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// Copyright CERN and copyright holders of ALICE O2. This software is
// distributed under the terms of the GNU General Public License v3 (GPL
// Version 3), copied verbatim in the file "COPYING".
//
// See http://alice-o2.web.cern.ch/license for full licensing information.
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
#ifndef ALGORITHM_PARSER_H
#define ALGORITHM_PARSER_H
/// @file Parser.h
/// @author Matthias Richter
/// @since 2017-09-20
/// @brief Utilities for parsing of data sequences
#include <functional>
#include <vector>
namespace o2 {
namespace algorithm {
/// helper function returning size of type with a specialization for
/// void returning 0
template<typename T>
struct typesize {
static const size_t size = sizeof(T);
};
// specialization for void
template<>
struct typesize<void> {
static const size_t size = 0;
};
/**
* @class ForwardParser
* Parser for a sequence of frames with header, trailer and variable payload.
* The size is expected to be part of the header.
*
* Trailer type can be void, which is also the default template parameter. That
* allows to define a frame consisting of only header and data.
*
* Usage:
* <pre>
* using SomeParser = ForwardParser<SomeHeaderType, SomeTrailerType>;
* SomeParser parser;
* std::vector<typename SomeParser::FrameInfo> frames;
* parser.parse(ptr, size,
* [] (const typename SomeParser::HeaderType& h) {
* // check the header
* return true;
* },
* [] (const typename SomeParser::TrailerType& t) {
* // check the trailer
* return true;
* },
* [] (const typename SomeParser::HeaderType& h) {
* // get the size of the frame including payload
* // and header and trailer size, e.g. payload size
* // from a header member
* return h.payloadSize + SomeParser::totalOffset;
* },
* [&frames] (typename SomeParser::FrameInfo& info) {
* frames.emplace_back(info);
* return true;
* }
* )
*
* // a reduced version without trailer check callback
* using SomeParser = ForwardParser<SomeHeaderType>;
* SomeParser parser;
* std::vector<typename SomeParser::FrameInfo> frames;
* parser.parse(ptr, size,
* [] (const typename SomeParser::HeaderType& h) {
* // check the header
* return true;
* },
* [] (const typename SomeParser::HeaderType& h) {
* // get the size of the frame including payload
* // and header and trailer size, e.g. payload size
* // from a header member
* return h.payloadSize + SomeParser::totalOffset;
* },
* [&frames] (typename SomeParser::FrameInfo& info) {
* frames.emplace_back(info);
* return true;
* }
* )
* </pre>
*/
template<typename HeaderT,
typename TrailerT = void
>
class ForwardParser {
public:
using HeaderType = HeaderT;
using TrailerType = TrailerT;
using PayloadType = unsigned char;
/// @struct FrameInfo
/// a compound of header, data, and trailer
struct FrameInfo {
using PtrT = const PayloadType*;
const HeaderType* header = nullptr;
const TrailerType* trailer = nullptr;
PtrT payload = nullptr;
size_t length = 0;
};
/// the length offset due to header
static const size_t headOffset = typesize<HeaderType>::size;
/// the length offset due to trailer
static const size_t tailOffset = typesize<TrailerType>::size;
/// total length offset due to header and trailer
static const size_t totalOffset = headOffset + tailOffset;
/// alias for callback checking the header, return true if the object
/// is a valid header
using CheckHeaderFct = std::function<bool(const HeaderType&)>;
/// alias for the argument type to be used in the CheckTrailer function
/// have to forward to a valid type in case of void TrailerType in order
/// to allow passing by reference
using CheckTrailerFctArgumentT = typename std::conditional<
!std::is_void<TrailerType>::value, TrailerType, int>::type;
/// alias for callback checking the trailer, takes reference to trailer
/// object if TrailerType is a valid type, no argument otherwise
template <typename U>
using CheckTrailerFct = typename std::conditional<
!std::is_void<U>::value,
std::function<bool(const CheckTrailerFctArgumentT&)>,
std::function<bool()>>::type;
/// alias for callback to get the complete frame size including header,
/// trailer and the data
using GetFrameSizeFct = std::function<size_t(const HeaderType& )>;
/// function callback to insert/handle one frame into, sequentially called
/// for all frames if the whole block has a valid format
using InsertFct = std::function<bool(FrameInfo&)>;
/// Parse buffer of size bufferSize, requires callbacks to check header
/// trailer, the frame size, and insert callback to handle a FrameInfo
/// object.
template<typename InputType>
int parse(const InputType* buffer, size_t bufferSize,
CheckHeaderFct checkHeader,
CheckTrailerFct<TrailerType> checkTrailer,
GetFrameSizeFct getFrameSize,
InsertFct insert) {
static_assert(sizeof(InputType) == 1,
"ForwardParser currently only supports byte type buffer"
);
if (buffer == nullptr || bufferSize == 0) return 0;
auto position = 0;
std::vector<FrameInfo> frames;
do {
FrameInfo entry;
// check the header
if (sizeof(HeaderType) + position > bufferSize) break;
entry.header = reinterpret_cast<const HeaderType*>(buffer + position);
if (!checkHeader(*entry.header)) break;
// extract frame size from header, this is expected to be the
// total frome size including header, payload and optional trailer
auto frameSize = getFrameSize(*entry.header);
if (frameSize + position > bufferSize) break;
// payload starts right after the header
entry.payload = reinterpret_cast<typename FrameInfo::PtrT>(entry.header + 1);
entry.length = frameSize - totalOffset;
// optionally extract and check trailer
if (tailOffset > 0) {
entry.trailer = nullptr;
} else {
auto trailerStart = buffer + position + frameSize - tailOffset;
entry.trailer = reinterpret_cast<const TrailerType*>(trailerStart);
if (!CheckTrailer(entry, checkTrailer)) break;
}
// store the extracted frame info and continue with remaining buffer
frames.emplace_back(entry);
position += frameSize;
} while (position < bufferSize);
if (position == bufferSize) {
// frames found and format consistent, insert entries to target
// Note: the complete block must be consistent
for (auto entry : frames) {
if (!insert(entry)) break;
}
return frames.size();
} else if (frames.size() == 0) {
// no frames found at all, the buffer does not contain any
return 0;
}
// format error detected
// TODO: decide about error policy
return -1;
}
/// Parse buffer of size bufferSize, specialization skipping the trailer
/// check, e.g. when its type is void, or when the integrity of the trailer
/// is not relevant. Requires callbacks to check header, frame size, and
/// insert callback to handle a FrameInfo object.
template<typename InputType, typename U = TrailerType>
typename std::enable_if<std::is_void<U>::value, int>::type
parse(const InputType* buffer, size_t bufferSize,
CheckHeaderFct checkHeader,
GetFrameSizeFct getFrameSize,
InsertFct insert) {
auto checkTrailer = [] () {return true;};
return parse(buffer, bufferSize, checkHeader, checkTrailer, getFrameSize, insert);
}
private:
/// internal function to check the trailer, distinguishes void and non-void
/// trailer type.
template <typename U = TrailerType>
typename std::enable_if<!std::is_void<U>::value, bool>::type
CheckTrailer(const FrameInfo& entry, CheckTrailerFct<TrailerType>& checkTrailer) const {
return checkTrailer(*entry.trailer);
}
template <typename U = TrailerType>
typename std::enable_if<std::is_void<U>::value, bool>::type
CheckTrailer(const FrameInfo&, CheckTrailerFct<TrailerType>&) const {
return true;
}
};
/**
* @class ReverseParser
* Parser for a sequence of frames with header, trailer and variable payload.
* The size is expected to be part of the trailer, the parsing is thus in
* reverse direction. Also the insert callback is called with the entries
* starting form the end of the buffer.
* TODO: an easy extension can be to reverse the order of the inserts, meaning
* that the entries are read from the beginning.
*
* Usage:
* <pre>
* using SomeParser = ReverseParser<SomeHeaderType, SomeTrailerType>;
* SomeParser parser;
* std::vector<typename SomeParser::FrameInfo> frames;
* parser.parse(ptr, size,
* [] (const typename SomeParser::HeaderType& h) {
* // check the header
* return true;
* },
* [] (const typename SomeParser::TrailerType& t) {
* // check the trailer
* return true;
* },
* [] (const typename SomeParser::TrailerType& t) {
* // get the size of the frame including payload
* // and header and trailer size, e.g. payload size
* // from a trailer member
* return t.payloadSize + SomeParser::totalOffset;
* },
* [&frames] (typename SomeParser::FrameInfo& info) {
* frames.emplace_back(info);
* return true;
* }
* )
* </pre>
*/
template<typename HeaderT, typename TrailerT>
class ReverseParser {
public:
using HeaderType = HeaderT;
using TrailerType = TrailerT;
using PayloadType = unsigned char;
/// @struct FrameInfo a compound of header, data, and trailer
struct FrameInfo {
using PtrT = const PayloadType*;
const HeaderType* header = nullptr;
const TrailerType* trailer = nullptr;
PtrT payload = nullptr;
size_t length = 0;
};
/// the length offset due to header
static const size_t headOffset = typesize<HeaderType>::size;
/// the length offset due to trailer
static const size_t tailOffset = typesize<TrailerType>::size;
/// total length offset due to header and trailer
static const size_t totalOffset = headOffset + tailOffset;
/// alias for callback checking the header, return true if the object
/// is a valid header
using CheckHeaderFct = std::function<bool(const HeaderType&)>;
/// alias for callback checking the trailer
using CheckTrailerFct = std::function<bool(const TrailerType&)>;
/// alias for callback to get the complete frame size including header,
/// trailer and the data
using GetFrameSizeFct = std::function<size_t(const TrailerType&)>;
/// function callback to insert/handle one frame into, sequentially called
/// for all frames if the whole block has a valid format
using InsertFct = std::function<bool(const FrameInfo&)>;
/// Parse buffer of size bufferSize, requires callbacks to check header
/// trailer, the frame size, and insert callback to handle a FrameInfo
/// object.
template<typename InputType>
int parse(const InputType* buffer, size_t bufferSize,
CheckHeaderFct checkHeader,
CheckTrailerFct checkTrailer,
GetFrameSizeFct getFrameSize,
InsertFct insert) {
static_assert(sizeof(InputType) == 1,
"ReverseParser currently only supports byte type buffer"
);
if (buffer == nullptr || bufferSize == 0) return 0;
auto position = bufferSize;
std::vector<FrameInfo> frames;
do {
FrameInfo entry;
// start from end, extract and check trailer
if (sizeof(TrailerType) > position) break;
entry.trailer = reinterpret_cast<const TrailerType*>(buffer + position - sizeof(TrailerType));
if (!checkTrailer(*entry.trailer)) break;
// get the total frame size
auto frameSize = getFrameSize(*entry.trailer);
if (frameSize > position) break;
// extract and check header
auto headerStart = buffer + position - frameSize;
entry.header = reinterpret_cast<const HeaderType*>(headerStart);
if (!checkHeader(*entry.header)) break;
// payload immediately after header
entry.payload = reinterpret_cast<typename FrameInfo::PtrT>(entry.header + 1);
entry.length = frameSize - sizeof(HeaderType) - sizeof(TrailerType);
frames.emplace_back(entry);
position -= frameSize;
} while (position > 0);
if (position == 0) {
// frames found and format consistent, the complete block must be consistent
for (auto entry : frames) {
if (!insert(entry)) break;
}
return frames.size();
} else if (frames.size() == 0) {
// no frames found at all, the buffer does not contain any
return 0;
}
// format error detected
// TODO: decide about error policy
return -1;
}
};
} // namespace algorithm
} // namespace o2
#endif // ALGORITHM_PARSER_H