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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/pipeline/document_source_skip.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/lite_parsed_document_source.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
using boost::intrusive_ptr;
DocumentSourceSkip::DocumentSourceSkip(const intrusive_ptr<ExpressionContext>& pExpCtx,
long long nToSkip)
: DocumentSource(pExpCtx), _nToSkip(nToSkip) {}
REGISTER_DOCUMENT_SOURCE(skip,
LiteParsedDocumentSourceDefault::parse,
DocumentSourceSkip::createFromBson);
constexpr StringData DocumentSourceSkip::kStageName;
DocumentSource::GetNextResult DocumentSourceSkip::getNext() {
pExpCtx->checkForInterrupt();
while (_nSkippedSoFar < _nToSkip) {
// For performance reasons, a streaming stage must not keep references to documents across
// calls to getNext(). Such stages must retrieve a result from their child and then release
// it (or return it) before asking for another result. Failing to do so can result in extra
// work, since the Document/Value library must copy data on write when that data has a
// refcount above one.
auto nextInput = pSource->getNext();
if (!nextInput.isAdvanced()) {
return nextInput;
}
++_nSkippedSoFar;
}
return pSource->getNext();
}
Value DocumentSourceSkip::serialize(boost::optional<ExplainOptions::Verbosity> explain) const {
return Value(DOC(getSourceName() << _nToSkip));
}
intrusive_ptr<DocumentSource> DocumentSourceSkip::optimize() {
return _nToSkip == 0 ? nullptr : this;
}
Pipeline::SourceContainer::iterator DocumentSourceSkip::doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
invariant(*itr == this);
auto nextSkip = dynamic_cast<DocumentSourceSkip*>((*std::next(itr)).get());
if (nextSkip) {
// '_nToSkip' can potentially overflow causing it to become negative and skip nothing.
if (std::numeric_limits<long long>::max() - _nToSkip - nextSkip->getSkip() >= 0) {
_nToSkip += nextSkip->getSkip();
container->erase(std::next(itr));
return itr;
}
}
return std::next(itr);
}
intrusive_ptr<DocumentSourceSkip> DocumentSourceSkip::create(
const intrusive_ptr<ExpressionContext>& pExpCtx, long long nToSkip) {
intrusive_ptr<DocumentSourceSkip> skip(new DocumentSourceSkip(pExpCtx, nToSkip));
return skip;
}
intrusive_ptr<DocumentSource> DocumentSourceSkip::createFromBson(
BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
uassert(15972,
str::stream() << "Argument to $skip must be a number not a " << typeName(elem.type()),
elem.isNumber());
auto nToSkip = elem.numberLong();
uassert(15956, "Argument to $skip cannot be negative", nToSkip >= 0);
return DocumentSourceSkip::create(pExpCtx, nToSkip);
}
}
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