/usr/include/fst/extensions/far/sttable.h is in libfst-dev 1.6.3-2.
This file is owned by root:root, with mode 0o644.
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// finite-state transducer library.
//
// A generic string-to-type table file format.
//
// This is not meant as a generalization of SSTable. This is more of a simple
// replacement for SSTable in order to provide an open-source implementation
// of the FAR format for the external version of the FST library.
#ifndef FST_EXTENSIONS_FAR_STTABLE_H_
#define FST_EXTENSIONS_FAR_STTABLE_H_
#include <algorithm>
#include <istream>
#include <memory>
#include <fstream>
#include <fst/util.h>
namespace fst {
static constexpr int32 kSTTableMagicNumber = 2125656924;
static constexpr int32 kSTTableFileVersion = 1;
// String-type table writing class for an object of type T using a functor
// Writer. The Writer functor must provide at least the following interface:
//
// struct Writer {
// void operator()(std::ostream &, const T &) const;
// };
template <class T, class Writer>
class STTableWriter {
public:
explicit STTableWriter(const string &filename)
: stream_(filename, std::ios_base::out | std::ios_base::binary),
error_(false) {
WriteType(stream_, kSTTableMagicNumber);
WriteType(stream_, kSTTableFileVersion);
if (stream_.fail()) {
FSTERROR() << "STTableWriter::STTableWriter: Error writing to file: "
<< filename;
error_ = true;
}
}
static STTableWriter<T, Writer> *Create(const string &filename) {
if (filename.empty()) {
LOG(ERROR) << "STTableWriter: Writing to standard out unsupported.";
return nullptr;
}
return new STTableWriter<T, Writer>(filename);
}
void Add(const string &key, const T &t) {
if (key == "") {
FSTERROR() << "STTableWriter::Add: Key empty: " << key;
error_ = true;
} else if (key < last_key_) {
FSTERROR() << "STTableWriter::Add: Key out of order: " << key;
error_ = true;
}
if (error_) return;
last_key_ = key;
positions_.push_back(stream_.tellp());
WriteType(stream_, key);
entry_writer_(stream_, t);
}
bool Error() const { return error_; }
~STTableWriter() {
WriteType(stream_, positions_);
WriteType(stream_, static_cast<int64>(positions_.size()));
}
private:
Writer entry_writer_;
std::ofstream stream_;
std::vector<int64> positions_; // Position in file of each key-entry pair.
string last_key_; // Last key.
bool error_;
STTableWriter(const STTableWriter &) = delete;
STTableWriter &operator=(const STTableWriter &) = delete;
};
// String-type table reading class for object of type T using a functor Reader.
// Reader must provide at least the following interface:
//
// struct Reader {
// T *operator()(std::istream &) const;
// };
//
template <class T, class Reader>
class STTableReader {
public:
explicit STTableReader(const std::vector<string> &filenames)
: sources_(filenames), error_(false) {
compare_.reset(new Compare(&keys_));
keys_.resize(filenames.size());
streams_.resize(filenames.size(), 0);
positions_.resize(filenames.size());
for (size_t i = 0; i < filenames.size(); ++i) {
streams_[i] = new std::ifstream(
filenames[i], std::ios_base::in | std::ios_base::binary);
int32 magic_number = 0;
ReadType(*streams_[i], &magic_number);
int32 file_version = 0;
ReadType(*streams_[i], &file_version);
if (magic_number != kSTTableMagicNumber) {
FSTERROR() << "STTableReader::STTableReader: Wrong file type: "
<< filenames[i];
error_ = true;
return;
}
if (file_version != kSTTableFileVersion) {
FSTERROR() << "STTableReader::STTableReader: Wrong file version: "
<< filenames[i];
error_ = true;
return;
}
int64 num_entries;
streams_[i]->seekg(-static_cast<int>(sizeof(int64)), std::ios_base::end);
ReadType(*streams_[i], &num_entries);
if (num_entries > 0) {
streams_[i]->seekg(-static_cast<int>(sizeof(int64)) * (num_entries + 1),
std::ios_base::end);
positions_[i].resize(num_entries);
for (size_t j = 0; (j < num_entries) && (!streams_[i]->fail()); ++j) {
ReadType(*streams_[i], &(positions_[i][j]));
}
streams_[i]->seekg(positions_[i][0]);
if (streams_[i]->fail()) {
FSTERROR() << "STTableReader::STTableReader: Error reading file: "
<< filenames[i];
error_ = true;
return;
}
}
}
MakeHeap();
}
~STTableReader() {
for (auto &stream : streams_) delete stream;
}
static STTableReader<T, Reader> *Open(const string &filename) {
if (filename.empty()) {
LOG(ERROR) << "STTableReader: Operation not supported on standard input";
return nullptr;
}
std::vector<string> filenames;
filenames.push_back(filename);
return new STTableReader<T, Reader>(filenames);
}
static STTableReader<T, Reader> *Open(const std::vector<string> &filenames) {
return new STTableReader<T, Reader>(filenames);
}
void Reset() {
if (error_) return;
for (size_t i = 0; i < streams_.size(); ++i)
streams_[i]->seekg(positions_[i].front());
MakeHeap();
}
bool Find(const string &key) {
if (error_) return false;
for (size_t i = 0; i < streams_.size(); ++i) LowerBound(i, key);
MakeHeap();
if (heap_.empty()) return false;
return keys_[current_] == key;
}
bool Done() const { return error_ || heap_.empty(); }
void Next() {
if (error_) return;
if (streams_[current_]->tellg() <= positions_[current_].back()) {
ReadType(*(streams_[current_]), &(keys_[current_]));
if (streams_[current_]->fail()) {
FSTERROR() << "STTableReader: Error reading file: "
<< sources_[current_];
error_ = true;
return;
}
std::push_heap(heap_.begin(), heap_.end(), *compare_);
} else {
heap_.pop_back();
}
if (!heap_.empty()) PopHeap();
}
const string &GetKey() const { return keys_[current_]; }
const T *GetEntry() const { return entry_.get(); }
bool Error() const { return error_; }
private:
// Comparison functor used to compare stream IDs in the heap.
struct Compare {
explicit Compare(const std::vector<string> *keys) : keys(keys) {}
bool operator()(size_t i, size_t j) const {
return (*keys)[i] > (*keys)[j];
};
private:
const std::vector<string> *keys;
};
// Positions the stream at the position corresponding to the lower bound for
// the specified key.
void LowerBound(size_t id, const string &find_key) {
auto *strm = streams_[id];
const auto &positions = positions_[id];
if (positions.empty()) return;
size_t low = 0;
size_t high = positions.size() - 1;
while (low < high) {
size_t mid = (low + high) / 2;
strm->seekg(positions[mid]);
string key;
ReadType(*strm, &key);
if (key > find_key) {
high = mid;
} else if (key < find_key) {
low = mid + 1;
} else {
for (size_t i = mid; i > low; --i) {
strm->seekg(positions[i - 1]);
ReadType(*strm, &key);
if (key != find_key) {
strm->seekg(positions[i]);
return;
}
}
strm->seekg(positions[low]);
return;
}
}
strm->seekg(positions[low]);
}
// Adds all streams to the heap.
void MakeHeap() {
heap_.clear();
for (size_t i = 0; i < streams_.size(); ++i) {
if (positions_[i].empty()) continue;
ReadType(*streams_[i], &(keys_[i]));
if (streams_[i]->fail()) {
FSTERROR() << "STTableReader: Error reading file: " << sources_[i];
error_ = true;
return;
}
heap_.push_back(i);
}
if (heap_.empty()) return;
std::make_heap(heap_.begin(), heap_.end(), *compare_);
PopHeap();
}
// Positions the stream with the lowest key at the top of the heap, sets
// current_ to the ID of that stream, and reads the current entry from that
// stream.
void PopHeap() {
std::pop_heap(heap_.begin(), heap_.end(), *compare_);
current_ = heap_.back();
entry_.reset(entry_reader_(*streams_[current_]));
if (!entry_) error_ = true;
if (streams_[current_]->fail()) {
FSTERROR() << "STTableReader: Error reading entry for key: "
<< keys_[current_] << ", file: " << sources_[current_];
error_ = true;
}
}
Reader entry_reader_;
std::vector<std::istream *> streams_; // Input streams.
std::vector<string> sources_; // Corresponding file names.
std::vector<std::vector<int64>> positions_; // Index of positions.
std::vector<string> keys_; // Lowest unread key for each stream.
std::vector<int64> heap_; // Heap containing ID of streams with unread keys.
int64 current_; // ID of current stream to be read.
std::unique_ptr<Compare> compare_; // Functor comparing stream IDs.
mutable std::unique_ptr<T> entry_; // The currently read entry.
bool error_;
};
// String-type table header reading function template on the entry header type.
// The Header type must provide at least the following interface:
//
// struct Header {
// void Read(std::istream &istrm, const string &filename);
// };
template <class Header>
bool ReadSTTableHeader(const string &filename, Header *header) {
if (filename.empty()) {
LOG(ERROR) << "ReadSTTable: Can't read header from standard input";
return false;
}
std::ifstream strm(filename, std::ios_base::in | std::ios_base::binary);
if (!strm) {
LOG(ERROR) << "ReadSTTableHeader: Could not open file: " << filename;
return false;
}
int32 magic_number = 0;
ReadType(strm, &magic_number);
int32 file_version = 0;
ReadType(strm, &file_version);
if (magic_number != kSTTableMagicNumber) {
LOG(ERROR) << "ReadSTTableHeader: Wrong file type: " << filename;
return false;
}
if (file_version != kSTTableFileVersion) {
LOG(ERROR) << "ReadSTTableHeader: Wrong file version: " << filename;
return false;
}
int64 i = -1;
strm.seekg(-static_cast<int>(sizeof(int64)), std::ios_base::end);
ReadType(strm, &i); // Reads number of entries
if (strm.fail()) {
LOG(ERROR) << "ReadSTTableHeader: Error reading file: " << filename;
return false;
}
if (i == 0) return true; // No entry header to read.
strm.seekg(-2 * static_cast<int>(sizeof(int64)), std::ios_base::end);
ReadType(strm, &i); // Reads position for last entry in file.
strm.seekg(i);
string key;
ReadType(strm, &key);
header->Read(strm, filename + ":" + key);
if (strm.fail()) {
LOG(ERROR) << "ReadSTTableHeader: Error reading file: " << filename;
return false;
}
return true;
}
bool IsSTTable(const string &filename);
} // namespace fst
#endif // FST_EXTENSIONS_FAR_STTABLE_H_
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