/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2005,2006,2007 INRIA

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation;

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 *

 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>

 */

#ifndef BUFFER_H

#define BUFFER_H

#include <stdint.h>

#include <vector>

#define BUFFER_HEURISTICS 1

#define BUFFER_USE_INLINE 1

#ifdef BUFFER_USE_INLINE

#define BUFFER_INLINE inline

#else

#define BUFFER_INLINE

#endif

namespace ns3 {

/**

 * \brief automatically resized byte buffer

 *

 * This represents a buffer of bytes. Its size is

 * automatically adjusted to hold any data prepended

 * or appended by the user. Its implementation is optimized

 * to ensure that the number of buffer resizes is minimized,

 * by creating new Buffers of the maximum size ever used.

 * The correct maximum size is learned at runtime during use by 

 * recording the maximum size of each packet.

 *

 * \internal

 * The implementation of the Buffer class uses a COW (Copy On Write)

 * technique to ensure that the underlying data buffer which holds

 * the data bytes is shared among a lot of Buffer instances despite

 * data being added or removed from them.

 *

 * When multiple Buffer instances hold a reference to the same 

 * underlying BufferData object, they must be able to detect when

 * the operation they want to perform should trigger a copy of the

 * BufferData. If the BufferData::m_count field is one, it means that

 * there exist only one instance of Buffer which references the 

 * BufferData instance so, it is safe to modify it. It is also

 * safe to modify the content of a BufferData if the modification

 * falls outside of the "dirty area" defined by the BufferData.

 * In every other case, the BufferData must be copied before

 * being modified.

 *

 * To understand the way the Buffer::Add and Buffer::Remove methods

 * work, you first need to understand the "virtual offsets" used to

 * keep track of the content of buffers. Each Buffer instance

 * contains real data bytes in its BufferData instance but it also

 * contains "virtual zero data" which typically is used to represent

 * application-level payload. No memory is allocated to store the

 * zero bytes of application-level payload unless the user fragments

 * a Buffer: this application-level payload is kept track of with

 * a pair of integers which describe where in the buffer content

 * the "virtual zero area" starts and ends.

 *

 * ***: unused bytes

 * xxx: bytes "added" at the front of the zero area

 * ...: bytes "added" at the back of the zero area

 * 000: virtual zero bytes

 *

 * Real byte buffer:      |********xxxxxxxxxxxx.........*****|

 *                        |--------^ m_start

 *                        |-------------------^ m_zeroAreaStart

 *                        |-----------------------------^ m_end - (m_zeroAreaEnd - m_zeroAreaStart)

 * virtual byte buffer:           |xxxxxxxxxxxx0000000000000.........|

 *                        |--------^ m_start

 *                        |--------------------^ m_zeroAreaStart

 *                        |---------------------------------^ m_zeroAreaEnd

 *                        |------------------------------------------^ m_end

 *

 * A simple state invariant is that m_start <= m_zeroStart <= m_zeroEnd <= m_end

 */

class Buffer {

public:

  /**

   * \brief iterator in a Buffer instance

   */

  class Iterator {

  public:

      Iterator ();

      /**

       * go forward by one byte

       */

      void Next (void);

      /**

       * go backward by one byte

       */

      void Prev (void);

      /**

       * \param delta number of bytes to go forward

       */

      void Next (uint32_t delta);

      /**

       * \param delta number of bytes to go backward

       */

      void Prev (uint32_t delta);

      /**

       * \param o the second iterator

       * \return number of bytes included between the two iterators

       *

       * This method works only if the two iterators point

       * to the same underlying buffer. Debug builds ensure

       * this with an assert.

       */

      uint32_t GetDistanceFrom (Iterator const &o) const;

      /**

       * \return true if this iterator points to the end of the byte array.

       *     false otherwise.

       */

      bool IsEnd (void) const;

      /**

       * \return true if this iterator points to the start of the byte array.

       *     false otherwise.

       */

      bool IsStart (void) const;

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by one byte.

       */

      BUFFER_INLINE void WriteU8 (uint8_t  data);

      /**

       * \param data data to write in buffer

       * \param len number of times data must be written in buffer

       *

       * Write the data in buffer len times and avance the iterator position

       * by len byte.

       */

      BUFFER_INLINE void WriteU8 (uint8_t data, uint32_t len);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by two bytes. The format of the data written in the byte

       * buffer is non-portable. We only ensure that readU16 will

       * return exactly what we wrote with writeU16 if the program

       * is run on the same machine.

       */

      void WriteU16 (uint16_t data);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by four bytes. The format of the data written in the byte

       * buffer is non-portable. We only ensure that readU32 will

       * return exactly what we wrote with writeU32 if the program

       * is run on the same machine.

       */

      void WriteU32 (uint32_t data);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by eight bytes. The format of the data written in the byte

       * buffer is non-portable. We only ensure that readU64 will

       * return exactly what we wrote with writeU64 if the program

       * is run on the same machine.

       */

      void WriteU64 (uint64_t data);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by two bytes. The data is written in network order and the

       * input data is expected to be in host order.

       */

      void WriteHtonU16 (uint16_t data);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by four bytes. The data is written in network order and the

       * input data is expected to be in host order.

       */

      void WriteHtonU32 (uint32_t data);

      /**

       * \param data data to write in buffer

       *

       * Write the data in buffer and avance the iterator position

       * by eight bytes. The data is written in network order and the

       * input data is expected to be in host order.

       */

      void WriteHtonU64 (uint64_t data);

      /**

       * \param buffer a byte buffer to copy in the internal buffer.

       * \param size number of bytes to copy.

       *

       * Write the data in buffer and avance the iterator position

       * by size bytes.

       */

      void Write (uint8_t const*buffer, uint32_t size);

      /**

       * \param start the start of the data to copy

       * \param end the end of the data to copy

       *

       * Write the data delimited by start and end in internal buffer 

       * and avance the iterator position by the number of bytes

       * copied.

       * The input interators _must_ not point to the same Buffer as

       * we do to avoid overlapping copies. This is enforced 

       * in debug builds by asserts.

       */

      void Write (Iterator start, Iterator end);

      /**

       * \return the byte read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       */

      BUFFER_INLINE uint8_t  ReadU8 (void);

      /**

       * \return the two bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in the format written by writeU16.

       */

      uint16_t ReadU16 (void);

      /**

       * \return the four bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in the format written by writeU32.

       */

      uint32_t ReadU32 (void);

      /**

       * \return the eight bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in the format written by writeU64.

       */

      uint64_t ReadU64 (void);

      /**

       * \return the two bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in network format and return in host format.

       */

      uint16_t ReadNtohU16 (void);

      /**

       * \return the four bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in network format and return in host format.

       */

      uint32_t ReadNtohU32 (void);

      /**

       * \return the eight bytes read in the buffer.

       *

       * Read data and advance the Iterator by the number of bytes

       * read.

       * The data is read in network format and return in host format.

       */

      uint64_t ReadNtohU64 (void);

      /**

       * \param buffer buffer to copy data into

       * \param size number of bytes to copy

       *

       * Copy size bytes of data from the internal buffer to the

       * input buffer and avance the Iterator by the number of

       * bytes read.

       */

      void Read (uint8_t *buffer, uint32_t size);

  private:

      friend class Buffer;

      Iterator (Buffer const*buffer);

      Iterator (Buffer const*buffer, bool);

      void Construct (const Buffer *buffer);

      bool CheckNoZero (uint32_t start, uint32_t end) const;

      bool Check (uint32_t i) const;

    /* offset in virtual bytes from the start of the data buffer to the

     * start of the "virtual zero area".

     */

      uint32_t m_zeroStart;

    /* offset in virtual bytes from the start of the data buffer to the

     * end of the "virtual zero area".

     */

      uint32_t m_zeroEnd;

    /* offset in virtual bytes from the start of the data buffer to the

     * start of the data which can be read by this iterator

     */

      uint32_t m_dataStart;

    /* offset in virtual bytes from the start of the data buffer to the

     * end of the data which can be read by this iterator

     */

      uint32_t m_dataEnd;

    /* offset in virtual bytes from the start of the data buffer to the

     * current position represented by this iterator.

     */

      uint32_t m_current;

    /* a pointer to the underlying byte buffer. All offsets are relative

     * to this pointer.

     */

      uint8_t *m_data;

  };

  /**

   * \return the number of bytes stored in this buffer.

   */

  uint32_t GetSize (void) const;

  /**

   * \return a pointer to the start of the internal 

   * byte buffer.

   *

   * The returned pointer points to an area of

   * memory which is ns3::Buffer::GetSize () bytes big.

   * Please, try to never ever use this method. It is really

   * evil and is present only for a few specific uses.

   */

  uint8_t const*PeekData (void) const;

  /**

   * \param start size to reserve

   *

   * Add bytes at the start of the Buffer. The

   * content of these bytes is undefined but debugging

   * builds initialize them to 0x33.

   * Any call to this method invalidates any Iterator

   * pointing to this Buffer.

   */

  void AddAtStart (uint32_t start);

  /**

   * \param end size to reserve

   *

   * Add bytes at the end of the Buffer. The

   * content of these bytes is undefined but debugging

   * builds initialize them to 0x33.

   * Any call to this method invalidates any Iterator

   * pointing to this Buffer.

   */

  void AddAtEnd (uint32_t end);

  /**

   * \param start size to remove

   *

   * Remove bytes at the start of the Buffer.

   * Any call to this method invalidates any Iterator

   * pointing to this Buffer.

   */

  void RemoveAtStart (uint32_t start);

  /**

   * \param end size to remove

   *

   * Remove bytes at the end of the Buffer.

   * Any call to this method invalidates any Iterator

   * pointing to this Buffer.

   */

  void RemoveAtEnd (uint32_t end);

  /**

   * \param start offset from start of packet

   * \param length

   *

   * \return a fragment of size length starting at offset

   * start.

   */

  Buffer CreateFragment (uint32_t start, uint32_t length) const;

  /**

   * \return an Iterator which points to the

   * start of this Buffer.

   */

  Buffer::Iterator Begin (void) const;

  /**

   * \return an Iterator which points to the

   * end of this Buffer.

   */

  Buffer::Iterator End (void) const;

  Buffer CreateFullCopy (void) const;

  Buffer (Buffer const &o);

  Buffer &operator = (Buffer const &o);

  Buffer ();

  Buffer (uint32_t dataSize);

  ~Buffer ();

private:

  void TransformIntoRealBuffer (void) const;

  bool CheckInternalState (void) const;

  void Initialize (uint32_t zeroSize);

  uint32_t GetInternalSize (void) const;

  uint32_t GetInternalEnd (void) const;

  static void Recycle (struct BufferData *data);

  static struct BufferData *Create (uint32_t size);

  /* This structure is described in the buffer.cc file.

   */

  struct BufferData *m_data;

#ifdef BUFFER_HEURISTICS

  /* keep track of the maximum value of m_zeroAreaStart across

   * the lifetime of a Buffer instance. This variable is used

   * purely as a source of information for the heuristics which

   * decide on the position of the zero area in new buffers.

   * It is read from the Buffer destructor to update the global

   * heuristic data and these global heuristic data are used from

   * the Buffer constructor to choose an initial value for 

   * m_zeroAreaStart.

   * It is possible to disable all these heuristics by undefining the

   * BUFFER_HEURISTICS macro at the top of buffer.h

   */

  uint32_t m_maxZeroAreaStart;

#endif /* BUFFER_HEURISTICS */

  /* offset to the start of the virtual zero area from the start 

   * of m_data->m_data

   */

  uint32_t m_zeroAreaStart;

  /* offset to the end of the virtual zero area from the start 

   * of m_data->m_data

   */

  uint32_t m_zeroAreaEnd;

  /* offset to the start of the data referenced by this Buffer

   * instance from the start of m_data->m_data

   */

  uint32_t m_start;

  /* offset to the end of the data referenced by this Buffer

   * instance from the start of m_data->m_data

   */

  uint32_t m_end;

};

} // namespace ns3

#ifdef BUFFER_USE_INLINE

#include "ns3/assert.h"

namespace ns3 {

void

Buffer::Iterator::WriteU8 (uint8_t data)

{

  NS_ASSERT (Check (m_current));

  if (m_current < m_zeroStart)

    {

      m_data[m_current] = data;

      m_current++;

    }

  else

    {

      m_data[m_current - (m_zeroEnd-m_zeroStart)] = data;

      m_current++;      

    }

}

void 

Buffer::Iterator::WriteU8 (uint8_t  data, uint32_t len)

{

  NS_ASSERT (CheckNoZero (m_current, m_current + len));

  if (m_current <= m_zeroStart)

    {

      memset (&(m_data[m_current]), data, len);

      m_current += len;

    }

  else

    {

      uint8_t *buffer = &m_data[m_current - (m_zeroEnd-m_zeroStart)];

      memset (buffer, data, len);

      m_current += len;

    }