1<?php
2
3declare(strict_types=1);
4
5namespace GuzzleHttp\Psr7;
6
7use Psr\Http\Message\UriInterface;
8
9/**
10 * Resolves a URI reference in the context of a base URI and the opposite way.
11 *
12 * @author Tobias Schultze
13 *
14 * @see https://datatracker.ietf.org/doc/html/rfc3986#section-5
15 */
16final class UriResolver
17{
18    /**
19     * Removes dot segments from a path and returns the new path.
20     *
21     * @see https://datatracker.ietf.org/doc/html/rfc3986#section-5.2.4
22     */
23    public static function removeDotSegments(string $path): string
24    {
25        if ($path === '' || $path === '/') {
26            return $path;
27        }
28
29        $results = [];
30        $segments = explode('/', $path);
31        foreach ($segments as $segment) {
32            if ($segment === '..') {
33                array_pop($results);
34            } elseif ($segment !== '.') {
35                $results[] = $segment;
36            }
37        }
38
39        $newPath = implode('/', $results);
40
41        if ($path[0] === '/' && (!isset($newPath[0]) || $newPath[0] !== '/')) {
42            // Re-add the leading slash if necessary for cases like "/.."
43            $newPath = '/'.$newPath;
44        } elseif ($newPath !== '' && ($segment === '.' || $segment === '..')) {
45            // Add the trailing slash if necessary
46            // If newPath is not empty, then $segment must be set and is the last segment from the foreach
47            $newPath .= '/';
48        }
49
50        return $newPath;
51    }
52
53    /**
54     * Converts the relative URI into a new URI that is resolved against the base URI.
55     *
56     * @see https://datatracker.ietf.org/doc/html/rfc3986#section-5.2
57     */
58    public static function resolve(UriInterface $base, UriInterface $rel): UriInterface
59    {
60        if ((string) $rel === '') {
61            // we can simply return the same base URI instance for this same-document reference
62            return $base;
63        }
64
65        if ($rel->getScheme() != '') {
66            return $rel->withPath(self::removeDotSegments($rel->getPath()));
67        }
68
69        if ($rel->getAuthority() != '') {
70            $targetAuthority = $rel->getAuthority();
71            $targetPath = self::removeDotSegments($rel->getPath());
72            $targetQuery = $rel->getQuery();
73        } else {
74            $targetAuthority = $base->getAuthority();
75            if ($rel->getPath() === '') {
76                $targetPath = $base->getPath();
77                $targetQuery = $rel->getQuery() != '' ? $rel->getQuery() : $base->getQuery();
78            } else {
79                if ($rel->getPath()[0] === '/') {
80                    $targetPath = $rel->getPath();
81                } else {
82                    if ($targetAuthority != '' && $base->getPath() === '') {
83                        $targetPath = '/'.$rel->getPath();
84                    } else {
85                        $lastSlashPos = strrpos($base->getPath(), '/');
86                        if ($lastSlashPos === false) {
87                            $targetPath = $rel->getPath();
88                        } else {
89                            $targetPath = substr($base->getPath(), 0, $lastSlashPos + 1).$rel->getPath();
90                        }
91                    }
92                }
93                $targetPath = self::removeDotSegments($targetPath);
94                $targetQuery = $rel->getQuery();
95            }
96        }
97
98        return new Uri(Uri::composeComponents(
99            $base->getScheme(),
100            $targetAuthority,
101            $targetPath,
102            $targetQuery,
103            $rel->getFragment()
104        ));
105    }
106
107    /**
108     * Returns the target URI as a relative reference from the base URI.
109     *
110     * This method is the counterpart to resolve():
111     *
112     *    (string) $target === (string) UriResolver::resolve($base, UriResolver::relativize($base, $target))
113     *
114     * One use-case is to use the current request URI as base URI and then generate relative links in your documents
115     * to reduce the document size or offer self-contained downloadable document archives.
116     *
117     *    $base = new Uri('http://example.com/a/b/');
118     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/b/c'));  // prints 'c'.
119     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/x/y'));  // prints '../x/y'.
120     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/b/?q')); // prints '?q'.
121     *    echo UriResolver::relativize($base, new Uri('http://example.org/a/b/'));   // prints '//example.org/a/b/'.
122     *
123     * This method also accepts a target that is already relative and will try to relativize it further. Only a
124     * relative-path reference will be returned as-is.
125     *
126     *    echo UriResolver::relativize($base, new Uri('/a/b/c'));  // prints 'c' as well
127     */
128    public static function relativize(UriInterface $base, UriInterface $target): UriInterface
129    {
130        if ($target->getScheme() !== ''
131            && ($base->getScheme() !== $target->getScheme() || $target->getAuthority() === '' && $base->getAuthority() !== '')
132        ) {
133            return $target;
134        }
135
136        if (Uri::isRelativePathReference($target)) {
137            // As the target is already highly relative we return it as-is. It would be possible to resolve
138            // the target with `$target = self::resolve($base, $target);` and then try make it more relative
139            // by removing a duplicate query. But let's not do that automatically.
140            return $target;
141        }
142
143        if ($target->getAuthority() !== '' && $base->getAuthority() !== $target->getAuthority()) {
144            return $target->withScheme('');
145        }
146
147        // We must remove the path before removing the authority because if the path starts with two slashes, the URI
148        // would turn invalid. And we also cannot set a relative path before removing the authority, as that is also
149        // invalid.
150        $emptyPathUri = $target->withScheme('')->withPath('')->withUserInfo('')->withPort(null)->withHost('');
151
152        if ($base->getPath() !== $target->getPath()) {
153            return $emptyPathUri->withPath(self::getRelativePath($base, $target));
154        }
155
156        if ($base->getQuery() === $target->getQuery()) {
157            // Only the target fragment is left. And it must be returned even if base and target fragment are the same.
158            return $emptyPathUri->withQuery('');
159        }
160
161        // If the base URI has a query but the target has none, we cannot return an empty path reference as it would
162        // inherit the base query component when resolving.
163        if ($target->getQuery() === '') {
164            $segments = explode('/', $target->getPath());
165            /** @var string $lastSegment */
166            $lastSegment = end($segments);
167
168            return $emptyPathUri->withPath($lastSegment === '' ? './' : $lastSegment);
169        }
170
171        return $emptyPathUri;
172    }
173
174    private static function getRelativePath(UriInterface $base, UriInterface $target): string
175    {
176        $sourceSegments = explode('/', $base->getPath());
177        $targetSegments = explode('/', $target->getPath());
178        array_pop($sourceSegments);
179        $targetLastSegment = array_pop($targetSegments);
180        foreach ($sourceSegments as $i => $segment) {
181            if (isset($targetSegments[$i]) && $segment === $targetSegments[$i]) {
182                unset($sourceSegments[$i], $targetSegments[$i]);
183            } else {
184                break;
185            }
186        }
187        $targetSegments[] = $targetLastSegment;
188        $relativePath = str_repeat('../', count($sourceSegments)).implode('/', $targetSegments);
189
190        // A reference to am empty last segment or an empty first sub-segment must be prefixed with "./".
191        // This also applies to a segment with a colon character (e.g., "file:colon") that cannot be used
192        // as the first segment of a relative-path reference, as it would be mistaken for a scheme name.
193        if ('' === $relativePath || false !== strpos(explode('/', $relativePath, 2)[0], ':')) {
194            $relativePath = "./$relativePath";
195        } elseif ('/' === $relativePath[0]) {
196            if ($base->getAuthority() != '' && $base->getPath() === '') {
197                // In this case an extra slash is added by resolve() automatically. So we must not add one here.
198                $relativePath = ".$relativePath";
199            } else {
200                $relativePath = "./$relativePath";
201            }
202        }
203
204        return $relativePath;
205    }
206
207    private function __construct()
208    {
209        // cannot be instantiated
210    }
211}
212