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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.
*/
#pragma once
#include <fmt/format.h>
#include <utility>
#include "mongo/db/storage/io_error_message.h"
#include "mongo/logv2/log.h"
#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kStorage
namespace mongo {
/**
* This template class provides a standardized input facility over StreamableInput or SeekableInput.
*
* This class inherits publicly from 'InputT' and expose all methods except InputT::read() so that
* InputStream::readBytes() is exposed for reading data instead of InputT::read(). If 'InputT' is
* seekable, seek() method is still exposed and the client can seek to a specific position before
* reading data.
*
* Type requirement: 'InputT' must meet the StreamableInput or SeekableInput concept, e.g. the
* NamedPipeInput class, which is the first class used as InputStream's parent.
*/
template <typename InputT>
class InputStream : public InputT {
public:
/**
* Constructs an InputStream object wrapped around a low-level class (e.g. NamedPipeInput).
*/
template <typename... ArgT>
InputStream(ArgT&&... args) : InputT(std::forward<ArgT>(args)...) {
using namespace fmt::literals;
InputT::open();
uassert(ErrorCodes::FileNotOpen,
"Named pipe still not open for read after exhausting retries. Error: {}"_format(
getErrorMessage("open"_sd, InputT::getAbsolutePath())),
InputT::isOpen());
}
/**
* Reads 'count' bytes from the stream into the caller-provided 'buffer'. Caller is responsible
* for ensuring 'buffer' size is >= 'count' bytes. The only reasons it should return fewer bytes
* is if it reaches EOF or gets an error. (Ensuring this requires looping on Windows, as a
* synchronous read, which we are using, will still return as soon as any bytes are available.)
*
* If any bytes were read AND no error was hit, the number read is returned. Always returns -1
* on error, even if some bytes were read successfully, so the caller will not see those bytes.
* EOF is not treated as an error, so repeated attempts to read past EOF will just return 0.
* The design avoids having to construct std::pair return values to return multiple pieces of
* information, as that would be much more expensive than returning an int, and this method may
* be called billions of times in a scan.
*
* May throw an exception when count < 0.
*/
int readBytes(int count, char* buffer) {
tassert(7005000, "Number of bytes to read must be greater than 0", count > 0);
int nReadTotal = 0;
int nReadNow = 0;
do {
if (MONGO_likely(InputT::isGood())) {
nReadNow = InputT::read((buffer + nReadTotal), (count - nReadTotal));
nReadTotal += nReadNow;
} else {
break;
}
if (MONGO_likely(nReadTotal == count)) {
return nReadTotal;
}
} while (nReadTotal < count && nReadNow > 0);
// If we reach this point, we accumulated fewer than 'count' bytes.
if (MONGO_likely(InputT::isEof())) {
return nReadTotal;
}
tassert(7005002, "Expected an error condition but succeeded", InputT::isFailed());
LOGV2_ERROR(7005003,
"Failed to read a named pipe",
"error"_attr = getErrorMessage("read", InputT::getAbsolutePath()));
return -1;
}
private:
// Hides InputT::read() so that readBytes() is the external interface for reading.
using InputT::read;
};
} // namespace mongo
#undef MONGO_LOGV2_DEFAULT_COMPONENT
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