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<?php |
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declare(strict_types=1); |
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namespace Usox\LanguageNegotiator; |
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use Psr\Http\Message\ResponseInterface; |
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use Psr\Http\Message\ServerRequestInterface; |
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use Psr\Http\Server\RequestHandlerInterface; |
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/** |
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* Negotiate the http client language |
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* |
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* @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language |
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*/ |
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final class LanguageNegotiator implements LanguageNegotiatorInterface |
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{ |
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/** @var string Public name of the psr server request attribute */ |
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public const REQUEST_ATTRIBUTE_NAME = 'negotiated-request-language'; |
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/** @var array<string> List of allowed accept-language header names */ |
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private const ACCEPT_LANGUAGE_HEADERS = ['accept-language', 'http_accept_language']; |
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/** |
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* @param array<string> $supportedLanguages List of language codes you application supports |
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* @param string $fallbackLanguage language code of the fallback language if negotiation fails |
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* @param null|array<string, mixed> $serverRequest Optional server request input ($_SERVER) |
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* @param string $attributeName Optional alternate name of the server request attribute for the negotiated language |
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*/ |
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public function __construct( |
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private array $supportedLanguages, |
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private string $fallbackLanguage = 'en', |
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private ?array $serverRequest = null, |
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private string $attributeName = self::REQUEST_ATTRIBUTE_NAME |
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) { |
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} |
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/** |
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* Negotiates the client language |
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* If the serverRequest was set by constructor, the parameter can be omitted |
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* |
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* @param array<string, mixed>|null $request Optional dict of server request variables; overwrites serverRequest defined in constructor |
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* |
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* @return string language code of the negotiated client language |
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*/ |
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public function negotiate( |
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?array $request = null |
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): string { |
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// return fallback if both, headerLine and serverRequest is not set |
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$requestHeaders = $request ?? $this->serverRequest ?? null; |
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if ($requestHeaders === null) { |
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return $this->fallbackLanguage; |
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} |
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$headerValue = $this->normalizeAcceptLanguageString($requestHeaders); |
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// return the fallback if the header is not usable |
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if ($headerValue === null) { |
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return $this->fallbackLanguage; |
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} |
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// split up the header to determine a list of all accepted languages |
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$acceptedLanguages = array_reduce( |
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explode(',', $headerValue), |
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static function (array $result, string $line): array { |
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[$language, $priority] = array_merge(explode(';q=', $line), [1]); |
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$result[trim((string) $language)] = (float) $priority; |
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return $result; |
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}, |
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[] |
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); |
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// sort by value which is actually the language priority defined within the client |
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arsort($acceptedLanguages); |
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// determine the intersection between supported and available languages |
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$result = array_intersect_key( |
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$acceptedLanguages, |
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array_flip($this->supportedLanguages), |
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); |
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// use the set fallback language if negotiation fails |
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if ($result === []) { |
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return $this->fallbackLanguage; |
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} |
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// returns the first element (the one having the highest priority) |
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return key($result); |
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} |
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/** |
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* Enriches the ServerRequest with the negotiated client language |
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*/ |
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public function process( |
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ServerRequestInterface $request, |
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RequestHandlerInterface $handler |
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): ResponseInterface { |
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$request = $request->withAttribute( |
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$this->attributeName, |
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$this->negotiate($request->getHeaders()) |
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); |
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return $handler->handle($request); |
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} |
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/** |
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* @param array<string, mixed> $headers |
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*/ |
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private function normalizeAcceptLanguageString(array $headers): ?string { |
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$headerValue = null; |
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// convert all keys to lowercase - just in case |
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$headers = array_change_key_case($headers); |
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// lookup all accepted header values |
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foreach (self::ACCEPT_LANGUAGE_HEADERS as $headerName) { |
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$headerValue = $headers[$headerName] ?? null; |
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if ($headerValue !== null) { |
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break; |
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} |
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} |
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// maybe something goes wrong and we end up with some other scalar values in here - jest ensure, it's a string |
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if (!is_string($headerValue)) { |
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return null; |
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} |
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7 |
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return strtolower($headerValue); |
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} |
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} |
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usox /
language-negotiator
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