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<?php |
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declare(strict_types=1); |
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namespace GraphQL\Executor\Promise\Adapter; |
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use Exception; |
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use GraphQL\Utils\Utils; |
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use SplQueue; |
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use Throwable; |
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use function is_object; |
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use function method_exists; |
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/** |
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* Simplistic (yet full-featured) implementation of Promises A+ spec for regular PHP `sync` mode |
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* (using queue to defer promises execution) |
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* |
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* Note: |
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* Library users are not supposed to use SyncPromise class in their resolvers. |
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* Instead they should use GraphQL\Deferred which enforces $executor callback in the constructor. |
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* |
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* Root SyncPromise without explicit $executor will never resolve (actually throw while trying). |
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* The whole point of Deferred is to ensure it never happens and that any resolver creates |
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* at least one $executor to start the promise chain. |
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*/ |
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class SyncPromise |
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{ |
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const PENDING = 'pending'; |
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const FULFILLED = 'fulfilled'; |
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const REJECTED = 'rejected'; |
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/** @var SplQueue */ |
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public static $queue; |
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/** @var string */ |
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public $state = self::PENDING; |
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/** @var mixed */ |
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public $result; |
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/** |
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* Promises created in `then` method of this promise and awaiting for resolution of this promise |
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* |
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* @var mixed[][] |
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*/ |
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private $waiting = []; |
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public static function runQueue() : void |
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{ |
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$q = self::$queue; |
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while ($q !== null && ! $q->isEmpty()) { |
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$task = $q->dequeue(); |
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$task(); |
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} |
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} |
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/** |
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* @param callable() : mixed $executor |
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*/ |
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public function __construct(?callable $executor = null) |
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{ |
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if ($executor === null) { |
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return; |
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} |
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self::getQueue()->enqueue(function () use ($executor) : void { |
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try { |
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$this->resolve($executor()); |
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} catch (Throwable $e) { |
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$this->reject($e); |
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} |
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}); |
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} |
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public function resolve($value) : self |
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{ |
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switch ($this->state) { |
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case self::PENDING: |
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if ($value === $this) { |
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throw new Exception('Cannot resolve promise with self'); |
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} |
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if (is_object($value) && method_exists($value, 'then')) { |
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$value->then( |
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function ($resolvedValue) : void { |
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$this->resolve($resolvedValue); |
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}, |
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function ($reason) : void { |
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$this->reject($reason); |
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} |
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); |
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return $this; |
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} |
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$this->state = self::FULFILLED; |
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$this->result = $value; |
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$this->enqueueWaitingPromises(); |
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break; |
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case self::FULFILLED: |
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if ($this->result !== $value) { |
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throw new Exception('Cannot change value of fulfilled promise'); |
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} |
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break; |
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case self::REJECTED: |
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throw new Exception('Cannot resolve rejected promise'); |
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} |
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return $this; |
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} |
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public function reject($reason) : self |
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{ |
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if (! $reason instanceof Throwable) { |
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throw new Exception('SyncPromise::reject() has to be called with an instance of \Throwable'); |
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} |
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switch ($this->state) { |
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case self::PENDING: |
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$this->state = self::REJECTED; |
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$this->result = $reason; |
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$this->enqueueWaitingPromises(); |
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break; |
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case self::REJECTED: |
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if ($reason !== $this->result) { |
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throw new Exception('Cannot change rejection reason'); |
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} |
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break; |
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case self::FULFILLED: |
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throw new Exception('Cannot reject fulfilled promise'); |
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} |
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return $this; |
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} |
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private function enqueueWaitingPromises() : void |
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{ |
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Utils::invariant( |
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$this->state !== self::PENDING, |
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'Cannot enqueue derived promises when parent is still pending' |
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); |
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foreach ($this->waiting as $descriptor) { |
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self::getQueue()->enqueue(function () use ($descriptor) : void { |
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/** @var self $promise */ |
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[$promise, $onFulfilled, $onRejected] = $descriptor; |
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if ($this->state === self::FULFILLED) { |
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try { |
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$promise->resolve($onFulfilled === null ? $this->result : $onFulfilled($this->result)); |
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} catch (Throwable $e) { |
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$promise->reject($e); |
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} |
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} elseif ($this->state === self::REJECTED) { |
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try { |
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if ($onRejected === null) { |
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$promise->reject($this->result); |
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} else { |
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$promise->resolve($onRejected($this->result)); |
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} |
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} catch (Throwable $e) { |
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$promise->reject($e); |
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} |
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} |
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}); |
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} |
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$this->waiting = []; |
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} |
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public static function getQueue() : SplQueue |
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{ |
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return self::$queue ?: self::$queue = new SplQueue(); |
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} |
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/** |
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* @param callable(mixed) : mixed $onFulfilled |
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* @param callable(Throwable) : mixed $onRejected |
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*/ |
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public function then(?callable $onFulfilled = null, ?callable $onRejected = null) : self |
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{ |
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if ($this->state === self::REJECTED && $onRejected === null) { |
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return $this; |
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} |
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if ($this->state === self::FULFILLED && $onFulfilled === null) { |
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return $this; |
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} |
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$tmp = new self(); |
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$this->waiting[] = [$tmp, $onFulfilled, $onRejected]; |
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if ($this->state !== self::PENDING) { |
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$this->enqueueWaitingPromises(); |
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} |
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return $tmp; |
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} |
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/** |
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* @param callable(Throwable) : mixed $onRejected |
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*/ |
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public function catch(callable $onRejected) : self |
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{ |
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return $this->then(null, $onRejected); |
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} |
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} |
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