Web Programming II

Difference Between Cookie and Session

Feature	Cookie	Session
Storage Location	Stored on the client’s machine (browser cache).	Stored securely on the web server.
Data Capacity	Limited to approximately 4 KB per cookie.	Virtually unlimited (bounded only by server RAM/disk).
Security	Vulnerable to user tampering, theft, and XSS.	Highly secure; client only holds an opaque Session ID.
Lifetime	Persists until expired or cleared manually.	Typically expires when browser closes or inactivity timeout.

Placing a Double Quote in a Double-Quoted String in PHP

To include a double quote (") inside a double-quoted string literal in PHP, use the backslash escape character \":

<?php
$str = "He said, \"Welcome to Tribhuvan University!\"";
echo $str; // Outputs: He said, "Welcome to Tribhuvan University!"
?>

Difference Between File Opening Modes “w” and “w+” in PHP

• "w" (Write-Only Mode): Opens the file for writing only. Truncates the file length to zero (erases existing contents) or creates a new file if it does not exist. File pointer is placed at the beginning. Reading is not allowed.
• "w+" (Read and Write Mode): Opens the file for both reading and writing. Like "w", it truncates the file to zero bytes or creates a new file if it does not exist, but allows the program to read back what was written.

Syntax to Declare a Function in PHP

<?php
function functionName(type $parameter1, type $parameter2 = defaultValue): returnType {
    // Function body
    return $value;
}
?>

Example:

<?php
function calculateTotal(float $price, int $quantity): float {
    return $price * $quantity;
}
?>

Finding the Length of an Array in PHP

In PHP, the length (number of elements) of an array is determined using the built-in count() function or its alias sizeof():

<?php
$fruits = ["Apple", "Banana", "Orange", "Mango"];
$length = count($fruits);
echo "Total items: " . $length; // Outputs: Total items: 4
?>

Setting Default Values for Function Parameters

Default values are assigned directly to parameter variables in the function definition header using the assignment operator =:

<?php
function greetUser(string $name, string $greeting = "Namaste"): string {
    return "$greeting, $name!";
}

echo greetUser("Suman");          // Outputs: Namaste, Suman!
echo greetUser("John", "Hello");   // Outputs: Hello, John!
?>

Default parameters should be placed after all non-default parameters.

Task of gettimeofday() Function in PHP

The gettimeofday() function retrieves the current system time with microsecond precision.

• When called with no arguments (gettimeofday()), it returns an associative array with keys:
  • sec: Seconds since the Unix Epoch.
  • usec: Microseconds.
  • minuteswest: Minutes west of Greenwich.
  • dsttime: Type of DST correction.
• When called with gettimeofday(true), it returns the current time as a floating-point number representing seconds since Unix Epoch.

What is a SQL Injection Attack?

A SQL Injection (SQLi) attack is a cybersecurity vulnerability where an attacker manipulates user inputs (via form fields, headers, or URL query parameters) to inject malicious SQL commands into an application’s database queries. This enables unauthorized actors to bypass authentication, dump sensitive database tables, modify data, or drop entire databases.

Why We Need the Default Values Feature in a Form

1. User Convenience & Speed: Pre-fills common answers (such as default country, current date, or standard quantity), minimizing repetitive typing.
2. Sticky Form State: Preserves the user’s previously typed input when re-rendering the form after validation errors, preventing frustration.
3. Data Quality & Guidance: Demonstrates expected input formats (e.g., standard placeholders and default radio button selections).

Declaring a Multi-Dimensional Array in PHP

<?php
$departments = [
    "IT" => [
        ["id" => 1, "name" => "Aayush", "role" => "Developer"],
        ["id" => 2, "name" => "Sneha",  "role" => "Architect"]
    ],
    "HR" => [
        ["id" => 3, "name" => "Rohan",  "role" => "Manager"]
    ]
];
?>

Variable Scope in PHP with Examples

The scope of a variable defines the region of code in which it can be referenced. PHP provides three primary variable scopes:

<?php
$globalVar = 100; // Global Scope

function testScope() {
    // 1. Local Scope
    $localVar = 50;

    // Accessing global variable requires 'global' keyword
    global $globalVar;
    echo "Global inside function: $globalVar <br>";
    echo "Local inside function: $localVar <br>";

    // 2. Static Scope: preserves value between calls
    static $counter = 0;
    $counter++;
    echo "Static Counter: $counter <br>";
}

testScope(); // Counter: 1
testScope(); // Counter: 2
// echo $localVar; // Fatal Error: Undefined variable in global scope
?>

Creating, Storing, and Retrieving Sessions in PHP

Sessions allow state preservation across multiple HTTP requests:

1. Starting a Session:

session_start() must be invoked at the top of every PHP script before sending any HTML or output headers:

<?php
session_start();

2. Storing Data in Session:

Store values using the superglobal $_SESSION associative array:

$_SESSION["authenticated"] = true;
$_SESSION["user_email"] = "student@tu.edu.np";
$_SESSION["cart_items"] = [101, 204, 305];

3. Retrieving Data from Session:

Check existence with isset() and read values:

if (isset($_SESSION["authenticated"]) && $_SESSION["authenticated"] === true) {
    echo "Welcome back, " . htmlspecialchars($_SESSION["user_email"]);
}

4. Terminating a Session:

$_SESSION = [];
if (ini_get("session.use_cookies")) {
    $params = session_get_cookie_params();
    setcookie(session_name(), '', time() - 42000, $params["path"], $params["domain"]);
}
session_destroy();

Parameters of the setcookie() Function in PHP

The setcookie() function sends a Set-Cookie HTTP header to the client browser.

Signature:

setcookie(name, value, expires_or_options, path, domain, secure, httponly);

Explanation of Parameters:

1. name (string, required): The identifier name of the cookie (e.g., 'auth_token').
2. value (string, optional): The text content stored in the cookie.
3. expires_or_options (int, optional): The Unix timestamp when the cookie expires (e.g., time() + 86400 for 1 day). 0 means session cookie.
4. path (string, optional): The server directory path on which the cookie is valid (e.g., '/' for entire domain).
5. domain (string, optional): The domain/subdomain that can access the cookie (e.g., 'tu.edu.np').
6. secure (bool, optional): If true, the cookie is transmitted only over HTTPS connections.
7. httponly (bool, optional): If true, prevents client-side JavaScript access (document.cookie), mitigating XSS cookie theft.

PHP Program: Display Associative Array of Books and Authors in HTML Table

<?php
// Associative array: Book Title => Author Name
$books = [
    "Computer Organization and Architecture" => "William Stallings",
    "Database System Concepts"               => "Silberschatz, Korth & Sudarshan",
    "Web Technologies: HTML, CSS & PHP"      => "Robin Nixon",
    "Data Structures Using C and C++"        => "Tanenbaum & Langsam",
    "Microprocessor Architecture (8085)"     => "Ramesh Gaonkar"
];
?>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Library Catalog</title>
  <style>
    table { border-collapse: collapse; width: 60%; margin: 20px auto; font-family: sans-serif; }
    th, td { border: 1px solid #ddd; padding: 10px 14px; text-align: left; }
    th { background-color: #2b2b2b; color: white; }
    tr:nth-child(even) { background-color: #f9f9f9; }
  </style>
</head>
<body>
  <h2 style="text-align: center;">Recommended Academic Textbooks</h2>
  <table>
    <thead>
      <tr>
        <th>Book Title</th>
        <th>Author Name</th>
      </tr>
    </thead>
    <tbody>
      <?php foreach ($books as $title => $author): ?>
        <tr>
          <td><?= htmlspecialchars($title) ?></td>
          <td><?= htmlspecialchars($author) ?></td>
        </tr>
      <?php endforeach; ?>
    </tbody>
  </table>
</body>
</html>

PHP Program to Export Employee Data from MySQL to CSV

<?php
// Database configuration as specified
$host     = "fomeed.edu.np";
$dbname   = "TU";
$username = "Tribhuvan";
$password = "BIM76";
$csvFile  = "employees.csv";

$dsn = "mysql:host=$host;dbname=$dbname;charset=utf8mb4";

try {
    // 1. Establish PDO Connection
    $pdo = new PDO($dsn, $username, $password, [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
    ]);

    // 2. Query Id, Name, and Address from employees table
    $stmt = $pdo->query("SELECT id, name, address FROM employees");

    // 3. Open CSV file for writing
    $fp = fopen($csvFile, "w");
    if ($fp === false) {
        die("Error opening file $csvFile for writing.");
    }

    // 4. Write CSV Header row
    fputcsv($fp, ["Employee ID", "Full Name", "Address"]);

    // 5. Fetch and write each row
    $rowCount = 0;
    while ($row = $stmt->fetch()) {
        fputcsv($fp, [$row['id'], $row['name'], $row['address']]);
        $rowCount++;
    }

    // 6. Close file resource
    fclose($fp);
    echo "Successfully exported $rowCount employee records to $csvFile.";

} catch (PDOException $e) {
    echo "Database connection failed: " . htmlspecialchars($e->getMessage());
}
?>

PHP Program to Find the Difference Between Any Two Dates

<?php
function getDateDifference(string $date1Str, string $date2Str): string {
    // Create DateTime objects
    $date1 = new DateTime($date1Str);
    $date2 = new DateTime($date2Str);

    // Calculate difference (returns DateInterval object)
    $interval = $date1->diff($date2);

    return sprintf(
        "%d years, %d months, %d days (Total days: %d days)",
        $interval->y,
        $interval->m,
        $interval->d,
        $interval->days
    );
}

// Example usage
$start = "2024-01-15";
$end   = "2026-09-11";
echo "Date 1: $start <br>";
echo "Date 2: $end <br>";
echo "Difference: " . getDateDifference($start, $end);
?>

PHP Program to Print Content Between Two Words in a File

<?php
$filename = "sport.txt";

if (!file_exists($filename)) {
    die("File $filename does not exist.");
}

// Read entire file content into string
$content = file_get_contents($filename);
$keyword = "cricket";

// Find first occurrence of "cricket" (case-insensitive)
$firstPos = stripos($content, $keyword);

if ($firstPos === false) {
    echo "Word '$keyword' not found in file.";
    exit;
}

// Offset index right after the first word
$startPos = $firstPos + strlen($keyword);

// Find second occurrence starting after the first
$secondPos = stripos($content, $keyword, $startPos);

if ($secondPos === false) {
    echo "Second occurrence of '$keyword' not found.";
    exit;
}

// Extract portion between the two words
$portion = substr($content, $startPos, $secondPos - $startPos);

echo "<h3>Portion between first two occurrences of '$keyword':</h3>";
echo "<blockquote>" . nl2br(htmlspecialchars(trim($portion))) . "</blockquote>";
?>

Self-Submitting Form with Validation and Error Reporting

<?php
$errors = [];
$age = "";
$gender = "";
$hobbies = [];
$isSubmitted = false;

if ($_SERVER["REQUEST_METHOD"] === "POST") {
    $isSubmitted = true;
    $age = trim($_POST["age"] ?? "");
    $gender = $_POST["gender"] ?? "";
    $hobbies = $_POST["hobbies"] ?? [];

    // 1. Age Validation: Integer between 1 and 100
    if ($age === "" || !filter_var($age, FILTER_VALIDATE_INT, ["options" => ["min_range" => 1, "max_range" => 100]])) {
        $errors[] = "Age must be a valid integer between 1 and 100.";
    }

    // 2. Gender Validation: Either Male, Female, or Other
    $allowedGenders = ["Male", "Female", "Other"];
    if (empty($gender) || !in_array($gender, $allowedGenders, true)) {
        $errors[] = "Please select a valid gender option (Male, Female, or Other).";
    }

    // 3. Hobbies Validation: Checkboxes (swimming, dancing, singing)
    $allowedHobbies = ["swimming", "dancing", "singing"];
    $invalidHobbies = array_diff($hobbies, $allowedHobbies);
    if (!empty($invalidHobbies)) {
        $errors[] = "Invalid hobby selected.";
    }
}
?>
<!DOCTYPE html>
<html>
<head>
  <title>User Registration & Hobbies Form</title>
  <style>
    .error-box { background: #ffebee; border: 1px solid #f44336; color: #c62828; padding: 12px; border-radius: 6px; }
    .success-box { background: #e8f5e9; border: 1px solid #4caf50; color: #2e7d32; padding: 12px; border-radius: 6px; }
  </style>
</head>
<body>
  <h2>Student Information Form</h2>

  <!-- Error Messages in Unordered List -->
  <?php if ($isSubmitted && !empty($errors)): ?>
    <div class="error-box">
      <strong>Please correct the following errors:</strong>
      <ul>
        <?php foreach ($errors as $err): ?>
          <li><?= htmlspecialchars($err) ?></li>
        <?php endforeach; ?>
      </ul>
    </div>
  <?php elseif ($isSubmitted && empty($errors)): ?>
    <div class="success-box">
      <p>Form validated successfully!</p>
      <p>Age: <?= htmlspecialchars($age) ?> | Gender: <?= htmlspecialchars($gender) ?> | Hobbies: <?= implode(", ", array_map('htmlspecialchars', $hobbies)) ?></p>
    </div>
  <?php endif; ?>

  <form method="POST" action="">
    <p>
      <label>Age (1 - 100):</label><br>
      <input type="text" name="age" value="<?= htmlspecialchars($age) ?>">
    </p>

    <p>
      <label>Gender:</label><br>
      <label><input type="radio" name="gender" value="Male" <?= ($gender === 'Male') ? 'checked' : '' ?>> Male</label>
      <label><input type="radio" name="gender" value="Female" <?= ($gender === 'Female') ? 'checked' : '' ?>> Female</label>
      <label><input type="radio" name="gender" value="Other" <?= ($gender === 'Other') ? 'checked' : '' ?>> Other</label>
    </p>

    <p>
      <label>Hobbies:</label><br>
      <label><input type="checkbox" name="hobbies[]" value="swimming" <?= in_array('swimming', $hobbies) ? 'checked' : '' ?>> Swimming</label>
      <label><input type="checkbox" name="hobbies[]" value="dancing" <?= in_array('dancing', $hobbies) ? 'checked' : '' ?>> Dancing</label>
      <label><input type="checkbox" name="hobbies[]" value="singing" <?= in_array('singing', $hobbies) ? 'checked' : '' ?>> Singing</label>
    </p>

    <button type="submit">Submit & Validate</button>
  </form>
</body>
</html>

Short Notes

a. Here Document (Heredoc) in PHP

A Heredoc is a syntax for defining multi-line strings in PHP without requiring double quotes or manual concatenation. It behaves identically to double-quoted strings (variables and escape sequences are parsed and interpolated).

<?php
$user = "Kishor";
$department = "BITM 4th Semester";

// Heredoc syntax starting with <<<IDENTIFIER
$htmlContent = <<<EOD
<div class="profile-card">
    <h3>Welcome, $user!</h3>
    <p>Enrolled Department: $department</p>
</div>
EOD;

echo $htmlContent;
?>

• Rules: The closing identifier (EOD;) must appear on its own line.
• Nowdoc: Similar to Heredoc but enclosed in single quotes (<<<'EOD'), behaving like single-quoted strings where no variable expansion takes place.

---

b. Inspecting File Permissions in PHP

PHP includes a suite of filesystem inspection functions:

1. fileperms($filepath): Returns full numeric permission mask (including file type bits). To extract the standard Unix permission mode (like 0755 or 0644), mask with 0777:

   $mode = decoct(fileperms("secure_data.txt") & 0777);
   

2. Boolean Capability Inspectors:
   • is_readable($path): Returns true if current web server process can read the file.
   • is_writable($path): Returns true if file exists and can be written to.
   • is_executable($path): Checks execution rights.