PHP Web Development: Lesson Three - Mastering Sessions, Cookies, and File Uploads

After covering the basics of PHP, form handling, interacting with databases, and securing your applications, it's time to delve into features that make web applications more dynamic and user-friendly. In this lesson, we focus on sessions and cookies for maintaining state and user data across pages, and we introduce handling file uploads—a common requirement for many web applications.

1. Understanding and Managing Sessions in PHP

Sessions provide a way to preserve certain data across subsequent accesses. This functionality is essential for identifying users across different pages of your application.

1.1 Starting a Session

To use sessions in PHP, start by calling session_start() at the beginning of your script:

<?php
session_start();
?>

This function must be called before any output is sent to the browser.

1.2 Storing and Accessing Session Data

You can store data in the $_SESSION superglobal array. For example, to save a username:

<?php
$_SESSION['username'] = 'JohnDoe';
?>

Access this data on subsequent pages by starting the session and then referencing the $_SESSION array:

<?php
session_start();
echo 'Hello, ' . $_SESSION['username'];
?>

2. Using Cookies to Remember User Preferences

Cookies allow your application to store data on the user's computer. They are commonly used for remembering login details and user preferences.

2.1 Setting Cookies in PHP

Set a cookie using the setcookie() function. Here’s how to create a cookie that remembers a user's name:

<?php
setcookie("user", "John Doe", time() + (86400 * 30), "/"); // 86400 = 1 day
?>

2.2 Accessing Cookies

Access cookies via the $_COOKIE superglobal array. For example, to display the user's name stored in a cookie:

<?php
if(!isset($_COOKIE["user"])) {
  echo "Guest";
} else {
  echo "Hello, " . $_COOKIE["user"];
}
?>

3. Handling File Uploads

File uploads enable users to send files from their computer to your server, an essential feature for many applications.

3.1 Creating a File Upload Form

Start with an HTML form that specifies an encoding type of multipart/form-data:

<form action="upload.php" method="post" enctype="multipart/form-data">
  Select image to upload:
  <input type="file" name="fileToUpload" id="fileToUpload">
  <input type="submit" value="Upload Image" name="submit">
</form>

3.2 Processing the Uploaded File in PHP

In your PHP script, you can access the uploaded file through the $_FILES superglobal array. Here's how to save the uploaded file to a specific directory:

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
  echo "The file ". htmlspecialchars( basename( $_FILES["fileToUpload"]["name"])). " has been uploaded.";
} else {
  echo "Sorry, there was an error uploading your file.";
}
?>