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/**
* Copyright (C) 2022-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/db/storage/multi_bson_stream_cursor.h"
#include "mongo/db/storage/record_store.h"
namespace mongo {
/**
* Expands '_buffer' by a multiple of two of its current size that is large enough to contain two
* objects of size 'bsonSize'. Copies the contents of the old buffer to position 0 of the new buffer
* and updates bookkeeping. This can never expand the buffer larger than (2 * BSONObjMaxUserSize).
*/
void MultiBsonStreamCursor::expandBuffer(int32_t bsonSize) {
tassert(6968308,
"bsonSize {} > BSONObjMaxUserSize {}"_format(bsonSize, BSONObjMaxUserSize),
(bsonSize <= BSONObjMaxUserSize));
tassert(6968309, "bsonSize {} < 0"_format(bsonSize), (bsonSize >= 0));
int newSizeTarget = 2 * bsonSize;
do {
_bufSize *= 2;
} while (_bufSize < newSizeTarget);
std::unique_ptr<char[]> newBuffer{new char[_bufSize]};
_bufEnd -= _bufBegin;
std::memcpy(newBuffer.get(), (_buffer.get() + _bufBegin), _bufEnd);
_buffer = std::move(newBuffer);
_blockReadSize = _bufSize / 2;
_bufBegin = 0;
}
/**
* Returns the next record from the current stream or boost::none if exhausted or error.
*/
boost::optional<Record> MultiBsonStreamCursor::nextFromCurrentStream() {
int32_t bsonSize; // size of the next BSON object
int readBytes; // number of bytes just read
int remBytes; // number of remainder bytes to read for either size field or object body
int availBytes; // number of unconsumed bytes in '_buffer'
// The while loop enables dynamically expanding the buffer as needed. If the buffer ever reaches
// (2 * BSONObjMaxUserSize) bytes it will not need to expand any more.
while (true) {
// There are four cases, but for performance they are not fully independent in code:
// 1. Next full object (size and data) is already in the buffer.
// 2. Next size is in the buffer but not all of the next object.
// 3. Next size is only partly present in the buffer.
// 4. No part of the next object is in the buffer. Reset buffer and read a big block.
availBytes = _bufEnd - _bufBegin;
if (availBytes > 0) { // Cases 1-3
// Cases 3: get the rest of size. This collapses case 3 into case 2.
if (availBytes < kSizeSize) {
remBytes = kSizeSize - availBytes;
readBytes = _streamReader->readBytes(remBytes, (_buffer.get() + _bufEnd));
if (MONGO_unlikely(readBytes < remBytes)) {
uasserted(6968303,
"Truncated file: {}"_format(_vopts.dataSources[_streamIdx].url));
return boost::none;
}
_bufEnd += readBytes;
availBytes += readBytes;
}
bsonSize = ConstDataView(_buffer.get() + _bufBegin).read<LittleEndian<int32_t>>();
// Cases 2-3: get the rest of the object. This collapses cases 2-3 into case 1.
if (availBytes < bsonSize) {
remBytes = bsonSize - availBytes;
if (MONGO_likely(remBytes <= _bufSize - _bufEnd)) { // 'remBytes' will fit
readBytes = _streamReader->readBytes(remBytes, (_buffer.get() + _bufEnd));
if (MONGO_unlikely(readBytes < remBytes)) {
uasserted(6968304,
"Truncated file: {}"_format(_vopts.dataSources[_streamIdx].url));
return boost::none;
}
_bufEnd += readBytes;
// Not used again: availBytes += readBytes;
} else {
expandBuffer(bsonSize);
continue;
}
}
} else { // Case 4: availBytes == 0; do a block read
_bufBegin = 0;
_bufEnd = 0;
readBytes = _streamReader->readBytes(_blockReadSize, _buffer.get());
if (readBytes == 0) { // EOF: okay here as the pipe ended at an object boundary
return boost::none;
}
if (MONGO_unlikely(readBytes < kSizeSize)) {
uasserted(6968305, "Truncated file: {}"_format(_vopts.dataSources[_streamIdx].url));
return boost::none;
}
_bufEnd += readBytes;
// Not used again: availBytes += readBytes;
bsonSize = ConstDataView(_buffer.get() + _bufBegin).read<LittleEndian<int32_t>>();
if (MONGO_unlikely(readBytes < bsonSize)) {
if (MONGO_likely(readBytes == _blockReadSize)) { // got all the bytes we requested
expandBuffer(bsonSize);
continue;
}
uasserted(6968306, "Truncated file: {}"_format(_vopts.dataSources[_streamIdx].url));
return boost::none;
}
}
break; // reaching here means we have the whole object in '_buffer' now
}
// All cases are now collapsed to Case 1: the full object is in the buffer at '_bufBegin'.
// 'recordData.data' includes the size in the first four bytes.
boost::optional<RecordData> recordData = RecordData{(_buffer.get() + _bufBegin), bsonSize};
_bufBegin += bsonSize;
tassert(
6968307, "_bufBegin {} > _bufSize {}"_format(_bufBegin, _bufSize), (_bufBegin <= _bufSize));
return {{RecordId{_nextRecordId++}, std::move(*recordData)}};
}
/**
* Returns the next record from the vector of streams or boost::none if exhausted or error.
* '_streamReader' is initialized to the first stream, if there is one, in the constructor.
*/
boost::optional<Record> MultiBsonStreamCursor::next() {
while (_streamIdx < _numStreams) {
auto record = nextFromCurrentStream();
if (MONGO_likely(record)) {
return record;
}
++_streamIdx;
if (_streamIdx < _numStreams) {
_streamReader = std::make_unique<InputStream<NamedPipeInput>>(
_vopts.dataSources[_streamIdx].url.c_str());
}
}
return boost::none;
}
} // namespace mongo
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