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/**
* Copyright (C) 2020-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/update/document_diff_calculator.h"
namespace mongo::doc_diff {
namespace {
// Note: This function is mutually with computeArrayDiff() and computeDocDiff().
template <class Node, class T>
void calculateSubDiffHelper(const BSONElement& preVal,
const BSONElement& postVal,
T fieldIdentifier,
Node* diffNode);
std::unique_ptr<diff_tree::ArrayNode> computeArrayDiff(const BSONObj& pre, const BSONObj& post) {
auto diffNode = std::make_unique<diff_tree::ArrayNode>();
auto preItr = BSONObjIterator(pre);
auto postItr = BSONObjIterator(post);
const size_t postObjSize = static_cast<size_t>(post.objsize());
size_t nFieldsInPostArray = 0;
for (; preItr.more() && postItr.more(); ++preItr, ++postItr, ++nFieldsInPostArray) {
// Bailout if the generated diff so far is larger than the 'post' object.
if (postObjSize < diffNode->getObjSize()) {
return nullptr;
}
if (!(*preItr).binaryEqual(*postItr)) {
// If both are arrays or objects, then recursively compute the diff of the respective
// array or object.
if ((*preItr).type() == (*postItr).type() &&
((*preItr).type() == BSONType::Object || (*preItr).type() == BSONType::Array)) {
calculateSubDiffHelper(*preItr, *postItr, nFieldsInPostArray, diffNode.get());
} else {
diffNode->addUpdate(nFieldsInPostArray, *postItr);
}
}
}
// When we reach here, only one of postItr or preItr can have more fields. If postItr has more
// fields, we need to add all the remaining fields.
for (; postItr.more(); ++postItr, ++nFieldsInPostArray) {
diffNode->addUpdate(nFieldsInPostArray, *postItr);
}
// If preItr has more fields, we can ignore the remaining fields, since we only need to do a
// resize operation.
if (preItr.more()) {
diffNode->setResize(nFieldsInPostArray);
}
return (postObjSize > diffNode->getObjSize()) ? std::move(diffNode) : nullptr;
}
std::unique_ptr<diff_tree::DocumentSubDiffNode> computeDocDiff(const BSONObj& pre,
const BSONObj& post,
size_t padding = 0) {
auto diffNode = std::make_unique<diff_tree::DocumentSubDiffNode>(padding);
BSONObjIterator preItr(pre);
BSONObjIterator postItr(post);
const size_t postObjSize = static_cast<size_t>(post.objsize());
std::set<StringData> deletes;
while (preItr.more() && postItr.more()) {
auto preVal = *preItr;
auto postVal = *postItr;
// Bailout if the generated diff so far is larger than the 'post' object.
if (postObjSize < diffNode->getObjSize()) {
return nullptr;
}
if (preVal.fieldNameStringData() == postVal.fieldNameStringData()) {
if (preVal.binaryEqual(postVal)) {
// They're identical. Move on.
} else if (preVal.type() == postVal.type() &&
(preVal.type() == BSONType::Object || preVal.type() == BSONType::Array)) {
// Both are either arrays or objects, recursively compute the diff of the respective
// array or object.
calculateSubDiffHelper(
preVal, postVal, preVal.fieldNameStringData(), diffNode.get());
} else {
// Any other case, just replace with the 'postVal'.
diffNode->addUpdate((*preItr).fieldNameStringData(), postVal);
}
preItr.next();
postItr.next();
} else {
// If the 'preVal' field name does not exist in the 'post' object then, just remove it.
// If it present, we do nothing for now, since the field gets inserted later.
deletes.insert(preVal.fieldNameStringData());
preItr.next();
}
}
// When we reach here, only one of postItr or preItr can have more fields. Record remaining
// fields in preItr as removals.
for (; preItr.more(); preItr.next()) {
// Note that we don't need to record these into the 'deletes' set because there are no more
// fields in the post image.
invariant(!postItr.more());
diffNode->addDelete((*preItr).fieldNameStringData());
}
// Record remaining fields in postItr as creates.
for (; postItr.more(); postItr.next()) {
auto fieldName = (*postItr).fieldNameStringData();
diffNode->addInsert(fieldName, *postItr);
deletes.erase(fieldName);
}
for (auto&& deleteField : deletes) {
diffNode->addDelete(deleteField);
}
return (postObjSize > diffNode->getObjSize()) ? std::move(diffNode) : nullptr;
}
template <class Node, class T>
void calculateSubDiffHelper(const BSONElement& preVal,
const BSONElement& postVal,
T fieldIdentifier,
Node* diffNode) {
auto subDiff = (preVal.type() == BSONType::Object)
? std::unique_ptr<diff_tree::InternalNode>(
computeDocDiff(preVal.embeddedObject(), postVal.embeddedObject()))
: std::unique_ptr<diff_tree::InternalNode>(
computeArrayDiff(preVal.embeddedObject(), postVal.embeddedObject()));
if (!subDiff) {
// We could not compute sub-diff because the potential sub-diff is bigger than the 'postVal'
// itself. So we just log the modification as an update.
diffNode->addUpdate(fieldIdentifier, postVal);
} else {
diffNode->addChild(fieldIdentifier, std::move(subDiff));
}
}
} // namespace
boost::optional<doc_diff::Diff> computeDiff(const BSONObj& pre,
const BSONObj& post,
size_t padding) {
if (auto diffNode = computeDocDiff(pre, post, padding)) {
auto diff = diffNode->serialize();
if (diff.objsize() < post.objsize()) {
return diff;
}
}
return {};
}
} // namespace mongo::doc_diff
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