App Services – Page 42 – My Point of View

Search string array in collection using LINQ

LINQ behavior is that LINQ wouldn’t return null when results are empty rather it will return an empty enumerable. We can check this with .Any() method;

if (!YourResult.Any())

This is a LinqPad example;

var lst = new List<int>() { 1, 2, 3 };
var ans = lst.Where( i => i > 3 );

(ans == null).Dump();  // False
(ans.Count() == 0 ).Dump();  // True

Let’s go through another example where I have this string array to search;
{“dog”,”cat”};

in this string;
“This is a string and may or may not contain a word we are looking for like cat”

string input = "This is a string and may or may not contain a word we are looking for like cat";
List<string> search = new List<string>() { "dog", "cat"};
bool found = input.Split(' ').Any(x => search.Contains(x));

It works like this: the string gets split into an array of words. Then Any checks whether there is an x in this array where search.Contains(x).

Enumerable.Any(TSource) Method (IEnumerable(TSource)) (System.Linq)

Reference

What does linq return when the results are empty

Find all items in list which exist in another list using linq

Hide/Show Div with javascript

To display and hide DIV in html;

<div class="card-body">
   <div id="divMessage">                
        @Html.Raw(@TempData["message"]);
    </div>
    </div>  
    <div> 
       <!--need to hide this form-->         
       <form method="post" asp-antiforgery="true" id="formDiv">
          <div class="card mb-3">
             <h5 class="card-header text-white">
                  Welcome To Div Hide/Display
             </h5>
        </form>
    </div>
</div>

Use this javascript;

@section Scripts
{
  <script>
     $(document).ready(function () {
            //show/hide login sections based on SSO
            divFormSection();
        });

        function divFormSection() {
            var isDivFormVisible = '@TempData["IsDivFormVisible"]';
            if (isDivFormVisible == 'false') {
                //alert(isDivFormVisible);
                $("#formDiv").hide();
            }
        }
     }
    </script>
}

We need to pass parameters from controller in TempData;

TempData["message"] = "Form Hide/Display demo";
TempData["IsDivFormVisible"] = "false";

Use TempData or ViewBag to render HTML

This is a very basic example;

Declare this in a controller.

var fontAwesomeIcon = "<span class=\"fa fa-redo\" style=\"font-size:30px; color: red; margin-bottom: 20px; \">&nbsp;Try again</span>";

TempData["message"] = $"{fontAwesomeIcon} <h5>Something went wrong. Please try again. If problem persist, reach out to your point of contact for additional information</h5>";

And you can use it in your view;

<div class="card-body">
  <div id="divMessage">
     @Html.Raw(@TempData["message"]);
  </div>
</div>

Return values from HttpContext.Current.User.Principal and WindowsIdentity.GetCurrent()

Here is a brief explanation;

According to this forum on WindowsIdentity.GetCurrent().Name vs. User.Identity.Name:

User.Identity.Name represents the identity passed from IIS.
WindowsIdentity.GetCurrent().Name is the identity under which the thread is running.

Depending on your app’s authentication settings in IIS, they will return different values:

`Anonymous`	`Impersonate`	`User.Identity.Name`	`WindowsIndentiy.GetCurrent()`
Yes	True	`Empty String`	`IUSR_<machineName>`
Yes	False	`Empty String`	`NT Authority\Network Service`
No	True	`domain\user`	`domain\user`
No	False	`domain\user`	`NT Authority\Network Service`

Legend:

Where domain\user will show up as:
- domain\user for Active Directory
- machineName\userName for local account
Where NT Authority\Network Service will show up as:
- NT Authority\Network Service for Windows Server or ASP.NET
- machineName\ASPNET_WP for Windows XP

Resource

https://stackoverflow.com/questions/5402249/httpcontext-current-user-principal-vs-windowsidentity-getcurrent

Access to XMLHttpRequest from origin has been blocked by CORS policy…

I did a Web API deployment in Azure Web API service. I was able to access the URL in browser and Postman. I started getting following error when I try to integrate in ASP.NET Web App in my local development environment;

Access to XMLHttpRequest at ‘https://xyz-dev.azurewebsites.net/api/Authentication/GetTestUser?name=testuser’ from origin ‘http://localhost:17686’ has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.
jquery.js:9172 GET https://xyz-dev.azurewebsites.net/api/Authentication/GetTestUser?name=testuser net::ERR_FAILED

To solve the problem, I did this;

Here is server-side (Web API) code;

Add following to Web API ConfigureServices method;

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(op =>
    {
       op.AddPolicy("AllOrigin", builder => builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());
    });
}

Add following to Web API Configure method;

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory)
{
      //-------use cords
      app.UseCors("AllOrigin");
}

Here is client-side AJAX call.

<input type="button" id="btnWebApiCall" name=" btnWebApiCall" value="Test CORS" class=" btn btn-primary btn-lg justify-content-center" />

@section Scripts
    {

    <script>

        $(document).ready(function () {

            $("#btnAuthenticateSSO").click(function (e) {
                e.preventDefault();
                $.ajax({
                    type: "GET",
                    url: "https://xyzapi-dev.azurewebsites.net/api/Authentication/GetTestUser?name=testuser",
                    contentType: "application/json; charset=utf-8",
                    //crossDomain: true,
                    dataType: "json",
                    success: function (data, status, xhr) {
                        alert(JSON.stringify(data));
                        console.log(data);
                    }, //End of AJAX Success function
                    error: function (xhr, status, error) {
                        alert("Result: " + status + " " + error + " " + xhr.status + " " + xhr.statusText);
                    } //End of AJAX error function

                });
            });

        });

    </script>

}

The pain is gone.

If interested in learning more about this, read below;

Researched and figured out that browser sends two requests to the server. Tiny request and actual request.

The browser sends a tiny request called a preflight request before the actual request. It includes details such as the HTTP method used and whether any custom HTTP headers are present. The preflight allows the server to see how the actual request would appear before it is sent. The server will then tell the browser whether or not to submit the request, or whether to return an error to the client instead.

See below for problem header without CORS and with CORS in web API;

Headers without CORS implementation in Web API (Problem);