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Displaying Twitter Updates in a Page by Page fashion with ASP.NET

Faisal Khan — Sat, 20 Jun 2009 06:49:00 GMT

Introduction
In this tutorial, we will develop a technique to retrieve and display a page full of Twitter updates to the user, giving him the ability to move to the next page. The user will be able to browse all the pages using 'Previous Page' and 'Next Page' links. Our technique will be highly efficient as we will be retrieving only enough number of Twitter updates from a given screen name, to display on a single page. Only when the user browses to the next page will another set of Twitter updates be retrieved. At the same time we will cache the results, page by page, giving seamless and smooth performance to the end user.

The code in this tutorial makes use of the code we developed in the previous tutorial: Retrieving Twitter Updates with ASP.NET. We will only be updating TwitterClient.cs a little bit to enable retrieval of Twitter updates page by page. Rest of the files will remain the same. We will develop an ASP.NET page to demonstrate the technique.

I advise that you read this series of tutorials from the beginning and create/place the files as advised in the previous tutorial.

This tutorial is 3rd in the series of tutorials regarding Twitter and ASP.NET:

Introduction to Twitter for ASP.NET Developers
Retrieving Twitter Updates with ASP.NET
Displaying Twitter Updates in a Page by Page fashion with ASP.NET

Demonstration of Twitter Updates being Displayed Page by Page
In this tutorial, we will develop an ASP.NET page that retrieves 5 status updates for a given screen name and displays them on a page. When 'Next Page' link is clicked, next 5 status updates are retrieved and displayed to the user.

Retrieving Twitter Updates with ASP.NET

Faisal Khan — Wed, 17 Jun 2009 07:33:00 GMT

Introduction
In this tutorial, we will learn how to retrieve Twitter status updates using Twitter API and ASP.NET. We will develop code that encapsulates calls to Twitter API and provides easy to use .NET classes to retrieve Twitter status updates, programmatically. We will demonstrate the code by developing an ASP.NET control that uses these .NET classes to retrieve and display Twitter status updates on our website.

This tutorial is 2nd in the series of tutorials regarding Twitter and ASP.NET:

Introduction to Twitter for ASP.NET Developers
Retrieving Twitter Updates with ASP.NET
Displaying Twitter Updates in a Page by Page fashion with ASP.NET

Things to know about Twitter API
Before getting started, it is prudent to know a few things about Twitter API.

Twitter API is entirely HTTP based. This means that all you need to do to retrieve or post status updates is to make simple HTTP GET and POST calls, respectively, over the internet.

Twitter API conforms to REST (Representational State Transfer) style of software architecture. You can use URL like http://twitter.com/statuses/user_timeline.format to retrieve status updates of a user. You can choose the desired format of the response by specifying the format in the URL. For instance, to retrieve the status updates in XML, the complete URL will be http://twitter.com/statuses/user_timeline.xml. You have the option of choosing the format between XML, JSON, RSS and Atom.

Introduction to Twitter for ASP.NET Developers

Faisal Khan — Sat, 13 Jun 2009 12:49:00 GMT

Introduction
Twitter is a free social networking service that lets its users communicate with each other through short text messages. There is a limit of 140 characters per message. Users can send messages using online website, mobile devices or by sending SMS from their cell phones. These messages, known as &apostweets' are then delivered, by a variety of means, to the users who have subscribed to receive them; known as 'followers'.

Guidelines for sending Messages
In text messages, username of the person you are replying to should start with &apos@' (at) sign e.g., @Stardeveloper. Twitter will convert these usernames in the text messages to clickable links e.g., "Hello @Stardeveloper!".

This tutorial is 1st in the series of tutorials regarding Twitter and ASP.NET:

Introduction to Twitter for ASP.NET Developers
Retrieving Twitter Updates with ASP.NET
Displaying Twitter Updates in a Page by Page fashion with ASP.NET

Connecting with your Audience
Twitter provides another opportunity for ASP.NET developers to connect with their website audience. ASP.NET developers can create accounts with screen names of their websites e.g., Stardeveloper (Faisal Khan). This account can then be used as a micro-blog for the website. Not only should the status updates include important website updates, but should also focus on the interesting things you, as a developer, are working on or can benefit your audience. A link is placed on the website linking to the Twitter profile, giving users the opportunity to view the profile, and if he/she chooses so, to start following this account.

Validating an XML Document using DTD in ASP.NET

Faisal Khan — Fri, 05 Jun 2009 03:36:00 GMT

Introduction
In this tutorial, we will learn how to validate an XML document using DTD. We will develop an ASP.NET page to demonstrate the code. After you are finished reading this tutorial, you will be proficient in writing C# code that validates XML documents using DTD.

Following topics will be covered in this tutorial:

Well-formedness vs Validation.
Validating XML Document using DTD.

This tutorial is 6th one in the series of tutorials about XML and ASP.NET:

Introduction to XML
Reading XML Files with ASP.NET
Introduction to XPath for ASP.NET Developers
Creating new XML Document in ASP.NET Programmatically
Introduction to DTD (Document Type Definition)
Validating an XML Document using DTD in ASP.NET

We will first refresh ourselves with basic XML concepts of well-formedness and validation, and later develop the code to validate XML document using DTD.

Introduction to DTD (Document Type Definition)

Faisal Khan — Tue, 26 May 2009 05:06:00 GMT

Introduction
In this tutorial, we will learn about "Document Type Definition". DTD is an XML schema language that is used to describe the structure of an XML document. It describes what elements an XML document can contain and in which order. It further specifies how these elements are arranged within one another and what attributes these elements can contain. The description of the structure and these constraints are written in a formal syntax, some of which we will learn in this tutorial. These declarations can be placed within an XML file, or more commonly in a separate file with ".dtd" extension.

Following topics will be covered in this tutorial:

Declaring elements in DTD.
Declaring attributes in DTD.
Associating DTD with XML Documents.

This tutorial is 5th one in the series of tutorials about XML and ASP.NET:

Introduction to XML
Reading XML Files with ASP.NET
Introduction to XPath for ASP.NET Developers
Creating new XML Document in ASP.NET Programmatically
Introduction to DTD (Document Type Definition)
Validating an XML Document using DTD in ASP.NET

We will now learn how elements and attributes are declared in DTD, and how DTD declarations can be associated with XML document(s).

Creating new XML Document in ASP.NET Programmatically

Faisal Khan — Thu, 19 Mar 2009 11:35:00 GMT

Introduction
In this tutorial, we will learn how to create an XML Document programmatically. We will make use of XmlDocument class from System.Xml namespace. Following topics will be covered in this tutorial:

How to create XML declaration and element nodes.
How to create attributes and append them to element nodes.
How to create CDATA sections within element nodes.
How to nest elements and attributes in one another to create a logical tree like structure.
How to send the dynamically generated XML document to the client browser with proper headers.

This tutorial is 4th one in the series of tutorials about XML and ASP.NET:

Introduction to XML
Reading XML Files with ASP.NET
Introduction to XPath for ASP.NET Developers
Creating new XML Document in ASP.NET Programmatically
Introduction to DTD (Document Type Definition)
Validating an XML Document using DTD in ASP.NET

Creating new XML Document
We will now write down the code to create new XML document.

Code for ASP.NET page
Copy and paste following code into a new text file and then save it as "CreateXmlDocument.aspx" in your ASP.NET web application:

Introduction to XPath for ASP.NET Developers

Faisal Khan — Tue, 10 Mar 2009 05:26:00 GMT

Introduction
XPath is a language for selecting nodes (parts or segments) within an XML document. As you are already familiar with XML, XML is a markup language which uses elements and attributes to encapsulate data in a logical manner. XPath furthers builds on it and provides navigational abilities in an XML document. For example, you can use an XPath query to select one or more nodes within an XML document that match a certain criteria. That criteria can by anything from an element matching a given name to an element whose attribute matches a specific value.

This tutorial is 3rd one in the series of tutorials about XML and ASP.NET:

Introduction to XML
Reading XML Files with ASP.NET
Introduction to XPath for ASP.NET Developers
Creating new XML Document in ASP.NET Programmatically
Introduction to DTD (Document Type Definition)
Validating an XML Document using DTD in ASP.NET

Tree like representation of an XML Document
In XPath, an XML document is represented as a tree of nodes. There is a parent node with one or more child nodes. While a node in XPath can be of 7 types; for practical purposes, a node in XPath corresponds to an element or attribute within an XML document. For example, have a look at following XML document:

Reading XML Files with ASP.NET

Faisal Khan — Sat, 07 Mar 2009 09:35:00 GMT

Introduction
In this tutorial, we will learn how to read the contents of an XML file with ASP.NET. We will make use of the sample XML file which we created in the previous tutorial (Introduction to XML). We will create an ASP.NET page which reads the contents of this XML file and then displays it to the user.

This tutorial is 2nd one in the series of tutorials about XML and ASP.NET:

Introduction to XML
Reading XML Files with ASP.NET
Introduction to XPath for ASP.NET Developers
Creating new XML Document in ASP.NET Programmatically
Introduction to DTD (Document Type Definition)
Validating an XML Document using DTD in ASP.NET

Sample XML File
Okay, let us get started now. Copy and paste the contents below in a new text file and then save that file as "sample.xml" in the /App_Data sub-folder of your ASP.NET web application. Placing the XML file in /App_Data sub-folder ensures that no one will be able to directly access this file from the web. It will only be accessed by our ASP.NET page which will read and display its contents.

Introduction to XML

Faisal Khan — Sun, 01 Mar 2009 05:48:00 GMT

Introduction
XML stands for Extensible Markup Language. An XML document stores data in the form of text. The data itself can be textual or binary. The binary data is not stored as binary data but is first converted to and is stored as text data. Elements and attributes are used in XML document to encapsulate data in a more logical hierarchical fashion.

This tutorial is 1st one in the series of tutorials about XML and ASP.NET:

Sample XML Document
Following is a simple XML document:

<?xml version="1.0" encoding="utf-8"?>
<article>
	<author isadmin="true">Faisal Khan</author>
	<title>Sample XML Document</title>
	<body>The body of the article goes here.</body>
</article>

XML Declaration
All XML documents start with <?xml version="1.0" ?>. This tells the XML parser that what is to follow is an XML document. An optional encoding attribute is often added as well.

Preventing SQL Injection Attacks in Classic ASP

Faisal Khan — Tue, 25 Nov 2008 09:56:00 GMT

The term "SQL Injection" means to inject malicious SQL statement(s) in an otherwise regular SQL to get access to secure data on a website. Most hackers who attempt this attack use SQL injection in querystring variables in a URL or in form contents being posted back to a web page. In this article, we will examine what SQL injection attacks are and what programming techniques can be used to prevent them. While we will assume classic ASP pages and the backend SQL Server database to demonstrate the method and means of prevention, the concept is equally applicable to other web programming technologies and database systems.

How a SQL Injection Attack is Carried Out?
Any time you generate a SQL statement dynamically in an ASP page using data retrieved from a querystring, form content, or even a cookie, you expose yourself to a SQL injection attack. To demonstrate this, have a look at the following insecure code which creates a dynamic SQL statement by retrieving data form a querystring:

Dim sql
	sql = "SELECT [Title], [Description] FROM [Articles] WHERE [ArticleID] = " & _
		Request.QueryString("articleId")

This code expects a querystring parameter with the name of articleId. While the developer may have provided a valid integer in the URLs on his website for this piece of code to work as expected, a hacker when he sees this URL will try to exploit this weakness by injecting his own SQL statement(s) to view, update or delete the content in the developer's database.

For example, all the hacker has to do to view the contents of [dbo].[sysobjects] table is to set the value of querystring to following: