rocksdb/third-party/fbson/FbsonStream.h

/*
 *  Copyright (c) 2014, Facebook, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

/*
 * This header file defines FbsonInBuffer and FbsonOutStream classes.
 *
 * ** Input Buffer **
 * FbsonInBuffer is a customer input buffer to wrap raw character buffer. Its
 * object instances are used to create std::istream objects interally.
 *
 * ** Output Stream **
 * FbsonOutStream is a custom output stream classes, to contain the FBSON
 * serialized binary. The class is conveniently used to specialize templates of
 * FbsonParser and FbsonWriter.
 *
 * @author Tian Xia <tianx@fb.com>
 */

#ifndef FBSON_FBSONSTREAM_H
#define FBSON_FBSONSTREAM_H

#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif

#include <inttypes.h>
#include <iostream>

namespace fbson {

// lengths includes sign
#define MAX_INT_DIGITS 11
#define MAX_INT64_DIGITS 20
#define MAX_DOUBLE_DIGITS 23 // 1(sign)+16(significant)+1(decimal)+5(exponent)

/*
 * FBSON's implementation of input buffer
 */
class FbsonInBuffer : public std::streambuf {
 public:
  FbsonInBuffer(const char* str, uint32_t len) {
    // this is read buffer and the str will not be changed
    // so we use const_cast (ugly!) to remove constness
    char* pch(const_cast<char*>(str));
    setg(pch, pch, pch + len);
  }
};

/*
 * FBSON's implementation of output stream.
 *
 * This is a wrapper of a char buffer. By default, the buffer capacity is 1024
 * bytes. We will double the buffer if realloc is needed for writes.
 */
class FbsonOutStream : public std::ostream {
 public:
  explicit FbsonOutStream(uint32_t capacity = 1024)
      : head_(nullptr), size_(0), capacity_(capacity), alloc_(true) {
    if (capacity_ == 0) {
      capacity_ = 1024;
    }

    head_ = (char*)malloc(capacity_);
  }

  FbsonOutStream(char* buffer, uint32_t capacity)
      : head_(buffer), size_(0), capacity_(capacity), alloc_(false) {
    assert(buffer && capacity_ > 0);
  }

  ~FbsonOutStream() {
    if (alloc_) {
      free(head_);
    }
  }

  void put(char c) { write(&c, 1); }

  void write(const char* c_str) { write(c_str, (uint32_t)strlen(c_str)); }

  void write(const char* bytes, uint32_t len) {
    if (len == 0)
      return;

    if (size_ + len > capacity_) {
      realloc(len);
    }

    memcpy(head_ + size_, bytes, len);
    size_ += len;
  }

  // write the integer to string
  void write(int i) {
    // snprintf automatically adds a NULL, so we need one more char
    if (size_ + MAX_INT_DIGITS + 1 > capacity_) {
      realloc(MAX_INT_DIGITS + 1);
    }

    int len = snprintf(head_ + size_, MAX_INT_DIGITS + 1, "%d", i);
    assert(len > 0);
    size_ += len;
  }

  // write the 64bit integer to string
  void write(int64_t l) {
    // snprintf automatically adds a NULL, so we need one more char
    if (size_ + MAX_INT64_DIGITS + 1 > capacity_) {
      realloc(MAX_INT64_DIGITS + 1);
    }

    int len = snprintf(head_ + size_, MAX_INT64_DIGITS + 1, "%" PRIi64, l);
    assert(len > 0);
    size_ += len;
  }

  // write the double to string
  void write(double d) {
    // snprintf automatically adds a NULL, so we need one more char
    if (size_ + MAX_DOUBLE_DIGITS + 1 > capacity_) {
      realloc(MAX_DOUBLE_DIGITS + 1);
    }

    int len = snprintf(head_ + size_, MAX_DOUBLE_DIGITS + 1, "%.15g", d);
    assert(len > 0);
    size_ += len;
  }

  pos_type tellp() const { return size_; }

  void seekp(pos_type pos) { size_ = (uint32_t)pos; }

  const char* getBuffer() const { return head_; }

  pos_type getSize() const { return tellp(); }

 private:
  void realloc(uint32_t len) {
    assert(capacity_ > 0);

    capacity_ *= 2;
    while (capacity_ < size_ + len) {
      capacity_ *= 2;
    }

    if (alloc_) {
      char* new_buf = (char*)::realloc(head_, capacity_);
      assert(new_buf);
      head_ = new_buf;
    } else {
      char* new_buf = (char*)::malloc(capacity_);
      assert(new_buf);
      memcpy(new_buf, head_, size_);
      head_ = new_buf;
      alloc_ = true;
    }
  }

 private:
  char* head_;
  uint32_t size_;
  uint32_t capacity_;
  bool alloc_;
};

} // namespace fbson

#endif // FBSON_FBSONSTREAM_H