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<?php
declare(strict_types=1);
namespace GuzzleHttp\Promise;
/**
* Promises/A+ implementation that avoids recursion when possible.
*
* @see https://promisesaplus.com/
*
* @final
*/
class Promise implements PromiseInterface
{
private $state = self::PENDING;
private $result;
private $cancelFn;
private $waitFn;
private $waitList;
private $handlers = [];
/**
* @param callable $waitFn Fn that when invoked resolves the promise.
* @param callable $cancelFn Fn that when invoked cancels the promise.
*/
public function __construct(
?callable $waitFn = null,
?callable $cancelFn = null
) {
$this->waitFn = $waitFn;
$this->cancelFn = $cancelFn;
}
public function then(
?callable $onFulfilled = null,
?callable $onRejected = null
): PromiseInterface {
if ($this->state === self::PENDING) {
$p = new Promise(null, [$this, 'cancel']);
$this->handlers[] = [$p, $onFulfilled, $onRejected];
$p->waitList = $this->waitList;
$p->waitList[] = $this;
return $p;
}
// Return a fulfilled promise and immediately invoke any callbacks.
if ($this->state === self::FULFILLED) {
$promise = Create::promiseFor($this->result);
return $onFulfilled ? $promise->then($onFulfilled) : $promise;
}
// It's either cancelled or rejected, so return a rejected promise
// and immediately invoke any callbacks.
$rejection = Create::rejectionFor($this->result);
return $onRejected ? $rejection->then(null, $onRejected) : $rejection;
}
public function otherwise(callable $onRejected): PromiseInterface
{
return $this->then(null, $onRejected);
}
public function wait(bool $unwrap = true)
{
$this->waitIfPending();
if ($this->result instanceof PromiseInterface) {
return $this->result->wait($unwrap);
}
if ($unwrap) {
if ($this->state === self::FULFILLED) {
return $this->result;
}
// It's rejected so "unwrap" and throw an exception.
throw Create::exceptionFor($this->result);
}
}
public function getState(): string
{
return $this->state;
}
public function cancel(): void
{
if ($this->state !== self::PENDING) {
return;
}
$this->waitFn = $this->waitList = null;
if ($this->cancelFn) {
$fn = $this->cancelFn;
$this->cancelFn = null;
try {
$fn();
} catch (\Throwable $e) {
$this->reject($e);
}
}
// Reject the promise only if it wasn't rejected in a then callback.
/** @psalm-suppress RedundantCondition */
if ($this->state === self::PENDING) {
$this->reject(new CancellationException('Promise has been cancelled'));
}
}
public function resolve($value): void
{
$this->settle(self::FULFILLED, $value);
}
public function reject($reason): void
{
$this->settle(self::REJECTED, $reason);
}
private function settle(string $state, $value): void
{
if ($this->state !== self::PENDING) {
// Ignore calls with the same resolution.
if ($state === $this->state && $value === $this->result) {
return;
}
throw $this->state === $state
? new \LogicException("The promise is already {$state}.")
: new \LogicException("Cannot change a {$this->state} promise to {$state}");
}
if ($value === $this) {
throw new \LogicException('Cannot fulfill or reject a promise with itself');
}
// Clear out the state of the promise but stash the handlers.
$this->state = $state;
$this->result = $value;
$handlers = $this->handlers;
$this->handlers = null;
$this->waitList = $this->waitFn = null;
$this->cancelFn = null;
if (!$handlers) {
return;
}
// If the value was not a settled promise or a thenable, then resolve
// it in the task queue using the correct ID.
if (!is_object($value) || !method_exists($value, 'then')) {
$id = $state === self::FULFILLED ? 1 : 2;
// It's a success, so resolve the handlers in the queue.
Utils::queue()->add(static function () use ($id, $value, $handlers): void {
foreach ($handlers as $handler) {
self::callHandler($id, $value, $handler);
}
});
} elseif ($value instanceof Promise && Is::pending($value)) {
// We can just merge our handlers onto the next promise.
$value->handlers = array_merge($value->handlers, $handlers);
} else {
// Resolve the handlers when the forwarded promise is resolved.
$value->then(
static function ($value) use ($handlers): void {
foreach ($handlers as $handler) {
self::callHandler(1, $value, $handler);
}
},
static function ($reason) use ($handlers): void {
foreach ($handlers as $handler) {
self::callHandler(2, $reason, $handler);
}
}
);
}
}
/**
* Call a stack of handlers using a specific callback index and value.
*
* @param int $index 1 (resolve) or 2 (reject).
* @param mixed $value Value to pass to the callback.
* @param array $handler Array of handler data (promise and callbacks).
*/
private static function callHandler(int $index, $value, array $handler): void
{
/** @var PromiseInterface $promise */
$promise = $handler[0];
// The promise may have been cancelled or resolved before placing
// this thunk in the queue.
if (Is::settled($promise)) {
return;
}
try {
if (isset($handler[$index])) {
/*
* If $f throws an exception, then $handler will be in the exception
* stack trace. Since $handler contains a reference to the callable
* itself we get a circular reference. We clear the $handler
* here to avoid that memory leak.
*/
$f = $handler[$index];
unset($handler);
$promise->resolve($f($value));
} elseif ($index === 1) {
// Forward resolution values as-is.
$promise->resolve($value);
} else {
// Forward rejections down the chain.
$promise->reject($value);
}
} catch (\Throwable $reason) {
$promise->reject($reason);
}
}
private function waitIfPending(): void
{
if ($this->state !== self::PENDING) {
return;
} elseif ($this->waitFn) {
$this->invokeWaitFn();
} elseif ($this->waitList) {
$this->invokeWaitList();
} else {
// If there's no wait function, then reject the promise.
$this->reject('Cannot wait on a promise that has '
.'no internal wait function. You must provide a wait '
.'function when constructing the promise to be able to '
.'wait on a promise.');
}
Utils::queue()->run();
/** @psalm-suppress RedundantCondition */
if ($this->state === self::PENDING) {
$this->reject('Invoking the wait callback did not resolve the promise');
}
}
private function invokeWaitFn(): void
{
try {
$wfn = $this->waitFn;
$this->waitFn = null;
$wfn(true);
} catch (\Throwable $reason) {
if ($this->state === self::PENDING) {
// The promise has not been resolved yet, so reject the promise
// with the exception.
$this->reject($reason);
} else {
// The promise was already resolved, so there's a problem in
// the application.
throw $reason;
}
}
}
private function invokeWaitList(): void
{
$waitList = $this->waitList;
$this->waitList = null;
foreach ($waitList as $result) {
do {
$result->waitIfPending();
$result = $result->result;
} while ($result instanceof Promise);
if ($result instanceof PromiseInterface) {
$result->wait(false);
}
}
}
}
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