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<?php
/*
* Copyright 2017 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
namespace MongoDB;
use Iterator;
use MongoDB\Driver\CursorId;
use MongoDB\Driver\Exception\ConnectionException;
use MongoDB\Driver\Exception\RuntimeException;
use MongoDB\Driver\Exception\ServerException;
use MongoDB\Exception\ResumeTokenException;
use MongoDB\Model\ChangeStreamIterator;
use function call_user_func;
use function in_array;
/**
* Iterator for a change stream.
*
* @api
* @see \MongoDB\Collection::watch()
* @see http://docs.mongodb.org/manual/reference/command/changeStream/
*/
class ChangeStream implements Iterator
{
/**
* @deprecated 1.4
* @todo Remove this in 2.0 (see: PHPLIB-360)
*/
const CURSOR_NOT_FOUND = 43;
/** @var array */
private static $nonResumableErrorCodes = [
136, // CappedPositionLost
237, // CursorKilled
11601, // Interrupted
];
/** @var callable */
private $resumeCallable;
/** @var ChangeStreamIterator */
private $iterator;
/** @var integer */
private $key = 0;
/**
* Whether the change stream has advanced to its first result. This is used
* to determine whether $key should be incremented after an iteration event.
*
* @var boolean
*/
private $hasAdvanced = false;
/**
* @internal
* @param ChangeStreamIterator $iterator
* @param callable $resumeCallable
*/
public function __construct(ChangeStreamIterator $iterator, callable $resumeCallable)
{
$this->iterator = $iterator;
$this->resumeCallable = $resumeCallable;
}
/**
* @see http://php.net/iterator.current
* @return mixed
*/
public function current()
{
return $this->iterator->current();
}
/**
* @return CursorId
*/
public function getCursorId()
{
return $this->iterator->getInnerIterator()->getId();
}
/**
* Returns the resume token for the iterator's current position.
*
* Null may be returned if no change documents have been iterated and the
* server did not include a postBatchResumeToken in its aggregate or getMore
* command response.
*
* @return array|object|null
*/
public function getResumeToken()
{
return $this->iterator->getResumeToken();
}
/**
* @see http://php.net/iterator.key
* @return mixed
*/
public function key()
{
if ($this->valid()) {
return $this->key;
}
return null;
}
/**
* @see http://php.net/iterator.next
* @return void
* @throws ResumeTokenException
*/
public function next()
{
try {
$this->iterator->next();
$this->onIteration($this->hasAdvanced);
} catch (RuntimeException $e) {
$this->resumeOrThrow($e);
}
}
/**
* @see http://php.net/iterator.rewind
* @return void
* @throws ResumeTokenException
*/
public function rewind()
{
try {
$this->iterator->rewind();
/* Unlike next() and resume(), the decision to increment the key
* does not depend on whether the change stream has advanced. This
* ensures that multiple calls to rewind() do not alter state. */
$this->onIteration(false);
} catch (RuntimeException $e) {
$this->resumeOrThrow($e);
}
}
/**
* @see http://php.net/iterator.valid
* @return boolean
*/
public function valid()
{
return $this->iterator->valid();
}
/**
* Determines if an exception is a resumable error.
*
* @see https://github.com/mongodb/specifications/blob/master/source/change-streams/change-streams.rst#resumable-error
* @param RuntimeException $exception
* @return boolean
*/
private function isResumableError(RuntimeException $exception)
{
if ($exception instanceof ConnectionException) {
return true;
}
if (! $exception instanceof ServerException) {
return false;
}
if ($exception->hasErrorLabel('NonResumableChangeStreamError')) {
return false;
}
if (in_array($exception->getCode(), self::$nonResumableErrorCodes)) {
return false;
}
return true;
}
/**
* Perform housekeeping after an iteration event.
*
* @param boolean $incrementKey Increment $key if there is a current result
* @throws ResumeTokenException
*/
private function onIteration($incrementKey)
{
/* If the cursorId is 0, the server has invalidated the cursor and we
* will never perform another getMore nor need to resume since any
* remaining results (up to and including the invalidate event) will
* have been received in the last response. Therefore, we can unset the
* resumeCallable. This will free any reference to Watch as well as the
* only reference to any implicit session created therein. */
if ((string) $this->getCursorId() === '0') {
$this->resumeCallable = null;
}
/* Return early if there is not a current result. Avoid any attempt to
* increment the iterator's key. */
if (! $this->valid()) {
return;
}
if ($incrementKey) {
$this->key++;
}
$this->hasAdvanced = true;
}
/**
* Recreates the ChangeStreamIterator after a resumable server error.
*
* @return void
*/
private function resume()
{
$this->iterator = call_user_func($this->resumeCallable, $this->getResumeToken(), $this->hasAdvanced);
$this->iterator->rewind();
$this->onIteration($this->hasAdvanced);
}
/**
* Either resumes after a resumable error or re-throws the exception.
*
* @param RuntimeException $exception
* @throws RuntimeException
*/
private function resumeOrThrow(RuntimeException $exception)
{
if ($this->isResumableError($exception)) {
$this->resume();
return;
}
throw $exception;
}
}