/**
* Turn asynchronous promise-based code into something that looks synchronous
* again, through the use of generators.
*
* Example without coroutines:
*
* $promise = $httpClient->request('GET', '/foo');
* $promise->then(function($value) {
*
* return $httpClient->request('DELETE','/foo');
*
* })->then(function($value) {
*
* return $httpClient->request('PUT', '/foo');
*
* })->error(function($reason) {
*
* echo "Failed because: $reason\n";
*
* });
*
* Example with coroutines:
*
* coroutine(function() {
*
* try {
* yield $httpClient->request('GET', '/foo');
* yield $httpClient->request('DELETE', /foo');
* yield $httpClient->request('PUT', '/foo');
* } catch(\Exception $reason) {
* echo "Failed because: $reason\n";
* }
*
* });
*
* @copyright Copyright (C) 2013-2015 fruux GmbH. All rights reserved.
* @author Evert Pot (http://evertpot.com/)
* @license http://sabre.io/license/ Modified BSD License
*/
function coroutine(callable $gen)
{
$generator = $gen();
if (!$generator instanceof Generator) {
throw new \InvalidArgumentException('You must pass a generator function');
}
// This is the value we're returning.
$promise = new Promise();
$lastYieldResult = null;
/**
* So tempted to use the mythical y-combinator here, but it's not needed in
* PHP.
*/
$advanceGenerator = function () use(&$advanceGenerator, $generator, $promise, &$lastYieldResult) {
while ($generator->valid()) {
$yieldedValue = $generator->current();
if ($yieldedValue instanceof Promise) {
$yieldedValue->then(function ($value) use($generator, &$advanceGenerator, &$lastYieldResult) {
$lastYieldResult = $value;
$generator->send($value);
$advanceGenerator();
}, function ($reason) use($generator, $advanceGenerator) {
if ($reason instanceof Exception) {
$generator->throw($reason);
} elseif (is_scalar($reason)) {
$generator->throw(new Exception($reason));
} else {
$type = is_object($reason) ? get_class($reason) : gettype($reason);
$generator->throw(new Exception('Promise was rejected with reason of type: ' . $type));
}
$advanceGenerator();
})->error(function ($reason) use($promise) {
// This error handler would be called, if something in the
// generator throws an exception, and it's not caught
// locally.
$promise->reject($reason);
});
// We need to break out of the loop, because $advanceGenerator
// will be called asynchronously when the promise has a result.
break;
} else {
// If the value was not a promise, we'll just let it pass through.
$lastYieldResult = $yieldedValue;
$generator->send($yieldedValue);
}
}
// If the generator is at the end, and we didn't run into an exception,
// we can fullfill the promise with the last thing that was yielded to
// us.
if (!$generator->valid() && $promise->state === Promise::PENDING) {
$promise->fulfill($lastYieldResult);
}
};
try {
$advanceGenerator();
} catch (Exception $e) {
$promise->reject($e);
}
return $promise;
}
/**
* This method is used to call either an onFulfilled or onRejected callback.
*
* This method makes sure that the result of these callbacks are handled
* correctly, and any chained promises are also correctly fulfilled or
* rejected.
*
* @param Promise $subPromise
* @param callable $callBack
* @return void
*/
private function invokeCallback(Promise $subPromise, callable $callBack = null)
{
// We use 'nextTick' to ensure that the event handlers are always
// triggered outside of the calling stack in which they were originally
// passed to 'then'.
//
// This makes the order of execution more predictable.
Loop\nextTick(function () use($callBack, $subPromise) {
if (is_callable($callBack)) {
try {
$result = $callBack($this->value);
if ($result instanceof self) {
// If the callback (onRejected or onFulfilled)
// returned a promise, we only fulfill or reject the
// chained promise once that promise has also been
// resolved.
$result->then([$subPromise, 'fulfill'], [$subPromise, 'reject']);
} else {
// If the callback returned any other value, we
// immediately fulfill the chained promise.
$subPromise->fulfill($result);
}
} catch (Exception $e) {
// If the event handler threw an exception, we need to make sure that
// the chained promise is rejected as well.
$subPromise->reject($e);
}
} else {
if ($this->state === self::FULFILLED) {
$subPromise->fulfill($this->value);
} else {
$subPromise->reject($this->value);
}
}
});
}
$promise->fulfill($value . ", how are ya?");
}, 2);
return $promise;
})->then(function ($value) {
echo "Step 4\n";
// This is the final event handler.
return $value . " you rock!";
})->wait();
echo $result, "\n";
/* Now an identical example, this time with coroutines. */
$result = coroutine(function () {
$promise = new Promise();
/* After 2 seconds we fulfill it */
Loop\setTimeout(function () use($promise) {
echo "Step 1\n";
$promise->fulfill("hello");
}, 2);
$value = (yield $promise);
echo "Step 2\n";
$value .= ' world';
echo "Step 3\n";
$promise = new Promise();
Loop\setTimeout(function () use($promise, $value) {
$promise->fulfill($value . ", how are ya?");
}, 2);
$value = (yield $promise);
echo "Step 4\n";
// This is the final event handler.
(yield $value . " you rock!");
})->wait();
echo $result, "\n";
/**
* Returns a Promise that will reject with the given reason.
*
* @param mixed $reason
* @return Promise
*/
function reject($reason)
{
$promise = new Promise();
$promise->reject($reason);
return $promise;
}
function testWaitRejectedNonScalar()
{
$promise = new Promise();
Loop\nextTick(function () use($promise) {
$promise->reject([]);
});
try {
$promise->wait();
$this->fail('We did not get the expected exception');
} catch (\Exception $e) {
$this->assertInstanceOf('Exception', $e);
$this->assertEquals('Promise was rejected with reason of type: array', $e->getMessage());
}
}
/**
* @expectedException \Exception
*/
function testResolvePromise()
{
$finalValue = 0;
$promise = new Promise();
$promise->reject(new \Exception('uh oh'));
$newPromise = resolve($promise);
$newPromise->wait();
}
/**
* This method is used to call either an onFulfilled or onRejected callback.
*
* This method makes sure that the result of these callbacks are handled
* correctly, and any chained promises are also correctly fulfilled or
* rejected.
*
* @param Promise $subPromise
* @param callable $callBack
* @return void
*/
protected function invokeCallback(Promise $subPromise, callable $callBack = null)
{
if (is_callable($callBack)) {
try {
$result = $callBack($this->value);
if ($result instanceof self) {
$result->then([$subPromise, 'fulfill'], [$subPromise, 'reject']);
} else {
$subPromise->fulfill($result);
}
} catch (Exception $e) {
$subPromise->reject($e);
}
} else {
if ($this->state === self::FULFILLED) {
$subPromise->fulfill($this->value);
} else {
$subPromise->reject($this->value);
}
}
}
