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Imagine that your biggest client calls because they are having trouble retrieving their email. Or they want to know what their best-selling item is right now. Or their most popular blog post. Perhaps their website has suddenly gone down. You can hardly reply, “No problem, I’ll get back to you in 24 to 48 hours.” And yet DNS gets away with it! If you need to move a website or change the way a domain’s email is handled, you’ll be faced with a vague 24 to 48-hour delay.
This is quite an anomaly in a world of ultra-convenience and super-fast everything. This article explains what DNS is, how it works, where that pesky delay comes from, and a couple of ways to work around it. DNS is the “domain name system.” It translates human-friendly website addresses like www.cnn.com into computer-friendly IP addresses like 220.127.116.11. Try visiting http://18.104.22.168 if you’d like to verify this.
The discussion glosses over another important factor: the speed with which your pages are actually put together on your server. Most big modern websites store their information in a database and use a language such as PHP or ASP to extract it, turn it into HTML and send it to the Web browser.
So, even if you get your home page down to 1.5 seconds (Google’s threshold for being considered a “fast” website), you can still frustrate customers if your search page takes too much time to respond, or if the product pages load quickly but the “Customer reviews” delay for several seconds.
In my last article26, I spoke about several common mistakes that show up in web applications. Of these, the one that causes the most trouble is insufficient input validation/sanitization. In this article, I’m joined by my colleague Peter (evilops) Ellehauge27 in looking at input filtering in more depth while picking on a few real examples that we’ve seen around the web. As you’ll see from the examples below, insufficient input validation can result in various kinds of code injection including XSS, and in some cases can be used to phish user credentials or spread malware.
To start with, we’ll take an example from one of the most discussed websites today. This example is from a site that hosts WikiLeaks material. Note that the back end code presented is not the actual code, but what we think it might be based on how the exploit works. The HTML was taken from their website. We think it’s fair to assume that it’s written in PHP as the form’s action is index.php.
Have you ever heard a colleague answer the phone like this: “Good afterno… Yes… What? Completely?… When did it go down?… Really, that long?… We’ll look into it right away… Yes, I understand… Of course… Okay, speak to you soon… Bye.” The call may have been followed by some cheesy ’80s rock ballad coming from the speaker phone, interrupted by “Thank you for holding. You are now caller number 126 in the queue.” That’s your boss calling the hosting company’s 24 hour “technical support” line.
An important website has gone down, and sooner or later, heads will turn to the Web development corner of the office, where you are sitting quietly, minding your own business, regretting that you ever mentioned “Linux” on your CV. You need to take action. Your company needs you. Your client needs you. Here’s what to do.
Web application developers today need to be skilled in a multitude of disciplines. It’s necessary to build an application that is user friendly, highly performant, accessible and secure, all while executing partially in an untrusted environment that you, the developer, have no control over. I speak, of course, about the User Agent. Most commonly seen in the form of a web browser, but in reality, one never really knows what’s on the other end of the HTTP connection.
There are many things to worry about when it comes to security on the Web. Is your site protected against denial of service attacks? Is your user data safe? Can your users be tricked into doing things they would not normally do? Is it possible for an attacker to pollute your database with fake data? Is it possible for an attacker to gain unauthorized access to restricted parts of your site? Unfortunately, unless we’re careful with the code we write, the answer to these questions can often be one we’d rather not hear.
In this article, I’ll introduce you to the fundamentals of PHP. We’ll focus on using PHP to access Web services and on turning static HTML pages into dynamic ones by retrieving data from the Web and by showing different content depending on what the user has entered in a form or requested in the URL. You won’t come out a professional PHP developer, but you’ll be well on your way to building a small page that uses Web services. You can find a lot of great PHP info on the Web, and most of the time you will end up on PHP.net38 itself. But I was asked repeatedly on several hack days and competitions to write this quick introduction article, so here it is.
PHP is a server-side language that has become a massive success for three reasons: it is a very easy and forgiving language. Variables can be anything, and you can create them anytime you want. It is part of the free LAMP stack (Linux, Apache, MySQL, PHP) and thus available on almost any server you can rent on the Web. And it does not need a special editor, environment or build process. All you do is create a file of the .php file type, mix PHP and HTML and then put it on your server for rendering.
Almost every movie has a scene in which a character pull the protagonist aside and says, “There’s something you should know about [insert another character’s name here].” Most of the time, we find out some dark secret about a supposed friend of the protagonist or that the main ally is actually an evil overlord. This is that moment, and I am here to tell you a few things about our friend in the Web 2.0 world: AJAX.
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