A file that contains a ton of cool constants for PHP projects. Geared for the CodeIgniter framework, but it is not required.

constants.php

<?php
/**
 * --------------------------------------------------------------------------
 *  Application Specific Constants
 * --------------------------------------------------------------------------
 *
 * The following constants are application specific. They cover items such as
 * writable path values, HTTP status codes and more!
 *
 * @package  Constants
 * @author   Jason Napolitano <[email protected]>
 * @updated  03.25.2025
 *
 * @license  MIT License
 * @version  2.0.0
 * @since    1.0.0
 */

// ----------------------------------------------------------------------------
// DIRECTORY_SEPARATOR Aliased as _DS_
define('_DS_', str_replace(DIRECTORY_SEPARATOR, '/', '\\'));

/**
 * --------------------------------------------------------------------------
 *  Client/Server HTTP status code constants
 * --------------------------------------------------------------------------
 *
 *  These are the constants that you may use anywhere in the application for
 *  allowing easier, quick access to status codes.
 */

// ----------------------------------------------------------------------------
// HTTP Status Codes
const HTTP_CONTINUE = 100;
const HTTP_SWITCHING_PROTOCOLS = 101;
const HTTP_PROCESSING = 102; // RFC2518

// ----------------------------------------------------------------------------
// The request has succeeded
const HTTP_OK = 200;

// ----------------------------------------------------------------------------
// The server successfully created a new resource
const HTTP_CREATED = 201;
const HTTP_ACCEPTED = 202;
const HTTP_NON_AUTHORITATIVE_INFORMATION = 203;

// ----------------------------------------------------------------------------
// The server successfully processed the request, though no content is returned
const HTTP_NO_CONTENT = 204;
const HTTP_RESET_CONTENT = 205;
const HTTP_PARTIAL_CONTENT = 206;
const HTTP_MULTI_STATUS = 207; // RFC4918
const HTTP_ALREADY_REPORTED = 208; // RFC5842
const HTTP_IM_USED = 226; // RFC3229

// ----------------------------------------------------------------------------
// Redirection
const HTTP_MULTIPLE_CHOICES = 300;
const HTTP_MOVED_PERMANENTLY = 301;
const HTTP_FOUND = 302;
const HTTP_SEE_OTHER = 303;

// ----------------------------------------------------------------------------
// The resource has not been modified since the last request
const HTTP_NOT_MODIFIED = 304;
const HTTP_USE_PROXY = 305;
const HTTP_RESERVED = 306;
const HTTP_TEMPORARY_REDIRECT = 307;
const HTTP_PERMANENTLY_REDIRECT = 308;   // RFC7238

// ----------------------------------------------------------------------------
// The request cannot be fulfilled due to multiple errors
const HTTP_BAD_REQUEST = 400;

// ----------------------------------------------------------------------------
// The user is unauthorized to access the requested resource
const HTTP_UNAUTHORIZED = 401;
const HTTP_PAYMENT_REQUIRED = 402;

// ----------------------------------------------------------------------------
// The requested resource is unavailable at this present time
const HTTP_FORBIDDEN = 403;

// ----------------------------------------------------------------------------
// The requested resource could not be found
const HTTP_NOT_FOUND = 404;

// ----------------------------------------------------------------------------
// The request method is not supported by the following resource
const HTTP_METHOD_NOT_ALLOWED = 405;

// ----------------------------------------------------------------------------
// The request was not acceptable
const HTTP_NOT_ACCEPTABLE = 406;
const HTTP_PROXY_AUTHENTICATION_REQUIRED = 407;
const HTTP_REQUEST_TIMEOUT = 408;

// ----------------------------------------------------------------------------
// The request could not be completed due to a conflict with the current state
// of the resource
const HTTP_CONFLICT = 409;
const HTTP_GONE = 410;
const HTTP_LENGTH_REQUIRED = 411;
const HTTP_PRECONDITION_FAILED = 412;
const HTTP_REQUEST_ENTITY_TOO_LARGE = 413;
const HTTP_REQUEST_URI_TOO_LONG = 414;
const HTTP_UNSUPPORTED_MEDIA_TYPE = 415;
const HTTP_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
const HTTP_EXPECTATION_FAILED = 417;
const HTTP_I_AM_A_TEAPOT = 418; // RFC2324
const HTTP_UNPROCESSABLE_ENTITY = 422; // RFC4918
const HTTP_LOCKED = 423; // RFC4918
const HTTP_FAILED_DEPENDENCY = 424; // RFC4918
const HTTP_RESERVED_FOR_WEBDAV_ADVANCED_COLLECTIONS_EXPIRED_PROPOSAL = 425; // RFC2817
const HTTP_UPGRADE_REQUIRED = 426; // RFC2817
const HTTP_PRECONDITION_REQUIRED = 428; // RFC6585
const HTTP_TOO_MANY_REQUESTS = 429; // RFC6585
const HTTP_REQUEST_HEADER_FIELDS_TOO_LARGE = 431; // RFC6585

// ----------------------------------------------------------------------------
// The server encountered an unexpected error
// Note: This is a generic error message when no specific message
// is suitable
const HTTP_INTERNAL_SERVER_ERROR = 500;

// ----------------------------------------------------------------------------
// The server does not recognise the request method
const HTTP_NOT_IMPLEMENTED = 501;
const HTTP_BAD_GATEWAY = 502;
const HTTP_SERVICE_UNAVAILABLE = 503;
const HTTP_GATEWAY_TIMEOUT = 504;
const HTTP_VERSION_NOT_SUPPORTED = 505;
const HTTP_VARIANT_ALSO_NEGOTIATES_EXPERIMENTAL = 506; // RFC2295
const HTTP_INSUFFICIENT_STORAGE = 507; // RFC4918
const HTTP_LOOP_DETECTED = 508; // RFC5842
const HTTP_NOT_EXTENDED = 510; // RFC2774
const HTTP_NETWORK_AUTHENTICATION_REQUIRED = 511;