ndn-cpp/util/blob.hpp

/**
 * Copyright (C) 2013 Regents of the University of California.
 * @author: Jeff Thompson <jefft0@remap.ucla.edu>
 * See COPYING for copyright and distribution information.
 */

#ifndef NDN_BLOB_HPP
#define	NDN_BLOB_HPP

#include "../common.hpp"
#include "../c/util/blob.h"

namespace ndn {

/**
 * A Blob holds a pointer to an immutable byte array implemented as const std::vector<uint8_t>.  
 * This is like a JavaScript string which is a pointer to an immutable string.  
 * It is OK to pass a pointer to the string because the new owner can't change the bytes
 * of the string.  However, like a JavaScript string, it is possible to change the pointer, and so this does allow
 * the copy constructor and assignment to change the pointer.  Also remember that the pointer can be null.
 * (Note that we could have made Blob derive directly from vector<uint8_t> and then explicitly use
 * a pointer to it like shared_ptr<Blob>, but this does not enforce immutability because we can't declare
 * Blob as derived from const vector<uint8_t>.)
 */
class Blob : public ptr_lib::shared_ptr<const std::vector<uint8_t> > {
public:
  /**
   * Create a new Blob with a null pointer.
   */
  Blob()
  {  
  }
  
  /**
   * Create a new Blob with an immutable copy of the given array.
   * @param value A pointer to the byte array which is copied.
   * @param valueLength The length of value.
   */
  Blob(const uint8_t* value, size_t valueLength)
  : ptr_lib::shared_ptr<const std::vector<uint8_t> >(new std::vector<uint8_t>(value, value + valueLength))
  {
  }
  
  /**
   * Create a new Blob with an immutable copy of the array in the given vector.
   * If you want to transfer the array without copying, the the vector has to start as a 
   * ptr_lib::shared_ptr<std::vector<uint8_t> > and you can use the Blob constructor with this type.
   * @param value A reference to a vector which is copied.
   */
  Blob(const std::vector<uint8_t> &value)
  : ptr_lib::shared_ptr<const std::vector<uint8_t> >(new std::vector<uint8_t>(value))
  {
  }
  
  /**
   * Create a new Blob with an immutable copy of the array in the given Blob struct.
   * @param blobStruct The C ndn_Blob struct to receive the pointer.
   */
  Blob(const struct ndn_Blob& blobStruct)
  : ptr_lib::shared_ptr<const std::vector<uint8_t> >(new std::vector<uint8_t>(blobStruct.value, blobStruct.value + blobStruct.length))
  {
  }
  
  /**
   * Create a new Blob to point to an existing byte array.  IMPORTANT: After calling this constructor,
   * if you keep a pointer to the array then you must treat the array as immutable and promise not to change it.
   * @param value A pointer to a vector with the byte array.  This takes another reference and does not copy the bytes.
   */
  Blob(const ptr_lib::shared_ptr<std::vector<uint8_t> > &value)
  : ptr_lib::shared_ptr<const std::vector<uint8_t> >(value)
  {
  }
  Blob(const ptr_lib::shared_ptr<const std::vector<uint8_t> > &value)
  : ptr_lib::shared_ptr<const std::vector<uint8_t> >(value)
  {
  }
  
  /**
   * Return the length of the immutable byte array.
   */
  size_t 
  size() const
  {
    if (*this)
      return (*this)->size();
    else
      return 0;
  }

  /**
   * Return a const pointer to the first byte of the immutable byte array, or 0 if the pointer is null.
   */
  const uint8_t* 
  buf() const
  {
    if (*this)
      return &(*this)->front();
    else
      return 0;
  }
  
  /**
   * Set the blobStruct to point to this Blob's byte array, without copying any memory.
   * WARNING: The resulting pointer in blobStruct is invalid after a further use of this object which could reallocate memory.
   * @param blobStruct The C ndn_Blob struct to receive the pointer.
   */
  void 
  get(struct ndn_Blob& blobStruct) const 
  {
    blobStruct.length = size(); 
    if (size() > 0)
      blobStruct.value = (uint8_t*)buf();
    else
      blobStruct.value = 0;
  }
};

}

#endif