsoft.Extensions.DependencyInjection;  
 using Microsoft.Extensions.Logging;  
 using Microsoft.Extensions.OptionsModel;  
 using MongoDB.Driver;  
 using System;  
 using System.Collections;  
 using System.Collections.Generic;  
 using System.Linq;  
 using System.Text;  
 /// <summary>  
 /// Mongo DB logger  
 /// </summary>  
 /// <typeparam name="TLog">The type of the log.</typeparam>  
 /// <seealso cref="Microsoft.Extensions.Logging.ILogger" />  
 public class MongoLogger<TLog> : ILogger  
   where TLog : ErrorLog, new()  
 {  
   /// <summary>  
   /// The indentation  
   /// </summary>  
   private const int Indentation = 2;  
   /// <summary>  
   /// The filter for log level  
   /// </summary>  
   private readonly Func<string, LogLevel, bool> Filter;  
   /// <summary>  
   /// The logger requester name  
   /// </summary>  
   private readonly string Name;  
   /// <summary>  
   /// The services  
   /// </summary>  
   private readonly IServiceProvider Services;  
   /// <summary>  
   /// The _mongo database  
   /// </summary>  
   private IMongoDatabase _mongoDb;  
   /// <summary>  
   /// Initializes a new instance of the <see cref="MongoLogger{TLog}"/> class.  
   /// </summary>  
   /// <param name="name">The name.</param>  
   /// <param name="filter">The filter.</param>  
   /// <param name="serviceProvider">The service provider.</param>  
   public MongoLogger(string name, Func<string, LogLevel, bool> filter, IServiceProvider serviceProvider)  
   {  
     Name = name;  
     Filter = filter ?? GetFilter(serviceProvider.GetService<IOptions<MongoLoggerOption>>());  
     Services = serviceProvider;  
   }  
   /// <summary>  
   /// Gets the database log.  
   /// </summary>  
   /// <value>  
   /// The database log.  
   /// </value>  
   protected IMongoCollection<ErrorLog> DbLog  
   {  
     get  
     {  
       _mongoDb = _mongoDb ?? Services.GetService<IMongoDatabase>();  
       return _mongoDb.GetCollection<ErrorLog>(nameof(ErrorLog));  
     }  
   }  
   /// <summary>  
   /// Begins a logical operation scope.  
   /// </summary>  
   /// <typeparam name="TState"></typeparam>  
   /// <param name="state">The identifier for the scope.</param>  
   /// <returns>  
   /// An IDisposable that ends the logical operation scope on dispose.  
   /// </returns>  
   public IDisposable BeginScope<TState>(TState state)  
   {  
     return null;  
   }  
   /// <summary>  
   /// Checks if the given <paramref name="logLevel" /> is enabled.  
   /// </summary>  
   /// <param name="logLevel">level to be checked.</param>  
   /// <returns>  
   ///  <c>true</c> if enabled.  
   /// </returns>  
   public bool IsEnabled(LogLevel logLevel)  
   {  
     return Filter(Name, logLevel);  
   }  
   /// <summary>  
   /// Writes a log entry.  
   /// </summary>  
   /// <typeparam name="TState"></typeparam>  
   /// <param name="logLevel">Entry will be written on this level.</param>  
   /// <param name="eventId">Id of the event.</param>  
   /// <param name="state">The entry to be written. Can be also an object.</param>  
   /// <param name="exception">The exception related to this entry.</param>  
   /// <param name="formatter">Function to create a <c>string</c> message of the <paramref name="state" /> and <paramref name="exception" />.</param>  
   public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception,  
     Func<TState, Exception, string> formatter)  
   {  
     if (!IsEnabled(logLevel))  
     {  
       return;  
     }  
     var message = string.Empty;  
     var values = state as IReadOnlyList<KeyValuePair<string, object>>;  
     if (formatter != null)  
     {  
       message = formatter(state, exception);  
     }  
     else if (values != null)  
     {  
       var builder = new StringBuilder();  
       FormatLogValues(  
         builder,  
         values,  
         level: 1,  
         bullet: false);  
       message = builder.ToString();  
       if (exception != null)  
       {  
         message += Environment.NewLine + exception;  
       }  
     }  
     else  
     {  
       message = $"{Convert.ToString(message)} [Check formatting]";  
     }  
     if (string.IsNullOrEmpty(message))  
     {  
       return;  
     }  
     var log = new TLog  
     {  
       Date = DateTime.UtcNow,  
       Level = logLevel.ToString(),  
       Logger = Name,  
       Message = message,  
       Thread = eventId.ToString(),  
     };  
     if (exception != null)  
     {  
       log.Exception = exception.ToString();  
     }  
     var httpContext = Services.GetRequiredService<IHttpContextAccessor>()?.HttpContext;  
     if (httpContext != null)  
     {  
       log.UserAgent = httpContext.Request.Headers["User-Agent"];  
       log.UserName = httpContext.User.Identity.Name;  
       try  
       {  
         log.IpAddress = httpContext.Connection.LocalIpAddress?.ToString();  
       }  
       catch (ObjectDisposedException)  
       {  
         log.IpAddress = "Disposed";  
       }  
       log.Url = httpContext.Request.Path;  
       log.ServerName = httpContext.Request.Host.Value;  
       log.Referrer = httpContext.Request.Headers["Referer"];  
     }  
     DbLog.InsertOne(log);  
   }  
   /// <summary>  
   /// Formats the log values.  
   /// </summary>  
   /// <param name="builder">The builder.</param>  
   /// <param name="logValues">The log values.</param>  
   /// <param name="level">The level.</param>  
   /// <param name="bullet">if set to <c>true</c> new item insert.</param>  
   private void FormatLogValues(StringBuilder builder, IReadOnlyList<KeyValuePair<string, object>> logValues, int level, bool bullet)  
   {  
     if (logValues == null)  
     {  
       return;  
     }  
     var isFirst = true;  
     foreach (var kvp in logValues)  
     {  
       builder.AppendLine();  
       if (bullet && isFirst)  
       {  
         builder.Append(' ', level * Indentation - 1)  
             .Append('-');  
       }  
       else  
       {  
         builder.Append(' ', level * Indentation);  
       }  
       builder.Append(kvp.Key)  
           .Append(": ");  
       if (kvp.Value is IEnumerable && !(kvp.Value is string))  
       {  
         foreach (var value in (IEnumerable)kvp.Value)  
         {  
           if (value is IReadOnlyList<KeyValuePair<string, object>>)  
           {  
             FormatLogValues(  
               builder,  
               (IReadOnlyList<KeyValuePair<string, object>>)value,  
               level + 1,  
               bullet: true);  
           }  
           else  
           {  
             builder.AppendLine()  
                 .Append(' ', (level + 1) * Indentation)  
                 .Append(value);  
           }  
         }  
       }  
       else if (kvp.Value is IReadOnlyList<KeyValuePair<string, object>>)  
       {  
         FormatLogValues(  
           builder,  
           (IReadOnlyList<KeyValuePair<string, object>>)kvp.Value,  
           level + 1,  
           bullet: false);  
       }  
       else  
       {  
         builder.Append(kvp.Value);  
       }  
       isFirst = false;  
     }  
   }  
   /// <summary>  
   /// Gets the filter.  
   /// </summary>  
   /// <param name="options">The options.</param>  
   /// <returns>Filtered item based on request.</returns>  
   private Func<string, LogLevel, bool> GetFilter(IOptions<MongoLoggerOption> options)  
   {  
     if (options != null)  
     {  
       return ((category, level) => GetFilter(options.Value, category, level));  
     }  
     else  
       return ((category, level) => true);  
   }  
   /// <summary>  
   /// Gets the filter.  
   /// </summary>  
   /// <param name="options">The options.</param>  
   /// <param name="category">The category.</param>  
   /// <param name="level">The level.</param>  
   /// <returns>Filtered item based on request.</returns>  
   private bool GetFilter(MongoLoggerOption options, string category, LogLevel level)  
   {  
     if (options.Filters != null)  
     {  
       var filter = options.Filters.Keys.FirstOrDefault(p => category.StartsWith(p));  
       if (filter != null)  
         return (int)options.Filters[filter] <= (int)level;  
       else return true;  
     }  
     return true;  
   }  
 }  

The Log<TState> is the main function where actual logging logic has to written which takes help of FormatLogValues for formatting exceptions.

The GetFilter uses MongoLoggerOption for checking the enabled filters from IsEnabled function

 /// <summary>  
 /// Mongo DB logger options.  
 /// </summary>  
 public class MongoLoggerOption  
 {  
   /// <summary>  
   /// Gets or sets the filters for logging.  
   /// </summary>  
   /// <value>  
   /// The filters for logging.  
   /// </value>  
   public Dictionary<string, LogLevel> Filters { get; set; }  
 }  


Till now we have created a model and Logger implementation. Now, it is time for creating configuration/structure to register logger. For registration, we can create logger provider and an extension method to register logger on startup.

Logger provider
The importance of this is just to create an instance of logger based on filter and service provider.

 using Microsoft.Extensions.Logging;  
 using System;  
 /// <summary>  
 /// Mongo DB logger provider  
 /// </summary>  
 /// <typeparam name="TLog">The type of the log.</typeparam>  
 /// <seealso cref="Microsoft.Extensions.Logging.ILoggerProvider" />  
 public class MongoLoggerProvider<TLog> : ILoggerProvider  
   where TLog : ErrorLog, new()  
 {  
   /// <summary>  
   /// The filter for logging.  
   /// </summary>  
   private readonly Func<string, LogLevel, bool> Filter;  
   /// <summary>  
   /// The service provider  
   /// </summary>  
   private readonly IServiceProvider ServiceProvider;  
   /// <summary>  
   /// Initializes a new instance of the <see cref="MongoLoggerProvider{TLog}"/> class.  
   /// </summary>  
   /// <param name="serviceProvider">The service provider.</param>  
   /// <param name="filter">The filter.</param>  
   public MongoLoggerProvider(IServiceProvider serviceProvider, Func<string, LogLevel, bool> filter)  
   {  
     Filter = filter;  
     ServiceProvider = serviceProvider;  
   }  
   /// <summary>  
   /// Creates the logger.  
   /// </summary>  
   /// <param name="name">The name.</param>  
   /// <returns></returns>  
   public ILogger CreateLogger(string name)  
   {  
     return new MongoLogger<TLog>(name, Filter, ServiceProvider);  
   }  
   /// <summary>  
   /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.  
   /// </summary>  
   public void Dispose()  
   {  
     // Nothing to dispose.  
   }  
 }  


ILoggerFactory implementation for registration

 using Microsoft.Extensions.Logging;  
 using System;  
 /// <summary>  
 /// Mongo DB logger registration.  
 /// </summary>  
 public static class MongoLoggerFactoryExtensions  
 {  
   /// <summary>  
   /// Adds the Mongo DB logger framework.  
   /// </summary>  
   /// <typeparam name="TLog">The type of the log.</typeparam>  
   /// <param name="factory">The factory.</param>  
   /// <param name="serviceProvider">The service provider.</param>  
   /// <param name="filter">The filter.</param>  
   /// <returns></returns>  
   /// <exception cref="ArgumentNullException"></exception>  
   public static ILoggerFactory AddMongoFramework<TLog>(this ILoggerFactory factory,  
     IServiceProvider serviceProvider, Func<string, LogLevel, bool> filter = null)  
     where TLog : ErrorLog, new()  
   {  
     if (factory == null)  
     {  
       throw new ArgumentNullException(nameof(factory));  
     }  
     factory.AddProvider(new MongoLoggerProvider<TLog>(serviceProvider, filter));  
     return factory;  
   }  
 }  

Startup.cs, logger registration

 public IServiceProvider ServiceProvider { get; set; }  
 // INFO: Just an helper to populate ServiceProvider  
 public void ConfigureServices(IServiceCollection services)  
 {  
      //...  
      ServiceProvider = services.BuildServiceProvider();  
 }  
 public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)  
 {  
      loggerFactory.AddMongoFramework<ErrorLog>(ServiceProvider);  
      //...  
 }  

That is all we need to for logging, have a look on usage https://docs.asp.net/en/latest/fundamentals/logging.html.


Global exception handling


Since logging is implemented, global exception handling would be straightforward in few easy steps.

Implementation of IExceptionFilter

 using Microsoft.AspNetCore.Mvc;  
 using Microsoft.AspNetCore.Mvc.Filters;  
 using Microsoft.AspNetCore.Routing;  
 using Microsoft.Extensions.Logging;  
 /// <summary>  
 /// Global exception filter for the application.  
 /// </summary>  
 /// <seealso cref="Microsoft.AspNetCore.Mvc.Filters.IExceptionFilter" />  
 public class GlobalExceptionFilter  
   : IExceptionFilter  
 {  
   /// <summary>  
   /// The logger  
   /// </summary>  
   private readonly ILogger<GlobalExceptionFilter> Logger;  
   /// <summary>  
   /// Initializes a new instance of the <see cref="GlobalExceptionFilter"/> class.  
   /// </summary>  
   /// <param name="logger">The logger.</param>  
   public GlobalExceptionFilter(ILogger<GlobalExceptionFilter> logger)  
   {  
     Logger = logger;  
   }  
   /// <summary>  
   /// Called after an action has thrown an <see cref="T:System.Exception" />.  
   /// </summary>  
   /// <param name="context">The <see cref="T:Microsoft.AspNetCore.Mvc.Filters.ExceptionContext" />.</param>  
   public void OnException(ExceptionContext context)  
   {  
     Logger.LogError(new EventId(999, "GlobalException"), context.Exception, "Unhandled Error");  
     context.ExceptionHandled = true;  
           // TODO: Create page/action for end user based on parameter.   
           // TIP: It can be further classified for AJAX and page request to change message accordingly.  
     context.Result = new RedirectToRouteResult(    
       new RouteValueDictionary(new  
       {  
         action = "Index",  
         controller = "Error",  
         id = "Unknown"  
       }));  
   }  
 }  

Filter factory for injecting logger

 using Microsoft.AspNetCore.Mvc.Filters;  
 using Microsoft.Extensions.Logging;  
 using System;  
 namespace MyProject.Web.Infrastructure.Filter  
 {  
   /// <summary>  
   /// <see cref="GlobalExceptionFilter"/> factory.  
   /// </summary>  
   /// <seealso cref="Microsoft.AspNetCore.Mvc.Filters.IFilterFactory" />  
   public class GlobalExceptionFilterFactory  
     : IFilterFactory  
   {  
     /// <summary>  
     /// Gets a value that indicates if the result of <see cref="M:Microsoft.AspNetCore.Mvc.Filters.IFilterFactory.CreateInstance(System.IServiceProvider)" />  
     /// can be reused across requests.  
     /// </summary>  
     public bool IsReusable => false;  
     /// <summary>  
     /// Creates an instance of the executable filter.  
     /// </summary>  
     /// <param name="serviceProvider">The request <see cref="T:System.IServiceProvider" />.</param>  
     /// <returns>  
     /// An instance of the executable filter.  
     /// </returns>  
     public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)  
     {  
       var loggerFactory = (ILogger<GlobalExceptionFilter>)serviceProvider.GetService(typeof(ILogger<GlobalExceptionFilter>));  
       return new GlobalExceptionFilter(loggerFactory);  
     }  
   }  
 }  

Global exception filter registration in Startup.cs

 services.AddMvc(option =>  
 {  
   if (!Environment.IsDevelopment())  
   {  
     option.Filters.Add(new GlobalExceptionFilterFactory());  
   }  
 })  


That is all we need to configure global exception handling. I have not added a controller for redirection of errors which can be easily done.

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