DevTut

# Cookies

An HTTP cookie is a small piece of data sent from a website and stored on the user's computer by the user's web browser while the user is browsing.

The value of a cookie can be modified by resetting the cookie

setcookie("user", "John", time() + 86400, "/"); // assuming there is a "user" cookie already

Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the browser.

When modifying a cookie make sure the path and domain parameters of setcookie() matches the existing cookie or a new cookie will be created instead.

The value portion of the cookie will automatically be urlencoded when you send the cookie, and when it is received, it is automatically decoded and assigned to a variable by the same name as the cookie name

A cookie is set using the setcookie() function. Since cookies are part of the HTTP header, you must set any cookies before sending any output to the browser.

Example:

setcookie("user", "Tom", time() + 86400, "/"); // check syntax for function params

Description:

  • Creates a cookie with name user
  • (Optional) Value of the cookie is Tom
  • (Optional) Cookie will expire in 1 day (86400 seconds)
  • (Optional) Cookie is available throughout the whole website /
  • (Optional) Cookie is only sent over HTTPS
  • (Optional) Cookie is not accessible to scripting languages such as JavaScript

A created or modified cookie can only be accessed on subsequent requests (where path and domain matches) as the superglobal $_COOKIEis not populated with the new data immediately.

Use the isset() function upon the superglobal $_COOKIE variable to check if a cookie is set.

Example:

// PHP <7.0
if (isset($_COOKIE['user'])) {
    // true, cookie is set
    echo 'User is ' . $_COOKIE['user'];
else {
    // false, cookie is not set
    echo 'User is not logged in';
}

// PHP 7.0+
echo 'User is ' . $_COOKIE['user'] ?? 'User is not logged in';

To remove a cookie, set the expiry timestamp to a time in the past. This triggers the browser's removal mechanism:

setcookie('user', '', time() - 3600, '/');

When deleting a cookie make sure the path and domain parameters of setcookie() matches the cookie you're trying to delete or a new cookie, which expires immediately, will be created.

It is also a good idea to unset the $_COOKIE value in case the current page uses it:

unset($_COOKIE['user']);

Retrieve and Output a Cookie Named user

The value of a cookie can be retrieved using the global variable $_COOKIE. example if we have a cookie named user we can retrieve it like this

echo $_COOKIE['user'];

# Syntax

  • bool setcookie( string $name [, string $value = "" [, int $expire = 0 [, string $path = "" [, string $domain = "" [, bool $secure = false [, bool $httponly = false ]]]]]] )

# Parameters

parameter detail
name The name of the cookie. This is also the key you can use to retrieve the value from the $_COOKIE super global. This is the only required parameter
value The value to store in the cookie. This data is accessible to the browser so don't store anything sensitive here.
expire A Unix timestamp representing when the cookie should expire. If set to zero the cookie will expire at the end of the session. If set to a number less than the current Unix timestamp the cookie will expire immediately.
path The scope of the cookie. If set to / the cookie will be available within the entire domain. If set to /some-path/ then the cookie will only be available in that path and descendants of that path. Defaults to the current path of the file that the cookie is being set in.
domain The domain or subdomain the cookie is available on. If set to the bare domain stackoverflow.com then the cookie will be available to that domain and all subdomains. If set to a subdomain meta.stackoverflow.com then the cookie will be available only on that subdomain, and all sub-subdomains.
secure When set to TRUE the cookie will only be set if a secure HTTPS connection exists between the client and the server.
httponly Specifies that the cookie should only be made available through the HTTP/S protocol and should not be available to client side scripting languages like JavaScript. Only available in PHP 5.2 or later.

# Remarks

It is worth noting that mere invoking setcookie function doesn't just put given data into $_COOKIE superglobal array.

For example there is no point in doing:

setcookie("user", "Tom", time() + 86400, "/");
var_dump(isset($_COOKIE['user'])); // yields false or the previously set value

The value is not there yet, not until next page load. The function setcookie just says "with next http connection tell the client (browser) to set this cookie". Then when the headers are sent to the browser, they contain this cookie header. The browser then checks if the cookie hasn't expired yet, and if not, then in http request it sends the cookie to the server and that's when PHP receives it and puts the contents into $_COOKIE array.

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