Generate absolute URL by relational path with base URL

create_absolute_uri.php

<?php
/**
 * 相対パスから絶対URLを返却する
 * 
 * @param string $base ベースURL, 絶対URL
 * @param string $relational_path 相対パス
 * @return string 相対パスの絶対URL
 * @link http://logic.stepserver.jp/data/archives/501.html
 * @link http://blog.anoncom.net/2010/01/08/295.html
 * @link https://blog.anoncom.net/2010/01/phpurluri.html
 */
function createUri( $base = '', $relational_path = '' ) {
    $parse = array(
        'scheme' => null,
        'user' => null,
        'pass' => null,
        'host' => null,
        'port' => null,
        'path' => null,
        'query' => null,
        'fragment' => null,
    );
    $parse = parse_url ( $base );
    
    // パス末尾が / で終わるパターン
    if ( strpos( $parse['path'], '/', ( strlen( $parse['path'] ) - 1 ) ) !== FALSE ) {
        $parse['path'] .= '.'; // ダミー挿入
    }
    if ( preg_match ( '#^https?\://#', $relational_path ) ) {
        // 相対パスがURLで指定された場合
        return $rel_path;
    } elseif ( preg_match ( '#^/.*$#', $relational_path ) ) {
        // ドキュメントルート指定
        return $parse['scheme'] . '://' . $parse ['host'] . $relational_path;
    } else {
        // 相対パス処理
        $basePath = explode ( '/', dirname ( $parse ['path'] ) );
        $relPath = explode ( '/', $relational_path );
        foreach ( $relPath as $relDirName ) {
            if ($relDirName == '.') {
                array_shift ( $basePath );
                array_unshift ( $basePath, '' );
            } elseif ($relDirName == '..') {
                array_pop ( $basePath );
                if ( count ( $basePath ) == 0 ) {
                    $basePath = array( '' );
                }
            } else {
                array_push ( $basePath, $relDirName );
            }
        }
        $path = implode ( '/', $basePath );
        return $parse ['scheme'] . '://' . $parse ['host'] . $path;
    }
}

test-code.php

<?php
/**
 * テストコード
 * Testing code
 */
$base = 'http://example.com/path/to/url';

$pathes[] = '/';
$pathes[] = '/index.html';
$pathes[] = '/foo/bar/baz/';
$pathes[] = './foo/bar/baz';
$pathes[] = '../../../foo/bar/baz/index.html';
$pathes[] = 'foo/bar/baz.html';
$pathes[] = 'foo/bar/baz/../index.html';

foreach ( $pathes as $path ) {
 echo createUri($base, $path) . PHP_ROL;
}