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ns3::Buffer Class Reference

automatically resized byte buffer More...

#include <buffer.h>

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Classes

struct  Data
 This data structure is variable-sized through its last member whose size is determined at allocation time and stored in the m_size field. More...
 
class  Iterator
 iterator in a Buffer instance More...
 

Public Member Functions

 Buffer (Buffer const &o)
 
 Buffer ()
 
 Buffer (uint32_t dataSize)
 
 Buffer (uint32_t dataSize, bool initialize)
 
 ~Buffer ()
 
bool AddAtEnd (uint32_t end)
 
void AddAtEnd (const Buffer &o)
 
bool AddAtStart (uint32_t start)
 
Buffer::Iterator Begin (void) const
 
void CopyData (std::ostream *os, uint32_t size) const
 Copy the specified amount of data from the buffer to the given output stream. More...
 
uint32_t CopyData (uint8_t *buffer, uint32_t size) const
 
Buffer CreateFragment (uint32_t start, uint32_t length) const
 
Buffer CreateFullCopy (void) const
 
uint32_t Deserialize (const uint8_t *buffer, uint32_t size)
 
Buffer::Iterator End (void) const
 
int32_t GetCurrentEndOffset (void) const
 
int32_t GetCurrentStartOffset (void) const
 
uint32_t GetSerializedSize (void) const
 
uint32_t GetSize (void) const
 
Bufferoperator= (Buffer const &o)
 
uint8_t const * PeekData (void) const
 
void RemoveAtEnd (uint32_t end)
 
void RemoveAtStart (uint32_t start)
 
uint32_t Serialize (uint8_t *buffer, uint32_t maxSize) const
 

Private Member Functions

bool CheckInternalState (void) const
 
uint32_t GetInternalEnd (void) const
 
uint32_t GetInternalSize (void) const
 
void Initialize (uint32_t zeroSize)
 
void TransformIntoRealBuffer (void) const
 

Static Private Member Functions

static struct Buffer::DataAllocate (uint32_t reqSize)
 
static struct Buffer::DataCreate (uint32_t size)
 
static void Deallocate (struct Buffer::Data *data)
 
static void Recycle (struct Buffer::Data *data)
 

Private Attributes

struct Datam_data
 
uint32_t m_end
 
uint32_t m_maxZeroAreaStart
 
uint32_t m_start
 
uint32_t m_zeroAreaEnd
 
uint32_t m_zeroAreaStart
 

Static Private Attributes

static uint32_t g_recommendedStart = 0
 location in a newly-allocated buffer where you should start writing data. More...
 

Detailed Description

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

Definition at line 92 of file buffer.h.

Constructor & Destructor Documentation

ns3::Buffer::Buffer ( Buffer const &  o)
inline

Definition at line 856 of file buffer.h.

References CheckInternalState(), ns3::Buffer::Data::m_count, m_data, and NS_ASSERT.

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ns3::Buffer::Buffer ( )

Definition at line 184 of file buffer.cc.

References Initialize(), and NS_LOG_FUNCTION.

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ns3::Buffer::Buffer ( uint32_t  dataSize)

Definition at line 190 of file buffer.cc.

References Initialize(), and NS_LOG_FUNCTION.

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ns3::Buffer::Buffer ( uint32_t  dataSize,
bool  initialize 
)

Definition at line 196 of file buffer.cc.

References Initialize(), and NS_LOG_FUNCTION.

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ns3::Buffer::~Buffer ( )

Definition at line 279 of file buffer.cc.

References CheckInternalState(), g_recommendedStart, ns3::Buffer::Data::m_count, m_data, m_maxZeroAreaStart, NS_ASSERT, NS_LOG_FUNCTION, and Recycle().

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Member Function Documentation

void ns3::Buffer::AddAtEnd ( const Buffer o)
Parameters
othe buffer to append to the end of this buffer.

Add bytes at the end of the Buffer. Any call to this method invalidates any Iterator pointing to this Buffer.

This is an optimization which kicks in when we attempt to aggregate two buffers which contain adjacent zero areas.

Definition at line 411 of file buffer.cc.

References AddAtEnd(), Begin(), CheckInternalState(), CreateFullCopy(), End(), GetSize(), ns3::Buffer::Data::m_count, m_data, ns3::Buffer::Data::m_dirtyEnd, m_end, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_ASSERT, NS_LOG_FUNCTION, ns3::Buffer::Iterator::Prev(), and ns3::Buffer::Iterator::Write().

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bool ns3::Buffer::AddAtStart ( uint32_t  start)
struct Buffer::Data * ns3::Buffer::Allocate ( uint32_t  reqSize)
staticprivate

Definition at line 159 of file buffer.cc.

References data, ns3::Buffer::Data::m_count, ns3::Buffer::Data::m_size, NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by Create().

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Buffer::Iterator ns3::Buffer::Begin ( void  ) const
inline
void ns3::Buffer::CopyData ( std::ostream *  os,
uint32_t  size 
) const

Copy the specified amount of data from the buffer to the given output stream.

Parameters
osthe output stream
sizethe maximum amount of bytes to copy. If zero, nothing is copied.

Definition at line 739 of file buffer.cc.

References anonymous_namespace{buffer.cc}::Zeroes::buffer, anonymous_namespace{buffer.cc}::g_zeroes, ns3::Buffer::Data::m_data, m_data, m_end, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_LOG_FUNCTION, and anonymous_namespace{buffer.cc}::Zeroes::size.

Referenced by ns3::Packet::CopyData(), and ns3::PcapFile::Write().

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Buffer::Data * ns3::Buffer::Create ( uint32_t  size)
staticprivate

Definition at line 151 of file buffer.cc.

References Allocate(), and NS_LOG_FUNCTION.

Referenced by AddAtEnd(), AddAtStart(), and Initialize().

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Buffer ns3::Buffer::CreateFragment ( uint32_t  start,
uint32_t  length 
) const
Parameters
startoffset from start of packet
length
Returns
a fragment of size length starting at offset start.

Definition at line 533 of file buffer.cc.

References CheckInternalState(), GetSize(), NS_ASSERT, NS_LOG_FUNCTION, RemoveAtEnd(), and RemoveAtStart().

Referenced by ns3::Packet::CreateFragment(), and BufferTest::DoRun().

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Buffer ns3::Buffer::CreateFullCopy ( void  ) const
void ns3::Buffer::Deallocate ( struct Buffer::Data data)
staticprivate

Definition at line 176 of file buffer.cc.

References data, ns3::Buffer::Data::m_count, NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by Recycle().

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uint32_t ns3::Buffer::Deserialize ( const uint8_t *  buffer,
uint32_t  size 
)
Returns
zero if a complete buffer is not deserialized
Parameters
bufferpoints to buffer for deserialization
sizenumber of bytes to deserialize

The raw character buffer is deserialized and all the data is placed into this buffer.

Definition at line 660 of file buffer.cc.

References AddAtEnd(), AddAtStart(), Begin(), End(), Initialize(), NS_ASSERT, NS_LOG_FUNCTION, ns3::Buffer::Iterator::Prev(), and ns3::Buffer::Iterator::Write().

Referenced by ns3::Packet::Deserialize().

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int32_t ns3::Buffer::GetCurrentEndOffset ( void  ) const

Definition at line 710 of file buffer.cc.

References m_end, and NS_LOG_FUNCTION.

Referenced by ns3::Packet::AddAtEnd(), ns3::Packet::AddByteTag(), ns3::Packet::AddPaddingAtEnd(), ns3::Packet::AddTrailer(), and ns3::Packet::GetByteTagIterator().

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int32_t ns3::Buffer::GetCurrentStartOffset ( void  ) const
uint32_t ns3::Buffer::GetInternalEnd ( void  ) const
private

Definition at line 298 of file buffer.cc.

References m_end, m_zeroAreaEnd, m_zeroAreaStart, and NS_LOG_FUNCTION.

Referenced by AddAtEnd().

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uint32_t ns3::Buffer::GetInternalSize ( void  ) const
private

Definition at line 292 of file buffer.cc.

References m_end, m_start, m_zeroAreaEnd, m_zeroAreaStart, and NS_LOG_FUNCTION.

Referenced by AddAtEnd(), and AddAtStart().

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uint32_t ns3::Buffer::GetSerializedSize ( void  ) const
Returns
the number of bytes required for serialization

Definition at line 570 of file buffer.cc.

References m_end, m_start, m_zeroAreaEnd, m_zeroAreaStart, and NS_LOG_FUNCTION.

Referenced by ns3::Packet::GetSerializedSize(), and ns3::Packet::Serialize().

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void ns3::Buffer::Initialize ( uint32_t  zeroSize)
private

Definition at line 240 of file buffer.cc.

References CheckInternalState(), Create(), g_recommendedStart, m_data, ns3::Buffer::Data::m_dirtyEnd, ns3::Buffer::Data::m_dirtyStart, m_end, m_maxZeroAreaStart, ns3::Buffer::Data::m_size, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by Buffer(), and Deserialize().

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Buffer & ns3::Buffer::operator= ( Buffer const &  o)

Definition at line 255 of file buffer.cc.

References CheckInternalState(), g_recommendedStart, ns3::Buffer::Data::m_count, m_data, m_end, m_maxZeroAreaStart, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_ASSERT, and Recycle().

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uint8_t const * ns3::Buffer::PeekData ( void  ) const
Returns
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.

Definition at line 729 of file buffer.cc.

References CheckInternalState(), ns3::Buffer::Data::m_data, m_data, m_start, NS_ASSERT, NS_LOG_FUNCTION, and TransformIntoRealBuffer().

Referenced by ns3::SixLowPanNetDevice::CompressLowPanNhc(), BufferTest::DoRun(), BufferTest::EnsureWrittenBytes(), ns3::WifiInformationElement::operator==(), ns3::PbbTlv::operator==(), ns3::Packet::PeekData(), ns3::Ipv6ExtensionHeader::Serialize(), ns3::dsr::DsrFsHeader::Serialize(), and PbbTestCase::TestSerialize().

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void ns3::Buffer::Recycle ( struct Buffer::Data data)
staticprivate

Definition at line 143 of file buffer.cc.

References Deallocate(), ns3::Buffer::Data::m_count, NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by AddAtEnd(), AddAtStart(), operator=(), and ~Buffer().

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void ns3::Buffer::RemoveAtEnd ( uint32_t  end)
Parameters
endsize to remove

Remove bytes at the end of the Buffer. Any call to this method invalidates any Iterator pointing to this Buffer.

Definition at line 497 of file buffer.cc.

References CheckInternalState(), LOG_INTERNAL_STATE, m_end, m_maxZeroAreaStart, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by CreateFragment(), ns3::Ipv6ExtensionHeader::Deserialize(), ns3::dsr::DsrFsHeader::Deserialize(), BufferTest::DoRun(), ns3::PacketMetadata::ItemIterator::Next(), ns3::Packet::RemoveAtEnd(), ns3::Packet::RemoveTrailer(), and ns3::PbbTlv::~PbbTlv().

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void ns3::Buffer::RemoveAtStart ( uint32_t  start)
Parameters
startsize to remove

Remove bytes at the start of the Buffer. Any call to this method invalidates any Iterator pointing to this Buffer.

Definition at line 452 of file buffer.cc.

References CheckInternalState(), LOG_INTERNAL_STATE, m_end, m_maxZeroAreaStart, m_start, m_zeroAreaEnd, m_zeroAreaStart, NS_ASSERT, NS_LOG_FUNCTION, and visualizer.core::start().

Referenced by ns3::SixLowPanNetDevice::CompressLowPanNhc(), CreateFragment(), BufferTest::DoRun(), ns3::PacketMetadata::ItemIterator::Next(), ns3::Packet::RemoveAtStart(), and ns3::Packet::RemoveHeader().

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uint32_t ns3::Buffer::Serialize ( uint8_t *  buffer,
uint32_t  maxSize 
) const
Returns
zero if buffer not large enough
Parameters
bufferpoints to serialization buffer
maxSizemax number of bytes to write

This buffer's contents are serialized into the raw character buffer parameter. Note: The zero length data is not copied entirely. Only the length of zero byte data is serialized.

Definition at line 590 of file buffer.cc.

References ns3::Buffer::Data::m_data, m_data, m_end, m_start, m_zeroAreaEnd, m_zeroAreaStart, and NS_LOG_FUNCTION.

Referenced by ns3::Packet::Serialize().

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void ns3::Buffer::TransformIntoRealBuffer ( void  ) const
private

Definition at line 718 of file buffer.cc.

References CheckInternalState(), CreateFullCopy(), NS_ASSERT, and NS_LOG_FUNCTION.

Referenced by PeekData().

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Member Data Documentation

uint32_t ns3::Buffer::g_recommendedStart = 0
staticprivate

location in a newly-allocated buffer where you should start writing data.

i.e., m_start should be initialized to this value.

Definition at line 597 of file buffer.h.

Referenced by Initialize(), operator=(), and ~Buffer().

uint32_t ns3::Buffer::m_maxZeroAreaStart
private

Definition at line 591 of file buffer.h.

Referenced by AddAtEnd(), AddAtStart(), Initialize(), operator=(), RemoveAtEnd(), RemoveAtStart(), and ~Buffer().


The documentation for this class was generated from the following files: