easy mode php last-modified/etag headers

HttpCache.php

<?php

class HttpCache {
	/**
	 * @param int $lastModifiedTimestamp
	 * @param int $maxAge
	 *
	 * @return void
	 */
	public static function Init( $lastModifiedTimestamp, $maxAge = null ) {
		if ( static::IsModifiedSince( $lastModifiedTimestamp ) ) {
			static::SetLastModifiedHeader( $lastModifiedTimestamp, $maxAge );
		} else {
			static::SetNotModifiedHeader( $maxAge );
		}
	}

	/**
	 * @param string $file
	 * @param int    $maxAge
	 *
	 * @return bool
	 */
	public static function InitFile( $file, $maxAge = null ) {
		if ( is_file( $file ) ) {
			$timestamp = max( filemtime( $file ), filemtime( __FILE__ ) );
			static::Init( $timestamp, $maxAge );

			return true;
		}

		static::SetNotFound();

		return false;
	}

	/**
	 * @param int $lastModifiedTimestamp
	 *
	 * @return bool
	 */
	public static function IsModifiedSince( $lastModifiedTimestamp ) {
		$allHeaders = getallheaders();

		if ( array_key_exists( 'If-Modified-Since', $allHeaders ) ) {
			$gmtSinceDate   = $allHeaders['If-Modified-Since'];
			$sinceTimestamp = strtotime( $gmtSinceDate );

			// Can the browser get it from the cache?
			if ( $sinceTimestamp !== false && $lastModifiedTimestamp <= $sinceTimestamp ) {
				return false;
			}
		}

		return true;
	}

	/**
	 * @param int $maxAge
	 *
	 * @return void
	 */
	public static function SetNotModifiedHeader( $maxAge = null ) {
		// Set headers
		header( 'HTTP/1.1 304 Not Modified' );
		if ( $maxAge !== null ) {
			header( "Cache-Control: public, max-age=$maxAge" );
		}
		die();
	}

	/**
	 * @param int $lastModifiedTimestamp
	 * @param int $maxAge
	 */
	public static function SetLastModifiedHeader( $lastModifiedTimestamp, $maxAge = null ) {
		// Fetching the last modified time of the XML file
		$date = gmdate( 'D, j M Y H:i:s', $lastModifiedTimestamp ) . ' GMT';

		// Set headers
		header( 'HTTP/1.1 200 OK' );
		if ( $maxAge !== null ) {
			header( "Cache-Control: public, max-age=$maxAge" );
		}
		header( "Last-Modified: $date" );
	}

	public static function SetNotFound() {
		header( 'HTTP/1.1 4004 Not Found' );
	}

	public static function SendDoNotCache() {
		header( 'Cache-Control: no-cache, no-store, must-revalidate' );
		header( 'Expires: Thu, 01 Jan 1970 00:00:00 GMT' );
		header( 'Pragma: no-cache' );
	}
}