byte-tag-list.h

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/*
 * Copyright (c) 2008 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 */
#ifndef BYTE_TAG_LIST_H
#define BYTE_TAG_LIST_H
 
#define __STDC_LIMIT_MACROS
#include "tag-buffer.h"
 
#include "ns3/type-id.h"
 
#include <stdint.h>
 
namespace ns3
{
 
struct ByteTagListData;
 
/**
 * @ingroup packet
 *
 * @brief keep track of the byte tags stored in a packet.
 *
 * This class is mostly private to the Packet implementation and users
 * should never have to access it directly.
 *
 * @internal
 * The implementation of this class is a bit tricky so, there are a couple
 * of things to keep in mind here:
 *
 *   - It stores all tags in a single byte buffer: each tag is stored
 *     as 4 32bit integers (TypeId, tag data size, start, end) followed
 *     by the tag data as generated by Tag::Serialize.
 *
 *   - The struct ByteTagListData structure which contains the tag byte buffer
 *     is shared and, thus, reference-counted. This data structure is unshared
 *     as-needed to emulate COW semantics.
 *
 *   - Each tag tags a unique set of bytes identified by the pair of offsets
 *     (start,end). These offsets are relative to the start of the packet
 *     Whenever the origin of the offset changes, the Packet adjusts all
 *     byte tags using ByteTagList::Adjust method.
 *
 *   - When packet is reduced in size, byte tags that span outside the packet
 *     boundaries remain in ByteTagList. It is not a problem as iterator fixes
 *     the boundaries before returning item. However, when packet is extending,
 *     it calls ByteTagList::AddAtStart or ByteTagList::AddAtEnd to cut byte
 *     tags that will otherwise cover new bytes.
 */
class ByteTagList
{
  public:
    /**
     * @brief An iterator for iterating through a byte tag list
     *
     * An iterator for iterating through a byte tag list
     *
     */
    class Iterator
    {
      public:
        /**
         * @brief An item specifies an individual tag within a byte buffer
         *
         * An item specifies an individual tag within a byte buffer
         *
         */
        struct Item
        {
            TypeId tid;    //!< type of the tag
            uint32_t size; //!< size of tag data
            int32_t start; //!< offset to the start of the tag from the virtual byte buffer
            int32_t end;   //!< offset to the end of the tag from the virtual byte buffer
            TagBuffer buf; //!< the data for the tag as generated by Tag::Serialize
 
            /// Constructs an item with the given TagBuffer
            /// @param buf The Tag Buffer
            Item(TagBuffer buf);
 
          private:
            /// Friend class
            friend class ByteTagList;
            /// Friend class
            friend class ByteTagList::Iterator;
        };
 
        /**
         * @brief Used to determine if the iterator is at the end of the byteTagList
         *
         * @returns true if there are more Items in the list
         */
        bool HasNext() const;
 
        /**
         * @brief Returns the next Item from the ByteTagList
         *
         * @returns the next Item in the ByteTagList
         */
        ByteTagList::Iterator::Item Next();
 
        /**
         * @brief Returns the offset from the start of the virtual byte buffer to the ByteTagList
         *
         * @returns offset to the start of this ByteTagList
         */
        uint32_t GetOffsetStart() const;
 
      private:
        /// Friend class
        friend class ByteTagList;
 
        /**
         * @brief Constructor
         * @param start Starting tag
         * @param end End tag
         * @param offsetStart offset to the start of the tag from the virtual byte buffer
         * @param offsetEnd offset to the end of the tag from the virtual byte buffer
         * @param adjustment adjustment to byte tag offsets
         */
        Iterator(uint8_t* start,
                 uint8_t* end,
                 int32_t offsetStart,
                 int32_t offsetEnd,
                 int32_t adjustment);
 
        /**
         * @brief Prepare the iterator for the next tag
         */
        void PrepareForNext();
        uint8_t* m_current;    //!< Current tag
        uint8_t* m_end;        //!< End tag
        int32_t m_offsetStart; //!< Offset to the start of the tag from the virtual byte buffer
        int32_t m_offsetEnd;   //!< Offset to the end of the tag from the virtual byte buffer
        int32_t m_adjustment;  //!< Adjustment to byte tag offsets
        uint32_t m_nextTid;    //!< TypeId of the next tag
        uint32_t m_nextSize;   //!< Size of the next tag
        int32_t m_nextStart;   //!< Start of the next tag
        int32_t m_nextEnd;     //!< End of the next tag
    };
 
    ByteTagList();
 
    /**
     *
     * Copy constructor, copies the data and increases reference count
     *
     * @param o The ByteTagList to copy
     *
     */
    ByteTagList(const ByteTagList& o);
 
    /**
     *
     * Assignment operator, deallocates current data and assigns
     * value of passed in ByteTagList.  Also increases reference count
     *
     * @param o reference to the ByteTagList to copy
     * @returns reference to the assignee
     *
     */
    ByteTagList& operator=(const ByteTagList& o);
    ~ByteTagList();
 
    /**
     * @param tid the typeid of the tag added
     * @param bufferSize the size of the tag when its serialization will
     *        be completed. Typically, the return value of Tag::GetSerializedSize
     * @param start offset which uniquely identifies the first byte tagged by this tag.
     * @param end offset which uniquely identifies the last byte tagged by this tag.
     * @returns a buffer which can be used to write the tag data.
     *
     *
     */
    TagBuffer Add(TypeId tid, uint32_t bufferSize, int32_t start, int32_t end);
 
    /**
     * @param o the other list of tags to aggregate.
     *
     * Aggregate the two lists of tags.
     */
    void Add(const ByteTagList& o);
 
    /**
     *
     * Removes all of the tags from the ByteTagList
     */
    void RemoveAll();
 
    /**
     * @param offsetStart the offset which uniquely identifies the first data byte
     *        present in the byte buffer associated to this ByteTagList.
     * @param offsetEnd the offset which uniquely identifies the last data byte
     *        present in the byte buffer associated to this ByteTagList.
     * @returns an iterator
     *
     * The returned iterator will allow you to loop through the set of tags present
     * in this list: the boundaries of each tag as reported by their start and
     * end offsets will be included within the input offsetStart and offsetEnd.
     */
    ByteTagList::Iterator Begin(int32_t offsetStart, int32_t offsetEnd) const;
 
    /**
     * Adjust the offsets stored internally by the adjustment delta.
     *
     * @param adjustment value to change stored offsets by
     */
    inline void Adjust(int32_t adjustment);
 
    /**
     * Make sure that all offsets are smaller than appendOffset which represents
     * the location where new bytes have been added to the byte buffer.
     *
     * @param appendOffset maximum offset value
     *
     */
    void AddAtEnd(int32_t appendOffset);
    /**
     * Make sure that all offsets are bigger than prependOffset which represents
     * the location where new bytes have been added to the byte buffer.
     *
     * @param prependOffset minimum offset value
     *
     */
    void AddAtStart(int32_t prependOffset);
    /**
     * Returns number of bytes required for packet serialization.
     *
     * @returns number of bytes required for packet serialization
     */
    uint32_t GetSerializedSize() const;
    /**
     * Serialize the tag list into a byte buffer.
     *
     * @param [in,out] buffer The byte buffer to which the tag list will be serialized
     * @param [in] maxSize Max The max size of the buffer for bounds checking
     *
     * @returns zero if complete tag list is not serialized
     */
    uint32_t Serialize(uint32_t* buffer, uint32_t maxSize) const;
    /**
     * Deserialize tag list from the provided buffer.
     *
     * @param [in] buffer The buffer to read from.
     * @param [in] size The number of bytes to deserialize.
     *
     * @returns zero if complete tag list is not deserialized
     */
    uint32_t Deserialize(const uint32_t* buffer, uint32_t size);
 
  private:
    /**
     * @brief Returns an iterator pointing to the very first tag in this list.
     *
     * @returns an iterator
     */
    ByteTagList::Iterator BeginAll() const;
 
    /**
     * @brief Allocate the memory for the ByteTagListData
     * @param size the memory to allocate
     * @returns the ByteTagListData structure
     */
    ByteTagListData* Allocate(uint32_t size);
 
    /**
     * @brief Deallocates a ByteTagListData
     * @param data the ByteTagListData to deallocate
     */
    void Deallocate(ByteTagListData* data);
 
    int32_t m_minStart;      //!< minimal start offset
    int32_t m_maxEnd;        //!< maximal end offset
    int32_t m_adjustment;    //!< adjustment to byte tag offsets
    uint32_t m_used;         //!< the number of used bytes in the buffer
    ByteTagListData* m_data; //!< the ByteTagListData structure
};
 
void
ByteTagList::Adjust(int32_t adjustment)
{
    m_adjustment += adjustment;
}
 
} // namespace ns3
 
#endif /* BYTE_TAG_LIST_H */