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<?php
/*
* Copyright 2019 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\Model;
use IteratorIterator;
use MongoDB\BSON\Serializable;
use MongoDB\Driver\Cursor;
use MongoDB\Driver\Monitoring\CommandFailedEvent;
use MongoDB\Driver\Monitoring\CommandStartedEvent;
use MongoDB\Driver\Monitoring\CommandSubscriber;
use MongoDB\Driver\Monitoring\CommandSucceededEvent;
use MongoDB\Exception\InvalidArgumentException;
use MongoDB\Exception\ResumeTokenException;
use MongoDB\Exception\UnexpectedValueException;
use function count;
use function is_array;
use function is_integer;
use function is_object;
use function MongoDB\Driver\Monitoring\addSubscriber;
use function MongoDB\Driver\Monitoring\removeSubscriber;
/**
* ChangeStreamIterator wraps a change stream's tailable cursor.
*
* This iterator tracks the size of each batch in order to determine when the
* postBatchResumeToken is applicable. It also ensures that initial calls to
* rewind() do not execute getMore commands.
*
* @internal
*/
class ChangeStreamIterator extends IteratorIterator implements CommandSubscriber
{
/** @var integer */
private $batchPosition = 0;
/** @var integer */
private $batchSize;
/** @var boolean */
private $isRewindNop;
/** @var boolean */
private $isValid = false;
/** @var object|null */
private $postBatchResumeToken;
/** @var array|object|null */
private $resumeToken;
/**
* @internal
* @param Cursor $cursor
* @param integer $firstBatchSize
* @param array|object|null $initialResumeToken
* @param object|null $postBatchResumeToken
*/
public function __construct(Cursor $cursor, $firstBatchSize, $initialResumeToken, $postBatchResumeToken)
{
if (! is_integer($firstBatchSize)) {
throw InvalidArgumentException::invalidType('$firstBatchSize', $firstBatchSize, 'integer');
}
if (isset($initialResumeToken) && ! is_array($initialResumeToken) && ! is_object($initialResumeToken)) {
throw InvalidArgumentException::invalidType('$initialResumeToken', $initialResumeToken, 'array or object');
}
if (isset($postBatchResumeToken) && ! is_object($postBatchResumeToken)) {
throw InvalidArgumentException::invalidType('$postBatchResumeToken', $postBatchResumeToken, 'object');
}
parent::__construct($cursor);
$this->batchSize = $firstBatchSize;
$this->isRewindNop = ($firstBatchSize === 0);
$this->postBatchResumeToken = $postBatchResumeToken;
$this->resumeToken = $initialResumeToken;
}
/** @internal */
final public function commandFailed(CommandFailedEvent $event)
{
}
/** @internal */
final public function commandStarted(CommandStartedEvent $event)
{
if ($event->getCommandName() !== 'getMore') {
return;
}
$this->batchPosition = 0;
$this->batchSize = null;
$this->postBatchResumeToken = null;
}
/** @internal */
final public function commandSucceeded(CommandSucceededEvent $event)
{
if ($event->getCommandName() !== 'getMore') {
return;
}
$reply = $event->getReply();
if (! isset($reply->cursor->nextBatch) || ! is_array($reply->cursor->nextBatch)) {
throw new UnexpectedValueException('getMore command did not return a "cursor.nextBatch" array');
}
$this->batchSize = count($reply->cursor->nextBatch);
if (isset($reply->cursor->postBatchResumeToken) && is_object($reply->cursor->postBatchResumeToken)) {
$this->postBatchResumeToken = $reply->cursor->postBatchResumeToken;
}
}
/**
* @see https://php.net/iteratoriterator.current
* @return mixed
*/
public function current()
{
return $this->isValid ? parent::current() : null;
}
/**
* 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->resumeToken;
}
/**
* @see https://php.net/iteratoriterator.key
* @return mixed
*/
public function key()
{
return $this->isValid ? parent::key() : null;
}
/**
* @see https://php.net/iteratoriterator.rewind
* @return void
*/
public function next()
{
/* Determine if advancing the iterator will execute a getMore command
* (i.e. we are already positioned at the end of the current batch). If
* so, rely on the APM callbacks to reset $batchPosition and update
* $batchSize. Otherwise, we can forgo APM and manually increment
* $batchPosition after calling next(). */
$getMore = $this->isAtEndOfBatch();
if ($getMore) {
addSubscriber($this);
}
try {
parent::next();
$this->onIteration(! $getMore);
} finally {
if ($getMore) {
removeSubscriber($this);
}
}
}
/**
* @see https://php.net/iteratoriterator.rewind
* @return void
*/
public function rewind()
{
if ($this->isRewindNop) {
return;
}
parent::rewind();
$this->onIteration(false);
}
/**
* @see https://php.net/iteratoriterator.valid
* @return boolean
*/
public function valid()
{
return $this->isValid;
}
/**
* Extracts the resume token (i.e. "_id" field) from a change document.
*
* @param array|object $document Change document
* @return array|object
* @throws InvalidArgumentException
* @throws ResumeTokenException if the resume token is not found or invalid
*/
private function extractResumeToken($document)
{
if (! is_array($document) && ! is_object($document)) {
throw InvalidArgumentException::invalidType('$document', $document, 'array or object');
}
if ($document instanceof Serializable) {
return $this->extractResumeToken($document->bsonSerialize());
}
$resumeToken = is_array($document)
? (isset($document['_id']) ? $document['_id'] : null)
: (isset($document->_id) ? $document->_id : null);
if (! isset($resumeToken)) {
$this->isValid = false;
throw ResumeTokenException::notFound();
}
if (! is_array($resumeToken) && ! is_object($resumeToken)) {
$this->isValid = false;
throw ResumeTokenException::invalidType($resumeToken);
}
return $resumeToken;
}
/**
* Return whether the iterator is positioned at the end of the batch.
*
* @return boolean
*/
private function isAtEndOfBatch()
{
return $this->batchPosition + 1 >= $this->batchSize;
}
/**
* Perform housekeeping after an iteration event.
*
* @see https://github.com/mongodb/specifications/blob/master/source/change-streams/change-streams.rst#updating-the-cached-resume-token
* @param boolean $incrementBatchPosition
*/
private function onIteration($incrementBatchPosition)
{
$this->isValid = parent::valid();
/* Disable rewind()'s NOP behavior once we advance to a valid position.
* This will allow the driver to throw a LogicException if rewind() is
* called after the cursor has advanced past its first element. */
if ($this->isRewindNop && $this->isValid) {
$this->isRewindNop = false;
}
if ($incrementBatchPosition && $this->isValid) {
$this->batchPosition++;
}
/* If the iterator is positioned at the end of the batch, apply the
* postBatchResumeToken if it's available. This handles both the case
* where the current batch is empty (since onIteration() will be called
* after a successful getMore) and when the iterator has advanced to the
* last document in its current batch. Otherwise, extract a resume token
* from the current document if possible. */
if ($this->isAtEndOfBatch() && $this->postBatchResumeToken !== null) {
$this->resumeToken = $this->postBatchResumeToken;
} elseif ($this->isValid) {
$this->resumeToken = $this->extractResumeToken($this->current());
}
}
}