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[WebLink] Add class to parse Link headers from HTTP responses
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‎CHANGELOG.md‎

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CHANGELOG
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=========
33

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7.4
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---
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* Add `HttpHeaderParser` to read `Link` headers from HTTP responses
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* Make `HttpHeaderSerializer` non-final
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4.4.0
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-----
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‎HttpHeaderParser.php‎

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<?php
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/*
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* This file is part of the Symfony package.
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*
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* (c) Fabien Potencier <fabien@symfony.com>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Symfony\Component\WebLink;
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use Psr\Link\EvolvableLinkProviderInterface;
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/**
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* Parse a list of HTTP Link headers into a list of Link instances.
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*
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* @see https://tools.ietf.org/html/rfc5988
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*
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* @author Jérôme Tamarelle <jerome@tamarelle.net>
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*/
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class HttpHeaderParser
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{
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// Regex to match each link entry: <...>; param1=...; param2=...
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private const LINK_PATTERN = '/<([^>]*)>\s*((?:\s*;\s*[a-zA-Z0-9\-_]+(?:\s*=\s*(?:"(?:[^"\\\\]|\\\\.)*"|[^";,\s]+))?)*)/';
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// Regex to match parameters: ; key[=value]
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private const PARAM_PATTERN = '/;\s*([a-zA-Z0-9\-_]+)(?:\s*=\s*(?:"((?:[^"\\\\]|\\\\.)*)"|([^";,\s]+)))?/';
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/**
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* @param string|string[] $headers Value of the "Link" HTTP header
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*/
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public function parse(string|array $headers): EvolvableLinkProviderInterface
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{
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if (is_array($headers)) {
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$headers = implode(', ', $headers);
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}
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$links = new GenericLinkProvider();
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if (!preg_match_all(self::LINK_PATTERN, $headers, $matches, \PREG_SET_ORDER)) {
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return $links;
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}
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foreach ($matches as $match) {
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$href = $match[1];
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$attributesString = $match[2];
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$attributes = [];
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if (preg_match_all(self::PARAM_PATTERN, $attributesString, $attributeMatches, \PREG_SET_ORDER)) {
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$rels = null;
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foreach ($attributeMatches as $pm) {
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$key = $pm[1];
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$value = match (true) {
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// Quoted value, unescape quotes
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($pm[2] ?? '') !== '' => stripcslashes($pm[2]),
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($pm[3] ?? '') !== '' => $pm[3],
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// No value
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default => true,
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};
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if ($key === 'rel') {
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// Only the first occurrence of the "rel" attribute is read
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$rels ??= $value === true ? [] : preg_split('/\s+/', $value, 0, \PREG_SPLIT_NO_EMPTY);
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} elseif (is_array($attributes[$key] ?? null)) {
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$attributes[$key][] = $value;
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} elseif (isset($attributes[$key])) {
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$attributes[$key] = [$attributes[$key], $value];
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} else {
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$attributes[$key] = $value;
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}
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}
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}
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$link = new Link(null, $href);
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foreach ($rels ?? [] as $rel) {
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$link = $link->withRel($rel);
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}
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foreach ($attributes as $k => $v) {
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$link = $link->withAttribute($k, $v);
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}
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$links = $links->withLink($link);
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}
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return $links;
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}
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}

‎HttpHeaderSerializer.php‎

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*
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* @author Kévin Dunglas <dunglas@gmail.com>
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*/
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final class HttpHeaderSerializer
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class HttpHeaderSerializer
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{
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/**
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* Builds the value of the "Link" HTTP header.

‎Link.php‎

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@@ -153,7 +153,7 @@ class Link implements EvolvableLinkInterface
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private array $rel = [];
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/**
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* @var array<string, string|bool|string[]>
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* @var array<string, scalar|\Stringable|list<scalar|\Stringable>>
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*/
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private array $attributes = [];
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return array_values($this->rel);
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}
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/**
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* Returns a list of attributes that describe the target URI.
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*
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* @return array<string, scalar|\Stringable|list<scalar|\Stringable>>
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*/
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public function getAttributes(): array
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{
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return $this->attributes;
@@ -210,6 +215,14 @@ public function withoutRel(string $rel): static
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return $that;
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}
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/**
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* Returns an instance with the specified attribute added.
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*
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* If the specified attribute is already present, it will be overwritten
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* with the new value.
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*
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* @param scalar|\Stringable|list<scalar|\Stringable> $value
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*/
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public function withAttribute(string $attribute, string|\Stringable|int|float|bool|array $value): static
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{
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$that = clone $this;

‎Tests/HttpHeaderParserTest.php‎

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<?php
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/*
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* This file is part of the Symfony package.
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*
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* (c) Fabien Potencier <fabien@symfony.com>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Symfony\Component\WebLink\Tests;
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use PHPUnit\Framework\Attributes\DataProvider;
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use PHPUnit\Framework\TestCase;
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use Symfony\Component\WebLink\HttpHeaderParser;
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class HttpHeaderParserTest extends TestCase
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{
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public function testParse()
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{
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$parser = new HttpHeaderParser();
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$header = [
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'</1>; rel="prerender",</2>; rel="dns-prefetch"; pr="0.7",</3>; rel="preload"; as="script"',
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'</4>; rel="preload"; as="image"; nopush,</5>; rel="alternate next"; hreflang="fr"; hreflang="de"; title="Hello"'
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];
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$provider = $parser->parse($header);
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$links = $provider->getLinks();
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self::assertCount(5, $links);
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self::assertSame(['prerender'], $links[0]->getRels());
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self::assertSame('/1', $links[0]->getHref());
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self::assertSame([], $links[0]->getAttributes());
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self::assertSame(['dns-prefetch'], $links[1]->getRels());
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self::assertSame('/2', $links[1]->getHref());
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self::assertSame(['pr' => '0.7'], $links[1]->getAttributes());
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self::assertSame(['preload'], $links[2]->getRels());
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self::assertSame('/3', $links[2]->getHref());
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self::assertSame(['as' => 'script'], $links[2]->getAttributes());
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self::assertSame(['preload'], $links[3]->getRels());
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self::assertSame('/4', $links[3]->getHref());
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self::assertSame(['as' => 'image', 'nopush' => true], $links[3]->getAttributes());
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self::assertSame(['alternate', 'next'], $links[4]->getRels());
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self::assertSame('/5', $links[4]->getHref());
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self::assertSame(['hreflang' => ['fr', 'de'], 'title' => 'Hello'], $links[4]->getAttributes());
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}
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public function testParseEmpty()
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{
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$parser = new HttpHeaderParser();
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$provider = $parser->parse('');
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self::assertCount(0, $provider->getLinks());
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}
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/** @dataProvider provideHeaderParsingCases */
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#[DataProvider('provideHeaderParsingCases')]
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public function testParseVariousAttributes(string $header, array $expectedRels, array $expectedAttributes)
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{
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$parser = new HttpHeaderParser();
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$links = $parser->parse($header)->getLinks();
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self::assertCount(1, $links);
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self::assertSame('/foo', $links[0]->getHref());
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self::assertSame($expectedRels, $links[0]->getRels());
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self::assertSame($expectedAttributes, $links[0]->getAttributes());
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}
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public static function provideHeaderParsingCases()
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{
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yield 'double_quotes_in_attribute_value' => [
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'</foo>; rel="alternate"; title="\"escape me\" \"already escaped\" \"\"\""',
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['alternate'],
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['title' => '"escape me" "already escaped" """'],
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];
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yield 'unquoted_attribute_value' => [
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'</foo>; rel=alternate; type=text/html',
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['alternate'],
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['type' => 'text/html'],
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];
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yield 'attribute_with_punctuation' => [
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'</foo>; rel="alternate"; title=">; hello, world; test:case"',
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['alternate'],
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['title' => '>; hello, world; test:case'],
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];
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yield 'no_rel' => [
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'</foo>; type=text/html',
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[],
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['type' => 'text/html'],
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];
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yield 'empty_rel' => [
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'</foo>; rel',
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[],
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[],
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];
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yield 'multiple_rel_attributes_get_first' => [
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'</foo>; rel="alternate" rel="next"',
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['alternate'],
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[],
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];
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}
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}

‎Tests/LinkTest.php‎

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->withAttribute('me', 'you')
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;
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$this->assertEquals('http://www.google.com', $link->getHref());
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$this->assertSame('http://www.google.com', $link->getHref());
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$this->assertContains('next', $link->getRels());
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$this->assertArrayHasKey('me', $link->getAttributes());
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$this->assertEquals('you', $link->getAttributes()['me']);
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$this->assertSame('you', $link->getAttributes()['me']);
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}
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public function testCanRemoveValues()
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$link = $link->withoutAttribute('me')
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->withoutRel('next');
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$this->assertEquals('http://www.google.com', $link->getHref());
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$this->assertSame('http://www.google.com', $link->getHref());
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$this->assertFalse(\in_array('next', $link->getRels(), true));
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$this->assertArrayNotHasKey('me', $link->getAttributes());
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}
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{
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$link = new Link('next', 'http://www.google.com');
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$this->assertEquals('http://www.google.com', $link->getHref());
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$this->assertSame('http://www.google.com', $link->getHref());
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$this->assertContains('next', $link->getRels());
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}
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