namespace GuzzleHttp\Promise;
* Promises/A+ implementation that avoids recursion when possible.
* @link https://promisesaplus.com/
class Promise implements PromiseInterface
private $state = self::PENDING;
* @param callable $waitFn Fn that when invoked resolves the promise.
* @param callable $cancelFn Fn that when invoked cancels the promise.
public function __construct(
callable $cancelFn = null
$this->cancelFn = $cancelFn;
callable $onFulfilled = null,
callable $onRejected = null
if ($this->state === self::PENDING) {
$p = new Promise(null, [$this, 'cancel']);
$this->handlers[] = [$p, $onFulfilled, $onRejected];
$p->waitList = $this->waitList;
// Return a fulfilled promise and immediately invoke any callbacks.
if ($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)
return $this->then(null, $onRejected);
public function wait($unwrap = true)
if ($this->result instanceof PromiseInterface) {
return $this->result->wait($unwrap);
if ($this->state === self::FULFILLED) {
// It's rejected so "unwrap" and throw an exception.
throw Create::exceptionFor($this->result);
public function getState()
if ($this->state !== self::PENDING) {
$this->waitFn = $this->waitList = null;
} catch (\Throwable $e) {
} catch (\Exception $e) {
// Reject the promise only if it wasn't rejected in a then callback.
/** @psalm-suppress RedundantCondition */
if ($this->state === self::PENDING) {
$this->reject(new CancellationException('Promise has been cancelled'));
public function resolve($value)
$this->settle(self::FULFILLED, $value);
public function reject($reason)
$this->settle(self::REJECTED, $reason);
private function settle($state, $value)
if ($this->state !== self::PENDING) {
// Ignore calls with the same resolution.
if ($state === $this->state && $value === $this->result) {
throw $this->state === $state
? new \LogicException("The promise is already {$state}.")
: new \LogicException("Cannot change a {$this->state} promise to {$state}");
throw new \LogicException('Cannot fulfill or reject a promise with itself');
// Clear out the state of the promise but stash the handlers.
$handlers = $this->handlers;
$this->waitList = $this->waitFn = null;
// If the value was not a settled promise or a thenable, then resolve
// it in the task queue using the correct ID.
if (!is_object($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, $handlers) {
foreach ($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, $handlers);
// Resolve the handlers when the forwarded promise is resolved.
static function ($value) use ($handlers) {
foreach ($handlers as $handler) {
self::callHandler(1, $value, $handler);
static function ($reason) use ($handlers) {
foreach ($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 $handler Array of handler data (promise and callbacks).
private static function callHandler($index, $value, array $handler)
/** @var PromiseInterface $promise */
// The promise may have been cancelled or resolved before placing
// this thunk in the queue.
if (Is::settled($promise)) {
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.
$promise->resolve($f($value));
} elseif ($index === 1) {
// Forward resolution values as-is.
$promise->resolve($value);
// Forward rejections down the chain.
$promise->reject($value);
} catch (\Throwable $reason) {
$promise->reject($reason);
} catch (\Exception $reason) {
$promise->reject($reason);
private function waitIfPending()
if ($this->state !== self::PENDING) {
} elseif ($this->waitFn) {
} elseif ($this->waitList) {
// If there's no wait function, then reject the promise.
$this->reject('Cannot wait on a promise that has '
. 'no internal wait function. You must provide a wait '
. 'function when constructing the promise to be able to '
/** @psalm-suppress RedundantCondition */
if ($this->state === self::PENDING) {
$this->reject('Invoking the wait callback did not resolve the promise');
private function invokeWaitFn()
} catch (\Exception $reason) {
if ($this->state === self::PENDING) {
// The promise has not been resolved yet, so reject the promise
// The promise was already resolved, so there's a problem in
private function invokeWaitList()
$waitList = $this->waitList;
foreach ($waitList as $result) {
$result->waitIfPending();
$result = $result->result;
} while ($result instanceof Promise);
if ($result instanceof PromiseInterface) {
It is recommended that you Edit text format, this type of Fix handles quite a lot in one request
