Build a canonical URL based on Request URI

If you are performing a redirect or adding a canonical header, you will need to reconstruct a canonical URL after removing the lonesome question mark. E.g:

// Construct the canonical URL without parameters
// E.g: https://beamtic.com/get-full-request-url-in-php

$full_request_url = '';  // Initialize the URL string

// Check if the request is made using HTTPS
if ((!empty($_SERVER['HTTPS'])) && ($_SERVER['HTTPS'] !== 'off')) {
  $full_request_url .= 'https://';
} else {
  $full_request_url .= 'http://';
}

// Append the HTTP_HOST and REQUEST_URI to the URL
$full_request_url .= $_SERVER['HTTP_HOST'] . parse_url($_SERVER["REQUEST_URI"], PHP_URL_PATH);

// Check if there are any URL parameters (GET parameters)
if (count($_GET) > 0) {
  $full_request_url .= '?';  // Add the '?' separator for URL parameters

  // Get the first key-value pair and add it to the URL
  $get_arr = $_GET;
  $full_request_url .= key($get_arr) . '=' . current($get_arr);
  next($get_arr);

  // Remove the first item from the array
  array_shift($get_arr);

  // Loop through the remaining key-value pairs and encode them
  foreach ($get_arr as $key => $value) {
    $full_request_url .= '&' . urlencode($key) . '=' . urlencode($value);
  }
}

// Set the content type and echo the full canonical URL
header('content-type: text/plain; charset=utf-8');
echo $full_request_url;

Why return a 400 Bad Request rather than a 404 or a redirect?

I have opted to show a 400 Bad Request message because it feels more true to the HTTP standard. Performing a redirect could be more user-friendly if the request was sent in error. E.g. The user mistyped the URL or clicked a malformed link, but not what you would intuitively expect to happen when requesting non-existent resources.

Consider the following:

1. If a resource does not exist, we should return a 404. See also: What to do About Deleted and Discontinued Products
2. If a resource has existed previously, but it was deleted, we should return a 404.
3. If a resource was moved to another permanent location, we should return a 301 redirect to the new location.

Ideally a redirect should remain in-place indefinitely, because old hyperlinks might still point to the old location, and someone might still follow those links. But, contrary to what you may have heard, SEO is an irrelevant consideration in these rare edge-cases, so I would do what makes sense technically and in terms of maintainability. Placing redirects just for the sake of SEO will potentially send a technically inaccurate signal to bots and search engines.

Because URL parameters are normally used to control behaviour of the requested resource, a 400 Bad Request message will be more appropriate than a 404.

Although Content Management Systems these days use friendly URLs, and make limited use of plain URL parameters, there may still be cases where the URL parameters themselves are used to request specific resources. E.g. If using a routing pattern like: ?page=[page name] to access resources, obviously a 404 response will be the more appropriate choice, but probably only when a requested resource is not found through such a specific parameter.

For a lonesome trailing question mark, I would personally stick with a 400 response regardless of how parameters are normally used in your application.

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