Reading Request Data

Remarks#

Choosing between GET and POST

GET requests, are best for providing data that’s needed to render the page and may be used multiple times (search queries, data filters…). They are a part of the URL, meaning that they can be bookmarked and are often reused.

POST requests on the other hand, are meant for submitting data to the server just once (contact forms, login forms…). Unlike GET, which only accepts ASCII, POST requests also allow binary data, including file uploads.

You can find a more detailed explanation of their differences here.

Request Data Vulnerabilities

Also look at: https://stackoverflow.com/questions/1301863/what-are-the-vulnerabilities-in-direct-use-of-get-and-post

Retrieving data from the $_GET and $_POST superglobals without any validation is considered bad practice, and opens up methods for users to potentially access or compromise data through code and or SQL injections. Invalid data should be checked for and rejected as to prevent such attacks.

Request data should be escaped depending on how it is being used in code, as noted here and here. A few different escape functions for common data use cases can be found in this answer.

Handling file upload errors

Reading POST data

Data from a POST request is stored in the superglobal $_POST in the form of an associative array.

Note that accessing a non-existent array item generates a notice, so existence should always be checked with the isset() or empty() functions, or the null coalesce operator.

Example:

$from = isset($_POST["name"]) ? $_POST["name"] : "NO NAME";
$message = isset($_POST["message"]) ? $_POST["message"] : "NO MESSAGE";

echo "Message from $from: $message";

$from = $_POST["name"] ?? "NO NAME";
$message = $_POST["message"] ?? "NO MESSAGE";

echo "Message from $from: $message";

Reading GET data

Data from a GET request is stored in the superglobal $_GET in the form of an associative array.

Note that accessing a non-existent array item generates a notice, so existence should always be checked with the isset() or empty() functions, or the null coalesce operator.

Example: (for URL /topics.php?author=alice&topic=php)

$author = isset($_GET["author"]) ? $_GET["author"] : "NO AUTHOR";
$topic = isset($_GET["topic"]) ? $_GET["topic"] : "NO TOPIC";

echo "Showing posts from $author about $topic";

$author = $_GET["author"] ?? "NO AUTHOR";
$topic = $_GET["topic"] ?? "NO TOPIC";

echo "Showing posts from $author about $topic";

Reading raw POST data

Usually data sent in a POST request is structured key/value pairs with a MIME type of application/x-www-form-urlencoded. However many applications such as web services require raw data, often in XML or JSON format, to be sent instead. This data can be read using one of two methods.

php://input is a stream that provides access to the raw request body.

$rawdata = file_get_contents("php://input");
// Let's say we got JSON
$decoded = json_decode($rawdata);

$HTTP_RAW_POST_DATA is a global variable that contains the raw POST data. It is only available if the always_populate_raw_post_data directive in php.ini is enabled.

$rawdata = $HTTP_RAW_POST_DATA;
// Or maybe we get XML
$decoded = simplexml_load_string($rawdata);

This variable has been deprecated since PHP version 5.6, and was removed in PHP 7.0.

Note that neither of these methods are available when the content type is set to multipart/form-data, which is used for file uploads.

Uploading files with HTTP PUT

Passing arrays by POST

Usually, an HTML form element submitted to PHP results in a single value. For example:

<pre>
<?php print_r($_POST);?>
</pre>
<form method="post">
    <input type="hidden" name="foo" value="bar"/>
    <button type="submit">Submit</button>
</form>

This results in the following output:

Array
(
    [foo] => bar
)

However, there may be cases where you want to pass an array of values. This can be done by adding a PHP-like suffix to the name of the HTML elements:

<pre>
<?php print_r($_POST);?>
</pre>
<form method="post">
    <input type="hidden" name="foo[]" value="bar"/>
    <input type="hidden" name="foo[]" value="baz"/>
    <button type="submit">Submit</button>
</form>

This results in the following output:

Array
(
    [foo] => Array
        (
            [0] => bar
            [1] => baz
        )

)

You can also specify the array indices, as either numbers or strings:

<pre>
<?php print_r($_POST);?>
</pre>
<form method="post">
    <input type="hidden" name="foo[42]" value="bar"/>
    <input type="hidden" name="foo[foo]" value="baz"/>
    <button type="submit">Submit</button>
</form>

Which returns this output:

Array
(
    [foo] => Array
        (
            [42] => bar
            [foo] => baz
        )

)

This technique can be used to avoid post-processing loops over the $_POST array, making your code leaner and more concise.