Musings on Cloud, BigData, AI, Machine Learning, Containers and IOT

Enable static website hosting in S3

AWS Simple Storage Service (S3) offers one of the powerful capability to host static websites. In this post let’s cover the steps for the same.

Create a sample bucket by name ‘mytestdomain.com’. The convention is that bucket name should match with the website domain name.

In this case the domain name for the static website is mytestdomain.com. The S3 bucket should match that name.

image

Enable public read access to this bucket.

image

Enable static web site hosting for the bucket by selecting ‘Use this bucket to host a static website’ and specifying the index document and error document.


image

Upload the index.html and error.html file and grant the public read access to it. Now access the static website url

provided by S3. It should be in this format.

http://s3bucketname.s3-website-region.amazonaws.com/

It should render the index.html in the browser

image

To render this website with the actual domain name, we need to leverage Route 53 DNS service offered by AWS.

Create a hosted zone for our custom domain.

image

Once the hosted zone is created, S3 presents with list of name servers. It should be mapped with the domain registrar for routing the request through Route 53.

The next step is to create a Record Set for the Hosted Zone bye selecting the Alias Target to the S3 bucket enabled for static website hosting.

image

It takes few minutes for the record set changes to get propagated. After that try accessing the website domain url. It should render the index page. This completes this article.





Working with a Github private repository from windows 10 PC

Github has become almost the defacto standard when it comes to code repository for DevOps. Github occupy large foot print in the Devops space – either in the form of open source GIT or in the form of commercially supported offerings through ISV’s. Github also comes into two flavors – public repository and private repository. As the name indicates, the public repositories are open to entire world without any restrictions. The private repositories are useful when a team wants to collaborate in a closed manner. The aim of this post is to elaborate the steps required for working with Github private repositories from Windows 10.


The first step is to set up keys for SSH and it to ssh key agent.

Open bash for windows 10.

ssh-keygen -t rsa -b 4096 -C “your_email@example.com

When prompted enter a filename to save the keypair.Also enter the passphrase for the keys.
image

You will see a confirmation for generation of keypair.
test
The next step is to add generated private key to the SSH agent. Before adding ensure that SSH agent is running
image
Navigate the path where the key pairs are present. Then type this command.
ssh-add keyname
It should prompt for the passphrase created with the key. Enter the passprase and you should get confirmation like below.
image
Now we have completed adding the private key portion of the key pairs to the SSK agent. The next 
step is to add the public key portion of this keypair into the Github repository.
Navigate to the folder in Windows 10 PC where the key pairs are located. Copy the contents of public key file (.pub).
image
Paste the contents of the public key file to the key field.
Now we can navigate to the bash on windows 10 and start performing all the regular git bash commands.
This completes the set up for accessing Github private repositories from Windows 10 PC.


Client.Timeout exception in docker client

I was trying to pull some docker images from DockerHub. I got this error message “Client.Timeout exceeded while waiting headers”.

image

After doing a bit of debugging and going through online forums, i tried this option of changing the DNS server to Fixed  and restarted the Docker engine.

image

After that I was able to execute all the Docker commands successfully.

image

Back to blogging

For almost three years I have not used this space for sharing my thoughts on technology. I could not do this for various reasons. In a span of three years lot has happened in my professional life and I’ve switched planes and nowadays I’ve diversified myself by exploring into open source technologies as well. We live an interesting time where we see a tremendous explosion in new technologies especially Artificial Intelligence, Big Data, Machine Learning etc. I will be sharing my experiences on what i work and learn from a developer standpoint. Stay tuned !!!

Overview of ASP.NET MVC Views and HTML Helpers

In ASP.NET web forms the request to an URL goes to a physical file on the web server. In ASP.NET MVC application the request to an URL does not represent a physical file, rather it invokes a method in a class (controller action). A controller action in an ASP.NET MVC application typically returns a View most of the times, however it can also perform other actions like returning a file or re-directing to another controller action.

A sample Controller action looks like below

http://serverurl/ControllerName/ActionName

http://serverurl/Home/Index

Home is the default controller that we will get when we create an ASP.NET MVC application in Visual Studio. Index is the default controller action that comes default in Visual Studio.

ASP.NET MVC framework works based on certain conventions. For every controller a sub-folder gets created under Views. For every controller action, a .cshtml file gets created under the respective sub-folder inside Views folder.

Now let’s move to understand HTMLHelpers. ASP.NET web forms have server controls which is used for data entry and UI form processing. In ASP.NET MVC we don’t have server controls, we need to rely on HTML Controls for data entry and UI form processing.

1. BeginForm

The BeginForm helper method denotes the start of an HTML form and it renders an HTML form element. The BeginForm method has 13 overrides and the i’m using the following  version of override in this post

   @using (Html.BeginForm("Index", "Home", FormMethod.Post))
        { 
        
        }

2.RadioButton helper

The Radio button helper helps us to render a RadioButton control. It can be bounded to a model property, which also can be set with values and group for the RadioButton.

 Male @Html.RadioButtonFor(model => model.Sex,"Male")
                Female @Html.RadioButtonFor(model => model.Sex, "Female")

3.Textbox helper

The @Html.EditorFor helper supports us to render a TextBox control for data capture. It can be bound to a model property.

        @Html.EditorFor(model => model.Age)

4.DropDownListControl

The @Html.DropDownListfor helper control supports us to render a dropdownlist control. It can be databound to a IEnumerable>T> which needs to be type casted as SelectList, while performing data binding.

 @Html.DropDownListFor(model => model.PolicyType, ViewData["PolicyType"] as SelectList)

5.CheckBox Control

The @Html.CheckBox control support us to to render a CheckBox control. It can be data bound to a boolean property in the Model.

@Html.CheckBoxFor(model=>model.ReceiveMails)

6.Label Control

The @Html.Label control supports us to render a Label control, whose literal value is bound from a string property in the Model.

 @Html.LabelFor(model => model.Age, new { @class = "control-label col-md-2" })

 

7. ActionLink Control

The @Html.ActionLink control supports us to link to an action method in a controller when the link is clicked.

  @Html.ActionLink("Back to List", "Index")

With the above briefing, i will be creating a View to capture the details for generating an InsuranceQuotation. The Model object definition looks like below :-

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace MVCDemo2.Models
{
    public class InsurancePolicy

    {

        public string FirstName { get; set; }
        public string LastNane { get; set; }
        public int Age { get; set; }
        public string Sex { get; set; }
        
        public string PolicyType { get; set; }

        public int PolicyTerm { get; set; }
        public int SumAssured { get; set; }

        public bool ReceiveMails { get; set; }


    }
}

My end goal is to create a View (shown below) to capture the details for generating Quotation.

image

The definition of my View ‘GenerateQuote.cshmtl’ looks like below :-

@model MVCDemo2.Models.InsurancePolicy

@{
    ViewBag.Title = "GenerateQuote";
}

<h2>GenerateQuote</h2>



@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()
    
    <div class="form-horizontal">
        <h4>InsurancePolicy</h4>
        <hr />
        @Html.ValidationSummary(true)

        <div class="form-group">
            @Html.LabelFor(model => model.FirstName, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.FirstName)
                @Html.ValidationMessageFor(model => model.FirstName)
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.LastNane, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.LastNane)
                @Html.ValidationMessageFor(model => model.LastNane)
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Age, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Age)
                @Html.ValidationMessageFor(model => model.Age)
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Sex, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                Male @Html.RadioButtonFor(model => model.Sex,"Male")
                Female @Html.RadioButtonFor(model => model.Sex, "Female")
                @Html.ValidationMessageFor(model => model.Sex)
            </div>
        </div>

        

        <div class="form-group">
            @Html.LabelFor(model => model.PolicyType, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.PolicyType, ViewData["PolicyType"] as SelectList)
                @Html.ValidationMessageFor(model => model.PolicyType)
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.PolicyTerm, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.PolicyTerm)
                @Html.ValidationMessageFor(model => model.PolicyTerm)
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.SumAssured, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.SumAssured)
                @Html.ValidationMessageFor(model => model.SumAssured)
            </div>
        </div>

        <div class="form-group">

            @Html.LabelFor(model=>model.ReceiveMails)
            @Html.CheckBoxFor(model=>model.ReceiveMails)
           
        </div>

            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <input type="submit" value="Create" class="btn btn-default" />
                </div>
            </div>
        </div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

This completes this article. My next post on ASP.NET MVC is here.

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Various options of passing data from ASP.NET MVC Controller to View

In ASP.NET MVC framework, we have got various options for passing data from Controller to View. Some of the options that i know and used are listed below :-

1. Use a strongly typed model object

2. Use a dynamic type (using @model syntax)

3.Use a ViewBag

This article focuses on explaining the above three methods of passing data from Controller to View.  Let’s create a simple ASP.NET MVC application to demo this one. Since there is a Cricket world cup fever going now, i will be creating a sample MVC application to display list of countries.

I’m adding the below model to the project

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web; 

namespace MVCDemo1.Models
{
    public class Countries
    { 

        public String Name { get; set; }
        public string Group { get; set; }
        public string DressColor { get; set; }
        public int NoOfTropies { get; set; }
    }
} 

I’ll be creating a new controller by name Country to handle various types of views(strongly typed views, loosely typed views and views accessing viewbag objects directly for the model Countries.

In the CountryController.cs, i’m setting up the values for CountryCollection

List<Countries> oCountries = new List<Countries> { 
        new Countries{Name="India",NoOfTropies=2,Group="A",DressColor="Blue"},
        new Countries{Name="Australia",NoOfTropies=3,Group="B",DressColor="Yellow"},
        new Countries{Name="SouthAfrica",NoOfTropies=0,Group="C",DressColor="Purple"}

        };

1.Use a strongly typed model object to pass data from Controller to View

In this approach, I’m adding a Controller action by name ‘StrongView’ to return the View for ActionResult.

public ActionResult StrongView()
        {

            return View(oCountries);

        }

Right click on the controller action and Add a View by choosing the Model class, which makes it a Strongly typed view.

image

Run the Solution and the View with CRUD operations look like below.

image

At the top of the View, model is referenced strongly which makes it Strongly typed View.

@model IEnumerable<MVCDemo1.Models.Countries>

Now, let’s move to the approach #2.

 

2. Use a dynamic type (@model syntax) to pass data from Controller to View

Let’s add another controller action by name ‘LooseView’ for passing loosely typed objects from Controller to View.

 public ActionResult LooseView()
        {

            return View(oCountries);
        
        }

Right click on the Controller action, Add View and do not choose any model class, that will make it as dynamically typed.

image

At the top of the View add a reference to dynamically typed view and Grab the Model data from dynamic object.

@model dynamic
@{
    ViewBag.Title = "LooseView";
}

<h2>LooseView</h2>

@foreach(var oCountry in Model)
{
    @oCountry.Name;
}

image

Now let’s move to the approach #3.

3. Use ViewBag to pass the data from Controller to View

Now let’s add a Controller action by name ‘ThirdView’ which sets the Country Collection and returns the View.

  public ActionResult ThirdView()
        {
            ViewBag.Countries = oCountries;
            return View();

        }

Let’s add a View by name ‘ThirdView’

image

I’ll be fetching the Model object from ViewBag and rendering it in the View.

@{
    ViewBag.Title = "ThirdView";
}

<h2>ThirdView</h2>

@foreach (var oCountry in ViewBag.Countries)
{
    @oCountry.Name;
}

image

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How to get list items in SharePoint 2013 Online using CSOM

In this post, we’ll see how we can fetch the list items of a SharePoint list in SharePoint 2013 online using REST. For the purpose of demonstration, I’ll be using a SharePoint hosted app.

Launch Visual Studio 2013.

File –> New –> Office/SharePoint –> Apps and name it as ‘GetListItemsREST’

I will be accessing the following REST endpoint for getting a web title

https://yoursite.sharepoint.com/_api/web/lists/GetByTitle(‘Shared%20Assets’)/items.

Since the call is initiating from AppWeb to HostWeb, it will present a classical cross-domain scenario, where I will be using the SP 2013 javascript cross-domain libraries to manage this call.

After creating the App project in Visual Studio 2013, the following points need to be considered.

a)The App Permission need to be left with default setting of Internal.

<AppPrincipal>
    <Internal/>
  </AppPrincipal>
  

With this setting, the SharePoint hosted app will have access to the Host Web by default.

b)The App need to be given full-control permission for site-collection. Otherwise, it will not be able to fetch the fields collection.

<AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="Read" />
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web" Right="Read" />
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web/list" Right="Read" />
  </AppPermissionRequests>

c)The executor object need to be instantiated with the parameter of ‘AppWebUrl’, not the ‘HostWebUrl.  (you’ll see more detailed code in the coming sections). If you instantiate it with ‘HostWebUrl, you will get an error like ‘App web not found’

var executor = new SP.RequestExecutor(AppWebUrl);

d)To access the HostWeb rest end points the url property in the cross-domain call need to be set in this fashion.

AppWebUrl + "/_api/SP.AppContextSite(@target)/web/lists/GetByTitle('Site%20Assets')/items?@target='" + HostWebUrl

Open the App.js and paste the following code

'use strict';

var context = SP.ClientContext.get_current();
var user = context.get_web().get_currentUser();
var HostWebUrl;
var AppWebUrl;


// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
    //getUserName();

    HostWebUrl =
                decodeURIComponent(
                    RetrieveQueryStringParameter("SPHostUrl")
            );
    AppWebUrl =
        decodeURIComponent(
            RetrieveQueryStringParameter("SPAppWebUrl")
    );

    var scriptbase = HostWebUrl + "/_layouts/15/";
    $.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

});


function successHandler(data) {

    var jsonObj = JSON.parse(data.body);
    var results = jsonObj.d.results;
    var resultcount = results.length;
    var finalresult;

    var i;
    var tempobject;


    for (i = 0; i < resultcount - 1; i++)
    {
        tempobject = results[i];
        finalresult = finalresult+ "Item title is" + tempobject["Title"] + "Item id is " + tempobject["Id"];
        
    }
   
    document.getElementById("message").innerText = finalresult;
  

   
    
   
    
}



function errorHandler(data, errorCode, errorMessage) {


    document.getElementById("message").innerText = "failure";

}

function RetrieveQueryStringParameter(ParamsforRetrieval) {
    var params =
        document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == ParamsforRetrieval)
            return singleParam[1];
    }
}

function execCrossDomainRequest() {

    var executor = new SP.RequestExecutor(AppWebUrl);

    executor.executeAsync({
        url: AppWebUrl + "/_api/SP.AppContextSite(@target)/web/lists/GetByTitle('Site%20Assets')/items?@target='" + HostWebUrl + "'",
        method: "GET",
        headers: {
            "accept": "application/json;odata=verbose",
            
        },
        success: successHandler,
        error: errorHandler
    });

}

Run the above piece of code and you will be see the below result.

image

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How to get a SharePoint group in SharePoint 2013 Online using REST

In this post, we’ll see how to get a SharePoint Group in SharePoint Online using REST. I’ll be using a SharePoint hosted app for the purpose of demonstration.

Launch Visual Studio 2013.

I will be accessing the following REST endpoint for getting a web title

https://yoursite.sharepoint/_api/web/sitegroups(index)

index – an integer that refers a group uniquely in the site.

Since the call is initiating from AppWeb to HostWeb, it will present a classical cross-domain scenario, where I will be using the SP 2013 javascript cross-domain libraries to manage this call.

After creating the App project in Visual Studio 2013, the following points need to be considered.

a)The App Permission need to be left with default setting of Internal.

<AppPrincipal>
    <Internal/>
  </AppPrincipal>

With this setting, the SharePoint hosted app will have access to the Host Web by default.

b)The App need to be given the following permission.

<AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="Read" />
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web" Right="Read" />
  </AppPermissionRequests>

c)The executor object need to be instantiated with the parameter of ‘AppWebUrl’, not the ‘HostWebUrl.  (you’ll see more detailed code in the coming sections). If you instantiate it with ‘HostWebUrl, you will get an error like ‘App web not found’.

var executor = new SP.RequestExecutor(AppWebUrl);

d)To access the HostWeb rest end points the url property in the cross-domain call need to be set in this fashion.

AppWebUrl + "/_api/SP.AppContextSite(@target)/web/sitegroups(index)?@target='" + HostWebUrl + "'",

e)Copy and paste the following code in the App.js (replace Ii t the existing code over there)

'use strict';

var context = SP.ClientContext.get_current();
var user = context.get_web().get_currentUser();
var HostWebUrl;
var AppWebUrl;


// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
    //getUserName();

    HostWebUrl =
                decodeURIComponent(
                    RetrieveQueryStringParameter("SPHostUrl")
            );
    AppWebUrl =
        decodeURIComponent(
            RetrieveQueryStringParameter("SPAppWebUrl")
    );

    var scriptbase = HostWebUrl + "/_layouts/15/";
    $.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

});


function successHandler(data) {

    var jsonObj = JSON.parse(data.body);
    var results = jsonObj.d;
    document.getElementById("message").innerText = "Field title is" + results["Title"] + "Field Id is" + results["Id"];

}

function errorHandler(data, errorCode, errorMessage) {


    document.getElementById("message").innerText = "failure";

}

function RetrieveQueryStringParameter(ParamsforRetrieval) {
    var params =
        document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == ParamsforRetrieval)
            return singleParam[1];
    }
}

function execCrossDomainRequest() {

    var executor = new SP.RequestExecutor(AppWebUrl);

    executor.executeAsync({
        url: AppWebUrl + "/_api/SP.AppContextSite(@target)/web/sitegroups(3)?@target='" + HostWebUrl + "'",
        method: "GET",
        headers: {
            "accept": "application/json;odata=verbose",
            "content-type": "application/json;odata=verbose"
        },
        success: successHandler,
        error: errorHandler
    });

}

Run the above piece of code, now you will be able to get the title and id for the site collection group (no: 3).

image

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How to get SharePoint fields collection in SharePoint 2013 Online using REST

In this post, we’ll see how we can fetch the fields collection of a SharePoint web in SharePoint 2013 online using REST. For the purpose of demonstration, I’ll be using a SharePoint hosted app.

Launch Visual Studio 2013.

File –> New –> Office/SharePoint –> Apps and name it as ‘GetFieldsREST’

I will be accessing the following REST endpoint for getting a web title

https://yoursite.sharepoint/_api/web/fields

Since the call is initiating from AppWeb to HostWeb, it will present a classical cross-domain scenario, where I will be using the SP 2013 javascript cross-domain libraries to manage this call.

After creating the App project in Visual Studio 2013, the following points need to be considered

a)The App Permission need to be left with default setting of Internal.

<AppPrincipal>
    <Internal/>
  </AppPrincipal>
  

With this setting, the SharePoint hosted app will have access to the Host Web by default.

b)The App need to be given full-control permission for site-collection. Otherwise, it will not be able to fetch the fields collection.

 <AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="FullControl" />
  </AppPermissionRequests>

c)The executor object need to be instantiated with the parameter of ‘AppWebUrl’, not the ‘HostWebUrl.  (you’ll see more detailed code in the coming sections). If you instantiate it with ‘HostWebUrl, you will get an error like ‘App web not found’

var executor = new SP.RequestExecutor(AppWebUrl);

d)To access the HostWeb rest end points the url property in the cross-domain call need to be set in this fashion.

AppWebUrl + "/_api/SP.AppContextSite(@target)/web/fields?@target='" + HostWebUrl + "'",

Open the App.js and paste the following code

'use strict';

var context = SP.ClientContext.get_current();
var user = context.get_web().get_currentUser();
var HostWebUrl;
var AppWebUrl;


// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
    //getUserName();

    HostWebUrl =
                decodeURIComponent(
                    RetrieveQueryStringParameter("SPHostUrl")
            );
    AppWebUrl =
        decodeURIComponent(
            RetrieveQueryStringParameter("SPAppWebUrl")
    );

    var scriptbase = HostWebUrl + "/_layouts/15/";
    $.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

});


function successHandler(data) {

    var jsonObj = JSON.parse(data.body);
    var results = jsonObj.d;
    document.getElementById("message").innerText = "Field title is" + results["Title"] + "Field Id is" + results["Id"];

}

function errorHandler(data, errorCode, errorMessage) {


    document.getElementById("message").innerText = "failure";

}

function RetrieveQueryStringParameter(ParamsforRetrieval) {
    var params =
        document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == ParamsforRetrieval)
            return singleParam[1];
    }
}

function execCrossDomainRequest() {

    var executor = new SP.RequestExecutor(AppWebUrl);

    executor.executeAsync({
        url: AppWebUrl + "/_api/SP.AppContextSite(@target)/web/fields?@target='" + HostWebUrl + "'",
        method: "POST",
        body: "{ '__metadata': { 'type': 'SP.Field' }, 'Title': 'Comments', 'FieldTypeKind': 3 }",
        headers: {
            "accept": "application/json;odata=verbose",
            "content-type": "application/json;odata=verbose"
        },
        success: successHandler,
        error: errorHandler
    });

}

image

This completes this demo.

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How to get SharePoint 2013 web property using REST in SharePoint Online

In this post, we’ll see how we can access the property of a SharePoint web in SharePoint 2013 online using REST. For the purpose of demonstration, I’ll be using a SharePoint hosted app.

Launch Visual Studio 2013.

File –> New –> Office/SharePoint –> Apps and and name it as ‘GetWebdetailsREST’

I will be accessing the following REST endpoint for getting a web title

https://yoursite.sharepoint/_api/web/title

Since the call is initiating from AppWeb to HostWeb, it will present a classical cross-domain scenario, where I will be using the SP 2013 javascript cross-domain libraries to manage this call.

After creating the App project in Visual Studio 2013, the following points need to be considered

a)The App Permission need to be left with default setting of Internal.

<AppPrincipal>
    <Internal/>
  </AppPrincipal>
  

With this setting, the SharePoint hosted app will have access to the Host Web by default.

b)The App need to be given read permission for site-collection

<AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="Read" />
  </AppPermissionRequests>

c)The executor object need to be instantiated with the parameter of ‘AppWebUrl’, not the ‘HostWebUrl.  (you’ll see more detailed code in the coming sections). If you instantiate it with ‘HostWebUrl, you will get an error like ‘App web not found’

var executor = new SP.RequestExecutor(AppWebUrl);

d)To access the HostWeb rest end points the url property in the cross-domain call need to be set in this fashion.

AppWebUrl + "/_api/SP.AppContextSite(@target)/web/title?@target='" + HostWebUrl + "'",

Open the App.js and paste the following code

'use strict';

var context = SP.ClientContext.get_current();
var user = context.get_web().get_currentUser();
var HostWebUrl;
var AppWebUrl;


// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
    //getUserName();

    HostWebUrl =
                decodeURIComponent(
                    RetrieveQueryStringParameter("SPHostUrl")
            );
    AppWebUrl =
        decodeURIComponent(
            RetrieveQueryStringParameter("SPAppWebUrl")
    );

    var scriptbase = HostWebUrl + "/_layouts/15/";
    $.getScript(scriptbase + "SP.RequestExecutor.js", execCrossDomainRequest);

});

// This function prepares, loads, and then executes a SharePoint query to get the current users information
function getUserName() {
   
}



function successHandler(data)
{
    
    var jsonObj = JSON.parse(data.body);
    document.getElementById("message").innerText = "Web title from REST call is"+ jsonObj.d["Title"];

}

function errorHandler(data, errorCode, errorMessage) {
   

    document.getElementById("message").innerText = "failure";

}

function RetrieveQueryStringParameter(ParamsforRetrieval) {
    var params =
        document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == ParamsforRetrieval)
            return singleParam[1];
    }
}

function execCrossDomainRequest() {

    var executor = new SP.RequestExecutor(AppWebUrl);
    executor.executeAsync(
        {
            url: AppWebUrl + "/_api/SP.AppContextSite(@target)/web/title?@target='" + HostWebUrl + "'",
            type: "GET",
            crossDomain:true,

            headers: {
                "accept": "application/json; odata=verbose",
                "content-type": "application/json;odata=verbose",
                "content-length": 1028,
                "X-RequestDigest": $("#__REQUESTDIGEST").val()

            },
            success: successHandler,
            error: errorHandler
        }
        );

}

image

Now you can see the updated site title in the App. This completes this demo.

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