RESTful Day #6: Request Logging And Exception Handing/Logging In Web APIs Using Action Filters, Exception Filters and NLog

The article is also written and compiled by Sachin Verma as co-author.

Table of Contents

1. Introduction
2. Roadmap
3. Request Logging
   • Setup NLog in WebAPI
     • Step 1: Download the NLog Package
     • Step 2: Configuring NLog
   • NLogger Class
   • Adding Action Filter
     • Step 1: Adding LoggingFilterAttribute class
     • Step 2: Registering Action Filter (LoggingFilterAttribute)
4. Running the application
5. Exception Logging
   • Implementing Exception logging
     • Step 1: Exception Filter Attribute
     • Step 2: Modify NLogger Class
     • Step 3: Modify Controller for Exceptions
     • Step 4: Run the application
6. Custom Exception logging
   • JSon Serializers
   • Modify NLogger Class
   • Modify GlobalExceptionAttribute
   • Modify Product Controller
   • Run the application
   • Update the controller for new Exception Handling
     • Product Controller
7. Conclusion
8. Other Series

Introduction

We have been learning a lot about WebAPI, its uses, implementations, and security aspects since the last five articles of the series. The article is also written and compiled by my co-author Sachin Verma. This article of the series will explain how we can handle requests and log them for tracking and for the sake of debugging, how we can handle exceptions and log them. We’ll follow a centralized way of handling exceptions in WebAPI and write our custom classes to be mapped to the type of exception that we encounter and log accordingly. I’ll use NLog to log requests and exceptions as well. We’ll leverage the capabilities of Exception Filters and Action Filters to centralize request logging and exception handling in WebAPI.

Roadmap

The following is the roadmap I have set to learn WebAPI step by step.

• RESTful Day #1: Enterprise-level application architecture with Web APIs using Entity Framework, Generic Repository pattern and Unit of Work.
• RESTful Day #2: Inversion of control using dependency injection in Web APIs using Unity Container and Bootstrapper.
• RESTful Day #3: Resolve dependency of dependencies using Inversion of Control and dependency injection in ASP.Net Web APIs with Unity Container and Managed Extensibility Framework (MEF).
• RESTful Day #4: Custom URL Re-Writing/Routing using Attribute Routes in MVC 4 Web APIs.
• RESTful Day #5: Basic Authentication and Token-based custom Authorization in Web APIs using Action Filters.
• RESTful Day #6: Request logging and Exception handing/logging in Web APIs using Action Filters, Exception Filters and NLog.
• RESTful Day #7: Unit Testing and Integration Testing in WebAPI using NUnit and Moq framework (Part1).
• RESTful Day #8: Unit Testing and Integration Testing in WebAPI using NUnit and Moq framework (Part 2).
• RESTful Day #9: Extending OData support in ASP.NET Web APIs.

I’ll purposely use Visual Studio 2010 and .NET Framework 4.0 because there are few implementations that are very hard to find in .NET Framework 4.0, but I’ll make it easy by showing how we can do it.

Request Logging

Since we are writing web services, we are exposing our endpoints. We must know where the requests are coming from and what requests are coming to our server. Logging could be very beneficial and helps us in a lot of ways such as debugging, tracing, monitoring, and analytics.

We already have an existing design. If you open the solution, you’ll get to see the structure as mentioned below or one can also implement this approach in their existing solution as well,

Setup NLog in WebAPI

NLog serves various purposes but primarily logging. We’ll use NLog for logging into files and Windows events as well. You can read more about NLog.

One can use the sample application that we used on Day#5 or can have any other application as well. I am using the existing sample application that we were following throughout all the parts of this series. Our application structure looks something like,

Step 1. Download NLog Package

Right-click the WebAPI project and select Manage Nuget Packages from the list. When the Nuget Package Manager appears, search for NLog. You’ll get Nlog like in the following image, install it to our project.

After adding this you will find the following NLog dll referenced in your application.

Step 2. Configuring NLog

To configure NLog with the application add the following settings in our existing WebAPI web. config file,

configuration

Configuration Section - I have added the <NLog> section to the configuration and defined the path and format dynamic target log file name, also added the event log source to API Services.

As mentioned in the above target path, I have also created an “APILog” folder in the base directory of the application.

Now we have configured the NLog in our application, and it is ready to start work for request logging. Note that in the rules section, we have defined rules for logging in files as well as in the Windows events log as well, you can choose both of them or opt for one too. Let’s start with logging requests in the application, with action filters.

NLogger Class

Add a folder “Helpers” in the API, which will segregate the application code for readability, better understanding, and maintainability.

To start add our main class “NLogger”, which will be responsible for all types of errors and info logging, to the same Helper folder. Here NLogger class implements the ITraceWriter interface, which provides a “Trace” method for the service request.

#region Using namespaces.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Tracing;
using NLog;
using System.Net.Http;
using System.Text;
using WebApi.ErrorHelper;
#endregion

namespace WebApi.Helpers
{
    /// <summary>
    /// Public class to log Error/info messages to the access log file
    /// </summary>
    public sealed class NLogger : ITraceWriter
    {
        #region Private member variables.
        private static readonly Logger ClassLogger = LogManager.GetCurrentClassLogger();

        private static readonly Lazy<Dictionary<TraceLevel, Action<string>>> LoggingMap = new Lazy<Dictionary<TraceLevel, Action<string>>>(() => new Dictionary<TraceLevel, Action<string>> { { TraceLevel.Info, ClassLogger.Info }, { TraceLevel.Debug, ClassLogger.Debug }, { TraceLevel.Error, ClassLogger.Error }, { TraceLevel.Fatal, ClassLogger.Fatal }, { TraceLevel.Warn, ClassLogger.Warn } });
        #endregion

        #region Private properties.
        /// <summary>
        /// Get property for Logger
        /// </summary>
        private Dictionary<TraceLevel, Action<string>> Logger
        {
            get { return LoggingMap.Value; }
        }
        #endregion

        #region Public member methods.
        /// <summary>
        /// Implementation of TraceWriter to trace the logs.
        /// </summary>
        /// <param name="request"></param>
        /// <param name="category"></param>
        /// <param name="level"></param>
        /// <param name="traceAction"></param>
        public void Trace(HttpRequestMessage request, string category, TraceLevel level, Action<TraceRecord> traceAction)
        {
            if (level != TraceLevel.Off)
            {
                if (traceAction != null && traceAction.Target != null)
                {
                    category = category + Environment.NewLine + "Action Parameters : " + traceAction.Target.ToJSON();
                }
                var record = new TraceRecord(request, category, level);
                if (traceAction != null) traceAction(record);
                Log(record);
            }
        }
        #endregion

        #region Private member methods.
        /// <summary>
        /// Logs info/Error to Log file
        /// </summary>
        /// <param name="record"></param>
        private void Log(TraceRecord record)
        {
            var message = new StringBuilder();

            if (!string.IsNullOrWhiteSpace(record.Message))
                message.Append("").Append(record.Message + Environment.NewLine);

            if (record.Request != null)
            {
                if (record.Request.Method != null)
                    message.Append("Method: " + record.Request.Method + Environment.NewLine);

                if (record.Request.RequestUri != null)
                    message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

                if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
                    message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
            }

            if (!string.IsNullOrWhiteSpace(record.Category))
                message.Append("").Append(record.Category);

            if (!string.IsNullOrWhiteSpace(record.Operator))
                message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

            
            Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
        }
        #endregion
    }
}

Adding Action Filter

Action filter will be responsible for handling all the incoming requests to our APIs and logging them using the NLogger class. We have an “OnActionExecuting” method that is implicitly called if we mark our controllers or global application to use that particular filter. So each time any action of any controller is hit, our “OnActionExecuting” method will execute to log the request.

Step 1. Adding LoggingFilterAttribute class

Create a class LoggingFilterAttribute to the “ActionFilters” folder and add the following code.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Filters;
using System.Web.Http.Controllers;
using System.Web.Http.Tracing;
using System.Web.Http;
using WebApi.Helpers;

namespace WebApi.ActionFilters
{
    public class LoggingFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext filterContext)
        {
            GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
            var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
            trace.Info(filterContext.Request, "Controller : " + filterContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + filterContext.ActionDescriptor.ActionName, "JSON", filterContext.ActionArguments);
        }
    }
}

The LoggingFilterAttribute class is derived from ActionFilterAttribute, which is under System.Web.Http.Filters and overriding the OnActionExecuting method.

Here I have replaced the default “ITraceWriter” service with our NLogger class instance in the controller's service container. Now GetTraceWriter() method will return our instance (instance NLogger class) and Info() will call the trace() method of our NLogger class.

Note that the following code.

GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());

Is used to resolve dependency between ITaceWriter and NLogger class. Thereafter we use a variable named trace to get the instance and trace.Info() is used to log the request and whatever text we want to add along with that request.

Step 2. Registering Action Filter (LoggingFilterAttribute).

In order to register the created action filter to applications filters, just add a new instance of your action filter to config.Filters in WebApiConfig class.

using System.Web.Http;
using WebApi.ActionFilters;

namespace WebApi.App_Start
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            config.Filters.Add(new LoggingFilterAttribute());
        }
    }
}

Now this action filter is applicable to all the controllers and actions in our project. You may not believe but request logging is done. It’s time to run the application and validate our homework.

Image credit: https://pixabay.com/en/social-media-network-media-54536/

Running the application

Let’s run the application and try to make a call, using token-based authorization, we have already covered authorization in day#5. You first need to authenticate your request using login service, and then that service will return a token for making calls to other services. Use that token to make calls to other services, for more details you can read day 5 of this series.

Just run the application, and we get the following.

We already have our test client added, but for new readers, just go to Manage Nuget Packages, by right-clicking WebAPI project and type WebAPITestClient in the searchbox in online packages,

You’ll get “A simple Test Client for ASP.NET Web API”, just add it. You’ll get a help controller in Areas-> HelpPage like the following screenshot.

I have already provided the database scripts and data in my previous article, you can use the same. Append “/help” in the application URL, and you’ll get the test client.

GET

POST

PUT

DELETE

You can test each service by clicking on it. Once you click on the service link, you'll be redirected to test the service page of that particular service. On that page there is a button Test API in the right bottom corner, just press that button to test your service.

Service for Get All products.

In the following case, I have already generated the token and now using it to make a call to fetch all the products from the products table in the database.

Here I have called all products API, Added the value for parameter Id and “Token” header with its current value, and click to get the result.

Now let’s see what happens to our APILog folder in the application. Here you can find that the API log has been created, with the same name we have configured in the NLog configuration in the web. config file. The log file contains all the supplied details such as Timestamp, Method type, URL, Header information (Token), Controller name, action, and action parameters. You can also add more details to this log that you deem important for your application.

Logging Done!

Exception Logging

Our logging setup is completed, now we’ll focus on centralizing exception logging as well so that none of the exception escapes without logging itself. Logging exception is of very high importance, it keeps track of all the exceptions. No matter business or application or system exceptions, but all of them have to be logged.

Implementing Exception logging

Step 1. Exception Filter Attribute.

Adding an action filter in our application for logging the exceptions, creating a class GlobalExceptionAttribute to the “ActionFilter” folder and adding the following code, the class is derived from ExceptionFilterAttribute, which is under System.Web.Http.Filters.

I have overridden the OnException() method, and replaced the default “ITraceWriter” service with our NLogger class instance in the controller's service container, same as we have done in Action logging in the above section. Now GetTraceWriter() method will return our instance (instance NLogger class) and Info() will call the trace() method of NLogger class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http.Filters;
using System.Web.Http;
using System.Web.Http.Tracing;
using WebApi.Helpers;
using System.ComponentModel.DataAnnotations;
using System.Net.Http;
using System.Net;

namespace WebApi.ActionFilters
{
    /// <summary>
    /// Action filter to handle for Global application errors.
    /// </summary>
    public class GlobalExceptionAttribute : ExceptionFilterAttribute
    {
        public override void OnException(HttpActionExecutedContext context)
        {
            GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
            var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
            trace.Error(context.Request, "Controller : " + context.ActionContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + context.ActionContext.ActionDescriptor.ActionName, context.Exception);

            var exceptionType = context.Exception.GetType();

            if (exceptionType == typeof(ValidationException))
            {
                var resp = new HttpResponseMessage(HttpStatusCode.BadRequest) { Content = new StringContent(context.Exception.Message), ReasonPhrase = "ValidationException", };
                throw new HttpResponseException(resp);
            }
            else if (exceptionType == typeof(UnauthorizedAccessException))
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.Unauthorized));
            }
            else
            {
                throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.InternalServerError));
            }
        }
    }
}

Step 2. Modify NLogger Class.

Our NLogger class is capable of logging all info and events, I have made some changes in the private method Log() to handle the exceptions.

#region Private member methods.

/// <summary>
/// Logs info/Error to Log file
/// </summary>
/// <param name="record"></param>
private void Log(TraceRecord record)
{
    var message = new StringBuilder();

    if (!string.IsNullOrWhiteSpace(record.Message))
        message.Append("").Append(record.Message + Environment.NewLine);

    if (record.Request != null)
    {
        if (record.Request.Method != null)
            message.Append("Method: " + record.Request.Method + Environment.NewLine);

        if (record.Request.RequestUri != null)
            message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

        if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
            message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
    }

    if (!string.IsNullOrWhiteSpace(record.Category))
        message.Append("").Append(record.Category);

    if (!string.IsNullOrWhiteSpace(record.Operator))
        message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

    if (record.Exception != null && !string.IsNullOrWhiteSpace(record.Exception.GetBaseException().Message))
    {
        var exceptionType = record.Exception.GetType();
        message.Append(Environment.NewLine);
        message.Append("").Append("Error: " + record.Exception.GetBaseException().Message + Environment.NewLine);
    }

    Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
}

#endregion

Step 3. Modify Controller for Exceptions.

Our application is now ready to run, but there is no exception in our code, so I added a throw exception code in ProductController, just the Get(int id) method so that it can throw exception for testing our exception logging mechanism, It will throw an exception if the product is not there in the database with the provided id.

// GET api/product/5
[GET("productid/{id?}")]
[GET("particularproduct/{id?}")]
[GET("myproduct/{id:range(1, 3)}")]
public HttpResponseMessage Get(int id)
{
    var product = _productServices.GetProductById(id);
    if (product != null)
        return Request.CreateResponse(HttpStatusCode.OK, product);

    throw new Exception("No product found for this id");
    //return Request.CreateErrorResponse(HttpStatusCode.NotFound, "No product found for this id");
}

Step 4. Run the application.

Run the application and click on Product/all API.

Add the parameter id value to 1 and the header Token with its current value, and click on the send button to get the result.

Now we can see that the Status is 200/OK, and we also get a product with the provided ID in the response body. Let’s see the API log now.

The log has captured the call of Product API, now provide a new product ID as a parameter, which is not there in the database, I am using 12345 as the product ID and the result is.

We can see there is a 500/Internal Server Error now in response status, let's check the API Log.

Well, now the log has captured both the event and error of the same call on the server, you can see call log details and the error with the provided error message in the log.

Custom Exception logging

In the above section, we have implemented exception logging, but there is a default system response and status ( i. e. 500/Internal Server Error), It will be always good to have your own custom response and exceptions for your API. That will make it easier for the client to consume and understand the API responses.

Step 1. Add Custom Exception Classes.

Add the “Error Helper” folder to the application to maintain our custom exception classes separately and add the “IApiExceptions” interface to the newly created “ErrorHelper” folder.

Add the following code in the IApiExceptions interface, this will serve as a template for all exception classes, I have added four common properties for our custom classes to maintain Error Code, ErrorDescription, HttpStatus (Contains the values of status codes defined for HTTP) and ReasonPhrase.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// IApiExceptions Interface
    /// </summary>
    public interface IApiExceptions
    {
        /// <summary>
        /// ErrorCode
        /// </summary>
        int ErrorCode { get; set; }
        /// <summary>
        /// ErrorDescription
        /// </summary>
        string ErrorDescription { get; set; }
        /// <summary>
        /// HttpStatus
        /// </summary>
        HttpStatusCode HttpStatus { get; set; }
        /// <summary>
        /// ReasonPhrase
        /// </summary>
        string ReasonPhrase { get; set; }
    }
}

Here, I divided our exceptions into the following three categories.

1. API Exceptions: for API level exceptions.
2. Business Exceptions: for exceptions at the business logic level.
3. Data Exceptions: Data-related exceptions.

To implement this create three new classes ApiException.cs, ApiDataException.cs, and ApiBusinessException classes to the same folder which implements the IApiExceptions interface with the following code to the classes.

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization;
#endregion


namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }

        string reasonPhrase = "ApiException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }
        #endregion
    }
}

I have initialized the ReasonPhrase property with different default values in these classes to differentiate the implementation, you can implement your custom classes as per your application needs.

The directives applied on class as Serializable and DataContract to make sure that the class defines or implements a data contract serializable and can be serialized by a serializer.

Note. Add reference of “System.Runtime.Serialization.dll” dll if you facing any assembly issues.

In the same way, add the “ApiBusinessException” and “ApiDataException” classes into the same folder with the following code.

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization;
#endregion

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Business Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiBusinessException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }

        string reasonPhrase = "ApiBusinessException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }
        #endregion

        #region Public Constructor.
        /// <summary>
        /// Public constructor for Api Business Exception
        /// </summary>
        /// <param name="errorCode"></param>
        /// <param name="errorDescription"></param>
        /// <param name="httpStatus"></param>
        public ApiBusinessException(int errorCode, string errorDescription, HttpStatusCode httpStatus)
        {
            ErrorCode = errorCode;
            ErrorDescription = errorDescription;
            HttpStatus = httpStatus;
        }
        #endregion

    }
}

#region Using namespaces.
using System;
using System.Net;
using System.Runtime.Serialization;
#endregion

namespace WebApi.ErrorHelper
{
    /// <summary>
    /// Api Data Exception
    /// </summary>
    [Serializable]
    [DataContract]
    public class ApiDataException : Exception, IApiExceptions
    {
        #region Public Serializable properties.
        [DataMember]
        public int ErrorCode { get; set; }
        [DataMember]
        public string ErrorDescription { get; set; }
        [DataMember]
        public HttpStatusCode HttpStatus { get; set; }

        string reasonPhrase = "ApiDataException";

        [DataMember]
        public string ReasonPhrase
        {
            get { return this.reasonPhrase; }

            set { this.reasonPhrase = value; }
        }
        #endregion

        #region Public Constructor.
        /// <summary>
        /// Public constructor for Api Data Exception
        /// </summary>
        /// <param name="errorCode"></param>
        /// <param name="errorDescription"></param>
        /// <param name="httpStatus"></param>
        public ApiDataException(int errorCode, string errorDescription, HttpStatusCode httpStatus)
        {
            ErrorCode = errorCode;
            ErrorDescription = errorDescription;
            HttpStatus = httpStatus;
        }
        #endregion
    }
}

JSON Serializers

There are some objects that need to be serialized in JSON, to log and transfer through the modules, for this I have added some extension methods to the Object class.

For that add a “System.Web.Extensions.dll” reference to the project and add the “JSONHelper” class to the Helpers folder with the following cod.

#region Using namespaces.
using System.Web.Script.Serialization;
using System.Data;
using System.Collections.Generic;
using System;
#endregion

namespace WebApi.Helpers
{
    public static class JSONHelper
    {
        #region Public extension methods.
        /// <summary>
        /// Extened method of object class, Converts an object to a json string.
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public static string ToJSON(this object obj)
        {
            var serializer = new JavaScriptSerializer();
            try
            {
                return serializer.Serialize(obj);
            }
            catch(Exception ex)
            {
                return "";
            }
        }
        #endregion
    }
}

In the above code “ToJSON()” method is an extension of the base Object class, which serializes the object to a JSON string. The method using the “JavaScriptSerializer” class which exist in “System.Web.Script.Serialization”.

Modify NLogger Class

For exception handling, I have modified the Log() method of NLogger, which will now handle different API exceptions.

/// <summary>
/// Logs info/Error to Log file
/// </summary>
/// <param name="record"></param>
private void Log(TraceRecord record)
{
    var message = new StringBuilder();

    if (!string.IsNullOrWhiteSpace(record.Message))
        message.Append("").Append(record.Message + Environment.NewLine);

    if (record.Request != null)
    {
        if (record.Request.Method != null)
            message.Append("Method: " + record.Request.Method + Environment.NewLine);

        if (record.Request.RequestUri != null)
            message.Append("").Append("URL: " + record.Request.RequestUri + Environment.NewLine);

        if (record.Request.Headers != null && record.Request.Headers.Contains("Token") && record.Request.Headers.GetValues("Token") != null && record.Request.Headers.GetValues("Token").FirstOrDefault() != null)
            message.Append("").Append("Token: " + record.Request.Headers.GetValues("Token").FirstOrDefault() + Environment.NewLine);
    }

    if (!string.IsNullOrWhiteSpace(record.Category))
        message.Append("").Append(record.Category);

    if (!string.IsNullOrWhiteSpace(record.Operator))
        message.Append(" ").Append(record.Operator).Append(" ").Append(record.Operation);

    if (record.Exception != null && !string.IsNullOrWhiteSpace(record.Exception.GetBaseException().Message))
    {
        var exceptionType = record.Exception.GetType();
        message.Append(Environment.NewLine);
        if (exceptionType == typeof(ApiException))
        {
            var exception = record.Exception as ApiException;
            if (exception != null)
            {
                message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
            }
        }
        else if (exceptionType == typeof(ApiBusinessException))
        {
            var exception = record.Exception as ApiBusinessException;
            if (exception != null)
            {
                message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
            }
        }
        else if (exceptionType == typeof(ApiDataException))
        {
            var exception = record.Exception as ApiDataException;
            if (exception != null)
            {
                message.Append("").Append("Error: " + exception.ErrorDescription + Environment.NewLine);
                message.Append("").Append("Error Code: " + exception.ErrorCode + Environment.NewLine);
            }
        }
        else
            message.Append("").Append("Error: " + record.Exception.GetBaseException().Message + Environment.NewLine);
    }

    Logger[record.Level](Convert.ToString(message) + Environment.NewLine);
}

The code above checks the exception object of TraceRecord and updates the logger as per the exception type.

Modify GlobalExceptionAttribute

As we have created GlobalExceptionAttribute to handle al the exceptions and create a response in case of any exceptions. Now I have added some new code to this in order to enable the GlobalExceptionAttribute class to handle custom exceptions. I am adding only the modified method here for your reference.

public override void OnException(HttpActionExecutedContext context)
{
    GlobalConfiguration.Configuration.Services.Replace(typeof(ITraceWriter), new NLogger());
    var trace = GlobalConfiguration.Configuration.Services.GetTraceWriter();
    trace.Error(context.Request, "Controller : " + context.ActionContext.ControllerContext.ControllerDescriptor.ControllerType.FullName + Environment.NewLine + "Action : " + context.ActionContext.ActionDescriptor.ActionName, context.Exception);

    var exceptionType = context.Exception.GetType();

    if (exceptionType == typeof(ValidationException))
    {
        var resp = new HttpResponseMessage(HttpStatusCode.BadRequest) { Content = new StringContent(context.Exception.Message), ReasonPhrase = "ValidationException", };
        throw new HttpResponseException(resp);
    }
    else if (exceptionType == typeof(UnauthorizedAccessException))
    {
        throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.Unauthorized, new ServiceStatus() { StatusCode = (int)HttpStatusCode.Unauthorized, StatusMessage = "UnAuthorized", ReasonPhrase = "UnAuthorized Access" }));
    }
    else if (exceptionType == typeof(ApiException))
    {
        var webapiException = context.Exception as ApiException;
        if (webapiException != null)
            throw new HttpResponseException(context.Request.CreateResponse(webapiException.HttpStatus, new ServiceStatus() { StatusCode = webapiException.ErrorCode, StatusMessage = webapiException.ErrorDescription, ReasonPhrase = webapiException.ReasonPhrase }));
    }
    else if (exceptionType == typeof(ApiBusinessException))
    {
        var businessException = context.Exception as ApiBusinessException;
        if (businessException != null)
            throw new HttpResponseException(context.Request.CreateResponse(businessException.HttpStatus, new ServiceStatus() { StatusCode = businessException.ErrorCode, StatusMessage = businessException.ErrorDescription, ReasonPhrase = businessException.ReasonPhrase }));
    }
    else if (exceptionType == typeof(ApiDataException))
    {
        var dataException = context.Exception as ApiDataException;
        if (dataException != null)
            throw new HttpResponseException(context.Request.CreateResponse(dataException.HttpStatus, new ServiceStatus() { StatusCode = dataException.ErrorCode, StatusMessage = dataException.ErrorDescription, ReasonPhrase = dataException.ReasonPhrase }));
    }
    else
    {
        throw new HttpResponseException(context.Request.CreateResponse(HttpStatusCode.InternalServerError));
    }
}

In the above code, I have modified the overridden method OnExeption() and created a new HTTP response exception based on the different exception types.

Modify Product Controller

Now modify the Product controller to throw our custom exception form, please look into the Get method I have modified to throw the APIDataException in case if data is not found and APIException in any other kind of error.

// GET api/product/5
[GET("productid/{id?}")]
[GET("particularproduct/{id?}")]
[GET("myproduct/{id:range(1, 3)}")]
public HttpResponseMessage Get(int id)
{
    if (id != null)
    {
        var product = _productServices.GetProductById(id);
        if (product != null)
            return Request.CreateResponse(HttpStatusCode.OK, product);

        throw new ApiDataException(1001, "No product found for this id.", HttpStatusCode.NotFound);
    }
    throw new ApiException() { ErrorCode = (int)HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..." };
}

Run the application

Run the application and click on Product/all API.

Add the parameter id value to 1 and the header Token with its current value, click on the send button to get the result,

Now we can see that the Status is 200/OK, and we also get a product with the provided ID in the response body. Let's see the API log now.

The log has captured the call of Product API, now provide a new product id as a parameter, which is not there in the database, I am using 12345 as the product ID and the result is.

We can see now there is a custom error status code “1001” and the message “No product found for this ID.” The generic status code “500/Internal Server Error” is now replaced with our supplied code “404/ Not Found”, which is more meaningful for the client or consumer.

Let's see the APILog now.

Well, now the log has captured both the event and error of the same call on the server, you can see call log details and the error with the provided error message in the log with our custom error code, I have only captured the error description and error code, but you can add more details in the log as per your application needs.

Update the controller for new Exception Handling

The following is the code for controllers with the implementation of custom exception handling and logging.

Product Controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using AttributeRouting;
using AttributeRouting.Web.Http;
using BusinessEntities;
using BusinessServices;
using WebApi.ActionFilters;
using WebApi.Filters;
using WebApi.ErrorHelper;

namespace WebApi.Controllers
{
    [AuthorizationRequired]
    [RoutePrefix("v1/Products/Product")]
    public class ProductController : ApiController
    {
        #region Private variable.

        private readonly IProductServices _productServices;

        #endregion

        #region Public Constructor

        /// <summary>
        /// Public constructor to initialize product service instance
        /// </summary>
        public ProductController(IProductServices productServices)
        {
            _productServices = productServices;
        }

        #endregion

        // GET api/product
        [GET("allproducts")]
        [GET("all")]
        public HttpResponseMessage Get()
        {
            var products = _productServices.GetAllProducts();
            var productEntities = products as List<ProductEntity> ?? products.ToList();
            if (productEntities.Any())
                return Request.CreateResponse(HttpStatusCode.OK, productEntities);
            throw new ApiDataException(1000, "Products not found", HttpStatusCode.NotFound);
        }

        // GET api/product/5
        [GET("productid/{id?}")]
        [GET("particularproduct/{id?}")]
        [GET("myproduct/{id:range(1, 3)}")]
        public HttpResponseMessage Get(int id)
        {
            if (id != null)
            {
                var product = _productServices.GetProductById(id);
                if (product != null)
                    return Request.CreateResponse(HttpStatusCode.OK, product);

                throw new ApiDataException(1001, "No product found for this id.", HttpStatusCode.NotFound);
            }
            throw new ApiException() { ErrorCode = (int)HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..." };
        }

        // POST api/product
        [POST("Create")]
        [POST("Register")]
        public int Post([FromBody] ProductEntity productEntity)
        {
            return _productServices.CreateProduct(productEntity);
        }

        // PUT api/product/5
        [PUT("Update/productid/{id}")]
        [PUT("Modify/productid/{id}")]
        public bool Put(int id, [FromBody] ProductEntity productEntity)
        {
            if (id > 0)
            {
                return _productServices.UpdateProduct(id, productEntity);
            }
            return false;
        }

        // DELETE api/product/5
        [DELETE("remove/productid/{id}")]
        [DELETE("clear/productid/{id}")]
        [PUT("delete/productid/{id}")]
        public bool Delete(int id)
        {
            if (id != null && id > 0)
            {
                var isSuccess = _productServices.DeleteProduct(id);
                if (isSuccess)
                {
                    return isSuccess;
                }
                throw new ApiDataException(1002, "Product is already deleted or not exist in system.", HttpStatusCode.NoContent);
            }
            throw new ApiException() { ErrorCode = (int) HttpStatusCode.BadRequest, ErrorDescription = "Bad Request..." };
        }
    }
}

Now you can see, that our application is so rich and scalable that none of the exceptions or transactions can escape logging. Once setup is in place, now you don’t have to worry about writing code each time for logging or requests and exceptions, but you can relax and focus on business logic only.

Image credit: https://pixabay.com/en/kermit-frog-meadow-daisy-concerns-383370/

Conclusion

In this article, we learned how to perform request logging and exception logging in WebPI. There could be numerous ways in which you can perform these operations but I tried to present this in as simple a way as possible. My approach was to take our enterprise level to the next level of development, where developers should not always be worried about exception handling and logging. Our solution provides a generic approach to centralizing the operations in one place; all the requests and exceptions are automatically taken care of. In my new articles, I’ll try to enhance the application by explaining unit testing in WebAPI and OData in WebAPI. You can download the complete source code of this article with packages from GitHub. Happy coding.

Read more

• C# and ASP.NET Questions (All in one)
• MVC Interview Questions
• C# and ASP.NET Interview Questions and Answers
• Web Services and Windows Services Interview Questions

For more technical articles you can reach out to CodeTeddy

My other series of articles.

• Learning MVC
• Learning OOP concepts with C#