stormatic

learning php for beginners 34

learning php error handling with Olatunji Akinkunmi 

The default error handling in PHP is very simple. An error message with filename, line number and a message describing the error is sent to the browser.

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PHP Error Handling

When creating scripts and web applications, error handling is an important part. If your code lacks error checking code, your program may look very unprofessional and you may be open to security risks.

This tutorial contains some of the most common error checking methods in PHP.

We will show different error handling methods:

• Simple "die()" statements
• Custom errors and error triggers
• Error reporting

---

Basic Error Handling: Using the die() function

The first example shows a simple script that opens a text file:

<?php
$file=fopen("welcome.txt","r");
?>

If the file does not exist you might get an error like this:

Warning: fopen(welcome.txt) [function.fopen]: failed to open stream:
No such file or directory in C:\webfolder\test.phpon line 2

To prevent the user from getting an error message like the one above, we test whether the file exist before we try to access it:

<?php
if(!file_exists("welcome.txt")) {
  die("File not found");
} else {
  $file=fopen("welcome.txt","r");
}
?>

Now if the file does not exist you get an error like this:

File not found

The code above is more efficient than the earlier code, because it uses a simple error handling mechanism to stop the script after the error.

However, simply stopping the script is not always the right way to go. Let's take a look at alternative PHP functions for handling errors.

---

Creating a Custom Error Handler

Creating a custom error handler is quite simple. We simply create a special function that can be called when an error occurs in PHP.

This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters (optionally: file, line-number, and the error context):

Syntax

error_function(error_level,error_message,
error_file,error_line,error_context)

Parameter	Description
error_level	Required. Specifies the error report level for the user-defined error. Must be a value number. See table below for possible error report levels
error_message	Required. Specifies the error message for the user-defined error
error_file	Optional. Specifies the filename in which the error occurred
error_line	Optional. Specifies the line number in which the error occurred
error_context	Optional. Specifies an array containing every variable, and their values, in use when the error occurred

Error Report levels

These error report levels are the different types of error the user-defined error handler can be used for:

Value	Constant	Description
2	E_WARNING	Non-fatal run-time errors. Execution of the script is not halted
8	E_NOTICE	Run-time notices. The script found something that might be an error, but could also happen when running a script normally
256	E_USER_ERROR	Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()
512	E_USER_WARNING	Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()
1024	E_USER_NOTICE	User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()
4096	E_RECOVERABLE_ERROR	Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())
8191	E_ALL	All errors and warnings (E_STRICT became a part of E_ALL in PHP 5.4)

Now lets create a function to handle errors:

function customError($errno, $errstr) {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Ending Script";
  die();
}

The code above is a simple error handling function. When it is triggered, it gets the error level and an error message. It then outputs the error level and message and terminates the script.

Now that we have created an error handling function we need to decide when it should be triggered.

---

Set Error Handler

The default error handler for PHP is the built in error handler. We are going to make the function above the default error handler for the duration of the script.

It is possible to change the error handler to apply for only some errors, that way the script can handle different errors in different ways. However, in this example we are going to use our custom error handler for all errors:

set_error_handler("customError");

Since we want our custom function to handle all errors, the set_error_handler() only needed one parameter, a second parameter could be added to specify an error level.

Example

Testing the error handler by trying to output variable that does not exist:

<?php
//error handler function
function customError($errno, $errstr) {
  echo "<b>Error:</b> [$errno] $errstr";
}

//set error handler
set_error_handler("customError");

//trigger error
echo($test);
?>

The output of the code above should be something like this:

Error: [8] Undefined variable: test

---

Trigger an Error

In a script where users can input data it is useful to trigger errors when an illegal input occurs. In PHP, this is done by the trigger_error() function.

Example

In this example an error occurs if the "test" variable is bigger than "1":

<?php
$test=2;
if ($test>1) {
  trigger_error("Value must be 1 or below");
}
?>

The output of the code above should be something like this:

Notice: Value must be 1 or below
in C:\webfolder\test.phpon line 6

An error can be triggered anywhere you wish in a script, and by adding a second parameter, you can specify what error level is triggered.

Possible error types:

• E_USER_ERROR - Fatal user-generated run-time error. Errors that can not be recovered from. Execution of the script is halted
• E_USER_WARNING - Non-fatal user-generated run-time warning. Execution of the script is not halted
• E_USER_NOTICE - Default. User-generated run-time notice. The script found something that might be an error, but could also happen when running a script normally

Example

In this example an E_USER_WARNING occurs if the "test" variable is bigger than "1". If an E_USER_WARNING occurs we will use our custom error handler and end the script:

<?php
//error handler function
function customError($errno, $errstr) {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Ending Script";
  die();
}

//set error handler
set_error_handler("customError",E_USER_WARNING);

//trigger error
$test=2;
if ($test>1) {
  trigger_error("Value must be 1 or below",E_USER_WARNING);
}
?>

The output of the code above should be something like this:

Error: [512] Value must be 1 or below
Ending Script

Now that we have learned to create our own errors and how to trigger them, lets take a look at error logging.

---

Error Logging

By default, PHP sends an error log to the server's logging system or a file, depending on how the error_log configuration is set in the php.ini file. By using the error_log() function you can send error logs to a specified file or a remote destination.

Sending error messages to yourself by e-mail can be a good way of getting notified of specific errors.

Send an Error Message by E-Mail

In the example below we will send an e-mail with an error message and end the script, if a specific error occurs:

<?php
//error handler function
function customError($errno, $errstr) {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Webmaster has been notified";
  error_log("Error: [$errno] $errstr",1,
  "someone@example.com","From: webmaster@example.com");
}

//set error handler
set_error_handler("customError",E_USER_WARNING);

//trigger error
$test=2;
if ($test>1) {
  trigger_error("Value must be 1 or below",E_USER_WARNING);
}
?>

The output of the code above should be something like this:

Error: [512] Value must be 1 or below
Webmaster has been notified

And the mail received from the code above looks like this:

Error: [512] Value must be 1 or below

This should not be used with all errors. Regular errors should be logged on the server using the default PHP logging system.

learning php for beginners 33

learning php filters advanced with Olatunji Akinkunmi 

Validate an Integer Within a Range

The following example uses the filter_var() function to check if a variable is both of type INT, and between 1 and 200:

Example

<?php
$int = 122;
$min = 1;
$max = 200;

if (filter_var($int, FILTER_VALIDATE_INT, array("options" => array("min_range"=>$min, "max_range"=>$max))) === false) {
    echo("Variable value is not within the legal range");
} else {
    echo("Variable value is within the legal range");
}
?>

Run example »

---

Validate IPv6 Address

The following example uses the filter_var() function to check if the variable $ip is a valid IPv6 address:

Example

<?php
$ip = "2001:0db8:85a3:08d3:1319:8a2e:0370:7334";

if (!filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) === false) {
    echo("$ip is a valid IPv6 address");
} else {
    echo("$ip is not a valid IPv6 address");
}
?>

Run example »

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Validate URL - Must Contain QueryString

The following example uses the filter_var() function to check if the variable $url is a URL with a querystring:

Example

<?php
$url = "http:// stormatic.blogspot.com ";

if (!filter_var($url, FILTER_VALIDATE_URL, FILTER_FLAG_QUERY_REQUIRED) === false) {
    echo("$url is a valid URL");
} else {
    echo("$url is not a valid URL");
}
?>

Run example »

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Remove Characters With ASCII Value > 127

The following example uses the filter_var() function to sanitize a string. It will both remove all HTML tags, and all characters with ASCII value > 127, from the string:

Example

<?php
$str = "<h1>Hello WorldÆØÅ!</h1>";

$newstr = filter_var($str, FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_HIGH);
echo $newstr;
?>

Run example »

learning php for beginners 32

learning php filters with Olatunji Akinkunmi 

Validating data = Determine if the data is in proper form.

Sanitizing data = Remove any illegal character from the data.

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The PHP Filter Extension

PHP filters are used to validate and sanitize external input.

The PHP filter extension has many of the functions needed for checking user input, and is designed to make data validation easier and quicker.

The filter_list() function can be used to list what the PHP filter extension offers:

Example

<table>
  <tr>
    <td>Filter Name</td>
    <td>Filter ID</td>
  </tr>
  <?php
  foreach (filter_list() as $id =>$filter) {
      echo '<tr><td>' . $filter . '</td><td>' . filter_id($filter) . '</td></tr>';
  }
  ?>
</table>

Run example »

---

Why Use Filters?

Many web applications receive external input. External input/data can be:

• User input from a form
• Cookies
• Web services data
• Server variables
• Database query results

	You should always validate external data!Invalid submitted data can lead to security problems and break your webpage! By using PHP filters you can be sure your application gets the correct input!

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PHP filter_var() Function

The filter_var() function both validate and sanitize data.

The filter_var() function filters a single variable with a specified filter. It takes two pieces of data:

• The variable you want to check
• The type of check to use

---

Sanitize a String

The following example uses the filter_var() function to remove all HTML tags from a string:

Example

<?php
$str = "<h1>Hello World!</h1>";
$newstr = filter_var($str, FILTER_SANITIZE_STRING);
echo $newstr;
?>

Run example »

---

Validate an Integer

The following example uses the filter_var() function to check if the variable $int is an integer. If $int is an integer, the output of the code above will be: "Integer is valid". If $int is not an integer, the output will be: "Integer is not valid":

Example

<?php
$int = 100;

if (!filter_var($int, FILTER_VALIDATE_INT) === false) {
    echo("Integer is valid");
} else {
    echo("Integer is not valid");
}
?>

Run example »

Tip: filter_var() and Problem With 0

In the example above, if $int was set to 0, the function above will return "Integer is not valid". To solve this problem, use the code below:

Example

<?php
$int = 0;

if (filter_var($int, FILTER_VALIDATE_INT) === 0 || !filter_var($int, FILTER_VALIDATE_INT) === false) {
    echo("Integer is valid");
} else {
    echo("Integer is not valid");
}
?>

Run example »

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Validate an IP Address

The following example uses the filter_var() function to check if the variable $ip is a valid IP address:

Example

<?php
$ip = "127.0.0.1";

if (!filter_var($ip, FILTER_VALIDATE_IP) === false) {
    echo("$ip is a valid IP address");
} else {
    echo("$ip is not a valid IP address");
}
?>

Run example »

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Sanitize and Validate an Email Address

The following example uses the filter_var() function to first remove all illegal characters from the $email variable, then check if it is a valid email address:

Example

<?php
$email = "john.doe@example.com";

// Remove all illegal characters from email
$email = filter_var($email, FILTER_SANITIZE_EMAIL);

// Validate e-mail
if (!filter_var($email, FILTER_VALIDATE_EMAIL) === false) {
    echo("$email is a valid email address");
} else {
    echo("$email is not a valid email address");
}
?>

Run example »

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Sanitize and Validate a URL

The following example uses the filter_var() function to first remove all illegal characters from a URL, then check if $url is a valid URL:

Example

<?php
$url = "http://" stormatic.blogspot.com ";

// Remove all illegal characters from a url
$url = filter_var($url, FILTER_SANITIZE_URL);

// Validate url
if (!filter_var($url, FILTER_VALIDATE_URL) === false) {
    echo("$url is a valid URL");
} else {
    echo("$url is not a valid URL");
}
?>

Run example »

learning php for beginners 31

learning php sessions with Olatunji Akinkunmi 

A session is a way to store information (in variables) to be used across multiple pages.

Unlike a cookie, the information is not stored on the users computer.

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What is a PHP Session?

When you work with an application, you open it, do some changes, and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are or what you do, because the HTTP address doesn't maintain state.

Session variables solve this problem by storing user information to be used across multiple pages (e.g. username, favorite color, etc). By default, session variables last until the user closes the browser.

So; Session variables hold information about one single user, and are available to all pages in one application.

	Tip: If you need a permanent storage, you may want to store the data in a database.

---

Start a PHP Session

A session is started with the session_start() function.

Session variables are set with the PHP global variable: $_SESSION.

Now, let's create a new page called "demo_session1.php". In this page, we start a new PHP session and set some session variables:

Example

<?php
// Start the session
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// Set session variables
$_SESSION["favcolor"] = "green";
$_SESSION["favanimal"] = "cat";
echo "Session variables are set.";
?>

</body>
</html>

Run example »

	Note: The session_start() function must be the very first thing in your document. Before any HTML tags.

---

Get PHP Session Variable Values

Next, we create another page called "demo_session2.php". From this page, we will access the session information we set on the first page ("demo_session1.php").

Notice that session variables are not passed individually to each new page, instead they are retrieved from the session we open at the beginning of each page (session_start()).

Also notice that all session variable values are stored in the global $_SESSION variable:

Example

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// Echo session variables that were set on previous page
echo "Favorite color is " . $_SESSION["favcolor"] . ".<br>";
echo "Favorite animal is " . $_SESSION["favanimal"] . ".";
?>

</body>
</html>

Run example »

Another way to show all the session variable values for a user session is to run the following code:

Example

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
print_r($_SESSION);
?>

</body>
</html>

Run example »

	How does it work? How does it know it's me? Most sessions set a user-key on the user's computer that looks something like this: 765487cf34ert8dede5a562e4f3a7e12. Then, when a session is opened on another page, it scans the computer for a user-key. If there is a match, it accesses that session, if not, it starts a new session.

---

Modify a PHP Session Variable

To change a session variable, just overwrite it:

Example

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// to change a session variable, just overwrite it 
$_SESSION["favcolor"] = "yellow";
print_r($_SESSION);
?>

</body>
</html>

Run example »

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Destroy a PHP Session

To remove all global session variables and destroy the session, use session_unset() and session_destroy():

Example

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// remove all session variables
session_unset(); 

// destroy the session 
session_destroy(); 
?>

</body>
</html>

Run example »

learning php for beginners 30

learning php cookies with Olatunji Akinkunmi 

A cookie is often used to identify a user.

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What is a Cookie?

A cookie is often used to identify a user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests a page with a browser, it will send the cookie too. With PHP, you can both create and retrieve cookie values.

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Create Cookies With PHP

A cookie is created with the setcookie() function.

Syntax

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

Only the name parameter is required. All other parameters are optional.

---

PHP Create/Retrieve a Cookie

The following example creates a cookie named "user" with the value "John Doe". The cookie will expire after 30 days (86400 * 30). The "/" means that the cookie is available in entire website (otherwise, select the directory you prefer).

We then retrieve the value of the cookie "user" (using the global variable $_COOKIE). We also use the isset() function to find out if the cookie is set:

Example

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

<?php
if(!isset($_COOKIE[$cookie_name])) {
    echo "Cookie named '" . $cookie_name . "' is not set!";
} else {
    echo "Cookie '" . $cookie_name . "' is set!<br>";
    echo "Value is: " . $_COOKIE[$cookie_name];
}
?>

</body>
</html>

Run example »

	Note: The setcookie() function must appear BEFORE the <html> tag.

Note: The value of the cookie is automatically URLencoded when sending the cookie, and automatically decoded when received (to prevent URLencoding, use setrawcookie() instead).

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Modify a Cookie Value

To modify a cookie, just set (again) the cookie using the setcookie() function:

Example

<?php
$cookie_name = "user";
$cookie_value = "Alex Porter";
setcookie($cookie_name, $cookie_value, time() + (86400 * 30), "/");
?>
<html>
<body>

<?php
if(!isset($_COOKIE[$cookie_name])) {
    echo "Cookie named '" . $cookie_name . "' is not set!";
} else {
    echo "Cookie '" . $cookie_name . "' is set!<br>";
    echo "Value is: " . $_COOKIE[$cookie_name];
}
?>

</body>
</html>

Run example »

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Delete a Cookie

To delete a cookie, use the setcookie() function with an expiration date in the past:

Example

<?php
// set the expiration date to one hour ago
setcookie("user", "", time() - 3600);
?>
<html>
<body>

<?php
echo "Cookie 'user' is deleted.";
?>

</body>
</html>

Run example »

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Check if Cookies are Enabled

The following example creates a small script that checks whether cookies are enabled. First, try to create a test cookie with the setcookie() function, then count the $_COOKIE array variable:

Example

<?php
setcookie("test_cookie", "test", time() + 3600, '/');
?>
<html>
<body>

<?php
if(count($_COOKIE) > 0) {
    echo "Cookies are enabled.";
} else {
    echo "Cookies are disabled.";
}
?>

</body>
</html>

Run example »