common/include/serde.hpp

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef DATASKETCHES_SERDE_HPP_
#define DATASKETCHES_SERDE_HPP_

#include <cstring>
#include <iostream>
#include <memory>
#include <string>
#include <exception>

#include "memory_operations.hpp"

namespace datasketches {

// serialize and deserialize
template<typename T, typename Enable = void> struct serde {
  // stream serialization
  void serialize(std::ostream& os, const T* items, unsigned num);
  void deserialize(std::istream& is, T* items, unsigned num); // items allocated but not initialized

  // raw bytes serialization
  size_t size_of_item(const T& item);
  size_t serialize(void* ptr, size_t capacity, const T* items, unsigned num);
  size_t deserialize(const void* ptr, size_t capacity, T* items, unsigned num); // items allocated but not initialized
};

// serde for all fixed-size arithmetic types (int and float of different sizes)
// in particular, kll_sketch<int64_t> should produce sketches binary-compatible
// with LongsSketch and ItemsSketch<Long> with ArrayOfLongsSerDe in Java
template<typename T>
struct serde<T, typename std::enable_if<std::is_arithmetic<T>::value>::type> {
  void serialize(std::ostream& os, const T* items, unsigned num) {
    bool failure = false;
    try {
      os.write(reinterpret_cast<const char*>(items), sizeof(T) * num);
    } catch (std::ostream::failure& e) {
      failure = true;
    }
    if (failure || !os.good()) {
      throw std::runtime_error("error writing to std::ostream with " + std::to_string(num) + " items");
    }
  }
  void deserialize(std::istream& is, T* items, unsigned num) {
    bool failure = false;
    try {
      is.read((char*)items, sizeof(T) * num);
    } catch (std::istream::failure& e) {
      failure = true;
    }
    if (failure || !is.good()) {
      throw std::runtime_error("error reading from std::istream with " + std::to_string(num) + " items");
    }
  }

  size_t size_of_item(const T&) {
    return sizeof(T);
  }
  size_t serialize(void* ptr, size_t capacity, const T* items, unsigned num) {
    const size_t bytes_written = sizeof(T) * num;
    check_memory_size(bytes_written, capacity);
    memcpy(ptr, items, bytes_written);
    return bytes_written;
  }
  size_t deserialize(const void* ptr, size_t capacity, T* items, unsigned num) {
    const size_t bytes_read = sizeof(T) * num;
    check_memory_size(bytes_read, capacity);
    memcpy(items, ptr, bytes_read);
    return bytes_read;
  }
};

// serde for std::string items
// This should produce sketches binary-compatible with
// ItemsSketch<String> with ArrayOfStringsSerDe in Java.
// The length of each string is stored as a 32-bit integer (historically),
// which may be too wasteful. Treat this as an example.
template<>
struct serde<std::string> {
  void serialize(std::ostream& os, const std::string* items, unsigned num) {
    unsigned i = 0;
    bool failure = false;
    try {
      for (; i < num && os.good(); i++) {
        uint32_t length = items[i].size();
        os.write((char*)&length, sizeof(length));
        os.write(items[i].c_str(), length);
      }
    } catch (std::ostream::failure& e) {
      failure = true;
    }
    if (failure || !os.good()) {
      throw std::runtime_error("error writing to std::ostream at item " + std::to_string(i));
    }
  }
  void deserialize(std::istream& is, std::string* items, unsigned num) {
    unsigned i = 0;
    bool failure = false;
    try {
      for (; i < num; i++) {
        uint32_t length;
        is.read((char*)&length, sizeof(length));
        if (!is.good()) { break; }
        std::string str;
        str.reserve(length);
        for (uint32_t j = 0; j < length; j++) {
          str.push_back(is.get());
        }
        if (!is.good()) { break; }
        new (&items[i]) std::string(std::move(str));
      }
    } catch (std::istream::failure& e) {
      failure = true;
    }
    if (failure || !is.good()) {
      // clean up what we've already allocated
      for (unsigned j = 0; j < i; ++j) {
        items[j].~basic_string();
      }
      throw std::runtime_error("error reading from std::istream at item " + std::to_string(i)); 
    }
  }
  size_t size_of_item(const std::string& item) {
    return sizeof(uint32_t) + item.size();
  }
  size_t serialize(void* ptr, size_t capacity, const std::string* items, unsigned num) {
    size_t bytes_written = 0;
    for (unsigned i = 0; i < num; ++i) {
      const uint32_t length = items[i].size();
      const size_t new_bytes = length + sizeof(length);
      check_memory_size(bytes_written + new_bytes, capacity);
      memcpy(ptr, &length, sizeof(length));
      ptr = static_cast<char*>(ptr) + sizeof(uint32_t);
      memcpy(ptr, items[i].c_str(), length);
      ptr = static_cast<char*>(ptr) + length;
      bytes_written += new_bytes;
    }
    return bytes_written;
  }
  size_t deserialize(const void* ptr, size_t capacity, std::string* items, unsigned num) {
    size_t bytes_read = 0;
    unsigned i = 0;
    bool failure = false;
    for (; i < num && !failure; ++i) {
      uint32_t length;
      if (bytes_read + sizeof(length) > capacity) {
        bytes_read += sizeof(length); // we'll use this to report the error
        failure = true;
        break;
      }
      memcpy(&length, ptr, sizeof(length));
      ptr = static_cast<const char*>(ptr) + sizeof(uint32_t);
      bytes_read += sizeof(length);

      if (bytes_read + length > capacity) {
        bytes_read += length; // we'll use this to report the error
        failure = true;
        break;
      }
      new (&items[i]) std::string(static_cast<const char*>(ptr), length);
      ptr = static_cast<const char*>(ptr) + length;
      bytes_read += length;
    }

    if (failure) {
      // clean up what we've already allocated
      for (unsigned j = 0; j < i; ++j)
        items[j].~basic_string();
      // using this for a consistent error message
      check_memory_size(bytes_read, capacity);
    }

    return bytes_read;
  }
};

} /* namespace datasketches */

# endif