123 lines
3.7 KiB
PHP
123 lines
3.7 KiB
PHP
<?php
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declare(strict_types=1);
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namespace Sabre\Event;
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use Generator;
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/**
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* Turn asynchronous promise-based code into something that looks synchronous
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* again, through the use of generators.
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*
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* Example without coroutines:
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*
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* $promise = $httpClient->request('GET', '/foo');
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* $promise->then(function($value) {
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*
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* return $httpClient->request('DELETE','/foo');
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*
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* })->then(function($value) {
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*
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* return $httpClient->request('PUT', '/foo');
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*
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* })->error(function($reason) {
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*
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* echo "Failed because: $reason\n";
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*
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* });
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*
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* Example with coroutines:
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*
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* coroutine(function() {
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*
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* try {
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* yield $httpClient->request('GET', '/foo');
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* yield $httpClient->request('DELETE', /foo');
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* yield $httpClient->request('PUT', '/foo');
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* } catch(\Throwable $reason) {
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* echo "Failed because: $reason\n";
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* }
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*
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* });
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*
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* @psalm-template TReturn
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*
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* @psalm-param callable():\Generator<mixed, mixed, mixed, TReturn> $gen
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*
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* @psalm-return Promise<TReturn>
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*
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* @copyright Copyright (C) fruux GmbH (https://fruux.com/)
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* @author Evert Pot (http://evertpot.com/)
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* @license http://sabre.io/license/ Modified BSD License
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*/
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function coroutine(callable $gen): Promise
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{
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$generator = $gen();
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if (!$generator instanceof \Generator) {
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throw new \InvalidArgumentException('You must pass a generator function');
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}
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// This is the value we're returning.
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$promise = new Promise();
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/**
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* So tempted to use the mythical y-combinator here, but it's not needed in
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* PHP.
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*/
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$advanceGenerator = function () use (&$advanceGenerator, $generator, $promise) {
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while ($generator->valid()) {
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$yieldedValue = $generator->current();
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if ($yieldedValue instanceof Promise) {
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$yieldedValue->then(
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function ($value) use ($generator, &$advanceGenerator) {
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$generator->send($value);
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$advanceGenerator();
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},
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function (\Throwable $reason) use ($generator, $advanceGenerator) {
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$generator->throw($reason);
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$advanceGenerator();
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}
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)->otherwise(function (\Throwable $reason) use ($promise) {
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// This error handler would be called, if something in the
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// generator throws an exception, and it's not caught
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// locally.
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$promise->reject($reason);
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});
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// We need to break out of the loop, because $advanceGenerator
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// will be called asynchronously when the promise has a result.
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break;
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} else {
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// If the value was not a promise, we'll just let it pass through.
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$generator->send($yieldedValue);
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}
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}
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// If the generator is at the end, and we didn't run into an exception,
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// We're grabbing the "return" value and fulfilling our top-level
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// promise with its value.
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if (!$generator->valid() && Promise::PENDING === $promise->state) {
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$returnValue = $generator->getReturn();
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// The return value is a promise.
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if ($returnValue instanceof Promise) {
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$returnValue->then(function ($value) use ($promise) {
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$promise->fulfill($value);
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}, function (\Throwable $reason) use ($promise) {
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$promise->reject($reason);
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});
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} else {
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$promise->fulfill($returnValue);
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}
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}
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};
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try {
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$advanceGenerator();
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} catch (\Throwable $e) {
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$promise->reject($e);
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}
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return $promise;
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}
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