Senior PHP Programmer

Here are the rules for determine the "truth" of any value not already of the Boolean type −

☛ If the value is a number, it is false if exactly equal to zero and true otherwise.

☛ If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.

☛ Values of type NULL are always false.

☛ If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.

☛ Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).

☛ Don't use double as Booleans.

SQL injections are a method to alter a query in a SQL statement send to the database server. That modified query then might leak information like username/password combinations and can help the intruder to further compromise the server.

To prevent SQL injections, one should always check & escape all user input. In PHP, this is easily forgotten due to the easy access to $_GET & $_POST, and is often forgotten by inexperienced developers. But there are also many other ways that users can manipulate variables used in a SQL query through cookies or even uploaded files (filenames). The only real protection is to use prepared statements everywhere consistently.

Do not use any of the mysql_* functions which have been deprecated since PHP 5.5 ,but rather use PDO, as it allows you to use other servers than MySQL out of the box. mysqli_* are still an option, but there is no real reason nowadays not to use PDO, ODBC or DBA to get real abstraction. Ideally you want to use Doctrine or Propel to get rid of writing SQL queries all together and use object-relational mapping which binds your rows from the database to objects in your application.

What exactly is meant by the sentence "For a complex resource such as an HTML document, the script would need

to parse it to find references to embedded, included resources:

javascript files, CSS files, iframes, etc."?

Well, as you probably know, an HTML page often uses other files to render the HTML page - like CSS file(s) for styling, Javascript file(s) for adding more functionality to the HTML page, and so on. But the question is how do we take an HTML page and find all of those resources in the HTML page. Of course, this is easy to do if we are reading the HTML page with the human eye. But, we want to find these resources using a program that will read the HTML for us. This is actually more complicated than it seems - and the process by which a program (like PHP) reads an HTML file and analyzes the text to extract meaningful data (like resources) is known as parsing the HTML. Any text can be parsed, but we are exclusively focused on HTML for the purpose of this interview question.

The question also asks us to find the total download size of a URL. But what if that URL passed into the script just points to a single file resource like a JPG file or a GIF file? Well, for a single file resource we just need to find the size of that particular file and then return it as the answer, and we are done. But, for an HTML document we will need to find the total size of all resources that are embedded and included on the page and return that as the answer - because you must remember that we want the total download size of a URL.

So, let's write a PHP function that will return the download size of a single file resource. How should we approach writing this function - what is the easiest way to find the download size of a single file resource on the web?

Well, there is an HTTP header called "Content-Length" which will actually tell us the size of a particular resource file in the HTTP response (after the resource is requested). So, all we have to do is use PHP's built in "get_headers" function, which will retrieve all the HTTP headers sent by the server in response to an HTTP request.

The get_headers function accepts a URL as an argument. So, the PHP code to retrieve the "Content-Length" header would look like this:

function get_remote_file_size($url) {

$headers = get_headers($url, 1);

if (isset($headers['Content-Length']))

return $headers['Content-Length'];

//checks for lower case "L" in Content-length:

if (isset($headers['Content-length']))

return $headers['Content-length'];

}

But, there is actually a problem with this code: you will not always receive the Content-Length header in an HTTP response. In other words, the HTTP Content-Length header is not guaranteed to be sent back by the web server hosting that particular URL, because it depends on the configuration of the server. This means that you need an alternative that always works in case the approach above fails.

Getters and setters are methods used to declare or obtain the values of variables, usually private ones. They are important because it allows for a central location that is able to handle data prior to declaring it or returning it to the developer. Within a getter or setter you are able to consistently handle data that will eventually be passed into a variable or additional functions. An example of this would be a user's name. If you are not using a setter and just declaring the $userName variable by hand you could end up with results as such: "kevin", "KEVIN", "KeViN", "", etc. With a setter you can not only adjust the value, for example, ucfirst($userName), but you can also handle situations where the data is not valid such as the example where "" is passed. The same applies to a getter - when the data is being returned, you can modify the results to include strtoupper($userName) for proper formatting further up the chain.

This is important for any developer who is looking to enter a team-based / application development job to know. Getters and setters are often used when dealing with objects, especially ones that will end up in a database or other storage medium. Because PHP is commonly used to build web applications you will run across getters and setters in more advanced environments, even as a junior developer. They are extremely powerful yet not talked about very much. You can really impress an interviewer by knowing what they are and how to use them early on.