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ASP.NET Core 2.2.3 Hosting - HostForLIFE.eu :: Show Alert Message Box using JavaScript jQuery in ASP.NET

clock March 20, 2019 12:03 by author Peter

Today, I will explain you about Showing Alert Message Box from client Side on ASP.NET Core 2.2.3 using JavaScript and JQuery. In the Following, this is jQuery Code Snippet to show/display alert message:

//Function for jQuery
$(function () {
$('#btnUsingjQuery').click(function () {
alert('Alert using jQuery Function!');
});
});

And, this is the JavaScript code to show or display alert message:
//Function for JavaScript
function alertUsingJavaScript() {
alert('Alert using JavaScript Function!');
}

Show Alert Message – (.aspx)
Here is the code snippet for your .aspx webpage:

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>How to show alert message using jQuery/JavaScript in ASP.NET
</title>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.6.2.js">
</script>
<script type="text/javascript">
//Function for JavaScript
function alertUsingJavaScript() {
alert('Alert using JavaScript Function!');
}
//Function for jQuery
$(function () {
$('#btnUsingjQuery').click(function () {
alert('Alert using jQuery Function!');
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<h4>
Show alert message using JavaScript/jQuery in Asp.net</h4>
<div>
<input id="btnUsingJavaScript" type="button" onclick="alertUsingJavaScript()"
value="Using JavaScript" />
<input id="btnUsingjQuery" type="button" value="Using jQuery" />
</div>
</form>
</body>
</html>

You can see i’d added onclick=”alertUsingJavaScript()” when calling function using JavaScript. Just in case of jQuery, we are able to bind click event directly on window load as $(‘#btnUsingjQuery’).click(function () ); });. And here is the result
:



European ASP.NET Core Hosting :: ASP.NET Core with MySQL and Entity Framework Core

clock March 14, 2019 07:58 by author Scott

This article shows how to use MySQL with ASP.NET Core 2.1 using Entity Framework Core.

The Entity Framework MySQL package can be downloaded using the NuGet package Pomelo.EntityFrameworkCore.MySql. At present no official provider from MySQL exists for Entity Framework Core which can be used in an ASP.NET Core application.

The Pomelo.EntityFrameworkCore.MySql package can be added to the csproj file.

<Project Sdk="Microsoft.NET.Sdk"> 

  <PropertyGroup>
    <TargetFramework>netcoreapp2.2</TargetFramework>
    <AssemblyName>DataAccessMySqlProvider</AssemblyName>
    <PackageId>DataAccessMySqlProvider</PackageId>
  </PropertyGroup> 

  <ItemGroup>
    <ProjectReference Include="..\DomainModel\DomainModel.csproj" />
  </ItemGroup> 

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.App"  />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.2.0" PrivateAssets="All" />
    <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="2.0.1" />
  </ItemGroup> 

  <ItemGroup>
    <Folder Include="Properties\" />
  </ItemGroup> 

</Project>

The web project which loads the project with EF Core needs to support migrations if you wish to create a database this way.

<Project Sdk="Microsoft.NET.Sdk.Web"> 

  <PropertyGroup>
    <TargetFramework>netcoreapp2.1</TargetFramework>
    <AssemblyName>AspNetCoreMultipleProject</AssemblyName>
    <PackageId>AspNet5MultipleProject</PackageId>
  </PropertyGroup> 

  <ItemGroup>
    <Content Update="wwwroot\**\*;Views;Areas\**\Views;appsettings.json;config.json;web.config">
      <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
    </Content>
  </ItemGroup> 

  <ItemGroup>
    <ProjectReference Include="..\DataAccessMsSqlServerProvider\DataAccessMsSqlServerProvider.csproj" />
    <ProjectReference Include="..\DataAccessMySqlProvider\DataAccessMySqlProvider.csproj" />
    <ProjectReference Include="..\DataAccessPostgreSqlProvider\DataAccessPostgreSqlProvider.csproj"
/>
    <ProjectReference Include="..\DataAccessSqliteProvider\DataAccessSqliteProvider.csproj" />
    <ProjectReference Include="..\DomainModel\DomainModel.csproj" />
  </ItemGroup>   

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.App"  />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.2.0" PrivateAssets="All" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.0" />
  </ItemGroup>
    <ItemGroup>
      <Folder Include="Migrations\" />
    </ItemGroup>
</Project>

An EfCore DbContext can be added like any other context supported by Entity Framework Core.

using System;
using System.Linq;
using DomainModel.Model;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration; 

namespace DataAccessMySqlProvider
{
    // >dotnet ef migration add testMigration
    public class DomainModelMySqlContext : DbContext
    {
        public DomainModelMySqlContext(DbContextOptions<DomainModelMySqlContext> options) :base(options)
        { }         

        public DbSet<DataEventRecord> DataEventRecords { get; set; } 

        public DbSet<SourceInfo> SourceInfos { get; set; } 

        protected override void OnModelCreating(ModelBuilder builder)
        {
            builder.Entity<DataEventRecord>().HasKey(m => m.DataEventRecordId);
            builder.Entity<SourceInfo>().HasKey(m => m.SourceInfoId); 

            // shadow properties
            builder.Entity<DataEventRecord>().Property<DateTime>("UpdatedTimestamp");
            builder.Entity<SourceInfo>().Property<DateTime>("UpdatedTimestamp"); 

            base.OnModelCreating(builder);
        } 

        public override int SaveChanges()
        {
            ChangeTracker.DetectChanges(); 

            updateUpdatedProperty<SourceInfo>();
            updateUpdatedProperty<DataEventRecord>(); 

            return base.SaveChanges();
        } 

        private void updateUpdatedProperty<T>() where T : class
        {
            var modifiedSourceInfo =
                ChangeTracker.Entries<T>()
                    .Where(e => e.State == EntityState.Added || e.State == EntityState.Modified); 

            foreach (var entry in modifiedSourceInfo)
            {
                entry.Property("UpdatedTimestamp").CurrentValue = DateTime.UtcNow;
            }
        }
    }
}

In an ASP.NET Core web application, the DbContext is added to the application in the startup class. In this example, the DbContext is defined in a different class library. The MigrationsAssembly needs to be defined, so that the migrations will work. If the context and the migrations are defined in the same assembly, this is not required.

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile("config.json", optional: true, reloadOnChange: true); 

    Configuration = builder.Build();
}         
public void ConfigureServices(IServiceCollection services)
{  
    var sqlConnectionString = Configuration.GetConnectionString("DataAccessMySqlProvider"); 

    services.AddDbContext<DomainModelMySqlContext>(options =>
        options.UseMySQL(
            sqlConnectionString,
            b => b.MigrationsAssembly("AspNetCoreMultipleProject")
        )
    );
}

The application uses the configuration from the config.json. This file is used to get the MySQL connection string, which is used in the Startup class.

{
    "ConnectionStrings": { 
        "DataAccessMySqlProvider": "server=localhost;userid=store;password=3333;database=store;"
        }
    }
}

MySQL workbench can be used to add the schema ‘store to the MySQL database. The user ‘store is also required, which must match the defined user in the connection string. If you configure the MySQL database differently, then you need to change the connection string in the config.json file.

Now the database migrations can be created and the database can be updated.

>
> dotnet ef migrations add mySqlMigration --context DomainModelMySqlContext
>
> dotnet ef database update --context DomainModelMySqlContext
>

If successful, the tables are created.

The MySQL provider can be used in a MVC controller using construction injection.

using System.Collections.Generic;
using DomainModel;
using DomainModel.Model;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json; 

namespace AspNet5MultipleProject.Controllers
{
    [Route("api/[controller]")]
    public class DataEventRecordsController : Controller
    {
        private readonly IDataAccessProvider _dataAccessProvider; 

        public DataEventRecordsController(IDataAccessProvider dataAccessProvider)
        {
            _dataAccessProvider = dataAccessProvider;
        } 

        [HttpGet]
        public IEnumerable<DataEventRecord> Get()
        {
            return _dataAccessProvider.GetDataEventRecords();
        } 

        [HttpGet]
        [Route("SourceInfos")]
        public IEnumerable<SourceInfo> GetSourceInfos(bool withChildren)
        {
            return _dataAccessProvider.GetSourceInfos(withChildren);
        } 

        [HttpGet("{id}")]
        public DataEventRecord Get(long id)
        {
            return _dataAccessProvider.GetDataEventRecord(id);
        } 

        [HttpPost]
        public void Post([FromBody]DataEventRecord value)
        {
            _dataAccessProvider.AddDataEventRecord(value);
        } 

        [HttpPut("{id}")]
        public void Put(long id, [FromBody]DataEventRecord value)
        {
            _dataAccessProvider.UpdateDataEventRecord(id, value);
        } 

        [HttpDelete("{id}")]
        public void Delete(long id)
        {
            _dataAccessProvider.DeleteDataEventRecord(id);
        }
    }
}

The controller api can be called using Fiddler:

POST http://localhost:5000/api/dataeventrecords HTTP/1.1
User-Agent: Fiddler
Host: localhost:5000
Content-Length: 135
Content-Type: application/json;  

{
  "DataEventRecordId":3,
  "Name":"Funny data",
  "Description":"yes",
  "Timestamp":"2015-12-27T08:31:35Z",
   "SourceInfo":
  {
    "SourceInfoId":0,
    "Name":"Beauty",
    "Description":"second Source",
    "Timestamp":"2015-12-23T08:31:35+01:00",
    "DataEventRecords":[]
  },
 "SourceInfoId":0
}

The data is added to the database as required.



European ASP.NET Core Hosting :: Smart Logging Middleware for ASP.NET Core

clock March 13, 2019 09:44 by author Scott

ASP.NET Core comes with request logging built-in. This is great for getting an app up-and-running, but the events are not as descriptive or efficient as hand-crafted request logging can be. Here is a typical trace from a single GET request to /about:



If the request fails because of an error, you'll see instead:



While these fine-grained events are sometimes useful, they take up storage space and bandwidth, and add noise to the log.

Spreading the information across many events also makes it harder to perform some analyses, for example, the HTTP method and elapsed time are on different events, making it hard to separate the timings of GET and POST requests to the same RequestPath.

In production we want:

One "infrastructure" event per normal request, with basic HTTP information attached

Extra information to help with debugging if a request fails due to a server-side (5xx) error

The same format and event type for all requests, so that logs from both successful and failed requests can be easily grouped, sorted and analyzed together

Here's the format we're aiming for, expanded so that you can see all of the attached properties:

Instead of five infrastructure events + one application event, just a single infrastructure event is logged. This makes the application's own "Hello" event much easier to spot.

This post includes the full source code for the middleware, so you can take it and modify it to include the information you find most useful.

Step 1: Install and Configure Serilog

ASP.NET Core includes some basic logging providers, but to get the most out of it you'll need to plug in a full logging framework like Serilog. If you haven't done that already, these instructions should have you up and running quickly.

Step 2: Turn off Information events from Microsoft and System

Where Serilog is configured, add level overrides for the Microsoft and System namespaces:

Log.Logger = new LoggerConfiguration() 
    .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
    .MinimumLevel.Override("System", LogEventLevel.Warning)
    // Other logger configuration

These can be turned back on for debugging when they're needed.

If you're using appsettings.json configuration, check out the level overrides example in the README.

Step 3: Add the SerilogMiddleware class

The SerilogMiddleware class hooks into the request processing pipeline to collect information about the requests:

using Microsoft.AspNetCore.Http; 
using Serilog; 
using Serilog.Events; 
using System; 
using System.Collections.Generic; 
using System.Diagnostics; 
using System.Linq; 
using System.Threading.Tasks;

namespace Datalust.SerilogMiddlewareExample.Diagnostics 
{
    class SerilogMiddleware
    {
        const string MessageTemplate =
            "HTTP {RequestMethod} {RequestPath} responded {StatusCode} in {Elapsed:0.0000} ms";

        static readonly ILogger Log = Serilog.Log.ForContext<SerilogMiddleware>();

        readonly RequestDelegate _next;

        public SerilogMiddleware(RequestDelegate next)
        {
            if (next == null) throw new ArgumentNullException(nameof(next));
            _next = next;
        }

        public async Task Invoke(HttpContext httpContext)
        {
            if (httpContext == null) throw new ArgumentNullException(nameof(httpContext));

            var sw = Stopwatch.StartNew();
            try
            {
                await _next(httpContext);
                sw.Stop();

                var statusCode = httpContext.Response?.StatusCode;
                var level = statusCode > 499 ? LogEventLevel.Error : LogEventLevel.Information;

                var log = level == LogEventLevel.Error ? LogForErrorContext(httpContext) : Log;
                log.Write(level, MessageTemplate, httpContext.Request.Method, httpContext.Request.Path, statusCode, sw.Elapsed.TotalMilliseconds);
            }
            // Never caught, because `LogException()` returns false.
            catch (Exception ex) when (LogException(httpContext, sw, ex)) { }
        }

        static bool LogException(HttpContext httpContext, Stopwatch sw, Exception ex)
        {
            sw.Stop();

            LogForErrorContext(httpContext)
                .Error(ex, MessageTemplate, httpContext.Request.Method, httpContext.Request.Path, 500, sw.Elapsed.TotalMilliseconds);

            return false;
        }

        static ILogger LogForErrorContext(HttpContext httpContext)
        {
            var request = httpContext.Request;

            var result = Log
                .ForContext("RequestHeaders", request.Headers.ToDictionary(h => h.Key, h => h.Value.ToString()), destructureObjects: true)
                .ForContext("RequestHost", request.Host)
                .ForContext("RequestProtocol", request.Protocol);

            if (request.HasFormContentType)
                result = result.ForContext("RequestForm", request.Form.ToDictionary(v => v.Key, v => v.Value.ToString()));

            return result;
        }
    }
}

I've deliberately kept this to a single (somewhat ugly!) source file so that it's easy to copy, paste and modify.

There are a lot of design details and trade-offs involved. You can see that when a request is deemed to have failed, some additional information is attached, including the headers sent by the client, and the form data if any.

Step 4: Add the middleware to the pipeline

In your application's Startup.cs file, you can add the middleware either before or after the outermost exception handling components. If you add it before this, you won't get the full Exception information in any error events, but you will always be able to record the exact status code returned to the client. Adding the middleware into the pipeline inside the exception handling components (i.e., after them in the source code) will provide all exception detail but has to assume that the status code is 500 in this case.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
                      ILoggerFactory loggerFactory)
{
    loggerFactory.AddSerilog();

    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
        app.UseBrowserLink();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
    }

    app.UseMiddleware<SerilogMiddleware>();

    app.UseStaticFiles();

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

Step 5: Profit!

Now you have a stream of request log events each with paths, status codes, timings, and exceptions:

We've seen how a simple customized logging strategy can not only produce cleaner events, but also reduce the volume of infrastructure log events.



ASP.NET Core Hosting :: How to Upload File using C# | SFTP Server

clock March 4, 2019 07:56 by author Scott

Although there are many Graphical Tools available for sending files to a server using SFTP. But as a developer, we may have a scenario where we need to upload a file to SFTP Serverfrom our Code.

A few days ago a job assigned to me was to develop a Task Scheduler for generating XML files daily on a specific time of the day & send these files on a Remote Server using File Transfer Protocol in a secure way.

In .Net Framework there are many Libraries available for uploading files to another machine using File Transfer Protocol but most of the libraries don’t work with .Net Core. In this Tutorial, we will develop a very simple SFTP client using C# for .Net Core.

Before start let’s have a quick look at SFTP.

What is SFTP?

SFTP stands for SSH File Transfer Protocol or Secure File Transfer Protocol. It is a protocol used to transfer files between remote machines over a secure shell.

 

In almost all cases, SFTP is preferable over FTP because of security features. FTP is not a secure protocol & it should only be used on a trusted network.

Choosing Library for C#

A lot of search & after testing many libraries I finally met with SSH.NET which was working perfectly with .Net Core 2.2 project & the good thing was that It does its job in a very few lines of Code.

So we’ll use SSH.NET

What is SSH.NET?

SSH.NET is an open-source library available at Nuget for .NET to work over SFTP. It is also optimized for parallelism to achieve the best possible performance. It was inspired by Sharp.SSH library which was ported from Java. This library is a complete rewrite using .Net, without any third party dependencies.

Here are the features of SSH.NET: 

Creating Project

I’m in love with VS Code right after its first release so I’m going to use VS Code for creating project to upload/transfer a file to a remote server using SFTP.

Create a console application using this command

dotnet new console

Installing SSH.NET

I won’t recommend you to install the latest version of SSH.NET. It has a bug, it can be stuck on transferring the file to the remote location.

version 2016.0.0 is perfect. 

run this command to install the library from NuGet

using package manager

Install-Package SSH.NET -Version 2016.0.0

or using .Net CLI

dotnet add package SSH.NET --version 2016.0.0

Code

Finally, It’s time to create a class for SFTP Client Code.

Create a file with the name as “SendFileToServer” & add the below code

using Renci.SshNet

public static class SendFileToServer
{
// Enter your host name or IP here
private static string host = "127.0.0.1";

// Enter your sftp username here
private static string username = "sftp";

// Enter your sftp password here
private static string password = "12345";
public static int Send(string fileName)
{
var connectionInfo = new ConnectionInfo(host, "sftp", new PasswordAuthenticationMethod(username, password));

// Upload File
using (var sftp = new SftpClient(connectionInfo)){

sftp.Connect();
//sftp.ChangeDirectory("/MyFolder");
using (var uplfileStream = System.IO.File.OpenRead(fileName)){
sftp.UploadFile(uplfileStream, fileName, true);
}
sftp.Disconnect();
}
return 0;
}
}

Now you can call this Method to transfer a file to SFTP Server like this

SendFileToServer.Send("myFile.txt");

“myFile.txt” is the name of the file which should be located in your project root directory. 



European ASP.NET Hosting - HostForLIFE.eu :: jQuery PJAX Implementation In ASP.NET Core

clock February 26, 2019 11:15 by author Peter

PJAX is a jQuery plugin that uses AJAX and pushState to deliver a fast browsing experience with real permalinks, page titles, and a working back button. It is available to download from GitHub.

In all websites, the header and footer remain the same for all pages. Only the page contents (the content in the middle area between the header and footer) are changed for each page. PJAX uses this concept to fetch only the page contents while the header and footer remains the same for each page. In short, you can also say PJAX is the brother of the Update Panel of Web Forms that works for ASP.NET Core.

With PJAX, you get the following advantages.

    The website becomes fast since the header and footer are not loaded for different pages.
    You website behaves like a SPA (Single Page Application), and you don’t need to employ Angular framework in your ASP.NET Core Application.
    If you have worked with Update Panel of ASP.NET Web Forms then it is quite similar to it.

This is how PJAX will work.
See the below video which illustrates the working of PJAX.

PJAX Implementation in ASP.NET Core

Integration of PJAX in ASP.NET Core involves the following things.

Layout.cshtml View
In your application _Layout.cshml View, add jQuery and PJAX script links. You do this inside the head section:
    <script src="https://code.jquery.com/jquery-2.2.4.js"></script> 
    <script src="~/js/jquery.pjax.js"></script> 
    Also call PJAX on all anchors inside the #main element.  
    <script type="text/javascript"> 
        $(function () { 
            // call pjax 
            $(document).pjax('#menu li a', '#main', { timeout: 10000 }); 
     
        }); 
    </script> 


Loading Image
If you want to show the loading image when a new page contents are being fetched then add the following code inside the script section of Layout:
    $(document).ajaxStart(function () { 
        $("#loadingDiv").show(); 
    }); 
     
    $(document).ajaxComplete(function (event, jqxhr, settings) { 
        $("#loadingDiv").hide(); 
    }); 


Also, place the loading image somewhere in your layout.
    <div id="loadingDiv" style="display:none;"> 
        <img src="~/loading.gif" /> 
    </div> 


Do not worry as the source code contains all the loading image codes. Do check it.

Add some links to your _Layout.cshtml View. On these links, PJAX will work so when these links are clicked then their page’s contents are loaded by PJAX (but the header and footer area are not loaded).
    <ul> 
        <li><a href="/Home/Index">Index</a></li> 
        <li><a href="/Home/About">About</a></li> 
        <li><a href="/Home/Contact">Contact</a></li> 
    </ul> 


Don’t forget to add the #main element on the Layout so that PJAX only fetches the contents inside this #main element with AJAX.
    <div id="main"> 
        @RenderBody()  
    </div> 

Controller
Add a controller called Home with the following 3 action methods:

    public IActionResult Index() 
    { 
        if (string.IsNullOrEmpty(Request.Headers["X-PJAX"])) 
            return View(); 
        else 
            return PartialView("/Views/Home/Index.cshtml"); 
    } 
     
    public IActionResult About() 
    { 
        if (string.IsNullOrEmpty(Request.Headers["X-PJAX"])) 
            return View(); 
        else 
            return PartialView("/Views/Home/About.cshtml"); 
    } 
     
    public IActionResult Contact() 
    { 
        if (string.IsNullOrEmpty(Request.Headers["X-PJAX"])) 
            return View(); 
        else 
            return PartialView("/Views/Home/Contact.cshtml"); 
    }  


Make sure that the Action methods that are called by PJAX (i.e. clicking on menu links in my case) return PartialViews. Since PJAX sends ‘X-PJAX’ request in the HTTP Header therefore I can easily make a selection of View or Partial View by checking the HTTP header.

The condition applied in each action method that does this work is:
    if (string.IsNullOrEmpty(Request.Headers["X-PJAX"])) 
        return View(); 
    else 
        return PartialView("/Views/Home/Index.cshtml");  


Views

Add the 3 Views called ‘Index.cshtml’, ‘About.cshtml’ and ‘Contact.cshtml’ inside the ‘Views/Home’ folder:

Index.cshtml
    <div class="templatemo_content_area"> 
        <h1>WELCOME TO Index Page</h1> 
    </div> 


About.cshtml
    <div class="templatemo_content_area"> 
        <h1>WELCOME TO About Page</h1> 
    </div> 


Contact.cshtml
    <div class="templatemo_content_area"> 
        <h1>WELCOME TO Contact Page</h1> 
    </div> 


Also add _ViewStart.cshtml View inside the ‘Views’ folder:
    @{ 
        Layout = "_Layout"; 
    }



European ASP.NET Core Hosting :: How to Use HTTP-REPL tool to test WEB API in ASP.NET Core 2.2

clock February 26, 2019 07:37 by author Scott

Today there are no tools built into Visual Studio to test WEB API. Using browsers, one can only test http GET requests. You need to use third-party tools like PostmanSoapUIFiddler or Swagger to perform a complete testing of the WEB API. In ASP.NET Core 2.2, a CLI based new dotnet core global tool named “http-repl” is introduced to interact with API endpoints. It’s a CLI based tool which can list down all the routes and execute all HTTP verbs. In this post, let’s find out how to use HTTP-REPL tool to test WEB API in ASP.NET Core 2.2.

HTTP-REPL Tool to test WEB API in ASP.NET Core 2.2

The “http-repl” is a dotnet core global tool and to install this tool, run the following command. At the time of writing this post, the http-repl tool is in preview stage
and available for download at 
dotnet.myget.org

dotnet tool install -g dotnet-httprepl --version 2.2.0-* --add-source https://dotnet.myget.org/F/dotnet-core/api/v3/index.json

Once installed, you can verify the installation using the following command.

dotnet tool list -g



Now the tool is installed, let’s see how we can test the WEB API. For this tool to work properly, the prerequisite here is that your services will have Swagger/OpenAPI available that describes the service.

We need to add this tool to web browser list so that we can browse the API with this tool. To do that, follow the steps given in the below image.



The location of HTTP-REPL tool executable is "C:\Users\<username>\.dotnet\tools". Once added, you can verify it in the browser list.

Run the app (make sure HTTP REPL is selected in browser list) and you should see a command prompt window. As mentioned earlier, it’s a CLI based experience so you can use commands like dir, ls, cdand cls. Below is an example run where I start-up a Web API.

You can use all the HTTP Verbs, and when using the POST verb, you should set a default text editor to supply the JSON. You can set Visual Studio Code as default text editor using the following command.

pref set editor.command.default "C:\Program Files (x86)\Microsoft VS Code\Code.exe"

Once the default editor is set, and you fire POST verb, it will launch the editor with the JSON written for you. See below GIF.

You can also navigate to the Swagger UI from the command prompt via executing ui command. Like,

Similarly, you can also execute the DELETE and PUT. In case of PUT command, you should use following syntax and in the default code editor, supply the updated data.

> delete 2 //This would delete the record with id 2.
>
> put 2010 -h "Content-Type: application/json"

When you fire PUT command, the behavior is same as the POST verb. The text editor will open with the JSON written for you, just supply the updated value to execute PUT command.

Pros and Cons

Pros

  • Helps in debugging WEB API
  • Fast and quickly switch between API endpoints
  • Descriptive error response shown

Cons:

  • Dependency on Swagger/Open API specification
  • Not as informative as UI tools

After playing with this for a while, I strongly feel it’s command line version of the Swagger UI and it would be very handy when there are many API endpoints. You can easily navigate or switch between the APIs and execute it. 



European ASP.NET Hosting :: Overriding ASP.NET Core Framework

clock February 20, 2019 10:57 by author Scott

OVERVIEW

In .NET it’s really easy to create your own interfaces and implementations. Likewise, it’s seemingly effortless to register them for dependency injection. But it is not always obvious how to override existing implementations. Let’s discuss various aspects of “dependency injection” and how you can override the “framework-provided services”.

As an example, let’s take a recent story on our product backlog for building a security audit of login attempts. The story involved the capture of attempted usernames along with their corresponding IP addresses. This would allow system administrators to monitor for potential attackers. This would require our ASP.NET Core application to have custom logging implemented.

LOGGING

Luckily ASP.NET Core Logging is simple to use and is a first-class citizen within ASP.NET Core.

In the Logging repository there is an extension method namely AddLogging, here is what it looks like:

public static IServiceCollection AddLogging(this IServiceCollection services)
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    services.TryAdd(ServiceDescriptor.Singleton<ILoggerFactory, LoggerFactory>());
    services.TryAdd(ServiceDescriptor.Singleton(typeof(ILogger<>), typeof(Logger<>)));

    return services;
}

As you can see, it is rather simple. It adds two ServiceDescriptor instances to the IServiceCollection, effectively registering the given service type to the corresponding implementation type.

FOLLOWING THE RABBIT DOWN THE HOLE

When you create a new ASP.NET Core project from Visual Studio, all the templates follow the same pattern. They have the Program.cs file with a Main method that looks very similar to this:

public static void Main(string[] args)
{
    var host = new WebHostBuilder()
        .UseKestrel()
        .UseContentRoot(Directory.GetCurrentDirectory())
        .UseIISIntegration()
        .UseStartup<Startup>()
        .UseApplicationInsights()
        .Build();

    host.Run();
}

TEMPLATES 

One thing that is concerning about a template like this is that the IWebHost is an IDisposable, so why then is this statement not wrapped in a using you ask? The answer is that the Run extension method internally wraps itself in a using. If you were wondering where the AddLogging occurs, it is a result of invoking the Build function.

[ Microsoft.AspNetCore.Hosting.WebHostBuilder ]
    public IWebHost Build() ...
        private IServiceCollection BuildCommonServices() ...
            creates services then invokes services.AddLogging()

A FEW WORDS ON THE SERVICE DESCRIPTOR

The ServiceDescriptor class is an object that describes a service, and this is used by dependency injection. In other words, instances of the ServiceDescriptor are descriptions of services. The ServiceDescriptor class exposes several static methods that allow its instantiation.

The ILoggerFactory interface is registered as a ServiceLifetime.Singleton and its implementation is mapped to the LoggerFactory. Likewise, the generic type typeof(ILogger<>) is mapped to typeof(Logger<>). This is just one of the several key “Framework-Provided Services” that are registered.

PUTTING IT TOGETHER

Now we know that the framework is providing all implementations of ILogger<T>, and resolving them as their Logger<T>. We also know that we could write our own implementation of the ILogger<T>interface. Being that this is open-source we can look to their implementation for inspiration.

public class RequestDetailLogger<T> : ILogger<T>
{
    private readonly ILogger _logger;

    public RequestDetailLogger(ILoggerFactory factory,
                               IRequestCategoryProvider requestCategoryProvider)
    {
        if (factory == null)
        {
            throw new ArgumentNullException(nameof(factory));
        }
        if (requestCategoryProvider == null)
        {
            throw new ArgumentNullException(nameof(requestCategoryProvider));
        }

        var category = requestDetailCategoryProvider.CreateCategory<T>();
        _logger = factory.CreateLogger(category);
    }

    IDisposable ILogger.BeginScope<TState>(TState state)
        => _logger.BeginScope(state);

    bool ILogger.IsEnabled(LogLevel logLevel)
        => _logger.IsEnabled(logLevel);

    void ILogger.Log<TState>(LogLevel logLevel,
                             EventId eventId,
                             TState state,
                             Exception exception,
                             Func<TState, Exception, string> formatter)
        => _logger.Log(logLevel, eventId, state, exception, formatter);
}

The IRequestCategoryProvider is defined and implemented as follows:

using static Microsoft.Extensions.Logging.Abstractions.Internal.TypeNameHelper;

public interface IRequestCategoryProvider
{
    string CreateCategory<T>();
}

public class RequestCategoryProvider : IRequestCategoryProvider
{
    private readonly IPrincipal _principal;
    private readonly IPAddress _ipAddress;

    public RequestCategoryProvider(IPrincipal principal,
                                   IPAddress ipAddress)
    {
        _principal = principal;
        _ipAddress = ipAddress;
    }

    public string CreateCategory<T>()
    {
        var typeDisplayName = GetTypeDisplayName(typeof(T));

        if (_principal == null || _ipAddress == null)
        {
            return typeDisplayName;
        }

        var username = _principal?.Identity?.Name;
        return $"User: {username}, IP: {_ipAddress} {typeDisplayName}";
    }
}

If you’re curious how to get the IPrincipal and IPAddress into this implementation (with DI). It is pretty straight-forward. In the Startup.ConfigureServices method do the following:

public void ConfigureServices(IServiceCollection services)
{
    // ... omitted for brevity

    services.AddTransient<IRequestCategoryProvider, RequestCategoryProvider>();
    services.AddTransient<IHttpContextAccessor, HttpContextAccessor>();
    services.AddTransient<IPrincipal>(
        provider => provider.GetService<IHttpContextAccessor>()
                           ?.HttpContext
                           ?.User);
    services.AddTransient<IPAddress>(
        provider => provider.GetService<IHttpContextAccessor>()
                           ?.HttpContext
                           ?.Connection
                           ?.RemoteIpAddress);
}

Finally, we can Replace the implementations for the ILogger<T> by using the following:

public void ConfigureServices(IServiceCollection services)
{
    // ... omitted for brevity
    services.Replace(ServiceDescriptor.Transient(typeof(ILogger<>),
                                                 typeof(RequestDetailLogger<>)));
}

Notice that we replace the framework-provided service as a ServiceLifetime.Transient. Opposed to the default ServiceLifetime.Singleton. This is more or less an extra precaution. We know that with each request we get the HttpContext from the IHttpContextAccessor, and from this we have the User. This is what is passed to each ILogger<T>.

CONCLUSION

This approach is valid for overriding any of the various framework-provided service implementations. It is simply a matter of knowing the correct ServiceLifetime for your specific needs. Likewise, it is a good idea to leverage the open-source libraries of the framework for inspiration. With this you can take finite control of your web-stack.



ASP.NET Core 2.2.1 Hosting - HostForLIFE.eu :: Cookies in ASP.Net

clock February 8, 2019 08:27 by author Peter

Today I am here to explain cookies in ASP.Net. You have seen “Remember Me” in every login portal or website. I will tell you how it works in this demo.

Cookies
It is a small text file stored in a client local machine or in the memory of a client browser session. It is used to state management. We can store a small piece of information in this file. It stores information in a plain text file.

How It Works

When the client sends a request to the server then the server sends response cookies with a session Id. If the cookies are saved the first time then the cookies are used for subsequent requests.

I am giving you a small demonstration. In this demonstration I will show you how to use use cookies and what “Remember Me” is.

When the user logs in with “Remember Me” selected then cookies play an important role. If Remember Me is selected then cookies will be created with the userid and an encrypted word. Cookies are easily readable for every user in the local machine. That’s why I use md5 to encryt my word for cookies.

Check cookies on Page_Load:
    HttpCookie _objCookie = Request.Cookies["Test"]; 
     
            if (_objCookie != null) 
            { 
                bool bCheck = IsValidAuthCookie(_objCookie, "encrypt"); 
                if (bCheck) 
                { 
                    Response.Redirect("WelcomePage.aspx?User=" + Convert.ToString(_objCookie.Value.ToString().Split('|')[0]) + ""); 
                } 
            } 


I check cookies on the login page load every time. If cookies exist then I redirect the welcome.aspx directly.
LoginButton_Click
    bool IsLogin = IsValidLogin(txtUserId.Text.Trim(), txtword.Text.Trim());   
    if (IsLogin)   
    {   
        if (chkRememberMe.Checked)   
        {   
            CreateAuthCookie(txtUserId.Text.Trim(), txtword.Text.Trim(), "encrypt");   
         }   
         Response.Redirect("WelcomePage.aspx?User=" + txtUserId.Text.Trim() + "");   
    }


If “Remember me” is checked then I create cookies with User Id and encrypted word.
Suppose you login with “Remember me” checked and close the application without LogOut. Now when you open again your login page it will redirect you to the welcome.aspx page automatically. And if you logout the application then your cookies will be removed. You will see this scenario on Gmail.com, Facebook.com and so on.

Create Hash word with Md5 encryption as in the following:
    public string CreateHash(string word, string salt) 
    { 
        // Get a byte array containing the combined word + salt. 
        string authDetails = word + salt; 
        byte[] authBytes = System.Text.Encoding.ASCII.GetBytes(authDetails); 
     
        // Use MD5 to compute the hash of the byte array, and return the hash as 
        // a Base64-encoded string. 
        var md5 = new System.Security.Cryptography.MD5CryptoServiceProvider(); 
        byte[] hashedBytes = md5.ComputeHash(authBytes); 
        string hash = Convert.ToBase64String(hashedBytes); 
     
        return hash; 
    }
 

Advantages
Cookies do not require any server resources since they are stored on the client.
Cookies are easy to implement.

Disadvantages
Cookies can be disabled on user browsers
Cookies are transmitted for each HTTP request/response causing overhead on bandwidth
No security for sensitive data.

HostForLIFE.eu ASP.NET Core 2.2.1 Hosting
European best, cheap and reliable ASP.NET hosting with instant activation. HostForLIFE.eu is #1 Recommended Windows and ASP.NET hosting in European Continent. With 99.99% Uptime Guaranteed of Relibility, Stability and Performace. HostForLIFE.eu security team is constantly monitoring the entire network for unusual behaviour. We deliver hosting solution including Shared hosting, Cloud hosting, Reseller hosting, Dedicated Servers, and IT as Service for companies of all size.



European ASP.NET Core Hosting :: How to Use IOptions for ASP.NET Core 2 Configuration

clock February 7, 2019 11:48 by author Scott

Almost every project will have some settings that need to be configured and changed depending on the environment, or secrets that you don't want to hard code into your repository. The classic example is connection strings and passwords etc which in ASP.NET 4 were often stored in the <applicationSettings> section of web.config.

In ASP.NET Core this model of configuration has been significantly extended and enhanced. Application settings can be stored in multiple places - environment variables, appsettings.json, user secrets etc - and easily accessed through the same interface in your application. Further to this, the new configuration system in ASP.NET allows (actually, enforces) strongly typed settings using the IOptions<> pattern.

While working on an RC2 project the other day, I was trying to use this facility to bind a custom Configuration class, but for the life of me I couldn't get it to bind my properties. Partly that was down to the documentation being somewhat out of date since the launch of RC2, and partly down to the way binding works using reflection. In this post I'm going to go into demonstrate the power of the IOptions<> pattern, and describe a few of the problems I ran in to and how to solve them.

Strongly typed configuration

 

In ASP.NET Core, there is now no default AppSettings["MySettingKey"] way to get settings. Instead, the recommended approach is to create a strongly typed configuration class with a structure that matches a section in your configuration file (or wherever your configuration is being loaded from):

public class MySettings
{
    public string StringSetting { get; set; }
    public int IntSetting { get; set; }
}

Would map to the lower section in the appsettings.json below.

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "MySettings": {
    "StringSetting": "My Value",
    "IntSetting": 23
  }
}

Binding the configuration to your classes

 

In order to ensure your appsettings.json file is bound to the MySettings class, you need to do 2 things.

1. Setup the ConfigurationBuilder to load your file

2. Bind your settings class to a configuration section

When you create a new ASP.NET Core application from the default templates, the ConfigurationBuilder is already configured in Startup.cs to load settings from environment variables, appsettings.json, and in development environments, from user secrets:

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

    if (env.IsDevelopment())
    {
        builder.AddUserSecrets();
    }

    builder.AddEnvironmentVariables();
    Configuration = builder.Build();
}

If you need to load your configuration from another source then this is the place to do it, but for most common situations this setup should suffice. There are a number of additional configuration providers that can be used to bind other sources, such as xml files for example.

In order to bind a settings class to your configuration you need to configure this in the ConfigureServices method of Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<MySettings>(options => Configuration.GetSection("MySettings").Bind(options));
}

Note: The syntax for model binding has changed from RC1 to RC2 and was one of the issues I was battling with. The previous method, using services.Configure<MySettings>(Configuration.GetSection("MySettings")), is no longer available

You may also need to add the configuration binder package to the dependencies section of your project.json:

"dependencies": {
  ...
  "Microsoft.Extensions.Configuration.Binder": "1.0.0-rc2-final"
  ...
}

Using your configuration class

 

When you need to access the values of MySettings you just need to inject an instance of an IOptions<> class into the constructor of your consuming class, and let dependency injection handle the rest:

public class HomeController : Controller
{
    private MySettings _settings;
    public HomeController(IOptions<MySettings> settings)
    {
        _settings = settings.Value
        // _settings.StringSetting == "My Value";
    }
}

The IOptions<> service exposes a Value property which contains your configured MySettings class.

It's important to note that there doesn't appear to be a way to access the raw IConfigurationRoot through dependency injection, so the strongly typed route is the only way to get to your settings.

You can expose the IConfigurationRoot directly to the DI container using services.AddSingleton(Configuration). (Thanks Saša Ćetković for pointing that out!)

Complex configuration classes

 

The example shown above is all very nice, but what if you have a very complex configuration, nested types, collections, the whole 9 yards?

public class MySettings
{
    public string StringSetting { get; set; }
    public int IntSetting { get; set; }
    public Dictionary<string, InnerClass> Dict { get; set; }
    public List<string> ListOfValues { get; set; }
    public MyEnum AnEnum { get; set; }
}

public class InnerClass
{
    public string Name { get; set; }
    public bool IsEnabled { get; set; } = true;
}

public enum MyEnum
{
    None = 0,
    Lots = 1
}

Amazingly we can bind that using the same configure<MySettings> call to the following, and it all just works:

{
  "MySettings": {
    "StringSetting": "My Value",
    "IntSetting": 23,
    "AnEnum": "Lots",
    "ListOfValues": ["Value1", "Value2"],
    "Dict": {
      "FirstKey": {
        "Name": "First Class",
           "IsEnabled":  false
      },
      "SecondKey": {
        "Name": "Second Class"
      }
    }
  }
}

When values aren't provided, they get their default values, (e.g. MySettings.Dict["SecondKey].IsEnabled == true). Dictionaries, lists and enums are all bound correctly. That is until they aren't...

Models that won't bind

 

So after I'd beaten the RC2 syntax change in to submission, I thought I was home and dry, but I still couldn't get my configuration class to bind correctly. Getting frustrated, I decided to dive in to the source code for the binder and see what's going on (woo, open source!).

It was there I found a number of interesting cases where a model's properties won't be bound even if there are appropriate configuration values. Most of them are fairly obvious, but could feasibly sting you if you're not aware of them. I am only going to go into scenarios that do not throw exceptions, as these seem like the hardest ones to figure out.

Properties must have a public Get method

 

The properties of your configuration class must have a getter, which is public and must not be an indexer, so none of these properties would bind:

private string _noGetter;
private string[] _arr;

public string NoGetter { set { _noGetter = value; } }
public string NonPublicGetter { set { _noGetter = value; } }
public string this[int i]
{
    get { return _arr[i]; }
    set { _arr[i] = value; }
}

Properties must have a public Set method...

 

Similarly, properties must have a public setter, so again, none of these would bind:

public string NoGetter { get; }
public string NonPublicGetter { get; private set; }

...Except when they don't have to

 

The public setter is actually only required if the value being bound is null. If it's a simple type like a string or and int, then the setter is required as there's no way to change the value. You can create readonly properties with default values, but they just won't be bound. For properties which are complex types, you don't need a setter, as long as the value has a value at binding time:

public MyInnerClass ComplexProperty { get; } = new MyInnerClass();
public List<string> ListValues { get; } = new List<string>();
public Dictionary<string, string> DictionaryValue1 { get; } = new Dictionary<string,string>();
private Dictionary<string, string> _dict = new Dictionary<string,string>();
public Dictionary<string, string> DictionaryValue2 { get { return _dict; } }

The sub properties of the MyInnerClass object returned by ComplexProperty would be bound, values would be added to the collection in ListValues, and KeyValuePairs would be added to the dictionaries.

Dictionaries must have string keys

 

This is one of the gotchas that got me! While integers, are obviously perfectly valid keys to dictionaries usually, they are not allowed in this case thanks to this snippet in ConfigurationBinder.BindDictionary:

var typeInfo = dictionaryType.GetTypeInfo();

// IDictionary<K,V> is guaranteed to have exactly two parameters
var keyType = typeInfo.GenericTypeArguments[0];
var valueType = typeInfo.GenericTypeArguments[1];

if (keyType != typeof(string))
{
    // We only support string keys
    return;
}

Don't expose IDictionary

 

This is another one that got me accidentally. While coding to interfaces is nice, the model binder uses reflection and Activator.CreateInstance(type) to create the classes to be bound. If your properties are interfaces or abstract then the binder will throw when trying to create them.

If you are exposing your properties as a readonly getter however, then the binder does not need to create the property and you might think the configuration class would bind correctly. And that is true in almost all cases. Unforunately while the binder can bind any properties which are a type that derives from IDictionary<,>, it will not bind an IDictionary<,> property directly. This leaves you with the following situation:

public interface IMyDictionary<TKey, TValue> : IDictionary<TKey, TValue> { }

public class MyDictionary<TKey, TValue>
    : Dictionary<TKey, TValue>, IMyDictionary<TKey, TValue>
{
}

public class MySettings
{
  public IDictionary<string, string> WontBind { get; } = new Dictionary<string, string>();
  public IMyDictionary<string, string> WillBind { get; } = new MyDictionary<string, string>();
}

Our wrapper type IMyDictionary which is really just an IDictionary will be bound, whereas the directly exposed IMyDictionary will not. This doesn't feel right to me and I've raised an issue with the team.

Make properties Implementing ICollection also expose an Add method

 

Types deriving from ICollection<> are automatically bound in the same way as dictionaries, however the ICollection<> interface exposes no methods to add an object to the collection, only methods for enumerating and counting. It may seem strange then that it is this interface the binder looks for when checking whether a property can be bound.

If a property exposes a type that implements ICollection<> (and is not an ICollection<> itself, as for IDictionary above, though that makes sense in this case), then it is a candidate for binding. In order to add an item to the collection, reflection is used to invoke an Add method on the type:

var addMethod = typeInfo.GetDeclaredMethod("Add");
addMethod.Invoke(collection, new[] { item });

If an add method on the exposed type does not exist (e.g. it could be a ReadOnlyCollection<>), then this property will not be bound, but no error will be thrown, you will just get an empty collection. This one feels a little nasty to me, but I guess the common use case is you will be exposing List<> and IList<> etc. Feels like they should be looking for IList<> if that is what they need though!

Summary

 

The strongly typed configuration is a great addition to ASP.NET Core, providing a clean way to apply the Interface Segregation Principle to your configuration. Currently it seems more convoluted to retrieve your settings than tin ASP.NET 4, but I wouldn't be surprised if they add some convenience methods for quickly accessing values in a forthcoming release.

It's important to consider the gotchas described if you're having trouble binding values (and you're not getting an exceptions thrown). Pay particular attention to your collections, as that's where my issues arose.



European ASP.NET Core Hosting :: ASP.NET Core 2.0 MVC Filters

clock January 28, 2019 09:58 by author Scott

The following is tutorial how to run code before and after MVC request pipeline in ASP.NET Core.

Solution

In an empty project update Startup class to add services and middleware for MVC:

        public void ConfigureServices
            (IServiceCollection services)
        {
            services.AddMvc();
        } 

        public void Configure(
            IApplicationBuilder app,
            IHostingEnvironment env)
        {
            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }

Add the class to implement filter:

    public class ParseParameterActionFilter : Attribute, IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            object param;
            if (context.ActionArguments.TryGetValue("param", out param))
                context.ActionArguments["param"] = param.ToString().ToUpper();
            else
                context.ActionArguments.Add("param", "I come from action filter");
        } 

        public void OnActionExecuted(ActionExecutedContext context)
        {
        }
    }

In the Home controller add an action method that uses Action filter:

        [ParseParameterActionFilter]
        public IActionResult ParseParameter(string param)
        {
            return Content($"Hello ParseParameter. Parameter: {param}");
        }

Browse to /Home/ParseParameter, you’ll see:

 

Discussion

Filter runs after an action method has been selected to execute. MVC provides built-in filters for things like authorisation and caching. Custom filters are very useful to encapsulate reusable code that you want to run before or after action methods.

Filters can short-circuit the result i.e. stops the code in your action from running and return a result to the client. They can also have services injected into them via service container, which makes them very flexible.

Filter Interfaces

Creating a custom filter requires implementing an interface for the type of filter you require. There are two flavours of interfaces for most filter type, synchronous and asynchronous:

    public class HelloActionFilter : IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            // runs before action method
        } 

        public void OnActionExecuted(ActionExecutedContext context)
        {
            // runs after action method
        }
    } 

    public class HelloAsyncActionFilter : IAsyncActionFilter
    {
        public async Task OnActionExecutionAsync(
            ActionExecutingContext context,
            ActionExecutionDelegate next)
        {
            // runs before action method
            await next();
            // runs after action method
        }
    }

You can short-circuit the filter pipeline by setting the Result (of type IActionResult) property on context parameter (for Async filters don’t call the next delegate):

    public class SkipActionFilter : Attribute, IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            context.Result = new ContentResult
            {
                Content = "I'll skip the action execution"
            };
        } 

        public void OnActionExecuted(ActionExecutedContext context)
        { }
    } 

    [SkipActionFilter]
    public IActionResult SkipAction()
    {
       return Content("Hello SkipAction");
    }

For Result filters you could short-circuit by setting the Cancel property on context parameter and sending a response:

        public void OnResultExecuting(ResultExecutingContext context)
        {
            context.Cancel = true;
            context.HttpContext.Response.WriteAsync("I'll skip the result execution");
        } 

        [SkipResultFilter]
        public IActionResult SkipResult()
        {
            return Content("Hello SkipResult");
        }

Filter Attributes

MVC provides abstract base classes that you can inherit from to create custom filters. These abstract classes inherit from Attribute class and therefore can be used to decorate controllers and action methods:

  • ActionFilterAttribute
  • ResultFilterAttribute
  • ExceptionFilterAttribute
  • ServiceFilterAttribute
  • TypeFilterAttribute

Filter Types

There are various type of filters that run at different stages of the filter pipeline. Below a figure from official documentation illustrates the sequence:

 

 

Authorization

 

 

This is the first filter to run and short circuits request for unauthorised users. They only have one method (unlike most other filters that have Executing and Executed methods). Normally you won’t write your own Authorization filters, the built-in filter calls into framework’s authorisation mechanism.

Resource

They run before model binding and can be used for changing how it behaves. Also they run after the result has been generated and can be used for caching etc.

Action

They run before and after the action method, thus are useful to manipulate action parameters or its result. The context supplied to these filters let you manipulate the action parameters, controller and result.

Exception

They can be used for unhandled exception before they’re written to the response. Exception handling middleware works for most scenarios however this filter can be used if you want to handle errors differently based on the invoked action.

Result

They run before and after the execution of action method’s result, if the result was successful. They can be used to manipulate the formatting of result.

Filter Scope

Filters can be added at different levels of scope: Action, Controller and Global. Attributes are used for action and controller level scope. For globally scoped filters you need to add them to filter collection of MvcOptions when configuring services in Startup:

            services.AddMvc(options =>
            {
                             // by instance
                options.Filters.Add(new AddDeveloperResultFilter("Tahir Naushad")); 

                // by type
                options.Filters.Add(typeof(GreetDeveloperResultFilter));
            });

Filters are executed in a sequence:

1. The Executing methods are called first for Global > Controller > Action filters.

2. Then Executed methods are called for Action > Controller > Global filters.

Filter Dependency Injection

In order to use filters that require dependencies injected at runtime, you need to add them by Type. You can add them globally (as illustrated above), however, if you want to apply them to action or controller (as attributes) then you have two options:

ServiceFilterAttribute

This attributes retrieves the filter using service container. To use it:

Create a filter that uses dependency injection:

    public class GreetingServiceFilter : IActionFilter
    {
        private readonly IGreetingService greetingService; 

        public GreetingServiceFilter(IGreetingService greetingService)
        {
            this.greetingService = greetingService;
        } 
        public void OnActionExecuting(ActionExecutingContext context)
        {
            context.ActionArguments["param"] =
                this.greetingService.Greet("James Bond");
        } 

        public void OnActionExecuted(ActionExecutedContext context)
        { }
    }

Add filter to service container:

services.AddScoped<GreetingServiceFilter>();

Apply it using ServiceFilterAttribute:

[ServiceFilter(typeof(GreetingServiceFilter))]
public IActionResult GreetService(string param)

TypeFilterAttribute

This attributes doesn’t need registering the filter in service container and initiates the type using ObjectFactory delegate. To use it:

Create a filter that uses dependency injection:

    public class GreetingTypeFilter : IActionFilter
    {
        private readonly IGreetingService greetingService; 

        public GreetingTypeFilter(IGreetingService greetingService)
        {
            this.greetingService = greetingService;
        } 

        public void OnActionExecuting(ActionExecutingContext context)
        {
            context.ActionArguments["param"] = this.greetingService.Greet("Dr. No");
        } 

        public void OnActionExecuted(ActionExecutedContext context)
        { }
    }

Apply it using TypeFilterAttribute:

[TypeFilter(typeof(GreetingTypeFilter))]
public IActionResult GreetType1(string param)

You could also inherit from TypeFilterAttribute and then use without TypeFilter:

public class GreetingTypeFilterWrapper : TypeFilterAttribute
{
   public GreetingTypeFilterWrapper() : base(typeof(GreetingTypeFilter))
   { }


[GreetingTypeFilterWrapper]
public IActionResult GreetType2(string param)
 



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